Synergistic effect of polyvinyl alcohol fibers and spindle-like calcium carbonate on the mechanical properties and drying shrinkage of geopolymer concrete

Geopolymer, a sustainable substitute for Portland cement in the construction industry, contributes to environmental sustainability for the escalating need for high-performance concrete. However, in comparison to Portland cement, geopolymer exhibits greater brittleness and drying shrinkage, which present significant challenges to its practical application in construction engineering. This study aims to address the shortcomings by investigating the mechanical properties and drying shrinkage of hybrid fiber-reinforced geopolymer concrete (HFRGC) using spindle-like calcium carbonate (SCC) and polyvinyl alcohol (PVA) fiber. Compared to the control group (without fibers), the compressive strength, flexural strength, and tensile strength increase by 71 %, 139 %, and 261 %, respectively. Moreover, the toughness index I 30 exceeds 30, and the drying shrinkage reduces by 37.3 %. These outperform favorably with those of other hybrid fiber geopolymers. The synergistic effect of hybrid fibers lies in PVA fibers bridging macroscopic cracks, while the SCC promotes hydration and strengthens the matrix by acting as a nucleation site. In addition, the spindle-like SCC bridges the microcracks and optimizes the pore structure through micro filling, leading to an 11.2 % reduction in total porosity. Besides, the drying shrinkage of HFRGC is found to be linearly correlated with the mesopore volume. SCC reduces the mesopore volume, leading to a decrease in pore tension and thus suppressing drying shrinkage. Finally, a new drying shrinkage prediction model for HFRGC is proposed by considering factors such as fiber volume fraction, aspect ratio, tensile strength, and compressive strength. This study reveals the enhancement mechanism of HFRGC reinforced with PVA fibers and SCC, providing valuable insights for the development of high-performance sustainable building materials. • High toughness geopolymer concrete is developed with hybrid of PVA fiber and spindle-like calcium carbonate. • PVA fibers bridge macroscopic cracks and increase toughness of concrete significantly. • SCC bridges the microcracks and optimizes the pore structure through micro filling. • PVA and SCC synergistically reduce the pore tension and thus suppress drying shrinkage. • A new drying shrinkage model for hybrid fiber-reinforced geopolymer concrete is proposed.