Red Clay Research Articles

Disintegration behaviors of red clay under wet-dry cycles

Cyclic wetting-drying alternation has a significant influence on the strength and structure of soils. It is prone to causing soil softening and disintegration, highlighting the importance to improve the soil's resistance to disintegration. This paper utilizes a self-developed disintegration test apparatus to analyze the disintegration characteristics of improved red soil under wet-dry cycles, focusing on the disintegration amount and ratio. Furthermore, XRD (X-ray diffraction), SEM (scanning electron microscope), tensile test, and contact angle test are employed to investigate the anti-disintegration behaviors of the improved red soil. The results show that the disintegrating amount and ratio of undisturbed and improved red soil are distinctly different under wet-dry cycles. Linear, stepped, constant and concave but perfect "S" shapes of the disintegrating ratio are observed in the cyclic tests. Cement and lime strengthen the red soil primarily through hydration reaction. The drop experiment confirms that cement plays a crucial role in restraining the disintegration. When the ameliorant content is low, the correlation between pore parameters and disintegration duration of red soil follows the order: mean shape coefficient > fractal dimension > probability entropy > area probability distribution index. With a high ameliorant content, the correlation remains similar, with slightly higher correlation for probability entropy. Under wet-dry cycle conditions, sludge and kaolin can improve the soil through the bonding of clay particles. The improved water repellency greatly enhances the resistance to disintegration of the altered red soil. The research provides valuable insights for the practical application of soil.

Effect of Pb(II) on hydraulic behavior and microstructure evolution of activated charcoal-bentonite-reticulated red clay barrier

Effect of Pb(II) on hydraulic behavior and microstructure evolution of activated charcoal-bentonite-reticulated red clay barrier

Metagenomic and isotopic insights into carbon fixation by autotrophic microorganisms in a petroleum hydrocarbon impacted red clay aquifer

Autotrophic microorganisms, the pivotal carbon fixers, exhibit a broad distribution across diverse environments, playing critical roles in the process of carbon sequestration. However, insights into their distribution characteristics in aquifers, particularly in those petroleum-hydrocarbon-contaminated (PHC) aquifers that were known for rich in heterotrophs, have been limited. In the study, groundwater samples were collected from red clay aquifers in the storage tank leakage area of a PHC site, a prevalent aquifer type in southern China and other regions. Metagenomics combined with hydrochemical and inorganic carbon isotope analyses were employed to elucidate the presence of microbial carbon fixation and its driving forces. Results showed that there were hundreds of autotrophic microorganisms participating in distinct carbon fixation processes in the red clay PHC aquifers. Reductive tricarboxylic acid (rTCA) and dicarboxylate/4-hydroxybutyrate (DC/4HB), as well as 3-hydroxypropionate (3HP or/and 3-hydroxypropionate/4-hydroxybutyrate (3HP/4HB)) were the predominant carbon fixation pathways. The abundances of carbon fixation genes and autotrophic microorganisms were significantly and positively correlated with hydrocarbon concentrations and δ13C of dissolved inorganic carbon (δ13C-DIC) values. This finding indicated that the petroleum hydrocarbon significantly promoted the proliferation of carbon fixation microorganisms, leading to a substantial uptake of inorganic carbon. Therefore, we deduce that this process holds considerable potential for carbon sequestration in PHC-contaminated aquifers.

Early-age structural build-up and rheological assessment of alkali-activated slag-red clay brick waste pastes: Influence of silica modulus and precursors proportions

Sustainability plays a crucial role in the current context of the cement industry, and alkali-activated materials (AAMs) are emerging as eco-efficient alternative binders. On the other hand, the massive generation of red brick waste worldwide and its lack of a defined destination emphasizes this material as an alternative precursor that has been insufficiently explored in the literature. Based on this context, the present study aims to investigate the structural build-up, reaction kinetics, and rheological properties of alkali-activated pastes based on blast furnace slag (BFS) and red clay brick waste (RBCW). Fresh properties such as structural build-up, rheology, and reaction kinetics are lacking in the literature on RCBW-based AAMs, highlighting these properties as a research gap to be filled and discussed in depth in this paper. The flow sweep test was performed, linked to yield stress and viscosity properties. The structural build-up was evaluated by strain sweep and small amplitude oscillatory shear (SAOS) tests based on viscoelastic parameters: storage modulus, loss modulus, and phase angle. Isothermal calorimetry and in-situ FTIR were also conducted to complement the analysis and provide insight into the reaction kinetics, chemical structure, and product formation. Higher silica modulus (Ms) resulted in a lower structural build-up rate and a delayed reaction. Higher content of RCBW resulted in a delayed structuration process, which was linked to a delay in the precipitation of aluminosilicate gels. Early increase in the structural build-up in 25 % and 50 % RCBW blends (Ms = 1.0) is associated with the early formation of a well-percolated network.

Research on the expansion, shrinkage properties and fracture evolution of red clay stabilised with phosphogypsum under dry-wet cycles.

In view of the special engineering properties of red clay and the waste of phosphogypsum resources, the expansion and contraction deformation and fissure evolution of phosphogypsum stabilized red clay under different conditions were investigated by laboratory tests and image processing system. The research results show that: (1) the absolute expansion and absolute shrinkage of phosphogypsum stabilized red clay are positively correlated with the compaction degree, the number of dry and wet cycles and the cement dosage, and negatively correlated with the initial water content and the phosphogypsum dosage; (2) the fissure rate increases with the increase of the number of dry and wet cycles, and decreases with the increase of the initial water content, the compaction degree, the cement, and the phosphogypsum dosage; (3) The relationship among absolute expansion rate (absolute shrinkage), degree of compaction and fracture rate can be fitted by the equation f(x,y) = ax+by+cx2+dy2+e; (4) Phosphogypsum has an obvious inhibiting effect on the expansion, shrinkage and cracking of the mix. It is recommended that the cement mixing amount of 6% and phosphogypsum: red clay = 1:1~1:2 as roadbed filler.

A Ground-Penetrating Radar-Based Study of the Structure and Moisture Content of Complex Reconfigured Soils

To increase the detection accuracy of soil structure and moisture content in reconstituted soils under complex conditions, this study utilizes a 400 MHz ground-penetrating radar (GPR) to examine a study area consisting of loess, sandy loam, red clay, and mixed soil. The research involves analyzing the single-channel waveforms and two-dimensional images of GPR, preprocessing the data, obtaining envelope information via amplitude envelope detection, and performing a Hilbert transformation. This study employs a least squares fitting approach to the instantaneous phase envelope to ascertain the thickness of various soil layers. By utilizing the average envelope amplitude (AEA) method, a correlation between the radar’s early signal amplitude envelope and the soil’s shallow dielectric constant is established to invert the moisture content of the soil. The analysis integrates soil structure and moisture distribution data to investigate soil structure characteristics and moisture content performance under diverse soil properties and depths. The findings indicate that the envelope detection method effectively identifies stratification boundaries across different soil types; the AEA method is particularly efficacious in inverting the moisture content of reconstituted soils up to 3 m deep, with an average relative error ranging from 2.81% to 7.41%. Notably, moisture content variations in stratified reconstituted soils are more pronounced than those in mixed soil areas, displaying a marked stepwise increase with depth. The moisture content trends in the vertical direction of the same soil profile are generally consistent. This research offers a novel approach to studying reconstituted soils under complex conditions, confirming the viability of the envelope detection and AEA methods for intricate soil investigations and broadening the application spectrum of GPR in soil studies.

Reused green glass for the production of low-density ceramic proppants

The reuse of waste to promote manufacturing processes that are respectful of the environment is a fundamental requirement in circular economy practices. In this work, it is assessed the feasibility of manufacturing ceramic proppants from a commercial red clay, sodium and potassium feldspars, and significant amounts of green bottle glass recovered from urban wastes.Different ceramic mixtures were formulated, and the sintering conditions were defined considering optical dilatometric, differential thermal, and thermogravimetric analysis. The obtained granules were characterised following the international standard for proppants, and also using X-ray diffraction, scanning electron microscopy, and individual diametral compression tests.The results show that competitive proppants are obtained, due to their low-density (2.5 g/cm3) and good breakage ratio (7.8 % at 5000 psi, or 34.5 MPa), but also considering the involved low-cost processing route and raw materials.

Fabrication of a Concrete Roof Tile by Geopolymerization of Red Clay with Container Glass Wastes

We report the production of concrete roof tiles using a red clay-based geopolymer binder with container glass waste and river sand as a concrete filler. Clear and colored container glass wastes were separately ground to powder and blended with low-grade red clay to achieve a SiO2/Al2O3 ratio of approximately 7.0. The powder blends were converted to geopastes with a solid-to-alkali solution ratio of approximately 0.8 using a 12-molar alkali activator solution containing a mixture of potassium hydroxide and sodium hydroxide. Rheological analysis showed that the geopaste binders with transparent and colored glass powders exhibited high shear thinning behavior. A higher viscosity was observed for the geopaste with colored glass powder due to the presence of colorants. Fine and coarse particles of river sand were prepared and mixed with different ratios of geopaste binder to river sand of 1:2.0, 1:2.5, and 1:3.0, respectively. All geopaste and river sand formulations were poured into acetate molds and heated in a metal chamber at 80 °C for 24 h, then aged at room temperature for 14 d. The highest flexural strength of 2.33 MPa was obtained from the formulation with a 1:2 ratio of geopaste with transparent glass powder and fine sand. The measured strength corresponded to an apparent porosity of 6.30% and a water absorption of 4.50%. The bulk density was approximately 1.16 g/cm³, which is classified as a lightweight material. A prototype geopolymer concrete roof tile was successfully produced with a sorption coefficient of approximately 0.170 mm/min1/2. This measured sorption coefficient and the physical properties indicate that the produced roof tile is a potential building material.

Disintegration characteristics and mechanism of red clay improved by steel slag powder

Red clay is prone to softening and disintegration when exposed to water, often triggering severe geological disasters. To enhance its resistance to disintegration, this paper employs a homemade wet-dry cycling disintegration apparatus, combined with XRD, SEM, MIP, and fractal theory, to analyze the effects of different activators on the disintegration characteristics and microscopic mechanisms of SSP-improved soil. Under wet-dry cycling, the disintegration process of SSP-improved soil can be divided into five stages: rapid water absorption, saturation wetting, rapid disintegration, softening and dissolution, and stable non-disintegration. As the activator and SSP content increase, the resistance to disintegration of SSP-improved soil gradually enhances. After the addition of activators, the porosity, pore area, pore length and width, and probability entropy of SSP-improved soil decrease (i.e., 7 % NS < 7 % CSW < 7 % NH < undisturbed soil), while the average shape factor, regional probability distribution index, and fractal dimension increase. This is because activators promote ion exchange, cementation, crystallization, and carbonation reactions in SSP-improved soil, generating a substantial amount of hydration products such as C-S(A)-H, Ca(OH)2 and CaCO3, which fill and encapsulate inter-particle pores, thereby reducing water flow channels within the pores. In contrast, the pore structure between particles in undisturbed soil is simple and well-connected, providing favorable conditions for the migration and dissolution of fine particles and the loss of cementing materials, which accelerates the destruction and disintegration of the soil structure.

Study on the dry shrinkage characteristics and size effect of swell-shrink characteristic soil.

Swell-shrink characteristic soils exhibit a high susceptibility to cracking during the drying process, which poses a significant risk of various geological disasters. Among these, the occurrence of drying shrinkage acts as a prerequisite for the cracking phenomenon. Therefore, it is of utmost importance to comprehend the specific characteristics associated with the drying shrinkage mechanism. To investigate the drying shrinkage behavior of swell-shrink characteristic soils, a series of drying shrinkage experiments were conducted on long strip samples of red clay and expansive soil. Utilizing three-dimensional digital image correlation (DIC) technology, the surface displacement, strain, and anisotropic shrinkage rates of the soil samples during the drying process were obtained, and the size effect on the drying shrinkage of swell-shrink characteristic soil were analyzed. The research findings are as follows: The displacement development of the soil samples in the X and Y directions can be divided into two stages: a linear growth stage and a stable displacement stage. In the Z direction, the soil surface deformation can be divided into three stages: soil surface arching, vertical shrinkage, and shrinkage stabilization. The drying shrinkage of swell-shrink characteristic soil exhibits anisotropy, with the vertical shrinkage rate being the largest, followed by the longitudinal and then the transverse directions. Additionally, the soil sample shrinkage exhibits a size effect, whereby the shrinkage rates in all directions increase with increasing sample width and thickness. During the drying shrinkage process, the stress state on the soil surface evolves from initial tensile strain to subsequent compressive strain. The strain at different positions and times within the soil sample is not uniform, resulting in the non-uniformity and anisotropy of the sample shrinkage. This study provides important insights into the cracking mechanism of swell-shrink characteristic soils and serves as a valuable reference for related laboratory experiments, which will contribute to better prediction and control the geological hazards caused by the drying shrinkage of swell-shrink characteristic soils.

From Red Clay to Fragrant Pine: The Search for Rootedness through Architecture

From Red Clay to Fragrant Pine: The Search for Rootedness through Architecture

Model Tests on the Red Clay Foundation Reinforced by the Coir-Geotextile

Model Tests on the Red Clay Foundation Reinforced by the Coir-Geotextile

Mechanical properties and stability of zinc-contaminated red clay cured by MICP synergistically activated MgO

Microbially Induced Carbonate Precipitation (MICP) technology offers an innovative approach for the solidification and stabilization of heavy metal-contaminated soils; However, the mechanical strength and long-term stability of this remediation method have not been thoroughly investigated. This study introduces an innovative curing and stabilization technique using MICP-activated MgO to address the geotechnical challenges posed by zinc ion-contaminated soils. To investigate the effect of zinc ions on soil and the optimal efficacy of MICP-activated MgO in curing zinc contamination, experiments were conducted on zinc-contaminated soils with varying zinc ion concentrations (0.05%, 0.1%, 0.5%, 1.0%), dry densities (1.35, 1.4, 1.45, 1.5g/cm³), and activated MgO admixtures (1%, 2%, 5%, 10%). The effectiveness of MICP-activated MgO was evaluated through macroscopic analysis and stability tests, including unconfined compressive strength tests, direct shear tests, and the Toxicity Characteristic Leaching Procedure (TCLP). The results indicated that zinc ions disrupted soil particle cementation, enlarged inter-particle pores, and significantly reduced both unconfined compressive strength and shear strength. The optimal dosage of MICP-activated MgO for curing zinc-contaminated soil was determined to be 10%, resulting in an unconfined compressive strength of 1.196MPa and a Zn2+ leaching concentration of 0.1414mg/L. The combined actions of MICP-activated MgO facilitated the formation of alkaline magnesium carbonate, calcium carbonate, and magnesium hydroxide. These compounds filled the inter-particle pores of zinc-contaminated soil, encapsulating and co-precipitating zinc ions, thereby enhancing the soil's strength and stability. These findings establish a theoretical foundation for the engineering application of MICP-activated MgO in the remediation of zinc-contaminated soils.

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.

Removal of Phosphate and Ammonium Ion from Domestic Wastewater Using Clay Feldspar in Wupa Sewage Treatment Plant Abuja

The aim of this study is centered on the sustainability of feldspar as an adsorbent as opposed to other clay minerals such as plastic clay, red clay and barite. Brauner-Emmert-Teller (BET) analysis of the clay minerals considered in this study revealed that raw feldspar had the highest surface area and pore volume of 332.8 m²/g and 0.218 cc/g respectively. Similarly, the clay minerals were used in adsorption study with feldspar producing the best removal efficiency of 90.00%and 73.96% for ammonium and phosphate ions respectively. The BET results and the adsorption test showed that feldspar was a better adsorbent than the other adsorbents. Thermal activation of feldspar was carried out at temperatures of 500–700 ◦C using muffle furnace. The BET results of the thermal activation revealed that feldspar activated at 600 ◦C has the highest surface area and pore volume of 533.9 m²/g and 0.272 cc/g respectively. The Fourier’s transformed infrared (FT-IR) results indicated that several functional groups were involved in the adsorption process of the phosphate and ammonium ions some of which were O-H, N-H and C-O groups. The results showed that irregular-layered structures of the raw feldspar became smooth and regular after thermal activation. The effects of pH, adsorbent dosage, temperature, contact time and initial PO₄3− and NH₄⁺ concentrations on the adsorption of phosphate ions and ammonium ions were investigated using atomic adsorption spectroscopy (ASS). The adsorption studies of phosphate ion and ammonium ion onto feldspar increased with contact time, adsorbent dosage and temperatures until optimum values were reached.

Development of lightweight structural concrete with artificial aggregate manufactured from local clay and solid waste materials

The partial replacement of conventional natural coarse aggregate (NCA) with artificial light weight aggregate (LWA) manufactured from local clay and solid waste to develop a lightweight aggregate concrete (LWAC) for the structural use was studied in this paper. Red clay and Savar clay were used individually with solid wastes like rice husk ash (RHA) and waste glass to produce LWA. The suitability of raw materials and LWA was evaluated by investigating various properties. The mechanical, thermal and durability properties of manufactured LWAC were explored. The results of physical, chemical, thermal and geotechnical properties revealed that Red clay is better than Savar clay for the preparation of LWA. All the physical and mechanical properties of LWA prepared from Red clay are suitable for the preparation of LWAC compared to Savar clay. The test results demonstrated that the concrete manufactured by replacing 30 % of NCA with LWA produced a concrete of lightweight properties. The compressive strength of LWAC for 7 and 28 days was observed as 28 and 48 MPa, respectively. The results of modulus of elasticity, splitting tensile strength, flexural deformation, and creep test of LWAC revealed that these mechanical properties meet the requirements for the structural concrete. The RCP test proves that chlorine permeability of LWAC is comparable with NCA. It was observed that the superior performance of LWAC can be achieved only when the optimized mix designed is followed strictly. The suitability of the replacement of natural aggregate by LWA may be helpful for Bangladesh due to the scarcity of natural coarse aggregate and reusability of solid waste materials.

Mechanisms of enhancing MgO for stabilization/solidification of Pb-contaminated red clay through CO2 sequestration

Pb-contaminated soil poses significant environmental and health risks as well as soil stability issues. Research on sandy soils highlights CO2-enhanced reactive MgO as a promising solution for improving the solidification of Pb-contaminated soils. However, carbonation effects can differ markedly between soil types owing to varying soil properties. In this study, we evaluated the effects of CO2-enhanced reactive MgO on the engineering and environmental characteristics of Pb-contaminated red clay and explored its mechanism of carbonation solidification. The results showed that CO2-enhanced reactive MgO increased the strength of Pb-contaminated red clay to over 3 MPa within 1 h, which was approximately 25 times the strength of untreated soil (0.2 MPa) and significantly higher than that of reactive MgO-treated, uncarbonated soil (0.8 MPa). The pH of the carbonated soil (9–10) facilitated Pb2+ immobilization, and the increase over the initial parameter elevated the electrical conductivity value. Moreover, CO2-enhanced reactive MgO reduced the Pb2+ leaching concentration to below 0.1 mg/L, even at high Pb concentrations (10,000 mg/kg). Pb2+ transformed into lead carbonates during the carbonation process, with the hydrated magnesium carbonates forming a dense internal structure. This solidification mechanism included chemical precipitation, physical adsorption, and encapsulation. Notably, the carbonation time should be controlled within 1 h to prevent soil expansion. Together, these findings support the potential of CO2-enhanced reactive MgO for efficient and low-carbon application in the solidification of Pb-contaminated red clay.

Fracture propagation characteristics of pre-cracked red clay in roadbed filling under three-point bending

Red clay was a special roadbed filling soil that was easy to expand and shrink because of the characteristics of high liquid limit and high porosity, leading to the appearance of a large number of cracks. In order to understand the cracking mechanism and nonlinear fracture failure process of red clay, the fracture toughness and crack sensitivity of red clay with different saturation, compaction and gravel content were analyzed by three-point bending cracking experiment and Image processing technology, and then the cohesive crack model was established to describe the fracture toughness. The results showed that the cracking process of red clay could be divided into three stages: crack incubation period, crack initiation and propagation period and visible cracks appearance stage. There was a conic function relationship between fracture toughness and saturation and a positive correlation between fracture toughness and compactness. The influence of gravel content on the final fracture path of red clay was the most significant, while the effects of saturation and compaction could be ignored. In addition, the fracture toughness converted from the cohesive crack model was basically as the same as the measured. This work provided a basis for theoretical analysis and numerical calculation for the fracture toughness of red clay under three-point bending.

Landslide Distribution and Development Characteristics in the Beiluo River Basin

The Beiluo River Basin, situated in the central region of the Loess Plateau, frequently experiences landslide geological disasters, posing a severe threat to local lives and property. Thus, establishing a detailed database of historical landslides and analyzing and revealing their development characteristics are of paramount importance for providing a foundation for geological hazard risk assessment. First, in this study, landslides in the Beiluo River Basin are interpreted using Google Earth and ZY-3 high-resolution satellite imagery. Combined with a historical landslide inventory and field investigations, a landslide database for the Beiluo River Basin is compiled, containing a total of 1781 landslides. Based on this, the geometric and spatial characteristics of the landslides are analyzed, and the relationships between the different types of landslides and landslide scale, stream order, and geomorphological types are further explored. The results show that 50.05% of the landslides have a slope aspect between 225° and 360°, 68.78% have a slope gradient of 16–25°, and 38.97% are primarily linear in profile morphology. Areas with a high landslide density within a 10 km radius are mainly concentrated in the loess ridge and hillock landform region between Wuqi and Zhidan Counties and in the loess tableland region between Fu and Luochuan Counties, with a significant clustering effect observed in the Fu County area. Loess–bedrock interface landslides are relatively numerous in the northern loess ridge and hillock landform region due to riverbed incision and the smaller thickness of loess in this area. Intra-loess landslides are primarily found in the southern loess tableland region due to headward erosion and the greater thickness of loess in this area. Loess–clay interface landslides, influenced by riverbed incision and the limited exposure of red clay, are mainly distributed in the northern part of the southern loess tableland region and on both sides of the Beiluo River Valley in Ganquan County. These results will aid in further understanding the development and spatial distribution of landslides in the Beiluo River Basin and provide crucial support for subsequent landslide susceptibility mapping and geological hazard assessment in the region.

Developing a low carbon brick for residential building construction

The construction industry is trying to become more eco-friendly and minimise environmental impact. One way to achieve this is by using innovative building materials. Traditional clay bricks are not eco-friendly due to the depletion of resources, emissions, and waste generated during production. In this study, a new alternative called the Novel Organic Brick (NOB) was produced and evaluated, which was made from recycled construction and demolition sand and red clay as partial replacements for traditional virgin clay. A Life Cycle Assessment (LCA) was conducted to compare the environmental impact of NOBs to that of Kiln Fired Bricks (KFBs). The inventory flows from material sourcing to brick shaping were modelled in SimaPro 8.1 and characterised into impact indicators using the ReCiPe 2016 method. The LCA showed that NOBs can reduce the impact of climate change by 39-56% compared to KFBs, depending on the type and source of recycled sand. This study encourages the construction industry to adopt alternative solutions for greater sustainability by demonstrating the viability of incorporating secondary materials and quantifying environmental performance improvements in India.