Abstract
An increase in the generation of biogenic wastes such as locust bean pods and eggshells coupled with the need to drive sustainability in the cement industry has led the use of these wastes as cement replacement materials. The paper aims to investigate the effect of locust bean pod ash (LBPA) and eggshell ash (ESA) on the mortar compressive and flexural strength of ternary cement blends. The LBPA was obtained by calcining locust bean pod (LBP) at various temperatures of 800-900 °C and time of 60–120 minutes at an interval of 50 °C and 30 minutes respectively to determine the optimal conditions. The chemical composition of Ordinary Portland cement (OPC), LBPA and ESA were obtained via X-ray Fluorescence (XRF) Spectrometer and LBPA chemical composition did not satisfy one of the requirements specified by ASTM C618-01 (2001) with SiO 2 + Al 2 O 3 +Fe 2 O 3 of 30.42 wt. % which is less than 50 wt. %, but satisfies SO 3 content requirement of 0.7 wt. % and Loss on Ignition (LOI) of 7.12 wt. % and contains 19.42 wt. % CaO which is within the range of 10-30 wt. % CaO is class C pozzolan. The compressive strength of blended cement mortars at the early age of 2 and 7 days produced better strengths for cement blends with higher ESA content than LBPA especially at LBPA/LBPA-ESA ratio of 0, 0.4 and 0.6 for 2.5 wt. % cement replacement respectively. The early strength gain could be attributed to the provision of more nucleation sites by ESA inclusion which results in the acceleration of cement hydration rate. On the other hand, the enhanced strengths at 28 days of cement blended with various replacement from 2.5–10 wt. % could be attributed to the pozzolanic reaction between the available lime and reactive silica from LBPA despite clinker diminution which was close to control. Another reason for enhanced strength' could be attributed to the increased potassium content by an increase in LBPA content resulting in a gradual strength gain (retarder) muscovite formation K 2 Al 2 Si 6 Al 4 O 20 (OH) 4 . All cement blends experienced an increase in the mortar compressive and flexural strengths as the curing day progressed with some blends producing enhanced strength compared to control especially with 1.5 ESA1LBPA produced the best strength at 50.15 (6.82) N/mm 2 against 48.80 (6.80) N/mm 2 . This enhanced strength could be related to the pozzolanic activity and the high potassium content from LBPA despite clinker diminution, especially at 28 days.
Highlights
The demand for cement arising from inadequate housing coupled with the need to solve the problem of release of CO2 leading to the greenhouse effect and an enormous amount of energy is required for cement production
The chemical composition of Ordinary Portland cement (OPC), locust bean pod ash (LBPA) and eggshell ash (ESA) were obtained via X-ray Fluorescence (XRF) Spectrometer and LBPA chemical composition did not satisfy one of the requirements specified by ASTM C618-01 (2001) with SiO2+ Al2O3+Fe2O3 of 30.42 wt. % which is less than 50 wt. %, but satisfies SO3 content requirement of 0.7 wt. % and Loss on Ignition (LOI) of 7.12 wt. % and contains 19.42 wt. % CaO which is within the range of 10-30 wt. % CaO is class C pozzolan
The enhanced strengths at 28 days of cement blended with various replacement from 2.5–10 wt. % could be attributed to the pozzolanic reaction between the available lime and reactive silica from LBPA despite clinker diminution which was close to control
Summary
The demand for cement arising from inadequate housing coupled with the need to solve the problem of release of CO2 leading to the greenhouse effect and an enormous amount of energy is required for cement production. One alternative solution to these challenges is the partial replacement of cement by appropriate materials such as pozzolans. These pozzolanic materials are siliceous or aluminous materials that themselves have little or no cementitious properties but when in finely divided form and the presence of moisture reacts with CaOH2 which is liberated during cement hydration at ordinary temperature to form more cementitious materials according to [7]. Pozzolan possesses the characteristics of reacting with free lime released during cement hydration to form stable insoluble calcium silicates to reduce sulfate, salt and chloride attacks [22]. Pozzolanic activity of a material can be assessed by the ability of the material to react with Ca(OH)2(CH) by monitoring the consumption of CH or measuring the strength development. The pozzolan influence is dependent on the quality and quantity of active phases in the pozzolan [10]
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