Browsing by Author "Chambua, Safiel"

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Compressive strength optimization of the ambient-cured metakaolin-based geopolymer mortar using the Taguchi design approach
(Elsevier, 2025-05-16) Hashimu Hamisi; Chambua, Safiel; Mansouri, Said; Hicham, Majdoubi; Yusufu Abeid; Chande, Jande,; Youssef, Tamraoui; Askwar, Hilonga
This study utilized raw natural kaolinite sourced along Pugu hills, Tanzania, as the aluminosilicate source. To optimize the compressive strength, nine (9) metakaolin geopolymer formulations were activated using the Taguchi technique at various Na2SiO3/NaOH mass ratios, NaOH concentrations, and alkaline/binder ratios. The ideal parameters were 12 M, 2.5, and 0.8 Na2SiO3/NaOH mass ratios, NaOH concentration, and alkaline/binder ratios, respectively, resulting in a compressive strength of 70.38 MPa. When the optimized geopolymer was exposed to a higher temperature, its compressive strength increased by 15.57 % at 200°C compared to room temperature. Compressive strength decreased with exposure over 200°C, and weight loss and water absorption were directly correlated with this. The SEM results show that the former lacks a well-linked geopolymer network when comparing weak and superior formulations. High-strength formulations are verified to include higher levels of orthoclase and albite, according to Rietveld refinement and XRD research. The XRD patterns showed the development of sanidine, chrysotile, and nepheline crystalline phases at temperatures higher than 200°C, which may have contributed to the decrease in strength of the geopolymer specimens.
Strength and durability properties of concrete blended with pumice and scoria under combined attack of sulphate and chloride
(NM-AIST, 2021-11) Chambua, Safiel
Concrete structures suffer serious deterioration under corrosive environment. Consequently, the safety of these concrete structures is decreased. The influence of natural pumice (NP) and natural scoria (NS) as supplementing cementing materials of concrete exposed to sulphate, chloride and combined effect of sulphate and chloride is studied. Portland cement (PLC) was replaced with NP or NS at a substitution level of 10%. Concrete samples were submerged in portable water for 28 days. Afterwards, the specimens were immersed in 5% sodium sulphate (Na2SO4), 5% sodium chloride (NaCl) and combined sodium sulphate and chloride solutions for 28, 56 and 90 days. The results were compared between concrete mixes with NP or NS and control mix (CT) with PLC. The effects of sulphate, chloride and combined sulphate and chloride were evaluated in terms of change in weight, variation in compressive strength and degree of damage. The compressive strength was not compromised at 10% substitution level. It was observed that, concrete containing NP and NS have compressive strength of 46 MPa (7.7%) and 44 MPa (3.04%) higher than 42.7 MPa of CT submerged in water for 90 days respectively. Concrete samples immersed in 5% Na2SO4 solution, NP and NS has a compressive strength around 45.5 MPa (15.4%) and 44.8 MPa (13.6%) higher than 39.4 MPa of CT mix at 90 days, respectively. However, under 5% NaCl solution the compressive strength of concrete containing NP and NS decreased up to 34.2 MPa (7.5%) and 32.5 MPa (7.2%) for 90 days cured samples. Moreover, under combined effect of 5% Na2SO4 and 5% NaCl concrete containing NP and NS has a compressive strength around 29.8 MPa (8%) and 29.2 MPa (7.3%) higher than 27.4 MPa of control mix at the exposure period of 90 days. It can be concluded that NP and NS have extraordinary potential to be utilized as a cementitious material in concrete.
Strength and Durability Properties of Concrete Containing Pumice and Scoria as Supplementary Cementitious Material
(Hindawi, 2021-05-24) Chambua, Safiel; Jande, Yusufu; Machunda, Revocatus
Concrete structures suffer serious deterioration under a corrosive environment. Consequently, the service life of these concrete structures is decreased and deteriorates under combined attack of sulphate and chlorides. Most studies confined on single deteriorating factor such as sulphate attack only or chloride attack only but the current study focused on the influence of natural pumice (NP) and natural scoria (NS) on the strength performance of concrete exposed to the combined attack of sulphate and chloride. Portland cement (PLC) was replaced with NP or NS at a substitution level of 10%. Concrete samples were cured in water for the curing period of 28 days. Afterwards, the specimens were immersed in 5% sodium sulphate (Na2SO4), 5% sodium chloride (NaCl), and combined sodium sulphate and chloride solutions for additional curing of 28, 56, and 90 days. /e results were compared between concrete mixes with NP or NS and control mix (CT) with PLC. /e effects of sulphate, chloride, and combined sulphate and chloride were evaluated in terms of change in weight, variation in compressive strength, and degree of damage. Conclusively, the application of NP and NS has extraordinary potential to be utilized as a cementitious material in concrete to increase the resistance against aggressive salts.