Cement-treated Clay Research Articles

Long-Term Compressibility and Shear Strength Properties of Cement-Treated Clay in Deep Cement Mixing Method

Long-Term Compressibility and Shear Strength Properties of Cement-Treated Clay in Deep Cement Mixing Method

Hydraulic conductivity of cement and fly ash stabilised clay mixes – Application to soil mixing techniques for seepage barrier construction

In-situ ground improvement techniques, namely, deep soil mixing, jet grouting, cutter soil mixing, and mass stabilisation are often utilized to improve the strength of soft grounds, and construct seepage barriers. Due to economic and environmental concerns, there is a global shift towards using industrial wastes such as fly ash (FA) from conventional binders such as ordinary Portland cement and lime. There is a plethora of literature on unconfined compressive strength (UCS) of cement-treated clays, and clays treated with fly ash-cement mixes with alkali activator (FCAA) binders. However, much remains unclear about the hydraulic conductivity of the FCAA-treated clays as low permeable hydraulic barrier systems. In this paper, the hydraulic conductivities of cement-treated and FCAA-treated clays are studied both quantitatively and qualitatively for different binder-content, FA:cement ratios, curing periods, and effective confining stress. The hydraulic conductivity of treated clay is measured by performing a series of accelerated permeability tests using a custom-fabricated triaxial system. The trends obtained from the measured hydraulic conductivity values are explained from the observations of X-ray diffraction analysis and scanning electron microscopy analysis. Results showed that the values of hydraulic conductivity for cement-treated clay were mostly higher than those of untreated clay. On the contrary, the hydraulic conductivities for the FCAA clay mixes were comparable to, or even lower than those for the untreated clay. The hydraulic conductivity reduced with the increase in effective confining stress; the influence of effective confining stress, however, became less substantial for 28 days curing period and higher cement-content (40 and 50 %). The relationships between the hydraulic conductivity, UCS, and water-binder (w/b) ratios were also determined for both cement-treated and FCAA-treated clays. The exponential function was found suitable to express the relationship between hydraulic conductivity and UCS of treated clays. In contrast, a strong logarithmic relationship was obtained for measured values of hydraulic conductivity and adopted w/b ratios. The results shall serve as a guide to adopting suitable binder-content or target UCS for achieving design hydraulic conductivity in ground improvement projects that involve cement and/or FCAA-treatment of clays.

Strength and Elastic Properties of Air–Cement-Treated Clays Under Cyclic and Monotonic Compression Tests

Strength and Elastic Properties of Air–Cement-Treated Clays Under Cyclic and Monotonic Compression Tests

The Strength Behaviour of Cement-Treated Clay at Different Moisture Content and Curing Time

This study involves the study on the properties of clay samples from Pagoh at natural state and stabilized state with Portland cement. The main objective of the study is to identify the unconfined compression strength of original and stabilized clay at different moisture content and curing time. The tests carried out include proctor test, moisture content and unconfined compression test (UCT). Therefore, clay was mixed with Portland cement at a concentration of 10 % by weight of dry soil for the proctor test. The original and stabilized samples were tested in an UCT at different curing period of 14 and 28 days. At the end, the actual result shows that the unconfined compressive strength of the stabilized clay is higher than the original. It is believed that the value of strength is highly affected by the different moisture content and curing time. Therefore, the control of water content and treatment time is essential to produce a strong and safe foundation for any construction purpose. As a result, new stabilization methods to prevent landslides in natural and developed quick clay slopes will be developed. In conclusion, cement stabilization improves the workability of clay.

A state parameter of cement admixed clay with different stress paths

ABSTRACT This paper presents an appropriate physical parameter for cement admixed clay, termed as the state parameter that combines the influence of void ratio, stress level, and cement content reference to an ultimate (steady) state. Data from a triaxial testing program on Pasak Clay with different stress paths was presented and demonstrated to be dependent on the state parameter. The strength and pore water pressure at the failure of cement mixed clay were directly associated with mean stress and decreasing state parameters. The 3-D surface for deviatoric stress, mean stress, and state parameter at certain distortional strains was proposed based on a stress path triaxial test. The stiffness of cement-treated clay increased with a decreasing state parameter and increase in mean stress. The concept of state parameter is a basic physical concept and has broad application as an empirical normalising parameter and constitutive modelling of soil behaviour.

Dynamic behavior of Haikou marine clay treated with cement

The dynamic properties of cement-treated soil are important in evaluating the performance of both cement-treated ground and overlying infrastructure subjected to dynamic loads such as earthquake and traffic-induced impact. In this study, using the marine clays collected from Haikou, China, a series of cyclic triaxial tests were performed to investigate the dynamic behavior of both pure and cement-treated marine clays, with the investigation focus placed on the equivalent shear modulus and damping ratio of cement-treated marine clay. Some important factors, namely confining pressure, loading frequency and cycle, cement content, strain amplitude, and curing period, were systematically taken into consideration. The results suggested that, different from the pure clay, the loading frequency and confining pressure have slightly intensifying and alleviating effects on the equivalent shear modulus and damping ratio of cement-treated clay, respectively; the curing period had a similar influence on the dynamic behavior of cement-treated clay. Among the factors considered, the cement content and strain amplitude were found to be the most influential on the dynamic properties of cement-treated clay, albeit the influencing trends being exactly opposite. Regardless of other factors considered, the equivalent shear modulus and damping ratio were found to attenuate significantly within the first 5–10 loading cycles, beyond which they became relatively unchanged. In addition, multivariate regression analyses were conducted based on the experimental results, and two semi-empirical equations were established for reasonably correlating the equivalent shear modulus and damping ratio with the factors considered in this study, respectively, which can serve to provide first-order predictions of them for similar cement-treated clays.

Geotechnical studies on cemented and untreated Behshahr loess and Amol clay of Iran

There has been little research into the effects of cement on the geotechnical properties of two types of fine-grained soil with roughly the same grain size. The cement percentages used in this investigation were 0, 4, and 8% by dry weight of soil. Compaction features, consolidation characteristics, unconfined compressive strength (UCS), and Atterberg limits were all determined in the laboratory. Furthermore, scanning electron microscopy (SEM) examinations were used to analyze the microstructures of cemented and untreated loess and clay. Notably, the MDD for loess and clay are 1.72 gr/cm3 and 1.57 gr/cm3 at CC = 0%, respectively, and 1.7 gr/cm3 and 1.55 gr/cm3 at CC = 4%. The OMC for loess and clay are 15% and 22% at CC = 0%, respectively, and 17% and 20% at CC = 4%. At CC = 0%, loess and clay have cohesion values of 25 kPa and 28.7 kPa, respectively, and 190 kPa and 140 kPa at CC = 8%. Internal friction degrees for loess and clay are 24 and 29 degrees at CC = 0%, respectively, and 36 and 34 degrees at CC = 8. The consolidation test findings demonstrated that increasing the cement proportion reduced cemented soils’ compressibility. The Plasticity Index (PI) rose as cement concentration increased. However, significant percentages of cement concentration reduced the plasticity index. Furthermore, adding cement agents resulted in significant improvements in elasticity modulus and UCS for both soils. The SEM results indicated that the cement-treated loess was denser and more homogenous than the cement-treated clay sample. Triaxial tests reveal that cement particles improve cohesiveness and internal friction angle.

Effect of limestone and granite stone powder on properties of cement-treated clay composites and their socioeconomic and environmental impacts

Large volumes of stone powder, i.e., limestone and granite waste are produced annually. When reused in cement-treated clay, the granite stone powder particle size affected the composites' unconfined compressive strength (UCS). However, limestone's effect on cement-treated clay has yet to be addressed comprehensively. This paper presents the effects of uncalcined limestone of different sizes on the particle size distribution, consistency indices, and the UCS of cement-treated clay composites at curing periods of 1, 3, 7, and 28 days. A comparison between the performance of cement-treated clay-limestone, cement-treated clay-granite powder composites, and cement-treated clay and their effect on sustainable construction is also presented. After 1 and 3 days of curing, the UCS of cement-treated clay-limestone composites was higher than the cement-treated clay control sample. However, at 7 and 28 days, the cement-treated clay-limestone composites possessed similar UCS to the cement-treated clay control sample regardless of their particle size. Cement-treated clay-granite powder composites are stronger than cement-treated clay-limestone composites. Regardless of the performance differences, both limestone and granite powder can be reused in cement-treated clay without significant loss in UCS and provide environmental benefits such as reduced cement usage and embodied airborne emissions, energy, and abiotic depletion, among other factors.

Evolution in macro-micro properties of cement-treated clay with changing ratio of red mud to phosphogypsum

To investigate the effect of combined red mud (RM) and phosphogypsum (PG) in cement-treated clay, unconfined compressive strength (UCS) tests and isotropically consolidated undrained triaxial (ICUT) tests were performed to explore the effects of RM/PG ratio on mechanical behavior of stabilized clay. Moreover, x-ray diffractometer (XRD) tests, thermogravimetric analysis/differential scanning calorimetry (TG/DSC) tests and scanning electron microscopy (SEM) tests were employed to observe the evolution in microstructure with changing RM/PG ratios. The results indicate that the combined RM and PG play a significant role in cement-based hydration reactions. The UCS at early curing stages nearly doubles with an optimal proportion of 7.5 %RM and 2.5 %PG. The stabilized clay with high contents of RM exhibits a higher maximum deviator stress and a brittle behavior in undrained shearing process. As the PG content increases, the peak strength decreases but the ductility of the specimen increases remarkably. It is believed that the RM acts as an alkali activator on clay minerals whereas the PG mainly contributes to the generation of ettringite. The combined RM and PG not only promotes sufficient pozzolanic reactions and stronger cementation bonds, but also brings out a principally denser microstructure, though a few large pores can be observed due to expansion potential of ettringite. However, the microstructure of stabilized clay becomes much looser with a high content of PG. Partial amounts of PG are found non-reactive with inadequate active aluminium ions. The mechanical behavior of stabilized clay also gets worse concerning negative effects of impurities in PG.

Influence of some factors on the mechanical properties of cement-treated clay for shallow mixing in Vietnam: A comparative study

The compressive strength of cement-treated soil is known as the most crucial factor, which governs the quality of cement-treated soils. Indeed, many factors affect the compressive strength of cement-treated soils, including cement types and contents, water/cement ratio, soil types, as well as curing conditions, etc. In which, curing conditions, cement types, and soil types are the most important factors that govern the compressive and durability of cement-treated clay. Three cement types and two types of clay were used to prepare the specimens of cement-treated clay with three cement dosages (100, 150, and 200 kg/m3 of soil). The specimens of cement-treated clay were cured under two conditions (sealed and drying). The results showed that drying conditions significantly increased the unconfined compressive strength of cement-treated soils regardless of cement types, cement contents, soil types, and ages as compared to those under sealed conditions. The unconfined compressive strength of specimens under drying conditions was approximately 1.3–2.5 times higher than that under sealed conditions. Cement type significantly affected the performance (compressive strength and elastic modulus) of cement-treated clay regardless of cement content. The cement-treated clay specimens under sealed conditions showed a ductile failure mode while those under drying conditions exhibited a brittle failure mode. Finally, soil type significantly influenced the compressive strength and elastic modulus of cement-treated clay regardless of cement content and curing condition.

Twenty-two-year investigation of strength development and surface deterioration of cement-treated clay in an in-situ field test

The long-term strength development and durability of in-situ cement-treated soil were investigated by physicochemical analysis and geochemical thermodynamic modeling. The measured strength of the volcanic cohesive clay treated with high-sulfate cement continuously increased for five years and then persisted until 22 years. X-ray analysis revealed that the ettringite formation through cement hydration contributed to the early strength, while the strätlingite formation through pozzolanic reaction contributed to the long-term strength. Thermodynamic modeling pointed at the alumina dissolution from the treated clay in an alkaline environment as the main driving force for the pozzolanic reaction. Further, calcium leaching and carbonation caused surface deterioration of the cement-treated soil, thereby decomposing the hydration products and lowering the strength of the treated clay.

Experimental Investigations on the Mechanical and Microscopic Behavior of Cement-Treated Clay Modified by Nano-MgO and Fibers

Cement is often used to stabilize soft clay; however, it has some limitations in increasing clay strength and improving clay failure mode. To solve this, two different additives, i.e., polypropylene fiber and nano-Magnesium Oxide (MgO), were tested with the purpose of improving the mechanical performance of cement-treated soft clay. Four groups of samples with different mixture ratios of coastal soft clay, cement, fiber, and nano-MgO were first designed. Microscopy tests including X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS), as well as unconfined compression test was then carried out. XRD and EDS test results show that the cement hydration reaction is the main source of strength increase and the nano-MgO can generate Magnesium Silicate Hydrates (M-S-H) gelation, which helps to fill the pores of the clay and increase clay compactness. The unconfined compressive strength test results show that adding fiber or nano-MgO alone has a poor effect on the strength improvement for cement-treated clay with high water content. However, adding both additives lead to a significant increase in the clay’s unconfined compressive strength, which is verified by the microscopic observation of clay compactness in SEM images. Moreover, the fiber is found to increase the ductility of cement-treated clay based on the observed failure modes of modified samples.

Study on the Effect of Amorphous Silica from Waste Granite Powder on the Strength Development of Cement-Treated Clay for Soft Ground Improvement

Granite powder (stone powder), a waste product generated from stone quarries, is increasingly being reused in cement-treated clays. The particle size of stone powders affects the cement-clay reaction by either increasing or reducing the unconfined compressive strength (UCS). This study investigated this phenomenon by separating stone powder from the same batch at the quarry into five particle sizes (A, B, C, D and E: 106–75 µm, 40–75 µm, 20–40 µm, <20 µm and 106–<1 µm, respectively). Flow value, fall cone, UCS and thermogravimetry-differential thermal analysis (TG-DTA), X-ray fluorescence, electrical conductivity and NaOH digestion tests were conducted. It was discovered that stone powder had an amorphization rate of up to 1.45% (14.5 mg/g of amorphous silica); hence, it was pozzolanic. However, the amorphousness varied with the particle size of the material in the order of D > E > C > B > A, which translated into UCS variation in the same order. Stone powders D and E played two roles in UCS development, i.e., nucleation of cementitious products and reaction with Ca(OH)2 to increase the UCS higher than the control sample. Linear regression equations determined the minimum concentration of amorphous silica for a UCS increment as 9.4 mg/g.

State parameter governing the mechanical properties of cement-treated clays

A new state parameter that is capable of characterizing the mechanical properties of cement-treated clays with different mixing proportions, curing time, and stress conditions is developed in this study. The development is conducted by combining the effect of stress level based on the critical state theory with the effective void ratio. Based on the experimental data of cement-treated Bangkok clay performed in this study together with those of cement-treated Singapore marine and Ariake clays reported in previous studies, the analyses reveal that the state parameter is proven to be an efficient parameter for characterizing the mechanical properties of cement-treated clays with different base clays under various mixing proportions and curing times tested under various stress conditions. Furthermore, empirical equations to assist the establishment of the effective void ratio on the critical state locus from the plastic limit value of the base clay are suggested based on regression analyses. The state parameter can thus be computed and the engineers can preliminarily estimate the mechanical properties of cement-treated clay in the planning stage.

Effects and evaluation of high temperature curing on the mechanical and chemical properties of cement-treated clay

Effects and evaluation of high temperature curing on the mechanical and chemical properties of cement-treated clay

Influence of stone powder content and particle size on the strength of cement-treated clay

Particle size of additive geomaterials could affect the cement–clay reaction, thereby reducing strength. The effects of five particle sizes (A, B, C, D and E: >75, 40–75, 20–40, <20 and < 1–106 µm, respectively) of waste granite powder in cement-treated clay mixed composites were investigated. The effects on the liquid limit, unconfined compressive strength (UCS) and microstructural characteristics were investigated. The particle size influenced the UCS in the order of D > A > C > B, and D exhibited higher UCS than the control sample. The increase in the UCS was due to the increased surface area and pozzolanic reactivity of stone powder D. A reduction in the UCS of cement-treated clay–stone powder E composites occurred as compared to the control sample with a 30% stone powder addition, and equal or improved strength was observed with 50% and 70% additions. Owing to the UCS increment derived from stone powder, we could reduce 28.6% of the cement.

Attempt to reproduce the mechanical behavior of cement-treated soil using elasto-plastic model considering soil skeleton structure

The improvement of sand and clay using lime or cement to control solidification is common practice. Among the many constitutive models for solidification proposed for clay and sand, few can reproduce the combined behavior of cement-treated clay and cement-treated sand. Here, four typical experimental results for cement-treated soil have been chosen from the literature to consider the shear and consolidation behavior for clay and sand, especially for a low cement mixing ratio. The elasto-plastic constitutive model was used to simulate this behavior considering the soil skeleton structure.The simulation results obtained using the model agreed with the experimental test results both for the cement-treated clay and the cement-treated sand. In the case of the clays, the experimental results were reproduceable using material constants for elasto-plastic and evolution parameters and only required changes in the initial state values, regardless of whether the soil was treated or untreated. In the case of the sands, the structure decay index of the treated sand became smaller than that of the untreated sand. Moreover, the cement-treated loose sand did not exhibit softening behavior. This was attributed to the slow rate of decay of the highly structured cement-treated loose sand due to the solidification of the cement. The degree of structure and the overconsolidation ratio both increased with higher amounts of admixed cement. The model developed in this study was capable of describing the mechanical behavior of both cement-treated clay and cement-treated sand.

Numerical simulation of triaxial tests on cement-treated clays using Hoek–Brown criterion

Triaxial tests are generally conducted to establish the mechanical behaviour of cement-treated clays. Numerical simulations of these tests involve selection of the correct constitutive model, which can capture the key features of the stress–strain response of the geomaterial. However, as cement-treated clays behave differently to untreated clay in its natural state, the classic constitutive models may not give reasonable results and the failure envelope has been found to be non-linear. An attempt was made in this work to simulate the behaviour of cement-treated clays using the Hoek–Brown model and the experimental and numerical simulation results were compared.

Microstructural Analyses of Cement-Based Binders in Stabilizing Champlain Sea Clay

This research investigated the strength development and the microstructural change in Champlain Sea clay when treated with five different cement-based binders. Champlain Sea clay, a marine clay, is commonly found in St. Lawrence Lowlands in eastern Canada. The unconfined compressive strength tests were conducted to measure the shear strength development of treated clay under different binder type, binder dosage, and curing time conditions. The scanning electronic microscopy (SEM) and X-ray diffraction (XRD) analyses were conducted to investigate the microstructural changes in the specimens. Based on the test results, it was found that cement is efficient to treat Champlain Sea clay with a significant strength improvement. For Champlain Sea clay used in this study, the optimum cement dosage was found to be around 100 kg/m3 per mixed volume in terms of strength improvement and cost-effectiveness. The clay samples treated with a mix of cement and cement kiln dust and a mix of cement with slag showed a substantial strength increase over time. These results proved the feasibility of using cement kiln dust mix or slag to replace a portion of cement in treating Champlain Sea clay. Based on SEM observations, a substantial transformation was observed in the microstructure of the clay due to cement mixing. A large amount of clay-binder aggregates were formed and the hydration products filled the porous network of the clay samples, which results in a strength improvement in the treated clay. Based on the XRD analysis, hydration products, such as calcium silicate hydrate and calcium tecto-dialumodisilicate tetrahydrate, were formed in the cement-treated clay specimens, which explains the strength improvement of Champlain Sea clay due to cement mixing.

Mixture design concept and mechanical characteristics of PS ash–cement-treated clay based on the water absorption and retention performance of PS ash

In an attempt to reduce environmental impact, paper sludge ash (PS ash) has recently been studied for its complementary reuse with cement for soil stabilization. In order to establish the optimal mixture design for combining PS ash and cement in soils, a detailed investigation into the stabilizing mechanism is required. To assess the combined effects of PS ash and cement on the strength development of stabilized clay soil, referred to as PS ash–cement-treated clay, a new critical parameter, the unabsorbed and unretained clay-water/cement ratio W*/C, was proposed. To determine W*/C, a new testing method for evaluating the water absorption and retention performance of PS ash was developed. It was revealed that the water absorption and retention rate Wab of PS ash increased with curing time. Unconfined compression tests conducted on the PS ash–cement-treated clay with various water-cement–PS ash mixture proportions and different curing times affirmed that the strength development was fundamentally governed by the parameter W*/C. This suggests that the water absorption and retention rate Wab obtained by the developed method is an essential material parameter in the mixture design for the PS ash–cement-treated clay. It was also found that the effect of the hybrid treatment method, which uses both cement and PS ash, was better than that of the method which uses cement alone, particularly under high W*/C conditions. This indicates that the water absorption and retention performance of PS ash can be fully utilized when the mixture has sufficient unabsorbed and unretained water for cement hydration.