ABSTRACT
Alkali-activation of agro-industrial wastes as alternative binder to Portland cement (PC) is receiving more consideration most especially in the developed nations due to the issue of green-house gas (CO2) emission from the production process of (PC) and the need to improve the fresh and hardened properties of agro-industrial waste-based mortar and concrete. This research focused on alkali-activated millet husk ash (MHA)-calcium carbide waste (CCW) binder-based mortar for appropriate characterization of the materials and evaluating the fresh / hardened properties of the mortar produced. MHA – an agricultural by-product and CCW – an industrial by-product was examined as possible materials to be combined as alternative to PC. Three combination proportions of MHA – CCW (40:60, 45:55 and 50:50) was determined from CaO and SiO2 content), activated with 5, 10, 15 and 20 molar concentrations of Sodium Hydroxide (NaOH) and mortar produced at 1:3 binder/sand (b/s) and 0.5 water/binder (W/B) examined for binding, strength development and water absorption at varied curing age (3, 7, 14, 28, and 56 days respectively) in accordance to BS EN 196-1: 2016. The chemical analysis of the supplementary cementitious materials via X-ray fluorescent (XRF) revealed MHA having 73.4 % silica (SiO2) content and the aggregation of the main oxides (SiO2 + Al2O + Fe2O3) gives 88.1 % which is above 70 % minimum limit stipulated in ASTM C618 (2015) standard while CCW primarily contain CaO (66.1 %). The fresh properties examination of the binder pastes results revealed 45-55 (MHA-CCW) at 15M NaOH molarity possessing similar fresh properties as the control (PC). The tested mortar samples exhibited increasing performance for both properties examined with increasing NaOH concentration up to 15M but decreased performance at 20M for all combination proportions. The 7- and 14-days strength for 45-55 MHA-CCW activated with 15M NaOH were 10.72 (67 %) and 15.96 N/mm2 (79 %) respectively of the PC-based sample at same age. The 28days strength for the 45-55 MHACCW, 15M NaOH sample showed higher strength gain (29 %) as against 23 % strength gain of the PC-based mortar. Further curing of the alkali-activated MHA-CCW mortar till 56days resulted in additional 24 % strength gain over the 28th day as compared to the 7 % increase of the control`. The trend is same for all the alkali-activated MHA-CCW mortar studied up to 15M NaOH concentrations. The 15M NaOH activation of 45-55 MHA-CCW is considered by this study as the indicated proportion for good strength. However, recommends the utilization of 45-55 MHA-CCW, 15M NaOH in 1:3 binder/sand at 0.5 W/C for masonry work and further studies into the examination of the morphology and nature of the hydration as well as the formed microstructure should be undertaken.
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