Improving the carbonation resistance of supersulfated cement by nano SiO2 and silica fume

Supersulfated cement (SSC) is a low-carbon material with limited carbonation resistance due to its high content of easily carbonated components (AFt) and low content of carbonation-resistant components (C-(A)-S-H gel and portlandite). This study aims to utilize reactive siliceous materials (nano-silica (NS) and silica fume (SF)) to optimize the product composition of SSC and enhance its carbonation resistance. Incorporating 3 % of ultrasonic-dispersed/non-ultrasonic-dispersed NS and SF into SSC, this study explores their effects on the mechanical properties of SSC before and after carbonation, carbonation depth, phase composition, and micro-morphology. Results show that both SF and NS promote the hydration, increasing hydration products and compressive strength, with NS being more significantly. While SF increases the flexural strength, NS reduces it. NS could modify the morphology and structure of AFt and C-(A)-S-H gel, resulting in a better carbonation resistance effect than SF. Both ultrasonic-dispersed NS and non-ultrasonic-dispersed NS have almost the same effect on the performance of SSC, with undispersed NS slightly reducing flexural strength more. This study highlights the critical role of AFt in the flexural strength and reveals that increasing the content of C-(A)-S-H gel is crucial for enhancing carbonation resistance. Combination of NS and SF (or other ultrafine powders) offers a promising approach to improving the carbonation resistance of SSC.