Study For Mix Proportion Design Method Of Manufactured Sand Concrete And Its Cracking Resistant Behavior

With gradually increasing of the civil construction and reducing of useable naturalsand in our country, the manufactured sand will be inevitably selected as fineaggregate used in concrete. However, the research of mix proportion design ofmanufactured sand concrete and its cracking resistance is insufficient.In this paper, with a series of aggregate and packing degree test, the calculationmethods of specific surface area and packing degree are determined. Including microfine as a ingredient, a manufactured sand concrete mix proportion design method wasbuilt based on minimal paste theory. The influence rules of micro fine on workability,mechanical properties, auto-shrinkage, tensile creep and cracking resistance inconcrete were investigated. The study results show that:1. Homemade specific surface area tester could be used to measure specificsurface area of natural sand and manufactured sand accurately and easily. Packingdegrees of manufactured sand and crushed stone mixes can be calculated by Toufaraggregate model.2. Minimal paste theory could be used to design the mix proportions ofmanufactured sand concrete reasonably, which meet the least paste and economicrequirements, and meanwhile meet various performance indexes of concrete.3. When micro fine content is less than6%, the slump of fresh manufactured sandconcrete has not obvious change; when micro fine content is between6%to30%,with the increase of micro fine, the slump of fresh manufactured sand concretereduces gradually.4. when micro fine is between0%to30%, with the increase of micro fine, themechanical properties of manufactured sand concrete first increase gradually, andthen reduce. When micro fine is24%, mechanical properties of concrete are to be thebest.5. With the increase of micro fine, in the hydration process of concrete, the totalhydrate heat of manufactured sand concrete reduces gradually; the humidity field ofmanufactured sand concrete does not appear obvious difference. With the increasingof micro fine, the auto-shrinkage of manufactured sand concrete reduces gradually. 6. When the micro fine content is less than18%, with the increase of micro fine,the tensile creep and cracking resistant behavior of manufactured sand concretereduce gradually. When the content of micro fine is24%, the tensile creep andcracking resistant behavior of manufactured sand concrete are improved.7. Considering the effect of micro fine on manufactured sand concrete, theadviced optional content of micro fine is24%.