A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1992

Today's interest to engineers toward predicting the durability of concrete is the author's concern of this study. The process of deterioration of concrete structures are partly and chiefly mediated by movement of water and the situation is more severe in case of alternate wetting and drying cycles. The problem is multiphase movement of water in concrete capillaries. In this study, the water movement in wetting cycle with respect to changing water to cement ratios, viz., 40%, 45%, 50%, 55% and 60%, and with varying sand contents, including cement pastes are conducted in laboratory test set-up conditions. The sorptivities values of the test specimens are found rather low, i.e., saturated level rise in the test specimens are very low despite the very high value of surface tensions in representative capillary. Here, a existence of some initial static resisting force in microscopic level is recognized as necessary. The previous work done, by Sharma, A., on this regard is enhanced here in two aspects, one by introducing a static resisting force 11 Yield Shear 11 in microscopic level and the next is a direct approach is applied to equiliberate the driving force from surface tension on a representative capillary to all resisting forces generated from the movement of water. The dynamic resisting force is associated with friction coefficient and rate of level rise. The yield shears and friction coefficients are computed by model with experimental results for given water to cement ratios and mix proportions of sands. These parameters are measure of material properties of a cement mortar. After conducting this investigations, the model is visualized as a development of interface channels system, just like a irrigation canal system and a rice field, with inclusion of sand in cement paste matrix as boulders. First inclusion of sand in dispersed state imparts high resistance to water movements as the path length increases than in a paste matrix without sand and as the absorbant agent to take capillary water from cement paste dispersion. On the other side, densely spaced sand particles are found to develop a sort of continuous interface channels system in which a rapid water movement is expected and paste matrix is in turn irrigated through these channels.