Hybrid Effect of Nano-CaCO3 and Polypropylene Fiber on Fresh and Hardened Properties of Alkali-Activated Material

AbstractCompared with traditional portland cementitious material, alkali-activated material (AAM) had the advantages of low carbon emission, energy saving, excellent durability, strength, and high temperature resistance. It has been proved that the addition of a fiber or nano-particle could improve the mechanical properties of AAM. The fresh and hardened properties of nano-CaCO3 (NCC) and polypropylene fiber (PPF) reinforced AAM were studied in this paper. The hybrid effects of PPF with various volume fractions (0%, 4%, and 8%), aspect ratios (0–464.52), and NCC with various content (0%, 1%, and 2%) on the slump spread, flow rate, flexural strength, compressive strength, and ultrasonic velocity of AAM were investigated. For flowability, the mixture with 0.4% 6 mm and 0.4% 12 mm PPF was the optimal, showing a positive hybrid effect. The hybrid use of PPF and NCC significantly improved the flexural strength, but the compressive strength was not significantly improved. The hybrid effect factors for compressive strength were lower than those for flexural strength. The positive hybrid effect of strength was most obvious when the nano-CaCO3 was 1%. The threshold for fiber factors was 200. Microstructure studies showed that the bridging effect of PPFs can limit the crack development and enhance the strength of AAM. Nano-CaCO3 promoted the denseness of AAM and bond between fiber and matrix. The hybrid of PPF in different lengths and NCC could decrease fiber consumption, reducing the cost and promoting the engineering application of fiber-reinforced AAMs. Practical ApplicationsThe effect of hybridization of calcium carbonate nano-particles with polypropylene fibers on the fresh and hardening properties of alkali-activated materials has practical applications in the construction industry. One of its main advantages is its excellent flowability, which allows the material to be self-consolidating. This property allows it to be used effectively in areas such as post-tensioned grouting, pipe concrete, and other grouting processes, where the material flows effortlessly and fills voids efficiently. In addition, the mixing effect of the CaCO3-nano-particles and the polypropylene fibers enhances the stability and strength of the material, which further enhances the durability and structural stability of the concrete elements. Overall, this blend has excellent flow and self-consolidation properties, making it an important choice for applications such as postgrouting and rein