Pozzolanic characteristics of municipal solid waste ash

Abstract

Earth as a building material has been used over the years in the construction industry. However its strength characteristics have been inadequate. Therefore, stabilizers are used to enhance its strength. Where conventional stabilizing agents like cement and lime have been used, they have considerably increased the cost of construction. It is with this backdrop that this paper describes the pozzolanic characteristics of municipal solid waste ash (MSWA) and its use as a stabilizing agent. The total elemental concentration in the MSWA was determined by use of Total X‐ray Florescence method, while the laser particle analysis method was used to determine the particle size distribution of the ash. X‐ray Diffractometer method was used to measure the level of molecular compounds including the oxides of silicon, aluminium and iron. The Total X‐Ray Florescence (TXRF) analysis indicated that the ash contained high levels of calcium (220,240 mg/kg) and mercury (23.76 mg/kg). According to the Canadian Public Health guidelines, this concentration of mercury exceeded the acceptable limit of 23 mg/kg. Calcite was the main oxide (57.6%) with its glass halos occurring between 20° to 50° two‐theta. The total amounts of SiO₂, Al₂O₃, and Fe₂O₃ were less than 70%, categorising the ash as Class F pozzolana meaning that MSWA was not self‐cementing. Laser diffraction particle size analysis showed that the ash was mainly composed of particles finer than 0.002 mm (55.82%), with its probability distribution function depicting a bimodal curve. The municipal solid waste (MSW) had a high loss of ignition (83.49%), an indication that it contained high amounts of un‐burnt carbon. Despite the low quartz (SiO₂) content as compared to that of pozzolana cement, MSWA had high calcite (CaCO₃) content enabling it to contribute to bonding effect of the ash. From the study, it is recommended that MSWA has to be used as a bonding agent and not as a cementing ash. Also the ash has to be finely ground prior to use as a pozzolanic material in soil stabilization, so as to increase both its filler and bonding effect.

Key words: bonding effect, municipal solid waste ash (MSWA), pozzolana