Effect of Aggregate Size on the Restrained Shrinkage of the Concrete and Mortar

Since the aggregate is 80 % of the total volume of the concrete and mortar, the characteristic properties of the aggregate affect the fresh and hardened properties of the concrete and mortar [1]. The characteristic properties of the aggregate such as the shape, the size and structure affect the properties of the fresh concrete and the mortar like workability, settlement, pumping and segregation and the properties of the hardened concrete and the mortar like the strength, the Young’s modulus, the shrinkage, the creep, the density, the permeability and the durability. The grading or the distribution of the aggregate size affects some properties of the concrete such as the density, some pores, workability, segregation and the durability. According to some researchers, the mixture with the proper distribution of the aggregate size has the appropriate workability than the mixture with the improper distribution of the aggregate size [2]. Moreover, the grading affects the properties of the hardened concrete and mortar. The mixture with the proper distribution has the high density, less permeability and high abrasion strength [2]. Consequently, the mixture with the proper distribution requires less cement paste thus less perspiration, less creep and shrinkage occur [3,4]. Aitcin [5] told that high amount of coarse aggregate decreases the free shrinkage but increases the micro-cracks in the paste. If the aggregate grain size is low or high, it causes poor workability and less durability [4,6]. The amount of the coarse and fine aggregate should be in equilibrium. For example, more sand requires more cement and viscous mixture forms, the pumping is difficult and finish and crack problems occur [4]. Additionally, perspiration and permeability increase [1]. On the other hand, less sand form lean mixtures and finish problems [1,4]. If the amount of fine aggregate is high, the perspiration, segregation, and hardening problems occur. However, if the aggregate is too much fine, the amount of the required water increases [6]. The proper sizing depends on the shape and tissue of the aggregate. The effect of the grading, the shape and the size of aggregates on the shrinkage is indirect, but it is important to determine how they affect the amount of water. On the other hand, the properties of the aggregate enrich the bond between the aggregate and the paste. For example, the surface structure, the shape, and the porosity decrease the drying (free) shrinkage.