Packing Density Links Concrete Mixture, Rheology, and Compressive Strength

Abstract

<p>Concrete is a mixture of cement, aggregate and water, whose properties, both fresh and hardened, depend on its composition. Establishing a link between the concrete mixture, the rheological properties of fresh concrete, and the compressive strength of hardened concrete provides a predictive tool for designing the rheology and the compressive strength on the basis of its constituents. Research has shown that packing density, which is a function of the constituents, influences the rheological and the compressive strength properties of concrete. Accordingly, it is postulated that packing density, a fundamental property, is the link. On this basis, representative models for rheology and compressive strength that employ packing density as a central variable have been developed for the latter and adopted from literature for the former.</p> <p>A fundamental approach was undertaken to develop a mathematical compressive strength model that is function of packing density and the concrete mixture. The proposed model accounts for the type of cement, cement degree of hydration, type and gradation of aggregates, mixture proportions and porosity. An experimental program was developed on the basis of fractional factorial design to implement, calibrate and validate the strength model. An evaluation of published models was then carried out in which the rational, limitations and potential use of these models were discussed. In addition, the applicability and accuracy of these models for different ages were investigated and compared to the proposed model using a large amount of data obtained from literature. Results reveal that the proposed model is one of the most representative and accurate models providing the highest predictability with a correlation factor of 0.93.</p> <p>A methodology for the postulated link, which provides a quantitative approach to design concrete mixtures to meet specific strength requirements and rheology, was proposed. The strength model developed for this purpose and the adopted rheological models were identified. An experimental program was developed to assess the postulated link. Results reveal that packing density links concrete mixture, rheology and strength. This was confirmed through successful generation and application of correlation nomographs whose trends were found consistent with what has been reported in literature.</p>