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

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 Na 2 SiO 3 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/Na 2 SiO 3 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.