The value of premixed cement (metakaolin or otherwise)
In 2012, a company specializing in precast concrete products wished to broaden the range of colours of its concrete slabs without affecting the mechanical properties. At the time, the company was using concrete produced by mixing cement with silica fume—a pozzolanic material recognized for its mechanical properties when combined with cement. In particular, this made the concrete resistant to compression and freeze−thaw cycles (i.e. flaking).

Since silica fume is dark, there was an esthetic issue. Therefore, the cement supplier suggested a fast and consistent colour cement, combined with metakaolin, to produce a pale concrete. This enabled the company to develop a wider range of colours without compromising on the quality of the products.

Metakaolins can be combined with any type of cement, generally in proportions of five to 15 per cent, replacing the cement. Precise batching is crucial to obtaining concrete with the desired mechanical properties. The various elements comprising concrete all react with each other, so by varying their percentages in the mix, completely different products are created. For a specific application, a concrete with specific mechanical properties is needed, which can only be obtained if the batching is precise, otherwise the concrete might not meet the requirements of its final purpose in terms of strength or durability. Experience has shown getting premixed cement directly from the supplier leads to an increase in precast productivity.

By doing this, the concrete producer benefits from a one-stop shop service and no longer needs to worry about numerous operational aspects that can prove costly. To prepare optimal and precise mixtures and ensure end product quality, it is preferable not to mix the elements manually, as it can lead to imprecise batching. However, investing in an additional silo can be difficult to depreciate with one-shot or specialized orders such as street furnishings.

Getting custom-premixed cement directly from the cement supplier is an advantage that today’s precast concrete producers have come to appreciate. It can be especially valuable not only in terms of savings but also with respect to efficiency. For each application, the cement supplier can bring its expertise and develop a customized mix that meets the needs of the precast concrete producers and of his clients.

Jean-Claude Leduc, Asct, is Holcim Canada’s technical services manager. He has more than 30 years of experience in the cement industry and expertise in concrete admixtures. Leduc can be contacted via e-mail at jean-claude.leduc@holcim.com.

Jacques St-Onge is a technical and sales services representative with Holcim Canada. He has more than 25 years of experience in the concrete business, with a specialty in precast manufacturing. St-Onge can be reached at jacques.st-onge@holcim.com.