Construction Materials
Dr. BUN Kim Ngun
Content of the course Chapter
1
Introduction
2 Aggregates 3 Asphalt 4
Portland Cement Concrete
5
Iron and Steel
6
Wood
7
Masonry
Chapter 3 – Asphalt What’s Bituminous Materials? • The term bituminous materials is generally used to denote substances in which bitumen is present or from which it can be derived.. • Bitumen is defined as an amorphous, black or darkcolored, (solid, semi-solid, or viscous) cementitions substance, composed principally of hydrocarbons, and soluble in carbon disulfide.
Chapter 3 – Asphalt What’s Bituminous Materials? • For civil engineering application, bituminous materials include primarily asphalt and tar. • Asphalts may occur in nature (natural asphalts) or may be obtained from petroleum processing (petroleum asphalts). • Tars do not occur in nature and ore obtained as condensates in the processing of coal, petroleum, oilshale, wood or other organic materials.
Chapter 3 – Asphalt What’s Bituminous Materials? ASTM defines asphalt and tar as follow: • Asphalt: a dark brown to black cementitious material, solid or semisolid in consistency, in which the predominating constituents are bitumens which occur in nature or are obtained as residue in refining petroleum.
Chapter 3 – Asphalt What’s Bituminous Materials? ASTM defines asphalt, and tar as follow: • Tar: brown or black bituminous material, liquid or semisolid in consistency, in which the predominating constituents are bitumens obtained as condensates in the destructive distillation of coal, petroleum, oil shale, or other organic materials, and which yields substantial quantities of pitch when distilled. • Destructive distillation is the chemical process involving the decomposition of feedstock by heating to a high temperature.
Chapter 3 – Asphalt What’s Bituminous Materials? • Pitch is formed where a tar is partially distilled so that the volatile constituents have evaporated off from it. • Asphalt should not be confused with coal tar because asphalt is readily soluble in most petroleum products and tar is resistant to petroleum-based solvents.
Chapter 3 – Asphalt Tar and Asphalt • Asphalt • Tar – Soluble in petroleum – Resistant to products petroleum products – Generally a by-product – Generally by-product of petroleum distillation of coke (from coal) process production – Can be naturally occurring
ď ą Tar and Asphalt Solid Bitumen
Solid Asphalt
A bottle of coal tar
Chapter 3 – Asphalt What’s Bituminous Materials? • Bituminous materials are important construction materials, can be found on all types of construction projects, from buildings to highway construction. They are usually used in roofing systems, sealants and coatings, and in pavements, especially • They are strong cements, durable, highly waterproof, and readily adhesive and they are also highly resistant to the action of most acids, alkalis, and salts.
Chapter 3 – Asphalt History • The use of asphalt by humans can be traced back to approximately 6000 B.C. Asphalts were used as cements to hold stonework and as waterproofing in pools and baths. They were mixed with sand used to pave streets. • The Egyptians made use of asphalt in mummification process and as a building materials. • The Greeks and Romans not only used as building material but also used burning asphalt as military weapon.
Chapter 2 - Aggregate ď ą History
Chapter 3 – Asphalt History • The asphalt used by these ancient civilizations was natural asphalt formed when crude petroleum oils rose to the Earth’s surface and formed pools (Figure 3-1). • The action of the sun and wind drove off the lighter oils and gases, leaving a heavy residue. The residue was asphalt with impurities such water and soil.
Chapter 3 – Asphalt History
Figure 3-1: Formation of natural asphalt
Chapter 3 – Asphalt Asphalt Binder • Even though natural asphalt does occur, the majority of asphalt used in construction today is distilled from petroleum crude oil. • Approximately 80% of the asphalt produced is used in paving and related industries, while the remaining 20% is used in the manufacture of roofing materials and miscellaneous areas such as metal coatings and waterproofing.
Chapter 3 – Asphalt Asphalt Binder
Petroleum Crude Oil
Chapter 2 - Aggregate ď ą Asphalt Binder
As paving material
Chapter 2 - Aggregate ď ą Asphalt Binder
As roofing material
Chapter 2 - Aggregate ď ą Asphalt Binder
As waterproofing material
Chapter 3 – Asphalt Asphalt Binder • Petroleum crude oils are generally classified on the basis of their crude oil content: i) Asphaltic base crude (almost entirely asphalt) ii) Paraffin base crude (contains paraffin but no asphalt) iii) Mixed base crude (contains both paraffin and asphalt)
• The amount of asphalt obtained from a crude oil is based on its API gravity. The higher the gravity, the lower the asphalt content.
Chapter 3 – Asphalt Asphalt Binder • Asphalt “binders”, sometimes called “cements”, are the bituminous glue that has been used for many years. In the modern world, asphalt has been used extensively for paving and roofing applications. • At cold temperature, asphalt is a very hard brittle material. As temperature of asphalt is increased, it softens, and higher temperature (about 135 oC), it becomes liquid.
Chapter 3 – Asphalt ď ą Asphalt Binder • At high temperature it is a liquid that flows well to coat aggregate and allows it to be workable during placement as a paving material. At normal climatic temperatures it is a strong durable material that has strong biding characteristics.
Chapter 3 – Asphalt Asphalt Binder
Figure 3-3: Relation between temperature and stiffness of asphalt binder
Chapter 3 – Asphalt Refining of Asphalt Binder • Paving asphalt binders are typically produced from petroleum oil. This asphalt binder is produced through a distillation process at a petroleum refinery. • Not all petroleum or crude oil is suitable for the production of asphalt binder. Crude oil designated as heavy, such as those originating from Venezuela, produces the highest percentage of asphalt binder. • Light or sweet crude oil, such as those originating from the Middle East, will produce little to no asphalt binder, but a higher percentage of light gas oils or gasoline.
Chapter 2 - Aggregate ď ą Refining of Asphalt Binder
Petroleum refining process and output
Chapter 3 – Asphalt ď ą Type of Bituminous Materials Used in Pavement Construction 1) Asphalt cement: is an asphalt which has been specially refined as to quality and consistency for direct use in the construction of asphalt pavement. An asphalt cement has to be heated to an appropriate high temperature in order to be fluid enough to be mixed and placed.
Chapter 3 – Asphalt ď ą Type of Bituminous Materials Used in Pavement Construction 2) Cutback Asphalt: is a liquid asphalt which is a blend of asphalt and petroleum solvents (such as gasoline and kerosine). A cutback asphalt can be mixed and placed with little or no application of heat. After a cutback asphalt is applied and exposed to the atmosphere, the solvent will gradually evaporate, leaving the asphalt cement to perform its function as a binder.
Chapter 3 – Asphalt ď ą Type of Bituminous Materials Used in Pavement Construction 3) Emulsified asphalt or Asphalt emulsion: is an emulsion of asphalt cement and water that contains a small amount of emulsifying agent. In normal emulsified asphalt, the asphalt cement is in the form of minute globules in suspension in water. An emulsified asphalt can be mixed and applied without any application of heat. After as asphalt emulsion is applied, sufficient time is required for the emulsion to break and the water to evaporate to leave the asphalt cement to perform its function as a binder.
Chapter 3 – Asphalt
Asphalt emulsion
Type of Bituminous Materials Used in Pavement Construction
Emulsion
Chapter 3 – Asphalt Superpave Binder • The Strategic Highway Research Program (SHRP) conducted a $50 millions research effort from October 1987 through March 1993 to develop performance-based test methods and specifications for asphalt and asphalt mixtures. • The resulting product is a new system called Superpave (SUperiorPERforming asphalt PAVEments), which includes a binder specification and an asphalt mixture design method.
Chapter 3 – Asphalt Superpave Binder • The Superpave binder tests and specifications have been standardized by the American Association of State Highway and Transportation Officals (AASHTO).
Chapter 3 – Asphalt Common Test on Asphalt Cement and Superpave Binder Tests on Asphalt Cement 1) 2) 3) 4) 5) 6)
Penetration test Viscosity test Flash Point test Solubility test Ductility test Rolling Thin Film Oven test (RTFOT)
Chapter 3 – Asphalt Common Test on Asphalt Cement and Superpave Binder Tests on Superpave Binder 1) 2) 3) 4) 5) 6)
Pressure Aging Vessel (PAV) Dynamic Shear Rheometer Test (DSR) Bending Beam Rheometer Test (BBR) Direct Tension Test (DTT) Brookfield Rotational Viscometer Test Rolling Thin Film Oven test (RTFOT)
Chapter 3 – Asphalt Asphalt Cement Test Penetration Test • The penetration test is one of the oldest and most commonly-used test on asphalt cement. It is an empirical measure of the relative hardness of asphalt cement at a specified test condition. • The standardized procedure for this test can be found in ASTM D5.
Chapter 3 – Asphalt Asphalt Cement Test Penetration Test (cont) • In the standard test condition, a standard needle of a total load of 100g is applied to the surface of an asphalt sample at temperature of 25 oC for 5 seconds. The amount of penetration of the needle at the end of 5 seconds is measured in units of 0.1 mm. • A softer asphalt will have a higher penetration, while a harder asphalt will have a lower penetration.
Chapter 3 – Asphalt
Penetration apparatus
Chapter 3 – Asphalt Penetration Test (cont)
Chapter 3 – Asphalt Penetration Test (cont) • Penetration test yields information about the “stiffness” of asphalt. • Penetration Specification: Five Grades • • • • •
40 - 50 60 - 70 85 - 100 120 - 150 200 - 300
Chapter 3 – Asphalt Asphalt Cement Test Viscosity Test • The viscosity of a binder is a measure of its flow characteristics, and the performance of a bituminous mix is greatly affected by its viscosity. • The degree of fluidity at the application temperature greatly influences the ability of bituminous material to spread, penetrate into the voids and also coat the aggregates and hence affects the strength characteristics of the resulting paving mixes.
Chapter 3 – Asphalt Asphalt Cement Test Viscosity Test (cont) • When the viscosity of an asphalt at lower temperature (60 oC), the most common test is the Absolute Viscosity Test by Vacuum Capillary Viscometer (ASTM D2171). The viscosity at 60 oC represents the viscosity of the asphalt at the maximum temperature a pavement is likely to experience in most parts of the United States.
Chapter 3 – Asphalt Asphalt Cement Test Viscosity Test (cont) • When the viscosity of an asphalt at higher temperature (such as 135 oC) is to be determined, the most commonly-used test is the Kinematic Viscosity Test (ASTM D2170). The viscosity at 135 oC represents the viscosity of the asphalt during mixing and placement of a hot mix. • The basic kinematic viscosity test measures the time it takes for a fixed volume of asphalt binder to flow through a capillary viscometer under closely controlled conditions of head and temperature.
Chapter 3 – Asphalt
Capillary Viscometer
Chapter 3 – Asphalt Asphalt Cement Test Flash Point Test • The flash point test determines the temperature to which as asphalt can be safely heated in the presence of an open flame. • The test is performed by heating an asphalt sample in an open cut at a specified rate and determining the temperature at which a small flame passing over the surface of the cup.
Chapter 3 – Asphalt Asphalt Cement Test Flash Point Test (cont) • The commonly-used flash point test methods include (1) Cleveland Open Cup (ASTM D92) and (2) Tag Open Cup (ASTM D1310) • The Cleveland Open Cup method is used on asphalt or asphalt cements with relatively higher flash point, while Tag Open Cut is used for cutback asphalt with flash point less than 79 oC.
Chapter 3 – Asphalt Asphalt Cement Test
Cleveland Open Cup
Chapter 3 – Asphalt Asphalt Cement Test Solubility Test • Asphalt consists of primarily of bitumens, which are high-molecular-weight hydrocarbons soluble in carbon disulfide. The bitumen content of a bituminous material is measured by means of its solubility in carbon disulfide. • Standard test for bitumen content can be found in ASTM D4. This test method covers the determination of bitumen content in materials containing at least 25 % bitumen.
Chapter 3 – Asphalt Asphalt Cement Test Solubility Test • Due to the extreme flammability of carbon disulfide, solubility in trichloroethylene, rather than solubility in carbon disulfide, is usually used in asphalt cement specification. The standard test is designated as ASTM D2042. • The solubility test is used to detect contamination in asphalt cement. Specifications for asphalt cements normally require a minimum solubility in trichloroethylene of 99.0 percent.
Chapter 3 – Asphalt Asphalt Cement Test Ductility Test • The ductility of a bituminous material (ASTM D113) is measured by the distance to which it will elongate before breaking under a standard testing condition (5cm/mm at 25 oC). • It is generally considered that an asphalt with a very low ductility will have poor adhesive properties and thus poor performance in service. Specifications for asphalt cements normally contain requirements for minimum ductility.
Chapter 3 – Asphalt Asphalt Cement Test Rolling Thin Film Oven Test (RTFOT) • When an asphalt cement is used in the production of asphalt concrete it has to be heated to an elevated temperature and mixed with a heated aggregate. The hot asphalt mixture is then hauled to the job site, placed and compacted. By the time the compacted asphalt concrete cools down to the normal pavement temperature.
Chapter 3 – Asphalt Asphalt Cement Test Rolling Thin Film Oven Test (RTFOT) (cont) • Since the performance of the asphalt concrete in service are significantly different from those of the original asphalt, the properties of the hardened asphalt in service need to be determined and controlled. • The Rolling Thin Film Oven Test (RTFOT) procedure (ASTM D2872) was developed to measure the effect of heating in a hot-mix plant operation on an asphalt cement.
Chapter 3 – Asphalt Asphalt Cement Test Rolling Thin Film Oven Test (RTFOT) (cont) • The rolling thin-film oven (RTFO) test simulates short-term aging by heating a moving film of asphalt binder in an oven for 85 minutes at 163° C (325° F). The effects of heat and air are determined from changes incurred in physical properties measured before and after the oven treatment by other test procedures.
Chapter 3 – Asphalt Asphalt Cement Test
RTFOT achieves the degree of hardening (aging) in the time of 85 minutes
Chapter 3 – Asphalt Conventional Methods of Grading and Specifications of Asphalt Cement • There are three conventional methods of grading asphalt cements. These three methods are: (1) grading by penetration at 25 °C; (2) grading by absolute viscosity at 60 °C; (3) grading by absolute viscosity of aged asphalt residue after the rolling thin film oven test (RTFOT) procedure
Chapter 3 – Asphalt Conventional Methods of Grading and Specifications of Asphalt Cement (1) grading by penetration at 25 °C • The method of grading of asphalt cements by standard penetration at 25 °C is the first systematic method developed and is still used by a few highway agencies in the world. • The standard grades by this method include 40/50, 60/70, 85/100, 120/150 and 200/300 asphalts, which have penetrations of 40 to 50, 60 to 70, 85 to 100, 120 to 150, and 200 to 300 (0.1mm), respectively.
Chapter 3 – Asphalt Conventional Methods of Grading and Specifications of Asphalt Cement (1) grading by penetration at 25 °C The Asphalt Institute recommends the use of: • 120/150 or 85/100 pen. asphalt for cold climate condition (7 oC or lower) • 85/100 or 60/70 pen. asphalt for warm climate condition (7 - 24 oC ) • 40/50 or 60/70 pen. asphalt for hot climate condition (24 oC or greater)
Chapter 3 – Asphalt Conventional Methods of Grading and Specifications of Asphalt Cement (2) grading by absolute viscosity at 60 °C • The temperature for grading asphalt by viscosity was at 60 °C, which represents approximately the highest temperature pavements may experience in most parts of the United States. • When an asphalt is graded by this system, it is designated as AC followed by a number which represents its absolute viscosity at 60 °C in units of 100 poises.
Chapter 3 – Asphalt Conventional Methods of Grading and Specifications of Asphalt Cement (2) grading by absolute viscosity at 60 °C • For example, an AC-20 would have an absolute viscosity of around 2,000 poises at 60 °C. An AC20 roughly corresponds to a 60/70 pen. asphalt.
Chapter 3 – Asphalt Conventional Methods of Grading and Specifications of Asphalt Cement (2) grading by absolute viscosity at 60 °C
Chapter 3 – Asphalt (3) grading by absolute viscosity of aged asphalt residue after the rolling thin film oven test (RTFOT): • An asphalt graded by this system is designated as AR followed by a number which represents the viscosity of the aged residue at 60 °C in units of poises. • For example, an AR-6000 would have an aged residue with an absolute viscosity of around 6000 poises. An AR-6000 would roughly correspond to an AC-20 or a 60/70 pen. asphalt.
Chapter 3 – Asphalt Superpave Binder Test Pressure Aging Vessel • The Superpave Pressure Aging Vessel (PAV) procedure is used for simulation of long-term aging of asphalt binders in service (occurs as a result of 5 to 10 years in service). According to the method, the asphalt samples are first aged in the standard RTFOT (short term aging). • The proposed range of PAV temperature to be used is between 90 and 110 °C.
Chapter 3 – Asphalt Superpave Binder Test Pressure Aging Vessel (cont) • The PAV is an oven-pressure vessel combination that takes RTFO aged samples and exposes them to high air pressure (2070 kPa) and temperature (90 °C, 100 °C or 110 °C) depending upon expected climatic conditions) for 20 hours.
Chapter 3 – Asphalt Superpave Binder Test
PAV sample Pressure Aging Vessel
Chapter 3 – Asphalt Superpave Binder Test Dynamic Shear Rheometer • The dynamic shear rheometer (DSR) is used to characterize the viscous and elastic behavior (viscoelastic property) of asphalt binders at medium to high temperature viscosities (the test is conducted between 46 oC and 82 oC). The actual temperature depends on the area where the asphalt binder will be placed.
Chapter 3 – Asphalt Superpave Binder Test Dynamic Shear Rheometer • The two values to be measured from each test are the complex shear modulus, G*, and the phase angle, δ. These two test values are then used to compute G*/sin δ and G*sin δ.
Chapter 3 – Asphalt Superpave Binder Test Dynamic Shear Rheometer • In the Superpave asphalt specification, permanent deformation is controlled by requiring the G*/sin δ of the binder at the highest anticipated pavement temperature to be greater than 1.0 kPa before aging and 2.2 kPa after the RTFOT process. • Fatigue cracking is controlled by requiring that the binder after PAV aging should have a G*sin δ value of less than 5000 kPa at a specified intermediate pavement temperature.
Chapter 3 – Asphalt
Dynamic Shear Rheometer
Dynamic Shear Rheometer sample
Chapter 3 – Asphalt Superpave Binder Test Bending Beam Rheometer • The bending beam rheometer (BBR) test was used to measure the stiffness of asphalts at low service temperatures. It meant that the asphalt binders should resist the thermal cracking at low temperature. • In the standard testing procedure, after the beam sample has been properly pre-conditioned, a vertical load of 100 gram-force is applied to the middle of the beam for a total of 240 seconds.
Chapter 3 – Asphalt Bending Beam Rheometer (cont) • The deflection of the beam at the point of load is recorded during this period, and used to compute for the creep stiffness of the asphalt by the following equation:
Chapter 3 – Asphalt Bending Beam Rheometer (cont) • The Superpave binder specification as stated in AASHTO requires the stiffness at the test temperature after 60 seconds to be less than 300 MPa to control lowtemperature cracking. • The second parameter obtained from the bending beam rheometer test result is the m-value (rate of change the stiffness). A higher m-value would mean that the asphalt would creep at a faster rate to reduce the thermal stress and would be more desirable to reduce low-temperature cracking. The Superpave binder specification as stated in AASHTO requires the m-value at 60 seconds to be greater than or equal to 0.30.
Chapter 3 – Asphalt Bending Beam Rheometer (cont)
BBR mould
BBR specimen
BBR equipment
Chapter 3 – Asphalt Superpave Binder Test Direct Tension Test (DTT) • The Superpave direct tension test measures the stress-strain characteristics of an asphalt binder in direct tension at low temperature. • The DTT is used because creep stiffness, S(t), as measured by the BBR is not sufficient to predict thermal cracking in some asphalt binders that exhibit high creep stiffness (> 300 MPa)
Chapter 3 – Asphalt Superpave Binder Test Direct Tension Test (cont) • Recall that a high creep stiffness BBR test value implies that the asphalt binder will possess high thermal stresses in cold weather as a result of shrinkage. • The DTT is only used for testing asphalt binders with a high BBR creep stiffness (300 - 600 MPa); asphalt binders with BBR creep stiffness values below 300 MPa are assumed satisfactory and the DTT is not needed.
Chapter 3 – Asphalt
DTT apparatus
Chapter 3 – Asphalt Superpave Binder Test Brookfield (or rotational) Viscosity Test (RV) • The Superpave binder specification uses the Brookfield rotational viscometer test as specified by ASTM D4402 for use in measuring the viscosity of binders at elevated temperatures to ensure that the binders are sufficiently fluid when being pumped and mixed at the hot mix plants. • The test is conducted at 135° C.
Chapter 3 – Asphalt Superpave Binder Test Brookfield (or rotational) Viscosity Test (cont) • The basic RV test measures the torque required to maintain a constant rotational speed (20 RPM) of a cylindrical spindle while submerged in an asphalt binder at a constant temperature • This torque is then converted to a viscosity and displayed automatically by the RV machine.
Chapter 3 – Asphalt Superpave Binder Test
Rotational Viscosity machine
Chapter 3 – Asphalt Asphalt Pavements • The basic idea in building a road or parking area for all weather use by vehicles is to prepare a suitable subgrade or foundation, provide necessary drainage, and construct a pavement that will do the following: (1) Have sufficient total thickness (2) Prevent the penetration of water (3) Have a top surface that is smooth and resistant to wear, distortion, and deterioration by weather.
Chapter 3 – Asphalt Asphalt Pavements • The subgrade ultimately carries all traffic loads. Therefore, the structural function of a pavement is to support a wheel load on the pavement surface and transfer and spread that load to the subgrade.
Chapter 3 – Asphalt Asphalt Pavements
Spread of wheel load through pavement structure
Chapter 3 – Asphalt Asphalt Pavements • The Figure shows wheel load W being transmitted to the pavement surface through the tire at an approximately uniform vertical pressure P0. The pavement then spreads the wheel load to the subgrade so that maximum pressure on the subgrade is only P1. By proper selection of pavement materials and with adequate pavement thickness, P1 will be small enough to be easily resisted by the subgrade.
Chapter 3 – Asphalt Asphalt Pavements • Asphalt pavement is a general term applied to any pavement that has a surface constructed with asphalt. • Normally, it consists of a surface course (layer) of asphalt concrete and one or more supporting courses, which may be of the following types: (1) Asphalt base, consisting of asphalt-aggregate mixtures (2) Crushed stone or gravel (3) Portland cement concrete (4) Old brick or stone block pavements
Chapter 3 – Asphalt Asphalt Pavements
Components of Asphalt Pavement
Chapter 3 – Asphalt Asphalt Pavements Basic Structural Elements A typical asphalt pavement structure consists of: • Surface Course: The layer in contact with traffic loads. It provides characteristics such as friction, smoothness, and drainage. In addition, it prevents entrance of surface water into the underlying base, subbase and subgrade. This top structural layer of material is sometimes subdivided into two layers: the wearing course (top) and binder course (bottom).
Wearing course and binder course Chapter 3 – Asphalt in surface course
Asphalt Pavements
Chapter 3 – Asphalt Asphalt Pavements Basic Structural Elements A typical asphalt pavement structure consists of: • Base Course: The layer immediately beneath the surface course. It provides additional load distribution. Base courses are usually constructed out of crushed aggregate or HMA or OPC concrete.
Chapter 3 – Asphalt Asphalt Pavements • Subbase Course: The layer between the base course and subgrade. It functions primarily as structural support but it can also minimize the intrusion of fines from the subgrade into the pavement structure. The subbase generally consists of lower quality materials than the base course but better than the subgrade soils. A subbase course is not always needed or used. Subbase courses are generally constructed out of crushed aggregate or engineered fill (soils).
Typical asphalt pavement structure
Typical asphalt pavement structure
Full Depth Asphalt Pavement
Asphalt Pavement with Untreated Base (and Subbase)
Asphalt Pavement with Portland Cement Concrete or Combined Portland Cement Concrete and Asphalt Base
Chapter 3 – Asphalt Determining required pavement thickness • There is no standard thickness for a pavement. However, the Asphalt Institute has published general guidelines to be used for parking areas and driveways.
Chapter 3 – Asphalt ď ą Determining required pavement thickness
Chapter 3 – Asphalt ď ą Determining required pavement thickness
Chapter 3 – Asphalt ď ą Determining required pavement thickness
Chapter 3 – Asphalt ď ą Determining required pavement thickness • Required total thickness for roadways and airfields is determined by engineering design procedure, which considers the following factors: (1) Traffic to be served in initially and over the design service life of the pavement. (2) Strength and other pertinent properties of the prepared subgrade. (3) Strength and other influencing characteristics of the materials available or chosen for the layers or courses in the total asphalt pavement structure. (4) Any special factors peculiar to the road being designed.
Chapter 3 – Asphalt Determining required pavement thickness Traffic Analysis • The weight and volume of traffic that a road is expected to carry influence the required thickness of asphalt pavement structure, as well as mix selection and mix design. • Initial data in terms of number of commercial vehicles per day (CVPD). • Traffic for many years was evaluated using annual average daily traffic (AADT).
Chapter 3 – Asphalt Determining required pavement thickness Traffic Analysis • Traffic growth rate (%) during design life. • The Superpave system introduced evaluation of traffic in terms of equivalent single axle loads (ESALs). • Using ESALs to more accurately determine the stress distribution from heavy loads of trucks and buses on a pavement.
Chapter 3 – Asphalt Determining required pavement thickness Traffic Analysis
Single axle of train
Chapter 3 – Asphalt Determining required pavement thickness Design life
• National Highways – 15 years • Expressways and Urban Road s– 20 years • Other Category Roads – 10 – 15 years
Chapter 3 – Asphalt Determining required pavement thickness Subgrade Evaluation • There are several methods for evaluating or estimating the strength and supporting capacity of a subgrade, including the following: 1. Loading tests in the field on the subgrade itself, for example, the plate bearing test. 2. Loading tests in laboratory using representative samples of the subgrade soil. Some commonly used tests are (a) California bearing ratio (CBR) and (b) triaxial test.
Chapter 3 – Asphalt Determining required pavement thickness Subgrade Evaluation • There are several methods for evaluating or estimating the strength and supporting capacity of a subgrade, including the following: 3. Evaluations based on classification of soils by identifying and testing the constituent particles of the soil.
Chapter 3 – Asphalt Types of Paved Surfaces • Basically, all hard surfaced pavement types can be categorized into two groups, flexible and rigid. • Flexible pavements: are those which are surfaced with bituminous (or asphalt) materials. • Rigid pavements: are composed of PPC surface course. Further, these pavements can have reinforcing steel, which is generally used to reduce or eliminate joints.
Chapter 3 – Asphalt Types of Paved Surfaces • Basically, state highway agencies generally select pavement type either by policy, economics or both. • Flexible pavements generally require some sort of maintenance or rehabilitation every 10 to 15 years. Rigid pavements, on the other hand, can often serve 20 to 40 years with little or no maintenance or rehabilitation. Thus, it should come as no surprise that rigid pavements are often used in high traffic areas.
Chapter 3 – Asphalt Types of Paved Surfaces
Chapter 3 – Asphalt
Chapter 3 – Asphalt Asphalt Paving-Mix Design • The design of asphalt paving mixes is a matter of selecting and proportioning materials to obtain the desired qualities and properties in the finished construction. • The overall objective for the design of asphalt paving mixes is to determine an economical blend and gradation of aggregates and asphalt that yields a mix having the following:
Chapter 3 – Asphalt ď ą Asphalt Paving-Mix Design 1. Sufficient asphalt to ensure a durable pavement. 2. Sufficient mix stability to satisfy the demands of traffic without distortion or displacement. 3. Sufficient voids in the total compacted mix to allow for a slight amount of additional compaction under traffic loading. 4. Sufficient workability to permit efficient placement of the mix.
Chapter 3 – Asphalt Asphalt Paving-Mix Design • There are currently three methods used to design asphalt paving mixtures:
1) Marshall method 2) Hveem method 3) Superpave system • All three methods target an air void range, at plant production, of 3 to 5 percent. The differences in the systems lie in their tests to predict performance and the method for compacting specimens for analysis.
Chapter 3 – Asphalt Asphalt Paving-Mix Design • The Marshall mix design method was developed by Bruce Marshall of the Department of Transportation in Mississippi in 1939. • Marshall method was prevalent form of mix design and analysis until the mid 1990s. However, after significant and widespread pavement failures, largely attributed to increase traffic volumes, truck traffic, and tire pressure, it has been replaced by the Superpave system.
Chapter 3 – Asphalt Asphalt Paving-Mix Design • Design criteria in Marshall method and Superpave Mix Design: 1) Air voids range (3 – 5 %) 2) VMA (Void in Mineral Aggregate) 3) VFA (Void Filled with Asphalt)
Chapter 3 – Asphalt Asphalt Paving-Mix Design Some definitions in the mix design: • Air voids (Va): are the percent by volume of air between coated aggregate particles in the compacted asphalt mixture. • Void in Mineral Aggregate (VMA): are the volume of compacted paving mix not occupied by the aggregate when the volume of the aggregate is calculated from its bulk specific gravity.
Chapter 3 – Asphalt Asphalt Paving-Mix Design
Chapter 3 – Asphalt Asphalt Paving-Mix Design Some definitions in the mix design: • Void Filled with Asphalt (VFA): is the percentage of VMA filled with asphalt binder. It is the effective asphalt volume divided by the voids in the mineral aggregate.
Chapter 3 – Asphalt Asphalt Paving-Mix Design Calculation: • Air voids (Va): Va
Gmm Gmb Va 100 Gmm
: air voids in the compacted specimen as a percent to total volume
Gmm : maximum specific gravity of paving mixture Gmb
: bulk specific gravity of compacted mixture
Chapter 3 – Asphalt Asphalt Paving-Mix Design Calculation: • VMA:
Gmb Ps VMA 100 Gsb
VMA : voids in mineral aggregate
Gmb
: bulk specific gravity of aggregate
Gmb
: bulk specific gravity of compacted paving mixture
Ps
: aggregate, percent of total weight of mixture
Chapter 3 – Asphalt Asphalt Paving-Mix Design Calculation: • VFA:
VMA Va VFA 100 VMA
VFA : voids filled with asphalt VMA : voids in mineral aggregate
Chapter 3 – Asphalt Type of Asphalt Pavement Construction Plant Mix • Asphalt concrete paving mixtures prepared in a hot mixture plant are known as hot mix asphalt or HMA. • HMA is considered the highest quality type of asphalt mixture because the processing at the plant removes all ambient moisture from aggregate, which ensures the best bond between the aggregate and the asphalt binder.
Chapter 3 – Asphalt Type of Asphalt Pavement Construction Plant Mix (cont) • In this process, the aggregates are heated from 135 to 160 oC and then mix with the binder in the central plant. • The HMA is hauled to the construction site, where it is spread on the roadway by a “spreader” or “paver”. • The smooth layer of HMA following the paver is compacted by rollers to proper density before the HMA cools.
Plant Mix ď ą Type of Asphalt Pavement Construction
Asphalt Paver ď ą Type of Asphalt Pavement Construction
Asphalt Paver ď ą Type of Asphalt Pavement Construction
Asphalt Paver
Tandem Roller
Pneumatic Roller
Chapter 3 – Asphalt Type of Asphalt Pavement Construction Mixed-in-Place (Road Mix) • Emulsified asphalt and cutback asphalts are fluid enough to be sprayed onto and mixed into aggregate at moderate – to warm-weather temperature. • When the sprayed process is done on the construction area, it is called mixed-in-place construction. Although mixed-in-place is the more general term, the term road mix is often used when construction is on a roadway.
Chapter 3 – Asphalt Type of Asphalt Pavement Construction Mixed-in-Place (Road Mix) (cont) • Mixed-in-place construction can be used for surface, base, or subbase courses. As a surface or wearing course, it is usually satisfactory for light and medium traffic rather than heavy traffic.
Road Mix ď ą Type of Asphalt Pavement Construction
Chapter 3 – Asphalt Type of Asphalt Pavement Construction Slurry Seal • Slurry seal is a thin asphalt overlay applied by a continuous process machine to seal and provide a new wearing surface. Slurry seals are produced with emulsified asphalt. • Aggregates used for slurry seal must be hard, angular, free of expansive clays.
Slurry Seal Type of Asphalt Pavement Construction Slurry Seal
Chapter 3 – Asphalt Asphalt Plants • Asphalt Concrete mixes made with asphalt cement are prepared at an asphalt mixing plant. Here, aggregates are blended, heated, dried, and mixed with asphalt cement to produce a hot mix asphalt (HMA). • Asphalt Concrete plants are basically of two types: 1) Batch or stationary plant 2) Drum mix or continuous-mix or portable plant
Chapter 3 – Asphalt Asphalt Plants • The two types of asphalt plants derive their names from their particular type mixing operation. In the batch-type mixing plant, hot aggregate and asphalt are withdrawn in desired amounts to make up one batch for mixing. After thoroughly mixing, the material is discharged from the pugmill in one batch. • In the drum-type mixing plant, the aggregate is dried, heated, and mixed with the asphaltic cement in the drum in a continuous operation.
Chapter 3 – Asphalt Batch Plant Basic flow diagram of a batch-type asphalt plant Component of batch-type plant: Cold aggregate storage Dryer Screening Hot storage Measuring and mixing
Chapter 3 – Asphalt ď ś Batch Plant • Aggregate is removed from storage, or stockpiles, in controlled amounts and passed through a dryer where it is heated and dried. The aggregate then passes over a screening unit that separates the material into different size fractions and deposits them into bins for hot storage. The aggregate and mineral, when used, are then withdrawn in controlled amounts, to make up one batch for mixing. The entire combination of aggregate is dumped into a mixing chamber called a pugmill. This mix is hauled to the paving site.
Chapter 3 – Asphalt Batch Plant Pugmill
ď ś Batch Plant
Chapter 3 – Asphalt Asphalt Plants Batch Plant
Chapter 3 – Asphalt Drum Mix (or Continuous Mix) Plant • Drum mixing is a relatively simple process of producing asphalt mixtures. In the drum mix plant, aggregate and asphalt are withdrawn, combined, mixed, and discharged in one uninterrupted flow. • The difference is that the aggregate is not only dried and heated within the drum, but also mixed with the asphalt cement. • Drum mixers can produce a hot mix or a low temperature mix.
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Chapter 3 – Asphalt ď ś Drum Mix (or Continuous Mix) Plant Aggregates with controlled gradations are place in the cold feed bins (1). The mix design determines the proportions of the aggregate drawn from the bins and moved to the drum mixer by the cold feed conveyor (2). The exact weight of the aggregate feed is monitored by the automatic weighting system (3), which is interlocked with the asphalt pump (5). The asphalt pump draws the correct quantity of asphalt cement from the storage tank (6) and feeds the asphalt into the drum where the aggregates and asphalts are blended together (4). Dust escaping from the mixing system is captured in the dust collector (7). The completely mixed asphalt concrete is continuously fed into a surge storage silo (9) by the hot mix conveyor (8). The entire production system is controlled and monitored by the plant operator stationed in the control house (10).
Chapter 3 – Asphalt Storage of Hot-Mix Asphalt • Should paving operations be temporarily interrupted, rather than stopping production at the plant, a surge bin (silo) may be installed and used for temporarily storing the hot mix. • The hot mix is dumped into the top of the silo and it will be withdrawn from the bottom, its uniformity is maintained. • Surge bins are insulated and can store 50 to 100 tons of the mix and they can usually store hot mix for up to 12 hours with no significant loss of heat or quality.
Chapter 3 – Asphalt Estimating Asphalt Concrete • The unit of measure for the purchase of asphalt concrete is ton. Therefore, the number of tons of asphalt concrete required to complete a paving job must be determined. • On small paving jobs the quantities are usually determined using a rule of thumb which states that 1 ton of asphalt concrete will cover about 7.4 m2, 5 cm thick.
Chapter 3 – Asphalt Estimating Asphalt Concrete • Example: Area to be paved is 500 m2 and 5 cm thickness. How much asphalt concrete is needed? about 67.6 tons will be required • On large paving jobs the estimates are based on the unit weight (bulk density) of the asphalt concrete. Asphalt concrete’s unit weight is generally range from 140 to 150 lb per cu ft or from 2250 to 2400 kg/m3.
Chapter 3 – Asphalt Estimating Asphalt Concrete • On large paving jobs:
T A t uw T : quantity of asphalt concrete required (tons) A : area to be paved (m2) t : thickness of pavement (m) uw : unit weight of asphalt concrete (ton/m3)
• Example: Area to be paved is 16700 m2, 10 cm thickness, and uw = 2400 kg/m3. How much asphalt concrete is needed? 4008 tons
Chapter 3 – Asphalt Preparation of Unpaved Surfaces • The following roadway surfaces are generally considered unpaved: 1. Compacted subgrade 2. Improved subgrade 3. Untreated base 4. Nonsurfaced aggregate roadway • Certain treated or stabilized granular base are considered unpaved surface when being prepared for asphalt paving. Bases that have been treated or stabilized with either asphalt or portalnd cement are considered paved surfaces.
Chapter 3 – Asphalt
Pavement structure
Chapter 3 – Asphalt Inspection of Mix • The plant inspector and paving inspector should be well communicated. When possible, the paving inspector and the plant inspector should frequently exchange visits. • Mistakes in batching, mixing, and temperature control can and do occur, and these errors may sometimes go unnoticed by the plant inspector. Consequently, loads arriving at the spreader may be unsatisfactory.
Chapter 3 – Asphalt Inspection of Mix Mix Deficiencies Some mix deficiencies that may justify discarding the mix are as follow: 1) Too hot: blue smoke rising from the mix indicating an overheated batch. 2) Too cold: a generally stiff appearance or improper coating of the large aggregate particle.
Chapter 3 – Asphalt ď ś Mix Deficiencies 3) Too much asphalt: when loads have been arrived at the spreader with the material domed up or peaked and suddenly a load appear lying flat, it may contain too much asphalt. 4) Too little asphalt: too little asphalt can be detected immediately. The mix has a lean, granular appearance and improper coating, and lacks the typical shiny, black luster. The pavement surface has a dull, brown appearance, and the roller does not compact it satisfactorily.
Chapter 3 – Asphalt ď ś Mix Deficiencies 5) Nonuniform mixing: nonuniform mixing shows up as spots of brown, dull-appearance material within areas having a rich, shiny appearance. 6) Excess coarse aggregate: a mix with excess coarse aggregate can be detected by the poor workability of the mix and its coarse appearance when it is on the road. 7) Excess fin aggregate: a mix with excess fine aggregate has a different texture from a properly graded mix after it has been rolled.
Chapter 3 – Asphalt ď ś Mix Deficiencies 8) Excess moisture: steam rising from the mix as it is dumped into the hopper of the spreader indicates moisture in the mix. 9) Miscellaneous: segregation of the aggregates in the mix may occur because of improper handling. Loads that have become contaminated because of spilled gasoline, kerosene, oil, and the like should not be used in the roadway.
Chapter 3 – Asphalt The Paving Operation • Spreading and compacting asphalt mixtures are the main operation processes of paving activity. • Asphalt mix is brought to the paving site in trucks and deposited directly into the paver or in windrows in front of the paver. The paver then spreads the mix at a set width and thickness as it moves forward. • Immediately or shortly thereafter and while the mix is still hot, steel-wheeled (tandem) rollers or rubbertired (pneumatic) rollers are driven over the freshly paved, further compacting the mix.
Chapter 3 – Asphalt The Paving Operation • Rolling is usually continued until the pavement is compacted to the required density.
Chapter 3 – Asphalt The Paving Operation Pavement Density • The degree or amount of compaction obtained by rolling is determined by Density tests. Ordinarily, specifications require that a pavement to be compacted to a minimum percentage of either maximum theoretical density or density obtained by the laboratory compaction. • For laboratory test method, Specific Gravity of Compressed Bituminous Mixtures (AASHTO T166)
Chapter 3 – Asphalt The Paving Operation Compaction degree or Percent Compaction • Example: The density of an asphalt concrete mix is determined by laboratory tests to be 2390 kg/m3. The density of a field core taken from a section of compacted pavement by test is 2346 kg/m3. What is the percent compaction? 98.2%
Chapter 3 – Asphalt The Paving Operation Compaction degree or Percent Compaction F PC 100 L PC : percent compaction (%)
F : density of field core (kg/m3) L : density of laboratory specimen (kg/m3)
Chapter 3 – Asphalt Other application of asphalt material
1) Asphalt roofing products 2) Asphalt pipe coating 3) Asphalt mulch treatments 4) Asphalt joint materials
Chapter 3 – Asphalt 1) Asphalt roofing products
Chapter 3 – Asphalt 2) Asphalt pipe coating
Chapter 3 – Asphalt 3) Asphalt mulch treatments • Asphalt spray mulch is usually emulsified asphalt sprayed on the newly seeded area. The thin film of asphalt has three beneficial effects: 1. It holds the seed in place against erosion. 2. Because of its dark color, it absorbs and conserves solar heat during the germination period. 3. It holds moisture in the soil, promoting speedy plant growth.
Chapter 3 – Asphalt 4) Asphalt joint materials