Cracking characteristics and pore development in concrete due to physical attack

Abstract

This study provides a fundamental understanding on the deterioration of concrete due to physical sulfate/salt attack (PSA), including local cracking and pore structure development. The results show that sulfate salt crystals in a partially immersed concrete specimen preferred to precipitate in relatively large pores (DP-III, from 1 to 100 µm in diameter) in the concrete at the early stage of exposure. The persistent formation of small pores (DP-I and DP-II) and pore throats (PT-I and PT-II) occurred at the late stage of exposure. The gel pores, transition pores and even small capillary pores played an important role in providing space for crystal growth. The pore filling during the early stage resulted in a transient gain of specimen mass due to the capacity of pre-existing voids to accumulate the precipitated crystals (buffer effect). The later cracking degeneration induced by the pressure from the crystals was found to be limited to the subflorescence zone. This cracking degeneration was a time-dependent process that primarily developed along with relatively unsubstantial zones in the concrete, such as the interfacial transition zone (ITZ), until the extensive coalescence of these pressure-induced cracks.