Investigating the mechanical properties of sprayable fiber reinforced cementitious composites containing limestone calcined clay cement

The construction industry is particularly cost-sensitive, thus new materials should be justified, and their economic advantages should be satisfactory. Over the last 50 years, using fiber-reinforced cement base materials has significantly increased. Among them, a particularly malleable category includes engineered cementitious composites (ECC), strain hardening cementitious composites (SHCC), and ultra-high toughness cementitious composites (UHTCC). These high-performance fiber reinforced cementitious based materials (HPFRCC) show considerable strain hardening capacity. Meanwhile, it is crucial to consider how these new materials (HPFRCC) will affect the environment. Indeed, the quantity of cement or cementitious materials used in their manufacturing may sometimes approach 1000 kg/m3. Substituting supplemental materials with cementitious properties for clinker is one of the greatest ways to reduce carbon dioxide emissions from HPFRCC manufacture (supplementary cementitious materials). Clays-containing kaolinite is one of the acceptable auxiliary ingredients for cement with good accessibility. These clays are among the substances that are widely distributed over the globe. When heated to 700-850°C, clays with at least 40% kaolinite produce metakaolin and become significantly pozzolanic. The simultaneous addition of calcined clay, and limestone to replace with part of the clinker in the mixed design results in LC3 or cement consisting of calcined clay and limestone, which reduces carbon emissions by roughly 30% turns into dioxide (CO2).  The optimal substitution ratio of OPC by LC3 is 50% clinker, 30% calcined clay (MK), 15% limestone powder, and 5% gypsum. Therefore, the optimal OPC substitution ratio by LC3 is 45% (55% OPC, 30% metakaolin, and 15% limestone powder) with kaolin content of around 40-50% in the clay. This study developed a sprayable HPFRCC using local materials such as limestone calcined clay cement (LC3) and ordinary polypropylene (PP) fiber to increase the durability of structures (as a material for repairing) without harming the environment. The developed composite's sprayability and mechanical performance were investigated through a flow table, compressive strength, uniaxial tension, and three-point flexural tests. Moreover, the material sustainability index (MSI) was used to evaluate the performance of the mixes in terms of consumed energy and carbon emissions. Finally, using LC3 and ordinary polypropylene fibers, it was possible to achieve sprayable HPFRCC with a tensile strain capacity of 3.5%. Furthermore, this composite exhibits low carbon production, low cost, and high ductility, promoting its use in infrastructure repairs. The compressive strength of cast specimens was 11% higher than that of the sprayed specimens. The reason for this was their apparent density difference and porosity (i.e. the compressive strength of the cast specimens was higher due to their lower porosity). The bending and tensile strengths of the cast specimens were, respectively, 14% and 22% lower than those of the sprayed specimens due to pneumatic compaction during the spraying process; the distribution of fibers in the sprayed specimens was more uniform, resulting in greater bending and tensile strengths. However, the flexural deformation and tensile strain capacity of the sprayed and cast specimens were almost equal. Moreover, A superplasticizer/binder (LC3 mass) ratio of 2.5% must be chosen for spraying HPFRCC containing calcined clay.