Search Results (15)

The structural clay of the Zhanjiang Formation exhibits significant thixotropy, and there are considerable differences in the ultimate bearing capacity of pulled-out piles under different resting times. Using the structural clay from the Zhanjiang Formation as the foundation, direct shear tests on the soil surrounding nine groups of model single piles of different sizes were conducted at various resting times, along with static pullout tests on the pile foundations. The results indicate that the cohesion and internal friction angle of the surrounding soil increase following a logarithmic function with increasing resting time; specifically, the growth rate is rapid in the early resting period and gradually slows down in the later period. A quantitative relationship describing the variation of cohesion and internal friction angle over time was established. The load–displacement curves for single piles at different resting times exhibit a distinct steep drop. The uplift single pile exhibits significant time-dependency, with the ultimate uplift bearing capacity increasing more rapidly in the early stages and gradually stabilizing in the later stages. Under different resting times, for each load level, the maximum side friction resistance of the pile gradually shifts to the middle and lower parts of the pile body, while the ultimate side friction resistance is evenly distributed along the lower part of the pile body, with the side friction resistance of the pile bearing the uplift load. Based on the quantitative relationship of the cohesion and internal friction angle of the surrounding soil around the pile varying with time, a predictive formula for the axial pullout ultimate bearing capacity of a single pile in the Zhanjiang Group structured clay foundation has been established. Using existing pile foundation projects, model experiments were designed to verify the validity of the formula; however, there is a lack of field-scale validation. The research findings can provide a reference for predicting the axial pullout ultimate bearing capacity of single piles in practical engineering applications. Full article

This study systematically investigates the colloidal stability, rheological properties, and filtration behavior of palygorskite–montmorillonite mixed clays in both freshwater and seawater systems. By varying the mass content and dispersion medium (freshwater/seawater), we analyze the colloidal stability, zeta potential, flow curves, viscosity, shear-thinning behavior, thixotropy, and fluid loss of the dispersions. The results show that palygorskite exhibits good rheological performance in both freshwater and seawater, while montmorillonite performs better in freshwater but suffers a significant decline in seawater. However, palygorskite demonstrates high fluid loss, which is unfavorable for drilling fluid function. Mixed clays can mitigate the limitations of individual clays to some extent, but the specific performance depends on the clay mineral content and dispersion medium. In freshwater, a small amount of montmorillonite improves the viscosity and shear-thinning behavior of the dispersion, with optimal montmorillonite contents of 22% and 38%, respectively. The thixotropy and fluid loss reduction in the mixed clays are positively correlated with montmorillonite content. In seawater, the rheological performance inversely correlates with Mt content due to montmorillonite’s high sensitivity to electrolytes. The addition of Pal enhances the colloidal stability and rheological properties of the mixed clays in seawater. This work provides theoretical insights into the behavior of mixed clays in different media, offering valuable guidance for the design of seawater-based drilling fluids. Full article

This study evaluated the effect of precursor particle size and calcium hydroxide (CH) incorporation on the microstructure, compressive strength, and rheological properties of clay brick waste (BW)-based geopolymers. Rheological analyses were used to evaluate the fresh state of the geopolymers. XRD, SEM, and EDS analyses were performed to analyze the microstructure. The results showed that the particle size reduction in BW and the incorporation of CH significantly contributed to obtaining better compressive strength in the geopolymers. Furthermore, the particle size reduction decreased the yield stress, plastic viscosity, and hysteresis area of the geopolymers, while the incorporation of CH promoted the opposite effect. Increasing the CH incorporation content accelerated the geopolymerization reactions and reduced the workability of the geopolymers over time. However, since the milling process is costly, milling BW for 2 h was more efficient from a technical–economic point of view. In addition, the incorporation of CH not only promoted the early hardening of the geopolymers when necessary, but also contributed to the improvement of the compressive strength through matrix densification. Therefore, the results of this study show the definition of more efficient material proportions for geopolymers using waste as an aluminosilicate source. Full article

Sustainability and limitations in embedded reinforcement are the main obstacles in digital fabrication with concrete. This study proposed a 3D printable fiber-reinforced calcined clay-limestone-based cementitious material (FR-LC³). The binder systems incorporating calcined clay (CC) and limestone filler (LF) were optimized by determining the flow characteristics and water retention ability of the paste. The effect of fiber volume on the key fresh and mechanical properties of the fiber-reinforced mortars made with the optimized binder was evaluated. A combination of offline assessments and inline printing were employed to investigate the printability of the FR-LC³ with various binder systems and viscosity-modifying admixture (VMA) dosages. The results revealed that the binary system with 20% CC and the ternary system containing 30% CC and 15% LF were highly advantageous, with enhanced packing density, robustness, and water retention ability. Incorporating 2% 6-mm steel fiber contributed to the highest 28-day compressive and flexural strengths and toughness without significantly compromising the fluidity. Finally, the developed FR-LC³ mixtures were successfully printed using an extrusion-based 3D printer. The LF addition in the ternary system decreased the maximum buildable height of a single-wall printed object while reducing the SP/VMA ratio significantly increased the height due to enhanced yield stress and thixotropy. Full article

Sodium-based bentonite is used for drilling operations because of its high swelling capacity. This type of bentonite clay is not sourced locally in many oil- and gas-producing nations. However, low-swelling clays (calcium- and potassium-based) are in abundant quantities in most of these countries. Hence, there is a need to convert low-swelling bentonite clays to sodium-based bentonite. The method used to convert low-swelling clays is more applicable to calcium-based bentonite. This research investigated a thermochemical treatment method that converted potassium-based bentonite to sodium-based bentonite. The raw clay materials were sourced from Pindinga (P) and Ubakala (U) clay deposits in Nigeria. An X-ray diffractometer (XRD), an energy dispersive X-ray (EDX), and a scanning electron microscope (SEM) were used to characterize the raw clay samples. Mud slurry was prepared by mixing 22 g of the local raw clays, 3 wt.% soda ash, and MgO at concentrations between 1 and 3 wt.% and heating at 90 °C. The result showed that the viscosities of samples P and U increased from 6 to 26 and 8 to 35.5 cP before and after thermochemical treatment, respectively. Also, due to the thermochemical treatment, the samples’ yield point, consistency factor, consistency index, and thixotropy behavior were all significantly improved. Full article

The clays of the Zhanjiang Formation in the coastal area of Beibu Gulf of China are thixotropic, and the existing constitutive relationship models relevant for clay are incapable of accurately simulating their stress–strain relationships. It is vital to study the changes of mechanical properties of Zhanjiang Formation clay that occur during thixotropy, and to establish a constitutive model considering thixotropy. The varying measures of its shear strength, cohesion, internal friction angle, and initial tangential modulus during thixotropy were investigated by means of triaxial consolidation and drainage tests. Furthermore, the quantitative relationships between the clay’s cohesion, internal friction angle, and initial tangential modulus of the clay and time were examined. This relationship was introduced into the Duncan–Chang model, and a Duncan–Chang model considering the thixotropy of clay was developed. The established model was used to make predictions to assume the validation of the experimental data, and numerical simulations were then carried out. All of the results from the model’s prediction, numerical simulation and experimental measurements were compared against each other in order to verify the reasonableness of the model we had utilized. The results positively demonstrated that: (1) the shear strength, cohesion, angle of internal friction, and initial tangent modulus of the clay gradually increases with longer curing times, and eventually it will stabilize; and (2) compared with the Duncan–Chang model not considering thixotropy, the established thixotropic model is better able to reflect the influence of clay thixotropy on the clay stress–strain relationship, as its mean relative error is smaller. The results of this study provide references for calculating strength and deformation of the clay thixotropy. Further, it also provides references for bearing load calculations of pile foundations in thixotropic clay strata when subjected to long-term loading conditions. Full article

We formulated and characterized oleogels based on montmorillonite clay and vegetable oils that could serve as eco-friendly semi-solid lubricants. In particular, we studied the influence of the physical-chemical properties of olive, castor, soybean, linseed, and sunflower oils on the rheological, chemical, thermal, and tribological properties of the semi-solid lubricants. We prepared the oleogels via the highly intensive mixing of vegetable oils with clay at a concentration of 30 wt.%. The oleogels exhibited shear-thinning, thixotropy, structural recovery, and gel-like behavior commonly related to that of a three-dimensional network. The results were corroborated via XRD measurements showing the presence of intercalated nanoclay structures well-dispersed in the vegetable oil. Empirical correlations between the content of saturated (SFAs), unsaturated (UFAs), mono-unsaturated (MUFAs) and poly-unsaturated (PUFAs) fatty acids and the plateau modulus of the aerogels were found. From these experimental results, we can conclude that the fatty acid profile of the vegetable oils exerts an important influence on the rheological and tribological properties of resulting clay and vegetable oil oleogels. Full article

The presence of clay-organic flocs in cohesive mud results in a complex rheological behavior of mud, including viscoelasticity, shear-thinning, thixotropy and two-step yielding. In this study, the effect of microbial degradation of organic matter on the rheological properties of mud samples, collected from different ports, was examined. The mud samples were collected from five different European ports (Port of Antwerp (PoA), Port of Bremerhaven (PoB), Port of Emden (PoE), Port of Hamburg (PoH) and Port of Rotterdam (PoR)), displaying varying sediment properties. The rheological analysis of fresh and degraded mud samples was performed with the help of several tests, including stress ramp-up tests, amplitude sweep tests, frequency sweep tests, time-dependent tests and structural recovery tests. The results showed: (i) a significant decrease in yield stresses and complex modulus after organic matter degradation for mud samples from PoA, PoH and PoR, (ii) a negligible change in rheological properties (yield stresses, crossover amplitude and complex modulus) for mud samples from PoB, and (iii) a significant increase in rheological properties for mud samples from PoE. For time-dependent tests, mud samples from PoB showed a substantial increase in hysteresis (~50% mean value) as compared to the changes in yield stresses and crossover amplitude. The analysis of gas production during degradation of organic matter showed a (i) significant release of carbon per g dry matter for mud samples from PoA, PoH and PoR, (ii) lower carbon release per g dry matter for mud samples from PoB, and (iii) a negligible carbon release per g dry matter for mud samples from PoE, which corresponded well with the change in rheological properties. Full article

Reductions in bleeding rates and bulk shrinkage of grouting repair materials comprise the key to solving the leakage of earth–rock dams. In this paper, an anti-seepage grouting material for earth–rock dam was developed by introducing mineral admixtures and graphene oxide (GO) nano sheets into low-cost clay–cement grouting materials and by adding polycarboxylate superplasticizers (PCs) to improve slurry viscosity. The experimental results show that the shear stress and viscosity of the slurry increase with the increase in GO concentration, and the slurry has a certain thixotropy. GO can provide a platform to promote the formation of hydration products and fill the pores of clay particles due to its high specific surface area and low volume; in this paper, the microstructure of clay–cement–graphene oxide (CCGO) grouting materials were improved. Therefore, the bleeding rate, bulk shrinkage rate, setting time and unconfined compressive strength (UCS) of the sample were macroscopically improved. In particular, the bleeding rate and bulk shrinkage rate were shown to be 0% when the content of GO reached 1.08 g/kg. Thus, the grouting anti-seepage and reinforcement performance of CCGO grouting materials were improved. Full article

The utilization of greens resources is a grand challenge for this century. A lot of efforts are paid to substitute toxic ingredients of the conventional drilling mud system with nontoxic natural materials. In this paper, the effect of the natural polymer chitosan on the rheology and stability of sodium-bentonite drilling mud was investigated in the polymer concentration range of 0.1–3.0 wt.%. Both the shear and time dependent rheological properties of pure chitosan, pure bentonite and bentonite–chitosan dispersions were studied. Moreover, zeta potential measurements were used to evaluate the stability of bentonite-chitosan suspension. Adding chitosan improved the natural properties of drilling mud, namely: yield stress, shear thinning, and thixotropy. The viscosity of bentonite suspension increased significantly upon the addition of chitosan in the concentration range of 0.5 to 3.0 wt.% forming network structure, which can be attributed to the interactions of hydrogen bonding between -OH clusters on the bentonite surface with the NH group in the chitosan structure. On the other hand, dispersed chitosan–bentonite suspension was observed at low chitosan concentration (less than 0.5 wt.%). Increasing both bentonite and chitosan concentrations led to the flocculation of the bentonite suspension, forming a continuous gel structure that was characterized by noteworthy yield stress. The desired drilling mud rheological behavior can be obtained with less bentonite by adding chitosan polymer and the undesirable effects of high solid clay concentration can be avoided. Full article

The negative environmental impacts of Portland cement as a binder in the construction industry have created a growing impetus to develop sustainable alternative binders. Various types of clay have been considered as potential cement replacements. The impact of clays as cement replacement depends on the dosage and treatment methods. This paper presents a comprehensive review to determine the effects of different types of clay on the fresh and hardened properties of concrete mixtures by analyzing the experimental database reported by the literature, including raw, calcined, modified, nano, and organo. This study intends to show the process of optimizing the use of clay in concrete, the reason behind converting raw clay to modified types, and research gaps through a comparison study between different types of clays. The present review study shows that clay-based concrete mixtures have higher thixotropy and yield stress values, improving shape stability. This results in lower early-age shrinkage of the concrete. However, the high floc strength of clay-based concrete causes a reduction in flowability. Treatment methods of raw clay, such as calcination and nano-sized clay particles, improve concrete compressive strength. General results of the previous studies highlight that all types of clay investigated positively affect the resistance of concrete to environmental attack. Full article

A transparent clay manufactured using Carbopol^® Ultrez^TM 10 (simplified as U10) was introduced, and its manufacturing processes were briefly described. Both relative transparency (RT) and modulation transfer function (MTF) methods were used to quantify the optical character variation via soil thickness. The transparency of this new transparent clay was analyzed and compared with four traditional transparent materials. The thixotropic properties of this synthetic transparent clay were measured in detail through the laboratory vane test. An exponential function was used to describe the thixotropy and sensitivity of the clay. The results showed that the new transparent clay has a relatively higher optical transparency than the majority of previous materials. Good-fitting results showed a similar development trend in thixotropy for the synthetic transparent clay and the natural ones. Furthermore, the sensitivity of the transparent clay was low to medium, which can simulate marine soil. With higher optical transparency than and similar thixotropy and sensitivity as natural clays, Carbopol^® Ultrez^TM 10 shows great potential as a substitute for natural clay and is expected to be widely used in model tests. Full article

The effect of air-entraining admixture (AEA) on the fresh and rheological behavior of mortars designed to be used in 3D printers was investigated. Blast furnace slag, calcined kaolin clay, polypropylene fiber, and various chemical additives were used in the mortar mixtures produced with Super White Cement (CEM I 52.5 R) and quartz sand. In addition to unit weight, air content, and compressive strength tests, in order to determine the stability of 3D printable mortar elements created by extruding layer by layer without any deformation, extrudability, buildability, and open time tests were applied. Fresh and rheological properties of 3D printable mortars were also determined. It was concluded that the addition of AEA to the mortars decreased the unit weight, viscosity, yield, and compressive strength, but increased the air content, spread diameter, initial setting time, and thixotropy of 3D printable mortar. It is recommended to develop a unique chemical admixture for 3D printable mortars, considering the active ingredients of the chemical additives that affect fresh and rheological performance of mortar such as superplasticizer, viscosity modifying, and cement hydration control. Full article

Recently, environment-friendly microbial biopolymer has been widely applied as a new construction material in geotechnical engineering practices including soil stabilization, slope protection, and ground injection. Biopolymer is known to exhibit substantial improvements in geotechnical properties, such as shear strength enhancement and hydraulic conductivity reduction, through the formation of direct ionic bonds with soil particles, especially clay particles. Moreover, the rheological characteristics (e.g., pseudoplasticity, shear-rate dependent thixotropy) of biopolymers render distinctive behaviors such as shear thinning and lubrication effect under a high strain condition, while recovering their viscosities and shear stiffnesses when they are at rest. To ensure the practical applicability of biopolymer-based soil treatment, it is important to understand the interfacial interaction (i.e., friction) between biopolymer-treated soil and adjoining structural members which can be constructed in a biopolymer-treated ground. Thus, in this paper, interfacial shearing behavior of biopolymer-treated soil along solid surfaces as well as internal shearing on biopolymer-soil matrix were explored via direct and interface shear test. Experimental results show a predominant effect of the soil moisture content on the interfacial shear behavior of biopolymer-treated soil which attributes to the rheology transition of biopolymer hydrogels. At low moisture content, condensed biopolymer biofilm mobilizes strong intergranular bonding, where the interfacial shear mainly depends on the physical condition along the surface including the asperity angle. In contrast, the biopolymer induced intergranular bonding weakens as moisture content increases, where most interfacial failures occur in biopolymer-treated soil itself, regardless of the interface condition. In short, this study provides an overall trend of the interfacial friction angle and adhesion variations of xanthan gum biopolymer-treated sand which could be referred when considering a subsequent structural member construction after a biopolymer-based ground improvement practice in field. Full article

Roma Plastilina No. 1 (RP1), an artist modeling clay that has been used as a ballistic clay, is essential for evaluation and certification in standards-based ballistic resistance testing of body armor. It serves as a ballistic witness material (BWM) behind the armor, where the magnitude of the plastic deformation in the clay after a ballistic impact is the figure of merit (known as “backface signature”). RP1 is known to exhibit complex thermomechanical behavior that requires temperature conditioning and frequent performance-based evaluations to verify that its deformation response satisfies requirements. A less complex BWM formulation that allows for room-temperature storage and use as well as a more consistent thermomechanical behavior than RP1 is desired, but a validation based only on ballistic performance would be extensive and expensive to accommodate the different ballistic threats. A framework of lab-scale metrologies for measuring the effects of strain, strain rate, and temperature dependence on mechanical properties are needed to guide BWM development. The current work deals with rheological characterization of a candidate BWM, i.e., silicone composite backing material (SCBM), to understand the fundamental structure–property relationships in comparison to those of RP1. Small-amplitude oscillatory shear frequency sweep experiments were performed at temperatures that ranged from 20 °C to 50 °C to map elastic and damping contributions in the linear elastic regime. Large amplitude oscillatory shear (LAOS) experiments were conducted in the non-linear region and the material response was analyzed in the form of Lissajous curve representations with the values of perfect plastic dissipation ratio reported to identify the degree of plasticity. The results show that the SCBM exhibits dynamic properties that are similar in magnitude to those of temperature-conditioned RP1, but with minimal temperature sensitivity and weaker frequency dependence than RP1. Both SCBM and RP1 are identified as elastoviscoplastic materials, which is particularly important for accurate determination of backface signature in body armor evaluation. The mechanical properties of SCBM show some degree of aging and work history effects. The results from this work demonstrate that the rheological properties of SCBM, at small and large strains, are similar to RP1 with substantial improvements in BWM performance requirements in terms of temperature sensitivity and thixotropy. Full article