Because insufficient air content can reduce durability, but excess air content can reduce strength, many concrete producers consider air content fluctuations a major problem. A recently introduced air-entraining agent for concrete is called Miracon Tough Air™. The polymer agent is aerated in a specially designed machine before it is injected into the concrete. The Miracon aeration machine is fully automated for integration into a ready mixed or precast concrete plant operation.

A concrete masonry unit (CMU) producer recently reported that a batch of their products developed little or no strength and were easily broken during handling. The producer’s staff claimed to have used the same material sources and production processes employed successfully with previous batches. To find the cause of the problem, samples of the defective CMU were examined, and hydration of the cement was investigated using calorimetry tests. Lessons learned from the investigation are presented.