A predictive solution for fracture modeling of alkali-activated slag and fly ash blended sea sand concrete after exposure to elevated temperature

Abstract

Because of the heterogeneous and discontinuous properties in concrete, realistic fracture parameters were hardly obtained rationally based on traditional methods. The material heterogeneity and discontinuity may be more significant under the attack of high temperature. Therefore, the intention of this paper is to propose a predictive solution for fracture modeling of AASC (alkali-activated ground granulated blast furnace slag (GGBFS) and fly ash (FA) blended sea sand concrete) after exposure to elevated temperature. First, fracture test was performed on AASC after exposure to four high temperatures plus one room temperature. The fracture process and failure mechanism were analyzed and clarified at both macro- and micro-scales. Subsequently, an analytical model was presented to determine the fracture parameters of AASC by incorporating the material heterogeneity and discontinuity. The realistic tensile strength ft, fracture toughness KIC and fracture energy GF were then explicitly linked to the maximum fracture load Fmax by virtue of boundary effect model. Results show that the load-displacement curve becomes gentler and the failure mode is changed from trans-granular fracture to inter-granular fracture as the temperature increases. Once the Fmax is obtained from the test, the realistic ft, KIC and GF from each specimen can be predicted conveniently. The scatters in the predicted parameters would be clarified assisted by statistical analysis. As the temperature increases, the ft is reduced and the reduction becomes larger. But the GF shows insignificant variation until the temperature attains 400 °C, and apparently decreases as the temperature is further enhanced. Moreover, the predicted fracture parameters of AASC with higher GGBFS/FA mass ratio are larger than those of the other AASC below 400 °C. However, the former has higher strength loss than the latter. The crack resistance of AASC after exposure to high temperature can be well clarified based on the proposed predictive model.