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EMPLOYING CAPILLARITY IN PORE RADIUS ESTIMATION IN

Abstract : Concrete is an inherently porous material. Pores have been classified in terms of pore size distribution parameters. Mean radius or equivalent radius has also been used in the assessment of porous material like concrete and it has been related to other parameters like water-cement ratio, degree of hydration, age etc. Different methods are used to estimate such a radius and overall radii distribution, Mercury Intrusion Porosimetry being the most common. The method has yielded appreciable results within its limitations and they have been extensively studied. But it is quite cumbersome to carry out and becomes increasingly costly for higher pressure applications. Other methods like water retention curves and imaging of individual pores require a lot of effort to generate statistically significant results. This paper presents the result of an effort to carry out pore radius estimation in essentially cement paste samples using the phenomenon of capillary absorption of water. Capillarity in porous materials is governed by the Lucas-Washburn equation to an appreciable extent. Five water-cement ratios(0.2,0.3,0.4,0.5,0.6) and five curing ages(1,3,7,28,90 days) have been used to widen the scope and observe the trends. Results have been compared with the MIP results from an earlier study in the same laboratory. The magnitude found for the effective pore sizes through Lucas Washburn Equation are two to three orders smaller than the corresponding mean pore radius as obtained in MIP studies. But the comparison trends between w/c ratios and curing ages are seen to be largely similar. It is believed that this parameter might be used for the purpose of comparative evaluation of materials based on actual rates of absorption.

  • Keyword : Effective pore size, Capillarity, Lucas Washburn Equation