Winter’s Efflorescence Control Challenges

We should be leaving winter behind.  But all the CMUs that were put in the yard though the cold months are being shipped now.  With the proper precautions this doesn’t have to lead to efflorescence complaint calls.  (For those of you that stumbled upon this post CMUs are Concrete Masonry Units.  The target audience for this post is ICT’s customers and potential customers that operate plants that make CMUs.  CMUs include interlocking pavers, hardscape items like garden wall, outdoor fireplace and grill kits, patio stones, and large segmental retaining wall {SRW}.)

What goes wrong in the winter?  Cold batch temperatures.  If you are making concrete for a bridge you can bet DOT would be monitoring concrete and ambient temperatures very closely.  If minimum criterion are not met no concrete gets made.

It is easy to forget how important batch temperatures are in the CMU plant.  Water gets colder, aggregates going into the bins are very cold.

Once batch temperatures get down to 55 hydration chemistry starts to misbehave.  Parts of the chain of hydration reactions fail to do their job.  The part we worry about transforms efflorescence causing calcium hydroxide into hardened concrete.  There is always plenty of troublesome calcium hydroxide left over (about 10% of the weight of cement) but cold batch and curing temperatures can double the usual amount.

That causes trouble when winter production goes to the customer in the spring.

Energy is the answer in the form of heat.  Batch water can be heated to nearly boiling.  Aggregate bins should be topped off at end of shift and allowed to warm in the HEATED plant.  Aggregate bins can be steamed.  Stick a thermometer in the concrete and keep it 55F or warmer.  Keep curing chamber temps were they belong.  Best advice saved for last, use ICT admix.

A little heat will make sure your CMU’s get a warm reception this spring.



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