Application Of Fls Systems In Landfill Cover Material

Sanitary landfill is the main method of treating municipal solid waste at present in our country. Considering cost and techniques of treatments, the choice of cover material is very import. It is essential to find a new substitute material, because clay which is widely used in the municipal solid waste sanitary landfill (MSWSL) makes a great deal of disadvantage. The properties of fly ash-lime-sulfate (FLS) system used as MSWSL cover material were investigated systemically through lab simulation experiment. The effect of raw materials, mix proportion and construction technics on characteristic of FLS system were researched.In former researches on FLS systems, sulfates usually used were Glauber's salt (Na₂SO₄) and dehydrate gypsum. The binders have lower strength in the early age, and higher strength in later age. MSWSL cover material request higher early strength for beautifying environment and shortening the period of project. Through the lab research about FLS system as cover material, it was found that hemihydrate gypsum played an important part in the system. It can accelerate the harding of the system, improve the early strength to meet the need of the strength for the cover material. So in this research, hemihydrate gypsum as sulfate was investigated.The mix proportion and w/c ratio of hemihydrate gypsum FLS system was determined through the strength experiments of various mix proportions, based on the mechanism of FLS system and the function of cover material. In the hemihydrate gypsum FLS system the optimal content of Ca(OH)₂ is 15%, and hemihydrate gypsum is 10-15%, the w/c ratio is 0.4. In this case, FLS system is satisfied in both early and later strength.In this article, permeability, anti-erode ability, water curing and dry-wet circle curing strength, dry shrinkage and pH value were well studied. Compared with clay, it is found that FLS has better permeability and anti-erode ability. Water curing may induce the strength of the FLS decrease, but it won't affect seriously. Because of the special hydrate mechanism of hemihydrate gypsum FLS system, the strength increased dramatically in dry-wet circle condition. After hardening, the volume of FLS system would alter a certain extent, less than 40‰, and it appeared expand mostly. Shrinkage crack can hardly be found in the hardnite, and the permeability of binders improved as well. The hydrating environment of FLS system is alkaline in early period, and with development in the age, it is tend to be neutral gradually. The alkaline environment in early period is advantageous to control the breed of fly and mosquito.FLS system has lots of advantage over clay as cover material. Fly ash, the main raw material of the system, is a kind of solid waste. Considering both economics and environment, FLS system is a desirable cover material.