Characteristics of Aggregate-Induced Deteriorated Microstructure in High-Strength Concrete

In this study, the causes of degradation of high-strength concrete are determined using a petrological approach that incorporates polarizing microscopy, electron microscopy, and EDS analysis, and the factors that lead to the formation of a DEF-like degradation textures are clarified, taking into account the aggregate structure, constituent minerals, and compressive strength of the concrete. Precast RC box culverts for bridge and pretensioned PC hollow girders were used as observation samples. For the bridge box culverts, ASR was the cause of deterioration in the box culverts where meta-gabbro was used as the coarse aggregate, and drying shrinkage cracking was the cause of deterioration in the box culverts where serpentinite was used as the coarse aggregate. Observations showed that the PC hollow girder was primarily ASR in granite cataclasite of the coarse aggregate and chert in the fine aggregate, which contains late expansive reactive minerals. In both cases, the cracks propagated through the relatively weak aggregate interface and into the cement paste. Inside the cracks, ettringite was formed due to the high cement content, forming a microstructure similar to DEF.