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.

As with all materials, the performance of concrete is strongly influenced by its physical structure. From its earliest origins, however, the performance of cement-based materials has also been controlled by the judicious addition of supplemental chemicals. From the examples discussed in this article, it’s clear that the engineering of concrete performance has historically used both physical and chemical approaches. Future engineering efforts will almost certainly maintain this tradition.

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.