Investigation on the flexural-tensile properties of ultra-high-strength engineered geopolymer composites (UEGC) with varied waterglass modulus

Waterglass modulus is the determining parameter in preparation of geopolymer, correspondingly, it also provides a significant impact on the physical and mechanical properties of ultra-high-strength engineered geopolymer composite (UEGC). This paper adopted direct tension test with dog-bone specimens and four-point bending test with prismatic and thin plate specimens to measure the flexural-tensile properties of UEGC with waterglass modulus of 1.0, 1.2, 1.4, and 1.6. Combining with the larger than 1 μm pores distribution obtained by X-ray computed tomography, the influence mechanism of waterglass modulus on flexural-tensile toughness and behavior of UEGC was clarified. The results showed that the variation in waterglass modulus of UEGC altered the SiO 2 /Al 2 O 3 ratio and alkalinity of the fresh mix, with a corresponding impact on its macroscopic properties and pores composition of larger than 1 μm. The σ - ε and F - δ curves of all UEGCs showed notable strain hardening and multi-crack cracking behavior, their lowest tensile strain was still up to 5.6%. When the waterglass modulus was 1.2, the compressive strength of UEGC cured for 28 days reached 115.6 MPa, its peak stress, maximum tensile strain and strain energy density of UEGC reached 5.95 MPa, 9.1% and 424.3 kJ/m 3 , respectively, its flexural toughness of both prism and thin plate specimen was 1.02×10 3 kJ/m 3 and 1.12×10 3 . The enhancement in the flexural-tensile toughness of UEGC was due to the multiscale cracking-resistant and toughening effect produced by PE fibers cooperated with 1-100 μm pores. The response amplitude on the toughness of UEGC under tensile stress to the waterglass modulus was lower than that subjected to bending stress, and presented a significant shape effect. • Clarify the influence law of waterglass modulus on the flexural-tensile deformation behaviors of UEGC. • Demonstrated the flexural-tensile toughness of UEGC profited from the multiscale cracking-resistant and toughening effect producing by PE fibers cooperated with 1-100 μm pores. • Revealed the shape effect of flexural toughness due to the prismatic and thin plate specimens.