| With the pulling of domestic demand and carrying out of the "Twelve Five-Year"program, More and more attentions should pay to instructions of highways and railway here and there, which lead to need a great deal of sands to produce heavy concrete. In order to protect ecological balance, a ban on selfishly excavating natural sands has been announced by our country; as a result, natural sand supply is a far cry from meeting demands for producing the concrete. So it is more important to explore machine-made sand. A certain amount of stone power with diameter smaller than 75 micron is brought in process of producing machine-made sand, redundant stone power need being cleaned out to satisfy the national specification requests, thus, a great deal of fuel will be consumed and give rise to environmental pollution. In this paper a new production process different from traditional production process of machine-made-sand is proposed, that is adding the rock whole washing work stage to control silt content of finished products sand before rocks being broken up and after rocks being broken up made it become finished products sand that no washed, consequently, the machine–made-sand which keep in-place is named proto-machine-made-sand. Practice shows that the content of stone power with proto-machine-made sand has a wider fluctuation margin under the range of satisfying the indexes fineness modulus and grading of machine-made-sand according to the specification of current standard. So the stone power content of proto-machine-made-sand how to affect concrete performances was studied through tests in this paper to provide research basis for engineering construction controls of machine-made-sand concrete.Firstly, the proto-machine-made sand with stone powder from 3% to 16% was used to mix the C30, C45 and C60 concrete with high performance and influence regulations that the stone power content act on fresh concrete workability and basic mechanics performance were also studied in the paper. The results showed that the coefficients ofαa=0.55andαb=0.19 can be used when calculate water-cement ratio in the process of mix design with proto-machine-made sand. On condition that the ethylene blue value of proto-machine-made sand according with specification of current standard of Sand for Building, the content of stone power broad from 5% to 13%,which not only can guarantee fresh concrete workability, but also satisfy request for basic mechanical properties of concrete based on the current specification of concrete structure design code.Secondly, the paper introduces a series of test results of grade C30 and C45 concrete mixed by proto-machine-made sand with stone powder in quality content of 3 %, 7 % and 13 %. Based on the experiments of the cubic compressive strength of concrete at different ages of 3 d, 7 d, 14 d, 28 d, 56 d, 90 d, 120 d, 150 d and 180 d, the strength developing regularities of concrete affected by the content of stone powder during the age of 180d were analyzed, and the formula for predicting the cubic compressive strength of concrete with grade of C30 and C45 at any ages was also proposed. It is proved that the effect of stone-powder in proto-machine -made sand on concrete strength is virtually different from that of the stone powder mixed with powdered mud in ordinary machine-made sand, and the limit value of stone powder content lower than 5 % is not suitable to proto-machine-made sand for mixing concrete with grade of C30 and C45.Next, combined with test results of previous period studied by topic team, A quantity of experimental study of the cubic compressive strength of concrete at different cement types and different water cement ratios are used, according to the relation between concrete strength and water cement ratio ,the regression coefficient ofαa=0.5,αb=0.1 belonged to mix design of proto-machine-made sand concrete is fitted, While by using strength formula of that designed machine-made sand concrete with different stone power content and strength grade. The results showed that above formula was used to design concrete can satisfy the requests for strength and workability, thus, it can provide theoretical reference for mix design of proto-machine-made sand concrete.At the same time, concrete shrinkage strain with proto-machine-made sand of 36 specimens of 12 groups is measured, and shrinkage strain change of concrete with age and predicting formulas under the constant temperature and humidity are also analyzed in the paper. Test results showed that concrete shrinkage strain changed with ages from increase to level off. For the machine-made-sand concrete with grade of C45,the shrinkage strain of stone power with content of 7% is least, while the stone power content of 3% and 5% are equivalent and much larger than that, the shrinkage strain of the others are equivalent well and located in medium between them. The change of stone powder content has no significant effect on shrinkage strain of proto-machine-made sand concrete with grade of C60.When logarithmic form adapted to fitting basic equation of concrete shrinkage will obtain a high precision.Finally, cement mortar specimens with different stone power content were made. By using microcosmic testing method of combing with XRD diffract meter and SEM scanning electron microscope, the mechanism of stone power in the cement mortar was studied. Compared with natural colloidal mortar, the colloidal mortar compression strength and flexural strength made up with machine-made sand are both greater than that; under the same age, the colloidal mortar compression strength of machine-made sand increased with adding of stone power and flexural strength first increased and then decreased. Through micro testing method, filling effect, active effect and crystal nucleus of stone power were discovered. Under the synthesis action of various effects from the stone powder, proper stone power can promote growing of strength,which is agreement with macro mechanical experimental results. |
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