Basic physical, mechanical, thermal and hygric properties of reactive powder concrete with basalt and polypropylene fibers after high-temperature exposure

Abstract

Spalling is a well-known phenomenon that seriously limits application possibilities of concrete, the high performance- or reactive powder ones in particular. The dense structure of theirs, that under common circumstances provides excellent mechanical properties, is prone to easily trap molecules of water or water vapor in pores which can subsequently lead to inner pressure increase when exposed to an extensive heat source such as fire. There are several measures that are supposed to reduce or eliminate spalling risks, mostly based on an adjustment of the mixture composition by means of addition of various fibers. This paper aims at investigation of effects of basalt and propylene fibers on spalling of reactive powder concrete. Even if it might be sidelined by more frequently mentioned steel or glass fibers, the proposed combination has a large potential as it exploits excellent mechanical properties of basalt in wide temperature ranges to maintain the concrete integrity and, at the same time, polypropylene fibers can release the inner pressure by creation of water vapor escape paths when burned out. The complex determination of basic physical, mechanical, thermal and hygric properties as presented in this paper enables to assess the impact of polypropylene fibers on the concrete performance. It was shown, the mechanical properties are not negatively affected in a significant way. The highest decrease of compressive strength was found to be smaller than 9%. On the other hand, the moisture transport parameters were improved to allow a faster water vapor transfer through the body by up to 46.8%. This might represent the key factor in the spalling elimination efforts. The complex data presented in this paper are also highly valuable as input parameters for computational modelling whose lack is frequently mentioned in the scientific community.