Finite Element Analysis Of Volume Stability Of Large Volume Expansive Concrete And Risk Assessment Of Cracking

At present,China's research on the field of temperature control of mass concrete is not enough in-depth and comprehensive,the relevant normative provisions are not perfect,many problems in engineering practice can only rely on experience,lack of theoretical basis.Therefore,it is of great practical significance to study and control the temperature difference of mass concrete and to reduce the thermal stress to prevent the temperature crack.In this paper,the thermal stress and temperature crack control measures of mass concrete foundation slab are studied by means of mechanical performance test and ANSYS simulation,temperature stress field calculation,concrete performance test and foundation slab temperature stress research,and the results are as follows:1.For concrete with expansive admixture,When the model temperature is 18.9 ?,the simulation internal temperature rise is about 38 ? and the points reach peaks within 5-7 days.After peaks,the internal temperature decreases slowly,the overall trend is the same as that without adding expansive admixture concrete,the difference is that temperature rises 7 ? and the temperature gradient decreases.The temperature difference between any two points in concrete is not more than 25 ?,and temperature rise and temperature difference meet the engineering design requirements.2.The large tensile strain at the upper surface edge corner of the model is more likely to be cracked than that of the concrete with expansive admixture.But for adding the expansion agent,the upper surface is still the most angular point tensile strain,but the main tensile stress and tensile strength ratio decreased,cracking risk decreased.3.The concrete with expansive admixture has good performance in this experiment.As a result of adding 6% of the total cement fly ash,the concrete adiabatic temperature rise is lower,about 38 ?,the temperature rises for a longtime.Under the standard curing condition,the 60 d compressive strength of concrete is 33.62 MPa,which satisfies the requirement of strength in engineering design.The high temperature excitation in mass concrete will accelerate the pozzolanic reaction rate of fly ash,so that the early elastic modulus and strength of concrete can increase rapidly.4.The temperature field of the full-scale model can be simulated well by the calculation of the heat release process model of the cementitious material under the influence of temperature and the finite element computation of the temperature field of the concrete,the reasonable material parameters and the boundary conditions,and the more accurate adiabatic temperature rise curve of the concrete.The temperature gradient of the model is mainly in the vertical direction,the intermediate temperature gradient is small,the upper and lower surface temperature gradient is the biggest.5.The concrete peaks with expansive admixture is about 60 ?,which is lower than the limit value of 85 ? in the design.The temperature development curve of the center point of the calculation model conforms well with the adiabatic temperature rise test,and the crack control after adding the expansion agent has achieved good results,which proves that the admixture has good effect on the control of the temperature crack of mass concrete.