It has been observed that concrete made with equal proportions of 10 mm and 14 mm thick aggregate had lower strengths compared to concrete made with 14 mm and 20 mm aggregates. Aggregates are essential for the strength, thermal and elastic properties, dimensional stability, and volume stability of concrete. Cement is more prone to shrinkage, and the inclusion of aggregates in the mixture can control the level of shrinkage and prevent cracking. This is usually achieved through proper storage of aggregates and reprocessing stockpiles to counteract excessive segregation (Photo.
Appropriate classification of coarse-grained aggregate can minimize the possibility of segregation, particularly for increased workability and improved concrete compatibility. If the aggregates are too humid, excess moisture should be subtracted from the expected amount of mixing water. Note that removing sand from a mix transforms conventional concrete into a fineless mix, also known as permeable concrete (see Permeable Concrete Pavements). Alternative sources of aggregates or additional aggregate mixtures can be considered to approach the ideal gradation that provides the best workability, pumpability, shrinkage reduction, and economy (Figure.
However, for concrete grades of M40 and above, the potential for joint failure would tip the balance in favor of an angular aggregate with more surface area. OD monitors the moisture content of coarse-grained and fine aggregates on a regular basis to promote consistency and uniformity from batch to batch. Optimized grading based on aggregate availability and project requirements will result in cost-effective concrete with good workability and finishability. The maximum aggregate size is often restricted by a transparent cover and a minimum distance between the reinforcing bars.
The fundamental relationship between the water-cement ratio and strength begins with the correction of the contribution or absorption of moisture by aggregates. To avoid post-placement issues in concrete that are difficult to rectify, verify that these limits are not exceeded at the time of sending the material. USE aggregates that meet ASTM C 33, Standard Specifications for Concrete Aggregates. Elongated and flaky coarse-aggregate particles not only increase water demand but also increase the tendency to segregate.
Crushed stone is preferred in pavement mixes, since the higher paste-aggregate bond produces greater flexural strengths (Photo courtesy of PCA). If their absorption is not satisfied, these sponges steal water from the designated amount of mixing water, reducing concrete settling. Concrete Mix Design and Control, Portland Cement Association (see Chapter 5, Aggregates for Concrete).