Understanding the Impact of Lime Stabilization on Expansive Soil for Grounding and Analysis Adopting LIBS
Stabilization of soil for grounding purposes has been performed by adding different wt% of lime. Electrical breakdown measurements under lightning impulse voltage showed a reduction in breakdown voltage and the time to breakdown with increment in the lime content in the soil. These parameters also increased with curing period for all concentrations of lime of stabilized soil samples. The results show that pH and electrical conductivity of the expansive soil increase as the lime content increases, but decrease with increasing the curing period. Mineralogical and micro-structural analysis has been made by means of X-ray diffraction (XRD) studies and by scanning electron microscope (SEM) analysis. The axial strength obtained from unconfined compressive strength (UCS) analysis, the plasma temperature and the electron number density calculated from Laser Induced Breakdown Spectroscopy (LIBS) data tend to increase with increment in lime content as well as the curing period of the lime stabilized soil. Using univariate analysis, the normalized intensity ratio of Ca II peaks from LIBS spectral data are correlated with lime content in the soil samples at various curing periods. The partial least squares regression (PLSR) technique is successful in determining the soil parameters with the help of LIBS spectral data, at different curing periods with an R2 value greater than 0.95 and the percentage RMSE value smaller than 4%.
Sulfate Effects on Lime and Sulfate-Resistant Cement-Stabilized Expansive Soil
It is well demonstrated in the past that the lime or sulfate-resistant cement effectively controls the volume change and increases the strength of stabilized expansive soil due to both soil modification and pozzolanic reactions. Also, the rapid industrialization has increased the chances of contamination of stabilized soils with sulfate which significantly deteriorates the stabilized soil. Therefore, the effect of sodium sulfate intrusion into the lime and sulfate-resistant cement-stabilized soil on the volume change and strength behavior is brought out in this study. To achieve this objective, the expansive soil was stabilized with lime and sulfate-resistant cement and cured for 1, 7, and 28 days. Upon completion of the required curing period, the stabilized soils were contaminated with sulfate solutions of 5,000, 10,000, and 20,000 ppm for a period of 30 days before evaluating the volume change and strength properties. The current study reveals that the performance of the sulfate-resistant cement-stabilized specimens cured for long periods (28 days) was better than the lime-stabilized expansive soil in terms of the strength.
Sulfate effects on sulfate-resistant cement–treated expansive soil
Even though the effectiveness of sulfate-resistant cement (SRC) in stabilizing the high sulfate-bearing expansive soils is proven, its effectiveness in controlling the volume change of expansive soils when exposed to external sulfate contaminants is not known. The physico-chemical and index properties provide basic insight into the volume change behavior of clays. Therefore, this study brings out the effect of external sulfate contamination on the physico-chemical and index properties of SRC-treated expansive soil. Three SRC contents of 5, 10, and 15% were added to the expansive soil separately and reconstituted with distilled water and cured for 1–28 days. After the desired curing period, the SRC-treated expansive soil was reconstituted with sulfate solutions of 5000, 10,000, and 20,000 ppm separately and moisture equilibrated for 1 day for the determination of the properties. The experimental results showed that the SRC treatment increased the pH from 8.75 to 11.95–12.21 and the subsequent sulfate contamination decreased the pH to 9.33–11, where the decalcification of calcium silicate hydrate occurred. Further, the effect of sulfate contamination on liquid limit of SRC-treated soil was negligible, while the plastic and shrinkage limits increased upon sulfate contamination. The increase in the shrinkage limit is attributed to the formation of ettringite/thaumasite in the voids of SRC-treated samples contaminated with 10,000–20,000 ppm sulfate solutions, whereas the monosulfate formation and destruction of cementation gels occurred in samples contaminated with 5000 ppm. These formations are evidenced with the scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction.
Effect of compaction time delay on compaction and strength behavior of lime-treated expansive soil contacted with sulfate
Application of lime as an additive for controlling the volume change behavior and improving the strength of expansive soils has been in use over several decades. However, the contamination of lime-treated expansive soil with sulfate always results in the deterioration of treated expansive soil. Therefore, this paper highlights the effect of sodium sulfate solution on compaction and strength behavior of lime-treated expansive soil. Further, the effect of compaction time delay and contact period of sulfate solution with lime-treated soil is also brought out in this paper. To bring out the above effects, the lime contents corresponding to the initial consumption of lime (ICL) and ICL ± 1% were used along with sulfate solutions of 5000, 10,000 and 20,000 ppm. The experimental study showed that upon mixing the lime-treated expansive soil with sulfate solutions, the maximum dry unit weight decreased and optimum moisture content increased with increase in concentration of sulfate solutions when compacted without any compaction delay. With compaction time delay, the lime-stabilized soils mixed with distilled water led to the formation of flocs and aggregation of clay particles and decreased the maximum dry unit weight and optimum moisture content. However, the effect of compaction time delay was negligible on maximum dry unit weight as the formation of flocs and aggregation of clay particles were inhibited in lime-treated soil mixed with sulfate solutions. These changes in dry unit weights and soil structure were reflected on the strength of lime-treated expansive soil as well.
Effect of Sulfate Contamination on Compaction and Strength Behavior of Lime Treated Expansive Soil
Lime is the most commonly used chemical admixture for the treatment of the expansive soils. But the intrusion of sulfate contaminant into the lime treated soil will always results in deterioration of the treated soil. The intrusion of sulfate occurs through acid rains, effluent from tannery industries or mine wastes, intrusion of sea water, construction waste, intrusion of leachate from solid waste fills and sulphate rich groundwater. Therefore, this paper aims at bringing out the effect of sodium sulfate (Na2SO4) solution on the compaction and strength behavior of the lime treated expansive soil. Further, the effect of compaction delay and curing period on the sulfate contaminated lime treated soil is also brought out in this paper. Lime contents of 2.5 (initial consumption of lime (ICL) −1%), 3.5 (ICL) and 4.5% (ICL +1%) were used in this study. The sulfate contamination was limited to 5000, 10000 and 20000 ppm. The experimental results showed that the sulfate contamination decreased the maximum dry density and optimum moisture content of the lime treated expansive soil. Further, the intrusion of sulfate solution into the lime treated expansive soil decreased the strength of the lime treated expansive soil.