Abstract
Construction of road embankments in peatlands commonly involves replacement of the peat with a fill-up soil of an adequate load-bearing capacity. This usually requires a lowering of the water level, turning a peatland from a carbon sink to a source of greenhouse gases. Thus, alternatives are sought that are less costly in both economic and ecological terms. Mass-stabilization technology can provide a cheap substitute for Portland cement. Calcareous ashes (waste materials), supplemented with pozzolanic and alkali additives to facilitate and accelerate the setting and hardening processes, are attractive alternatives to soil excavation or replacement techniques. Silica fume and waterglass were used as pozzolanic agents and KOH as a soil-alkalizing agent. X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analyses and stress–strain tests were performed for the hardened samples. Crystallization of alkali feldspars was observed in all test samples. Comparable hardening of peat soil was achieved for both ashes. It was shown that the ashes of Estonian kukersite (oil shale) from both pulverized firing and a circulating fluidized bed incineration process (produced in energy sector as quantitatively major solid waste in Estonia) can be used as binding agents for peat stabilization, even without the addition of Portland cement. Hardened peat soil samples behaved as a ductile material, and the cellulose fibers naturally present in peat gave the peat–ash composite plasticity, acting mechanically in the same way as the steel or glass fiber in ordinary reinforced concrete. The effect of peat fiber reinforcement was higher in cases of higher load and displacement of the composite, making the material usable in ecological constructions.
Highlights
Peatlands cover vast areas of the land surface, especially in the temperate and cold climate zones of the Northern Hemisphere, but they are found in the hot regions.Peatlands cover 22% of the land area of Estonia [1,2]
The main types of oil shale ashes released are circulating fluidized bed (CFB) ash, ash from pulverized firing (PF) collected from cyclones or electrostatic precipitators, and deSOx ash
The results of this study reveal that ashes from the PF and CFB processes can be applied as a cheap and widely available binder for the stabilization of peat columns, without any addition of Portland cement, when pozzolanic additives such as silica fume and waterglass and alkali pH modifiers are used
Summary
Peatlands cover vast areas of the land surface, especially in the temperate and cold climate zones of the Northern Hemisphere, but they are found in the hot regions.Peatlands cover 22% of the land area of Estonia [1,2]. Peat is highly compressible under high loading, which makes it one of the most difficult soils on which to construct buildings, roads, railroads, or other structures. To achieve an adequate load-bearing capacity of the roadbed, soil stabilization is usually required when a road or railway embankment will be constructed over a wetland area containing a peaty soil. The most common approach to the construction of road and rail track beds over peatlands is soil replacement [3]. This involves the excavation and displacement of peat and sapropel, removal of the peat to reveal the bedrock layer, and filling up the cavities with a material with a higher load-bearing capacity. The displaced material requires disposal, which needs to be ecologically safe [4]
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