Freeze-thaw resistance of alkali-slag concrete based on response surface methodology

Alkali-slag concrete (ASC), with the frost resistant grade of above F300 and frost resistant coefficient DF of about 90%, is prepared using slag and composite activator composed of Na2SiO3 and NaOH. Response surface methodology (RSM) is applied to study the freeze-thaw resistance of ASC. The effects of activator solution-slag ratio (A/S), slag content and sand ratio on the freeze-thaw resistance are analyzed using the softwares of Design Expert and Box-Benhnken Design (BBD). Models are established for DF and the influence of air-void structure of hard concrete on the freeze-thaw resistance, respectively. The result shows that the DF model coincides well with the test results and can be used to analyze and predict the freeze-thaw resistance of ASC. The influence on the freeze-thaw resistance from high to low is A/S, slag content and sand ratio. The interaction of A/S and slag content is the most prominent and air-void structure is the crucial factor. The air bubble space coefficient and its specific surface area have good correlation with DF. The freeze-thaw resistance tends to better with smaller air bubble space coefficient and bigger specific surface area.