Research Of Effects And Mechanism Of Micro Fines On Manufactured Fine Aggregate Concretes

The limits of micro fines content in manufactured fine aggregate (MFA) stipulated in current standard are still disputed and restrict application of MFA and rational utilization of micro fines. On the basis of analyzing characteristics of MFA and micro fines, effects of micro fines on properties of cement and concrete are studied and limits of micro fines content in MFA for concrete are discussed in this dissertation. Characteristics of preparation of MFA concrete and an optimized mix design philosophy for concrete system with MFA containing micro fines are also proposed. Furthermore, the effecting mechanisms of micro fines on MFA concrete are analyzed.Main characteristic parameters of MFA and micro fines and regression relations between these parameters were statistically investigated through analyzing 57 samples. The investigation reveals the interrelation between fineness module and 2.36 mm sub-tailing. The particle shape parameters of MFA were studied through DIP technology and interrelations between these parameters and roughness measures are discussed. Interrelation between bulk density and micro fines content, and interrelation between methylene blue value and content & earthiness of clay are studied. Particle-size distribution of aggregate micro fines was tested by laser granulometer.Effects of micro fines on various cements and effects of different micro fines on cements including those blended various additions are researched in aspects of water demands of standard consistence, setting times and strength when substituting micro fines for part of cements; and consistence, strength, shrinkage and resistance to cracking of mortar are also researched when substituting micro fines for part of sand.The effects of micro fines on properties of concretes are researched. The interrelations of best workability and optimum water/powder ratio are discussed and the concept of bleeding latency time and its correlation with bleeding ratio are described. For MFA with poor gradation, the micro fines can improve workability of concrete. The compressive strength, flexural strength and drying shrinkage increase with micro fines content, and go down after the maximum. Both axial compressive...