SPOTLIGHT
JUNE 2021
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Cement concrete
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A U T O C L A V E D A E R AT E D CONCRETE
VINTAGE CONCRETE COMPOSITE PANELS USED IN HOLIDAY HOME
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GENERAL PURPOSE WHITE PORTLAND CEMENT
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CONCRETE COUNTERTOP PRE-CASTING MIX
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C O N C R E T E C A N VA S
I M P O R TA N C E O F W AT E R QUALITY IN THE CONCRETE
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CUSTOM-MADE AND ONE-OFF PRECAST CONCRETE PRODUCTS
A FEW WORDS FROM EVERITE Since the commissioning of the AAC plant by Everite in 2017, the company has enjoyed considerable success in specification of the product to notable South African projects. Says Jurgen Stragier, managng director for Everite, “The company is delighted with the response from architects and engineers with the acceptance of the product. The grasp by specifiers of AAC’s superior functional properties has seen it being used in several commercial buildings refurbished for residential accommodation. This is attributed to its high strength to weight ratio – which means existing floor slabs did not need additional reinforcing leading to a financial saving. In addition, AAC’s sound and fire resistant properties when compared to other walling materials made it a natural choice for these projects.”
Recent projects of note include: • • • •
The Leonardo 75 Maude St, Sandown, Absa Towers Main Redevelopment; 304 Oak street, Randburg: office conversion of 200 rental apartments Hatfield Square: new student housing and retail development
Speed up construction
A U TO C L AV E D A E R AT E D CONCRETE
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ebel is a lightweight autoclaved aerated concrete which is completely cured, inert and stable form of calcium silicate hydrate. It is a structural material, approximately one quarter the weight of conventional concrete, composed of minute cells which give the material light weight and high thermal insulation properties. It is available as blocks and pre-cast reinforced units, i.e. floors, roofs, walls and lintels. Autoclaved Aerated Concrete (AAC) is made from sand, lime, cement, water and aluminium powder acting as a foaming agent to form a homogenous cellular structure known as calcium silicate hydrate. This porcelainic reaction results in a unique and extremely stable tobermorite chemical structure. The mixing results in a chemical reaction which expands the mixture to form
small, finely-dispersed air spaces. The mix is poured into moulds and allowed to set for a few hours while the chemical reaction continues. The semi solid material is removed from the moulds and then cut to shape in various lengths and profiles. The final phase in the production process is high pressure steam curing in autoclaves for up to 12 hours. It is this autoclaving process that gives this material its unique and superior performance characteristics over any other. Hebel reinforced elements, such as slab panels and wall panels, contain specially coated steel to prevent corrosion and gives the material both dimensional accuracy and stability. The steel reinforcing is placed in the moulds before the mix is added. The manufacturing process is then the same as described above
Being a masonry product, Hebel blocks and panels provide the attributes of being solid, strong and secure - all of these normally only associated with traditional bricks.
for unreinforced elements. Features and Benefits The following impressive attributes of AAC make Hebel an innovative, sustainable and proven building material and are summarised by the following qualities: High speed of construction for an economical building process Hebel panels are faster to construct and require significantly less labour when compared to traditional masonry construction techniques leading to substantial savings and reduced on-site costs depending on finish required. • • • • •
Building with Hebel also means a cleaner safer work area during construction and less clean-up at completion of building. Fast installation and easy workability with simple tools result in lower construction costs. Can be cut and shaped like wood with simple hand tools. Chasing of walls can be done by hand or with a wood router. Smooth finish can substantially remove plastering trades.
• Load-bearing capacity for the most unexpected situations
Being a masonry product, Hebel blocks and panels provide the attributes of being solid, strong and secure - all of these normally only associated with traditional bricks. Our 600 kg/m density product has a 5 MPa compressive strength and is rated for building up to 4 stories and in earthquake zones due to its high strength to weight ratio. Outstanding fire resistance for maximum protection and safety Non-combustible and renowned for its highly fire resistant properties. For example, a 150 mm thick AAC Hebel wall withstands direct fire exposure for up to 6 hours. A standard 100 mm thick Hebel wall can withstand temperatures for 4 hours. Thermal insulation in winter and summer for long-term reduction in energy consumption The enhanced insulation performance is 5 times that of brick of the same thickness. The thermal efficiency reduces the reliance on heating and cooling appliances, and provides up to 60% reduction in heating and cooling costs.
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Being a masonry product, Hebel blocks and panels provide the attributes of being solid, strong and secure - all of these normally only associated with traditional bricks.
Close-up view of aerated autoclaved concrete - a homogenous cellular structure known as calcium silicate hydrate. These minute cells give the material its light weight and high thermal insulation properties.
Project: Holiday Home, Oostkapelle | The Netherlands Architects: Architektenburo TEN HOVE b.v., Wilnis | The Netherlands Fabricator: MZAllpro, Waalwijk | The Netherlands Installer: Cladding Partners B.V., Oosterhout | The Netherlands Façade System: Tray Panels Special Design Year of Construction: 2018 Product: ALUCOBOND® PLUS vintage Rough Concrete
V I N TA G E C O N C R E T E C O M P O S I T E PA N E L S U S E D I N H O L I D AY H O M E P R OJ E C T
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ndogmatic and with a dash of humour, the architects from the Architektenburo Ten Hove have built a holiday home in Dutch Oostkapelle. The North Sea weather, which can change out of the blue, dictated their choice of material and shape. The task at hand was to create a house facilitating alfresco living and yet still providing its inhabitants’ protection against strong winds, sun and rain. In addition, in order to maintain that holiday feeling during the colder months, a lot of light and warmth from the low sun needed to be channelled into the interior. With all these prerequisites in mind, the architects opted for a specific shape: a pent roof planted with vegetation and a solid exterior wall on the north-facing side; a south-facing glass façade below a large, projecting roof and a façade inclined towards the sun above it. The architects made an undogmatic choice, a hybrid combining the best aspects from every type of construction. They employed solid, weatherproof masonry for the north and east sides and created an expansive open space
stretching out to the patio at the south and west by adding slender timber beams and supports The roof is set on steel trapezoidal sheet, which is inexpensive, quick to assemble and very robust. The building’s hybrid nature is, however, not at all noticeable because its outer appearance is a whole new chapter: The architects have set the outer wooden supports at right angles to the roof, tilting them to emphasize the unfurling cubature. It is as if the roof of a campervan has just been opened up for the holiday season. They have clad the very different construction parts in ALUCOBOND® vintage Concrete composite panels to give the house a consistent external appearance. They also make the building look more powerful, more grounded and cause surprised viewers to stop and take a second look. A concrete building, effortlessly unfurled by matchstick-thin, tilted supports? The viewer is amazed to find that something so small can be such a huge enigma. ALUCOBOND ® PLUS vintage
GENERAL PURPOSE WHITE PORTLAND CEMENT
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be.® CEM-blanc is a general purpose white Portland cement, specially manufactured to provide superior early strength with the added advantage of providing a wide range of aesthetic and decorative opportunities due to its key features of whiteness, high strength and durability. In addition to affording great design and colour versatility abe® CEMblanc complies fully with the requirements specified in SANS 50197-1 for type CEM II 42.5N cement.
abe® CEM-blanc white cement is ideally suited for the following applications:
Uses
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A wide variety of white and light coloured finishes can be produced with selected white/light coloured aggregates or with pigments.
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High early strength specialist products particularly where the added feature of whiteness and improved aesthetics is desirable Coloured mortars, plasters and screeds Architectural colour finishes in buildings, bridges, retaining walls Readymix and precast walls, columns and floors Decorative pavements, blocks and pavers Formulated, pre-bagged repairs, tile grouts, adhesives and screeds Swimming pool finishes and plaster Exposed aggregate finishes
CONCRETE COUNTERTOP PRE-CASTING MIX
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ountertop Mix is a 3 component pre-casting mix that contains a proprietary blend of cement, and other admixtures to produce a high strength countertop.
Benefits • • • • • •
Suitable for use in commercial, residential and restaurant use Fully customisable to your specific requirements such as size, colour, shape, built-in features, etc. Produces a high-strength countertop Fully customisable casting mix i.e. can use a variety of aggregates to change the appearance Can cast counters according to any mould Unique cement counter and not pre-manufactured
FAQs
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: Do you have to add aggregates to Countertop Mix? And if you don’t add aggregates what will the coverage be? And do you need to add extra reinforcing?
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: No you don’t have to add aggregates, it depends on what look you want. Coverage without extra aggregate or ColourCem will yield a countertop of 1m x 1m x 30mm thick. Reinforcing is always required.
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: What kind of aggregates can you add to the mix?
: You can add any stones that are dense enough to polish and when using glass, it should be tumbled otherwise the glass might not bond sufficiently with the cement.
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: What kinds of marble chips does Cemcrete sell and in what colours? : We have white, grey and pink chips.
: Do you have to add ColourCem to Countertop Mix? And if you don’t add ColourCem what will the coverage be?
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: No, ColourCem is only added to change the colour. The addition or exclusion of the ColourCem will not alter the coverage.
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beeswax or carnauba wax for extra stain protection.
: Can it stain?
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: Yes, much like Granite and other countertop options, our countertops can stain. We always advise when working with oils and wines that you take extra care to ensure that it does not come into contact with the countertop. If this does however happen, be sure to quickly wipe the surface with an ammonia-free product and a soft cloth. It is also advisable to polish the counter with
Q A
Countertop Mix White with various colours and sizes of glass
: Can I put hot pots directly onto the countertop?
: No, much alike Granite and Caesarstone, it is not advisable to put any extremely hot object on the countertop as the isolated heat can cause thermal shock and lead to cracking, as well as the possibility of burn marks.
A PVC backing ensures the CC is completely waterproof. CC can be hydrated by spraying or full immersion in fresh or salt water.
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C O N C R E T E C A N VA S
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oncrete Canvas® is used for a wide range of erosion control and weed suppression applications. It allows concrete construction with minimal plant and specialist training. Typically ten-times faster to install than conventional solutions, essentially its Concrete on a Roll™: simply unroll and Just Add Water. CC consists of a 3-dimensional fibre matrix containing a specially formulated dry cementitious mix. A PVC backing ensures the CC is completely waterproof. CC can be hydrated by spraying or full immersion in fresh or salt water.
Once set, the fibres reinforce the cementitious mix, preventing crack propagation and providing a safe plastic failure mode. As a result, CC provides a thin, durable, water proof and lower carbon alternative to traditional concrete. CC is available in 3 thicknesses: CC5™, CC8™ and CC13™, which are respectively 5, 8 and 13mm thick. Concrete Canvas® is a world-leading concrete alternative for erosion control applications, providing erosion control, abrasion resistance and even weed suppression for a wide range of applications.
I M P O R TA N C E O F W AT E R QUALITY IN THE CONCRETE MIX
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ith water in short supply in many parts of South Africa, concrete producers could face increasing pressure to use water from sources other than municipal tap water in future, says John Roxburgh, senior lecturer at Cement and Concrete SA’s School of Concrete Technology. Poor quality water could affect the quality of concrete, says CCSA.
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But the quality of concrete may be adversely affected by using poor quality water,” Roxburgh warns.
He says likely consequences could include:
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Alteration of the concrete’s setting times; • Increase in water demand; • Entraining of excessive air; • Change in the concrete’s strength gain characteristics; • Degradation of the hardened concrete; • Corrosion of the reinforcement in the concrete; • Staining and production of efflorescence. “Mixing water makes up about 8% of the total mass of concrete. So, the proportion of impurities in the mixing water compared to the mass of cement is typically very low. Nevertheless, non-potable water should always be assessed for suitability for use as mixing water in concrete. The limits to the
quantities of impurities in the water should be checked against the requirements of the South African National Standards’ SANS 51008 which contains specifications for sampling, testing and assessing the suitability of water for concrete production,” Roxburgh states. He says when assessing the suitability of water of unknown quality, both the composition of the water and proposed application of the concrete should be considered. In general, the suitability of water for concrete depends on its origin. The following types could be encountered: Potable water is suitable for use in concrete and needs no testing. Water recovered from processes in the concrete industry will normally be suitable but must conform to SANS 51008. Water from underground sources may be suitable but must also be tested and assessed in accordance with the requirements of SANS 51008. Natural surface water and industrial waste water may be suitable for use in concrete, but here also needs testing in terms of SANS 51008. Sea water or brackish water may be used for
concrete that will not contain steel reinforcement or other embedded metal. For concrete with steel reinforcement, or embedded metal, the permitted total chloride content in the concrete is the determining factor. Sewage water is not suitable for use in concrete. Sea water may be used for concrete – but only when it will not contain steel reinforcement or other embedded metal. “Some common substances deleterious to concrete and found in water are chlorides, sulphates, acids, alkalis, humic matter, oil, algae, sugar and detergents. There are many more and SANS 51008 should be consulted. “Water for use in concrete must conform to the requirements for preliminary assessment and for chloride, sulphate and alkali contents. The water must also conform to either the chemical requirements for harmful contamination, or the requirements for setting time and compressive strength,” Roxburgh adds.
de-ionised water. The final setting time must not exceed 12 hours and not differ by more than 25% from the final setting time obtained on specimens made with distilled or de-ionised water. “The mean compressive strength at seven days of the concrete, or mortar specimens prepared with the water, must be at least 90% of the mean compressive strength of corresponding specimens prepared with distilled or de-ionised water,” he advises. When sampling water, volumes of at least
“The sulphate content of the water must not exceed 2 000 mg/ℓ. This limit should always be assessed with regards to sulphate content within the aggregate and cement. If alkali-reactive aggregates are to be used in the concrete, the water must be tested for its alkali content. If high, the water may be used only if it can be shown that actions have been taken to prevent deleterious alkali-silica reactions,” Roxburgh explains. Regarding harmful contamination, firstly qualitative tests for sugars, phosphates, nitrates, lead and zinc must be carried out. If the qualitative tests are not performed or show a positive result, either the quantity of the substance concerned must be determined or tests for setting time and compressive strength be performed. “The initial setting time obtained on specimens made with the unknown water must not be under an hour and not differ by more than 25% from the initial setting time of specimens made with distilled or
five litres must be used, taking the possible effects of seasonal fluctuations in consideration. The water must be tested within two weeks of sampling. “SANS 51008 also provides test methods for the tests required, applicable frequencies for testing and detailed requirements for the use of water recovered from processes in the concrete industry,” Roxburgh concludes.
Cement and Concrete SA’s School of Concrete Technology
CUSTOM-MADE AND ONE-OFF PRECAST CONCRETE PRODUCTS
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winstar Precast is the industry-leading expert in SA for the design, manufacture, delivery, and placement of custom-made and one-off precast concrete products for construction companies working on projects in the public and private sector, and civil engineering contractors.
requires additional skills and supervision. This makes custom-made, one-off product manufacture an unprofitable business for mainstream, high volume operations. However, not all building contractors have the necessary expertise, manpower and facilities to manufacture such products on-site.
With 26 years of experience in the precast industry, owner-operator Annemerie Coetzee realized that there was a gap in the precast concrete market for custom-made products and one-off items. In the concrete pipe and manhole market, for example, the emphasis is on high volumes, and the effort and time required to design and build once-off moulds for non-standard products disrupt any normal well-oiled production line, and also
Twinstar Precast was founded in 2014 with the express aim of assisting specifying civil engineers and civil engineering contractors with complicated sites and situations where currently available precast concrete products would not work. Twinstar Precast strives to be a problem solver and is solution-driven in all aspects of precast concrete. With products ranging in weight from 2kg up to 6 tons, the company is capable of solving almost all pre-
cast problems and turning the nightmare requirements into a quick and affordable solution. To date, it is the only company in South Africa specialising in custom-made and one-off precast concrete products, only keeping a few fast-moving products in stock that are standard spec for tenders and drawings. Twinstar Precast has a unique relationship with mainstream precast concrete companies that pass on referrals and use Twinstar to supply certain non-standard products to keep their clients happy. As far as possible, Twinstar Precast uses small local suppliers and SMMEs, rather than large corporate companies, to transport its products. Marketing is done mostly online, but direct contact is made with specifying engineers to make them aware that their need for custom-made products can be met. Achievements include manufacturing of polymer products In 2016, Twinstar Precast assisted a client in successfully closing old mineshafts in Gauteng which were previously closed but could not withstand vandalism, and were
A custom-made precast concrete bench
rife with illegal mining activities. Twinstar Precast's mineshaft slabs are still intact, and no illegal activity has been reported since. In 2018, Twinstar Precast started with the inhouse manufacturing of polymer products. The risk of theft of products with steel and cast iron components increases daily. These polymer products have no metal components and reduce the safety risk of open manholes as well as the financial implication this has on councils and developers. The company manufactures manhole covers and frames as well as stormwater gratings. These components can be bought as a loose item, or cast into the required precast concrete slabs. In 2012, Annemerie Coetzee was part of the team which received the CMA Award for Excellence in Innovation for her contribution in the design and development of bombproof ATM enclosure. Twinstar Precast’s manufacturing facility is situated in Olifantsfontein, Gauteng, but deliver anywhere in South Africa. Its crane mounted trucks can offload the product directly on site. The company also offers a service where the crane-mounted trucks can assist with placing slabs during installation.
