Assessment of interfacial mortar-mortar bond and pure shear strength of metakaolin-based geopolymer

PurposeThis paper aims to investigate the bond strength of metakaolin-based geopolymer mortar with cement mortar.Design/methodology/approachThe mortar-mortar bond strength is assessed by slant shear and split tensile tests; pure shear strength is evaluated by Mohr's criterion for result validation. Metakaolin-based geopolymer mortar is cast over the cured cement mortar specimen with two levels of surface roughness: smooth or grooved interface. The influence of the alkaline solution to metakaolin ratio on geopolymer bond strength is studied. Compressive strength, ultrasonic pulse velocity, permeability and flow table tests are also performed.FindingsThe paper's findings are highlighted as follows: (1) strong mortar-mortar bond properties achieved for geopolymer mortar in all tests and conditions and validated by Mohr's criterion and pure shear, (2) a lower alkaline solution to metakaolin ratio achieves higher bond strength to Portland cement mortar and (3) geopolymer mortar has higher compressive strength and ultrasonic pulse velocity than cement mortar at all curing ages; additionally, it is more flowable and less permeable.Practical implicationsThe full replacement of Portland cement with metakaolin, a more sustainable cementitious material, will contribute to the decarbonization of the construction industry.Originality/valueLimited research has been carried out on the bond strength of metakaolin-based geopolymer mortar to Portland cement mortar. Also, computing the pure shear using Mohr's circle criterion of metakaolin-based geopolymer to validate the results can be considered original.