Unconfined Compressive Strength Research Articles

Study on Mechanism of Mechanical Property Enhancement of Expansive Soil by Alkali-Activated Slag.

Expansive soil poses significant challenges for engineering due to its susceptibility to swelling and shrinkage. This study aims to explore effective methods for improving its mechanical properties using single alkaline activators, single slag, and their combination. Laboratory experiments were conducted to evaluate the unconfined compressive strength (UCS) and analyze curing mechanisms through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrate that all three treatments enhance soil strength, with the combination of alkali-activated slag being the most effective, followed by the single alkaline activator and single slag. Optimal dosages were determined as 15% for the activator and slag individually and 15% activator combined with 20% slag, yielding the densest structure and highest UCS. The activator's modulus of 1.5 was found to be optimal, and strength improved further with extended curing time. A microscopic analysis revealed that alkaline activation formed gel-like substances and dense needle-like structures, while slag generated CaCO3 and Ca(OH)2. The combination produces a synergistic effect, creating substantial amounts of C-S-H, C-A-S-H gel, and dense needle-like structures, which enhance soil compactness and strength by binding particles and filling voids. These findings provide insights into the curing mechanisms and offer practical solutions for improving expansive soil in engineering applications.

Optimization of CLSM performance through integration of GGBS and red mud

This study investigates the engineering and dynamic properties of Controlled Low Strength Materials (CLSM) to evaluate their practical applicability. CLSM is characterized by its self-flowing and self-compacting nature, making it an ideal candidate for various construction applications. The experimental program includes testing for unconfined compressive strength, flowability, setting time, fresh and hardened densities, water absorption, sorptivity, and shear wave velocity. These properties are critical in determining the material's suitability for backfill applications, ensuring both strength and ease of excavation. The results indicate that both fresh and hardened densities conform to established guidelines. The shear wave velocity test conducted helps gauge the seismic capability of CLSM mixes. The findings highlight CLSM's potential as a cost efficient and efficient material for construction use, particularly in backfill scenarios.

Wetting-Drying Durability of Lateritic Soil Stabilized with One-Part High-Calcium Fly Ash Geopolymer

This study investigates the durability under wetting and drying conditions of marginal lateritic soil (MLS) stabilized with a one-part high-calcium fly ash geopolymer (OPFAG). The variables include an MLS: fly ash ratio of 70:30, solid sodium hydroxide content ranging from 0 to 40%, and the number of wet-dry cycles. Durability is evaluated by measuring the unconfined compressive strength (UCS) of MLS samples stabilized with OPFAG and MLS samples stabilized with ordinary Portland cement (OPC). The results show that OPFAG improved the engineering properties of MLS. The highest UCS values are achieved at 20% solid sodium hydroxide, achieving a UCS of 1889 kPa for the geopolymer-stabilized MLS and at 5% OPC for OPC-stabilized MLS (1320 kPa). The UCS of both stabilized MLS samples increases with the number of wet-dry cycles up to 6 cycles, after which a decline is observed.

Research on the properties of polymer stabilized coal gangue materials in rubber powder slag base

In order to solve the problems of high energy consumption in cement production, environmental pollution by coal gangue, shortage of aggregate resources in road engineering, and improvement of shrinkage performance of semi-rigid base materials, the properties of rubber powder slag-based polymer stabilized coal gangue materials were studied. On the basis of raw material tests, the mechanical properties and durability of slag-based geopolymer stabilized materials with different geopolymer content and coal gangue substitution rate were studied. The unconfined compressive strength, indirect tensile strength, compressive rebound modulus, freeze–thaw and dry shrinkage tests of geopolymer stabilized crushed stone/coal gangue (GSS/GSG) mixtures with different rubber powder contents were carried out. The microstructure of geopolymer stabilized coal gangue mixture was analyzed by scanning electron microscopy and energy spectrum analysis. The results show that with the increase of geopolymer content, the compressive strength, indirect tensile strength and frost resistance of GSS continue to increase, but its drying shrinkage performance will be adversely affected. When coal gangue replaces natural gravel, its performance in all aspects has decreased, and the mechanical properties and frost resistance have decreased significantly. The incorporation of rubber powder will slightly reduce the mechanical properties of geopolymer stabilized coal gangue material, but can effectively improve its drying shrinkage performance. The optimum content of rubber powder is 1.2%, and the dry shrinkage coefficient is reduced by 12.1%. The bonding effect of C–S–H generated by slag can promote the formation of N–A–S–H gel from fly ash. The rubber powder can stabilize the pore of the coal gangue material and the energy absorption of the rubber powder by filling the geopolymer, so as to achieve the purpose of stabilizing the shrinkage performance and compressive resilient modulus of the coal gangue material by the geopolymer.

Stabilising highly expansive soil by using Nano-Clay additive

ABSTRACT This study aims to investigate the efficacy of hydrophilic bentonite Nano-Clay in improving the geotechnical characteristics of expansive soil sourced from the Al-Mushaqar region in Jordan. In this study sonic wave-assisted and manual mixing techniques applied to expansive soil specimens. Subsequently, a comparative analysis was conducted to explain the disparities in outcomes between these two mixing methods. Various proportions of Nano-Clay were introduced into the soil, ranging from 0% to 2.5% by dry weight of the soil. The study focused on evaluating their influence on key parameters, including compaction, Unconfined Compressive Strength (UCS), and Free Swell Index (FSI). The introduction of Nano-Clay into the soil exhibited a noteworthy enhancement in its strength characteristics, accompanied with a reduction in its swelling tendencies. Notably, the application of 0.5% Nano-Clay during sonication led to a remarkable 53.4% augmentation in UCS and a simultaneous 41% reduction in FSI. In contrast, non-sonicated samples treated with 1% Nano-Clay exhibited a notable 35.21% increase in UCS and a substantial 52.4% reduction in FSI. These findings underscore the significant potential of Nano-Clay in fortifying expansive soils, thereby offering promising prospects for geotechnical engineering applications.

Assessing the impact of recycled carpet waste (RCW) on unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) in cement-stabilized sandy soil: an experimental study

Assessing the impact of recycled carpet waste (RCW) on unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) in cement-stabilized sandy soil: an experimental study

Mechanical and Durable Performance of Lime-Steel Slag-Coal Gangue Mixtures Prepared by a Uniform Design Method for Pavement Base Applications

To reduce the accumulation of coal gangue and steel slag, a mixture of lime-steel slag-coal gangue for pavement base was prepared. Six groups of lime-steel slag-coal gangue mixtures were designed using a uniform design method. The 7 d unconfined compressive strength, 180 d compressive resilience modulus and 180 d splitting tensile strength tests, the freeze-thaw cycles, and the wet and dry cycles were carried out to study the mechanical properties, frost resistance and water stability. The expansion effect of f-CaO in steel slag on the mixtures was investigated by water immersion. SEM was used to explore microscopic changes in the mixtures. The field application of coal gangue mixture was carried out for two years. The results show that the regression equations obtained by the uniform test have high accuracy. With the increase of lime in the mixture, the mechanical strength, frost resistance, and water stability of the mixtures were first enhanced and then decreased. With the increase of steel slag, the unconfined compressive strength increased, the compressive resilience modulus increased at first and then decreased, the splitting tensile strength decreased, the BDR value decreased, and the strength loss of water stability increased gradually. The internal structure of the mixtures is stable and has good frost resistance. There is no obvious microscopical difference before and after freeze-thaw cycles. The immersion expansion rate of the mixtures was far less than 1.5 %.

Mechanical properties of double-solid waste cement stabilized Macadam

Cement stabilized macadam base has high strength and excellent bearing capacity, but the problems of water-temperature sensitivity, easy shrinkage cracking and large demand for aggregate limit the further development and application of cement stabilized macadam base. At the same time, with the economy development, the increase of solid waste, such as waste tires and construction waste, has caused great pressure on the ecological environment. In order to ensure better mechanical properties and shrinkage resistance of the cement stabilized macadam on the basis of full use of solid waste. In this paper, mechanical properties tests such as unconfined compressive strength, splitting strength, compressive resilient modulus and shrinkage properties tests such as dry shrinkage and temperature shrinkage were conducted. Double-solid waste cement stabilized macadam mixture were prepared by partially replace fine and coarse aggregates with waste crumb rubber of different mesh and replacement ratios and recycled concrete aggregate of different replacement ratios, and their properties were investigated. The experimental results show that: (1) The good elasticity and toughness of waste crumb rubber can improve the crack resistance of cement stabilized macadam mixture. While the mechanical properties such as unconfined compressive strength and splitting strength will be reduced. (2) The mechanical properties of double-solid waste cement stabilized macadam mixture can be improved by partially replacing coarse aggregate with appropriate amount of recycled concrete aggregate with porous and rough surface, but it will adversely affect its shrinkage resistance. (3) The recommended particle size and replacement ratio of waste crumb rubber in double-solid waste cement stabilized macadam mixture are 40 mesh and 0.5%, respectively, and the recommended replacement ratio of recycled concrete aggregate is 75%. The mechanical properties indexes of double-solid waste cement stabilized macadam mixture can meet the specification requirements.

Hydroelectric simulation of the phreatic water response of mining cracked soil based on microbial solidification

Abstract Coal mining in ecologically fragile areas results in the failure of aquiclude layers and the loss of surface water bodies. Herein, research was conducted on the microbial solidification of cracked soils and the corresponding response of the ecological water table. A simulation of mining-induced cracked soils was performed via microbial solidification. The mechanical and hydrological properties of cracked soil samples repaired with different filling materials were compared via unconfined compressive strength and falling head permeability tests. Hydraulic-electric similarity modeling techniques were employed to evaluate the effectiveness of microbial solidification in the aquiclude layers. After low-temperature acclimation, Bacillus megaterium adapted to the geological environment of the study area, exhibiting a high viable cell density. When the cracked soil was filled with a 1:1 ratio of aeolian sand to clay particles, the microbially remediated soil demonstrated optimal mechanical and hydraulic properties. Hydraulic-electric similarity numerical simulations revealed that the ecological water table at the coalface remained within a reasonable range following microbial solidification, suggesting that microbial solidification achieved water-preserving coal mining. These findings provide a reference for restoring aquiclude layers damaged by coal mining.

Effects of zeolite and palm fiber on the weathering resistance and durability characteristic of cement soil

This paper aims to investigate the effects of zeolite and palm fiber on the strength and durability of cement soil. Based on the findings of previous research, optimal proportions of zeolite, palm fiber, and cement, as well as the appropriate curing age, were determined. Subsequently, unconfined compressive strength tests, dry-wet cycle tests, and freeze-thaw tests were conducted, utilizing NaCl and Na2SO4 solutions over the specified curing period. The strength and durability characteristics of the samples were evaluated by assessing mass and strength loss, taking into account the combined effects of NaCl and Na2SO4 solution erosion. The test data also provide a fitting relationship between strength and the number of cycles under the influence of different solutions, thereby offering a basis for theoretical predictions without the need for additional experiments. Finally, the microscopic mechanisms were analyzed using scanning electron microscopy (SEM). The results indicate that the cement soil composite of zeolite and palm fiber, when combined in optimal proportions, exhibits the best durability and minimal loss of strength and mass, irrespective of whether exposed to clean water or salt erosion, as well as during dry-wet or freeze-thaw cycles.

Role of Calcined-Clay-Based Geopolymers for Effective Stabilization of Expansive Soils

Effective stabilization of expansive soils remains a challenge for transportation infrastructure. In line with the United Nations' sustainability goals, most research on eco-friendly stabilizers is still in its early stages, focusing primarily on laboratory evaluations. This study aims to evaluate the efficacy of alkali-activated calcined clay-based geopolymers (CCBGPs) and investigate the most effective minerals contributing to its stabilization of expansive soils. Four locally available clays were used to synthesize CCBGPs, and based on unconfined compressive strength, two of them were selected for further stabilization of expansive soils. The treated soils underwent comprehensive engineering, microstructural, and mineralogical analyses. A machine learning (ML)-based regression model was developed and tested to examine the effects of CCBGP and soil mineralogy on engineering performance of the treated soils. Engineering tests on treated specimens showed improved performance with increasing CCBGP dosage and curing periods, while microstructural and mineralogical analyses revealed physical and chemical interactions with soil particles that enhanced engineering properties. The ML model identified kaolinite as the most influential factor, which enhanced geopolymerization by forming more binder gel, and improved engineering properties. Overall, the research indicated that selection of kaolinite-rich, locally available CCBGPs could serve as sustainable source for improving expansive soils in transportation infrastructure.

Using One-Part Geopolymer in Stabilizing High-Water-Content Soft Clay: Towards an Eco-Friendly and Cost-Effective Solution

To achieve environmental and economic goals in ground improvement, a one-part geopolymer (OPG), synthesized from binary precursors (fly ash [FA] and granulated blast furnace slag [GGBFS]) and a solid activator (solid sodium silicate [NS]), was used to replace ordinary Portland cement (OPC) for stabilizing high-water-content soft clay. The effects of different initial water content (50%, 80%, 100%, and 120%) and various OPG binder content (10%, 20%, 30%, and 40%) on the strength development of the OPG-stabilized soft clay were investigated through unconfined compressive strength (UCS) and unconsolidated undrained (UU) triaxial tests. Additionally, the microstructure evolution and the distribution of pores in the OPG-stabilized soft clay were examined by the utilization of mercury intrusion porosimetry (MIP) and scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) techniques, respectively. The life cycle assessment (LCA) methodology was then used to analyze the environmental and economic advantages of employing an OPG binder for soil stabilization. It was revealed that the optimal content of OPG binder was contingent upon the water content of soft clay, with variations in requirements for strength development. Specifically, for soft clay not demanding early strength, a maximum binder content of 20% is proposed. Conversely, for soft clay that necessitated rapid strength gain, the OPG binder content escalated with increasing water content of the soft clay, in which soft clays with different water contents had corresponding required amounts of OPG binder. For soil with water content ranging from 50% to 80%, the recommended OPG binder content is 20%. While for soil with 100% and 120% water content, the designed OPG binder content is suggested to be 30% and 40%, respectively. The environmental assessment demonstrated that the utilization of OPG as a binder for the stabilization of soft clay reduces costs and carbon emissions in comparison to OPC. The present study provides substantial theoretical validation for the utilization of OPG as a novel binder to stabilize soft clay with elevated water content, which holds promise as an eco-friendly and cost-effective solution in ground improvement.

Experimental Study on the Flexural Performance of Geogrid-Reinforced Foamed Lightweight Soil

The flexural behavior of geogrid-reinforced foamed lightweight soil (GRFL soil) is investigated in this study using unconfined compressive and four-point bending tests. The effects of wet density and reinforcement layers on flexural performance are analyzed using load–displacement curves, damage patterns, load characteristics, unconfined compressive strength, and flexural strength. A variance study demonstrates that increasing the wet density significantly increases unconfined compressive strength. Bond stress mechanisms enable geogrid integration, efficiently reroute stresses internally, and greatly increase flexural strength. With a maximum unconfined compressive strength of 3.16 MPa and a peak flexural strength increase of 166%, this reinforcement increases both strength and ductility by changing the damage pattern from brittle to ductile. The principal load is initially supported by the foamed lightweight soil, and in later phases, geogrids take over load-bearing responsibilities. Additionally, the work correlates the ratio of unconfined compressive to flexural strength with wet density and informs the development of predictive models for unconfined compressive strength as a function of reinforcing layers and wet density.

Geotechnical Properties of Soil-Lightweight Aggregate Mixtures

This study investigates the stabilization and strengthening of clayey soils using several Lightweight Aggregates (LWAs), including Lightweight Expanded Clay Aggregate (LECA), Ponza (Pumice), and Thermostone. LWAs were incorporated into the soil to evaluate their impact on critical geotechnical parameters, such as compaction, consolidation, Unconfined Compressive Strength (UCS), and shear strength. The results revealed that incorporating LWAs effectively reduces the soil density, increases the void ratios, and enhances certain soil properties. LECA demonstrated the most substantial impact in decreasing soil density and increasing porosity, achieving a maximum density reduction of 60% and a void ratio increase of 75% at a 60% addition. While LWAs enhanced the internal friction angle by up to 90% -with Thermostone showing the highest increase at a 60% addition- cohesion diminished across all concentrations. The UCS peaked with a 94% increase at a 10% LECA addition but decreased with higher LWA percentages due to the porous nature of the additives disrupting the soil matrix. Optimal performance was observed with LWA concentrations between 10% and 30%, balancing improved strength and soil integrity. These findings suggest that LWAs can effectively stabilize and strengthen clayey soils, particularly in applications requiring reduced weight and enhanced shear strength, provided that the mixing ratios are carefully calibrated to align with project-specific requirements.

Improving the Engineering Properties of Highly Expansive Soil by adding Psyllium Seed Biogel

This study investigates the use of environmentally sustainable materials, particularly biopolymers, to enhance the engineering properties of expansive soils. Psyllium Seed (PS) biogel, added in four percentages, 0.4%, 0.8%, 1.2%, and 1.6% by dry weight of soil, was evaluated as a biopolymer additive for highly expansive soil. A series of tests were conducted on treated and untreated soil samples. The results revealed a slight decrease in the Atterberg limits with 1.6% PS biogel, where the liquid limit (LL) reached 75.3%, the plastic limit (PL) dropped to 32.65%, and the plasticity index (PI) was reduced to 42.65%. The swelling potential decreased significantly by 76% at 1.6% PS biogel. Compressibility improved with a 52.3% reduction in the compression index (Cc) and a 96% reduction in the recompression index (Cr) at 1.6% PS biogel content. The Unconfined Compressive Strength (UCS) increased, with the best improvement being observed at 0.8% PS biogel (81.6%), and continued enhancement with longer curing periods. Elasticity also improved, with the strain at failure increasing by 83.75% at 1.2% PS biogel. The SEM analysis confirmed that 0.8% PS biogel rearranged the clay particles and reduced voids, leading to enhanced UCS and reduced swelling. These findings highlight the PS biogel as an environmentally sustainable and effective material for improving the engineering properties of expansive soils.

Mechanical properties and micro-mechanisms of polyurethane foam treatment of construction waste

ABSTRACT The generation of construction and demolition waste (CDW) has been rising rapidly in recent years. However, the recycling rate of CDW remains low due to inherent challenges such as easy fragmentation, inadequate strength, and poor engineering properties of CDW particles. To address these issues, this study investigates the application of polyurethane foam adhesive (PFA) as a strengthening agent to enhance the mechanical and structural properties of CDW for use in civil engineering infrastructure. Unconfined compressive strength (UCS) tests and consolidated undrained triaxial compression (CU) tests were performed to evaluate the mechanical performance of PFA-modified CDW, while the microstructure was analyzed using Scanning Electron Microscopy (SEM). The results indicate a substantial increase in UCS with varying PFA content after 24 h of gelling. Specifically, UCS values increased by 123.7, 263.93, 497.78, and 737.18 kPa with successive increments in PFA content. Moreover, PFA exhibited a more pronounced enhancement of shear strength compared to UCS. At a PFA content of 6%, cohesion increased dramatically from 5.29 kPa to 868.96 kPa, while the internal friction angle rose from 35.83° to 39.53°. SEM analysis revealed that PFA improves the internal structure of CDW by cementing particles, filling voids, and forming cohesive aggregates. These findings propose a novel method for CDW recycling, offering significant potential for the broader adoption of PFA-enhanced CDW in engineering applications.

Stabilization of Peat soil using Ordinary Portland Cement and Crushed Seashells

Abstract In the fields of environmental and civil engineering, peat soil is regarded as one of the most troublesome types of soil in the world. Furthermore, the peat soil is a high compressible material. This paper discussed about stabilization of the peat soil using an ordinary portland cement and crushed seashells which are to determine the physical properties of the peat soil such as moisture content, specific gravity, liquid limit and organic content and to analyse engineering properties through unconfined compressive strength and scanning electron microscope. The samples were prepared with various ratio of mixture whereas 40% cement 20% mixed seashell (C40CS20), 30% cement 30% mixed seashell (C30CS30) 50% cement 10% mixed seashell (C50MS10) with curing day 14 and 28 days. From the observation, it was found that C40MS20 achieved the highest unconfined compressive strength compared to C30MS30 and C50MS10 which was 67.79 kN/m2 at 28 curing days. Meanwhile, the untreated peat soil had very low compressive strength which was only 18.29 kN/m2. Therefore, the ordinary portland cement and the mixed seashell was proved to have significant effect in reaching moderate compressive strength in peat soil.

Experimental study on physical and mechanical properties of expanded soil improved by lime activated blast furnace slag

Abstract To address environmental concerns related to cement-stabilized expansive soil and the safety risks of caustic-activated blast furnace slag, this study explores the use of lime-activated blast furnace slag as an alternative stabilizer in northern Hebei, China. The effects of slag dosage, curing time, and osmotic pressure on the expansion, osmotic properties, and strength of the improved soil were evaluated through free expansion rate, permeability coefficient, and unconfined compressive strength tests. Results show that adding slag-lime significantly reduces soil expansion. As slag content increases, the free expansion rate decreases exponentially. During the curing period of 3–7 days, expansion declines and stabilizes between 7–14 days. Similarly, the permeability coefficient permeability coefficient decreases with higher slag content, following a quadratic trend. Under osmotic pressures of 0.1–0.2 MPa, the permeability coefficient permeability coefficient increases but stabilizes between 0.2–0.4 MPa.Furthermore, slag-lime significantly enhances unconfined compressive strength, which increases linearly with slag content. The stress–strain curve follows a logistic function in the rising stage and a rational fractional equation in the descending stage.This study demonstrates that lime-activated blast furnace slag is a sustainable and effective alternative for stabilizing expansive soils while reducing dependence on cement.

Effects of specimen size and loading rate on the mechanical property of Bentonil-WRK bentonite for engineered barrier system

Effects of specimen size and loading rate on the mechanical property of Bentonil-WRK bentonite for engineered barrier system

Automated gradation design of natural waste gravel soil stabilized by composite soil stabilizer based on a novel DNNSS-APDM-PFC model.

Automated gradation design of natural waste gravel soil stabilized by composite soil stabilizer based on a novel DNNSS-APDM-PFC model.