Research On The Low-strength Pump Concrete With MFA Of High AMF Contents

When prepare low-grade and high-fluid concrete, the high W/C ratio and water consumption are so great that it is reason for segregating and bleeding, and the concrete also has some problems such as bad impervious performance, easy shrinkage crack, and so on. The method of increasing the amount of bond materials to reduce water bond ratio is usually adopted to improve the performances of concrete. In other hand, the amount of aggregate micro fines (AMF) is up to 10 to 15 percent in manufacturing fine aggregate (MFA), and the AMF can be used to improve the performances of concrete mixture by reducing the water powder ratio, and so the performances of imperviousness and durability. The advantages of AMF and MFA can be fully exerted for the promotion and application of MFA concrete.Mortar and concrete with the 0.50 of w/c ratio are the main subjects investigated, and the technology line of macro and micro means, experimental and theoretical analysis, and laboratory and field tests combining has been adopted in this paper. Some aspects listed are studied as follows:①Effects of four kinds of sands on workability and compressive strength of mortar and concrete were comparatively studied;②Effects of contents of three kinds of rock AMF on workability of mortar and concrete were systematically studied, and effects on durability of concrete were also studied;③Take limestone powder for example, the effects of MFA as mineral admixtures on performances of concrete were studied;④Effects of limestone powder, quartzite powder, granitic powder on physical and chemical performances of cement were comparatively studied;⑤The mix proportion design method of low-grade MFA concrete were studied.It is showed that the void ratios of limestone, quartzite, granitic MFA are less than that of natural sand, so their influences on performances of concrete are different. With the influences of water powder ratio on the fluid performance of concrete, it is showed that when water powder ratio is less than 0.40, increasing the amount of aggregate micro fines can improve the working performance of concrete. The rule of AMF to the compactness of cement with water state, have certain relation to the influence of MAF as mineral admixtures on the impervious performance of concrete. Proper amount of AMF fills void of MAF and reduces water powder ratio, so stability and compactness of concrete mixture can be improved, and so the compressive strength, impervious performance and other performances of concrete. Contents of AMF with more than 10% have bad influences on frost-resistant performance, but it doesnot have bad influences on sulfate corrosion with increment of AMF content. Fly ash, chemical admixture, fiber can improve impervious performance; but it also have some bad effects on other performances of concrete. Combined with experiment results and theoretical analysis, the active mechanism of AMF in the low-grade concrete may be generalized as: water-reducing effect, compact effect, hydrated effect.The mix proportion design method of low-grade MFA concrete is presented in this paper based on the mix proportion design of ordinary concrete and high performance concrete with the example of limestone MFA. The optimization content of MFA can be identified flexibly according to the actual proportion by this method.Partly these research results are tested in the construction of equal and less than C30 concrete for the Hurongxi highway, which has not only good reference value, but also conference value for preparation of low strength, fluidity, impervious concrete with MFA. To improve workability, strength, impervious performances of concrete it is suggested that contents of MFA should be between 10 and 15 percent.