Highest Unconfined Compressive Strength Research Articles

Geomechanical aspects of stabilizing arsenic trioxide roaster waste in cemented paste backfill at the Giant Mine, Canada

Giant Mine, an abandoned gold mine near Yellowknife in the Northwest Territories of Canada, generated significant arsenic trioxide roaster waste (ATRW) during its operations, posing a substantial environmental hazard. This study explored the feasibility of stabilizing ATRW by incorporating it into cemented paste backfill (CPB). Using response surface methodology (RSM), CPB samples with varying mixing ratios were analyzed to identify key parameters influencing strength. Unconfined compressive strength (UCS) tests assessed physical stability, while saturated hydraulic conductivity and computed tomography (CT) analyses examined the microstructure of the CPB. The results revealed that CPB samples prepared with general use (GU) cement exhibited significantly higher strength than those with a GU and lime kiln dust (LKD) mixture. Binder and solid contents were identified as the most critical factors influencing UCS, with binder content having a more pronounced influence. Curing time was found to be non-significant. Higher binder and solid contents correlated with higher UCS values in the CPB samples. The addition of 10% wt. ATRW reduced the UCS by over 30%, particularly in samples with lower binder and solid contents. Although microstructure differences were not evident in saturated hydraulic conductivity tests, CT scans showed increased formation of high-density arsenic-containing materials in samples with the highest UCS, especially those using GU binder. These findings suggest that optimizing binder and solid contents is crucial for enhancing CPB strength and effectively stabilizing ATRW.

Strength and leaching behavior of CaO- and MgO-treated Cd-contaminated soils subjected to partial and full carbonation

Cadmium (Cd)-contaminated soils may pose a significant threat on human health. They are often treated with quick lime (CaO) and reactive magnesia (MgO), but these treatments often result in low strength. Hence, in this study, partial and full carbonation are used to enhance the stabilization/solidification of CaO- and MgO-treated Cd-contaminated soils, aiming to achieve CO2 sequestration, strength improvement, and Cd immobilization. Performance of treated contaminated soils is evaluated through unconfined compressive strength (UCS), leaching, X-ray diffraction (XRD), and thermogravimetric analysis (TGA) tests. The results indicate that carbonation significantly enhances the UCS of both CaO- and MgO-treated Cd-contaminated soils. After carbonation, MgO-treated soils exhibit higher UCS than CaO-treated soils. Partial and full carbonation yield similar UCS in CaO-treated soils, while full carbonation results in higher UCS in MgO-treated soils. For CaO-treated soils, partial carbonation keeps Cd leachability below the 1 mg/kg limit, but full carbonation increases it beyond this limit. In contrast, fully carbonated MgO-treated soils maintain Cd leachability below the limit, though partial carbonation leads to higher leachability. Formation of Ca and Mg carbonates contributes to the strength improvement of soils. Cd(OH)2 and its complex, as well as CdCO3 exist in partially and fully carbonated soils, lowering leached Cd concentration. Overall, partial carbonation is better for CaO-treated soils, while full carbonation is preferable for MgO-treated soils.

Use of rise husks to improve the efficiency of MICP-based soil improvement technique

Biogrouting has been identified as the best alternative approach for the conventional cement and chemical grouts. Among the various types of biogrouting techniques, microbial induced carbonate precipitation (MICP) has been recently recognized as a promising pathway for producing biogrout material, hence densifying the weak soils. In MICP, calcium carbonate (CaCO3) biocement is produced through biochemical reactions induced by the urease enzyme. The efficiency and productivity of MICP can be further improved by introducing various additives, including fibers, organic polymers, powders, waste materials, etc. In this research, rice husk was sustainably incorporated into the MICP process, and (i) the effect of the rice husk content, (ii) the concentration of the cementation solution and (iii) the treatment time on the unconfined compressive strength (UCS) of the sandy soil were investigated at the laboratory-scale. Cementation solutions with higher concentrations exhibited a higher UCS values than solutions with lower concentrations. Interestingly, the content of rice husk had a marked influence on the UCS, and the optimum rice husk content was 15%. Compared to that of the control sample (0% rice husk), a threefold greater UCS was obtained for 15% of the rice husk content sample. The outcomes further suggested that longer treatment with lower concentration of cementation solution was the best combination for achieving effective cementation within the sand matrix. Rice husk acted as the template for CaCO3 crystals to nucleate while promoting the efficient formation of CaCO3, indicating that the rice husk is an excellent additive to improve the efficiency of the MICP biocementation in a sustainable way.

Mechanical properties and microscopic mechanism of solid waste based binder solidified stone waste

The stone waste generated by stone industry occupy land resources, cause safety hazards and need to be efficiently resourcefully utilized. In this study, the CGF solid waste based binder (abbreviated as CGF) with calcium carbide residue (CCR), ground granulated blast furnace slag (GGBS), and fly ash (FA) as components was developed to solidify the stone waste. Through “treating waste with waste”, the resource utilization of solid waste was realized. The mechanical properties and reaction mechanism of CGF solidified stone waste were investigated through unconfined compressive strength (UCS), XRD, and SEM–EDS tests. The results show that CGF has the better solidify effect on stone waste, and its strength meets the requirements of the road base material standards. Compared to cement, the CGF solidified stone waste existed higher UCS at both 7 and 28 d of curing. The UCS of CGF solidified stone waste reaches 2.93 and 4.42 MPa under curing of 7 and 28 d at 5% binder content, which is 1.61 and 1.37 times higher that of P.O. 42.5 cement. Furthermore, the primary mineral-based stone wastes will not react with the binder, and the CGF generates gelling products such as C-S–H C-A-H, and C-A-S–H through alkali-activated reactions between the components of CGF. These gelling products enhance the UCS of solidified stone wastes through cementing and filling effects. The findings provide a feasible approach with low-carbon emission and low-cost for resourceful utilization of stone wastes.

Application of recycled lignin powder as a sustainable additive for soil improvement against water resistance

To evaluate the engineering performance against water resistance of lignin-modified soil, unconfined compressive strength (UCS) tests and direct shear tests were conducted on silty sand modified with varying lignin contents (2%, 5%, 8%, 12%, and 15%) following wet-dry cycles. The results demonstrate that 8% lignin-modified soil has the highest UCS and shear strength. The addition of lignin to soil enhances its wet-dry durability, with soil modified by 8% lignin exhibiting the highest durability. The structural properties of lignin-modified soil subjected to wet-dry cycles can be quantified using a combined structural stability index and structural variability index. A model relevant to the structural properties was proposed to predict the shear strength of lignin-modified soil following wet-dry cycles. Notably, the addition of lignin to silty sand does not result in the formation of new minerals, indicating that lignin addition is an environmentally-friendly soil treatment.

Exploring the Potential of Native Urease-Producing Bacteria of Hilly Terrain for Soil Strength Enhancement

Bio-cementation of weathered soils of hilly regions using native ureolytic bacteria is a practical approach to improve soil strength. This study aimed to isolate and characterize native urease-producing bacterial strains from different slope failure regions of Uttarakhand, India, through multi-step screening, and showcased their potential in soil improvement. A total of 80 bacterial strains were isolated from thirteen landslide-prone sites to screen for potent native urease-producing strains. Interestingly, nine native strains exhibited high calcium carbonate precipitation (158–187 mg/10 ml) and urease activity (657–3495 µM/mL) compared to Sporosarcina pasteurii (NCIM 2477), a potent bacterium commonly used for bio-cementation. These strains belonged to various genera, including Lysinibacillus sp., Sporosarcina sp., Pseudochrobactrum sp., and Cytobacillus sp. Cohesionless soil samples treated with the native strains exhibited high unconfined compressive strength values ranging from 0.1 MPa to 1 MPa, whereas those treated with S. pasteurii were 0.15 MPa. The urease-producing bacterial strains with CaCO3 precipitation activity influenced the soil strength and failure patterns. FESEM, XRD, and acid-washing tests revealed that native bacterial strains precipitated CaCO3 more than S. pasteurii strain. The study explores, for the first time, the potential of native ureolytic bacteria from different regions of Uttarakhand, India, for soil strength enhancement.

Efficacy of soybean-derived crude extract in enzyme-induced carbonate precipitation as soil-improvement technique

Calcium carbonate precipitation using a urease enzyme, referred to herein as Enzyme-Induced Carbonate Precipitation (EICP) is a technique for soil improvement. In this technique, a mixed solution composed of reagents and the urease enzyme, which produces calcite, is utilized as the grouting material. Recently, alternative materials to the urease enzyme have been examined to resolve the cost issue of using the urease enzyme. In this study, several tests were conducted to compare commercial urease and soybean-derived crude urease. A comparison of their hydrolysis rates was done through urease activity tests. The microscopic structures and mineralogy of the precipitated materials, produced during various loading periods, were investigated through SEM and XRD analyses. Moreover, the reinforcing effect of the grouting solutions on the treated soil specimens was evaluated by measuring the unconfined compressive strength (UCS) of the treated samples. Interestingly, the precipitated CaCO3 was vaterite and calcite when using soybean urease, while it was mostly calcite when using the urease enzyme. Higher UCS values were obtained with the soybean urease samples because the precipitated CaCO3 seemed to be concentrated at the inter-grain contacts. It was concluded that soybean powder shows great efficacy as a replacement for commercially produced enzyme urease in soil-improvement techniques mediated by carbonate precipitation.

Reusing COVID-19 personal protective equipment wastes for pavement base, subbase, and subgrade applications

Since 2019, the coronavirus disease (COVID-19) pandemic has caused a substantial increase in personal protective equipment waste generation, resulting in significant environmental concerns. In addition, the expansive clay subgrade (ECS) must be stabilized prior to pavement construction because of its unfavorable engineering properties. The use of recycled concrete aggregates (RCA) in pavement bases/subbases offers a sustainable solution to decrease the demand for quarry materials and waste pile-up. However, RCA should be reinforced for base and subbase applications because of its low shear and dynamic properties. This study explores an innovative waste solution by recycling shredded nitrile gloves (SNG) to stabilize clay subgrades and reusing discarded shredded face masks (SFM) to treat RCA for base/subbase applications. A series of experiments including compaction, unconfined compression strength, and repeated-load triaxial tests were conducted. The test results showed that the incorporation of SNG and SFM improved the strength and stiffness of the pavement layers. The addition of 1.5% SNG to ECS resulted in the highest unconfined compressive strength (UCS) value (315.50 kPa) and highest resilient modulus (Mr) (79.98 MPa). Furthermore, introducing 1% SFM into RCA increased the UCS and Mr to peak values of 216 kPa and 314.35 MPa, respectively.

Evaluating the performance and durability of concrete paving blocks enhanced by bio-cement posttreatment

Concrete pavement often experiences accelerated deterioration due to water and chemical ingress through micro-cracks and surface voids. Particularly, the ingress of aggressive agents into the concrete matrix results in irreversible changes and deterioration on its endurance. Numerous studies unveiled that hydrophobic surface protection could be an inexpensive and effective way of enhancing the durability of concrete. This research work aims to assess the feasibility of bio-cement posttreatment for facilitating hydrophobic surface protection, thus enhancing the performance and durability of concrete blocks. Enzyme induced carbonate precipitation (EICP) is one of the promising bio-cement methods. Concrete blocks casted in four different grades were subjected to EICP treatment with different treatment schemes and recipes of cementation media. The treated blocks were tested for water absorption, ultrasonic pulse velocity (UPV) measurements, unconfined compressive strength (UCS), thermal performance, and scanning electron microscopy (SEM). The results indicated that the concrete blocks subjected to EICP posttreatment showed over a 55% reduction in water absorption, a 15% higher UCS and a 6.7% higher UPV when compared with control blocks. The SEM analysis suggested that the EICP posttreatment could enhance the durability of concrete paving blocks by enabling a layer of calcite on the surface and by plugging the transport pore channels of the concrete. Although most of the posttreatment strategies investigated herein were found to be operative, a better response was seen in the posttreatment by spraying scheme with 0.5 mol/L cementation media (CM). With the successful demonstration, the EICP treatment prior to the use of concrete blocks can be recommended to the pavement construction industry.

Systematic assessment of a multi–solid waste cementitious material: Feasibility and environmental impact

This study systematically assessed the feasibility of replacing ordinary Portland cement (OPC) with a multi–solid waste cementitious material (MSC) composed of ground granulated blast furnace slag (GGBS), steel slag (SS), red mud (RM), fly ash (FA), limestone powder (LP), and desulfurized gypsum (DG) in specific proportions of 28%, 25%, 21%, 11.5%, 9%, and 5.5%, respectively. The hydration characteristics were analyzed using hydration heat, XRD, TG–DTG, FTIR, and SEM–EDX tests. The heavy metal content and leaching concentration of the MSC were determined using inductively coupled plasma mass spectrometry (ICP–MS). The unconfined compressive strength (UCS), indirect tensile strength (ITS), and water stability of the MSC-stabilized clayey sand and stone chips were investigated. The results showed that synergistic hydration among multiple solid wastes generated abundant hydration products, including Ca(OH)2, C–(A)–S–H gels, and AFt crystals, which formed dense and compact microstructures. Furthermore, Pb and Cd in the raw material were effectively solidified by MSC hydration, with leaching concentrations as low as 0.181 and 0.002 mg/L, respectively. The contents and leaching concentrations of the other heavy metals were significantly lower than their limits. The pH of the MSC mortar leachate was stable at 11.56 with curing age, which complied with environmental safety standards. Moreover, MSC as a binder demonstrated higher UCS, ITS, and water stability in comparison to OPC. When MSC was added at a 6% dosage to stabilize clayey sand and stone chips, the UCS values measured after 7 days of curing were 2.82 MPa and 4.83 MPa, respectively. Finally, the MSC was successfully applied in practical projects, demonstrating its promising application prospects.

Remediation effectiveness of aging diesel-contaminated soil using thermochemical treatment: Soil microstructure transformation and reusability

This study investigated the microstructure transformation observed in an aging diesel-contaminated soil after thermochemical treatment (DT150°C + PS) to explore its impact on engineering reusability. Three thermal remediation procedures (i.e., DT150°C, DT350°C, and DT550°C) were selected as the control group. The results show that: (a) Pyrolytic carbon was produced in the DT350°C and DT550°C, while none was produced in DT150°C and DT150°C + PS; (b) Iron-based minerals and organic matter in DT150°C + PS, DT350°C, and DT550°C were combusted and decomposed to release the Fe(II) substances; under stronger oxidation environments, Fe(II) substances would further transform into more stable Fe(Ⅲ) substances; and (c) Halloysites and illites were formed in DT350°C, palygorskites and cordierites were formed in DT550°C, and oxidation in DT150°C + PS produced the sulfate minerals. The formed sulfate minerals in the DT150°C + PS sample filled pores and provided the skeleton strength, resulting in high unconfined compressive strength and poor permeability. Using a self-developed assessment model, only the DT150°C + PS sample showed an improvement (calculated as 2.96 × 10−5) in engineering performance and other methods led to the deterioration of soil mechanical properties. Thermochemical treatment is more suitable for engineering reuse, and this study can provide a theoretical basis for evaluating the greener reusability of contaminated soil after thermal or thermochemical remediation.

Strengthening mechanism of red mud with calcium oxide

Currently, the utilization rate of red mud is very low, and the problems of occupying land and polluting the environment are becoming increasingly prominent. This study utilized CaO to prepare Red Mud-based cementitious material (RMC) to achieve clean and efficient utilization of red mud. The mechanism of Ca2+ enhancing the strength of RM and the carbonation reaction in RMC were studied using X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), Thermogravimetric Analysis (TGA), Scanning electron microscopy (SEM) and other analysis methods. The results showed that the carbonization of CaO in RMC bonded the red mud particles and provided early strength. CaO activated the components of gibbsite, diaspore, and silica in RM, and hydration reaction generated gel-like Al-substituted tobermorite (Ca5Si5Al(OH)O17·5 H2O), ensuring the increase of later strength. At the age of 28 days, the RMC with a CaO content of 25% had the highest unconfined compressive strength, reaching 2.19 MPa. When the CaO content exceeded 25%, the compressive strength of RMC gradually decreased. This is due to the reaction of calcium carbonate and aluminate to form a large number of sheets of calcium aluminate monocarbonate (Ca4Al2O6CO3·11 H2O), which weakened the carbonation binding effect and competitively consumed aluminate, resulting in an increase in structural cracks and pores, and a decrease in the compressive strength of RMC.

Mechanical Behavior and Microstructure Evaluation of Quicklime-Activated Cement Kiln Dust-Slag Binder Pastes.

Cement kiln dust (CKD) is a by-product of cement production, which has the shortcomings of low utilization and high-temperature activation. This study combined CKD and slag as precursors for preparing pastes through quicklime activation under ambient conditions. The effects of quicklime and CKD content on the workability (flowability and setting time), macro-mechanical properties, and micro-structure of the CKD-slag binders were analyzed. The experimental results showed that the rapid precipitation of Ca2+, Si4+, and Al3+ ions from the CKD provided more nucleation sites for the formation of calcium aluminosilicate hydrate (C-(A)-S-H) gel and enhanced the reactivity of the binder system under the influence of the activator (CaO). The specimens had the highest unconfined compressive strength (UCS) (24.6 MPa) after 28 days with 10% quicklime content and 60% CKD content; scanning electron microscopy with energy-dispersive X-ray (SEM-EDX) analysis showed that the Ca/Si ratio of the C-(A)-S-H gel was minimized, leading to a denser microstructure and better binding ability under this mixing proportion. Therefore, this study may provide novel binder materials with a high proportion of CKD under ambient conditions.

Bio-cementation practice on electric-arc steel slag and comparison with natural sand

In construction projects in Khuzestan province in Iran, electric-arc steel slag (EASS) materials are used as fill materials. In this research study, bio-cementation practice on EASS materials is examined and compared with that on natural sand. For this purpose, direct shear, unconfined compressive strength (UCS) and constant head permeability tests, together with scanning electron microscopy images obtained using an instrument equipped with an energy-dispersive X-ray spectroscope, were used to analyse and compare untreated and treated materials. The results showed that despite higher urease activity and higher calcite production of EASS materials compared with natural sand, the latter showed slightly higher UCS, higher cohesion intercept enhancement and higher permeability decrease after bio-cementation treatment.

Microbial Induced Calcite Precipitate Improvement of Aeolian Soil for Use as a Construction Material

An environmentally friendly and successful technique of soil improvement known as Microbial Induced Calcite Precipitation (MICP) has attracted the attention of geotechnical engineers. This study was conducted to modify the engineering behaviour of an aeolian soil bio-treated with Bacillus brevis (B. brevis) to evaluate its suitability for use in construction works. Stepped B. brevis suspension density (i.e., 0.5, 2.0, 4.0, 6.0 and 8.0 McFarland standards equivalent to 0, 1.50 × 108, 6.0 × 108, 1.20 × 109, 1.80 × 109 and 2.40 × 109 cells/ml, respectively) and cementation reagent (i.e., 0.25, 0.5, 0.75 and 1.0 M), respectively, were utilized to activate the MICP process. Compaction was conducted using British Standard light (BSL) (or standard Proctor) energy. Tests results indicate that the engineering behaviour of the bio-treated non-plastic aeolian silt soil improved. The maximum dry density (MDD) and the angle of internal friction values marginally increased, while cohesion and optimum moisture content (OMC) decreased with higher B. brevis suspension density and cementation reagent concentration. Peak angle of internal friction and minimum cohesion were recorded at 1.5 x 108 cells/ml. Highest unconfined compressive strength (UCS) value of 215.58 kN/m2 was obtained for specimen treated with 25 % B. brevis (6.0 × 109 cells/ml): 75 % cementation reagent (0.75 M) mix ratio. The results recorded show that the improved aeolian soil could be used in engineering works.

Effect of Permeation Grouting Using Cement Kiln Dust (CKD) On Some Mechanical Properties of Sandy Soil

Permeation grouting is a suitable technique to enhance the geotechnical characteristics of granular soils, several researches have proved that permeation grouting using conventional grouting materials has improved the behavior of the treated soils, but the use of conventional materials causes additional costs. Cement Kiln Dust (CKD) is a significant by-product produced in considerable quantities during the production of Ordinary Portland Cement. This study was conducted to assess the effect of permeation grouting using (CKD) grouts on enhancing some mechanical properties of coastal sandy soil in Syria. To achieve the objective of this study; a laboratory grouting model was manufactured. The studied sand has been grouted with suspensions consisting of different percentages of (CKD) (2, 4, 6, 8, 10, and 12%) as a proportion of the dry weight of the treated sand, and various mixing ratios (Water: CKD) (2:1, 4:1, 6:1, 8:1, and 10:1). Then an inclusive laboratory study was carried out before and after grouting for (7 & 28) days of treatment. The results of this study proved the effectiveness of (CKD) grouts; the grouted sand has obtained a high unconfined compressive strength. Also, the values of both shear strength and cohesion increase, and the values of permeability coefficient decrease as (CKD) content and curing period increase.

Recycled polyester fiber reinforcing red mud-improved volcanic ash as a sustainable construction material

Recycling waste for soil improvement is a cost-effective strategy to mitigate the energy consumption and carbon emission of traditional stabilization materials (cement, lime, etc.). This paper proposes an eco-friendly geotechnical improvement using recycled polyester fiber (RPF) and red mud to synergistically reinforce volcanic ash. For red mud -reinforced volcanic ash (RV) with five different RPF contents, a series of mechanical tests, water stability tests, microstructure tests and environmental impact tests were performed. Results show that RPF can significantly improve the mechanical performance and water stability of RV. The reinforcement increases with increasing RPF content, and the optimum contents of RPF is 0.9%. For specimens with optimum RPF incorporation, Unconfined compressive strength (UCS), splitting tensile strength are increased by 122%, 180%, respectively. It also allows saturated soil to still maintain higher UCS and the soil does not completely disintegrate in submerged environment. The pH value and toxicity leaching indicators of specimens both satisfy the specification limits and therefore the material has no environmental hazard. TGA, FT-IR and SEM-EDS indicate that the reinforcement mechanism of RPF on RV derives mainly from fiber-matrix interactions, including interface bonding, bridging effect and limiting micro-cracks development. RPF reinforced RV presents favorable engineering performance as a sustainable construction material and can contribute to the win-win objective of environmental conservation and waste recycling. This low-carbon and sustainable soil improvement technology can serve and guide the design of geotechnical engineering in volcanic areas.

Development and characterization of volume-stabilized grouts used for borehole heat exchangers

This study aims to develop volume-stabilized grouts made of ordinary Portland cement (OPC)-calcium sulfoaluminate (CSA) cement-calcium sulfate (CS) ternary systems for borehole heat exchanger (BHE) applications. A series of experimental tests were carried out to characterize their properties and evaluate the applicability of grouts used in BHE. The grouts made of ternary systems exhibited satisfactory flowability within four hours and excellent volumetric stability compared with the grouts made of OPC only. Moreover, the thermal conductivities of grouts composed of ternary systems reached a range of 0.582–0.628 W/mK under oven-dry conditions and 1.940–1.949 W/mK under saturated conditions. In addition, grouts exhibited high unconfined compressive strength within a range of 14.19-16.31 MPa, indicating that the grouts have sufficient capacity to maintain the stability of boreholes. Overall, the grouts made of ternary systems exhibited good flowability, remarkable volumetric stability, and high thermal conductivity under saturated conditions. Among them, the grout composed of 70% OPC, 15% CSA cement and 15% gypsum showed superior volumetric stability and satisfactory performance in other aspects, indicating that it has the potential for BHE applications.

Experimental study of the mechanical and thermal properties of metakaolin based geopolymer stabilized soil during low temperature curing

To address the challenges associated with significant thermal disturbance and carbon emissions resulting from the conventional stabilization of frozen soil using cement, geopolymer material is used to replace cement to stabilize frozen soil. The unconfined compressive strength (UCS) of the geopolymer stabilized soil was investigated in relation to the proportions of metakaolin (MK), calcium carbide slag (CCS), curing temperature, and curing age. Microscopic analysis was conducted to unveil the stabilized mechanism. The UCS, shear strength, thermal conductivity, hydration products and microstructure of geopolymer stabilized soil and cement soil were compared in parallel. A total of 240 experiments were conducted in this study. The outcomes indicate that the optimal content of MK and CCS is 10% and 6% respectively. The UCS of samples with the optimal content after 28d of curing at 20 °C, −2 °C, and − 10 °C are 3.783 MPa, 1.164 MPa, and 0.901 MPa respectively. The primary causes of the rise in UCS of the geopolymer stabilized soil are the production of amorphous calcium silicate hydrate and calcium aluminate hydrate gel as a result of the stimulation of MK based geopolymer with CCS. The UCS of the geopolymer stabilized soil decreases with a decrease in curing temperature. In frozen conditions, the expansion of ice crystals in the soil creates voids and promotes crack growth, leading to a decrease in the efficiency of geopolymerization reactions. After 28d of curing at room temperature and low temperature, the geopolymer stabilized soil with the optimal content exhibits higher UCS, failure strain, shear strength, cohesion, and internal friction angle compared to the cement soil. At all curing temperatures and ages, the geopolymer stabilized soil has a lower thermal conductivity than the cement soil. The geopolymer stabilized soil is less susceptible to low temperature curing than cement soil, demonstrating a larger amount of hydration products and a denser microstructure, according to experimental results from XRD and SEM. The results of this work offer a theoretical foundation for using geopolymer in place of cement to stabilize soils in permafrost regions.

Elevated Temperature Basic Oxygen Furnace Slag Stabilisation of Desilicated Foundry Sand

This study presents the use of Basic Oxygen Furnace slag (BOFS) as a stabilizer for disilicated waste foundry (DWF) sand and therefore provides an opportunity for high-volume use of waste material for low-cost, low-volume building and construction material. DWF was stabilized with BOFS to 40 %. The effect of composite moisture content, BOFS content, curing time and curing temperature was studied. A 50:50 DWF: BOFS composite cured at 80 °C for 96 h had the highest unconfined compressive strength (UCS) of 7.83 MPa, a 15.5 % water absorption after a 24 h soak with a corresponding 20.5 % reduction in UCS. The green specimen (70:30) was then used to stabilize expansive soil. The formation of hydration products was responsible for the strength gain in the stabilized DWF specimens. It was concluded that BOFS was successful in stabilizing DFS. The stabilised DWF for ASTM C34-13, C129-14a and South African standards (SANS227: 2007).