Concrete Pros Choose UV Coatings System for Warehouse Showroom
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June/July 2015
Now available online and on your iPad!
TWO THEORIES RELATED TO CRACKS AND REBAR CORROSION Do cracks increase the risk of steel reinforcement corrosion? 14
BUILDING DEEP
FOUNDATIONS The 2015 CFA Grand Project of the Year 26
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WHAT’S INSIDE
June/July 2015 | Issue 4, Volume 15
COVER STORY
Photo Credit: Ballinger
26 Building Deep Foundations
Departments
The Concrete Foundations Association 2015 Project of the Year — Overall Grand Project winner was awarded for the foundation of a new science and research building at George Washington University.
Features 14 Two Theories Related to Cracks and Rebar Corrosion Do cracks increase the risk of steel reinforcement corrosion?
22 Elevation Control System Helps Meet Ff Specifications Easy-to-use screed support system brings efficiency and precision to flatwork projects.
32 Concrete Pros Choose Diamapro UV for Warehouse Showroom Turner Concrete Professionals decides to resurface a badly worn concrete floor in their own facility.
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38 Grading Systems Offer Money Saving Options to Contractors Consider using a laser guided grading system or an excavator guidance system when preparing your next jobsite for construction.
44 The Constructible Model: What’s In It For You Contractors who invest in BIM technology will reap the benefits including improved efficiency and increased profitability.
50 Propane Burnishers Offer a Green Alternative, Profit A new generation of propane burnishers maximize efficiency, minimize waste and are environmentally friendly.
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4 Editor’s Letter 6 Challenging the System 8 New Products 12 Legal Matters 53 Foundations Q&A 58 The Last Placement
What’s Online Read these online exclusive articles at www.forconstructionpros. com/concrete
US Route 67 Reroute Benefits from Machine Automation Concrete paver uses GPS machine control to ensure accurate grade and no wasted material.
Search: 12072354
CIM Students Work With ASCC To Evaluate ACI Document CIM students at Middle Tennessee State University are evaluating different methods for measuring the area of air voids on concrete wall surfaces. Search: 12078416
www.forconstructionpros.com/concrete | June/July 2015 | Concrete Contractor 3
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EDITOR’S LETTER
Contractor Creates Career Choice Education for Students Ryan Olson, Editor
I
f there is a noticeable theme about 2015, I’d say attracting and retaining a qualified labor force seems to be on everyone’s mind. J.P. Cullen & Sons, based in Janesville, Wisconsin, held the company’s first Cullen Career Fair in April, with the goal of educating young people about a promising and prosperous career in construction. “What we want to accomplish is to get serious candidates to come see us,” says Joe Schwengels, construction superintendent at J.P. Cullen & Sons. “We’ll host the event, include hands-on activities, and give exposure to the other trades we work with. We look at this as an opportunity for a community outreach event to get people excited about construction.” With a total of 150 students plus teachers and staff in attendance, Schwengels considers it a success. Cullen invited 20 schools to participate in the event, 14 of which accepted the offer. “We created the opportunity for students to meet a variety of trades,” he says. “Believing in the trades as an opportunity for a career is the Facebook.com/ ConcreteContractor
Advisory Board
ROlson@ ACBusinessMedia.com (800) 538-5544
mindset we had. It’s clear that college, as a means to a career, is not the path for everyone. We need to educate the parents, the school staff and the kids on the career opportunities that our available in construction,” he says. “This was our way of trying to accomplish that need.” The Cullen Career Fair is anticipated to be an annual event as planning for the spring 2016 event is currently underway. Congrats J.P. Cullen & Sons, we salute you for trying to make a difference. We’d like to invite you to visit ForConstructionPros.com’s new content channel: Profit Matters. This new channel highlights how contractors are improving profitability by implementing technology and best practices throughout their company operating structure. Visit www.ForConstructionPros.com/ Profit-Matters to learn more.
Follow us @ Concreteinsider
Kim Basham KB Engineering Cheyenne, Wyo.
Jim Cuviello Cuviello Concrete Polished|Stained|Crafted Stevensville, Md.
Jim Baty Concrete Foundations Association Mt. Vernon, Iowa
Chris Klemaske T.B. Penick & Sons, Inc. San Diego, Calif.
Search: Concrete Polishing
Dennis Purinton Purinton Builders, Inc. East Granby, Conn. Joe Reardon SASE Orlando, Fla.
4 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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Published and copyrighted 2015 by AC Business Media Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording or any information storage or retrieval system, without written permission from the publisher. CONCRETE CONTRACTOR (USPS 021-799 , ISSN 1545-4193) is published 7 times a year: January, February/March, April/May, June/July, August/September, October/November and December by AC Business Media Inc., 201 N. Main Street, Fort Atkinson, WI 53538. Printed in the U.S.A. Periodicals postage paid at Fort Atkinson, WI, and additional entry offices. POSTMASTER: Send address changes to Concrete Contractor, PO Box 3605 Northbrook, IL 60065-3605 June/July 2015. Issue 4, Volume 15 One year subscription to nonqualified individuals: U.S. 1 year: $35, 2 years: $70. Canada & Mexico 1 year: $60, 2 years: $105. All other countries 1 year: $85, 2 years: $160 (payable in U.S. funds drawn on U.S. banks). Single copies available (prepaid only) $10.00 each (U.S., Canada & Mexico), $15.00 each (International). Canada Post PM40612608. Return Undeliverable Canadian Addresses to: Concrete Contractor, PO Box 25542, London, ON N6C 6B2.
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CHALLENGING THE SYSTEM
Ward R. Malisch, PE, PhD, FACI is concrete construction specialist for the American Society of Concrete Contractors. Reach him at wmalisch@ascconline.org. Bruce A. Suprenant, PE, PhD, FACI, is technical director for the American Society of Concrete Contractors. Reach him at bsuprenant@ bsuprenant.com.
INNOCENT UNTIL PROVEN GUILTY: Unless You’re a Contractor
I
t’s frustrating for concrete contractors to be held responsible for alleged defects discovered by owners’ representatives. It’s especially frustrating when owner’s reps search specifications and find a requirement that, to them, is the “smoking gun” needed to prove the contractors’ culpability and thus, establish their guilt. Consider this scenario: You’re placing a concrete slab on metal decking in December. Ambient
temperature is 25 degrees Fahrenheit and rising. Mixed concrete temperature is 60 degrees Fahrenheit and in-place temperature is maintained above 55 degrees Fahrenheit for three days with insulated blankets. After the blankets are removed, there are no cracks. Three months later the owner’s rep notices cracks in the deck. You say shrinkage and temperature cracks are normal for this kind of construction and produce several references to
back your position. But the rep isn’t buying it. You’re guilty. After a few weeks of researching the specification, he points to Section 5. 3.2.1.b, Cold Weather, in “Specifications for Structural Concrete (ACI 301-10),” which requires the following: “Unless otherwise permitted do not place concrete in contact with surfaces less than 35 degrees Fahrenheit.” Surfaces in your case include metal decking, reinforcement, and embedments. Now for the smoking gun. An hour before the placement, the owner’s rep had used an infrared thermometer and noted in his report the temperature of the reinforcement and metal deck was 33 degrees Fahrenheit. Hence, he decides the deck was too cool, you didn’t comply with the specifications, and that’s the reason for the cracking—even though the cracking occurred three months after the deck placement. You’re guilty. Or how about this? You’ve just finished placing concrete for a parking structure for which specifications required a maximum water-tocementitious-materials ratio (w/cm) of 0.40 and a minimum strength of 5,000 psi, based on durability concerns. The average compressive strength for all concrete tests was 6,140 psi. But there is again a concern with some random cracking over the entire deck. In studying the delivery tickets for 30 loads of concrete to search for clues, the owner’s rep finds that two truckloads of concrete had w/cms of 0.41 and 0.43 as a result of a one-time addition of water at the jobsite because the slump was below a minimum limit. The concrete producer’s on-site quality control technician noted the amount of
6 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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water added and that test cylinders were cast after the water addition. Another example of a smoking gun. In spite of the acceptable strength tests, which are probably a better indicator of w/cm than batch tickets and records of water added at the jobsite, he concludes that not only are you responsible for the cracking of the entire deck, but now the longterm durability of all the deck is questionable. So you’re guilty and responsible for all 30 of the trucks even though water was added to only two. In both cases, the evidence is circumstantial at best. But in the court of law on the construction site, circumstantial evidence is often all that’s needed to establish guilt and force the contractor to perform expensive repairs or provide additional protection based on an alleged potential durability problem. Can contractors fight back? Sure they can. But if they
It sounds like legalized extortion, but it exists on most jobs. do the math, it often costs less to just buckle under and spend some money they hadn’t planned on. In cases much more complex than the two described, filing a claim and then fighting a legal battle to win the case may involve hiring a lawyer and one or more expert witnesses. Adding in the lost productivity and opportunity time as result of producing documents, giving depositions, and perhaps testifying in court, the costs can easily run to more than $100,000. So unless the cost of fixing the problem exceeds $100,000 it makes little sense to follow this route.
There’s one other key factor that discourages contractors from pleading not guilty. It’s called retainage and it is a powerful weapon owners can use in forcing contractors to repair alleged defects. When it might cost $20,000 to repair the cracks in that concrete slab, but the owner is holding $200,000 of your retainage, the math gets even simpler. Just do the repairs and get at least some of your money owed. It sounds like legalized extortion, but it exists on most jobs. When there is an alleged defect and a specification noncompliance is identified, the two must be correlated. A root cause analysis should be performed to determine if the specification noncompliance is the cause of the alleged defect. If that root cause is removed, the problem goes away. Without this analysis, circumstantial evidence can lead to prosecution and conviction.
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10 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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LEGAL MATTERS
By David Whitlock
Training Supervisors Key to Avoiding Discrimination Claims
David C. Whitlock has over 25 year’s experience in business immigration, compliance, employment counseling and training. He is the founding attorney of Whitlock Law LLC and can be reached at (404) 626-7011 or at davidcwhitlock@gmail.com.
Knowing how to handle employee complaints may prevent a costly lawsuit later.
A
recent Fourth Circuit Court of Appeals case held that an employee can bring a claim of harassment discrimination based upon a supervisor’s single remark. Perhaps more important, the court also held that the employee is protected from retaliation even if the incidents complained of would not amount to a hostile work environment. What does this mean for the construction contractor? Contractors need to understand that they are liable for the conduct of supervisors. In general, supervisors – as members of management – are viewed as speaking on behalf of the employer. For this reason, contractors are automatically liable when a supervisor engages in “quid pro quo” discrimination, or “give me sex or else. . .” While quid pro quo cases are pretty obvious and serious, verbal conduct is less so. The Fourth Circuit case involved a white supervisor alleged to have made two racial comments to an African-American employee. The employee complained but was fired, and sued the employer alleging hostile work environment and retaliation. The company tried to dismiss the case by arguing the comments did not create a hostile work environment and since there was no illegal work environment the employee’s retaliation claim was groundless. The court disagreed on both grounds.
The construction industry is usually allowed a little more leeway when it comes to verbal remarks on the theory that it is a “hurly-burly” environment where harsh words and sometimes violent acts occur. That is increasingly problematic and risky.
DOCUMENT TRAINING OF MANAGERS Contractors need to document training of managers and supervisors. The training should specifically address verbal remarks and the consequences. Supervisors need to know that a single adverse remark may be enough to justify a discrimination claim that exposes the company to liability. The other important lesson here is that contractors need to be open and welcome any sort of complaint by an employee. You need to have a credible, sensible “open door” policy that allows employees to complain and, most important, protects them from retaliation. Here is some sample language: “We want our workplace to be safe and pleasant for everyone here. If you have a complaint or problem, please bring it to me or your manager/supervisor. If you do not feel comfortable raising the matter with your supervisor or me, please take it to (name person of opposite gender). In all cases, you will not be adversely affected by bringing the matter to our attention, although we reserve the right to do what we think is legally required and correct given all of the facts and circumstances.”
Note that the sample language features a male and female to bring a compliant to. This is deliberate and is required in sexual harassment scenarios to protect the contractor. The employee has a duty to report conduct but the process must facilitate reporting and not discourage it. Reporting harassment to a person of the opposite gender may discourage such reports and create liability for the contractor. An effective “open door” policy should list a person of each gender who will accept complaints on behalf of the company.
EMPLOYEE HANDBOOK Contractors with employee handbooks should consider putting similar language in their handbooks. Those contractors without a formal handbook can post similar language where it is likely to be seen by all employees. If and when an employee makes a complaint or reports a problem, contractors should reassure the employee that the matter will be treated with respect and, to the extent possible, confidentiality. Then, conduct whatever investigation or inquiry is warranted. Finally, draw a conclusion and take action. It is advisable to sit the employee down in private and explain why you have reached that conclusion. If you follow these steps, you will reduce the chances of getting sued and improve the chances of winning a lawsuit if you are sued.
12 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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e C on it dishink ork anks
FLATWORK/ SLABS
By Kim Basham, PhD PE FACI
Two Theories Related to Cracks and Rebar Do cracks increase the risk of steel reinforcement corrosion?
C
oncrete cracks for various reasons including plastic concrete shrinkage and settlement, thermal contraction, drying shrinkage and loading of the structure. Because the tensile strength of concrete is only about 10 percent of the compressive strength, even small tensile stresses associated with shrinkage and loads can crack concrete. Regardless of the cause, cracks in new structures typically raise concerns about an increased risk of rebar corrosion and premature concrete damage, especially if the structure is exposed to moisture. Historically, there have been two theories related to cracks and steel reinforcement corrosion:
THEORY 1 Cracks significantly reduce the service life of structures by permitting access of carbon dioxide, chlorides, water and oxygen to the reinforcing steel that accelerate the onset of reinforcement corrosion.
THEORY 2 While cracks may accelerate the onset of corrosion, it is localized and confined to the bar area intersected by the crack.
Random cracks in reinforced slabs caused by thermal contraction and drying shrinkage are not longitudinal cracks and typically do not increase the risk of reinforcement corrosion in concrete. Photo Credit: Kim Basham
Over the years, researchers have debated theories one and two using both laboratory and field test data (Ref 1). An abundance of published information appears to support both theories. However, A.W. Beeby, Dr. Chanakya Arya, and Professor Laurence Wood essentially ended the debate by concluding both theories are correct (Ref. 2 and 3). Briefly, these researchers (and others) concluded the following: 1. Crack width have little influence on corrosion. 2. Major factors controlling corrosion are concrete quality (e.g., cementitious materials content and water to cementitious materials ratio - w/cm ratio) and concrete cover 3. Corrosion potential is strongly influenced by the orientation of the crack relative to the reinforcement (i.e., coincident versus intersecting) Theory One applies to cracks that coincide with the
reinforcement and Theory Two applies to cracks that intersect the reinforcement.
REINFORCEMENT CORROSION Corrosion of steel reinforcement in concrete is due to an electrochemical process as illustrated in Figure 1. There are four essential parts to an electrochemical corrosion cell: 1. Anodic site where ferrous ions (Fe++) pass into solution and due to a secondary reaction with oxygen and water form rust (or the expansive product of steel corrosion). 2. Conductor (steel reinforcement) that provides a conduit for excess electrons (e-) to move to the cathodic site 3. Cathode where electrons are consumed in the presence of oxygen and moisture. 4. Electrolyte or wet concrete that provides a conduit for hydroxyl ions (OH-) to flow to the anodic site. Steel reinforcing bars embedded
14 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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FLATWORK/ SLABS
Figure 1: Simple illustration of the electrochemical corrosion process for steel reinforcing in concrete. Photo Credit: Kim Basham
in concrete do not corrode because the high alkaline conditions in concrete (pH > 13) produce a passive oxide film on the surface of the steel. The passive oxide film prevents corrosion. However, carbonation and/ or chlorides in solution can destroy the passive oxide film. Carbonation and loss of passivity can occur when atmospheric carbon dioxide penetrates into the concrete and in the presence of moisture reacts with the calcium hydroxide to produce calcium carbonate. Calcium hydroxide is a cement hydration product that helps create the high alkaline condition in concrete. Due to the formation of calcium carbonate around the steel, the alkalinity (pH) of the concrete falls from above 13 to less than nine. Subsequently, the low alkalinity destroys the passive oxide film. Carbonation is a very slow process in good quality concrete. Therefore, the risk of depassivation of steel reinforcing and onset of corrosion depends on the permeability of the concrete, concrete cover and exposure conditions (i.e., moisture). Of course, cracks can open a direct pathway for carbon dioxide to reach the steel and disrupt the passive oxide film. If the other essential conditions for corrosion
exist, then an anodic site can form and corrosion can occur where the crack intersects the reinforcing bar. For corrosion to occur, oxygen and moisture must be available at both the cathodic region and along the hydroxyl ion conduit (concrete) between the cathode and anode. Since these two requirements for corrosion are independent of the crack width, it follows that the corrosion rate of the steel reinforcing is also independent of the crack width. Many researchers report there is no correlation between crack width and steel reinforcing corrosion in concrete (Ref 4). Therefore, the major factors controlling the risk of steel reinforcing corrosion of cracked concrete are the quality of concrete and concrete cover — not the crack width. Good quality concrete (i.e., low permeability) and adequate concrete cover inhibits the cathodic site and the hydroxyl ion conduit from forming. Without the cathode and hydroxyl ion conduit, the electrochemical corrosion cell does not form and steel corrosion does not occur. High quality of more specifically dense concrete reduces the risk of
Figure 2: Longitudinal and transverse cracks. Photo Credit: Kim Basham
corrosion by restricting the penetration of oxygen and moisture into the concrete, restricting ionic movements within the concrete and increasing the bond strength of the concrete to the steel. Of course, the quality or more specifically, the permeability of the concrete depends on several factors including the cementitious materials content, water-cementitious materials ratio, concrete consolidation and curing. Increasing the cement content can help reduce permeability but also increases the alkali loading or content of the concrete that helps maintain the concrete’s alkalinity and preserve the passive oxide film on the steel reinforcement. Building codes establish the minimum concrete cover according to the anticipated exposure of the concrete to moisture. As the concrete’s exposure to moisture increases, the minimum specified concrete cover increases. For a #6 bar, the specified minimum concrete cover is three-quarters of an inch when concrete is not exposed to weather or in contact with the ground, two-inches when concrete is exposed to earth or weather and three-inches when concrete is cast against and permanently exposed to earth. Increasing the concrete cover reduces the risk of steel reinforcing corrosion.
CRACK ORIENTATION There are two orientations of cracking in reinforced concrete: 1. Longitudinal (i.e., cracks running parallel or coincidental with the steel reinforcing) 2. Transverse (cracks intersecting the steel reinforcement) as illustrated in Figure 2. Longitudinal cracks follow the line of reinforcement and transverse cracks cross the reinforcement. Transverse cracks include diagonal cracks.
LONGITUDINAL CRACKS Depending on the width of the crack where it intersects the steel, longitudinal cracks may promote corrosion of the steel
16 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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FLATWORK/ SLABS reinforcement. Increased risk of corrosion occurs because passivity of the steel may be lost at several locations along the reinforcing. In addition, the same crack may allow the migration of oxygen and moisture to the cathodic sites and to the hydroxyl ion conduit completing the formation of the electrochemical corrosion cells. Theory One applies to longitudinal cracks. Typically, longitudinal cracks occur due to plastic settlement or subsidence of the concrete, poor concrete quality and inadequate concrete cover. Poor concrete quality and inadequate cover may allow the formation of electrochemical corrosion cells and expansive corrosion products and subsequently cause longitudinal cracks to occur. Of course, the formation of longitudinal cracks typically and classically promotes the corrosion of the steel reinforcing.
TRANSVERSE CRACKS
REFERENCES
Intersecting cracks may open a direct path for carbon dioxide, oxygen and moisture to reach the steel reinforcing. However, because the cathodic sites are primarily confined to the crack-free regions of the concrete, any oxygen and moisture that penetrates into the crack will not affect the onset or rate of steel corrosion along the rebar or where the crack intersects the rebar. Therefore, transverse cracks do not increase the risk of steel corrosion unless the concrete is of poor quality and/or the concrete cover is inadequate so that oxygen and moisture easily penetrate the concrete. Theory Two applies to transverse cracks. When evaluating new cracks and the potential for rebar corrosion, crack orientation, concrete cover, quality of the concrete and exposure conditions are just as or more important than crack widths.
1. Darwin, D., “Debate: Crack width, cover, and corrosion,” Concrete International, American Concrete Institute, www.concrete.org, May 1985 2. Beeby, A. W., “Cracking, Cover and Corrosion of Reinforcement,” Concrete International, American Concrete Institute, www.concrete.org, February 1983 3. Technical Report No. 44, “The Relevance of Cracking in Concrete to Corrosion of Reinforcement,” A Report of a Concrete Society Working Party, The Concrete Society, www.concrete.org.uk, 1995 4. Beeby, A.W., “Cracking, Cover and Corrosion of Reinforcement,” Concrete International, American Concrete Institute, www.concrete.org, February 1983
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18 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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FLATWORK/ SLABS
By Ryan Olson
Elevation Control System Helps Meet Ff Specifications Easy-to-use screed support system brings efficiency and precision to flatwork projects.
M
aurin Construction began business in 2007 as a concrete subcontractor and found success working on public works projects. As the company’s work load grew, project specifications regarding Fl and Ff numbers were tightening up making it difficult for the contractor to meet the expectations of their clients. When the company accepted a project at a local school district featuring a 12,000 square foot footprint, slab-on-grade and one elevated deck, approximately 7,000 square feet, meeting the required specifications was crucial. The slabon-grade was to be six inches thick with two inches of sand, a vapor barrier and four inches of aggregate to be placed underneath the vapor barrier. The architect of the project demanded the floor meet the Ff 35 specification. “We were looking for a better, more accurate way to meet the Ff numbers on flatwork projects,” General Superintendent, Craig Whitaker says. “Specifically, we were looking for a solution to be able to offer the most level, flattest floor we could build, without puncturing the vapor barrier that was placed between the slab and the ground.” With a variety of products on the market, Whitaker says none of those
products met their needs. “The reason we got involved with MAKO Products is specifically because the vapor barrier options the company offers,” he says. “The MAKO product allows us to use a non-penetrating system that is accurate, sturdy and adjustable—which is really nice.” Whitaker is referring to MAKO’s Base Plate and FinCap 4.5 Screed Support System. The system provides exact elevation control for concrete slabs. The stay-in-place screed supports are fully adjustable to accommodate sub-grade variances or deflection in elevated decks. “The vapor barrier we were using is 15 mil thick, so it’s tough and hard to accidentally puncture, but it’s one of those things where you have to maintain the integrity of the vapor barrier,” Whitaker says. “That’s why
MAKO’s Base Plate and FinCap 4.5 Screed Support System provides exact elevation control for concrete slabs. Photo Credit: MAKO
the MAKO Base Plate and FinStands came in handy.” He says the crew was able to set the Base Plate and FinStands on top of the vapor barrier. For added protection, the contractor brushed the bottom of each stand with a mastic from W.R. Meadows – PERMINATOR Underslab Vapor Barrier Retarder and glued down the base plates. “This was not the recommended installation from the manufacturer,” Whitaker says, “but to me it was something that helped make the installation quicker and easier.”
22 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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FLATWORK/ SLABS PLACING THE CONCRETE
To ensure the correct elevation was maintained, the contractor periodically checked it using a string line and adjusted the height as needed. Photo Credit: MAKO
MAKO’s Base Plate 4.5 used with the FinStand system was designed for uses with vapor barriers, sandy soil or any other type of substructure. The FinStand snaps and securely locks into the Base Plate. Setup continues by inserting a ½” rod between the bottom of the FinStand and the Base Plate. Adding a hex nut and washer for additional height gain and fine tuning the adjustments will achieve the exact elevation required on the job. Set-up is complete by installing the non-metal FinCap which will work with a variety of mounting structures from 3/8” to 5/8”. The FinCaps support a nominal 1-1/2”– schedule 40 or higher screed pipe; or a 1-1/4” ID or 2” ID screed pipe may also be used. Whitaker says the installation was quick and easy. “It was the first time we used this system completely. We would set each base plate down, install the threaded rods and set the height nut to the designated height. We then periodically checked to ensure we were maintaining the correct elevation using a string line and adjust the height as needed.”
With the screed support system in place, the pour was scheduled to occur the following day. “In preparation of the pour, we tend to map out our pouring and screeding strategy depending upon the type of obstacles that might be within the slab,” he says. “We like to get the bulk of the mud down in order not to stall the pour and in this case, the pour was a fairly wide open area.” “One of the things I discovered was using the MAKO product caused our pour to go more efficiently. We spent the day prior trying to get things right and install the screed support system. It took us a few more hours than what I thought, but to me, it’s one of those things where all we have to worry about during the pour is picking up the pipe and moving it over to the next bay and making sure it is sitting in the cradle flush. During the pour, we had set up our TopCon laser system to make sure the finished floor stayed within the specifications.” As the concrete was placed, the four man crew followed behind with Multi-Vibe GX35 vibra screeds and continued to strike off the concrete, all while maintaining the proper height and levelness of the floor. “In our operation, we run the vibra screeds and then use a check rod to correct the highs and lows on the
floor,” Whitaker says. “After approximately three to four hours, crews make one pass with our Whiteman ride-on trowel installed with float pans. We then use a bump cutter behind the float pans for cut and fill.” To finish the floor, crews install the ride-on trowel with float pans and make another pass in three different directions before switching out the float pans with combo blades to lay down the concrete. Finish blades were installed on the ride-on trowel to finish the floor. “Considering our main challenge was making sure not to puncture the vapor barrier and achieve the desired Ff numbers, I was really impressed with the MAKO product, even if everything about it was plastic. It’s a very sturdy product.” Whitaker says he will be starting an elevated deck project soon and plans on using the product on that project as well. “It’s a lot easier and more efficient to use the Base Plates and the FinCaps on an elevated deck. We’ll still have the grade issues and this product will work just as well on these scenarios as it does on any slab-on-grade project.”
The FinStand snaps and securely locks into the Base Plate. Photo Credit: MAKO
24 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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FOUNDATION WALLS
By Joe Nasvik
Building Deep
FOUNDATION A new science and research building for George Washington University
E
ach year the Concrete Foundations Association (CFA) based in Mt. Vernon, Iowa holds a contest to honor the best and most difficult foundation projects of the year. Over the years, contractors occasionally submitted projects that were complicated beyond one’s ability to foresee all the problems and therefore become
financial losers. So Jim Baty, the executive director of the CFA, says they changed the rules of the competition so that submissions will reflect cutting edge technology but will also be profitable. “The quality of a project should not be based solely on its economic success but rather the quality of design and craftsmanship that go into it. A project that loses money is likely to be one that doesn’t stack up to such qualities,” he adds. Most contractor members of the CFA build residential and commercial foundations that go only one story into the ground and those have been the most frequently awarded projects
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The new Science Building for George Washington University presented big challenges to both the engineer and the contractor. It is nestled into a very narrow space surrounded by three dormitories and the Washington D.C. Metro tunnel. Photo Credit: Ballinger
ONS
along with above grade concrete homes. But this year they voted to recognize a large commercial deep foundation with the grand prize award. This also marks the first time a project application was submitted by the engineer of record for the job and the first time the winner is a commercial project—not a residential one. The award winning project is the new Science Building for George Washington University in Washington D.C. and the engineering group is Ballinger, located in Philadelphia, Pennsylvania. Articles appearing in the Concrete Contractor are usually told through the eyes of the contractor but this time you will have the opportunity to understand the challenges faced by the engineer and how his team addressed each challenge.
BUILDING IN WASHINGTON D.C. In Washington D.C., if you want to build a tall building you don’t build up, you build “down”. That’s because of the “Height Act” enacted by Congress in 1899 and amended in 1910. It stipulates that commercial structures cannot exceed 130 feet in height (there are a few exceptions in designated areas) in order that government buildings and shrines won’t be eclipsed. So when George Washington University wanted to build a new science building they decided to build the first six stories underground. This included two floors with research labs having floor to floor heights of 16 feet and four floors of parking below that. The above grade Supporting foundation walls and the protection of surrounding buildings was handled in several ways. Shown here, large steel tubes help to counter large lateral forces. Photo Credit: Ballinger
PROJECT INFORMATION Size: 1,200 lineal feet, 700,000 square feet Layers of Rock Requiring Excavation: Varies from 35 to 80 feet in depth Excavated Material: 4.2 million cubic feet Concrete: Walls: 5,100 cu. yds. Footings: 1,350 cu. yds. Reinforcing Steel: Walls: 190 tons Footings: 52 tons Basement Wall Height: 74 feet Wall Thickness: Varies from 20 inches to 32 inches Floors: • Two floors of 16 foot high research labs designed for 750,000 pound live loads • Four sloping floors for parking with 10-foot high floor to floor • Curving facetted speed ramp for driving from street level to the parking levels Substructure Cost: Approx. $20 million Substructure Construction Time: One year from start of excavation to completion of main street floor level. eight floors plus a mechanical penthouse include research labs, classrooms, offices and visitor spaces. Edward Zinski, Associate Principal and Chief Structural Engineer for Ballinger, says his company specializes in this kind of work but the complexities of this substructure and its 74 foot deep excavation provided many unusual challenges for both his company and the contractor, Clark Construction.
LOCATION CHALLENGES The new 700,000 square foot “Science and Engineering Hall”— with 300,000 square feet of the space being below grade—is located next to three dormitory buildings
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There are several sloping columns on the project, adding to the complexity of the design. Photo Credit: Ballinger
The vertical supports are “tangent piles”—drilled shafts filled with steel soldier piles and grouted. Tangent piles without steel fill the spaces between. You can see how close the excavation is to the dormitory building.
the floor diaphragms, with sloping parking ramps and other discontinuities in the floors.
Photo Credit: Ballinger
PROTECTING THE HOLE AND THE SURROUNDINGS
that were occupied during the entire time of construction. The shallow footings of these buildings at the edge of the excavation required deep underpinning. In addition, the Washington D.C. Metro tunnel was located within the adjacent street and care was taken to prevent damage to that structure. Rock elevations on the site varied from 35 feet to 74 feet so significant amounts had to be excavated and removed. Some of this was accomplished by blasting, completed while the surrounding buildings were occupied—students occupied the dorms, with times coordinated as to when the blasts occurred. The depth of the foundation created other unique challenges. Zinski said they had to plan on lateral soil pressures as high as 3,500 pounds per square foot (psf) on the basement walls. They then had to extensively evaluate the substructure’s two-way concrete floors for enormous lateral buckling forces translating through
Holes this deep with surrounding buildings must be protected from collapse and several methods were employed by Clark Excavation to do that. Zinski says near the existing dormitories they used “tangent piles”— drilled shafts filled with steel soldier piles, supported by tiebacks into the adjacent earth. These drilled holes were then filled with grout to encompass the steel piles. Secondary all-concrete tangent piles without steel were then drilled between the steel and grout filled piles. In other areas they used more conventional H-piles and lagging with tiebacks. In the lower areas where rock faces were exposed, workers installed standard shotcrete slurry walls. At the west wing between opposing dormitories, workers installed large diameter bracing pipe struts and at the north wing where the Metro subway tunnel abutted the new basement walls, diagonal bracing raker beams were used to brace the sheeting.
ENGINEERING A DEEP FOUNDATION From an engineering point of view there were major challenges to be resolved: • As noted, the deep basement walls had to be designed to resist maximum soil pressures of up to 3,500 psf—to put that in perspective, normal shallow foundation walls typically see only maximum soil pressures in the 45 to 60 psi range • “Surcharging” (vertical-load forces which add to soil pressures) due to the dormitories foundations had to be identified and engineered into the substructure. • The dormitory footings adjacent to the excavation of the new building required deep under-pinning to bring the loads down to rock. • Numerous aesthetically angled columns required engineered solutions, adding to the
28 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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FOUNDATION WALLS complexity of the project. Many other heavily loaded columns had to be transferred to adjacent columns because of driving lanes in the lower levels of parking. • The close proximity of the Metro Subway tunnel had to be addressed; specifically, the two substructure research floors housing sensitive lab equipment had to be isolated from the Metro vibrations. And if this was not enough, there was the daunting task of providing a complete three story tall highbay test-lab for George Washington’s Civil Engineering School within the building’s substructure. Zinski says they designed “strong walls” and “strong floors” on the second sublevel, located four floors above the building’s foundations. “This high-bay space, complete with 20 ton crane for moving the specimens, will be used for testing in academics and industry, with the potential to apply forces as high as 750,000 pounds vertically and 900,000 pounds laterally on materials being tested,” he says. “And this is the first instance we are aware of for a facility to have such a high capacity testing area free-spanning from column to column several stories above the subgrade.” The strongwall and strongfloor
consists of 4.0 feet and 4.5 feet thick highly reinforced concrete. Specifications required 6,000 psi compressive strengths but Zinski says concrete cylinders often broke at strengths in the range of 10,000 psi. In addition, 1-3/4 inch diameter solid post-tensioning (PT) Dywidag threaded rods were used instead of multi strand tendons to achieve 260,000 pounds per bar forces. They were inserted through metal conduit pipes cast into the floor and walls in critical areas. After they were tensioned the tubes were filled with grease in the floors and MCI-309 powder in the walls, for corrosion protection so that tensioning could be adjusted if necessary over the course of time. Zinski says there are other engineering features besides the superstructure, including a multitude of sloping columns throughout the project. On the street level many of these sloping columns are constructed using exposed architectural concrete for aesthetic appeal and hopefully to inspire the science and engineering students to greater innovation and creativity. There are also uniquely designed exposed concrete and steel composite trusses to create open spaces for multipurpose gathering on the main floor reception areas. An eight-level steel framed monumental stairway hangs through a full height atrium from concrete beams at roof level. Zinski made it clear that this extremely challenging project was only a success because of the many high caliber companies involved—the Boston Properties management team as the owner’s represetative, Clark Construction and their Excavation and Concrete divisions, Ballinger, A+F Engineers in Washington D.C. with superstructure, composite truss, and high-bay area design expertise, and Colin Gordon Associates in Brisbane,
In Washington D.C., if you want to build a tall building you don’t build up, you build “down”.
PROJECT PARTICIPANTS Owner: George Washington University Owners Representative: Boston Properties Architect: Ballinger, Philadelphia, Penn. Structural Engineer: Ballinger, Philadelphia, Penn. Vibration Consultant: Colin Gordon Associates, Brisbane, Calif. Structural Framing Consultant: A+F Engineers, Washington D.C. Ready-mix Producer: Vulcan Materials Company, Springfield, Va. General Contractor: Clark Construction, Bethesda, Md. Excavation and Concrete Contractor: Clark Construction Post-tensioning Company: VSL
California as the project’s vibration analysis consultants. Zinski says almost every engineering software was used to analyze the myriad of structural components and systems within this project. These included STAAD, SAP2000, ADAPT, RAM Elements, RAM Concept, RAM Concrete, ETabs, SP-COL, and SP-SLAB. At this writing the building is complete and the project has been very well received by the University. Zinski says Ballinger is honored to receive the CFA award. He believes that foundations are often overlooked by the building community, yet they can require so much more thought and care than people realize, and are absolutely crucial to the success of a building.
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DECORATIVE CONCRETE
By Wade Christensen
Concrete Pros Choose
DIAMAPRO UV for Warehouse Showroom
The DiamaPro UV System is a single component, aliphatic urethane that is ultraviolet lightcured. The result is a coating with excellent adhesion that is highly resistant to weathering, abrasion, and chemical corrosion. Photo Credit: Niagara Machine
T
urner Concrete Professionals, located in Atlanta, Ga, specializes in concrete surface restoration for general contractors, developers, architects, property managers and end-users throughout the eastern, southern and midwestern regions of the U.S. The company provides a multitude of services ranging from cleaning and repairs to resurfacing, sealing, densifying and coating.
After a decade of rugged use, company president Ken Turner decided to resurface the badly worn 4,000 square foot concrete floor in his own facility. It was Turner’s plan not only to rejuvenate the floor, but also to turn it into a warehouse showroom for his customers, as well as for a large property management company that also occupied the building. Turner’s plan included finishing the floor with the most recent advancement in concrete coatings, DiamaPro UV Systems. “We saw the resurfacing
of our own warehouse floor as a convenient means of familiarizing ourselves with this new product,” said Turner. “What better way to evaluate it than to try it out on our floor?” The company got in touch with Niagara Machine, Inc., exclusive distributor of DiamaPro UV, and the resurfacing project was underway. The DiamaPro UV System is a single component, aliphatic urethane that is ultraviolet light-cured. It requires no mixing, and is not dependent on ambient temperature to
32 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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Floors are prepped using the same process as traditional coatings: filling cracks and pop-outs, removing stains and soil, and evenly grinding the floor to achieve a flat service. Pictured here, stripped lines are applied to the floor first and then the UV coating will be applied to the floor. Photo Credit: Niagara Machine
obtain full cure. Photoinitiators in DiamaPro UV are stimulated under exposure to ultraviolet light and react with acrylates in the coating to provide an instantaneous cure. During the chemical process, double-bonded acrylate molecules in the coating cross-link to form dense polymer chains that yield an extremely hard and chemically resistant surface. The result is a coating with excellent adhesion that is highly resistant to weathering, abrasion, and chemical corrosion. The single greatest benefit of DiamaPro UV is the curing times required for conventional epoxies and urethanes are eliminated. With ultraviolet light-cured coatings, a concrete floor is immediately ready for use. UV coatings give managers the option to prep and coat entire floors, or portions of floors, as required, without significant downtime or service interruption. It can even be done overnight, yielding a ready to use floor when doors open the next day. “We’ve surveyed customers across the nation in industrial, food service, retail and health care applications, and they all mention downtime as the single
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DECORATIVE CONCRETE biggest drawback to resurfacing their concrete floors,” says Scott Thome, coating specialist at Niagara Machine. “Conventional epoxies and urethanes can require 48 to 72 hours to completely cure. DiamaPro eliminates that lost time. The floor is ready for normal traffic the moment the UV-light passes over the surface.” UV coatings are an inherently safe surface for employees and customers. The statice coefficient of friction (SCOF) for DiamaPro UV meets the National Floor Safety Institute’s certifications, ensuring a safe surface to walk on. And DiamaPro is environmentally friendly. UV curing involves 99 percent solids in a fluid state. It has an extremely low VOC level of 4.8 and is virtually odor-free. Since minimal volatile organic compounds (VOC) or hazardous substances are released during the process, there are no regulatory compliance issues. And DiamaPro has an unlimited pot life, so the formula
Curing is done using a portable machine emitting UV light. Photo Credit: Niagara Machine
can be readily stored for future use. The advantages of UV coatings aren’t limited to curing time and safety. One of the most important benefits of UV coatings is they result in a smooth, sanitary floor surface. “For applications such as food service, health care, pharmaceutical and retail operations, a sanitary surface is imperative,” says Thome,
“and DiamaPro results in a smooth floor that minimizes the entrapment of soil, dust and foreign particles.” Thome also stresses that DiamaPro UV coatings are easy to clean and maintain, and also resistant to the harsh chemicals often found in concrete floor cleaning agents. “The irony of concrete floor maintenance is that often the cleaning agent itself causes a coating to break down,” he notes. “Our studies have shown that DiamaPro UV is highly resistant to chemical corrosion. Regular cleaning doesn’t break it down.” UV coatings require no special preparation or application procedures. Floors are prepped using the same process as traditional coatings: filling cracks and pop-outs, removing stains and soil, and evenly grinding the floor to achieve a flat service. Diligent floor preparation enhances the effectiveness of any final coating, and UV products are no exception.
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DECORATIVE CONCRETE Diamond grinding with a threeheaded minimum planetary grinder is the preferred method for UV coatings since it results in an exceptionally flat surface. The UV coating is then applied with a squeegee, rolled out with a standard floor roller, and lightly back rolled with a wide roller. Curing is done using a portable machine emitting UV light. The existing concrete floor at the Turner Concrete Professionals headquarters had been coated and stripped numerous times by previous tenants. The first step in the prepping process was to remove previous coatings and repair spalls, pop-outs, and bolt holes from old shelving. The Turner crew used Metzger/McGuire Rapid Refloor and Pit Grout to repair scratches, gouges, pitting and other defects in the floor. Metzger/ McGuire RS 88 was used to fill and protect joints. Grinding and dust collection was done with three Lavina
Turner Concrete Professionals planned to rejevunate the floor and turn their warehouse into a showroom for their customers. Photo Credit: Niagara Machine
30G-X grinders paired with Ermator S-36 HEPA dust extractors. The Lavina grinders are propane powered and utilized a belt-driven planetary movement. The new X series boast a new stacked chain driven planetary system. An additional axis allows the entire base to float over the surface
in any direction. The Ermator S-36 dust collectors feature three vacuum motors providing 350 CFM and 110 inches of waterlift. Jet Pulse filter cleaning enables filters to be purged during operation, and drop-down dust collection bags ensure easy, dust-free handling and disposal. In addition to resurfacing, Turner’s plan called for the application of a company logo and corporate colors. The crew used Ameripolish SureLock Dyes in slate and patriot blue to recreate the logo and decorative design. To ensure a safe, non-slip footing in the dock area, an anti-slip aggregate was incorporated into the second layer of the UV coating. The DiamaPro UV coating was then applied and instantly cured with a portable Hammerhead ultraviolet light leased from Niagara Machine. Niagara Machine technicians provided onsite instruction and certification for Turner Concrete employees, a step-by-step, hands-on service that qualifies them to apply DiamaPro UV coatings for their own customers. “We like what we see,” said Ken Turner. “I think it says a lot that we chose DiamaPro for our own floor, and I’m looking forward to showing my customers the final results of this new coating technology.” Ed. Note: Wade Christensen is the Vice President of Niagara Machine. For more information visit www. niagaramachine.com.
36 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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Concrete Grinding Just Got a Whole Lot Easier! The Scan Combiflex 800DSP is a new type of concrete floor grinder unlike anything the industry has seen before. This machine is engineered with an integrated computer system and smart floor grinding and polishing technology that guides you through the entire job, virtually eliminating all guesswork from the grinding and polishing process.
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The Scan Combiflex 800DSP features a built-in touch display that shows tool wear, tool lifetime, machine speed, and power consumption. It provides recommendations for the kind of tool that should be used on the machine as well as the speed to reach an optimal wear. The 800DSP has pre-programmed hardness settings that correspond to the Mohs scale hardness readings from the floor. It then calculates the speed necessary to reach as optimal a performance as possible. It also features a gauge that gives you an estimate as to how much time is left before the tool needs to be replaced. A series of sensors throughout the machine continuously transmits data, providing operators critical information they need to do the job right. Instead of completing a job only to discover that it could have been done better, the 800DSP provides clear recommendations and warnings so you can make the right decisions at the right time.
« Senses the hardness of the concrete surface and calculates the speed necessary to reach as optimal a performance as possible. « Estimates how much time is left before the tool needs to be replaced.
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« Three-head planetary drive system with 9-inch heads for increased efficiency and smooth operation. This allows the 800DSP to grind or polish at higher speeds with minimal vibration and stress. « With a 32-inch grinding path, the ability to hold up to 18 tools, and a weight topping 882 lbs, the 800DSP is ideal for large commercial applications. Available in a 400V and 230V 3-phase.
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Call your Jon-Don Concrete Sales Rep to find out more about the Scan Combiflex 800DSP!
6/11/15 1:43 PM
PRODUCT FOCUS
By Ryan Olson and Curt Bennink
Grading Systems Offer Money Saving Options to Contractors Consider using a laser guided grading system or for larger jobs, an excavator guidance system when preparing your next jobsite for construction.
A
s a contractor you know proper surface preparation prior to construction contributes to the uniform and consistency of your finished product. Thanks to the latest in technology developments, Bobcat Company and Caterpillar Inc. have developed tools to help you perform your job more efficiently and save money in the process.
The grader attachment grades surfaces with precision and control while maximizing productivity. It features blades that move six different ways and a front bolster that oscillates 12-degrees to the right or left, allowing for grading on any surface.
LASER-GUIDED SYSTEM Designed for compact loaders, the Bobcat laser guided system helps contractors grade with greater accuracy in less time. “A larger factor contractor’s would want to worry about is the cost of doing the job,” says Katie Althoff, Attachment Product Specialist at Bobcat Company. “These costs include material costs and operating time. When a contractor uses a laserguided system, you are able to affect both of those factors.” Operators will increase their efficiency to reduce fatigue since they can focus on the
Photo Credit: Bobcat Company
machines’ travel, rather than the blade position. Additionally, Althoff says fewer laborers are needed on the jobsite because there is no need for a crew to continually check grade on the jobsite. “If you can produce a more accurate grade, you will use less material
and save money,” Althoff says. “You’ll be more accurate, and you won’t have to put in more grade fill. The end product is better. The job is completed faster. You’re using less material and hopefully you’re passing these reduced costs on to your customer to make your bids more competitive.”
38 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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PRODUCT FOCUS Bobcat Company offers three laser transmitters: one single slope model and two dual slope models. The laser control system increases precision when operating the box blade or grader attachment. Both the box blade and grader work well on flat and single slopes. On dual slopes, the grader attachment delivers increased functionality, with each side of the blade operating independently.
LASER GRADING ATTACHMENTS The grader attachment grades surfaces with precision and control while maximizing productivity. Designed for use in landscaping, curb and concrete flatwork, the grader attachment features blades that move six different ways and a front bolster that oscillates 12 degrees to the right or left, allowing for grading on any surface while minimizing the effect of uneven ground.
The box blade attachment allows contractors to grade with laser accuracy. The box blade incorporates end wings to help carry soil and features elevation control, which allows the box blade to travel up and down slopes while still delivering accurate results. On the jobsite, the laser transmitter is mounted on a tripod to provide a 360-degree plane of reference at a set elevation and slope. Laser receivers, mounted on a mast attached to the box blade or grader attachment, capture the light from the laser transmitter. In manual control mode, the receivers inform the operator via LED lights when the blade needs to move up or down, or that the blade is on grade. In automatic control mode, the receiver informs the blade that it needs to move up or down to stay on grade. With the box blade attachment, one receiver—mounted in the
middle—moves the entire blade up or down. With the grader attachment, two receivers are mounted so that so each side of the blade will adjust independently. Moving the grade up or down, beginning at 0.1 inch increments and up to two inches in either direction makes it easier for the operator to make adjustments on-the-fly without leaving the cab to raise or lower the transmitter. For added efficiency, the company introduced a 96-inch blade and a 108-inch blade to complement the
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flail grinder, diamond shaver, groover, floor grinder/polisher, coating removal 40 hp Kohler engine Quick change tooling Hydraulically driven tool Hydraulic power steering LED dual head lights LED rear tail lights 12 volt electrical system Lifting eyes at four points Hydrostatic vehicle drive Optional canopy Solid or pneumatic tires www.rotatorsolutions.com www.roadproonline.com 405.598.6547 Tecumseh, OK
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The box blade attachment incorporates end wings to help carry soil and features elevation control, which allows the box blade to travel up and down slopes while still delivering accurate results. Photo Credit: Bobcat Company
previous 84-inch blade set-up. “This introduction has had a big impact on how people see the system being used,” Althoff says. “As you can imagine, with a 108-inch blade, a contractor can get a lot done on the jobsite.”
EASE OF USE? Operators who are familiar with running this type of equipment will find the system to be learned quickly. For those contractors who might be weary of embracing new technology, Althoff says not to worry. “The overall setup time is about 30 minutes and all a contractor needs to do is plug in the device, fill in your slope, set your tripod on top of the grade stake
and set up your receivers. It’s not as complicated as people might think.” Althoff offers this piece of advice, “Don’t be afraid of the technology that is coming. It will help you do your job better and more efficiently.” In fact, Althoff sites one contractor she recently spoke with who said, “I need to buy a laser system because the competitive contractor in my area has one and he is beating me on every single quote.” “This is the perfect example of contractors needing to keep up with the competition,” she notes. “It’s in your best interest to be competitive as well. If there isn’t a competitor in your area, now is the time to learn more about these technologies and take advantage of the opportunity to become more proficient and in turn, win bids and quotes with your clients.” As far as the future is concerned, Bobcat is looking at other areas to expand to a full
line of technology enhancements. “There are different uses for the laser guidance systems and exploring how else we could use the system beyond the grade line is exciting,” Althoff says.
EXCAVATOR GUIDANCE SYSTEMS While excavator guidance systems have been around for a few years, the adoption rate has been slow. Caterpillar recently introduced excavators with integrated grade control technology to help customers realize the true potential of this technology. Caterpillar offers an integrated 2D guidance system that can be simply upgraded to 3D to allow customers to witness the productivity gains with minimal risk. Scott Hagemann, market professional for the machine control and guidance group, Caterpillar, says customers have been slow to adopt grade
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PRODUCT FOCUS control technologies for excavators because the systems are indicate only. “As the customers transfer to using technology on motors graders and dozers, they will not want to set stakes just for the excavator. Without trying the technology on their excavators, the customer does not know the productivity being lost. Once the system is demoed, they see how much of a benefit even indicate-only technology is and the need to have it.” Cat Grade Control Depth and Slope is a 2D depth and slope guidance system designed to help guide the operator to a preset grade. Caterpillar chose to integrate the system on its standard 323F L excavator, which is in the highest volume size class — 50,000 to 55,000 lbs. “It is a 23-metric ton machine,” says Brian Stellbrink, market professional for F Series Excavators, Caterpillar. The system comes standard on all excavator model configurations equipped with
The Caterpillar system works by utilizing a series of sensors, including a sensor in the bucket cylinder, a rotary sensor at the boom to stick connection and a sensor at the base of the boom. Photo Credit: Caterpillar
the 9.5-foot. stick. “It needs only to be activated at the dealership as part of a routine delivery.” While integrated on the 323F, the system makes sense for other size excavators, as well. “It is beneficial to order Depth and Slope on all sizes,” says Hagemann. Using 2D depth and slope guidance, the excavator knows where the bucket teeth are relative to the base of the machine. It works by using a series of sensors, including a sensor in the bucket cylinder, a rotary sensor at
Cat Grade Control Depth and Slope is a 2D depth and slope guidance system, so the machine knows where the bucket teeth are relative to the base of the machine. Photo Credit: Caterpillar
the boom-to-stick connection and a sensor at the base of the boom. The sensors allow the machine to calculate the position of the stick relative to the boom and the position of the boom relative to the base of the machine. “Knowing all that geometry, the machine can calculate automatically
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where the teeth are relative to the base of the machine,” says Stellbrink. The operator can now set the desired depth and slope from inside the cab. “For example, if you’re doing a 10 foot cut with a two percent slope, you can enter that in the monitor, bench that bucket off a known point and start to dig,” says Stellbrink. “[The system] will guide you through audible alarms in the cab and a standard display on the monitors to dig toward that preset grade.” It helps operators to be more productive, finish the job faster and rely less on ground support. It can also lower labor costs, since you are not as reliant on a grade checker. “The 2D system will help our customers dig footings and basements where a flat surface is needed, or dig a sloped surface for a drainage pipe,” says Hagemann. Cat Grade Control Depth and Slope is available on excavators only from the factory. “This system cannot be installed at the dealer,” says
Hagemann. “The basic advantage of having Cat Grade Control Depth and Slope installed at the factory is integration. We can route the harness out of harm’s way. We relocate the bucket sensor from the bucket linkage, which is exposed to being damaged, and put the sensor into the bucket cylinder.” He adds, “For the operator interface, we use the standard display that is in every one of our F Series excavators. We also use the joystick switches to control the functions of the system, so operators don’t have to remove their hands from the controls to interact with the Depth and Slope system.”
A BUILDING BLOCK APPROACH There are two advantages to the Cat system. “One is the 2D functionality and the other is the ability to use integration to add 3D,” says Hagemann. “Our dealers have told us it takes less than four hours to install
3D on an excavator that has Cat Grade Control Depth and Slope.” Without the system, a lot of time is spent routing harnesses and welding brackets. “It can take dealers up to 16 hours to install 3D on an excavator that has no technology on it.” Cat Grade Depth and Slope makes it easy to transition to 3D. “It’s a building block to go to the full 3D system,” says Stellbrink. “It’s very cost effective even for those customers who know they want a full 3D GPS system. This system is working very well for those who are digging basements, single trench digging—task-specific jobs within a given jobsite. As you start to move around a jobsite and load plans, that’s often when customers will go to full 3D GPS, which can be built directly on top using the same sensors. The 3D GPS basically adds a radio, masts on the back of the machine, satellite receivers and one more monitor inside the cab.”
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CONCRETE TECHNOLOGY
By Carl Taylor
The Constructable Model: What’s In It For You? Contractors who invest in BIM technology will reap the benefits including improved efficiency and increased profitability.
B
uilding Information Modeling (BIM) is no longer just for architects, design engineers and general contractors. New advances in BIM technology allow concrete contractors to build constructable models that can streamline internal processes to improve efficiency and productivity throughout the project lifecycle. While constructable models are BIM, not all Building Information Models are constructable. The difference between design models and constructable models center on the level of accuracy, development and detail present in the model. To be useful to a concrete contractor, a 3D project model must be constructable. That means it includes accurate, actionable geometry and data that concrete
contractors can use to estimate, plan and manage pours. It will include accurate geometry and accurately sized and located embedded items to ensure conflicts are immediately obvious. It also might include pour breaks, rebar, and formwork and shoring detail, as well as associated data such as grade and mix designs.
CONSTRUCTABLE MODELS: THEY’RE NOT JUST FOR THE BIG JOBS Concrete contractors began testing the waters with 3D modeling three years ago. Their successes have spurred others to follow suit, and the rate of adoption has rapidly accelerated within the last 12 months. This is largely due to improvements in 3D modeling tools that now include functions geared towards the specific needs of concrete construction trades as well as a healthier economy. The adoption of the technology is directly related to management’s
vision and desire to improve internal processes and become more competitive. Today, concrete contractors building constructable models range from small businesses doing local work to national companies, and their projects range from building homes to high rises. When a concrete contractor is the first to use constructable models in a market, competitors commonly follow suit soon thereafter—a strong testament to the value of the technology.
BARRIERS TO ADOPTION Concrete contractors might delay adopting 3D modeling for several reasons; mostly due to misconceptions on what it entails and not understanding how it can benefit the business. In most cases, a concrete contractor’s only exposure to models are the design models supplied by engineers, which are often of little use to them as they lack detail and are very different from models created for constructability. Others may use BIM when the general contractor demands it, but not on projects where it’s not a requirement because they don’t fully understand how it can benefit their business through internal process improvements.
Concrete contractors that build constructable models improve their internal processes and productivity, which directly impacts profitability. Photo Credit: Tekla
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CONCRETE TECHNOLOGY Some concrete contractors believe adopting 3D modeling will be too much of an effort and too great a change to tackle, especially when business is brisk. Or they believe they will have to buy expensive computers and hire a BIM expert. In truth, most computers used for CAD will support 3D modeling, and current employees can be trained to build and use constructable models within a few days. There is no reason to hire a BIM expert since the purpose of using 3D modeling is to help staff do their jobs better. Most companies phase the technology into their businesses. They may start by building constructable models for estimating or planning and then expand the use to other areas, mastering each before moving on. Another barrier to adoption is the belief that building a model is difficult and time-consuming. In reality, working from the contract documents supplied by the structural engineer, it doesn’t take much time to build a
constructable model. Moreover, the process of the building the model provides a greater understanding of the job. Taken together, the benefits far outweigh the investment.
THE BENEFITS OF USING CONSTRUCTABLE MODELS Concrete contractors that build constructable models improve their internal processes and productivity, which directly impacts profitability. The model can help them throughout the project lifecycle, from estimating the job through construction. • Job estimating: Because of the accuracy of details included in a constructable model, estimates can be quickly generated with a very high degree of accuracy and confidence. Modelgenerated estimates are more competitive because they don’t need to include the large contingencies common with traditional estimates.
• Pre-construction planning: Constructable concrete models help people understand exactly what the project entails. Potential problems can be identified and resolved during
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46 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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Building constructable models allows contractors a greater understanding of a job and better communication and collaboration with the field crew as well as construction site productivity gains. Photo Credit: Tekloa
the planning stage, preventing expensive, schedule-delaying fixes at the jobsite. • Communication: Constructable models are invaluable tools for communication, both internally
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and with other stakeholders. It’s much easier and faster to share a model or take a snapshot of the area in question to resolve an issue than it is to rely on written descriptions in an RFI. • Project drawings: Accurate 2D drawings can be automatically generated from the model as needed. When changes are made to the model, updated drawings can be produced to reflect those changes. • Construction: Constructable models are being used for pour planning and scheduling as well as managing rebar and formwork. Concrete contractors who use robotic total stations to layout points at the jobsite can
take direct feeds from the model instead of taking the information from 2D drawings, which results in dramatic productivity improvements. Formwork utilization is also improved by using information contained in the 3D model to order exact sizes and quantities and then optimizing the sequencing for reusing pieces throughout the project. Similarly, the model can be used to visually communicate the pour schedule to the general contractor and follow-on trades.
REAL-WORLD PRODUCTIVITY PROOF POINTS Many concrete contractors and self-performing general contractors have already experienced the productivity gains of building constructable models, including Cidon Construction, Haselden Construction and The Weitz Company.
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CONCRETE TECHNOLOGY Within six months of generating estimates from constructable models, UK concrete contractor Cidon Construction reduced the cost to create bids by 50 percent. They expect to reduce this by another 10 percent over the next six months. Moreover, their ratio of winning bids has improved from winning one in ten to winning one in four. This is because the information they are getting from the model is complete and accurate, which increases their confidence in the numbers and allows them be more aggressive in their pricing. Haselden Construction has seen a 33 percent reduction in concrete waste during estimating and placement since they began using constructable models. In addition, their quantitative errors in estimates have been reduced to nearly zero. They also report a 75 percent time savings when pricing change orders.
On the jobsite, they have reduced the time it takes to lay out points, typically reducing the task from a week to a day. Finally, they’ve cut their paper waste by 66 percent. The Weitz Company was able to layout over 500 points, including sleeves and anchors, on a 15,000 square foot deck in a single day by taking information directly from the model to the robotic total station. This was a dramatic time savings over using tape and string. The benefits of building constructable models extend across the concrete process. Some such as greater clarity and understanding of a job and better communication and collaboration with the field crew or other stakeholders are not quantifiable but are clear benefits for process improvement. Other benefits are distinctly quantifiable, including estimating and construction site productivity gains. Concrete
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contractors who embed constructable models into their businesses will quickly see process improvements, resulting in winning more new and repeat business, better results, cost savings and profit. Ed. Note: Carl Taylor is Segment Manager—Concrete, North America, at Tekla, a Trimble Company. Tekla Structures is an open BIM software package designed specifically to streamline the construction process by enabling general contractors, concrete contractors, steel, rebar and pre-cast fabricators, steel detailers and structural engineers to build constructable building information models that can be shared with the entire project team. For more information, call 877-TEKLA-OK or visit www.tekla.com.
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48 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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RIDE AND UTILIZATION
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EQUIPMENT: BURNISHER
By Whit Beverly
Propane Burnishers Offer a Green Alternative, Profit A new generation of propane burnishers maximize efficiency, minimize waste and are environmentally friendly.
I
n commercial cleaning today, everybody wants the job done quicker, cheaper and “greener.” The contractor’s only chance to survive and prosper is to maximize efficiency; which means the right tool for the right job—do not kill a fly with a hammer. For example, when choosing cleaning chemicals, you should choose one just strong enough to do the job quickly and completely. Too much of a chemical (or too strong a chemical) will leave dangerous residue or affect Indoor Air Quality (IAQ). Similarly, an alternative chemical that is too weak might be “greener” but require much more chemical to do the job. Any initial savings are eliminated in increased material or labor, eliminating your green benefit and your efficiency. The larger impact of the larger environmental lifecycle for cleaning methods should also be considered. For example, an electric car seems very green to the consumer who just plugs it in, however it actually has significant environmental lifecycle drawbacks. The making of electric car batteries is so damaging to the environment that only two countries in the world allow it. The batteries
only last six to eight years then need to be replaced, filling landfills with heavy metals. Additionally, while electricity seems clean, most is still generated from burning coal—a significantly dirtier process than burning gasoline or propane. Propane floor burnishers are made to maximize efficiency and minimize waste. They are extremely fast and contrary to popular belief— very green. The new generation of propane burnishers are the greenest burnishing machines on the market based on machine expense, labor expense and emission certifications.
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Based on the above, it would take two battery powered machines or three corded electric machines to do the same job in the same time. Battery burnishers cost $6,000, corded electrics $1,500 and propanes $2,200. (See Figure 1)
Figure 1: Machine Expense
Total Machine Expense to Polish Floors at a Rate of 20,000 sq. ft./hr.: Corded Burnishers
Qty. Req.: 3
3 x $1500 each
$4,500
Battery Burnishers
Qty. Req.: 2
2 x $6000 each
$12,000
Propane Burnishers
Qty. Req.: 1
1 x $2200 each
$ 2,200
MACHINE EXPENSE The purpose of a burnisher is to polish the floor to a “wet-look” shine. According to The Official ISSA 447 Cleaning Times, a propane burnisher will polish a floor at 19,355 square feet per hour. The production rate of a 2,000 rpm corded electric machine is 8,333 square feet per hour—or less than half the speed of the propane. Practically speaking, corded electric machine is really only about one-third the speed of a propane because of the need to change plug locations. A battery machine will do 9,677 square feet per hour—or exactly half the speed of the propane. Because there is no need to worry about cords, this work rate is accurate.
Ideally you would be able to stretch the machine life to six years with any of these machines, but with the battery burnisher you should expect to go through two additional sets of acid lead batteries at about $2,000 per set, increasing your total expense to $16,000 for a six-year machine life.
LABOR EXPENSE The other major expense in cleaning is labor. Using the above The Official ISSA 447 Cleaning Times, and based on a 60,000 square foot store with a labor rate of $15 per hour. (See Figure 2 and Figure 3)
50 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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Figure 2:
Labor Expense based on a 60,000 sq. ft. store with a labor rate of $15/hr. Corded Burnishers
Man-Hours Req: 9
9 x $15/hr
$135
Battery Burnishers
Man-Hours Req: 6
6 x $15/hr
$ 90
Propane Burnishers
Man-Hours Req: 3
3 x $15/hr
$ 45
EMISSIONS AND IAQ (INDOOR AIR QUALITY) Obviously there are no emissions from corded electric machines, however most electricity is generated from very dirty coal burning plants, contributing to greenhouse gases, global warming and acid rain. There are also dangerous emissions connected with battery powered machines. Lead acid batteries vent lead acid fumes when they charge. Propane machines create very low levels of carbon monoxide emissions— so low they have to be measured in parts per million (ppm). The vast majority of propane burnishers made by responsible companies also use catalytic converters to mitigate the chance of problems with carbon monoxide. Like in an automobile, these catalytic converters change carbon monoxide to carbon dioxide.
dusty or settle back on the floor. A dust control buffer can significantly reduce the amount of shelf dusting and dust mopping required to keep a store clean.
In the USA, the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) very carefully regulate the use of propane indoors. Each manufacturer of propane equipment is required to submit their propane engine to be tested and approved. Once it is approved the manufacturer is required to make every future engine the same way and to test the emissions on each new machine before it leaves the building. Additionally, the EPA requires a performance bond of up to $1,000,000 from small and midsize manufactures to assure strict compliance to approved conversion procedures.
Total Costs Break Down for a 60,000 sq. ft. store: Machine Expense
Labor Expense
Total Expense
Corded Electric
$ 4,500 (3)
$63,180
$67,680
Battery Electric
$12,000 (2)
$42,120
$54,120
Propane
$ 2,200 (1)
$21,060
$23,260
Dust control is another major advancement in green cleaning —specifically in the area of IAQ. A propane burnisher with dust control collects the dust, powdered finish and pad fiber particulate in a vacuum bag located on the machine. Because this dust is captured, it is not released into the air to clog lungs, make store shelves
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www.forconstructionpros.com/concrete | June/July 2015 | Concrete Contractor 51
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EQUIPMENT: BURNISHER section 5.5.1.2 covering hard floor maintenance machinery.
THE EDUCATED CONSUMER As technology progresses, the advances that have been made with equipment, chemicals and processes are truly amazing. But as products benefits improve, they typically become more complicated. It is
very important for the consumer to adequately self-educate and clearly understand what he is buying and how it will benefit his business. Often the people who are yelling the loudest about their products are substituting volume for facts or sensationalizing intangibles. Do your own homework. Make sure to take into account all the expenses of the
process lifecycle, including initial machine expense, labor expense, replacement parts expense and disposal expense – both to you and to the environment. Make profit and be a good steward. Ed. Note: Whit Beverly is the President of Aztec Products. He can be reached at whitbev@aztecproducts.com.
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52 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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By James R. Baty II
FOUNDATION Q&A
Standing Water in Prepared Footings: A PROBLEM OR
A PRECAUTION? The Concrete Foundations Association explains the concern for structural integrity of concrete footings due to water in the excavation.
Q
uestion: I visited the site of my new home and noticed a lot of water standing where the concrete walls will soon be poured. Won’t this be a problem for the quality of concrete in my footings? – Home Owner (Missouri)
A
NSWER: This is a very common question, particularly during the predominantly rainy spring construction season. Concrete, as we know, is a basic mixture of water, cement, sand and large aggregate. There are also chemicals in virtually all of modern mixes for a variety of performance enhancements. One of the most critical parts of the mix design is the specified watercementitious material ratio (w/cm). This specification will ultimately determine the effective strength properties of the mix as well as controlling the volumetric change during the hardening changes. This column has previously addressed the nature of increased water in mix designs. At the very heart of this question is
Spring rains left this foundation with standing water in the excavation. Concrete placements should take place promptly before saturation of the grade occurs. Photo Credit: Concrete Foundations Association
the basic idea that if a concrete mix is placed into water it will be harder for it to dry and therefore harden to be strong enough to support the structure. After all, most homeowners see concrete as a fluid that must first dry to get hard and if even more water is present, it must be like the glue their children use in school and weaken as the water mixes in. Although the homeowner may be justified with some concern for the presence of standing water, the strength of the concrete in the foundation is more than likely not part of it. As a contractor, your duty is to provide assurance for the performance of your construction. When it comes to a concrete mix, that assurance includes some basic facts: • The strength of a concrete mix comes from the ratio of water to cement (or cementitious material)
and is referred to as the w/cm. • Once created at the ready mix plant, the introduction of water “into” the mix will weaken the concrete and may upset the w/ cm ratio more than the design calls for. • Concrete weighs more than water and it will displace the water when introduced into any container or form rather than mixing with that water. • Concrete hardens due to a chemical reaction and does not “dry” to harden. Water is required for the chemical reaction to occur with the cementitious material. Concrete piers for a bridge over a body of water is an excellent example of concrete hardening in water. ACI 332-141 states in the commentary section R6.2.4: …If the footing
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FOUNDATION Q&A form permits water to exit, the hydraulic pressure of the concrete placement is sufficient to displace the water from the formed areas and prevent segregation. This commentary builds on the minimum code requirement for not placing concrete in confined areas with water. This section provides recognition that concrete has a mass greater than that of water and during a placement operation, the concrete will displace or move the water due to a combination of this mass and the force of discharge creating a greater hydraulic pressure than the water can withstand. Moving ahead of the concrete placement, the water will exit the formed footing space at the first opportunity. If the footings are excavated into the undisturbed soil and there is no point at which the slope produces a natural exit, the concrete placement force and weight is still likely to force the water to exit over
the top of the footing space. As long as the placement proceeds to fully displace the water, there should be no cause for concern. Only when the concrete does not fully displace the water will the partial volume of concrete and water result in segregation of the concrete mix where the large aggregate is separated from the cement paste. Some precautions to follow include: • Prevent the water from segregating the mix or being incorporated in the mix by pushing the water with the flow of the concrete. A recommended practice for all concrete placement, this keeps the hydraulic pressure of the concrete flow influencing the water. • Provide a way for water to escape during the placement at key junctures in the forms if possible. The homeowner is likely also concerned with seeing mud, knowing that mud is softer than dry soil and
thinking it is not ready to carry the load of the concrete foundation and therefore the house. There are some facts that can assure the homeowner for this concern as well: • Footings and foundations are prepared on an excavation of “undisturbed” soil. This means the surface of the soil is cohesive or of a consistent strength. • Standing water does not absorb quickly or easily into the surface of a cohesive soil. • Water can be removed from an excavation without requiring compaction of the soil. Water present on the top of soil does not immediately present a problem as saturation takes time. Depending on the type of soil and likely for most soils encountered for a foundation, that time can be considerable. However, the contractor must determine if the water presence has been sufficient to alter the surface of
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54 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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FOUNDATION Q&A the prepared excavation. The IRC2 provides reference to this condition as follows in section R401.4.2: Compressible or shifting soil. Instead of a complete geotechnical evaluation, when top or subsoils are compressible or shifting, they shall be removed to a depth and width sufficient to assure stable moisture content in each active zone and shall not be used as fill or stabilized within each active zone by chemical, dewatering or presaturation. In other words, when the surface condition of the excavation is changing or no longer holds the condition of the designed soil capacity, remediation needs to occur. This is often a last resort that can be prevented with some common precautions including: • Limit the time water stands in the excavation by moving forward with concrete placement or removing the water. • Control the amount of traffic in the excavation. Foot traffic in areas of standing water will accelerate working the moisture into the soil, impacting the surface condition and the compaction of that top layer. • Prior to concrete placement, all loose, silty soils should be removed with a shovel along the
bottom of the formwork, exposing the cohesive base. Saturated soils do have a lower bearing capacity than the predicted or assumed condition. This is mainly due to expansion of the soils as the volume is increased with water. If concrete placement can be achieved soon enough, it is unlikely the water will have moved into the soil sufficient to disturb the compaction and bearing capacity will be maintained. When soils are determined to be saturated or when the placement could not be made quickly enough, the excavation should be cleared of the loosened soils, mud and water sufficient to re-establish the soil-bearing capacity assumed for the design. Contractors should not be surprised to hear this concern from the homeowner. Knowing the facts, providing the reassurance and identifying the resources that can support your position are keys to a productive conversation on this issue. In fact, the contractor may very well have anticipated the inclement weather, and as stated previously, designed the forms for the movement of water. The contractor may also have experience in the remediation of the saturated soil condition, either removing the affected regions or drying out the
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excavation and ensuring compaction. Knowing the provisions of ACI 33214, and the IRC, will help deliver a positive outcome to a natural part of the construction process. Ed. Note: Want to know more? Contact CFA Executive Director, Jim Baty at 866-232-9255 or by email at jbaty@cfawalls.org. The CFA is a national association with the mission to support the cast-in-place contractor as the voice and recognized authority for the residential concrete industry. ACI 332-14 can be obtained by contacting the CFA or by visiting the American Concrete Institute (www.concrete.org) and ordering from their bookstore. REFERENCES: 1. Residential Code Requirements for Structural Concrete (ACI 33214) and Commentary published by the American Concrete Institute, 38800 Country Club Drive, Farmington Hills, MI 48331 | Phone: 248-848-3700 | www.concrete.org 2. 2012 International Residential Code For One- and Two-Family Dwellings published by the International Code Council, Inc., 4051 West Flossmoor Road, Country Club Hills, IL 604785795 | Phone 1-888-422-7233 | www.iccsafe.org Jim Baty is the Executive Director for the Concrete Foundations Association after having served as Technical Director since 2001. He is currently chair of ACI 332 and a voting member for ACI 306 with priorities of establishing better guidance and structure for residential concrete construction. For more information on this topic, contact Jim Baty at jbaty@cfawalls.org. Find out more at www.cfawalls.org. The CFA is a national association to support the cast-in-place contractor as the voice and recognized authority for the residential concrete industry.
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56 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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THE LAST PLACEMENT: BACK TO BASICS
By Ryan Olson
How to Plan Your
CONCRETE POUR
A
s a contractor, you know concrete is a perishable product. As such, taking the time to plan out your concrete pour is critical to your success on the jobsite. A successful pour requires a thorough review of every detail from the mix design to the final finished specifications. Here are a few tips you should consider in order to complete the pour.
PLANNING THE POUR Schedule a pre-slab meeting between the project superintendent and the crew foreman. The pre-slab meeting will allow all parties involved in the pour to review explicit details of the project: • Finish requirements • Equipment required to complete the job • Pour date and schedule • Labor requirements • Review the mix design • Rebar chairing/pulling • Saw cut layout This meeting should be scheduled at least one week in advance of the pour. This is also a good time to
start reviewing the weather forecast for the day of the pour.
PREPARE FOR THE POUR Three to five days prior to the pour, you should schedule a meeting between the concrete superintendent and the ready-mix service tech. The ready-mix tech needs to know exactly where the trucks are going and how the jobsite will be marked. This is also an opportunity to identify the staging and washout areas on site. The layout of the saw cuts are reviewed and confirmed with specifications, as well as the method of curing. Some contractors utilize a prepour checklist to provide a simple reminder of the key points in your preparation. A pre-pour checklist will also ensure consistency on each and every pour. The day before the pour, call your concrete supplier to double check your order. On the call, you’ll want to make sure the correct mix is ordered and if you’ll have enough concrete to complete the job. You should also make sure you have your curing product and all required equipment onsite to complete the pour.
PROCEED WITH THE POUR
On the day of the pour, the concrete superintendent is responsible for: • Making certain the testing company is checking slumps of trucks • Staging of the trucks and avoiding bottlenecks while unloading and washing out • Making sure all trucks are cycling to return to the plant and back to the project in a timely manner • Maintaining visual contact with the pour to avoid damage to underground plumbing/electrical by trucks • Ensuring reinforcing rebar/mesh is being chaired and/or pulled correctly • Ensuring that vibrating is being done correctly • Ensuring that carpenters are watching forms to avoid bowing/blow-outs and installing necessary cold joints During the pour, some contractors take pictures to document the pour. Should a problem arise in the future, documenting the job with pictures may be beneficial to you.
58 Concrete Contractor | June/July 2015 | www.forconstructionpros.com/concrete
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