Laboratory investigation on the fracture toughness (Mode I) and durability properties of eco-friendly cement emulsified asphalt mortar (CRTS II) exposed to acid attack

Cement Emulsified Asphalt Mortar (CEAM) has gained prominence as a vital material for its energy and noise damping properties between the concrete roadbed and track slab in a high-speed railway system. Therefore, it is evident that CEAM properties need to be better understood and optimized. Since cracking caused by traffic loading and atmospheric conditions is one of the primary causes of failure in CEAM, addressing this issue is of great importance. Furthermore, there is a growing need for more environmentally friendly and durable CEAM due to the environmental impact of cement production in the form of greenhouse effect. The objective of this study is to assess the impact of partially replacing cement content in CEAM Type II (CRTS II) specimens with pozzolanic materials such as silica fume, metakaolin, and granite sludge to investigate how these pozzolans affect the fracture toughness (Mode I) performance under both normal (water curing) and sulfuric acid exposure conditions with the main focus on evaluating the pozzolans ability to resist acid attack from a fracture toughness perspective as the research novelty. For this purpose, specimens containing pozzolans at 5%, 10%, and 15% substitution level (by weight of cement) were subjected to Semi-Circular Bending (SCB) test both under normal and exposure to 5% sulfuric acid solution conditions. Moreover, water absorption test was conducted on specimens in normal condition as a durability index. The test results of this study revealed that substitution of these pozzolanic materials enhanced the fracture toughness in normal condition. Specifically, at a 10% substitution as the optimal level, silica fume and metakaolin resulted in 18% and 15% increase in fracture toughness performance compared to the control specimen in normal condition. However, granite sludge exhibited almost the same performance as the control specimen at 5% substitution as its optimal level. In acid exposure condition, the detrimental effect of acid on the fracture toughness performance of specimens was reduced by 61%, 55% and 13% for samples containing silica fume, metakaolin and granite sludge at 15% substitution level, respectively. Furthermore, water absorption test results showed that inclusion of silica fume and metakaolin at a substitution level of 15% results in 56% and 47% reduction in water absorption compared to the control specimen, respectively, while for granite sludge, it was almost the same as control specimen. These results were also confirmed by SEM studies. Since the use of these pozzolans as cement substitution not only improves the fracture toughness in normal condition but also provides protection against acid-induced degradation, this study contributes to the development of a more durable and environmentally friendly CEAM.