An Introduction to Concrete Mixtures for Pavements Professional Engineers

Concrete is a two-component mixture: aggregates and paste. In this mixture, the aggregate particles are completely coated with the paste. The paste consists of cementitious materials and water and incorporates entrapped air or purposely entrained air. Aggregates make up about 60 percent to 75 percent of the total volume of concrete. The quality of the concrete depends on the quality of the aggregates and paste and the bond between the two. The quality of the paste is significantly influenced by the amount of water used. Typically, less water improves the quality of the concrete. A maximum w/cm ratio is typically specified to avoid excess water and ensure good quality paste is achieved. Cleanliness of the aggregates also influences paste/aggregate bond and the quality of the concrete. The properties of freshly mixed (plastic) concrete are changed by adding chemical admixtures to the concrete, usually in liquid form, during batching. Chemical admixtures are commonly used to improve or control the following attributes: - Workability- Entrained air- Water demand- Setting time- Other properties