Development of structural grade lightweight geopolymer concrete using eco-friendly materials

Geopolymer lightweight concrete has been produced using environmentally sustainable materials by completely replacing conventional concrete with ground granulated blast furnace slag (GGBFS) as the binder, manufactured sand as the fine aggregate, and CS as coarse aggregate. The CS are used as a full replacement for natural coarse aggregate in geopolymer concrete (GPCSC) and are compared with the geopolymer concrete containing 100% crushed granite (natural coarse aggregate) used in a control mix (GPCC). The GGBFS binder was activated with sodium silicate (Na2SiO2) and sodium hydroxide (NaOH) as alkaline activator solutions (Na2SiO2/NaOH) with the ratio of 2.5 was taken, and the concentration of NaOH was maintained at 10M for all mixes. The mechanical and microstructural properties of CS concrete were compared with the control mix. Flexural strength, split tensile strength (STS), ultrasonic pulse velocity, bond strength, impact resistance, and elastic modulus of the geopolymer concrete were measured at 28 days, while the compressive strength of the geopolymer concrete was measured at 3, 7, and 28 days under concealed curing at an ambient temperature. Relevant Indian and ASTM standards were used to measure all the above properties. The microstructure analysis shows that the presence of CS weakens the strength of the mix and the structure of the interfacial transition zone. On the contrary, due to the alkali-Activated GGBFS binder in geopolymer concrete, the matrix homogeneity improved due to the formation of a three-dimensional aluminosilicate network. Test results show that the compressive strength, STS, flexural strength, bond strength, impact resistance, ultrasonic pulse velocity, and elastic modulus of geopolymer coconut shell concrete (GPCSC) satisfy the structural criteria and can be used as structural-grade lightweight concrete. A comparison was made between conventional geopolymer concrete (GPCC) and lightweight GPCSC in terms of their behaviour with previous literature studies. The findings indicate that GPCSC can be utilized as a structural-grade geopolymer lightweight concrete, offering promising mechanical properties and reduced density.