Influence of aggregate gradation and type on the microstructure and durability of cement based materials
Abstract
The influence of aggregate gradation and type on the microstructure and durability of concrete and mortar was studied with the aim of linking the parameters used in mixture proportioning to the performance of cementitious materials. The effect of aggregate size on the microstructure of the surrounding cement paste was studied and the results were compared to the microstructure of the bulk cement paste. Two sizes of aggregate gradation were used in this study. The first one conformed to range of 150μm–300μm, the second size gradation ranged between 2.36 mm and 4.75 mm. The results suggested that the porosity of the interfacial transition zone (ITZ) increased with increasing the aggregate size. The effect of aggregate type on the microstructure of the surrounding cement paste was studied by comparing the porosity and UH content of the paste surrounding lightweight aggregate to that around normal aggregate. The results indicted that paste within 10 μm of the aggregate surface was virtually not affected by the aggregate type. However, paste located 10 μm and farther from the lightweight aggregate appeared to have porosity lower than that observed for normal aggregate and lower than the level of porosity observed in the bulk paste. The effect of aggregate gradation on the durability of cementitious materials was investigated by comparing the results of absorption, sorptivity, electrical conductivity, and resistance to sodium sulfate attack. The results indicted that increasing the aggregate surface area increased electrical conductivity and porosity, but decreased sorptivity. The resistance to sulfate attack appeared to depend on the mode of transportation of the sulfate ions and the aggregate surface area. The effect of aggregate type on durability was examined by comparing mortars prepared with normal and lightweight aggregate. The results indicated that lightweight aggregate mortar had better durability than normal aggregate mortar. The improvement in durability was linked to the dense paste surrounding lightweight aggregate.
Degree
Ph.D.
Advisors
Olek, Purdue University.
Subject Area
Civil engineering
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