Research On The Compressive Strength Of Desert Sand Concrete After Exposure To Elevated Temperature

In today's procession of urban construction and development progress,our lives have changed rapidly.However,our countr's economy and life and property has cast a shadow because of fire accidents' occurrence,so for desert sand concrete after high temperature mechanical properties of the changes and destructions of law has been urgent.At the same time,it is necessary to use desert sand resources in the surrounding area,which is scientifically and effectively alleviate the economic expenses of sand mining,and decrease the destruction of the environment and topography during sand mining.No doubt that study of desert sand concrete has also obtained many scholars' attention.The main contents of this paper are as follows:Through the design of orthogonal test,the compressive strength of C40 ordinary desert sand concrete after six levels high temperatures of 100 ?,300 ?,500 ?,700 ? and 900 ? is analyzed.The heating rate is 10 ?/min,and temperature when rises to the set temperature maintains 1h.The effects of water-cement ratio,fly ash content,sand rate and desert sand replacement rate on the compressive strength of ordinary desert sand concrete after two different cooling methods were analyzed.The test results show that:?Under two cooling methods,high temperature weight loss rate of desert sand concrete increases with temperature increasing,while early growth is slower and later growth is faster.?Under natural cooling,compressive strength at 100? increases slightly compared with strength under room temperature,which starts to decrease at 300?,come up at 500 ?,sharp decrease after 700?.Under water cooling,compressive strength with natural cooling has a similar changing trend below 300?,which has eased at 500? and sharp decrease after 900?.?Considering influences of factors and cooling methods on the compressive strength,the optimal ratio of orthogonal experiment is A1B1 C2 D1,which called water-cement ratio is 0.39,fly ash content is 10%,sand rate is 35%,and desert sand replacement rate is 10%.The microstructures of ordinary desert sand concrete were observed by scanning electron microscopy(SEM).The changes of microstructure of desert sand concrete at different temperatures and different cooling methods were analyzed.Combined with differences in microscopic state of specimens under corresponding temperature,test results draw that:?At room temperature,the microstructure of ordinary desert sand concrete is complete and hydration product is continuous and compact.With increasement of high temperature,capillary water and gel water of desert sand concrete evaporate,and hydration product is decomposed gradually.In the meanwhile the hole connected and overall structure damage seriously.?Under water cooling,the pores in desert sand concrete is reduced and structure is relatively dense when temperature is low.When the temperature is high,the scouring effect of water is serious and loose,and structural damage is serious without any intact crystal.