Experimental and numerical analysis of shear behaviour at the interface geopolymer mortar and sand

This study aimed to examine the impact of various production parameters on the shear performance at the interface between geopolymer mortar (GPM) and sand soil. Initially, the effects of varying NaOH concentrations (5, 10 and 15 M), aggregate types (stream aggregates (SA), crushed stone aggregates (CS) and construction and demolition waste (CDW) aggregates) and alkali/binder ratios (0.5 and 0.6) on GBFS-based GPM specimens were investigated. For this purpose, compressive strength, water absorption and ultrasonic pulse velocity (UPV) tests were carried out on GPM samples cured for 28 days. The maximum 28-day compressive strength (43.6 MPa) and the minimum water absorption (3.78%) were observed in GPM specimens activated with 15 M NaOH, produced with CS, water-cured and cast at an alkali/binder ratio of 0.5. Experimental findings revealed that the effects of aggregate type on high mechanical and low permeability properties were graded as CS > SA > CDW. Additionally, UPV test results showed positive correlation with compressive strength and water absorption values. Subsequently, the shear performance between GPM and sand soil were determined by using shear box test. In direct shear experiments, decreasing the alkali/binder ratio from 0.6 to 0.5 and the usage of CS increased the sand-GPM friction angle. Moreover, numerical modelling was employed to analysed soil-GPM interaction using the finite element method (FEM) in ABAQUS. FEM results showed that the obtained numerical findings demonstrated strong consistency with experimental data, capturing force-displacement trends therefore the numerical model can be used for parametric studies.