Coupled thermodynamic and experimental approach to evaluate ettringite formation in a soil stabilized with fluidized bed ash by-product: A case study

Akula, Pavan; Little, Dallas N.

doi:10.1016/j.trgeo.2020.100352

Cited by 12 publications

(6 citation statements)

References 44 publications

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“…The lower expansion behavior in the mixtures containing additional fly ash may be attributed to the pozzolanic reaction between free calcium, amorphous silica, and alumina which are provided by both soil and fly ash. The calcium silicate hydrate (C-S-H) or calcium silicate aluminate hydrate (C-S-A-H) gel obtained from hydration and pozzolanic reaction can bind soil particles together, therefore reducing the expansion of soil mixture (27,28).…”

Section: -D Swelling Testmentioning

confidence: 99%

Characterization of Mellowing Process to Control Expansion in High-Sulfate-Bearing Soil

Shon

Scullion

Blackmon

et al. 2021

Transportation Research Record: Journal of the Transportation R

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Calcium-based stabilizing materials (CBSMs) such as lime and fly ash are extensively used in subgrade primarily to enhance mechanical strength and improve resistance to chemical attack, resulting in more durable roadway. The soluble sulfate phase contained in some soils, however, can react with CBSMs and form ettringite minerals. If the soil is compacted before the end of this reaction, large, unstable, and volumetric swelling can occur. Among several methods to control sulfate-induced swelling, a “mellowing” approach is typically used because of its efficient, economical, and practical benefits when dealing with calcium-based stabilization of soils with significant soluble sulfate contents. Although the mellowing method is one of the frequently used methods, little data is available on the characterization of the specified mellowing process in the high-sulfate-bearing soil during the mellowing period. A research program investigated key factors influencing the mellowing process during the mellowing period, explaining how stabilizer type and content, remixing interval, mellowing period, and temperature play a role in reducing soluble sulfate content. Moreover, for selected mixtures, the 3-dimensional volumetric expansion and retained strength were measured after the mellowing process. Laboratory test results have revealed that a single mellowing process with higher lime content and daily remixing at high temperature leads to the rapid reduction of sulfate content in the soil. Moreover, after the mellowing process, additional soil treatment with fly ash or a combination of lime and fly ash leads to lower expansion and higher retained unconfined compressive strength of the soil mixture.

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Section: -D Swelling Testmentioning

confidence: 99%

Characterization of Mellowing Process to Control Expansion in High-Sulfate-Bearing Soil

Shon

Scullion

Blackmon

et al. 2021

Transportation Research Record: Journal of the Transportation R

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“…The admixtures for cement-stabilized soils are generally categorized as either mineral or chemical admixtures [5]. Fly ash [6], slag [7,8] and silica fume [9] are the typical mineral admixtures and their modification effects and corresponding mechanisms have long been investigated and are well clarified. Regarding chemical admixtures, one common type comprises the alkaline activators R 2 O-SiO 2 , ROH, R 2 SO 4 , R 2 CO 3 (R = K or Na or 0.5 Ca) and combinations of these [3,[10][11][12].…”

Section: Introductionmentioning

confidence: 99%

An Investigation on Mineral Dissolution and Precipitation in Cement-Stabilized Soils: Thermodynamic Modeling and Experimental Analysis

Hua

et al. 2022

Applied Sciences

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Thermodynamic modeling helps to reveal insights into the basic chemical kinetics of dissolution and precipitation in cementitious materials, but relevant applications to cement-stabilized soils have seldom been reported. Based on the thermodynamic database of Cemdata18 and the pore solution composition of cement-stabilized soils, this study formulated a specialized thermodynamic model, using essential thermodynamic constants for soil minerals that were calculated to ensure the model’s accuracy. Two commercial admixtures of alkaline activator and polynaphthalene sulfonate were selected for the different modification mechanisms and plain and modified cement-stabilized soils were prepared. Compressive strength was tested to determine the specimens for pore solution analysis and the influences of the admixture type and dose on dissolution and precipitation were investigated by modeling the ionic activity products and saturation indexes. An X-ray diffraction (XRD) analysis was performed to verify and complement the thermodynamic results. The major research findings were that (1) thermodynamic modeling can be reliably applied to cement-stabilized soils by providing the essential thermodynamic data and an appropriate product model, (2) the pozzolanic reaction is accelerated by increasing the OH− concentration in the pore solution, while the cement hydration is highly dependent on the dissolution of Ca(OH)2 and the relevant complexes and (3) the dissolution equilibrium of Ca(OH)2 is directly affected by the alkaline activator dissolution and is indirectly affected by the polynaphthalene sulfonate adsorption of the reactants.

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“…Clay releases ammonia at pH values > 10.5 and this ammonia interacts with Ca 2+ (contained in lime or cement), soil sulphate ions, and available soil water to form calcium silicate trisulphate hydrate (ettringite) [ 11 , 14 , 15 , 16 ]. This ettringite can be converted to calcium-silicate-hydroxide-sulphate-carbonate-hydrated material (thaumasite) at temperatures < 15 °C [ 17 , 18 , 19 ]. The reaction of sulphate-rich soil with calcium-based soil stabilizers is explained in Figure 1 .…”

Section: Introductionmentioning

confidence: 99%

Novel Approach to the Treatment of Gypseous Soil-Induced Ettringite Using Blends of Non-Calcium-Based Stabilizer, Ground Granulated Blast-Furnace Slag, and Metakaolin

2021

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Gypseous soil is one type of expansive soil that contains a sufficient amount of sulphate. Cement and lime are the most common methods of stabilizing expansive soil, but the problem is that lime-treated gypseous soil normally fails in terms of durability due to the formation of ettringite, a highly deleterious compound. Moisture ingress causes a significant swelling of ettringite crystals, thereby causing considerable damage to structures and pavements. This study investigated the suitability of various materials (nano–Mg oxide (M), metakaolin (MK), and ground granulated blast-furnace slag (GGBS)) for the stabilization of gypseous soil. The results showed soil samples treated with 20% M-MK, M-GGBS, and M-GGBS-MK to exhibit lower swelling rates (<0.01% change in volume) compared to those treated with 10% and 20% of lime after 90 days of curing. However, soil samples stabilized with 10% and 20% binder of [(M-MK), (M-GGBS), and (M-GGBS-MK)] exhibited higher strengths after 90 days of soaking (ranging from 0.96–12.8 MPa) compared to those stabilized with 10% and 20% lime. From the morphology studies, the SEM and EDX analysis evidenced no formation of ettringite in the samples stabilized with M-MK-, M-GGBS-, and M-GGBS-MK. These results demonstrate the suitability of M-MK, M-GGBS, and M-GGBS-MK as effective agents for the stabilization of gypseous soil.

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Coupled thermodynamic and experimental approach to evaluate ettringite formation in a soil stabilized with fluidized bed ash by-product: A case study

Cited by 12 publications

References 44 publications

Characterization of Mellowing Process to Control Expansion in High-Sulfate-Bearing Soil

Characterization of Mellowing Process to Control Expansion in High-Sulfate-Bearing Soil

An Investigation on Mineral Dissolution and Precipitation in Cement-Stabilized Soils: Thermodynamic Modeling and Experimental Analysis

Novel Approach to the Treatment of Gypseous Soil-Induced Ettringite Using Blends of Non-Calcium-Based Stabilizer, Ground Granulated Blast-Furnace Slag, and Metakaolin

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