Highway embankment construction using fly ash in cold regions

摘要

Mineral wastes or by products provide great potential to alleviate demand for large volumes of low cost mineral resources for highway construction. Fly ash, the inorganic residue of coal burning thermal power plants, has been used widely in the construction industry. However, compaction of fly ash is very sensitive to water content which complicates use of fly ash in highway embankment. One or two percent over optimum water content makes compaction impossible. On the other hand, an excess amount of water is needed to enhance reactions leading to formation of cementitious products, which increases strength. This paper presents a new technique for adding water to fly ash samples to enhance the conditions for cementitious mineral formation without sacrificing compactibility. Fly ash at optimum water content, and fly ash with additional 10% by weight crushed ice were compacted, sealed and cured for 1, 7, 14, 28, and 90 days at 21 degreesC. Unconfined compression tests and splitting tensile tests were conducted after completion of each curing period. Cementitious mineral formation, and changes in microfabric with curing time were observed using powder X-ray diffraction (XRD) analysis and environmental scanning electron microscopy (ESEM). The addition of snow into fly ash increased the unconfined compressive strength and splitting tensile strength noticeably beginning from 14 days of curing. X-ray diffractograms and ESEM micrographs are used to explain the mechanisms leading to increase in shear strength. More important than the higher performance obtained by using snow, the new technology will allow construction of highway embankments, bases and subbases during wintertime at cold regions, where construction activities are ceased normally due to snow and low temperatures. (C) 2004 Elsevier B.V. All rights reserved.