1. What should be paid attention to when coarse and fine aggregates enter the site?
Coarse aggregate should mainly control its particle size, gradation, particle shape, stone powder content, mud block content, and mud content. A macroscopic inspection is carried out for each vehicle, and the vehicle cannot be unloaded if it is unqualified; in addition, various indicators must be inspected in batches according to the requirements of the specification.
Fine aggregate should control fineness modulus, mud content and mud content. Carry out a macro inspection for each car, and do not unload the car if it is unqualified; it should also be inspected in batches according to the requirements of the specification.
2. What kind of sand does concrete need?
Concrete needs to use medium sand. In addition to the sand gradation, mud content and mud block content, etc. according to the specification requirements, it is also necessary to pay attention to the sand passing through the 0.315mm sieve hole. Not less than 15%. This has a great impact on the pumpability of concrete. If the value is too low, the pump will be easily blocked, and the concrete will have poor water retention and easy to bleed.
3. What impact will fine sand have?
If the sand is too fine, the water demand of the concrete will increase, and the pumpability and plasticity of the concrete prepared with fine sand will be extremely poor, the strength of the concrete will decrease, and it will be easy to crack.
4. What if there is only fine sand?
If there is a problem with the sand source, fine sand and some machine-made sand can be used to prepare pumped concrete. For example, fine sand with a fineness modulus of less than 2.0 can be mixed with machine-made sand with a fineness modulus of 3.0-3.2, at a ratio of about 6:4. Observe its fluidity and pumpability, and specifically determine the ratio through experiments.
5. What are the consequences of the sand content meeting?
The sand and mud content is large, the water demand of the concrete is large, the plasticity is poor, the shrinkage is increased, the concrete strength is reduced, and the structure is easy to crack. Therefore, the sand and mud content should be controlled to ≤3% (C30-C50), and the high-strength concrete requires more mud content. high.
6. What is the effect of mud in sand and gravel on concrete?
In addition to the same impact as the mud contained in the sand and gravel, the mud block will also seriously affect the strength of the concrete. For example, mud blocks will weaken the concrete section; when the ground is poured, the mud blocks will float up, and after drying and shrinking, defects such as pits will be formed on the surface.
7. Why should stones with smaller particle sizes be used when preparing high-strength concrete?
As the particle size of the coarse aggregate increases, its bond with the cement paste weakens, which increases the discontinuity of the internal structure of the concrete material, resulting in a decrease in the strength of the concrete.
Coarse aggregate acts as a constraint on cement shrinkage in concrete. Since the modulus of elasticity of coarse aggregate and cement paste is different, internal stress is generated inside the concrete. This internal stress increases with the particle size of the coarse aggregate and leads to a decrease in the strength of the concrete.
With the increase of coarse aggregate particle size, the degree of directional arrangement of Ca(OH)2 crystals in the interface transition zone of coarse aggregate increases, which weakens the interface structure and reduces the strength of concrete.
