The reason why precast concrete is so hard to decarbonize

Ricardo Remus
11 Jan 2022

Precast concrete has a lot of advantages like constant production throughout the year, weather independence and a high automation potential. Especially the latter is getting more important since skilled workers are scarce.

On the other hand, precast manufacturing requires a fast concrete hardening, since the economic operation of a precast plant relies heavily on the number of precast parts produced during a shift. This is the reason why precast concretes are often designed reaching high early strength to further transport and process the parts. Typically, a high cement content and highly reactive cements are used to do so.

With cement clinker being one of the main sources of the carbon emissions of concrete, you'd think there'd be a huge saving potential. Unfortunately it is not that simple. So, what makes it so hard for precast manufacturers to reduce the cement clinker?

Well, it’s mostly due to the fast production cycles and therefore the need for high early strength. Switching from CEM I to CEM II will save between 5 – 10 % CO2. But, at the same time this decreases the early compressive strength by up to 25 % depending on the cement, meaning stripping is delayed for several hours. If further optimizing the concrete recipe (e.g. lower w/c-ratio, chemical accelerators) is no option, this leaves two possibilities: you may either choose to produce less and strip later or you have to buy more molds for your concrete, right?

Producing less means reducing the overall output. Doing so reduces the profitability of the factory. The owner can now decide to cut costs (less staff) or increase prices (not competitive). If he decides to buy more molds the costs of the molds, their maintenance, and of course the storing capacity must be included in the calculation. Tricky situation.

This is where sonocrete comes into action. As a new degree of freedom in this equation, our system enables producers to strongly reduce their carbon footprint. So far, we were already able to prove a carbon-reduction of up to 30% for prestressed concretes.

And together with an intelligent concrete mix design, new high performance low carbon cements, admixtures and SCM’s way more will be possible.

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