Mistakes that builders make when specifying, ordering and receiving concrete can have far reaching effects on houses and structures built by them and may affect the future strength and performance of the structures.
According to Southern Africa Readymix Association general manager, Johan van Wyk, it is very important that project managers, and everyone involved in ordering and buying concrete, as well as onsite contractors, learn the right processes and procedures to use when working with readymix.
“There are hundreds of different types of readymix on the market for use in different applications. But it is important to remember that it can be supplied in different forms to make allowance for workability and many other factors that can affect the success of concrete on site. The relationship between the buyer/user and the professional readymix company therefore needs to be accurate and measured,” he says.
Getting concrete right
Van Wyk explains: “The most important thing is to make sure you are dealing with a reputable readymix company. The only way you can do this is to deal with a SARMA-accredited company. In this way there can be no confusion about meeting quality standards and honest, professional business practices are assured.
Remember that all SARMA plants are checked and audited to ensure they have the right staff and processes to make quality products. They look after the environment and consider the health and safety of workers and surrounding communities.
In addition, SARMA members must comply with road traffic regulations and rules to make sure they are safe on the road.
“When using a SARMA member, you and your client are also assured that the company has the necessary skills to see that concrete supplied is fit-for-purpose and complies with Sans 878: 2004 for generic readymix concrete.
Thereafter your technical requirements for the concrete can be specified and you can agree with the readymix company on the type of tests that need to be performed on site.
“You must remember to also spell out the workability that you need and tell them exactly where the delivery points are for the different types of concrete you require.
Also, you must tell them how they must offload the concrete as well as how the concrete will be moved to the place where it is going to be used (it can be pumped or transported in wheelbarrows etc). If you are unsure of the best way, ask the readymix company – they have experience in the field and it pays to check the details with their technical staff before finalising your specification.
Ordering correctly
“When making the final arrangements and ordering, always use the specification you have drawn-up and discuss your exact needs on site. If the project is big or difficult, it is a good idea to have the readymix company’s technical staff on site to look at the way it should be done and watch for any possible problems.
“Your specifications need to be made very clear and you must ensure that the strength and working characteristics of the concrete are right for the job. You also need to say exactly how much is required, where and when – and please remember that you can be charged if any of the concrete needs to be disposed of if it is not used on site. Workability and slump (consistence) of concrete must be agreed; discuss the type of equipment that will be used to receive the concrete and transport it on site.
For example if it is to be moved using wheelbarrows, it is important to know that the average mixer carries at least 90 wheelbarrow loads – so cannot possibly be offloaded by a couple of labourers.
Fresh concrete
“When a truck arrives with new fresh concrete then the time it takes to use the concrete is critical. Remember, experts say that you have seven minutes per cubic metre to offload and place the concrete. If the truck stands for too long, the concrete may begin to harden and change its workability characteristics, potentially affecting the end result.
Also, if the truck stands too long beyond the agreed time you may be charged a‘demurrage’ fee. A good tip is to first agree with the readymix company on the rate of offloading on your site.
“Last but not least, always make sure that your workers are ready and that they have the right equipment and tools needed to accept the concrete when the truck arrives. Also, ensure that you have organised access for the truck in terms of permission, physical space and how close the truck can get to point of discharge (SARMA members do assist by visiting site beforehand to identify any potential problems).
“Next you must discuss how the concrete will be cured and ensure that you are happy with the testing methods and that they are being adhered to. Also, have a clear procedure to follow if the tests fail at any point in the delivery, placing and curing of the concrete.”
Concrete on site
Few builders realise that if the planning is done correctly when specifying and ordering, then the job of accepting concrete on site is much easier. Van Wyk reminds building professionals that end users are increasingly specifying that contractors use only SARMA-accredited readymix suppliers, so it is important that contractors follow the right steps to make sure that the correct specification and handling methods are put in place.
“The reason behind the strong shift towards readymix is most often as a result of quality requirements and cost savings.
Customers want to make sure there are no strength concerns or failures that may ruin the project. Also, with readymix there is less need for storage and no theft on site and customers prefer having a clean site with no leftover concrete and waste when the job is done.
“Remember, professional readymix concrete producers can supply a wide range of mixes to meet different requirements and have ready-made design mixes for the various applications (foundations, floors, walls, retaining walls, facades etc). This is far easier, as site mix designs are time-consuming and have to move from design to approval and testing, which takes 28 days if done correctly. Using readymix also gives builders the flexibility to use many different types of concrete on the same site at the same time, while site mixing can only deliver one type at a time.
More information from SARMA, Tel:+27(0)117913327 www.sarma.co.za
