Abstract
Many early Iowa portland cement concrete (PCC) pavements provided good performance without deterioration for more than 50 years. In the late 1950s, Iowa was faced with severe PCC pavement deterioration called D-cracking due to crushed limestone containing a bad pore system. Selective quarrying solved the problem. In 1990, cracking deterioration was identified on a 3-year-old US-20 pavement in central Iowa. The coarse aggregate was a crushed limestone with an excellent history of performance in PCC pavement. Examination of cores showed very few cracks through the coarse aggregate particles. The cracks were predominately confined to the matrix. A high-resolution, low-vacuum Hitachi scanning electron microscope with an energy dispersion detector was used to investigate the deterioration. Subsequent evaluation identified a very small concentration of silica gel (silicon) but substantial amounts of sulfur and aluminum (assumed to be ettringite) in the air voids. Some of these voids have cracks radiating from them leading to the conclusion that the ettringite-filled voids were centers of pressure causing the cracks. The ettringite in the voids, after being subjected to sodium chloride brine, initially swelled and then dissolved. The research has indicated that the premature deterioration may be due to ettringite and may have been mistakenly identified as alkali-silica reactivity.
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