Effect of Temperature on Porosity, PSD and Hence, Performance of Concrete

Abstract

The porosity and pore size distribution (PSD), tortuosity, degree of interconnectivity and nature of pore etc., govern most of the important properties of cement based materials. The mechanical properties, namely, strength, elastic modulus etc. are governed by porosity and pore sizes. The durability performance on the other hand is governed by tortuosity, degree of interconnectivity. Thermal conductivity is governed by nature of the pores and moisture content. Concrete and other cement based materials, when subjected to elevated temperatures, under goes nearly irreversible physical and chemical changes. Such physical and chemical changes results in change in porosity and pore size distribution leading to changes in properties and performances. Porosity and pore size distribution can be measured through Mercury Intrusion Porosimetry (MIP), Back Scattered Electron (BSE) microscopy and some other techniques. In spite of some of drawbacks and disadvantages MIP is a popular method for investigation of PSD. Thus effect of elevated temperature on PSD of concrete had been studied using MIP and outcomes are presented in this paper. A general equation for pore size distribution (PSD) of cement based materials including concrete is considered. The equation relates cumulative pore fraction volume to pore size. The constant parameters of the equation are porosity, mean distribution radius and a dispersion coefficient. The relationship of these pore size distribution parameters with temperature of exposure is presented and discussed. Hence effect of elevated temperature on PSD is presented. The strength, and durability related material properties of concrete can be related to pore-size distribution parameters and other features of microstructure of concrete. Thus effect of exposure temperature on variation of strength and other performance parameter can be better understood through the relationship and discussion presented.