Construction World April 2018

Wasteful and dangerous Poor quality concrete wastes time and money, ruins contractors’ reputations – and could be dangerous to users of sub-standard structures, warns John Roxburgh, lecturer at The Concrete Institute’s School of Concrete Technology.

development, and its versatility allows it to be used on its own or with other mineral components, depending on the application. The result of this close collaboration with the AfriSam CPE is that Opehst has been able to produce good quality products at low cost. This allowed the new company to enter the market with competitive pricing right from the start of its operation. It was also able to ensure that its products conformed to the specification required by the South African Bureau of Standards (SABS), so the end user could be confident that the products were fit-for- purpose. These quality standards which underpin the products will ensure the sustainability of the business going forward, and lay the groundwork for repeat business. In a similar intervention, the CPE worked with CPM Smartcrete in Centurion to increase their output by double-casting their products within the normal working cycle. Smartcrete makes concrete tables, windowsills, wall caps, wall copings, stairs, treads, water channels and spouts. The company was casting products on one day and demoulding the following day. This cycle took anything between 18 and 24 hours, and created a bottleneck right at the time when the demand from customers increased. When the company needed to start casting twice a day, they approached AfriSam’s CPE to assist with a mix design that would allow them to demould within six hours. The collaboration process began as usual with a site visit from AfriSam, where CPE experts could look at the resources employed by the customer. The whole process was evaluated to consider where improvements could be made in terms of personnel, equipment, material, flow of work and overall cost. The aggregate material used by Smartcrete was sampled and taken to the AfriSam’s CPE laboratory in Roodepoort for analysis and internal trials. In the end, AfriSam Rapid Hard cement (52.5R) was recommended for its fast strength gaining qualities. This product is designed for use in applications where quick form turnaround and form stripping times are required. A combination superplasticiser admixture and accelerator was added to the mix, supplied by chemical admixture supplier Chryso Southern Africa. The support provided to these customers is a good example of AfriSam’s commitment to building a sustainable construction industry and uplifting communities; moreover, the support is provided at no charge to the customer, wherever AfriSam cementitious products are available. 

Roxburgh says it has sadly become a fact of life that the contracting fraternity pleads poverty when it comes to doing a project properly – but then ends up having to find funds to fix disasters later. “In concrete works, this is especially true: by not getting the job right the first time, the contract is going to run over time and costs will escalate drastically,” he states. Roxburgh says concrete quality typically encapsulates three elements: • Firstly, the concrete must perform structurally. It should have the correct strength and required deformation properties • Secondly, it should be aesthetically pleasing. “Of course, there will be many cases where aesthetics is irrelevant, such as in foundations. But in exposed concrete, appearance will be important and will often be the only way a client will judge a contractor’s work. Attractive concrete calls for precision of work and a good off-shutter finish.” • Lastly – and this is the element of quality often overlooked – is how well the concrete will perform over time within the environment it has been placed. Durable

concrete will have a low maintenance cost over its lifecycle “So how does a contractor produce quality concrete? The quote by the American war hero, William A. Foster, sums it up beautifully. Foster said: ‘Quality is never an accident, it is always the result of high intentions, sincere effort, intelligent direction and skilful execution’. To produce quality concrete, having the correct intentions is just the first step: doing the necessary preparations is even more important. “The correct concrete mix design to meet the required strength, durability and workability requirements, must be formulated. And a suitable mix design can only be found by trial testing. Mock-ups of the formwork – which represent the shape of the actual formwork in the project – should be made. The concreting teams should practice on these mock-ups to develop the correct placing techniques and to ensure the correct surface finish to the concrete. “For concrete with high durability, good site practice is vital and this should include a thorough curing regime. Curing can never be rushed. Quality supervision will also go a long way towards producing quality concrete. Concrete producers should provide clients with evidence of their concrete’s quality by having an intensive testing programme at SANAS accredited laboratories,” Roxburgh adds.  John Roxburgh, lecturer at the School of Concrete Technology. Concrete quality is essential when it comes multi-billion rand projects like the Berg River Dam – pictured above before the current devastating drought hit the Western Cape.

49

CONSTRUCTION WORLD APRIL 2018