Relationship between Phase Composition and Mechanical Properties of Peat Soils Stabilized Using Oil Shale Ash and Pozzolanic Additive

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.

The Implementation of Industrial Byproduct in Malaysian Peat Improvement: A Sustainable Soil Stabilization Approach

“…The silicon dioxide reacts with the calcium hydroxide in the presence of water to produce calcium silicate hydrate gel, which is responsible for the strength improvement of problematic soil [ 7 ]. Therefore, SF has been extensively adopted in the stabilization of peat soil [ 7 , 8 , 9 ]. For instance, Kalantari et al [ 7 ] utilized SF in the presence of cement to assess the mechanical and compressibility characteristics of peat.…”

“…The micrographs of untreated and cement-, silica-sand-, and kaolin-stabilized peat reported by Wong et al [ 10 ] revealed a clear transformation from loosely packed peat to a compact solid matrix. Moreover, Rikmann et al [ 9 ] performed microstructural testing (XRD, XRF, and FTIR) of the utilization of cement and shale ash in peat stabilization; their results supported the application of pozzolanic additives such as silica fume, pH-modified alkali, and water glass without the addition of ordinary Portland cement for the stabilization of peat soil. In summation, previous findings have shown that both silica fume and OPC are potential binders in peat stabilization.…”

Physicochemical and Microstructural Characterization of Klias Peat, Lumadan POFA, and GGBFS for Geopolymer Based Soil Stabilization

“…Peat soils are defined as highly heterogeneous materials, as they are derived from decomposing organic matter, i.e., plant leaves and roots, and are typically brown or black in color [1]. Peat soil is considered a problematic soil because it has a high natural moisture content and low shear strength [2]. The problems associated with peat soils should be resolved by means of soil stabilization.…”

Stabilization of Road Embankments on Peat Soils Using Oil Shale Ash and Pozzolanic Additives

“…Low pH values caused by organic acids (incl. humic and fulvic acids) can prevent the dissolution of clay minerals [3]. Additionally, the effect of humic acids on the setting process of cement is not fully understood.…”