Mitigation of efflorescence, drying shrinkage and water demand of calcined clay-based geopolymers with biological waste ashes as activator and hardener

Abstract

Uncertainties associated with durability and sustainability of geopolymer due to formation of efflorescence, shrinkage and activator cost are setbacks for its real-life applications. Therefore, the aim of this study was to produce geopolymers with improved durability and sustainability using local kaolin clay as precursor, cocoa-pods-ash (CPA) as alternative alkali hydroxide activator, periwinkle-shells-ash (PSA) as hardener and quarry-dust (QD) as filler. Local kaolin clay calcined at 700 °C (M7C), was replaced with some fractions of CPA and activated with only Na₂SiO₃ to produce binders (CPAG). The PSA was added to the best fit of M7C/CPA as fast-setting-agent, while QD was added to the best fit of M7C/CPA/PSA to produce mortars. 100% kaolin clay activated with 8MNaOH/Na₂SiO₃ was used as reference geopolymer. The geopolymers were cured at R.T for 7 and 28 days and characterised for physical, mechanical and durability properties. Clay, CPA, PSA, QD and geopolymers were characterised using XRF, ATR-FTIR and XRD. Reactivity was studied using isothermal conduction calorimetry. The ATR-FTIR and XRD results indicated transformation of kaolinite to metakaolinite in the clay, presence of K-C-O bond in CPA and O-C-O bond in PSA. Reference geopolymers set at 4 h while CPAG ranged from 14 to 19 h. With the addition of PSA, setting time reduced to values between 4 and 11 h. The compressive strength of reference geopolymer was 18.1 ± 0.3 MPa at 28 days, while CPAGs values ranged from 23.5 ± 0.3 to 35.6 ± 0.3 MPa. Best compressive strength was achieved with 2% PSA addition. No shrinkage in CPA-containing geopolymers while reference geopolymer had value of 0.03%. Efflorescence tendencies of the CPA-containing geopolymers reduced by 25–75% when compared with reference. Application of CPA as alternative activator improved the mechanical property, durability and sustainability of geopolymers.