Study On PCLH Behavior And Mechanical Properties Of Ice Storage Phase Change Cooling Shotcrete Material

With the slogan of "marching to the deep earth",the exploitation and utilization of deep energy resources is imperative.The problem of high ground temperature is serious and inevitable.The innovation of mine cooling method and the improvement of stope working environment are very important.In this paper,it is proposed that cold storage phase change cooling shotcrete material containing ice particles has special function of cooling nearby stope under the condition of meeting the fluidity and strength characteristics by adding unequal amount of ice particles into the concrete mixing slurry.Therefore,this paper refers to the relevant norms and previous research experience to carry out experimental research.This paper focuses on the evolution of heat transfer,hydration reaction process,micro-meso-pore structure,mechanical strength of concrete mixing slurry with different initial ice content(0%,10%,20%,30%,40%,50%,60%).Then the PCLH behavior and mechanical properties of concrete containing ice particles are analyzed and studied.Major research work and achievements include:(1)The multi-channel temperature tester was used to collect the internal temperature variation law of concrete mixing slurry containing ice particles in real time.The heat of concrete mixing slurry containing ice particles is transferred from outside to inside and the temperature tends to be balanced in a short time.The temperature change curve experienced a process of heating up first and then cooling down,and the corresponding temperature change rate showed three stages of change.The initial temperature decreases with the increase of ice-water ratio.The temperature change rate is positively correlated with the ice-water ratio,and the corresponding cooling efficiency is also positive.And the contribution rate of ice particles to the cooling efficiency is greater than that of water.(2)The mechanical strength of concrete samples containing ice particles were carried out after the ultrasonic wave velocity test.With the increase of the initial ice-water ratio of concrete samples,the ultrasonic wave velocity increases correspondingly.And the peak stress of concrete is positively correlated with the initial ice-water ratio.The conical failure of concrete containing ice grains is shown in the compression test.The width and the deflection angle of crack decreases with the increase of the initial ice-water ratio of concrete samples.With the increase of the initial ice-water ratio,the surface fluctuation of fracture morphology decreases.The fractal dimension is negatively correlated with the fracture strength.(3)The NMR analysis system was used to test the T2 distribution of concrete samples containing ice particles.In concrete samples,the micropores are the most,the macropores are the second,and the mesopores are less.With the increase of the initial ice-water ratio,the macropores and mesopores gradually decreased,while the micropores showed an increasing trend.However,the overall porosity of the sample has little change,generally about 5%.(4)The hydration products and meso-pores were analyzed by XRD and MIP.The hydration reaction products of concrete containing ice particles are insufficient due to the influence of temperature within 24h.At the later stage of curing,the hydration product is slightly higher than that of concrete without ice particles.With the increase of the initial ice-water ratio,the macropores in concrete decrease gradually,the primary pores are mainly mesopores,and gradually transition to micropores with the continuous hydration reaction.The ice particles have an optimization effect on the primary pores in concrete.(5)The concrete samples with different initial ice-water ratio were observed by SEM.The initial hydration reaction of concrete without ice particles is fast,and more C-S-H gel is produced in a short time,which is conducive to aggregate cementing.The hydration reaction of concrete containing ice particles is inhibited by low temperature,and the development of all kinds of hydration products is slow and the cementing effect is poor,and the bearing capacity of concrete material is insufficient in a short period of time.After 28 days,the primary pores of concrete with ice grains are dominant and the strength is improved.