Research On The Expansion And Mechanical Properties Of Concrete Damaged By Alkali-aggregate Reaction Considering The Restraint Effect Of Reinforced Bars

Alkali-aggregate Reaction(AAR)is a kind of physical and chemical Reaction of concrete composition.AAR can change the internal structure of concrete and reduce the mechanical properties of RC structure.Now the research on alkali aggregate mainly focuses on the mechanism of material deterioration,but the influence of reinforcement on concrete alkali aggregate damage has not been considered at the structural level.Therefore,the systematical research was studied in this paper.This paper considered the influence of many factors,such as the size of steel,stirrup and AAR reaction time,on bond performance of reinforced concrete structures.Accelerated AAR reaction test and pull-out test were carried out on 192 pull-out specimens,so that the function of AAR expansive deformation of concrete with the restriction of steel and stirrup was quantified,the quantitative relationship between the expansion rate of alkali aggregate with the bonding strength of reinforced concrete was cleared,the interaction between reinforcement and concrete AAR expansion products and the bonding degradation mechanism of reinforced concrete were revealed.It is found that steel and stirrups can restrain the degradation of concrete expansion and bonding properties.When the expansion rate of concrete AAR is small,the expansion stress caused by the expansion of AAR products can increase the bonding strength of reinforced concrete.The chemical-mechanical simulation method,based on the theory of AAR chemical mechanism and pore mechanics,can simulate the AAR expansion rate of concrete and expansion stress in reinforced concrete and quantitatively describe the damage of concrete caused by AAR expansion by established skeleton element and pore element.Based on the principle of effective stress,the skeleton element and medium element were assembled to form an isotropic two-phase composite material.The mechanism of the alkali aggregate reaction at the micro scale and the weakening of the bonding property at the micro scale can be analyzed by coupling the mesoscopic skeleton stress with the micro pore pressure.This method realizes the simulation of concrete multi-scale weakening under the same model.Through the simulation of accelerating AAR test and pull-out test that the accuracy of the calculation method was verified,the model of concrete expansion rate and expansion strain characteristics are similar with test results,so it can better predict the changes of mechanical performance in different concrete expansion ratio.This study enriched and deepened the understanding of the damage mechanism of concrete alkali aggregate that establishing a solid foundation for the alkali aggregate reaction evolution research in the performance of a reinforced concrete structure.