Study On The Mechanical Behavior Of Desert Sand Concrete After High Temperature

Currently,building fires have occurred frequently,and have become one of the most serious loss disasters.In the face of the severe building fire situation at present,there are more and more researches focused on the performance of concrete after high temperature.In the western part of our country,due to many years of economic construction,the medium coarse sand resources are shortened.It is of significance to use desert sand instead of medium sand to confect desert sand concrete in the view of economy,ecological protection and sustainable development.In order to study the mechanical properties of desert sand concrete after high temperature,a high temperature experiment of desert sand concrete with different desert sand replacement ratio under five different temperature’s were carried out by means of natural cooling and water cooling,respectively.The effects of temperature,desert sand replacement ratio,cooling method and fly ash dosage on the compressive strength,axial compressive strength and elastic modulus of desert sand concrete after high temperature were analyzed.The degradation model of strength and elastic modulus of desert sand concrete after high temperature were established.Then,samples were taken from crushed specimen after high temperature,analyzed XRD and SEM of those samples were carried out,the deterioration mechanism of desert sand concrete after high temperature was discussed from the microscopic level.The main conclusions are as follows:1)Experiment of compressive strength of desert sand concrete after high temperatures were carried out.The influences of temperature and desert sand replacement ratio on the compressive strength of desert sand concrete were analyzed.The degradation model of strength of desert sand concrete after high temperature was established.Experimental results showed that the color of desert sand concrete specimen became shallow and cracking with the temperature,which was similar to normal concrete.The compressive strength of desert sand concrete increased firstly,and then declined with temperature.With the enhancement of desert sand replacement ratio,the compressive strength of desert sand concrete increased firstly,and then declined.When the desert sand replacement ratio was equal to 40%,the compressive strength of desert sand concrete after high temperature reached maximum value.2)Experiment of axial compressive strength and elastic modulus of desert sand concrete after high temperatures were carried out.The influences of temperature and desert sand replacement ratio on the axial compressive strength and elastic modulus of desert sand concrete were analyzed.The degradation models of axial compressive strength and elastic modulus of desert sand concrete after high temperature were established.Experimental results showed that the axial compressive strength and elastic modulus of desert sand concrete decreased gradually with temperature.With the enhancement of desert sand replacement ratio,the axial compressive strength and elastic modulus of desert sand concrete increased firstly,and then declined.When desert sand replacement ratio was equal to 40%,the axial compressive strength and elastic modulus of desert sand concrete reached the maximum value.3)XRD and SEM of desert sand concrete after high temperature showed that desert sand concrete had a complete internal structure and good compactness under normal temperature.Besides the original cement clinker and aggregate,there was a new phase structure calcium hydroxide(CH)production in desert sand concrete samples.The flocculent C-S-H gel structure at 300 ℃ became denser and the white crystal CH decreased.The inner structure of desert sand concrete was more compact than that at room temperature,which resulted in the increase of compressive strength.After 500℃ the whole network structure of C-S-H gel crushed.A small amount of cracks occurred between aggregate and cement matrix.The overall structure was loose and compressive strength of desert sand concrete began to decline obviously.After 700℃,the cement matrix in desert sand concrete was shriveled.The cavity was clear.The cracks were obvious and penetrated,which resulted in the sharp decrease of compressive strength.