Investigation on preparation and compressive strength model of steel slag foam concrete

In order to improve its resource utilization rate, an aged steel slag (SS) was utilized as fine aggregate to prepare SS based foam concrete (SSFC). Firstly, the optimal mixture ratio was determined as:(i) SS particle size of 1.18 mm with uniform gradation, (ii) SS substitution rate (SSR) of 20%, and (iii) water-binder ratio of 0.45, in accordance with the 7-day unconfined compressive strength. Note that the increasing order of influence of these three factors on the compressive strength of SSFC (CS_SSFC) was: SSR > particle size of SS > water-binder ratio. In addition, the effect of SS content on strength was also investigated using scanning electron microscopy (SEM) analysis. The SEM micrographs revealed that the concrete incorporating 20% SSR exhibited the most uniform pore distribution, such that the pore diameter was small and had compact structure. Based on the aforementioned optimal mixture ratio, high CS_SSFC was obtained with low thermal conductivity and improved water stability characteristics. Moreover, the relationship between CS_SSFC and porosity of SSFC (under optimal mixture ratio) has been established by deploying the fractal theory. The fractal dimension of the block can be calculated by box counting method. Finally, the predicted values of CS_SSFC calculated using the fractal model was in good agreement with the experimental values.