Prediction Of Alkali-silica Reaction Life Of Concrete Based On Accelerated Mortar-bar Test

In order to be able to quickly and accurately predict the life of alkali-silica reaction(ASR)of concrete structures and reduce the hazards caused by alkali-silica reaction,this thesis is centered on the experimental research and theoretical analysis of establishing a life prediction model for alkali-silicate reaction of concrete based on theaccelerated mortar-bar test(AMBT).Through the life prediction model established in this paper,the overall life of concrete alkali-silica acid reaction can be predicted more accurately and quickly,and the suitable inhibitor can be screened out more quickly in the actual project,and suitable repair measures can be taken at the right time to save resources and costs.Based on the above research purpose and significance,the main research contents and conclusions of this paper are as follows:First,in order to find suitable active and inactive aggregates,14 different aggregates were tested for alkali activity by the long-age accelerated mortar-bar test,alkali active aggregates were determined according to the determination criteria,and the applicability of the AMBT determination criteria was evaluated.The results showed that,except for Jiangsu Xinyi quartz sand(N),the rest of the aggregates were weakly alkali active,and N was determined by the test to be an alkali active aggregate.In addition,the AMBT criterion is applicable to aggregates with strong preliminary alkali activity,and the criterion does not accurately evaluate the alkali activity of all periods for aggregates that do not have strong preliminary alkali activity.The main parameters of ASR life prediction are:(1)reaction rate constant(k_T)and final expansion rate(ξ_u)of ASR at different temperatures;(2)activation energy(E_a)and pre-exponential factor(A)of different materials;(3)latency time(τ_L)and characteristic time(τ_c)of ASR life.To obtain the reaction rate constants and final expansion rates of mortar bars and concrete prisms at different temperatures,extended tests were performed for the accelerated mortar-bar test and the concrete prism test at 40℃and 80℃,respectively,and the expansion rate data were substituted into the hyperbolic equation.The results show that high temperature has a strong promotion effect on ASR,and the higher the temperature,the higher the reaction rate constant.The relationship between the reaction rate constants of mortar bar and concrete prism conversion at 40℃and 80℃and the final expansion rate conversion at 80℃were found,and then the activation energy and pre-exponential factor of the corresponding materials were obtained,and the expansion rate conversion equations of mortar bar and concrete prism at different temperatures were established.To determine the latency and characteristic time of ASR occurring in concrete prisms,axial compressive test,splitting tensile test and dynamic elastic modulus test were conducted,and it was found that ASR has a strong weakening effect on concrete axial compressive strength,splitting tensile strength and relative dynamic elastic modulus.The damage limits of each parameter under the influence of alkali-silica acid reaction were defined by comparing and analyzing the relative axial compressive strength,relative splitting tensile strength,expansion rate and mass increase rate based on the relative dynamic elastic modulus to obtain the damage criterion for the alkali-silica acid reaction of concrete at 40℃.Based on the determination criterion,the latent time and characteristic time determination ranges for concrete prisms at 40℃were obtained.With the help of the equivalent time method,the latent time and characteristic time at 40℃can be converted into the corresponding time nodes at room temperature of 20℃.Based on the obtained equations for the expansion rate transformation of mortar bars and concrete prisms at different temperatures,and the range of latent time and characteristic time determination and transformation method of concrete prisms at 40℃,a concrete alkali-silicate life prediction model based on the fast mortar bar method was finally established.After substituting the mortar bar data from the test into the model calculation,it can be better transformed into the alkali silica reaction life of concrete prisms at room temperature.