Mix Design Optimisation: One mix to rule them all?

When working with concrete, it is important to know the effect that temperature has on its behaviour. Both cold and hot temperature can greatly change the rate at which the concrete achieves strength.

For example, concrete curing at higher temperatures normally develops higher early strength than concrete produced and cured at normal temperature. In cold weather, the opposite is true. The pace at which concrete strengthens is much slower. In addition, the temperature differentials within the concrete increase the chance of cracking and can have a harmful effect on its durability.

What to do? Well, the first course of action should be optimising your mix design for different seasons. It may sound obvious, but many companies currently use the same mix design for both summer and winter months.

A recent study we conducted with a customer showed 700% variability in performance during different seasons when using the same mix. That means more inaccurate data, more structural failures, and more programme delays.

Approximately 700% variation in time taken to reach 10 N/㎟ between summer and winter temperatures.

So you’ve changed your mix design to accommodate different temperatures? You’re not out of the woods yet.

You’ve put all that effort into adjusting your mix for the weather — Great! But are you still testing your concrete in standard lab conditions?

There are many limitations to using cube crushing for determining the strength of your concrete slab (see our post on that here), one of which, is that lab conditions do not reflect the conditions of your slab. If your mix design is optimised for cold temperatures (typically under 5℃), but you are still crushing your cube at 20℃, nothing has been achieved. The data you base your decisions on will still remain inaccurate.

The most accurate way of determining when your concrete has reached strength, is testing the in-situ itself. See our post common methods of in-situ testing.

To sum up, don’t ignore your environment. You can save valuable time and money with two simple steps:

  1. Optimise your mix designs.
  2. Test in-situ.