Effects of Water Content, Packing Density and Solid Surface Area on Cement Paste Rheology

This dissertation, "Effects of Water Content, Packing Density and Solid Surface Area on Cement Paste Rheology" by Hin-cheong, Henry, Wong, 黃憲昌, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled EFFECTS OF WATER CONTENT, PACKING DENSITY AND SOLID SURFACE AREA ON CEMENT PASTE RHEOLOGY submitted by Wong Hin Cheong Henry for the degree of Doctor of Philosophy at The University of Hong Kong in September 2007 High-performance concrete (HPC) has become increasingly popular in recent years. To produce HPC, addition of supplementary cementitious materials is virtually an essence. The use of these materials renders numerous possible mix combinations, making it difficult to optimize HPC mixes and limiting the usage of conventional mix design methods on HPC. In this regard, a comprehensive study aiming at developing a scientific mix design method for HPC has been launched. This thesis presents the findings on the first part of the study, which focuses on studying the scientific parameters governing the cement paste rheology. Due to the lack of a generally accepted method for measuring the packing density of cementitious materials, the postulation that the packing density has considerable influence on cement paste rheology has not yet been verified experimentally. Herein, a new wet packing method, which directly obtains the packing density by measuring the apparent density and voids content of cement paste, is developed. Using this method, the packing characteristics of pure ordinary Portland cement (OPC) and several blended cementitious materials measured under different conditions were acquired and compared with those obtained indirectly from consistence test. Based on the comparison, it is advocated that the packing density and water demand should be measured directly using the new wet packing method rather than other indirect methods. By using the wet packing method, the packing densities of cementitious materials containing OPC, pulverized fuel ash (PFA) and condensed silica fume (CSF) were measured. Results showed that the packing densities of pure cementitious materials could be improved by double blending and further increased by triple blending at appropriate proportions. The results also proved experimentally the postulation that packing density of cementitious materials could be improved by blending. Using the results, a ternary packing density diagram for determining the mix proportions for maximum packing density has been produced. Apart from experimental method, three existing packing models were also examined for their applicability on predicting the packing density of cementitious materials. By comparing the measured and predicted packing densities, together with some additional test results, it was found that in the presence of a third-generation superplasticizer the packing density of CSF is dependent on the lime content. When the effect of lime on the packing density of CSF is taken into accounted, very good agreement between the measured and predicted packing densities has been achieved, which verified the applicability of the models on cementitious materials. Although it is known that water content, packing density and solid surface area are the important parameters governing cement paste rheology, little progress has been made in evaluating the combined effect of these parameters on the rheology. In this thesis a new parameter called the excess water to solid surface area ratio is proposed to quantify the combined effect. A number of cement paste samples con