Using Unconfined Compressive Strength Research Articles

Strength characteristics of cement stabilized construction waste slurry modified by polyacrylamide with different moisture contents

Waste slurry is a major component of construction waste, and its resource utilization can effectively reduce its environmental impact. The effect of polyacrylamide (PAM) content and moisture content on the strength characteristics of PAM modified cement stabilized construction waste slurry (PCMS) was studied using unconfined compressive strength (UCS) and triaxial tests. It can be concluded that, 1) The UCS of PCMS increases with the increase of curing age and significantly decreases with the increase of moisture content. As the content of PAM increases, it first increases and then decreases, with UCS reaching its maximum at a PAM content of 0.5%. 2) When the moisture content is 50%, PAM can increase the elastic modulus of PCMS. When the content of PAM is 0.5%, the elastic modulus reaches its maximum value. When the moisture content is 80% and 100%, the effect of PAM on the elastic modulus of PCMS is not significant. 3) The addition of PAM can improve the shear strength of PCMS. Under the same confining pressure, the shear strength of PCMS increases first and then decreases with the increase of PAM content, and the optimal content is 0.5%. 4) The variation pattern of PCMS cohesion is basically consistent with the shear strength. PAM improves the shear strength of PCMS by enhancing its cohesion. The addition of PAM has a relatively small impact on the internal friction angle of PCMS. These findings provide valuable insights for research into modification technology and the resource utilization of construction waste slurry.

Experimental analysis of mechanical properties of dredged sludge solidified by carbonized under the synergistic action of magnesium oxychloride cement and lime

The environmentally friendly magnesium oxychloride cement (denoted as MOC thereinafter) shows promising application prospects. Meanwhile, more emphasis is being paid to the environmental issues created by CO2 emissions. In this paper, carbonation-composite solidification technology is adopted to introduce MOC-lime cementitious material into sludge solidification. The effects of initial water content (H2O/MgCl2 molar ratio), lime content, MgO/MgCl2 molar ratio, and carbonation time on the mechanical properties and micro-mechanisms of sludge solidification were investigated using unconfined compressive strength (UCS), pH value, carbonation depth, mass loss rate, scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests. The results show that the UCS of sludge solidification decreases with an increase in H2O/MgCl2 molar ratio, and increases first and then decreases with an increase in lime content, reaching a maximum value at H2O/MgCl2 molar ratio of 24.3 and lime content of 4 %. Notably, carbonation significantly improves the UCS of the samples, and with an increase in carbonation time, the mass loss rate and carbonation depth increase, while the pH value decreases. Additionally, uncarbonated samples show an increase in compressive strength with an increase in MgO/MgCl2 molar ratio, as the hydration products gradually transform from amorphous gel to crystalline phases 3, phases 5, and brucite (Mg(OH)2). Finally, XRD and SEM results indicate that the underlying mechanism for the significant improvement in strength and microstructure of the samples after carbonation is the formation of a block-like crystalline network with good binding ability, consisting of chlorartinite, nesquehonite, calcium carbonate, and C-S-H gel. This study promotes the use of MOC-based gel materials as a green stabilizer for sludge solidification, and the carbonation technique employed can improve the mechanical properties of solidified soil and significantly reduce the curing time.

Sustainable Stabilization of Cadmium (Cd)-Contaminated Soil with Biochar-Cement: Evaluation of Strength, Leachability, Microstructural Characteristics, and Stabilization Mechanism

ABSTRACT To facilitate the solid waste reuse of cadmium (Cd)-contaminated soil and biochar and reduce the high emission of cement materials, we employed biochar-cement composite stabilizer to remedy Cd-contaminated soil. We assessed the effects of the biochar-cement composite stabilizer dosage and curing time on stabilized soil strength by using unconfined compressive strength (UCS) tests, leaching concentration and stabilization rate in Cd-contaminated soil stabilized by biochar-cement by using toxicity characteristic leaching procedure, and mechanism of change in strength and leaching characteristics by using scanning electron microscopy and X-ray diffraction. The research results demonstrate that biochar addition to cement-stabilized soil promoted cement hydration reaction and increased particle agglomeration. A low dosage of biochar improved stabilization effects. The optimal biochar dosage was 5%, which enhanced the early growth speed of the UCS. More cement improved the stabilized soil’s UCS. At a 5% cement dosage, adding biochar significantly reduced Cd leaching concentration, and improved the stabilization rate. At a 10% cement dosage, the biochar-cement composite stabilized soil’s stabilization rate was >99.8%. Calcium silicate hydrate, calcium aluminate hydrate, and ettringite were the main products of biochar-cement stabilized soil that filled soil and biochar pores; these substances encapsulated, adsorbed, or exchanged ions of Cd2+, achieving stabilization effects.

Strength and load-bearing behaviors of cement-industrial by-products solidified crust layer over soft subsoil

Industrial by-products have a broad application prospect in sustainable soft soil treatment. The applicability and characteristics of a cement-slag-phosphogypsum based ternary cement (TC) are investigated for solidifying soft clay to create a crust layer. The strength and load-bearing behaviors of the solidified crust are characterized using unconfined compressive strength (UCS), triaxial compression, and small-scale loading tests. The ascending trends in UCS with increasing binder content (Cb) differ between TC solidified clay and cement solidified clay, and the UCS ratio between them increases with Cb. Besides, the failure strain and secant modulus of TC solidified clay have functional relationships with UCS, and the same functions work for cement solidified clay as well. In triaxial compression tests, the relationship curves of the deviatoric stress and excess pore water pressure with axial strain change to present more significant shear dilation characteristics as Cb rises from 6% to 8%, along with a sharp rise in the friction angle, suggesting the solidification performance improved to a higher level. The results of small-scale loading tests show that the ultimate bearing capacity (pu) increases with Cb and crust thickness (h), along with the potential crust failure mode transiting from punching to bending failure; the pu gets a sharp rise as Cb and h are just raised high enough to ensure the crust integrity. In more details, it is suggested to prioritize the effective solidification critical for stress spreading before enlarging h in order to achieve higher pu. Finally, TC has been applied and proven effective in engineering practice.

Remediation of Lead and Cadmium Contaminated Soil Using Lime with Nanosolicamaterials

Soil contamination by heavy metals significantly damages the environment, human health, plants, and animals, which has become a burning issue recently. The presence of contaminated soils due to industrials and mining activities is a major concern in today’s heavily industrialized world. With the rapid development of society, more and more soils are polluted by heavy metals, which leads to a change in soil engineering properties. Several types of technology have long been in use to remedy the heavy metal-contaminated soil. Among them, solidification and stabilization have been widely adopted. In engineering practice, engineers usually use additives to solidify and stabilize (s/s) heavy metal-contaminated soils. Solidification and Stabilization is an economic and effective technology in the remediation of contaminated soil by heavy metals, as well as sludge and sediment. The main purpose of the study was to investigate the effect of (nanomaterial materials) on the remediation of contaminated soil by the (S/S) technique. The soil was polluted with (2000 mg/kg and 1000 mg/kg) of Lead and Cadmium respectively by using Lead and Cadmium nitrates. The Pb and Cd- impacted soil was remediation using rich silicon materials of (nano-silica ) as an alternative cementitious material, and replaced with contaminated soil at (3, 5, and 7%) respectively with (5% and 10%) Lime. Nanosilica was prepared from plant extracts. The binder performance was analyzed by using unconfined compressive strength ( UCS) on the solidified soil at three curing times which were 7, 14, and 28 days. TCLP was also applied to investigate the treatment degree of solidified soil for the specimens within 28 days. The result of (UCS) indicated development in strength with curing day for all binders and proved that all mix ratios exceed the minimum Criteria of landfill disposal which is 340 kPa (0.34 N/mm2). It also showed increases in strength with using nano-silica with a lime binder. The result of the leaching test for the stabilized soil after 28 days of curing, showed a reduction in lead and cadmium leaching rate for all binders, below the EPA lead leachability limit of 5 mg/l and cadmium 1 mg/l. The results showed that the sample SH2N5L10 after 28 days is the best percentage for decreasing the leaching rate of lead and cadmium, as it reached (1.4 mg /l and 0.012 mg/l) respectively with the highest compressive strength of 4852 Kpa.

Preparation, mechanism, and application of silica fume–steel slag composite cementitious material based on the D-optimal mixture method

Steel slag and silica fume as cementitious materials to replace cement have been subjected to many recent investigations. However, the optimization of the mix ratio of silica fume–steel slag composite cementitious materials has rarely been reported. This study aims to design and optimize a novel composite cementitious material of the steel slag–silica fume–ordinary Portland cement (SSP) using the D-optimal mixture design (DOD) method. A DOD model was developed to determine the optimal mix ratio of SSP. Microscopic tests were conducted to investigate the synergistic effect of SSP. The mechanical properties of SSP-stabilized macadam and stone chips were evaluated using unconfined compressive strength (UCS), water stability, and split strength tests. The results indicate that the optimal content of steel slag in SSP was determined to be 16.238%, and that of silica fume was 1.917%. Silica fume consumes the Ca(OH)2 generated during hydration, and as a filler, it also provides nucleation sites for hydration reactions, promoting the secondary reaction to generate calcium silicate hydrate (C–S–H) gels wrapped around the steel slag particles, optimizing the pore structure and reducing the porosity of SSP. The SSP promoted the development of mechanical strength in the later stages. The greatest growth observed in SSP-stabilized stone chips, from 7 days to 28 days of curing, the UCS, water stability coefficient, and split strength increased by 62.6%, 9.9%, and 71% respectively. A significant correlation was observed between UCS and split strength, with UCS being approximately 9.0 to 9.8 times higher than the split strength. This study contributes to the optimal design of similar solid waste composite materials and provides a reference for the use of silica fume and steel slag in road construction.

Applicability of Soybean Crude Urease-Calcite Precipitation Method in Various Liquefiable Sandy Soils

Liquefaction is a process in which pore-water pressure generated in the soil, usually by earthquake, is equal or almost equal to the total stress in the soil. This process reduces the effective stress to zero or near-zero, leading to reduction in shear strength and stiffness of soil. Hence, when liquefaction occurs, structures above and within the liquified soil, buildings, bridges, tunnels, docks, underground pipelines, and many other structures can get damaged. Soils which are susceptible to liquefaction are granular soil such as sand and silt. One of the methods that can be adopted to prevent liquefaction is soybean crude urease-calcite precipitation. This method uses urease enzyme in soybean crude as a biocatalyst to hydrolyze urea to produce carbonate ions and ammonium ions. In the presence of calcium ions, the carbonate ions react to produce calcium carbonate (calcite) precipitate. This research investigates the applicability of soybean crude urease-calcite precipitation method to improve various liquefiable sandy soil (fine, medium, coarse sand) at different relative density (40-60%). The soil strength after improvement was evaluated by using unconfined compressive strength (UCS) test, while calcite content was measured using acid leaching method. The results of the UCS test and calcite content analysis varies depending on the type of sand and relative density. The UCS value obtained from medium sand is higher than 50 kPa, potentially sufficient to prevent liquefaction. However, treatment on coarse sand failed to develop UCS, whereas treatment on fine sand produces limited UCS (< 10 kPa).

On the use of one-part geopolymer activated by solid sodium silicate in soft clay stabilization

The application of geopolymers in ground improvement has garnered significant attention in recent years. However, most geopolymer preparations have focused on the two-part method, which not only has negative environmental impacts but also falls short of meeting practical requirements. This study aimed to address these limitations by employing solid sodium silicate (Na2O·nSiO2, n is the molar ratio, NS) to activate binary precursors (fly ash [FA] and ground granulated blast furnace slag [GGBFS]), along with water, to synthesize a one-part geopolymer (OPG) for soft clay stabilization. The primary factors on the properties of the OPG binder were firstly identified through macro- and micro-tests. Subsequently, the optimization of the OPG mixing proportion was achieved by reducing the molar concentration of NS, and was further used for soft clay stabilization. The effects of the FA/GGBFS ratio (0, 0.1, and 0.2), curing period (7, 14, and 28 days), and binder content (0.15, 0.20, and 0.25) on the mechanical properties of the OPG-stabilized soft clay were then evaluated using unconfined compressive strength (UCS) tests. Furthermore, mercury intrusion porosimetry (MIP), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS), and X-ray diffraction (XRD) techniques were employed to examine the evolution of microstructure, hydrate composition, and mineral/phase of the OPG-stabilized soft clay samples. The experimental results indicated that an appropriate OPG stabilizer proportion was achieved with an FA/GGBFS ratio of 0.1, water/precursor ratio of 0.8, molar ratio of NS of 1.0, and molar concentration of 3 mol/L. The high-early-strength feature of OPG binder contributed to the rapid strength development of the stabilized soft clay at an early age. A noticeable pozzolanic reaction was observed in the OPG-stabilized soft clay sample with an FA/GGBFS ratio of 0.1. Additionally, a binder content of 0.20 was recommended for the stabilization of soft clay due to its optimal balance between economic benefits and meeting the required UCS criteria in soil stabilization. Finally, a reliable nonlinear relationship between UCS and porosity of OPG-stabilized soft clay was established to assess the mechanical properties and stabilization effects of the OPG-stabilized soft clay for practical applications. This study greatly enhances the scientific understanding of geopolymerization in the OPG system by using a combination of the binary precursor of FA and GGBFS and the solid NS activator. It sheds light on the stabilization mechanism of OPG-stabilized soft clay. The outcomes of this study make a valuable contribution to the advancement of environmentally friendly soil stabilizers, promoting green and low-carbon practices in the field of ground improvement.

Optimization of synergy between cement, slag, and phosphogypsum for marine soft clay solidification

Ground granulated blast furnace slag (GGBS) and waste gypsum are cost-effective and environment-friendly substitute materials for Portland cement. This work aims to investigate and optimize the synergy of ordinary Portland cement (OPC), GGBS, and phosphogypsum (PG) in solidifying marine soft clay. The soft clay is treated with the ternary blending designed, and NaOH (NH), Na2SO4 (NS), calcium aluminate cement (CA), and γ-nano-Al2O3 (NA) are used as additives to it. The effectiveness of the ternary blending and the additives is evaluated using unconfined compressive strength (UCS), consolidation, and durability tests, and the associated mechanisms are revealed by pH evaluation, X-ray diffraction (XRD), and scanning electron microscopy (SEM) tests. A high-efficiency ternary cement (TC) is developed by blending OPC, GGBS, and PG in the optimum ratio of 5:3:2. TC solidified clay (TCSC) exhibits better strength performance than cement or binary cement (OPC–GGBS/PG) solidified clay, due to the combined action of pozzolanic reaction and ettringite formation. The single additives, particularly NH and NS, can dramatically improve the early strength of TCSC, whereas the composite additives NS/CA and NS/NA finally result in greater strength gains. Besides, the lower compressibility and stronger sulfate resistance also verify TCSC as a preferable reinforced material over cement solidified clay, and these mechanical properties can be further improved using the composite additives. The increased basicity and the more effective role of ettringite explain the improved mechanical performance. In particular, the NS/CA and the NS/NA induce ettringite to grow in clustered and oriented patterns, providing effective pore filling and structural support, respectively.

Integrated Interpretation of Electrical Conductivity Changes, Heat Generation, and Strength Development in the First Week in Cemented Paste Backfill

Underground mining operations need nondestructive test methods to assess placed backfill strength development at early age (especially up to 1 week of curing time) so that they can continue proximate mining quickly. Recent developments in electrical conductivity (EC) transducers for field applications offer this possibility, but the EC measurements must be correlated to backfill strength. To determine the feasibility of this approach, a laboratory test program used a mine’s backfill materials mixed with varying water and binder contents and tested these over a 7-day period. Strength was characterized using unconfined compressive strength (UCS) tests and correlated to EC. Comparisons were also made to complementary test results using Vicat and heat generation measurement techniques. Strong and consistent correlations were determined between EC and UCS for a given binder content and water content. But moreover, a lower-bound correlation was determined and could also be used in the field if as-placed properties vary to an unknown extent within the limits of parameters considered in the study. This provides the basis to use EC measurements in the field and confidently assess the backfill’s minimum attained strength in real time.

A Study on Uniaxial Compressive Strength and Ultrasonic Non-Destructive Analysis of Fine-Grained Soil in Seasonally Frozen Regions

Understanding the physical and mechanical properties of soils subjected to freeze-thaw cycles, including both micro and macrostructures, is critical for achieving the required performance of structures employing it as a structural or support material. An experimental study was carried out on clay soil with varying water content (18%, 21.5%, and 23%) after repeated freeze-thaw cycles (0, 2, 5, 7, 12, and 15). The performance of soil was evaluated using unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) tests. The experimental results demonstrated that UCS peak values were observed at the lowest water content before and after the freeze-thaw cycles. The stress-strain curves exhibited strain-softening behavior, and this condition transitioned to strain hardening behavior after freeze-thaw cycles with increment in the water content. Moreover, the highest values of UPV were observed to increase UCS values due to capillary forces at minimum water content. Also, an increase in the number of freeze-thaw cycles resulted in a decrease in the UPV. According to correlations between UPV and UCS values, the highest correlations for water contents were obtained at optimum water content, and a decreasing trend was observed after experiencing a number of freeze-thaw periods. In addition, the Grey Correlation Analysis was performed to show the degree of correlation between the UCS and UPV, water content as well as the freeze-thaw cycles. The results demonstrated that the UPV values have a greater impact on the UCS than other parameters.

Geomechanical Behaviour of Clay Stabilised with Fly-Ash-Based Geopolymer for Deep Mixing

Geopolymer has recently become an attractive alternative to traditional binders (e.g., cement and lime) used for chemical soil improvement, with several environmental benefits including lower toxic emissions and energy consumption. This paper presents an evaluation of the geomechanical behaviour of soft clay treated with fly-ash-based geopolymer incorporating slag for deep soil mixing (DSM) applications. The geomechanical properties of stabilised clay were evaluated using unconfined compressive strength (UCS) tests and durability against wetting–drying. Thermal conductivity and pH tests along with microstructural analysis using scanning electron microscopy (SEM) were also performed to provide insights into the effect of geopolymer on treated clay. The results indicate that the inclusion of geopolymer with the increase in curing time and activator content considerably improves the geomechanical performance of geopolymer-treated soft clay in terms of stress–strain response and attainable peak compressive strength. Although it was found that a small percentage of geopolymer can enhance the initial compressive response, a larger dosage of geopolymer up to 30% was necessary to maintain stable durability performance over successive wetting–drying cycles. Such improved durability performance is related to the enhanced soil structure due to the cementation development and overall reduction in thermal conductivity. The reduction in thermal conductivity of treated clay was found to be activator-dependent and was suppressed steadily with the increase in activator concentration. Overall, geopolymer-treated clay showed promising potential for DSM applications due to its enhanced strength and durability responses.

Effectiveness of waste paper ash for stabilization on clay soil

Through this paper, three main approaches were adopted to evaluate the effectiveness of waste paper ash (WPA) for stabilization on clay soil. First, the physical properties of mixing soil were studied. Furthermore, the swelling potential of mixing soil with different percentage was also discussed. Finally, the compressive strength using unconfined compressive strength (UCS) apparatus was evaluated. It was found that after mixing with waste paper ash (WPA), the percentage of soil passing sieving number 200 and plasticity index reduces by increasing of the waste paper ash (WPA) percentage. It might be attributed to the bonding of the chemical content of waste paper ash (WPA) to the soil particles. In addition, the swelling potential slightly reduces by increasing of waste paper ash (WPA) percentage. Furthermore, the compressive strength increases with waste paper ash (WPA) 5% and 10%.

Effectiveness of waste paper ash for stabilization on clay soil

Through this paper, three main approaches were adopted to evaluate the effectiveness of waste paper ash (WPA) for stabilization on clay soil. First, the physical properties of mixing soil were studied. Furthermore, the swelling potential of mixing soil with different percentage was also discussed. Finally, the compressive strength using unconfined compressive strength (UCS) apparatus was evaluated. It was found that after mixing with waste paper ash (WPA), the percentage of soil passing sieving number 200 and plasticity index reduces by increasing of the waste paper ash (WPA) percentage. It might be attributed to the bonding of the chemical content of waste paper ash (WPA) to the soil particles. In addition, the swelling potential slightly reduces by increasing of waste paper ash (WPA) percentage. Furthermore, the compressive strength increases with waste paper ash (WPA) 5% and 10%.

Surface Stabilization of Soils Susceptible to Wind Erosion Using Volcanic Ash–Based Geopolymer

This study evaluates the surface application of a volcanic ash-based geopolymer for the stabilization of soils susceptible to wind erosion. To achieve this, the mechanical properties of different soil types treated with various geopolymeric mix designs are evaluated using unconfined compressive strength (UCS) tests. The effects of volcanic ash (VA) and alkaline activator (AA) on the stabilization of silty sand soil are analyzed for two different curing conditions and over an extended curing period of 3 to 100 days. As different types of nonplastic fine-grained soil are vulnerable to various modes of wind erosion. The effectiveness of the geopolymer in the treatment of different types of nonplastic fine-grained soils (with fines content between 0% and 100%) is assessed through the UCS tests. Furthermore, the mechanical strength of soil samples prepared by three different preparation methods is evaluated. The impact of crust thickness, activator solution quantity, and curing conditions on the erodibility and friction velocity of three different soil types (clean sand, silty sand, and silty soil specimens) are measured by wind tunnel experiments. The results show that treatment with the geopolymer can notably increase the threshold friction velocity and reduce the soil wind erodibility. It is concluded that proper determination of the geopolymer mix design requires consideration of the soil type, maximum wind speed, and ambient conditions.

A Study of the Strength Performance of Peat Soil: A Modified Cement-Based Stabilization Agent Using Fly Ash and Polypropylene Fiber.

The use of cement as a soil stabilization agent is one of the common solutions to enhancing the engineering properties of soil. However, the impact and cost of using cement have raised environmental concerns, generating much interest in the search for alternative materials to reduce the use of cement as a stabilizing agent in soil treatment. This study looked into limiting cement content in peat soil stabilization by using fly ash waste and polypropylene fiber (PPF). It focused on soil mechanical mediation for stabilization of peat with fly ash cement and PPF cement by comparing the mechanical properties, using unconfined compressive strength (UCS) and California bearing ratio (CBR) tests. The control (untreated) peat specimen and specimens with either fly ash (10%, 20% and 30%) and PPF (0.1%, 0.15% and 0.2%) were studied. Test results showed that 30% of fly ash and cement content displays the highest UCS and CBR values and gives the most reliable compressibility properties. On the other hand, UCS and CBR test results indicate optimum values of PPF–cement stabilizing agent content in the specimen of 0.15% PPF and 30% cement. Selected specimens were analyzed using scanning electron microscopy (SEM), and PPF threads were found to be well surrounded by cement-stabilized peat matrices. It was also observed that the specimen with 30% fly ash generated more hydration products when compared to the specimen with 100% cement content. It is concluded that the use of fly ash cement and PPF cement as stabilizing agents to limit the cement usage in peat soil treatment is potentially viable.

Influence of Soil Particle Size on the Engineering Properties and Microstructure of a Red Clay

Particle size exerts a significant influence on the mechanical behavior of soil. However, insufficient research has been carried out on red clay formations, which are widespread in some Chinese provinces. Here, using unconfined compressive strength (UCS) tests, wetting–drying (WD) tests, and low-temperature nitrogen adsorption tests, we examined the relationship between the particle size and a number of mechanical and microstructural characteristics of a red clay outcropping at a construction site in China. Our results suggest that, depending on the surface area, porosity, particle size, and dry density, the failure mechanism in UCS tests will be different. That is, as the particle size increases, the failure mode of soil changes from split failure into shear failure. In addition, as the dry density increases, the UCS of the soil sample is significantly improved, and its total porosity and fractal dimension decrease. We also evaluated a dependence on particle size and the number of WD cycles on the distribution and size of cracks in WD tests. We conclude by suggesting that particle size, dry density, and WD behavior should all be taken into account in roadbed designs in red clay formations.

Study on Mechanical and Microscopic Properties of Nickel–Copper-Contaminated Soil Solidified by Cement, Fly Ash and Desulfurization Gypsum Under Carbonization Condition

The engineering characteristics of remediated soil are easily affected by CO2 erosion in nature. However, there are limited investigations on the mechanical and microscopic properties of heavy metal-contaminated soil. This study introduces effect of accelerated carbonization on the mechanical and microscopic properties of nickel–copper-contaminated soil, and the soil has been treated with a novel curing agent, formed by mixing cement, fly ash and desulfurization gypsum (CFG). The objective of the study is to ascertain CO2 erosion resistance of nickel–copper-contaminated soil solidified by CFG. Using unconfined compressive strength (UCS) tests, carbonization depth, X-ray diffraction, and scanning electron microscopy, the sample’s characteristics are investigated under different carbonization times and heavy metal ion concentrations. The results demonstrate that the UCS of samples of Ni0Cu0, Ni0.02, and Ni0.4 decrease with the increasing carbonization time, while that of Ni1, Cu1, and Ni1Cu1 increase initially and then decrease; in addition, when the concentration of heavy metals is lower, the effect of carbonization on UCS of samples is more significant. Moreover, the carbonization depth of samples increases with the increasing carbonization time, and the prediction model is given. Furthermore, the microscopic analysis demonstrates that calcium carbonate is the main carbonization product. The decomposition of hydrated calcium silicate gel leads to poor integrity of the structure and more pores produced in samples, which is the main reason for the decrease of the UCS in the process of carbonization. The outcomes of this investigation provide a reference for the durability in practical engineering of heavy metal-contaminated soil solidified by CFG.

Comparison between CaO- and MgO-activated ground granulated blast-furnace slag (GGBS) for stabilization/solidification of Zn-contaminated clay slurry

Stabilization/solidification (S/S) is a low-cost and effective remedial technique for dredged contaminated sediments. Quick lime (CaO)-activated and reactive magnesia (MgO)-activated ground granulated blast furnace slag (GGBS) are effective and low-carbon S/S binders. However, the existence of metals, especially Zn, in contaminated sediments, may hinder the hydration of GGBS. This study compared the performance and mechanisms of CaO-GGBS, MgO-GGBS and ordinary Portland cement (OPC) for the treatment of Zn-contaminated clay slurry using unconfined compressive strength (UCS) test, one-stage batch leaching test, and mineralogical and thermal analyses. The results showed that the application of the MgO-GGBS (GGBS dosage of 10 % and MgO of 0 %–3 % (of dry clay by mass)) had positive effects on the mechanical strength and Zn immobilization of the contaminated clay slurry while the CaO-GGBS affected negatively and the situation became even worse at a higher CaO dosage (0 %–1.5 % of dry clay by mass). In comparison with OPC, the application of MgO-GGBS produced higher mechanical strength and that for CaO-GGBS was the lowest. The Zn leaching difference depends on initial Zn concentrations. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) results showed that a retarder, calcium zinc hydroxide, formed in the immobilization process when adding the CaO-GGBS binder, hindering the GGBS hydration and further leading to inferior strength and higher Zn leachability. The clay slurry treated by the MgO-GGBS binder was found to have a higher calcium silicate hydrate content which explained its high strength and low leachability.

Effects of Nanoclay and Silica Flour on the Mechanical Properties of Class G Cement.

The mechanical properties of oil well cement slurry are usually measured to evaluate the durability, sustainability, and long-lasting behavior of a cement sheath under wellbore conditions. High-pressure and high-temperature (HPHT) conditions affect the mechanical properties of cement slurry such as its strength, elasticity, and curing time. In this study, an organically modified montmorillonite nanoclay (NC) and silica flour (SF) materials are used to enhance the strength of the class G cement. Four different cement slurries with the addition of different concentrations of NC (1% and 2%) and SF (20%) in a class G cement were tested under temperatures ranging between 70 and 100 °C and pressure ranging between 1000 and 3000 psia. The slurries were prepared by maintaining a water to cement ratio of 0.44. All the slurries were cured for 24 h before any test was conducted. Extensive laboratory experiments were carried out to measure the compressive and tensile strength of cement slurries cured at HPHT conditions. Compressive strength was measured using unconfined compressive strength (UCS) tests, scratch tests, and ultrasonic cement analyzer (UCA). Tensile strength was measured using breakdown pressure tests and Brazilian disc test analysis. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and petrophysical analysis were also carried out to evaluate the performance of new cement additives at HPHT conditions. Results showed that the addition of organically modified NC and SF significantly increased the compressive and tensile strength of the class G cement slurry cured at HPHT conditions.