Sulfate-bearing Soils Research Articles

Effect of sulfate types on strength and swelling properties of sulfate-bearing soils stabilized with cement

Effect of sulfate types on strength and swelling properties of sulfate-bearing soils stabilized with cement

Dynamic Mechanical Performance of Sulfate-Bearing Soils Stabilized by Magnesia-Ground Granulated Blast Furnace Slag

Sulfate soils often caused foundation settlement, uneven deformation, and ground cracking. The distribution of sulfate-bearing soil is extensive, and effective stabilization of sulfate-bearing soil could potentially exert a profound influence on environmental protection. Ground granulated blast furnace slag (GGBS)–magnesia (MgO) can be an effective solution to stabilize sulfate soils. Dynamic cyclic loading can be used to simulate moving vehicles applied on subgrade soils, but studies on the dynamic mechanical properties of sulfate-bearing soil under cyclic loading are limited. In this study, GGBS-MgO was used to treat Ca-sulfate soil and Mg-sulfate soil. The swelling of the specimens was analyzed by a three-dimensional swelling test, and the change in compressive strength of the specimens after immersion was analyzed by an unconfined test. The dynamic elastic properties and energy dissipation of GGBS-MgO-stabilized sulfate soils were evaluated using a fatigue test, and the mineralogy and microstructure of the stabilized soils were investigated by X-ray diffraction and scanning electron microscopy. The results showed that the maximum swelling percentage of stabilized Ca-sulfate soil was achieved when the GGBS:MgO ratio was 6:4, resulting in an expansion rate of 14.211%. In contrast, stabilized Mg-sulfate soil exhibited maximum swelling at GGBS:MgO = 9:1, with a swelling percentage of 5.127%. As the GGBS:MgO ratio decreased, the dynamic elastic modulus of stabilized Ca-sulfate soil diminished from 2.8 MPa to 2.69 MPa, and energy dissipation reduced from 0.02 MJ/m3 to 0.019 MJ/m3. Conversely, the dynamic elastic modulus of stabilized Mg-sulfate soil escalated from 2.16 MPa to 6.12 MPa, while energy dissipation decreased from 0.023 MJ/m3 to 0.004 MJ/m3. After soaking, the dynamic elastic modulus of Ca-sulfate soil peaked (4.01 MPa) and energy dissipation was at its lowest (0.012 MJ/m3) at GGBS:MgO = 9:1. However, stabilized Mg-sulfate soil exhibited superior performance at GGBS:MgO = 6:4, with a dynamic elastic modulus of 0.74 MPa and energy dissipation of 0.05 MJ/m3. CSH increased significantly in the Ca-sulfate soil treated with GGBS-MgO. The generation of ettringite increased with the decrease in the GGBS-MgO ratio after immersion. MSH and less CSH were formed in GGBS-MgO-stabilized Mg-sulfate soil compared to Ca-sulfate soils. In summary, the results of this study provide some references for the improvement and application of sulfate soil in the field of road subgrade.

Micro-mechanical behavior of nanosilica-treated high-sulfate soils

The addition of calcium (Ca)-based stabilizers to sulfate-rich expansive soils is associated with the formation of ettringite, a deleterious reactant that can cause moderate-to-severe swell-related damage to overlying lightweight infrastructures. This research study was conducted to understand the effects of combining nanosilica admixtures with a traditional Ca-based stabilizer to effectively treat high-sulfate soils with an intent to suppress the ettringite formation. Engineering and microstructural studies were thus performed to gain a comprehensive understanding of the behavior of sulfate-bearing soils treated with lime in the presence of amorphous nanosilica. The engineering studies on treated and untreated soils included strength tests before and after capillary soaking, free swell strain tests, and resilient moduli studies that were performed to study and understand the macrostructural behavior of these soils at different curing periods. Supplemental studies using scanning electron microscope imaging and energy dispersive X-ray spectroscopy, thermal analyses using differential scanning calorimetry, and X-ray diffraction studies were also conducted to determine the microstructural changes that occur within these sulfate-rich soils. The results showed that additional silica phases furnished from nanosilica suppressed the precipitation of ettringite and correspondingly increased the formation of cementitious phases. This study also provided ample evidence that the application of amorphous siliceous nanomaterials positively impacts chemical treatments and reduces the precipitation of ettringite in sulfate-rich soils, thus enhancing their engineering performance.

Treating sulfate-bearing soil by using sodium silicate and NaOH-activated ground granulated blast-furnace slag

Treating sulfate-bearing soil by using sodium silicate and NaOH-activated ground granulated blast-furnace slag

Behavior of Natural Pozzolana-Lime-stabilized Clayey Soils Artificially Contaminated by Sulfates

The use of lime in sulfate-bearing clayey soils has historically caused structural damage to infrastructures due to the formation of an expansive ettringite mineral. In this paper, a research was conducted to study the effectiveness of natural pozzolana (NP) for providing better stabilization of sulfate-bearing soils. Compaction and free-swell potential tests were first performed on lime-stabilized grey and red clayey soils (GS and RS) containing different contents of added sodium and calcium sulfates (2, 4 and 6% Na2SO4 or CaSO4·2H2O). Then, the same tests were repeated by adding 20%NP. The test results indicated that the presence of 4% and 6% Na2SO4 in the soil resulted in an abnormal increase in the swell potential of both lime-stabilized GS and RS. The X-ray diffraction (XRD) results confirmed the growth of the ettringite mineral responsible for this higher swell potential. However, the use of 8% lime with 20%NP in stabilizing sulfate-bearing clayey soils produced significant improvements in the optimum moisture content (OMC) and maximum dry density (MDD), as well as in the swell potential. The addition of 20%NP into the lime-stabilized GS and RS eliminated the harmful effect of Na2SO4. In addition, for 120-day curing period, the use of 6% CaSO4·2H2O was found very effective by reducing the swell potential of NP-lime-stabilized GS and RS from 7.33% to 0.4% and from 2.79% to 0.2%, respectively trips. KEYWORDS: Clayey soils, Mineral additives, Sulfates, Compaction, Swell potential, Stabilization.

Swelling of sulfate-bearing soil: A case study of A1 highway pavement failure

Lime stabilization is one of the most commonly used methods for improving weak road subgrades, but it becomes very problematic in sulfate-bearing soils. This article presents results of a case study in which the sulfate attack was the most probable reason for a significant deformation of a highway pavement founded on lime-stabilized Doggerian clay. Macroscopic analysis revealed partial degradation of the concrete structure, a larger extent of stabilization than designed, and large gypsum crystals in the native soil. Chemical tests indicated a very high content of sulfates in the soil (> 10,000 mg/kg of SO4) and in the groundwater (> 3,000 mg/l of SO42-). The maximum free swelling strain (εvolmax = 3–6%) and the swelling pressure (pcmax = 56 kPa) of the clay, determined in the Wasiliew apparatus and the oedometer tests, were not large enough to be considered as the only cause of the pavement damage. Sand-cement and clay-lime mixtures, which simulated stabilized soil layers in the road profile, were observed for several months in oedometric tests, under various loading conditions. The swelling of Sa-Cem was negligible, but the Cl-Lim mixtures turned out to be much more expansive than the natural soil (εvolmax up to 21%, pcmax = 230 kPa) with a much longer duration of volume increase. The samples were flooded with distilled water or hard groundwater to clarify whether the constant access of the material to sulfates is important in the swelling process, but the results were unequivocal. X-ray diffraction revealed that the addition of lime resulted in the formation of secondary minerals: butlerite, portlandite, and ettringite. The presence and swelling of ettringite in the stabilized sub-base soil layers was eventually agreed to be the most probable reason for the pavement deformation. These results indicate the need to introduce an obligatory investigation of the level of sulfates in clayey subbase soils subject to lime stabilization.

An assessment of different alkali-activated cements as stabilizers of sulfate-bearing soils

The stabilization of sulfate-bearing soils with traditional calcium-based stabilizers is not recommended, as reactions between the calcium and sulfates in the presence of water could lead to soil heave. Alternative stabilization methods are therefore required, and this paper proposes innovative alkali-activated cements (AACs), whose use for soil stabilization and especially sulfate-bearing soils is little researched. To fill this knowledge gap, AAC systems with a ground granulated blast-furnace slag precursor and different alkaline activators, including commercial lime, wastepaper sludge ash (PSA), potassium hydroxide (KOH) and potassium carbonate (K 2 CO 3 ), were used to treat an artificial sulfate-bearing clay. AAC-treated clay specimens cured for 7 and 28 days, respectively, were soaked in water for 45 days; their one-dimensional swelling, unconfined compressive strength (UCS), pH and ultrasonic pulse velocity (UPV) were measured and compared to those of specimens not exposed to water. Material characterization (scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR)) was performed to attest cementation and detect ettringite. In AAC systems, CaO/Ca(OH) 2 did not lead to specimen heave and damage, and developed the highest strengths. Potassium-based activators performed less well but combined PSA–K 2 CO 3 in time led to strength gain. Overall, AACs lead to greater strengths than lime only or lime and admixtures, and show promise as sulfate-bearing soil stabilizers. Thematic collection: This article is part of the Leading to Innovative Engineering Geology Practices collection available at: https://www.lyellcollection.org/topic/collections/leading-to-innovative-engineering-geology-practices

Comparison of Two Sulfate-Bearing Soils Stabilized with Reactive Magnesia-Activated Ground Granulated Blast Furnace Slag: Swelling, Strength, and Mechanism

Sulfate-bearing soils, which causes many engineering problems, e.g., cracking, collapse, and pavement layer settlement, are often encountered in the construction of pavements. Ground granulated blast furnace slag (GGBS)-magnesia (MgO) has been regarded as an effective curing agent in the treatment of sulfate-bearing soil containing gypsum. However, field sulfate-bearing soils usually include other forms of sulfates, such as sodium sulfate (Na2SO4) and magnesium sulfate (MgSO4). Currently, few studies have investigated the effect of the type of sulfate on the properties of sulfate-bearing soil stabilized with GGBS-MgO. In this study, GGBS-MgO was used to treat Ca-sulfate-soil and Mg-sulfate-soil. Swelling, unconfined compressive strength (UCS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) tests were employed to investigate the properties of the stabilized soils. The results showed that when suitable GGBS:MgO ratios were achieved, the swelling of the two types of sulfate-bearing soils could be well suppressed. However, the trend that the swelling varied with the decrease in the GGBS:MgO ratios was opposite between the two soils. The UCS of Mg-sulfate-soils was much lower than that of the Ca-sulfate-soils after the stabilization of GGBS-MgO irrespective of the curing or soaking stage. CSH significantly occurred in Ca-sulfated soils treated by GGBS-MgO. Ettringite was not observed in the soil with GGBS-MgO = 9:1 but was observed in 6:4. Compared to Ca-sulfate-soils, MSH and less CSH were formed in Mg-sulfate-soils stabilized with GGBS-MgO, which caused the lower strength of the stabilized Mg-sulfate-soils. No ettringite was formed in such soils. Hence, the sulfate type contained in the soils had a significant effect on the swelling and strength properties of sulfate-bearing soils with GGBS-MgO, and so the sulfate needs to be identified before the soil’s stabilization.

Ettringite Formation and Stabilization Methods of Sulfate-Bearing Soil: A State-of-the-Art Review

Ettringite Formation and Stabilization Methods of Sulfate-Bearing Soil: A State-of-the-Art Review

High Sulfate-Bearing Kaolin Clay Stabilization with Waste Glass Powder before and after Mellowing Process

Road construction on sulfate-bearing soils is a worldwide concern because it is associated with a volume swelling stability issue due to the ettringite formation. Several treatment techniques were developed to solve this problem and improve geotechnical soil properties, including using pozzolanic materials and applying the mellowing process. This research evaluated the combined effect of cement and waste glass powder (WGP) on stabilizing sulfate-bearing soil before and after the mellowing procedure. Total six mixtures were developed, which includes 4% cement, 4% cement + 2% WGP, and 4% cement + 6% WGP before and after soil mellowing. The experimental program included particle size distribution of soil and stabilizers, chemical analyses of stabilizers, soil properties, unconfined compressive strength, and three-dimensional (3-D) swelling for the high sulfate-bearing kaolin clay. The test results demonstrated that the use of WGP in soil with a high sulfate content WGP improved strength development, decreased volumetric swelling, and reduced moisture susceptibility.

Performance of repaired concrete piles partially embedded in Sulfate-Bearing soil

Physical salt attack (PSA) is a key damage mechanism of concrete in salt-bearing environments. Multiple case studies were reported throughout literature on PSA of concrete; yet, without any case on the performance of repaired concrete elements. The current paper presents a case study analyzing the condition of repaired concrete piles in 47-year-old administrative building in Winnipeg, MB, Canada, after 22 years from repair works. Deterioration of the concrete piles was visually observed above the ground level and repair zones, in the form of scaling, crumbling and reduction of cross section. In addition to fluid transport and pore structural features tests, mineralogical, thermal and microscopy analyses were performed on concrete chunks/cores extracted from the piles to elucidate the underlying mechanisms of damage. The repair concrete was capable of mitigating chemical and physical sulfate attacks; however, it could not stop the progress of PSA on the concrete above it, urging for careful design of repair strategies for elements subjected to PSA. Recommendations for future repair in this case are also presented.

Suppression of Sulfate-Induced Expansion with Lime-Silica Fume Blends.

Sulfate-induced expansion resulting from the formation of ettringite in sulfate-bearing soil stabilised with calcium-based stabilisers is a problematic issue with technical and economic implications. Thus, this research examines the viability of the co-addition of lime (L) and silica fume (S) at varying binder dosages (4, 6, and 10 wt%), with a view of establishing the optimum blend of L–S for suppressing the ettringite-induced expansion of artificially high sulfate-dosed soil (kaolinite-K and gypsum-G). To do so, a series of laboratory specimens, designed using different gypsum and lime concentrations, were investigated using unconfined compression strength (UCS), linear expansion, and derivative thermo-gravimetric analysis (DTG) as the main criteria for the examination. The research outcomes indicated that the increasing substitution of L with S induces a gradual reduction on the UCS and linear expansion at binder levels of 4 and 6 wt%, while its usage in a high binder level (10 wt%), can yield an expansion reduction, with no compromise on the UCS performance. Therefore, silica fume has the potential for restricting ettringite formation and suppressing the expansion, of which 3L7S is the optimum blending ratio for suppressing the expansion.

Utilization of Blast-Furnace Slag as a Standalone Stabilizer for High Sulfate-Bearing Soils

This paper presents experimental results and analysis of sulfate-bearing soils treated with ground granulated blast-furnace slag (GGBS). The experiments involve the unconfined compression strength test, shrinkage, free swelling, suction measurements, and microstructural examination. Short- and long-term swelling tests were conducted to inspect the durability of GGBS stabilization against the sulfate-induced heave. The concept of the shrinkage curve was employed to elucidate how GGBS stabilization alleviates soil shrinkage behavior and alters the pore size distribution. The results manifested that 7% GGBS was sufficiently adequate to improve the 28-day strength of the tested sulfate-bearing soils about five times. The GGBS treatment mainly results in the decline of calcium sulfate content and the formation of calcium silicate hydrate, ettringite, and calcite. The results of long-term swelling tests indicated a delayed sulfate-induced heave that started beyond a month from the time of exposing the treated soils to water. The delayed heave was still not significant as compared with that of the untreated control soil specimens. Accordingly, it is recommended that the treated sulfate-bearing soils are tested with the selected GGBS content for any delayed swelling before application in the field. The GGBS treatment has significantly escalated suction magnitude during curing mainly due to the consumption of water in the hydration process and the formation of ettringite.

Novel Approach for Suppression of Ettringite Formation in Sulfate-Bearing Soil Using Blends of Nano-Magnesium Oxide, Ground Granulated Blast-Furnace Slag and Rice Husk Ash

The treatment of sulfate-bearing soil with calcium-based stabilizers such as cement or lime often results in ettringite formation, consequently leading to swelling and strength deterioration. Ettringite formation has negative environmental and economic effects on various civil engineering structures. This study was conducted to investigate the use of different materials (nano–magnesium oxide (M), ground granulated blast-furnace slag (GGBS), and rice husk ash (RHA)) for gypseous soil stabilization to prevent ettringite formation. Various tests were performed, including flexural strength, unconfined compression strength, linear expansion, and microstructure analysis (SEM/EDX), on lime (L)-, (M)-, (M-RHA)-, (M-GGBS)-, and (M-GGBS-RHA)-stabilized gypseous soil samples to determine their properties. The results indicated that the swelling rates of the soil samples mixed with 20% M-RHA, M-GGBS, and M-GGBS-RHA binders were much lower (less than 0.01% of volume change) than those of the soil samples mixed with 10% and 20% lime-stabilized binders after a curing period of 90 days. Meanwhile, the strengths of the soil samples mixed with 20% of M-RHA, M-GGBS, and M-GGBS-RHA soil specimens after soaking of 90 days were obviously higher (with a range from 2.7–12.8 MPa) than those of the soil samples mixed with 20% of lime-stabilized binder. The SEM and EDX results showed no ettringite formation in the M-RHA-, M-GGBS-, and M-GGBS-RHA-stabilized soils. Overall, the test results proved the potential of M-RHA, M-GGBS, and M-GGBS-RHA as effective soil stabilizers.

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

Expansive sulfate-bearing soils are frequently encountered in transportation and construction practices. These soils are often treated with a lime or cement stabilizer to improve the relevant qualities. However, the reaction between sulfate and alumina in soils and calcium of lime or cement can lead to the formation of ettringite, an expansive sulfate mineral resulting in soil swelling or heaving. The underlying mechanisms often involve intricate interactions between chemical processes and mechanical responses. The present study explores a chemo–mechanical approach in an attempt to quantify several mechanisms potentially responsible for the volume expansion, including the geochemical formation of ettringite, crystallization pressure, and osmosis-induced swelling. The geochemical reaction leading to ettringite formation is examined with a specific focus on the circumstances under which it may lead to volume change. The crystallization pressure developed during the ettringite formation may also play a significant role in the soil expansion and is investigated in the present study based on thermodynamic formulations, and the resulting volume expansion is simulated. The osmosis-induced swelling is studied within the context of the chemo–mechanical framework, and its kinetics is also explored. Numerical simulations are performed in the present study to examine different scenarios driven by distinct predominant mechanisms. In particular, the interplay between ettringite formation and osmosis swelling as interpreted from some recently-reported experimental studies shows that these mechanisms can all contribute to the observed expansion processes, and overall, the modeling results are consistent with the experimental findings.

Alkali-activated GGBS and enzyme on the swelling properties of sulfate bearing soil

Use of cement in stabilizing the sulfate-bearing clay soils forms ettringite/ thaumasite in the presence of moisture leads to excessive swelling and causes damages to structures built on them. The development and use of non-traditional stabilisers such as alkali activated ground granulated blast-furnace slag (AGGBS) and enzyme for soil stabilisation is recommended because of its lower cost and the non detrimental effects on the environment. The objective of the study is to investigate the effectiveness of AGGBS and enzyme on improving the volume change properties of sulfate bearing soil as compared to ordinary Portland cement (OPC). The soil for present study has been collected from Tilda, Chhattisgarh, India and 5000 ppm of sodium sulfate has been added. Various dosages of the selected stabilizers have been used and the effect on plasticity index, differential swell index and swelling pressure has been evaluated. XRD, SEM and EDX were also done on the untreated and treated soil for identifying the mineralogical and microstructural changes. The tests results show that the AGGBS and enzyme treated soil reduces swelling and plasticity characteristics whereas OPC treated soil shows an increase in swelling behaviour. It is observed that the swell pressure of the OPC-treated sulfate bearing soil became 1.5 times higher than that of the OPC treated non-sulfate soil.

Applying high resolution SyXRD analysis on sulfate attacked concrete field samples

High resolution synchrotron X-ray diffraction (SyXRD) was applied for a microstructural profile analysis of concrete deterioration after sulfate attack. The cement matrices consist of ordinary Portland cement and different amounts of supplementary cementitious materials, such as fly ash, natural pozzolana and granulated blast furnace slag. The changes of the phase composition were determined along the direction of sulfate ingress. This approach allows the identification of reaction fronts and zones of different phase compositions and conclusions about the mechanisms of sulfate attack. Two reaction fronts were localized in the initial 4mm from the sample surface. The mechanism of deterioration caused by the exposition in the sulfate-bearing soil is discussed. SyXRD is shown to be a reliable method for investigation of cementitious materials with aggregates embedded in natural environments.

Calcium-based stabiliser treatment of sulfate-bearing soils

Stabilisation of sulfate-bearing soils has proven to be a challenging engineering problem for the pavement and geotechnical engineering community. Pavement distress caused by the heaving of sulfate soils often necessitates pavement rehabilitation and frequent road closures. Although the current literature provides a few reasons for sulfate heaving, there are still remaining issues with respect to normalisation of sulfate levels at which this heave will occur in the field. This paper presents sulfate heave issues, soluble sulfate measurement techniques for soils and various factors that complicate the establishment of threshold sulfate levels. Sulfate heave mechanisms by crystal growth and ettringite hydration are explained. Then an overview is provided of various soluble sulfate measurement techniques; a couple of case histories of sulfate-induced failures are also included. A comprehensive summary is given of various alternative treatments used in an attempt to stabilise sulfate soils. In conclusion, a few other issues related to this heaving and ongoing research developments to address these issues are briefly mentioned.

Killing the Ettringite Reaction in Sulfate-Bearing Soils

The formation of ettringite in sulfate-bearing clay soils often results in rapid and significant expansion when calcium-based stabilizers are added to the soil. The researchers tested the hypothesis that ettringite crystal growth could be inhibited by adding a specific chemical that would prevent nucleation of ettringite crystallites, much like retarding the setting of portland cement by using organic additives. The researchers created ettringite in the laboratory by using clay mineral standards mixed with hydrated lime, gypsum, and water, with an ultrasonic homogenizer to catalyze the reaction. A natural soil from Texas (State Highway 289) that had caused sulfate-induced heave problems was also used. Diatomaceous earth, volcanic glass (amorphous silica), and calcium phosphate monobasic monohydrate were added in different proportions to see whether the formation of ettringite could be stopped. The diatomaceous earth and volcanic glass did not inhibit the growth of ettringite in any of the clay mineral standards or natural soil tested. However, the calcium phosphate monobasic monohydrate generated tricalcium aluminate monosulfate hydrate instead of ettringite in the kaolinite and in the natural soil, prevented the formation of both ettringite and tricalcium aluminate monosulfate hydrate. Therefore, phosphates may be a viable additive for prevention of heave in sulfate-bearing soils.

Effects of ground granulated blastfurnace slag (GGBS) on the swelling properties of lime-stabilized sulfate-bearing soils

The use of calcium-based stabilizers such as calcium oxide (lime) in sulfate-bearing clay soils has historically caused structural distress due to the formation of ettringite, an expansive mineral which develops in the presence of sulfate, calcium, and aluminum compounds of clay fraction. In this work, a research was conducted to study the effectiveness of ground granulated blastfurnace slag (GGBS), an industrial by-product, for providing better stabilization of sulfate bearing soils. Laboratory tests were first performed on the lime-treated expansive soil containing different concentrations of added sulfate and then the same tests were repeated on the lime-treated soil, containing the same concentration of sulfate but this time adding 6% slag. Three different sulfate concentrations (2000, 5000, and 10,000ppm) were used in the study and the compaction relationships, Atterberg limits, linear shrinkage and swell potentials were investigated. Test results indicated that the presence of sulfate in the soil resulted in abnormal increase in the plasticity and the swell potential of the lime-treated soil with 5000 and 10,000ppm sulfate concentrations. The swell potential of the lime-treated soil with 10,000ppm sulfate concentration became three times higher than that of the natural soil. The scanning electron micrograph of this higher swell potential soil confirmed the growth of the ettringite minerals. On the other hand, test results indicated that the use of lime with GGBS in stabilizing sulfate bearing clays produced significant improvements in the plasticity as well as the swell potential. Addition of 6% slag into the lime treated soil eliminated the harmful effect of sulfate in the soils. In the presence of 6% slag, the swell potential of the lime-treated soil with 10,000ppm sulfate concentration decreased from 8% to 1%, whereas the lime-treated soil with 5000ppm sulfate concentration showed no swelling.