Mechanisms of Distress Associated with Sulfate-Induced Heaving in Lime-Treated Soils

Abstract

Field observations suggest that ettringite-induced swell in lime-treated soils may manifest rapidly after placement and compaction or after months or even years after lime treatment. In either case, forensic investigations have identified the presence of the mineral ettringite in distressed sections. However, the time window between the observation of distress and the subsequent forensic evaluations has left room for doubt as to whether the ettringite caused the observed distress or was formed between the time of the observed distress and the time of the forensic investigation. The study focuses on identifying alternative, probable mechanisms of swelling when sulfate-laden soils are stabilized with lime. The research addresses the hypothesis that swelling in sulfate-bearing fine-grained soils results from one or a combination of three mechanisms: (a) volumetric expansion during ettringite formation, (b) water movement triggered by a high osmotic suction caused by sulfate salts, and (c) the ability of the ettringite mineral to absorb water and contribute to the swelling process. The data validate the conclusion that a synergy of the mechanisms discussed contributes to swelling distress. The study also addresses the impact of matrix strength of the stabilized soil on damage potential.

The Feasibility of Using Marble Cutting Waste in a Sustainable Building Clay Industry

“…Also, it was observed with vanishing of the main stabilizer (HL) in the mix R4 the ettringite and gypsum phases appear. The ettringite formation will leads to the increase of the soil volume, water absorption, reduction of effective cohesion and soil strength loss [26]. The high pH value creates favorable condition for local dissolution of the likely releasing alumina and silica within the specimen body.…”

Fundamentals of soil stabilization

“…One of the sulfate salts existing in the soil and two lime carbonation. In the soils containing sulfates, any calcium-based additives results in heaving and disintegration leading to a loss in strength [79][80][81]. Soil composition, groundwater and mixed water can be the source of sulfates [82][83][84].…”

Chemo-Mechanical Interactions in the Ettringite Induced Expansion of Sulfate-Bearing Soils

“…In analogy to clayey soils, it may be possible to assume that 1/R e should be related to the diffusion properties and/or pore size characteristics of the adsorbed water around clay clusters. Incidentally, Coussy's formulation [34] based on a poro-mechanics approach leads to similar results to Equation (14). Figure 5 shows the time evolution of the osmosis-induced swelling strain of the two soils with different sulfate contents as discussed in Section 5.1.…”

“…Of course, this consideration of volume contraction implies that the water is supplied within the soil matrix (i.e., a closed system); if the water consumed in ettringite formation comes from outside the matrix (i.e., an open system) and hence is excluded from the original reactant volume considered, then indeed, the reaction produces a volume expansion of 137%, and the increase is almost entirely due to the water supplied externally. Therefore, the source, timing, and availability of the water consumed may have a profound effect on the ettringite formation and induced expansion [13,14]. It is also of interest to note that the percentage of volume change mentioned above is based on the original volume of the involved reactants, which likely occupy only a small to modest fraction of the total volume of the soil; for example, even a sulfate content as high as 10,000 ppm (widely considered as high to unacceptable risk in engineering practice) represents only 1% mass content of soil; even with the 137% volume expansion for ettringite formation as discussed, it is difficult to conceive that such a small amount of sulfate can lead to 10∼20% swelling strains as routinely reported.…”

“…Experimental investigations by Abdi and Wild [1] and Wild et al [12] indicated that the primary mechanism in sulfate-bearing lime-stabilized clays might be the imbibition of water by osmosis, rather than the direct formation of solid reaction products. Little and co-workers [13,14] suggested that the overall swelling and distress associated with sulfate-induced heaving in lime-treated clay was caused by a synergy of multiple mechanisms, including the formation of ettringite, water absorption of formed ettringite, and osmosis-induced swelling of clay minerals.…”