1.Strength suitability principle
At present, there are still many testers regard strength as the main index of concrete quality control, and pay little attention to the crack resistance and durability of concrete. They even think that as long as the strength of concrete is good, the quality of concrete is good.
In practice, some concrete enterprises produce C35 concrete with 28d strength of 45MPa or even above, which is unreasonable and a waste of resources.
The principle of suitable strength requires that the strength of concrete should not be too high, and the surplus coefficient of concrete strength should be 115%, that is, it is suitable for C35 concrete to reach 38 ~ 40MPa in its age.
2.Principles of good work
Workability is a necessary condition for easy construction of concrete. With the rapid development of admixtures, it is not suitable to use slump method as the evaluation standard of concrete.
Many scholars believe that reducing the slump of concrete as much as possible, giving priority to the use of dry rigid, semi-dry rigid or molded concrete, as little as possible with large flow concrete, is still an important principle for the current situation to do a good job in the mix ratio.
In the test, it is found that using the same material, water consumption and cementing material unchanged, change the admixture amount, sand fineness modulus, sand rate and other one to two parameters, it is possible to make the concrete slump from 160mm to 220mm.
At the same time does not change other properties, so can not deny the low slump as an important measure to improve concrete crack resistance is correct. But the appropriate amplification of liquidity does not necessarily crack resistance is not good, because the fluidity of modern concrete can be adjusted in a large space, in a certain range, the size of the slump and crack resistance does not necessarily have a direct relationship.
