Unconfined Compressive Strength Research Articles

Experimental investigations on physico-mechanical properties of kaolinite clay soil stabilized at optimum silica fume content using clamshell ash and lime

This investigation examines the effect of clamshell ash (CSA) and lime additives on the physico-mechanical characteristics of kaolinite clay soil stabilized at the optimum silica fume content. Laboratory tests were performed to assess plasticity, shrink-swell characteristics, compaction characteristics, unconfined compressive strength (UCS), shear strength characteristics, mineralogical and morphological microstructure characteristics of stabilized soil specimens. The kaolinite clay soil was stabilized at its optimum silica fume content (6%) to produce the highest strength and was altered with three non-identical proportions of clamshell ash and lime (3%-9%). Cylindrical soil specimens, 76 mm in height and 38 mm in diameter, were moulded and treated for curing periods of 1, 7, 14, and 30 days to examine the strength of the altered soil. The findings revealed that, adding clamshell ash and lime significantly alters the plasticity, shrink-swell, maximum dry unit weights, and optimum moisture contents of the silica fume-stabilized soil. In terms of strength, the beneficial effects of CSA and lime additives were found to be more significant with more extended curing periods. Incremental increases in curing periods resulted in further enhancements in UCS, cohesion, and internal friction angle, indicating continued strength development over time. Microstructural analysis using field emission scanning electron microscopy and X-ray diffraction provided insights into the interparticle bonding mechanisms and microstructural changes induced by the addition of CSA and lime. The emergence of cementitious phases and pozzolanic responses between soil particles and stabilizers contributed to the densification and strengthening of the stabilized soil matrix. The findings of this study provide valuable insights into the potential of clamshell ash and lime additives to enhance the engineering properties of kaolinite clay soil stabilized with silica fume. These results have implications for sustainable soil stabilization practices, offering a promising approach to improve the performance of soils for various engineering applications, including construction and geotechnical projects.

Experimental study on mechanical and hydraulic properties of xanthan gum improved low liquid limit silty soil

The low liquid limit silty soil in the North China plain area is generally unsuitable for direct use as roadbed and slope soil. In order to improve the performance of low liquid limit silty soil, xanthan gum was used as an improver. Through a series of tests, the improvement effect of xanthan gum on low liquid limit silty soil was studied. The test results showed that Xanthan gum as an improver could significantly improve the unconfined compressive strength of silty soil. With the increase in dosage and curing age, the unconfined compressive strength of improved silty soil continued to improve and eventually tended to stabilize. The optimal dosage and curing period were 2% and 7 days, respectively. In addition, Xanthan gum could greatly improve the permeability and disintegration of low liquid limit silty soil. The permeability coefficient of improved silty soil with a content of 0.75% Xanthan gum and a 7-day curing period was 4.73 × 10−4 m·s−1, which was only 1.10% of that of plain silty soil at the same curing period. After immersion in water for 12 h, the soil only experienced slight disintegration. The scanning electron microscope image showed that the gel generated by the hydration reaction of Xanthan gum could improve the compactness and integrity of the soil by filling the voids, thus significantly improving the mechanical and hydraulic properties of the low liquid limit silty soil.

Micro- and nano-Illite to improve strength of untreated-soil as a nano soil-improvement (NSI) technique

Soil stabilization is a technique of improving the geotechnical properties of soils for various engineering applications. However, conventional stabilizers such as cement and lime have some limitations, such as high cost, environmental impact, and durability issues. Therefore, there is a need for alternative and innovative stabilizers that can overcome these challenges. This study introduces nano-Illite, a type of clay mineral, as a novel and effective soil stabilizer. Nano-Illite can form nano-cementation (NC) in soil, which is a process of enhancing the durability of various building materials. NC is also known as nano soil-improvement (NSI), a technique that has been developed in recent years. Four formulations of micro- and nano-Illite with concentrations of 0, 1, 2, and 3% were separately added to soil samples. The unconfined compressive strength (UCS) and the secant modulus at 50% of peak stress (E50) of the treated samples were measured and compared with the untreated samples. The results showed that 3% nano-Illite increased the UCS of soil by more than 2.2 times and the E50 by more than 1.5 times after 7 days of curing. Micro-Illite also improved the UCS and E50 of soil, but to a lesser extent. X-ray fluorescence (XRF), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses revealed the micro- and nano-structures of the soil specimens and the performance of Illite as a nano-additive. This research demonstrates the effectiveness of nano-Illite in soil improvement as a NSI technique, and its potential to replace or reduce the use of conventional stabilizers. This study also contributes to the understanding of the mechanisms and factors that influence the NC process in soil.

Mechanical behavior and microstructure evolution of slag-fly ash based geopolymer stabilized sand

Geopolymers made from ground granulated blast-furnace slag and fly ash could effectively address the issues of high energy consumption and emissions associated with Portland cement, which is commonly used as a soil curing agent. In this study, the unconfined compressive strength and microstructure of geopolymer-solidified sand were presented and analyzed. The study focused on effect of the type and ratio of activator, the ratio of slag to fly ash, and the ratio of water to (activator and cementitious materials) (W/(A + C)) on the behavior of geopolymer stabilized sand. The results of computed tomography (CT), and scanning electron microscope (SEM) indicate that the variation in initial water content significantly affects the porosity of the specimen, which increased as initial water content increased. The cracks were mainly found at the joints between the individual aggregates and at the edges of the individual aggregates. The pore size distribution of the specimens was concentrated in the range 0.0761–5 μm, while the polymer particle distribution was concentrated in the range 0.0761–10 μm, with a concentration of over 90 %. A significant amount of cementing material was densely distributed around both the aggregates and the pores. CT and SEM testing techniques enable a thorough analysis and mutual verification of the self-compacting process, pore distribution, and size, as well as the distribution of cementing material within the specimens. The optimum ratio for B-S19 has been determined.

An experimental study on 3D printed concrete reinforced with fibers recycled from wind turbine blades

The large-scale retirement and high recycling difficulty of wind turbine blades (WTB) pose great challenges to environment and society. To explore the practical applicability of recycled WTB in 3D printed concrete (3DCP), a systematic experimental study was conducted on the printability and physical-mechanical properties of 3DCP incorporating RWTB fiber. The distribution of RWTB fiber and porosity were analyzed using X-ray CT scan and Scanning Electron Microscopy, with the aim of unveiling the reinforcing and anisotropic mechanisms of 3DCP with RWTB fiber. The concrete with 3%–7% of RWTB fiber presented good extrudability and buildability, although slightly decreased the fluidity. Due to the directional effect and the layer-by-layer stacking process inherent in 3D printing, the RWTB fiber exhibited enhanced alignment along the printing direction, leading to modifications in the porosity. Incorporating 5% RWTB fiber in 3DCP significantly improved mechanical properties, with notable increases of 13.2%–29.9% in unconfined compressive strength and up to 147.4%–465.4% in bending toughness in the Y and Z loading directions, as compared to samples without fiber. Moreover, the mechanical anisotropy of 3DCP with RWTB fiber was less significant than that with the fiber having higher tensile strength, leading to a promising way to repurpose WTB and promote sustainability of 3DCP.

Mix Design and Field Detection of Large-Particle-Size Graded Crushed Stone Mixtures for Pavement Reconstruction

Large-particle-size graded crushed stone mixtures (LPS-GCSMs) can improve the shortcomings of conventional graded crushed stone, such as low strength, high deformation, and a low modulus of resilience. At present, there is no systematic research on the gradation design and field evaluation of the LPS-GCSMs. In this study, compaction and California bearing ratio (CBR) tests and field construction conditions were combined to design six kinds of gradation of LPS-GCSM, and the optimum gradation was revealed. In order to improve the mechanical properties of LPS-GCSM, 2.5% cement was added to the mixture to prepare a low-content cement-modified LPS-GCSM (LCC-LPS-GCSM) based on the suggested gradation. The mechanical properties of the LCC-LPS-GCSM were investigated through unconfined compression strength (UCS) and compression rebound modulus (CRM) tests. Moreover, the compaction and deflection properties of LPS-GCSM and LCC-LPS-GCSM were examined through the test battery. The results showed that the optimum gradation of LPS-GCSM can be achieved with a combination of aggregate sizes of 20–40 mm, 10–20 mm, 5–10 mm, and 0–5 mm at a ratio of 44:20:10:26. The passing rates of 19 mm and 4.75 mm should be approximately at the median value of the gradation in view of field construction uniformity and a coarse aggregate interlocking effect. The UCS and CRM values of LCC-LPS-GCSM increased rapidly from 0 day to 28 days while they slowed after 28 days, which was similar to those of cement-stabilized materials. The field detection suggested that LPS-GCSM exhibited favorable compaction and that the addition of cement improved the stability of the field compaction of the mixture. Adding a subbase course of LPS-GCSM between the old pavement and the LCC-LPS-GCSM base can lead to more uniform stress on the base. The results of this study provide a reference for the gradation design of LPS-GCSM and optimization of the design indicators.

Optimizing properties of clayey soil using lime and waste marble powder: a sustainable approach for engineering applications

Several studies have explored the potential of waste marble powder (WMP) and lime (LM) as solutions for issues associated with clayey soils. While WMP enhances mechanical properties and addresses environmental concerns, LM effectively improves soil characteristics. This research investigates the efficacy of LM and WMP, both individually and in combination, in addressing challenges specific to clayey soils in Bouzaroura El Bouni, Algeria. These soils typically exhibit low load-bearing capacity, poor permeability, and erosion susceptibility. LM demonstrates promise in enhancing soil properties, while WMP not only addresses environmental concerns but also enhances mechanical characteristics, providing a dual benefit. The study utilizes a three-variable experiment employing Response Surface Methodology (RSM) Box-Behnken Design, with variations in clay content (88%–100%), LM treatment (1.5%–9%), and WMP inclusion (1.5%–9%). Statistical analysis, including ANOVA, reveals significant patterns with p-values <5%. Functional relationships between input variables (clay, LM, and WMP) and output variables (cohesion, friction angle, and unconfined compressive strength) are expressed through high determination coefficients (R2 = 99.84%, 77.83%, and 96.78%, respectively). Numerical optimization identifies optimal mixtures with desirability close to one (0.899–0.908), indicating successful achievement of the objective with 88% clay content, 3% LM, and 6% WMP. This study provides valuable insights into optimizing clay soil behavior for environmental sustainability and engineering applications, emphasizing the potential of LM and WMP as strategic additives.

Sustainable Application of Pyrolytic Oxygen Furnace Slag in Cement-Stabilized Macadam: Volume Stability, Mechanical Properties, and Environmental Impact

As an industrial waste, basic oxygen furnace (BOF) slag is an ideal substitute for natural rubble and sand. However, its potential instability of volume restricts the application of the BOF slag in engineering. This study aims at investigating the volume stability and mechanical properties of BOF slag and its application as an aggregate in cement-stabilized macadam. As part of this research, the physicochemical properties, especially the volume stability, of two types of BOF slags and andesite were first studied. Then, mechanical properties, volume stability, and an environment analysis are used to evaluate the application of pyrolytic BOF slag in cement-stabilized macadam. The experimental results show that different types of BOF slags have similar thermal expansion coefficients, which are higher than andesite. The free CaO content of pyrolytic BOF slag is much lower than that of ordinary BOF slag and the volume expansion of pyrolytic BOF slag is less than 0.5%. The unconfined compressive strength (UCS) of cement-stabilized macadam using pyrolytic BOF slag is about 30% higher than that of andesite. Although the water loss rate is higher than a natural aggregate, dry shrinkage of pyrolytic BOF slag cement-stabilized macadam is about 30–50% less than that of a natural aggregate. Meanwhile, its shrinking speed is also slower than that of a natural aggregate. The micro-expansion properties of pyrolytic BOF slag could effectively partially offset the shrinkage characteristics of cement-stabilized macadam. Finally, the Toxicity Characteristic Leaching Procedure (TCLP) test results indicated that the metal leaching concentration meets the Chinese environmental standards. This study provides a direction for the large-scale and effective sustainable application of pyrolytic BOF slag.

Macroscopic properties and microscopic characterisation of an optimally designed anti-cracking stone base course filled with cement stabilised macadam

Stone base course filled with cement stabilised macadam (SFC) is a promising solution for addressing reflection cracks in semi-rigid base asphalt pavement due to its satisfactory crack resistance. However, its limited strength and construction challenges have impeded its widespread application. To overcome these challenges, an optimised mix proportion design method of SFC was proposed. Natural crushed limestones with specific particle sizes were selected to serve as skeletal coarse aggregates; fine aggregates and their proportions were step-by-step determined using aggregate and unconfined compressive strength tests. The multi-scale analysis integrating the performance tests and the microscopic detections was performed to evaluate the effectiveness of the proposed SFC, and compared with common cement stabilised macadam (CSM). The results indicate that the material exhibits satisfactory mechanical strength through a tightly interlocked skeleton structure and excellent crack resistance by dissipating strain energy and retarding cracking of SFC through the weak interface transition zone (ITZ).

Experimental Study on the Strength and Microstructure of Red Mud-Based Silty Sand Modified with Lime–Fly Ash

This study aimed to assess the viability of utilizing lime–fly ash (LF) and red mud (RM) in the modification of silty soil (LF-RMS) for subgrade filling. The primary objective of this research was to analyze the mechanical characteristics and examine the curing mechanisms associated with said modified materials. Different curing times were utilized in the analysis of mechanical properties (e.g., via unconfined compression testing), microstructure (via scanning electron microscopy, X-ray diffraction, and thermogravimetric-differential thermal analysis), and environmental indices (via assessment of corrosivity, heavy metal concentration, and radioactivity) with various dosages of red mud (DRM) and Lime–fly ash (DLF). Analyses of the curing mechanisms, failure modes, microstructures, and degrees of environmental impact associated with LF-RMS were also undertaken. The tests indicated that the unconfined compressive strength (UCS) exhibited an initial increase followed by a decrease as the DRM and DLF levels increased. Additionally, the strength of LF-RMS increased with an increase in curing time. It is worth noting that the specimen composed of 20% LF and 23% RM (D20%LF+23%RM) demonstrated a maximum UCS value of 4.72 MPa after 90 days of curing, which indicates that it has the strongest ability to resist deformation. The strength of the specimen cured for 90 days was 1.4 times higher than that of the specimen cured for 7 days (1.97 MPa). Furthermore, the toxic concentration and radionuclide index of LF-RMS were significantly reduced compared to those of pure RM. The overall concentration of heavy metals in the D20%LF+23%RM specimen decreased by more than 60% after curing for 28 days. The internal irradiation index and the external irradiation index decreased by 1.63 and 1.69, respectively. The hydration products in LF-RMS play a key role in the solidification of heavy metals, and the alkaline environment provided by RM also contributes to the precipitation and replacement of heavy metals. In this study, red mud, fly ash and lime were used to modify silty soil. The central tenets of sustainable development may be achieved through the reuse of RM as a road filler.

Study about the rehydration of phosphogypsum hemihydrate in tropical soil mixtures

ABSTRACT The objective of this paper is to verify the occurrence of phosphogypsum hemihydrate (PG-HH) rehydration and its influence on the mechanical behaviour in tropical soil mixtures. The studies were carried out in mixtures with lateritic clay, PG and Portland cement. Were carried out microstructural and mineralogical analyses with scanning electron microscopy and X-ray diffraction experiments, compaction tests at different setting times and unconfined compressive strength tests on saturated samples subjected to weathering. This study showed that PG-HH can rehydrate when it is in contact with water. This fact changes its crystals’ shape and impacts the mechanical behaviour of tropical soil mixtures. Saturated samples exposed to weathering presented strength reduction. However, the strength of mixtures with PG-HH, even when rehydrated, is superior to the strength of mixtures with PG-DH. The incorporation of PG-HH in mixtures with tropical soil and cement in geotechnical works is possible despite its rehydration.

The Design of a Novel Alkali-Activated Binder for Solidifying Silty Soft Clay and the Study of Its Solidification Mechanism

In order to overcome the problems of the high economic and environmental costs of a traditional ordinary portland cement-based binder, this study used self-combusted coal gangue (SCCG), granulated blast furnace slag (GBFS) and phosphorous slag (PS) to prepare a novel SCCG-GBFS-PS (SGP) ternary alkali-activated binder for solidifying silty soft clay (SC). Firstly, the parameters of the SGP ternary binder were optimized using orthogonal experiments. Then the effects of the SGP ternary binder content (mass ratio of the SGP ternary binder and the SGP-solidified soil), initial water content of SC (mass ratio of SC’ water and SC) and types of additives on the unconfined compressive strength (UCS) of the SGP-solidified soil were analyzed. Finally, the hydration products and microstructure of the SGP-solidified soil were analyzed to investigate the solidification mechanism of the SGP ternary binder. The results showed that the optimal mass ratio of GBFS and PS is 2:1, and the optimal alkali activator content (mass ratio of Na2O and the SGP ternary binder) and modulus of alkali activator (molar ratio of SiO2 and Na2O of alkali activator) were 13% and 1.3, respectively. When the SGP ternary binder content was 16% and the initial water content of SC was 35%, the SGP-solidified soil met the requirement of UCS for tertiary cured soil. The incorporation of triethanolamine and polyvinyl alcohol improved the UCS, while the incorporation of Na2SO4 significantly deteriorated the UCS of the SGP-solidified soil. The C-S-H gels and C(N)-A-S-H gels generated by hydration of the SGP-solidified soil were interspersed, interwoven and adhered to each other to form a network-like space structure that played the roles of skeleton, bonding soil particles and filling pores, which improved the macroscopic properties of the SGP-solidified soil. The results of this study provide a reference for the design and development of a solid waste-based binder for solidifying SC.

Properties of road subbase materials manufactured with geopolymer solidified waste drilling mud

In this study, geopolymer was adopted as an eco-friendly binding material to solidify waste drilling mud to fabricate geopolymer solidified waste drilling mud (GSWDM) as a pavement material in the subbase. Using precursor dosage, Na2SiO3 solution dosage, and slag powder (SP) dosage as parameters of mix proportion, the optimal mix proportions of GSWDM were determined through compressive strength tests. Based on a series of tests of unconfined compressive strength, splitting tensile strength, elastic modulus, and compressive resilient modulus, the effects of the SP percentage in the precursor and curing age on the mechanical properties of GSWDM were analyzed. The results indicated that all the mechanical properties of GSWDM were improved with the increasing SP percentage in the precursor. The 28-day unconfined compressive strength, splitting tensile strength, elastic modulus, and compressive resilient modulus of GSWDM were improved by 80.8%, 56.3%, 65.3%, and 76.72%, respectively, when the SP percentage in the precursor increased from 60% to 100%. A nonlinear increase in the mechanical properties of GSWDM was observed as the curing age increased, with a significant increase in the curing age from 7 days to 14 days and a slight increase in the curing age from 14 days to 28 days. Moreover, the microstructure of GSWDM was denser as the curing age and the SP percentage in the precursor grew. The results of this study verified that GSWDM can be used as construction material for road subbase.

Laboratory Evaluation of Strength Performance of Full-Depth Reclamation with Portland Cement Material

Laboratory Evaluation of Strength Performance of Full-Depth Reclamation with Portland Cement Material

Mitigation of Soil Erosion and Enhancement of Slope Stability through the Utilization of Lignin Biopolymer.

Human activities have had a profound impact on the environment, particularly in relation to surface erosion and landslides. These processes, which are natural phenomena, have been exacerbated by human actions, leading to detrimental consequences for ecosystems, communities, and the overall health of the planet. The use of lignin (LIG) as a biopolymer soil additive material is regarded as an eco-friendly solution against soil erosion and slope failure which holds immense promise. However, significant research gaps currently hinder a comprehensive understanding of its mechanisms and effectiveness. Experimental studies offer a robust platform to address these gaps by providing controlled conditions for assessing soil stability, exploring mechanisms, and evaluating adaptability. Bridging these research gaps will contribute to the development of innovative and sustainable strategies for mitigating soil erosion and preventing slope failure, thereby promoting environmental resilience and resource conservation. This study aimed to investigate the effect of the LIG biopolymer on mitigation of soil erosion, slope failure and the enhancement of soil strength by conducting laboratory tests (UU triaxial, unconfined compressive strength (UCS), and soaking) as well as flume experiments under uniform rainfall events. The alterations in the engineering characteristics and erosion resistance of silty soil mixed with a LIG additive at concentrations of 1% and 3.0% by weight have been examined. The results show that the LIG-treated samples demonstrated an enhanced resistance to surface erosion and an enhanced prevention of slope failure, as well as improved shear stress, cohesion, stiffness, and resistance to water infiltration.

Analysis of Mechanical Properties of Fiber-Reinforced Soil Cement Based on Kaolin.

Adding fibers into cement to form fiber-reinforced soil cement material can effectively enhance its physical and mechanical properties. In order to investigate the effect of fiber type and dosage on the strength of fiber-reinforced soil cement, polypropylene fibers (PPFs), polyvinyl alcohol fibers (PVAFs), and glass fibers (GFs) were blended according to the mass fraction of the mixture of cement and dry soil (0.5%, 1%, 1.5%, and 2%). Unconfined compressive strength tests, split tensile strength tests, scanning electron microscopy (SEM) tests, and mercury intrusion porosimetry (MIP) pore structure analysis tests were conducted. The results indicated that the unconfined compressive strength of the three types of fiber-reinforced soil cement peaked at a fiber dosage of 0.5%, registering 26.72 MPa, 27.49 MPa, and 27.67 MPa, respectively. The split tensile strength of all three fiber-reinforced soil cement variants reached their maximum at a 1.5% fiber dosage, recording 2.29 MPa, 2.34 MPa, and 2.27 MPa, respectively. The predominant pore sizes in all three fiber-reinforced soil cement specimens ranged from 10 nm to 100 nm. Furthermore, analysis from the perspective of energy evolution revealed that a moderate fiber dosage can minimize energy loss. This paper demonstrates that the unconfined compressive strength test, split tensile strength test, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) pore structure analysis offer theoretical underpinnings for the utilization of fiber-reinforced soil cement in helical pile core stiffening and broader engineering applications.

Pb2+ Leachability in the Cement-Based Solidified/Stabilized Contaminated Clay Under Saline and Alkaline Environments

ABSTRACT Harsh environments such as saline and alkaline environments will affect solidification/stabilization quality, especially considering the long-term service cycle. To investigate the environmental influence on the leaching behavior of solidified/stabilized soils, the Pb2+ leaching behaviors of cement-stabilized contaminated clay (CSC) and ternary binder (CSG)-stabilized contaminated clay (CSGSC) under the endo/exogenous saline and alkaline attacking environment were discussed. Note that, the ternary CSG binder, consisting of cement, silica fume (SF), and desulfurization gypsum powder (DGP) in a ratio of 1:0.25:0.19, underwent pre-screening based on its unconfined compressive strength (UCS). Scanning electron microscopy was employed to reveal the environment-resisting mechanism. The leaching concentration of Pb2+ in the leachate from CSGSC was lower than that from CSC in both saline and alkaline environments with a same incorporation ratio (15%) to dry soils, indicating CSG’s efficiency. Under the exogenous environment, the Pb2+ cumulative leaching mass from the stabilized clays in saline environment was more than that in deionized water, while that under the endogenous environment was opposite. Microstructure analysis indicated that the SF and DGP in CSG facilitated the formation of calcium silicate hydrate and ettringite, resulting in a denser structure that greatly enhances the physical encapsulation and chemical fixation of Pb2+ cation. At the end, the different mechanism under endo/exogenous attacking environments was attributed to the cation influence on clay minerals and the formation of new substance. These findings provide a guidance for the remediation of contaminated soil in harsh environments.

Preparation and evaluation of GCD-1 lunar regolith simulant based geopolymer activated by solid sodium silicate

In this study, a new lunar regolith simulant, named "GCD-1", was formulated by combining various minerals, such as anorthite, albite, pyroxene, ilmenite, slag, and fly ash. Through X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD) analysis, it was verified that the main mineral composition of GCD-1 was basically the same as that of the lunar soil at the Apollo 14 landing site, in which the deviation in the main compound (i.e., SiO2 and Al2O3) was within 0.5%. Furthermore, GCD-1 based geopolymer was prepared by the one-part method, which was a mixture of solid GCD-1 precursor, solid sodium silicate (SS) activator, and water. The average daytime temperature at the lunar equator, which was calculated to be 60°C, was set as the curing temperature for the GCD-1 based geopolymer. The strength development of the GCD-1 based geopolymer was then characterized by unconfined compressive strength (UCS) for 3, 7, and 12 curing days to consider the effectiveness of the factors (solid SS to lunar regolith simulant [S/L] and water to binder ratio [W/B]). The micro-analysis tests including scanning electron microscope-energy dispersive spectrometer (SEM-EDS), mercury intrusion porosimetry (MIP), and brunner-emmet-teller (BET), were further conducted to investigate the microstructural development of the GCD-1 based geopolymer. Results showed that the increase of the W/B ratio in the GCD-1 based geopolymer tended to increase the total porosity of the sample, thereby inducing a lower UCS. At the same time, for a fixed W/B ratio, the higher S/L ratio had a certain inhibition effect on the hydration reaction, which caused the reduction in the UCS of the sample. The highest UCS of the GCD-1 based geopolymer reaching 30.54MPa, was achieved under the simulated lunar equatorial daytime temperature for 12 days with W/B and S/L ratios set at 0.25 and 0.18, respectively. Microstructure and mineralogy analyses indicated that the hydrated sodium aluminosilicate (N-A-S-H) gels contributed to reducing the sample's porosity, thereby enhancing the UCS. The relationship between the UCS and total porosity of GCD-1 based geopolymer was then derived. The results of the current study are crucial for lunar base construction with in-situ resources.

Bioengineering solutions for expansive soil stabilization using waste materials: An experimental evaluation

Municipal solid waste incineration ash is the outcome/product of bioengineering science. The incineration or burning of municipal solid waste (MSW) reduces the volume of this biomass by 90%, and the residual ash can be used in several applications. In this study, the potential of municipal solid waste incineration (MSWI) ash and calcium carbide residue (CCR) waste for stabilization of expansive soil has been experimentally evaluated. The abnormal shrink–swell characteristics of expansive soils pose several problems for civil engineering structures when these soils are used for construction in their original form. The study presents an experimental set-up to determine the best combination of additives to achieve the most favorable technical characteristics of expansive soil for civil engineering activities. The percentage of expansive soil has been kept fixed at 60% of the total weight of the mix for varying ratios of stabilizing agents. The optimization of the stabilizing materials is based on the highest strength parameters of the mix achieved for a particular ratio of additives and soil. The two stabilizing agents are waste materials, and their disposal through landfilling has become costly due to a scarcity of space and handling mechanisms. The values of strength parameters, unconfined compressive strength (UCS), and split tensile strength (STS) of a treated mix are found to be highest for a unique combination of 60% lime stabilized expansive soil and 20% MSWI ash and an equal quantity (20%) of CCR. The cumulative effect of adding the best mix of additives to soil and curing time depicts an improvement of 526.03% in UCS and 463.41% in STS of the mix compared to one day and 28 days of curing time. There is scope for further study, such as adding some fibers to the finalized mix to reinforce the soil mix.

Synergistic Effects of Recycled Demolition Waste and GGBS-FA based Geopolymers on the Mechanical Properties and Stabilization Mechanism of High Plasticity Clay

Recycled demolition waste (RDW) and ground granulated blast furnace slag-fly ash-based geopolymer (GFG) are promising materials for treating high-plasticity clay (CH) in highway subgrades. However, the underlying synergistic stabilization mechanisms remain unclear. To elucidate the fundamental mechanisms governing post-treatment soil stabilization, a multi-scale laboratory investigation was undertaken. This investigation encompassed the evaluation of mechanical properties (compaction, California bearing ratio (CBR), and unconfined compressive strength (UCS)) to quantify the enhanced performance of the treated soil. Additionally, microstructural and mineralogical characterization was performed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), and atomic force microscopy (AFM) to elucidate the microscopic mechanisms responsible for this improvement. The results indicated that the addition of RDW led to a reduction in the optimum moisture content (OMC) while increasing the maximum dry density (MDD) of CH. Moreover, upon incorporating RDW-GFG, the mechanical properties of the cured soil exhibited significant improvement. Specifically, the addition of 25% RDW to CH resulted in a 184% increase in CBR and effective improvement in water stability (immersion swelling percentage is reduced). Furthermore, when 25% RDW and 15% GFG were added to CH, the UCS has increased significantly by 8 times. The addition of RDW effectively enhanced the particle size distribution, compacted the soil, thus increased the shear strength. The results from XRD and SEM analyses revealed that the inclusion of GFG could generate geopolymer cementitious bonding network in the soil matrix. These materials facilitated bonding between CH particles and RDW, filling the pores and densifying the overall structure, thus increasing its strength. The synergy of RDW-GFG substantially improved the highly plastic soil through physicochemical actions, markedly elevating both its strength and water stability. Consequently, the outcomes of this experimental study offer valuable insights for road engineering applications.