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This paper reports the influence of delay time on the index and engineering properties of geopolymer-, cement-, and lime-treated expansive soil. Locally available expansive soil was treated with different doses of slag-based geopolymer, cement, and lime. The index and engineering properties like Atterberg's limits, free swell index, grain-size distribution, compaction properties, and unconfined compressive strength (UCS) were evaluated at delay periods of 0, 6, 12, 24, 48, 72, and 168 h. Further, the mineralogical characteristics and microstructure of the stabilized materials were examined using X-ray diffraction (XRD) and scanning electron microscopic (SEM) images. It was observed that with an increase in delay time, the plasticity and swelling characteristics of the treated soil reduced with improvement in the soil grain size along with the formation of hydration and geopolymeric compounds. The delay in compaction results in the decline of the compacted density and UCS. The formation of hydrated products and flocs during the delay period caused loose packing under dynamic loading and affects the mechanical properties. A significant improvement in plasticity and engineering properties of the expansive soil was observed with geopolymer stabilizers. Thus, it is noteworthy to consider geopolymers as a new generation eco-friendly stabilizer for treating expansive clays for geotechnical constructions. [ABSTRACT FROM AUTHOR]

Granular soils are sensitive to internal erosion due to the presence of lesser fines and need to be stabilized to improve their geoengineering properties. An investigation is made to explore the efficacy of fly ash-slag (FA-GGBS) geopolymer in stabilizing granular soil through a set of experimental studies. The experimental program focused on compaction characteristics, unconfined compressive strength, bearing resistance, and durability of geopolymer stabilized granular soil to assess its suitability as a construction material. Microstructural analysis has been carried out and correlated with strength development. Based on the test results, a maximum unconfined compressive strength of about 7 MPa and California bearing ratio (CBR) ranging from 52% to 416% is obtained. The geopolymer stabilized soil showed excellent stability against wetting–drying and freezing–thawing cycles, slaking water, and aggressive chemical environments. The microstructural developments are greatly influenced by the geopolymer content and curing period, indicating the formation of hydration and geopolymeric reaction products. [ABSTRACT FROM AUTHOR]

Characterization of pond ash-bentonite mixes is made to assess their suitability as liner material for waste disposal facilities by examining the relevant index and engineering properties. Further, a comparative assessment is made between sand-bentonite and pond ash-bentonite mixes for the range of bentonite content varying from 0 to 30% by weight at an interval of 5% to ensure an effective substitution of sand with pond ash. Addition of bentonite to sand or pond ash significantly influences the plasticity, strength and permeability properties. Besides, the shape parameters of the coarser fraction and morphology of compacted mixes also influence the engineering properties. A multiple linear regression equation is suggested to predict the hydraulic conductivity of these mixes by considering the basic material properties such as liquid limit, plasticity index and void ratio as an input variable with a correlation coefficient of 0.92 between the measured and predicted hydraulic conductivity values. At comparable conditions, compacted pond ash-bentonite mixes exhibit higher strength but also higher permeability than sand-bentonite mixes. Pond ash-bentonite and sand-bentonite mixes met the liner requirements when compacted with modified Proctor compaction effort at a minimum bentonite content of 20% and 15%, respectively. [ABSTRACT FROM AUTHOR]

This paper presents the effectiveness of xanthan gum (XG) biopolymer in stabilising the expansive soil. The XG biopolymer is mixed with expansive soil in different proportions such as 0%, 0.2%, 0.5%, 0.8% and 1.0% by weight of the dry soil mass. The plasticity, compaction, swelling, compressibility, hydraulic conductivity, strength and durability characteristics of the treated and un-treated expansive soil are examined. Results show that the plasticity index of the treated soil mass initially increases but beyond 0.5% biopolymer addition it decreases sharply. The optimum moisture content and maximum dry density of treated soil, found out from light and heavy compaction tests, do not follow any definite trend. It is also found that increasing XG content increases compressibility slightly but, it reduces swelling pressure, differential free swelling value and hydraulic conductivity remarkably. On the other hand, time-dependent compressive strength and resistance to mass loss increases with increasing XG content. Microscopic examination confirms the formation of gel-like linkage, which brings about the modifications in the treated expansive soil. [ABSTRACT FROM AUTHOR]

This paper reports the strength and compressibility properties of sedimented ash beds treated with chemical columns. Sedimented model ash beds were prepared by simulating the natural sedimentation process in a laboratory environment and allowing them to undergo consolidation under the self-weight for a period of 30 days. Then, the ash beds were treated with three different configured chemical columns of sodium hydroxide (NaOH) with a concentration of 18 M for 60 days. After the 60 days of treatment, the in-situ dry unit weight, moisture content, bearing resistance, collapse potential, compressibility properties, and pore structure at different locations of the treated ash beds were examined. The contours of the bearing resistance were found to be bell-shaped with larger spreading towards the bottom end of the columns. The magnitude of the strength development was found to diminish rapidly with an increase in the radial distance from the column surface. After 60 days, the void ratio and collapse potential values in the column's peripheral region of the ash beds treated with full, ½, and 1/4 columns were found to be 0.89, 0.93, and 0.95 and 0.75%, 0.89%, and 0.97%, respectively, compared to 1.64 and 7.46% of an untreated ash bed. These changes were attributed to the development and distribution of reaction products, which are functions of the column configuration and sampling location. The void ratio gradually increased with an increase in the radial distance from the chemical column. The decrease in void ratio was attributed to the blockage of the capillary pores by the reaction products. Primarily sodium- and calcium-based reaction products were observed along with hybrid compounds of sodium-calcium-based alumino-silicates. These reaction products encapsulated the ash particles within the matrix structure, thus modifying the bearing resistance, collapse potential, and compressibility properties of the sedimented ash beds. The morphology of the stabilized ash specimens showed a mixture of partially reacted ash particles, semi-crystalline structures, and reacted gel phase as the geopolymerization products. [ABSTRACT FROM AUTHOR]

The paper delineates the effect of mineral admixtures on the strength and hydration products of lime-activated slag cement. The slag cement was prepared by activating ground granulated blast-furnace slag with lime and plaster of Paris. The compressive strength of mortar specimens made with admixtures such as silica fume, fly ash, glass powder and ordinary Portland cement (OPC) in different proportions were compared with the control specimen at similar test conditions. X-ray diffraction, scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry and porosity tests were performed to examine the hydration products and/or the microstructure. A correlation was established between the developmental strength with the type of mineral admixture through analysis of the hydration products and microstructure. For the present test variables silica fume was found to be a better admixture compared to fly ash, glass powder and OPC. [ABSTRACT FROM AUTHOR]