With the pandemic having created a survival mode for much smaller and emerging building contractors, it is now more important than ever for site staff to have at least a basic knowledge of concrete behaviour and performance in construction, says John Roxburgh, senior lecturer at the School of Concrete Technology.
Here Roxburgh deals with the importance of 10 topics covered in the School’s popular online training course, SCT10 “Introduction to Concrete”.
1. The properties of concrete: For any successful concrete project, understanding both the plastic and hardened properties of concrete is essential. With the correct plastic properties, staff will be able to transport, place, compact and finish off the concrete correctly so that it can then have the correct hardened properties, which includes strength, and durability with minimum shrinkage.
2. Materials for concrete: Knowing the function of each material in the concrete mix – and the consequence these materials have on both the plastic and hardened properties of concrete – is essential in obtaining concrete that will perform well over its design life.
3. Receiving and storing materials: The overall quality of concrete depends on many factors. Often, the receiving, storage and handling of the original materials are overlooked. Contracting staff must know how to prevent contamination of stored materials and have methods in place to ensure that they are receiving and using the correct materials.
4. Batching, mixing, and testing concrete: There are specific requirements for accurately batching and mixing concrete. Control of water content is probably the most important because the strength of concrete is strongly related to the water content. Concrete quality must be assured throughout and this requires a good working knowledge of the various tests that need to be performed on both the plastic and hardened concrete.
5. Transporting, placing and compacting: There is only a limited amount of time to transport, place and compact plastic concrete and contractors’ staff inevitably have to work against time to ensure that the full potential of the concrete is reached. Staff need to know how to achieve dense non-segregated concrete – and to do it timeously.
6. Finishing and surface preparation: Finishing and surface preparation require a unique set of skills, coupled with practical experience. Here also timing is of utmost importance and, for proper finishing, staff must have a detailed knowledge of concrete technology to apply their skills on the surface of the concrete in good time.
7. Protection and curing: So often all other aspects of the concrete works are completed acceptably – and then curing is botched up. For good durable concrete, proper curing is essential. It cannot, for example, just be interrupted and then resumed many hours later.
8. Formwork and reinforcement: Formwork is crucial for moulding the concrete to the correct shape but is also very influential in the final off-shutter finish. Knowledge of shutter materials and the types of release agents allows contractors’ staff to make the correct decision when it comes to achieving the desired off-shutter finish.
9. Sand-cement mixes: Sand-cement mixes are typically problematic. When there is excessively high water content, the concrete tends to shrinks substantially and is very weak. So, it is important to know how and where sand-cement mixes should be applied. Often the mixes are misused, and a contractor should be able to advise a client before this happens.
10. Durability: Sustainability is an important consideration in the world today with materials having a low carbon footprint given preference. Cost-effective concrete is sustainable and has a low carbon footprint as it does not need excessive maintenance or repair over its service life. It is therefore essential for small and medium, as well as micro-enterprises, and junior technical and sale staff in the building and construction industry, to receive training on matters such as listed above, as all these topics are intrinsically linked to concrete durability.
For further information about the “Introduction to Concrete” and other online courses presented by the School of Concrete Technology, phone 011 315 0300, email [email protected] or visit www.cemcon-sa.org.za.