Posted: 2019 01 10 Source: Kefid Shanghai Machinery Views: 424
Aggregate is one of the main constituent materials of concrete. It mainly acts as a skeleton and reduces the volume changes of the cementitious material caused shrinkage and swelling in the process of condensation hardening. It also acts as an inexpensive filler for the cementitious material.
Aggregate is divided into coarse aggregate and fine aggregate according to particle size. Generally, coarse aggregates with a particle size greater than 4.75 mm, such as stones and pebbles, and fine aggregates with a particle size of less than 4.75 mm, such as sand, etc.
When we formulate high-strength concrete, why use a smaller grain of stone?
This is because as the coarse aggregate has an increased particle size, its adhesion to the cement paste is weakened, which increases the discontinuity of the internal structure of the concrete material, resulting in a decrease in concrete strength.
Coarse aggregates constrain the shrinkage of cement in concrete.
Since the coarse aggregate and the cement slurry have different elastic moduli, tensile stress is generated inside the concrete.
This internal stress increases with the increase in the particle size of the coarse aggregate and causes a decrease in the strength of the concrete.
As the particle size of the coarse aggregate increases, the degree of orientation of the Ca(OH)2 crystal in the transition zone of the coarse aggregate increases, and the interface structure is weakened, thereby reducing the strength of the concrete.
Reasonable adjustment of the ratio of coarse and fine aggregates can produce higher performance concrete to ensure the quality of construction projects.