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.