The Effects of Aggregate Properties on Concrete Mix Design and Behaviour

Due to the fact that aggregates are the largest component in concrete (typically 60–70% by volume), the characteristics of the aggregates significantly affect the performance properties of fresh and hardened concrete. This article reviews the literature on the effects of coarse aggregate type on the mix design of concrete. Key parameters are identified, and a chart is plotted to help organize them. The relevant characteristics of aggregates are categorized into physical characteristics and geological characteristics. It is found that shape, texture and gradation have the most important role on the properties of fresh concrete, particularly workability. The porosity of the aggregate is reported to affect the workability during the first 15 min of mixing, as well as the creep and shrinkage. Depending on the mineralogy of the aggregate source, aggregates may react negatively with the matrix or beneficial interactions may occur between the matrix and the aggregates. Consequently, mechanical and strength properties of concrete can be affected by the aggregate mineralogy. Another important characteristic of aggregate is the presence and type of surface coatings which can affect workability and plastic shrinkage of concrete. Generally, an increase in dust content, increases the water demand of the mixture, which decreases workability and reduces air content. Aggregate type does not affect the setting time of concrete directly; however, the presence of soluble salts or organic contamination on the surface of aggregate may influence the setting time. Due to these impacts on the properties of concrete, adjustments to the mix designs are necessary when concrete suppliers are switching from one source of aggregate to another source.