With modern computerized batch plants, we are capable of closely controlling the amount of sand, coarse aggregate, cement, and water added into a batch of concrete. This gives us the ability to consistently produce a nearly infinite variety of concrete mix designs with varying properties.
The easiest way to produce higher strength concrete is to add more cement to the mix. By adding more cement, we increase the amount of “paste” binding the aggregates together which increases the strength of the hardened mass.
As we adjust the mix design, the water-to-cement ratio (w/c) has the greatest influence on the final concrete properties. As the w/c ratio increases (more water in the batch), the strength (as well as every other desirable property) of the concrete will be negatively affected. Similarly, reducing the water added during mixing will increase the final strength of the batch.
We also stock a variety of admixtures (chemical additives) that are mixed in to a batch of concrete to change the concrete’s properties.
How does concrete harden?
Concrete hardens through a chemical process called hydration. Cement particles react with water to form new stable compounds that coat and bind the aggregate particles in the mix.
What is “28-day” strength?
Concrete hardens and gains strength as it hydrates. The hydration process proceeds very rapidly initially, but will continue at a slower and slower rate for years after placement. Since it is not practical to wait years to determine the ultimate strength of the concrete, a 28-day period was chosen by engineering authorities as a suitable length of time for curing before strength testing of samples. In general, when we refer to a concrete’s strength, we are referring to its 28-day strength.
What is “MPa”?
MPa is an abbreviation for “mega Pascal,” and is the metric unit of measure for the compressive strength of concrete.
