Research On Bond Property And Application Of Reinforced Concrete In Freeze-thaw Environment

In accordance with the strategic goals of China to achieve carbon neutrality by 2060 and to address the demands of sustainable development,the pursuit of novel concrete solutions to reduce carbon emissions has become a pressing necessity.Employing desert sand as an innovative material in practical engineering not only alleviates the excessive extraction of river sand but also utilizes local resources to decrease substantial carbon emissions produced during the transportation of river sand.China’s northwest region,which is rich in desert sand resources,endures harsh winter conditions,making it crucial to study the bond performance between desert sand concrete and steel reinforcement in freeze-thaw environments.In this research,we designed test groups of steel reinforcement embedded in desert sand concrete,considering varying desert sand substitution rates,freeze-thaw cycles,and reinforcement types.The bond performance and degradation mechanisms of the steel reinforcement and desert sand concrete,both pre-and post-freeze-thaw cycles,were analyzed using freeze-thaw tests and central pull-out tests.Based on the central pull-out test results,we developed a bond-slip constitutive model that takes into account freeze-thaw cycles and desert sand substitution rates.The primary research findings are as follows:(1)The bonding properties of plain steel bar,rebar and desert sand concrete were analyzed by freezethaw test and central pull-out test.The effects of freeze-thaw cycle and desert sand substitution rate on the bonding properties of steel bar and desert sand concrete were analyzed.The test results show that the bond performance between desert sand concrete and steel bar and the strength degradation law after freeze-thaw are similar to those of ordinary concrete.With the increase of freeze-thaw times,the bond performance between desert sand concrete and steel bar tends to weaken.The bonding performance of specimens with40 % and 60 % desert sand replacement rate before and after freeze-thaw is better than that of ordinary concrete.(2)The frost resistance coefficient was introduced to describe the degradation of the ultimate bond strength of the specimens with different replacement rates of desert sand after freeze-thaw cycles under different freeze-thaw times.The results show that the ultimate bond strength of the specimens with 20 %replacement rate after 75 freeze-thaw cycles is only 30 % of that before freeze-thaw.The frost resistance is poor,and the ultimate bond strength of the specimens with rebar after 75 freeze-thaw cycles is higher than80 % of that before freeze-thaw.Therefore,in practical application,desert sand reinforced concrete specimens with desert sand replacement rate of 20 % should be avoided,and rebar should be used as far as possible to enhance the bonding performance between desert sand concrete and rebar after freeze-thaw.(3)The degradation mechanism of bond strength between desert sand concrete and steel bar specimens after freeze-thaw cycles is analyzed in detail from the macro test and micro level.The results show that the degradation of bond performance is related to the content of desert sand.When the content of desert sand is40 % and 60 %,the bond strength between internal aggregate and mortar interface can be improved,the strength of concrete at the interface between steel rib and concrete can be improved,the compactness of concrete can be improved to reduce the occurrence of initial cracks,and the development of micro cracks during freeze-thaw process can always maintain higher ultimate bond stress than ordinary concrete.(4)Based on the regression analysis of the characteristic values of the bond-slip curves of each group of specimens,the characteristic equation of bond stress considering the number of freeze-thaw cycles and the replacement rate of desert sand is proposed.On this basis,the bond-slip constitutive model of desert sand concrete and steel bar is established.After calculation,the model is in good agreement with the experimental values,which can provide theoretical basis for engineering practice.