The Civil Engineering Contractor April 2018 | Page 30

INSIGHT Getting the mix right By George Evans Concrete quality is made of as many elements as the material itself. Getting them into perfect balance is critical. C oncrete is a composite material. It is made up of various constituents, among them cement, sand, aggregates, and various chemical compounds. When you know this, you can begin to understand that, when it comes to concrete, quality is equally complex. The first point of call should be to define what we mean by quality. There is simply no absolute measure: in the final analysis, quality is related to how closely the product meets the need of a specific user. When producing concrete, it is thus critical to understand fully what it is being used for. One must also understand that measuring quality presents challenges, because concrete is made up of so many different types of material and can be 28 - CEC April 2018 influenced by other factors such as how it is transported and stored. Clearly, the more consistent the quality of the cement and other elements that go into concrete, the more consistent and predictable its results will be — and thus the higher the quality. In practical terms, then, consistency is a key driver of concrete quality. While there are many factors that influence concrete quality in South Africa, looking at them in four categories gives us the opportunity to understand where South Africa fares globally. • Quality of the raw materials. There are many facets to this category. Obviously, the consistent quality of the cement itself is paramount, but variations in each of the raw materials must be taken into account. For example, the moisture content of the sand would likely vary from load to load. If this is not monitored, the producer or the builder might have to adjust the amount of water used, but this would in turn affect the plasticity and durability of the finished product. • The proportions of the mix. It is necessary to control the proportion of each raw material very tightly or the characteristics of the concrete will be affected, and thus its ability to meet the use case. Raw material quality and proportion mix obviously interact with each other. Together, they have the largest influence on concrete quality. • Type of sampling used. An