Utilization of Coal Ash As Recycling Material Options in View Point of Geoenvironment

Abstract

Disposed coal ash is result from the residual of coal refinery processes and become environmentalimportant issues. Coal ash consists of bottom ash and fly ash. The number of coal ash production is abundant, and can be considered as waste material if it is not effectively reused or recycled for other application. In engineering practice, utilization of fly ash as additive materials is limited and in small quantity while the disposal of fly ash is quite high. The major aim of this paper is to stress the characterization, classification and utilization of coal ash as recycling structural material in view point of geoenvironment. Also, to prove of coal ash contribution in geotechnical engineering, give benefit in engineering practice and also become as part of engineering material that is environmental friendly. Material characteristics involve physical, mechanical, mineral composition and chemical properties, including environmental aspect by laboratory tests are presented. Uniaxial test, CBR test, sulphate resistance test and leaching test of heavy metal contents of coal ash as recycling structural material were also conducted to ensure environmentally acceptable based on Indonesian standard SNI. Fly ash is grouped in F class. Based on SNI-03-2460-1991, fly ash sample is available as additive material in concrete. Mix design of coal ash paving block is conducted toward several mixes, different volumes of coal ash and cement to grasp optimum utilization of coal ash and qualify minimum standard requirement of Indonesian standard SNI 03-0691-1996. Coal ash paving block with quality B, i.e. has compression strength 200 kg/cm2 can be mixed with fly ash adding 30% maximum as additive, or use of 50% fly ash as substitution with cement content is kept or using fly ash 30% and bottom ash 40%. Coal ash paving block samples resist to sulphate. Effect of addition of fly ash, bottom ash and lime on physical and mechanical properties can improve the index properties of soft soil sub grade layer, increases bearing capacity, as well as decreases swelling potential. Coal ash-soil mixture contains some heavy metals, but concentration values is still under boundary threshold of government act PP No. 20, 1990 about criteria of water quality in group D.