Pozzolanic Potential of Anacardium Occidentale Nutshell Ash (Aonsa) and Its Impact on the Mechanical Properties of Concrete

Abstract

Investigating agricultural residue as pozzolans offers a two-fold benefits. It mitigates indiscriminate disposal what appears as a waste to some end users and promotes the sustainability of concrete. Tons of empty shells from Anacardium Occidentale Nutshells (AON), a by-product of the Anacardium Occidentale processing industry, are disposed indiscriminately in the environment where they eventually become nuisance.  However, there is a notable paucity of all-inclusive studies exploring the pozzolanic potential and the impact of Anacardium Occidentale nutshell ash (AONSA) on the mechanical properties of concrete.

This study aims to contribute to the available knowledge base on the pozzolanic potential of AON being an agricultural residue, which serves as an outlet for AON. Mechanical properties of AONSA incorporated concrete was investigated. AONSA was obtained from the incineration of Anacardium Occidentale nutshell sourced from local Anacardium Occidentale processing unit in Ogbomoso and subjected to air-drying after getting rid of the nuts. Open ignition under ambient air took place to obtain AONS ash and this was calcinated in an Engineering Laboratory in LAUTECH.

AONSA samples A and B were placed differently inside furnace at 800 for 5 hours and 500 for 7 hours for calcination. X-Ray Diffraction (XRD) analysis and X-Ray Fluorescence (XRF) analysis and Scanning Electron Microscopy (SEM) analysis, were employed to assess the pozzolanicity of AONSA while notable observations of the effects of time and elevated temperatures on AONSA were noted.

The percentage XRD result of Quartz, Muscovite, Glauconite, Osumilite, Illite and Albite present in samples A and B are 6.4 (2), 47.8 (9), 18.3 (6), 23.6 (7), 3.9 (7), 0 and 24.3 (10), 21.3 (9), 29.9 (11), 0, 19.8 (9), 4.7 (2) respectively. XRF has these results for MgO, SiO₂, P₂O₅, SO₃, K₂O, CaO, TiO₂, MnO, Fe₂O₃, NiO, CuO, ZnO and Y₂O₃ for samples A and B are 7.620, 2.849, 4.761, 1.868, 20.88, 4.309, 583.5ppm,0.119, 10.073, 4.3 ppm, 388.9 ppm, 4.3 ppm, 388.9 ppm, 0.443, 75.0 and 5.691, 2.788, 4.817, 1.750, 21.893, 425.3 ppm, 0.115, 9.718, 0.0, 387.8 ppm, 0.851, 7.6 ppm, respectively. The element in SEM for samples A and B are K, Fe, Mg, Ca, P, Na, S, Si, Al, Cl, Ti with these percentages: 39.04, 12.24, 18.95, 6.81, 6.98, 6.93, 2.81, 3.02, 2.04, 1.18, 0.0 and 45.34, 7.28, 20.90, 5.93, 6.08, 6.27, 2.25, 2.48, 2.46, 1.01, 0.00, respectively.

The presence of silicate, lime, and aluminum oxides oxide in AONSA contributes to its suitability as a pozzolan. The SEM analysis shows that with increase temperature at 5 hours, the atomic weight of Potassium got reduced compared to decrease in temperature at 7 hours.  The availability of SiO₂ and Y₂O₃ in AONSA is essentially the same as that of cement. Furthermore, availability of MgO in AONSA is roughly 5.6912%, which is lower than 6% specified for cement in IS: 12, 269 – 1987. The amount of lime (CaO) in AONSA is roughly one-third that of Ordinary Portland Cement, as compared to alternative cement substitutes like fly ash.