Investigation of the microstructure and carbonation of CS¯A-based concretes removed from service

The microstructure, mineralogy and depth of carbonation of two concrete samples, one removed from a normal strength crane column and the other from a high-strength pile, are reported. The normal strength CS¯A cement concrete had a high w/c ratio; microstructural images show that clinker tends to hydrate almost completely. But for high-strength CS¯A cement concretes, made with low w/c ratios, large amounts of partially hydrated clinker grains remain as a microaggregate.CS¯A cements and concretes are subject to carbonation in service conditions. The usual method of determining depth of carbonation, the phenolphthalein test, does not work with aged CS¯A matrices. A new method, using infrared microscopy, has been used to determine carbonation depth of aging CS¯A cement concrete. It has been shown that carbonation of a normal strength CS¯A cement concrete exposed to open air for 16 years averages ∼0.5 mm/year, and is thus comparable with reported rates of carbonation of OPC concretes. The high-strength CS¯A concrete carbonated at a maximum rate of ∼60 μm/year.