Studies Of Mineral Particles Grading Effects On Cement-based Compound Cementitious Materials

The thesis studies the influence of grading effects of mineral particles on the rheological and hardened properties of cement-based compound cementitious materials with low water-binder ratio using Compressible packing model (CPM).First, the CPM is fully investigated in terms of its theoretical basis, computational algorithms and computer program. The problems when CPM is applied to fine systems are attacked as well. Then the comparison of two often used packing models, CPM and Toufar model, are carried out by minimum water requirement test. The comparison shows the superior of CPM to the Toufar model. The influence of particle distribution and volumetric content on packing density is studied using CPM. Based upon those observations, experimental studies are carried out on the rheological properties of fresh pastes as well as the strength and dry shrinkage of harden paste. Finally, the influence of grading effects of mineral particles on rheological properties of fresh pastes and compressive strength and dry shrinkage ratio of hardened pastes are investigated through the packing density from CPM.The studies have shown that: 1) CPM is an efficient tool in predicting the packing density of fine particle systems; 2) the influence of mineral particles grading with cement on granular mixtures is important; the better particle grading, the higher the packing density of granular mixtures; 3) particle grading is closely relevant to rheological characteristics of fresh pastes and its change with time. Under identical water content, the yielding shear stress and plastic viscosity reduce with increasingly better particle grading and thus higher packing density of granular mixture; 4) particle grading is also closely relevant to the compressive strength of hardened pastes since for better particle grading, the packing structure would be tighter in case of lower water content, which leads to higher compressive strength; 5) the effect of particle grading on properties of fresh and hardened pastes is more significant for low water content than for higher water content because only in low water-binder ratio does the packing effects of mineral mixtures begin to appear; 6) there is correlation between the particle grading and dry shrinkage ratio of hardened pastes. When the sizes of mineral mixtures lie in a certain range, the shrinkage ratio decreases with increasingly packing density of granular systems. Out of the range, however, the shrinkage increases prominently since most of the free water has been used up by cement; 7) CPM is expected to be an efficient tool to optimize the mixture proportion of compoundcementitious materials aiming to achieve a maximum packing density of granular systems.