Temperature Control And Crack Prevention Technology For Mass Concrete Based On Functional Aggregates

The total heat of hydration of mass concrete is large and difficult to dissipate,which easily generates a large temperature difference between inside and outside,resulting in temperature stresses exceeding the tensile stress of the material and causing cracking of concrete.It is extremely important to study the enhancement technology of temperature control and anticracking of mass concrete to control the temperature stress within the permitted range for the project.In this paper,two kinds of aggregates with thermal insulation or heat storage functions were used in concrete to reduce the temperature difference between the inside and outside of concrete,and improve the cracking resistance of concrete,while meeting the basic performance requirements of concrete.Based on the design requirements of the cable tower and bearing platform,C55 tower concrete and C30 bearing concrete were formulated with different types of spherical functional aggregates in different dosing amounts.The early hydration process of concrete mixed with functional aggregate was studied by the tests of the heat of hydration and electrical resistivity.The effect of the addition of functional aggregate on the workability,thermal,mechanical properties,long-term deformation,and durability of concrete with different strength grades was studied.The results showed that the addition of 50～80 kg/m~3 functional aggregates will increase the hydration and dissolution period of cement,and reduce the hydration heat release and the heat release peak.The heat storage aggregate can also increase the early resistivity rapidly,indicating that the heat storage aggregate has an obvious self-curing effect in the early stage.The results showed that the semi-dry state functional aggregates can improve the workability of concrete,reduce the early drying shrinkage and increase the impermeability of concrete.The strength of 3d did not decrease or even increase slightly due to the self-curing effect,but it will slightly reduce the mechanical properties of the 7d and later periods.The workability of concrete is controlled to be similar,and the reduction of water consumption will improve the mechanical properties.Both insulation fine aggregates and heat storage aggregates can reduce the peak temperature of mass concrete.Heat storage aggregates have a better temperature control effect on mass concrete than insulation fine aggregates because of their better heat storage capacity.It can slow down the heating/cooling rate of concrete,delay the appearance of peak temperature,and reduce the temperature difference between inside and outside,which greatly reduces the risk of cracking of mass concrete.The concrete adiabatic temperature rise experiment showed that the maximum temperature rise of C55 concrete mixed with 50～80 kg/m~3 insulation fine aggregate was reduced by 0.7～1.5℃,while the maximum temperature rise of C55 concrete mixed with heat storage aggregate was reduced by 3.9～5.3℃,the maximum temperature difference decreased by 7.2%～9.8%.The semi-adiabatic temperature rise experiment showed that the average heating rate of C30 concrete added with 160 kg/m~3 heat storage aggregate decreased by 1.13 °C/d,a decrease of 13.8%,and the average cooling rate down 16.1%.According to the test data and on-site construction parameters,the results of the finite element simulation calculation of the tower column concrete showed that the addition of only 50 kg/m~3 or 80 kg/m~3 heat storage aggregates made the central temperature of C55 concrete decrease by about 8.2 ℃ and 9.9 ℃,and its reduction rate reaches 13.2% and 15.9%.The addition of functional aggregates can reduce the early drying shrinkage of concrete,improve the crack resistance of mass concrete,delay the appearance of cracks,and reduce the number of cracks and the width of the largest cracks.Under the same dosage,the crack resistance of insulation fine aggregate is better than that of heat storage aggregate.As the content of functional aggregate increased from 80 kg/m~3 to 160 kg/m~3,the effect of improving the crack resistance of concrete in the early stage showed a trend of first increasing and then decreasing.