What characteristic of aggregates contributes most significantly to the bond strength between the aggregate and cement paste?

The surface texture of aggregates contributes most significantly to the bond strength between the aggregate and cement paste. The bond between aggregate and cement paste is crucial for the overall strength and durability of concrete. A rough surface texture provides a larger surface area for the cement paste to adhere to and creates mechanical interlocking between the aggregate and the paste. This mechanical interlock enhances the bond strength by providing resistance to sliding or slippage at the interface. Aggregates with a smooth or polished surface texture offer less surface area and minimal mechanical interlock, resulting in a weaker bond. While other aggregate characteristics, such as mineral composition, particle shape, and size grading, also influence the bond strength, surface texture has the most direct and significant impact. For example, crushed aggregates, which typically have a rougher surface texture compared to rounded gravels, generally exhibit better bond strength with the cement paste. The rough surface provides more 'grip' for the cement paste, improving the overall strength and resistance to cracking of the concrete. Therefore, selecting aggregates with an appropriate surface texture is essential for achieving the desired performance characteristics of concrete.