Post Date:18,Sep,2023

Aggregate occupies the main volume of concrete, but for a long time, there are many misunderstandings about the standard of judging the quality of aggregate, and the biggest misunderstanding is the requirement of cylinder compressive strength. This misunderstanding comes from its role in concrete, that is, sand and gravel, like the human skeleton, is an important parameter to determine the strength of concrete. Therefore, many textbooks and many current standards and norms still require the strength of aggregates to be 1.5 to 1.7 times, or even 2 times the strength of the concrete prepared. The author believes that when the early concrete design grade is still very low, this requirement is put forward, that is, the cylinder compressive strength of the aggregate is ≥40MPa, which is obviously just to remove those stone with severe weathering as the aggregate; However, the strength of concrete design has been greatly improved, and it still follows the relationship between the two earlier, which is obviously seriously divorced from reality. In fact, the lightweight aggregate concrete at home and abroad has been prepared and applied to engineering, and the cylinder compressive strength of the lightweight aggregate used is only 15MPa or lower, while the concrete strength can reach 80 to 100MPa.

Another important misconception is the maximum particle size applicable to pumped concrete or self-compacting concrete (SCC) stones. Since there must be relative motion between stones in the process of such mix traveling in the pump pipe and flowing in the template, the thicker the mortar lubrication film layer required for the relative movement between stone particles with larger particle size, that is, the more pulp volume may be required. This is also the reason why 19mm(British 3/4inch) is the maximum particle size of stones used in preparing such mixes abroad. Although the maximum particle size of the stones used is small, the void ratio that needs to be filled in the mix is large, which exists a balance point between the above conditions, and the amount of mortar required for the mix is small.