Fracture Theory Under Freeze-Thaw Cycles and Freeze-Thaw Resistance of Alkali-Slag Concrete

Abstract

Alkali-slag concrete (ASC) is prepared with Na 2 SiO 3 and NaOH composite activator. Fracture properties of ASC under freeze-thaw cycles are studied using response surface methodology (RSM), Design Expert software and Box-Benhnken design (BBD). T-he RSM model of fracture toughness is built, then the influence law of sol ratio, slag content, age on fracture toughness is put forward. The relationship between initiation fracture toughness (Q IC K) and unstable fracture toughness (S IC K) is established. The influence law of freeze-thaw, sol ratio and slag content on S IC K is built, and the impact mechanism of the two factors on S IC K is analyzed. Results show that the RSM model fits well and can be used to analyze and predict ASC fracture toughness. The influential significance rank for S IC K is slag content>age>sol ratio, and the most significant interaction is between slag content and age. Q IC K is about 50%~70% of S IC K , crack initiation should be the warning indicator of ASC structure. Fracture toughness decreases with the increased freeze-thaw times. With sol ratio increasing, more intense is the alkali slag reaction, reducing density and hindering depolymerization. With more cementitious material, effective water-cement ratio is decreased, subsequent hydration is limited, some slag powder doesn't participate in the reaction, reducing ASC toughness.