Improving Concrete Sustainability and Durability by Optimization of Aggregate Particle Packing and Use of Microfine Fillers.

摘要

A methodology was developed in this study to increase the packing efficiency of concrete aggregate combinations and use of microfine fillers (finer than 75 mum) in order to make better use of scarce aggregate resources near urban centres while simultaneously reducing the required cement paste content of concrete to improve sustainability, durability, strength, workability, and cost. A 32% reduction in the portland cement content of a typical 35 MPa concrete mixture was successfully made, meeting all performance criteria evaluated, including workability, CSA A23.1 low-shrinkage and C-1 exposure class requirements, while significantly improving compressive strength. Several concretes that included a significant aggregate volume proportion of low-value intermediate aggregate materials and/or manufactured sands successfully met all performance criteria evaluated.;Concrete mixtures conducted indicate that the effectiveness of the predominantly used 0.45 Power Chart for optimization of the total combined aggregate gradation can be substantially improved by considering the influence of aggregate particle shape, angularity and surface texture. A practical method for accurately measuring separate shape, angularity, and surface texture parameters, along with specific surface area of aggregates was developed in this study using images acquired from a flatbed scanner and an optical microscope, combined with use of ImageJ analysis software. Subsequently, this information was used to more effectively optimize the combined aggregate proportions by using the Excess Paste Theory to maximize the thickness of the excess cement paste available to coat the aggregate particles after filling the voids between compacted aggregate particles. Fresh concrete performance, measured by multi-range water-reducing admixture dosage needed to meet workability requirements, improved while compressive strength and drying shrinkage were similar to those concretes optimized using the 0.45 Power Chart. The thickness of excess cement paste had a strong correlation with RCPT charge passed, and moderately strong correlation with multi-range water-reducing admixture dosage needed to meet workability requirements.