Evaluation of pore and fiber distribution characteristics of hybrid fiber reinforced lightweight aggregate concrete using X-ray computed tomography

The contribution of lightweight aggregate (LWA) and fibers to the mechanical performance of concrete is still controversial due to the unclear understanding of the enhancing mechanism. Clarifying pore structure and fiber orientation characteristics is the key to it. In this study, pore characteristics and fiber distribution properties as well as their correlations with concrete strengths were evaluated. To separate the effect of LWA's internal pores and LWA's internal curing, pore parameters were calculated in two ways, i.e., containing and excluding LWA. Results show that the internal pores of LWA are detrimental to the overall pore structure while the in-ternal curing optimizes the pore distribution by decreasing porosity and pore size and increasing sphericity. Pore sphericity has a positive linear correlation with compressive strength only when LWA's internal pores are included. When the inner pores of LWA are excluded, sphericity is positively correlated with flexural strength. It indicates that LWA's internal pores have a more significant effect on compressive strength while LWA's internal curing effect has a more promi-nent impact on flexural strength. In addition, adding fibers benefits pore characteristics given that more pores are in the spheroid shape with higher sphericity. Furthermore, fibers are well distributed in this study with a mean orientation coefficient of 0.59, which exhibits a positive correlation with flexural strength but an insignificant correlation with compressive strength.