Interaction of ASR and DEF in Determining the Cause of Cracks in Prestressed Sleepers in India

In prestressed sleepers used in India, longitudinally extending and map-shaped cracks occurred at many service points 6–9 years after manufacture. Polarizing microscopy and electron microscopy of thin sections made from the concrete showed that the gneissic aggregate had a distinct ASR. Other gaps at the aggregate-cement paste interface and reticulated cracks, which were different from the extension of the ASR cracks, were also observed. The filling of ettringite within the gaps and cracks confirmed that DEF had occurred. It was therefore concluded that the cause of deterioration of the Indian sleepers was combined ASR and DEF deterioration. The very high alkali content of the cement used in India, coupled with the hot and humid environment, may have contributed to the development of ASR and DEF. In addition, an estimation of whether ASR or DEF occurred prior to the ASR or DEF was made from microscopic texture observations. The results showed that both were considered to have occurred prior to each other.