Moisture dependency of variation of pore structure and property of cementitious materials due to high speed impact

Abstract

In some numerical simulations of collisions on concrete, the densification of the pore structure has been assumed to be attributed to collisions. However, a previous experimental study conducted by the authors revealed that the pore structure can be coarsened by impact. The conditions of this coarsening have not yet been clarified. In this study, impact tests were conducted on cementitious materials with and without sand, admixture materials, and with different moisture contents, to understand the influences of these factors on the cracking, pore structure, and compositional changes caused by impacts. In the water-saturated cement paste specimens, mercury intrusion porosimetry showed that the pore structure of the region near the impact point was coarsened. Conversely, the pore structure of the cement paste specimens with low-water content was densified. In the mortar, the pore structure was coarsened in both the saturated and dried specimens. To explain the mechanism of incurred pore structure changes due to collision, mechanical and thermal effects were proposed. These include compaction due to mechanical action, the expansion force generated by liquid-water pressure upon impact, and vapor pressure changes due to heat, respectively. The study’s findings improve our understanding of the responses of cementitious materials subjected to impact loads and allow us to obtain more accurate damage estimations. The findings revealed the necessity of the investigation on the cause of the high-stiffness response at impact other than compaction. If the liquid or vapor pressure caused the pore coarsening at impact, it may be reduced by the effective release of these pressures.