Study On Prevention And Control Measures For Temperature Cracks Of Mass Concrete In Foundation Slabs Of Super High-Rise Buildings

With the rapid development of China’s construction industry,a large number of high-rise and super-high-rise buildings have emerged.Those buildings’ foundation soleplates belong to mass concrete construction generally.While in the construction process,the mass concrete produces temperature cracks easily due to the influence of the external environment and the change of its own temperature and the construction control measures,which has a negative impact on the durability of the building structure and concrete strength.Therefore,it is necessary to select effective measures to prevent and cure temperature cracks in mass concreteBased on the mass concrete project of foundation slab of a super high-rise building in a commercial square in Changsha,this paper studies the temperature crack control measures of mass slab concrete from three parts:cement raw material selection and mix ratio optimization,concrete thermal calculation and temperature control,and numerical simulation of mass concrete temperature field.Firstly,cement is selected as the key factor affecting the performance of concrete.and the relevant mechanical properties of concrete under different hydration heat of cement and different cement assumptions are analyzed,and the cement types are selected.On this basis,the mix proportion of 6 groups of concrete is optimized.Secondly,the thermal insulation material thickness of mass slab concrete was selected by temperature calculation.the anti-crack performance of concrete was judged by anti-crack calculation,and the thermal insulation measures of slab surface were adjusted by on-site temperature measurement.Finally,ANSYS simulation software is used to simulate the temperature field and stress field of mass slab concrete,and the numerical simulation temperature and thermal calculation temperature are compared with the field measured temperature to provide data basis for the relevant research in this paper.The specific research conclusions are as follows(1)The study on the selection of mass concrete raw materials and the optimization of mixing ratio shows that through the study on the hydration heat of four brands of ordinary silicon cement,the brand of A cement with lower hydration heat is selected.On this basis,to the brand ordinary Portland cement,middle thermal cement and low thermal cement hydration heat and related study of mechanical performance,under the same conditions the initial hydration heat curve form basic same,but in the 7 d age when ordinary Portland cement hydration heat curve has leveled off,heat of cement hydration heat curve in low thermal cement and there is still the A rose slightly,ordinary Portland cement compressive strength and splitting tensile strength is superior to hot in low thermal cement and cement,so the A brand ordinary Portland cement was chosen for study.From 6 groups of mixture ratio is proposed to choose to double dosage,water-cement ratio,compressive strength and slump,cooling speed limit and limit expansion ratio as evaluation index,the comprehensive selected the optimal mixing proportion of concrete.(2)The study on the thermal calculation and temperature control of concrete shows that:through the calculation of the thermal insulation temperature rise of hydration heat,the actual maximum temperature inside,the temperature difference between concrete surface and concrete inner surface,it is preliminarily determined that the method of 1 layer of plastic film and 2 layers of hemp bag is adopted for the insulation of concrete.The on-site temperature measurement of concrete temperature under water cooling condition is consistent with the rising and falling trend of thermal calculation temperature,but the overall thermal calculation temperature is on the high side.At the same time,the insulation measures of the floor surface are adjusted by the field measured temperature to ensure that the temperature difference between the concrete inside and outside is within a reasonable temperature range.By anti-crack calculation,the maximum self-restraint stress of concrete is 0.14N/mm2 and the tensile strength of concrete is 1.42N/mm2,which determines that concrete meets the anti-crack requirements.(3)The numerical simulation of the temperature field of mass concrete shows that compared with the results of thermal calculation,the simulated data calculated by ANSYS software is more accurate and closer to the measured data.The numerical simulation method of ANSYS software can be used to effectively grasp the temperature of mass concrete before construction,reasonably control of the internal and external temperature difference of cement and avoid the temperature crack of concrete.