Study On The Durability Of Concrete Mixed With Large Limestone Powder

In the production process of coarse aggregate and fine aggregate, it will generate a lot of limestone powder, leading powder in the mountain because of carelessly discarding, not only a waste of resources, but also the environmental pollution, and fine aggregate including the powder may also have some bad influence on the performance of concrete. With the increasing demand for mineral admixture, the problem of quality admixture in short supply is urgency to solve, so limestone powder used as mineral admixture, will be raised as a research subject. The concrete, mixed with different specific surface area,different quantity and different qualities of limestone powder, was discussed in this paper. Workability, mechanics performance of concrete are researched. Then the research focuses on the durability of concrete, including the resistance to chloride ion penetration, carbonation resistance, shrinkage, frost resistance. The studies show that:(1) Limestone powder on concrete can reduce the slump loss of concrete and improve workability performance in a range of admixture. With the quantity increase, performance is improved. In this experiment, the impact of the work performance of fresh concrete is mainly quantity of limestone powder, not the specific surface area of limestone powder. When other conditions are not different, different CaCO3 content of powder on concrete have the same workability performance on concrete.(2) Limestone powder mixed with 10% on the concrete can be improved 3d,28 d compressive strength, while the additional quantity increases to 20% and 30%, the concrete compressive strength decreases. Powder on concrete 3 days strength with the 28-day rate is basically the same, mixing powder on concrete can not promote cement hydration. Content within 10%, the powder surface area increases, concrete strength has greatly improved. In this experiment, different qualities of powder have little effect on the mechanical properties of concrete.(3) No matter what kind of additional quantity, what surface area of limestone powder, permeability coefficient of 28d is between 2.4-2.7x10-12m2/s.The electric flux is between 1000-1200C, and chloride ion penetration levels are low. (4) Replacement of cement 30% with limestone powder, the carbonation resistance of concrete is evidently reduced. While mixing quantity of powder is 10%, surface area is 779m2/kg, carbonation depth in concrete is below the benchmark concrete.(5) As replacement of cement is 10%, when the surface area of powder reach 619m2/kg, the shrinkage of concrete is basically the same as the benchmark concrete; and the surface area of powder reach 779m2/kg, the shrinkage of concrete is even less.If replacement of cement is above 10%,the shrinkage of any powder concrete in this study is greater than benchmark concrete, and with the increase of quantity, shrinkage increase.(6) As replacement of cement is 30%, the relative dynamic elastic modulus of the powder concrete has been less than 60%, while the benchmark concrete also more than 90%. Mixing 30% powder on concrete significantly reduces the frost resistance of concrete.