The Effect of Substituting Rdf on the Physical and Environmental Properties of Coal Fly Ash
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THE EFFECT OF SUBSTITUTING RDF ON THE PHYSICAL AND ENVIRONMENTAL PROPERTIES OF COAL FLY ASH ASHAARI B. MOHAMAD and DAVID L. GRESS Environmental Research Group, Department of Civil Engineering, University of New Hampshire, Durham, NH 03824. Received 16 November, 1988; refereed ABSTRACT Refuse-derived-fuel (RDF) consisting mainly of waste paper and plastics is a viable fuel source for the production of power. An experimental test burn partially substituting coal with RDF was undertaken by the Public Service of New Hampshire at the Merrimack Power Station. Five percent and ten percent RDF were substituted, on a BTU basis, for coal in the test bums. The chemical and physical properties of the resulting fly ash were determined. Twelve test burn days were run with 4 days of 5% RDF and 8 days of 10% RDF. Emphasis was placed on investigating the effect of the RDF fly ash on Portland cement concrete. Most of the chemical and physical properties of the coal-RDF fly ash were found to be comparable with ordinary coal fly ash except for the amount of cadmium and lead, the pozzolanic activity index and the compressive strength of fly ash concrete. Cadmium and lead were at average levels of 5.1 ppm and 102.6 ppm for the 5% RDF, and 7.8 ppm and 198.3 ppm for the 10% RDF, respectively. Although the pozzolanic activity index of coal-RDF fly ash increases over normal coal fly ash, preliminary results show that the 28-day compressive strength of concrete with direct replacement of cement and sand decreases by up to 30%. Leaching tests on crushed concrete were conducted to evaluate the environmental effect of acid rain. INTRODUCTION Considerable interest exists across the country in the reclamation and/or utilization of municipal waste. One form of municipal waste that can be reclaimed to produce high BTU fuel is refuse-derived fuel (RDF). The ash from RDF is known to contain a high level of lead due to the ink in the paper printing materials [1]. Burning RDF with bituminous coal creates fly ash with increased heavy metal content, which may or may not be hazardous as dictated by the EPA. Previous investigation of the ash produced when burning coal with RDF showed an increase in lead content, specific surface area, cadmium and the amount of soluble materials [1]. The presence of cadmium in fly ash can be hazardous and can also be detrimental to the properties of concrete. Cadmium in Portland cement paste has been shown to deteriorate from sulphate attack in the presence of salt water [2]. A high lead content in fly ash is not expected to be detrimental to concrete, but a potential hazard to the environment could exist if it leaches out over time. Limiting the percentage of RDF to be burnt with coal can produce fly ash that can be effectively used in concrete. EXPERIMENTAL Sample Collection During June and July of 1987, the Public Service of New Hampshire at the Merrimack Power Station conducted a large-scale test burn utilizing RDF as a partial replacement for bituminous coal. The test was done at full load, utilizing Unit 1 of the powe
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