Study On Effect Of Free Mica In Manufactured Sand Powder On Performance Of Cement Mortar And Concrete

Most of the hydropower projects in our country are mainly concentrated in the central and western regions. These projects usually use local natural rock to crush artificial aggregate, because of the lack of sufficient natural aggregate resources. Even some hydropower projects use rocks with high content of mica, which can cause higher content of free mica in powder. The current specification method can only test the content of mica which particle size is greater than0.3mm in manufactured sand, and can’t test free mica content in the powder. Also there is little pertinence and systemic research that the harmful effect on mortar and concrete performance which is caused by free mica in powder.This paper mainly carry out experimental research relies on the gneiss aggregate in the Danwuqian quarry of Miaowei hydropower, on the one hand free mica content in powder is measured by specification method, oil-immersed analysis, X-ray diffraction method and floating separation method, and the test results are analyzed experimentally; on the other hand, by adjusting free mica content in manufactured sand powder, systematically experimental study on mortar compressive strength and frost resistance by different free mica content has been carried out, meanwhile the influence of mica upon concrete compressive strength, splitting tensile strength and frost resistance has been studied. The main conclusions are as follows:(1) The test result of mica content in parent rocks of schist, gneiss were47%and40%by lithofacies analysis, the test result of mica content in manufactured sand was closed to0by specification method. The test result of mica content in powder of schist, gneiss were56%and40%by oil-immersed analysis, and the test result of mica content in powder of gneiss were35%by floating separation method, these test results were lower than the real content of free mica in the powder; the test result of mica content in parent rocks of schist, gneiss were65%and60%by X-ray diffraction method, it was close to the free mica real content in the powder.(2) Free mica in manufactured sand powder would be bring some adverse effect on compressive strength and frost resistance of mortar. With the same ratio, when the mica content in sand increased from0%to9.0%, the mortar compressive strength and frost resistance gradually decreased, and the compressive strength of mortar in28d and60d age decreased about10%,the quality loss rate in50times of freeze-thaw cycle of mortar increased from0.11%to0.15%,but the strength loss rate were similar, slightly down.(3) When fixed the gelled material consumption, by mica content in sand increased from0%to9.0%, the unit water consumption of C9o30concrete increased11kg, compressive strength in28d age decreased5.5MPa, compressive strength in90d age decreased7.7MPa. When fixed water-binder ratio of concrete, by mica content in sand increased from0%to9.0%, the amount of concrete gelled material consumption most increased22kg, also the compressive strength of concrete in different ages were decreased a little, but the decreased range changed little.