Clay Specimens Research Articles

Influence of the coefficient of non-uniformity of expansion of clay soil specimen on mechanical characteristics

Influence of the coefficient of non-uniformity of expansion of clay soil specimen on mechanical characteristics

Improving clay-geogrid interaction: Enhancing pullout resistance with recycled concrete aggregate encapsulation

In this study, Recycled Concrete Aggregate (RCA) was employed as a sandwich technique around the geogrid to enhance the pullout resistance of the geogrid in clayey backfills. Large-scale pullout tests were conducted on three configurations: geogrid-reinforced clay, geogrid-reinforced RCA, and geogrid sandwiched between layers of RCA, aimed at investigating pullout resistance and deformation. The experiments encompassed two different geogrid types (designated as G1 and G2), varying normal pressures ranging from 10 to 50 kPa, and RCA layers with thicknesses of 40, 80, 160, and 320 mm. Results from the experiments revealed that the inclusion of RCA layers around the geogrid substantially enhanced pullout resistance, with improvements ranging from 1.5 to 3 times compared to clay specimens. Optimal RCA thicknesses were determined in order to enhance soil-geogrid bonding and pullout resistance. For G1 geogrid, a thickness of 160 mm (equivalent to replacing 25% of clay volume with RCA) was identified as optimal, while for G2 geogrid, an 80 mm thickness (equivalent to replacing 15% of clay volume with RCA) was found to be sufficient. These thicknesses were established to achieve over 80% of the pullout force compared to full RCA specimens.

Basalt Fibers versus Plant Fibers: The Effect of Fiber-Reinforced Red Clay on Shear Strength and Thermophysical Properties under Freeze–Thaw Conditions

Freeze–thaw cycling has a significant impact on the energy utilization and stability of roadbed fill. Given the good performance of basalt fiber (BF) and plant fiber (PF), a series of indoor tests are conducted on fiber-reinforced red clay (RC) specimens to analyze the shear strength, thermophysical, and microstructural changes and damage mechanisms of the RC under the freeze–thaw cycle–BF coupling, meanwhile, comparing the improvement effect of PF. The results indicate that the RC cohesion (c) first increases and then decreases with the increasing fiber content under BF improvement, reaching the maximum value at the content of 2%, and the change in the internal friction angle (φ) is relatively small. As the number of freeze–thaw cycles increases, cohesion (c) first decreases and then gradually stabilizes. The thermal conductivity increases with increasing moisture content, and the thermal effusivity increases and then decreases with increasing moisture content and fiber content. The heat storage capacity reaches the optimum level at a moisture content of 22.5% and a fiber content of 1%. Microanalysis reveals that at 2% fiber content, a fiber network structure is initially formed, and the gripping effect is optimal. The shear strength of PF-improved soil is higher than that of BF at a fiber content of 4–6%, and the thermal conductivity is better than that of BF. At the same fiber content, the heat storage and insulation capacity of BF-improved soil is significantly higher than that of PF.

Enhancing Mechanical Properties of Clay Brick by Using Stone Powder

Abstract Hundreds of studies have been written in the last several decades on the advantages of using stone powder as a raw material in the production of fired clay bricks. The durability and long-term behavior of the finished product, however, have received very little attention in the literature. Clay bricks are generally fired at high temperatures in developing countries, which reduces the mechanical performance of the bricks. This is especially evident in extreme environmental settings where weathering leads to significant damage. The evaluation of concrete waste (stone powder) used to make fired clay bricks is the main topic of this study. There are two sections: the first evaluates how adding stone powder to clay bricks improves their physical characteristics such absorption, efflorescence, density, and firing shrinkage. The impact of stone powder on the mechanical characteristics of specimens of burned clay bricks, such as compressive and flexural strengths, is covered in the second section. The percentages of stone powder in the clay bricks are 0 %, 5 %, 10 %, 15 %, and 20%. While the ratio of dry soil to water content remains is 0.3. In this work three fire phases are used untel to the maximum temperature is reached. The first one is 300 °C, the second phase is 600 °C, and 900 °C for the third phase. The water absorption of specimens decreased as the quantity of stone powder increased, and efflorescence also decreased, according to the results for the physical attributes. The density does, however, somewhat rise with the amount of stone powder. Additionally, when the amount of stone powder was increased, the experimental results indicated that firing shrinkage decreased. Mechanically considered, clay brick specimens with 20% more stone powder showed stronger compressive flexural capabilities.

Constitutive modeling of anisotropic small-strain stiffness behavior of Shanghai soft clay

Small strain stiffness plays an important role in determining the deformation of geotechnical engineering in soft soils. To model the anisotropic small strain stiffness behavior of soft clay, an enhancement to the bounding surface plasticity model is proposed. This enhancement involves incorporating the anisotropy in soil stiffness at very small strains and its non-linear degradation. Small strains are considered via cross-anisotropy elasticity, while the concept of intergranular strain is used to reflect the non-linear degradation of stiffness with strains and the effect of recent stress history. Using the proposed model, the triaxial test results on K0 consolidated Shanghai clay specimens are simulated to investigate the model’s performance. In the simulation, three typical shear stress paths are adopted. The comparison of the model simulations against experimental evidence is discussed, where the effects of anisotropy in initial soil stiffness and stress-induced anisotropy on the variation of small-strain stiffness, pore pressure, and shear-volume coupling response are highlighted.

Shear rate and roughness effect on clay-steel interface strength properties in CU and CPD drainage conditions

Based on the concept of the preformed failure plane, this paper conducted a series of clay-interface tests using a modified triaxial apparatus that can directly measure the interface pore pressure, to investigate the shear rate and interface roughness effect on the deviator stress, interface excess pore pressure, interface stress path, and interface friction angle in both consolidated undrained (CU) and consolidated partially drained (CPD) interface drainage conditions. In general, the specimen with the clay-steel interface had a lower shear strength than the pure clay specimen under the same testing conditions. In CU tests, the total and effective interface friction angles increase approximately linearly with the shear rate in the semi-logarithmic scale, while in CPD tests, both the total and effective interface friction angles decrease with increasing shear rate. Moreover, the increased surface roughness is found to enhance the interface shear strength and the maximum interface pore pressure at a given shear rate and confining pressure. In CU tests, both the normalized efficiency parameter E and the corresponding interface friction angle increase with the average roughness (Ra) in a logarithmic relationship, but it is difficult to describe the positive correlation perfectly in CPD tests.

Comparison of soil improvement techniques on the development of efficient consolidation response

A comprehensive experimental program including two distinct series of consolidation tests was performed on clay specimens prepared at different dry weight proportions including 0%, 1%, 2.5%, 5%, 7.5%, 10% polypropylene fiber or lime by weight mixed with clayey soil. Fiber inclusion into clay resulted in enhancement of compressive strength characteristics, improvement of hydraulic properties that is an advantage for modification of stability and durability properties of clayey soil under loads. Similarly, the higher hydraulic conductivity of clay resulted that will shorthen duration of consolidation settlement, hence, eventually influence completion of plastic consolidation deformation favorably for soft clays. Lime-treatment on clay specimens showed that the compressibility properties are improved such that the strength of clay against loading enhances, exhibits less consolidation deformation under load owing to increase in lime content. On the other hand, clay becomes highly impermeable, displays substantially larger water-resistant properties because of increased lime mass proportion (i.e. time-extension) in clayey soil that results in prolongation of expulsion of excess porewater pressure from clay due to load application, relevant induced stresses. Fiber-inclusion resulted in exhibiting logarithmic decrement with a mild rate of decline while lime-treatment led to exponential reduction with a sharp rate of drop for compression index (Cc), compressibility coefficient (αv), volume compressibility coefficient (mv). Further, fiber-inclusion stimulated exponential and quadratical increment whereas lime-treatment induced exponential decrement for coefficient of consolidation (cv), hydraulic conductivity (k), respectively. As a result, the Cc, αv, mv enhanced on the order of within 10 at average of 80% to 90% with a minimum of 70% by value for both fiber-reinforcement and lime-stabilization soil-stabilization techniques. The cv, k improved on the order of within 10 at average of 75% to 85% by value for fiber-reinforcement whereas dis-improved on the order of within 10 at average of 70% to 80% by value for lime-stabilization.

Experimental study on the water and heat dynamic characteristics of silty clay at different depths under temperature gradient

Soil properties play a crucial role in the stability of engineering foundations, particularly in cold regions where temperature gradients impact water migration and soil conditions. This study utilized MRI-Cryogenic Soil-Moisture Analyzer (MRI-CSMA) to conduct indoor freeze-thaw experiments on silty clay specimens with varying initial water contents (12.0 %, 16.8 %, and 21.1 %). Dynamic changes in water content and temperature at different soil depths were analyzed. The results revealed distinct stage decrease characteristics in both temperature and water content as freezing progressed, with more pronounced changes closer to the cold end. Conversely, during thawing, temperatures and water content gradually increased as the boundary temperature rose. Notably, after the freeze-thaw cycle, the frozen zone consistently retained higher water content than the unfrozen zone, indicating water redistribution, regardless of initial water content levels. Furthermore, in three soil samples with different initial water contents, the water migration flux in the unfrozen soil layer decreased exponentially as freezing time increased. This phenomenon can be attributed to the combined effects of water boundary conditions, temperature gradients, and soil structure changes during soil freezing. These findings are likely to have significant implications for understanding water-heat dynamics in cold region soils as well as ensuring the stability of engineering projects.

Use of industrial wastes for stabilizing expansive clays in pavement applications: durability and microlevel investigation

Expansive clays feature high compressibility and large swelling-shrinkage potential, which may cause significant damage to the infrastructures, including pavements. This study investigates the potential use of industrial waste ash generated from municipal solid waste incineration (MSWI) as a more sustainable treatment method to treat expansive soils compared to the use of conventional coal fly ash. A series of tests was conducted to study the mechanical, durability, and environmental performance of the MSWI fly ash in comparison with the coal fly ash. The study reveals that the compressive strength and resilient modulus of 20% MSWI fly ash treated sample increased to 0.86 MPa and 213 MPa respectively, depicting an increase of 150% and 240% of the control clay specimen. Results also indicate that MSWI treated expansive clay shows better performance during the soaked California bearing ratio (CBR) testings, moisture susceptibility and cyclic wetting–drying tests compared to coal fly ash treated samples. Microlevel investigations reveal that the influence of cation exchange is more decisive in the MSWI-treated clays due to the presence of higher Ca2+ ions, during the early stages, and the influence of hydration is stronger at the later stage of stabilisation. X-ray diffraction (XRD) results show that gismondine, albite, calcite, portlandite, andradite, and ettringite are the main crystalline phases formed during the stabilization. Heavy metal concentrations after the stabilisation are within the allowable limit defined by state regulations. Applying MSWI fly ash as a ground treatment for expansive clays can reduce the consumption of natural resources, promoting a “zero landfill” policy.

Investigation on strength characteristics of fly ash treated dredged marine clay with various pore water salinities

This study investigated the strength characteristics of dredged marine clays treated with fly ash with varying porewater salinities. A series of laboratory tests were conducted on fly ash-treated dredged marine clay specimens with various salinities and curing times. In the direct shear tests, observed patterns revealed a consistent initial rapid increase in shear stress with the increase of horizontal displacement, followed by either a gradual decline or stabilization after reaching the peak shear stress. The variation curve consistently positioned the lower salinity or longer curing time above the higher salinity or shorter curing time. Furthermore, the shear strength at a given vertical stress consistently decreases with increasing salinity while ascending with increasing curing time. This indicated that curing time positively influences shear strength development, while the presence of salt negatively affects it. Both strength parameters cohesion and friction angle exhibited growth trends with increased curing time but displayed a decline as salinity increased from 0% to 6%. Unconfined compressive strength test results showed a strain-softening behavior for all tested specimens. The compressive strength demonstrated a declining trend with rising salinity, with a more pronounced decrease observed within the initial 7d compared to the less significant change between 7d and 28d.

Experimental investigation on strength characteristics of marine soft clay under monotonic and cyclic loading

Sea areas with an average water depth of 5-15 m in the East China Sea are mostly muddy soft-foundation seabed. The wind power infrastructure built on them must fully consider the mechanical properties of marine soft clay during design process. In this study, monotonic and cyclic tests were conducted to study the strength characteristics of soft clay at various strain rates, cyclic stresses and initial effective vertical stresses using a simple shear apparatus. The test results showed that, as the strain rate increased, the peak shear stress of the samples under different confining pressures increased. However, the failure lines of the effective stress path of samples under different strain rates and vertical stresses are uniform. Compared to the traditional cyclic failure criteria, the failure criterion based on the inflection point of double amplitude strain can reflect the deformation characteristics of the specimen more accurately. The peak shear strength obtained from the monotonic tests was used to normalize the cyclic stress. Subsequently, the relationship between the number of failure cycles and normalized cyclic stress level of the soft clay specimens was established.

Ceramic Properties of Three Specimens of Alluvial Clays Used in Local Constructions from Mbouda Clay Deposit, West Cameroon

Ceramic Properties of Three Specimens of Alluvial Clays Used in Local Constructions from Mbouda Clay Deposit, West Cameroon

Application and comparison of multistage triaxial compression test procedures on reconstituted Ankara clay

The ability to conduct conventional triaxial compression tests on multiple identical specimens is restricted by available sample quantity, sample homogeneity, as well as testing duration. Multistage triaxial testing is an alternative method to tackle these issues by using a single specimen sheared under different confining stresses to attain the strength parameters. Although there are widely accepted procedures to decide when to stop each shearing stage and proceed to the next stress level, the applicability of these procedures on different soil types is still a question. This study examines the applicability of combinations of two multistage triaxial testing procedures (Rational Procedure and Minimum Slope) under two different deviator stress conditions (Sustained or Cyclic) during confining stress increase. The outcome is compared to conventional triaxial test results for undrained and drained shearing of reconstituted specimens of high-plasticity Ankara Clay. Out of the four options, the rational procedure with cyclic deviator loading and minimum slope with cyclic deviatoric loading conditions, are found to give the most accurate strength parameters in reference to single-stage test results. The maximum number of the shearing-reconsolidation sequences applicable before strength loss is also investigated for each multistage triaxial testing procedure.

Evolution of excess pore water pressure in undrained claystructure interface shear tests

Recent studies focused on the shear behaviour of clay-structure interfaces have shown the importance of the shearing rate on the strength of these interfaces. In normally-consolidated clays, increasing the shearing rate results in a decrease in the interface strength, while the trend is opposite in heavily overconsolidated clays. While analytical and empirical interpretation methods indicate that the generation of shear-induced excess pore pressures are responsible for theaforementioned trends, experiments with pore water pressure measurements at the clay-structure interface are rare. In this paper, we first describe a modified interface shear box testing setup that is equipped with a pore water pressure sensor. For this equipment, the fully rough structural surface was manufactured with a port at the centre of the clay-surface interface to measure the pore water pressure. We present the results of undrained clay-structure interface tests on normally consolidated (NC) and overconsolidated (OC) specimens of kaolin clay. The results agree with the expectations, where the NC specimens generate excess pore pressures with greater magnitudes and heavily OC specimens generate negative excess pore pressures. Measurements of the pore water pressures allow calculating vertical effective stresses, which can be used to investigate the effective stress paths followed by the clay-structure interface during the tests. This paper also provides a comparison of the measured values of beta and adhesion factors with previously published results and relationships used for the design of deep foundations.

Characterization and Suitability Assessment of Ameskroud Clay Deposits for Ceramic Applications

The identification of natural clay deposit parameters is critical for the development of ceramics. This research underscores the essential role of understanding clay properties in producing high‐quality ceramics and represents a comprehensive characterization methodology, shedding light on the untapped potential of natural clay deposits for ceramic applications. This study investigates red clays from the Triassic, as well as yellow and gray clays from the Cretaceous period, collected from the western High Atlas of Morocco (Ameskroud). The characterization of clays from this geographic region is innovative, as they have not been previously investigated for their suitability within ceramic applications. The investigation encompasses an examination of the geological context, mineralogy, chemical composition, and physicochemical attributes of these clays. Furthermore, the thermal behavior, firing characteristics, and compressive strength of the clay samples were assessed when fired at 900°C, 1000°C, and 1100°C. Mineralogical analysis reveals that illite predominates with relatively low levels of kaolinite and chlorite. The primary chemical constituent is SiO2, followed by Al2O3 and Fe2O3. Notably, yellow clay exhibits a significant CaO content exceeding 10%. At 1100°C, the clay specimens exhibit reduced water absorption rates (ranging from 9.88% to 17.1%) and enhanced mechanical performance, with compressive strengths ranging from 22.33 MPa to 36.07 MPa, attributable to the sintering process. The findings affirm that the raw clays sourced from the Ameskroud region possess characteristics suitable for various ceramic applications, making them ideal candidates for the production of dense bricks and ceramic tiles.

Comparative Experimental Study on Strength Properties of Red Clay Modified by Cement and Industrial Solid Waste Powder

Because of the existence of clay minerals such as montmorillonite in red clay, the strength of red clay decreases significantly as water content increases. This study aims to improve the strength of red clay by using three different kinds of industrial solid waste powder, i.e., steel slag (SS) powder, fly ash (FA), and ground-granulated blast furnace slag (GGBS). At the same time, the ordinary Portland cement (OPC) was selected as a comparison of the improvement effect on the strength of red clay modified by the aforementioned industrial solid waste powder. The properties of the red clay and the industrial solid waste powder were documented comprehensively. The unconfined compressive strength (UCS) tests were conducted on the specimens of the red clay and the red clay modified by the OPC, SS, FA, and GGBS, which had been cured for 3, 7, and 21 days at a temperature of 25°C, respectively. The results showed that the strength of red clay can be significantly improved by the three kinds of industrial solid waste powder. After a 21-day curing period, the experimental results showed that the UCS of the red clay modified by 7% SS, 5% FA, and 5% GGBS increased by 252%, 131%, and 140% compared to that of the red clay without modification. However, the modification effects of the SS, FA, and GGBS on the red clay were generally inferior to that of the OPC. By observing the microstructures of the modified clay, the mechanism of industrial solid waste powder and cement improving the strength of the red clay was analyzed. The findings in this study can provide a reference for improving subgrade strength by a soil-modification method in road constructions.

Fibre-Reinforced Geopolymers (FRGPs) as Inorganic Composites for Flexural Strengthening of Brick Masonry

ABSTRACT This study presents an assessment of externally bonded Fibre-Reinforced GeoPolymers (FRGPs) as strengthening material for masonry structures. Geopolymer matrices can also potentially fulfil the requirements of restoration criteria for historical buildings, with heat-resistant performances generally better than Fibre-Reinforced Polymers (FRPs). Four FRGPs, embedding either unidirectional steel or bidirectional carbon, basalt or glass mesh as reinforcement, were tested by means of local shear and bending tests on fired clay brick specimens, either alone or coupled with hydraulic lime mortar. In addition, the behaviour of each reinforcement exposed to alkaline environments was investigated through tensile tests on coupons. Results confirmed the interesting potential of FRGPs for strengthening masonry elements, highlighting a good performance of steel and carbon reinforcements.

Effect of Loading Direction on Deformation and Strength of Heterogeneous Paleo Clay Samples

Landslides result from weak surfaces with varying rock-soil properties, posing a significant concern for engineering and accurate deformation analysis. This study investigated the macroscopic physical and mechanical properties of paleo clay specimens during triaxial compression testing, aiming to elucidate the deformation mechanisms exhibited by these specimens under varying loading directions at both the loading and unloading ends, and numerical simulation methods were carried out to simulate actual engineering scenarios. The analysis encompasses deformation patterns, stress–strain relationships, Mohr stress circles, and numerical simulation failure cloud diagrams for soil samples under different loading directions. The results showed that the loading end of heterogeneous specimens exhibited noticeable deformations. Alteration of the loading direction induced variations in the failure mode. The position and size of the deformations for the only iron-manganese clay, loading end iron-manganese clay, and loading end reticulated clay samples changed with the clay layer at the loading end of the sample. Moreover, the stress–strain curves under different loading directions were different, with strain hardening and strain softening appearing in the two loading directions, respectively. The results of this study contribute to an in-depth understanding of the impact of the loading direction on the deformation and strength of paleo clay, thereby providing a foundation for landslide prevention and control measures.

Characterization of net-zero pozzolanic potential of thermally-derived metakaolin samples for sustainable carbon neutrality construction

Metakaolin (MK) is one of the most sustainable cementitious construction materials, which is derived through a direct heating procedure known as calcination. Calcination process takes place substantially lower temperatures than that required for Portland cement, making it a more environmentally sustainable alternative to traditional cement. This procedure causes the removal of hydroxyl water from the naturally occurring kaolin clay (Al2Si2O5(OH)4 with MK (Al2O3·2SiO2) as its product. Kaolin naturally exists in large amount within 5°29′N–5°35′N and 7°21′E–7°3′E geographical coordinates surrounding Umuoke, Obowo, Nigeria. Alumina and silica are the predominant compounds in MK, which provide it with the pozzolanic ability, known as the 3-chemical pozzolanic potential (3CPP), with high potential as a cementitious material in concrete production and soil stabilization. Over the years, researchers have suggested the best temperature at which MK is derived to have the highest pozzolanic ability. Prominent among these temperature suggestions were 800 °C (3CPP of 94.45%) and 750 °C (3CPP of 94.76%) for 2 h and 5 h’ calcination periods, respectively. In this research paper, 11 different specimens of Kaolin clay obtained from Umuoke, Nigeria, were subjected to a calcination process at oven temperatures from 350 to 850 °C in an increment of 50 °C for 1 h each to derive 11 samples of MK. The MK samples and Kaolin were further subjected to X-ray fluorescence), scanning electron microscopy (SEM) and X-ray diffraction (XRD) Brunauer–Emmett–Teller (BET) tests to determine the microstructural behaviour and the pozzolanic properties via the 3CPP as to exploit the best MK with the highest cementing potential as a construction material. The results show that the MK heated at 550 °C and 800 °C produced the highest pozzolanic potentials of 96.26% and 96.28%, respectively. The enhancement in pozzolanic potential at optimum calcination temperature is attributed to an increase in the specific surface area upon calcination of kaolinite confirmed by BET results. The SEM and XRD results further supported the above result with the strengthened crystal structure of the MK at these preferred temperatures. Generally, 550 °C is more preferred due to the less heat energy needed for its formulation during 1 h of calcination, which outperforms the previous results, that suggested 750 °C and 800 °C in addition to longer hours of heat exposure.

Geomechanical Properties of Clay Stabilised with Fly Ash-Based Geopolymer Subjected to Long-Term Sulfate Attack

Fly ash-based geopolymers have emerged as an eco-friendly alternative binder compared to conventional Portland cement for soil stabilisation. However, the gap in the current literature is the lack of a comprehensive study regarding the geomechanical behaviour of fly ash geopolymer-treated clay subjected to long-term sulfate attack, particularly in terms of potential ettringite formation and the corresponding impact on cementitious soil structure. The goal of this paper is to address this knowledge gap and provide a comprehensive study to fulfil it. In this work, sulfate attack was simulated by submerging geopolymer-treated clay specimens in two distinct sulfate-based solutions (i.e., sodium and magnesium), for one year. Subsequently, comparative analyses of the geomechanical and microstructural changes in geopolymer-treated clay under various curing conditions were conducted through unconfined compressive strength, direct shear, volume change and microscopic tests. The findings indicate that the addition of geopolymer for the stabilisation of clay soil significantly improves soil strength without affecting the soil volumetric response. Although the clay used exhibited similar qualitative stress–strain behaviour across all simulated attacks, notable quantitative differences emerged in the peak strength, stiffness and shear strength parameters. Such discrepancies can primarily be attributed to the varying buffering capacities (i.e., pH changes associated with acidification) of the sulfate solutions and the subsequent residual pH, cementitious product formation and strength enhancement within the treated clay.