Characterizing the thermal properties of hybrid polypropylene-steel fiber reinforced concrete under heat exposure: Insights into fiber geometry and orientation distribution

Abstract

In this paper, both modeling and experimental efforts are made to characterize the effects of fiber geometry and orientation on the effective thermal conductivity of hybrid polypropylene-steel fiber reinforced concrete (HFRC) when exposed to high temperatures. Based on the Mori-Tanaka scheme, a multiscale thermal conductivity model is developed for predicting the thermal conductivity of HFRC as a function of temperature, and the aspect ratio and orientation distribution of hybrid fibers are incorporated. In what follows, one-side heating tests are conducted on composite slabs reinforced with hybrid polypropylene (PP) and steel fibers, and the thermal conductivity of slabs is obtained through the back analysis of measured temperature–time curves. It is founded that the thermal conductivity of HFRC increases with the increasing geometry of PP fibers, and the predictions are in good agreement with the experimental results at high temperatures. More importantly, microstructural analysis reveals that hybrid fibers are tightly arranged due to the weak dispersion of micro fibers, suggesting the combined effects of fiber geometry and orientation distribution on thermal conductivity. The findings provide insights into the optimal design of hybrid fibers to achieve desirable thermal properties of composite structures.