L.G. Li

Improving Packing Density of Powder in Cement Paste for Production of High-Performance Concrete

The packing density of the powder in cement paste has great influence on the performance of the concrete. A higher packing density could at the same water/powder ratio increase the amount of excess water for lubricating the cement paste and thereby improve the flowability of the concrete. Alternatively, it would allow the water/powder ratio to be reduced to improve the strength of the concrete without compromising the flowability. Therefore, it is of great interest, especially for production of high-performance concrete, to maximize the packing density of the powder. This study aims to investigate the roles of superplasticizer and fillers in the packing density of the powder in cement paste. Packing density tests were carried out to determine the packing density of cement with various dosages of superplasticizer and different fillers (limestone fine, superfine cement and condensed silica fume) added using a newly developed wet packing method. The results showed that the addition of superplasticizer can significantly improve the packing density of cement while the addition of fillers can further improve the packing density of the powder.

Wet Packing Method for Blended Aggregate and Concrete Mix

Although it is well known that the packing density of the particles in a concrete mix has great influence on the performance of concrete, the packing density is seldom directly measured and all codified methods for measuring packing density are carried out under dry condition. These dry packing methods do not account for the effects of water and any chemical admixture present and are not really suitable for water-solid mixtures containing cementitious materials and fine aggregate, which tend to form agglomerates under dry condition. To solve these problems, a new method, called the wet packing method, for measuring the packing density of cementitious materials, fine aggregate and mortar under wet condition has been developed. In this study, the wet packing method was extended to measure the packing density of blended fine and coarse aggregate as well as concrete mix. The results revealed that the packing density of blended aggregate and concrete mix is highly dependent on whether the aggregate and concrete mix are dry or wet. Hence, when measuring the packing density of blended aggregate and concrete mix, the wet packing method should always be used.