Properties and Testing

This chapter discusses the basic properties of aggregates and the associated test standards. Aggregate properties are defined, and the significance of each property is briefly discussed. At the same time, commonly used tests for determining the properties of aggregates are described. General properties of aggregates mainly include the petrographic description of the aggregate, which provides valuable information about the mineralogy, chemical composition, grain size, and texture of the aggregate particles. Geometrical properties are those related to particle size distribution (gradation), shape (i.e., roundness) and surface texture (i.e., broken surfaces) as well as the content and quality of the fines. All these properties are key features that control the utilization of aggregates in many end-uses. The mechanical and physical properties of aggregates include physical properties such as density, water absorption, and porosity as well as mechanical properties such as resistance to abrasion and resistance to polishing. The importance of the thermal (thermal volume change, thermal conductivity and integrity during heating) and weathering (freezing and thawing and wetting and drying) properties of aggregates depends on their end-use, with some of the properties (i.e., thermal properties) being rarely needed. Chemical properties are very important in applications such as concrete or asphalt because some types of aggregate contain minerals that are chemically reactive and can affect the final behavior of the mixture.