An experimental study on silica fume and metakaolin doped portland cement-based mortars using silica aerogel and air-entraining admixture

Ordinary Portland Cement (OPC) is an expensive material and has negative effects on environmental health as it increases greenhouse gas emissions. These problems accelerate the search for substitute materials. Although metakaolin (MK) and silica fume (SF) show high potential as substitute materials, they are used at a limited rate in the construction industry. Considering plain Portland Cement may be insufficient in aggressive conditions, it was aimed to increase interest and awareness regarding the application by using two materials together. For this study, a critical substitution ratio (20%), was shared equally between metakaolin (10%) and silica fume (%10). In addition, silica aerogel (SA) (at 1, 2, 3, and 4%) and air-entraining admixture (AEA) (at 0.1, 0.4, 0.7, and 1%) were examined in terms of mechanical and thermal properties for the building construction in sustainable cities. Although these additives bring important advantages, their information is limited, especially in aggressive conditions. The 7 and 28 days compressive and flexural strengths and physical properties were found for 10 series. Also, the freezing–thawing and high-temperature tests were applied, and the scanning electron microscopy (SEM) analyzes were performed. According to the results, metakaolin and silica fume increased flexural strength by 5.67% and compressive strength by 8.07% due to their high pozzolanic properties. Also, 1% silica aerogel strengthened the cement paste and increased the compressive strength by 2%. Also, it maintained this performance after the durability tests. Although 0.1% air-entraining admixture decreased the strength results, it increased the compressive strength by 4% after freezing–thawing.