Mechanical properties and tensile constitutive model of engineered cementitious composites based on geopolymer aggregates

To investigate the influence of geopolymer aggregates (GPA) on the mechanical properties of high-strength engineered cementitious composites, compressive strength tests and uniaxial tensile tests were conducted on geopolymer aggregates engineered cementitious composites (GPA/ECC) with different replacement rates of GPA. The compressive performance, tensile performance, and stress-strain relationship of GPA/ECC were studied by analyzing the compressive strength and tensile stress-strain relationship curves of GPA/ECC. At the same time, SEM-EDS analysis was used to reveal the influence mechanism of GPA on the macroscopic mechanical properties of GPA/ECC by analyzing its microstructure and element content. The results indicate that compared to the fine quartz sand matrix, as the GPA replacement rate increases, the overall strength and elastic modulus of GPA/ECC slightly decrease. However, its strain hardening capacity, crack control ability, and matrix toughness significantly improve. The corresponding ultimate tensile strain increases by about 19.3%, 50.3%, 64.6%, and 130.7%. The strength improvement rate in the hardening stage increases by about 5.6%, 34.3%, 42.4%, and 91.4%. The strain energy density shows the highest increase of 20.0%. GPA reacts with the hydration product Ca(OH)₂ of cement and generates additional reaction products such as hydrated calcium silicate (C-S-H) and hydrated calcium aluminate (C-A-H) at the interface transition zone between the aggregates and matrix, which improves the compactness of GPA/ECC microstructure. Based on the experimental results, regression analysis of the tensile stress-strain curve of GPA/ECC was performed using the least squares method. A constitutive model for GPA/ECC under tension was established, providing a reference for the performance design and engineering application of GPA/ECC.