Cement-treated Clay Research Articles

Analysis of cement-treated clay behavior by micromechanical approach

Experimental results show the significant influence of cement content on the mechanical properties of cement-treated clays. Cementation is produced by mixing a certain amount of cement with the saturated clay. The purpose of this paper is to model the cementation effect on the mechanical behavior of cement-treated clay. A micromechanical stress-strain model is developed considering explicitly the cementation at inter-cluster contacts. The inter-cluster bonding and debonding during mechanical loading are introduced in two ways: an additional cohesion in the shear sliding and a higher yield stress in normal compression. The model is used to simulate isotropic compression and undrained triaxial tests under various confining stresses on cement-treated Ariake clay and Singapore clay with various cement contents. The applicability of the present model is evaluated through comparisons between numerical and experimental results. The evolution of local stresses and local strains in inter-cluster planes are discussed in order to explain the induced anisotropy due to debonding at contact level under the applied loads. The numerical simulations demonstrate that the proposed micromechanical approach is well adapted for taking into account the main physical properties of cement-treated clay, including damage and induced anisotropy under mechanical loading.

Micromechanics-based model for cement-treated clays

Cementation is produced by mixing a certain amount of cement with the saturated clay. The purpose of this paper is to model the cementation effect on the mechanical behavior of cement-treated clay. A micromechanical stress-strain model is developed considering explicitly the cementation at inter-cluster contacts. The inter-cluster bonding and debonding during mechanical loading are introduced in two ways: an additional cohesion in the shear sliding and a higher yield stress in normal compression. The model is used to simulate isotropic compression and undrained triaxial tests under various confining stresses on cement-treated Singapore clay with various cement contents. The applicability of the present model is evaluated through comparisons between numerical and experimental results. The evolution of local stresses and local strains in inter-cluster planes is discussed in order to explain the induced anisotropy due to debonding at contact level under the applied loads.

高含水比の海成粘土を原料土とするセメント固化処理土の強度発現過程に関する研究

各種の含水比，セメント添加率で作製したセメント固化処理土の経時的な強度発現を調べた結果，強度発現過程が，添加直後から3日までの前期強度発現過程と3日以降の後期強度発現過程に分かれることを示した。各過程の強度発現をモデル化し，5つのパラメータによりセメント処理土の経時的な強度発現を予測する式を提案した。本提案式はすでに提案している体積固体分率による強度予測式と整合し，さらに発展させている。12種類の海底浚渫粘土の配合試験結果について提案式のパラメータを求め，実測強度と計算強度を比較した結果，セメント固化処理土の経過時間ごとの強度発現を適切に予測できた。

Mechanical characteristics of soft clay treated with fibre and cement

ABSTRACT: In this study, the influence of three types of fibre – polypropylene, recycled carpet and steel – on the mechanical properties of cement-treated clay is investigated. Cement-treated clay specimens were prepared with cement contents of 5%, 10% and 15% by weight of dry soil, and cured for 14 days. To investigate and understand the influence of different fibre types and contents, three different percentages of fibre content were adopted. The results of unconfined compression tests on 90 cylindrical samples of cement-treated clay with varied cement and fibre contents are analysed to discern the relationships between these parameters and the key mechanical properties, including unconfined compressive strength and stiffness of treated soil. Furthermore, indirect tension test results of a further 90 treated soil samples have been used to determine the influence of fibre and cement content on the tensile strength of the treated soil. The fibre reinforcement increases the peak compressive strength. The addition of fibres increases the residual strength and changes the brittle behaviour of the cement-treated clay to that of a more ductile material. The tensile strength of the cement-treated clay is increased by adding carpet and steel fibres, but small quantities of polypropylene fibres do not influence the tensile strength.

海成粘土を用いたセメント固化処理土の強度推定法

港湾の浚渫土を原料土とするセメント固化処理土に関する強度推定式を提案した。提案式はセメント硬化体の強度理論であるゲル空隙比説と類似性があり，セメント処理土の強度はセメントを含めた体積固体分率，セメントによる強度増加係数，セメント処理土の間隙構造が強度に及ぼす効果を示す定数N，固体分全体に対するセメントの質量比率で与えられる。提案式をわが国の6箇所の海成粘土を用いた配合試験結果に適用した結果，Nの値を3.5～4.5の範囲で設定することにより高い相関係数で強度を予測できた。浚渫粘土を用いた気泡混合処理土と発泡ビーズ混合処理土の強度に関しても，Nを2.1～2.5の範囲で設定することで適用できることがわかった。

The Effect of Air Foam Inclusion on the Permeability and Absorption Properties of Light Weight Soil

Cement-treated clay with air foam, which is called Super Geo-Material (SGM), was developed to utilize dredged clay in an effective way. As SGM is mainly used at levels below the ground water table, water permeability and absorption properties of SGM will affect the durability of the material. In this research, the changes in SGM permeability and absorption as functions of the air foam fraction were investigated. First, permeability tests with triaxial apparatus and constant rate of consolidation tests were conducted on samples containing less than 10% of air foam by volume. From the results, air foam was found to be an impermeable medium in SGM. Secondly, a series of permeability tests and absorption tests were conducted for the SGM with different fractions of air foam while observing the specimen with a micro focus X-ray Computed Tomography (CT) scanner. The results showed that the permeability of SGM increased dramatically due to the appearance of interior water channels when the air foam fraction exceeded 30% by volume. The density distribution change and water absorbed zones of the specimens during absorption tests were estimated using the X-ray CT data. From these results, the air in the SGM was found to be progressively substituted with water from the surface to the inside of the specimen and the substituted zone expanded as it made its way to the specimen interior. The expansion velocity of the substituted zone was not affected by the coefficient of permeability but by the fraction of the air in the specimen.

Effect of strain rate on strength and deformation properties of cement-treated clay

Effect of strain rate on strength and deformation properties of cement-treated clay

Effective Void Ratio for Assessing the Mechanical Properties of Cement-Clay Admixtures at High Water Content

Portland cement is widely used for the improvement of soft clay in many applications and construction methods. Because of the high initial water content of in situ soft clay, the additional water in the cement slurry to be mixed, and the added air in some applications, the mixtures have a high water content and void ratio in either almost-saturated or unsaturated conditions. The mechanical properties of cement-clay admixtures—including cement-treated clay and air-cement-treated clay—are affected by several parameters, e.g., mixing proportions, curing time, and the initial state of the mixture. To facilitate engineering decisions regarding mixing design and the development of a constitutive model, a single parameter that can characterize the mechanical properties of such mixed materials is advantageous. This paper recommends a parameter defined as the effective void ratio that could appropriately quantify the dependency of the mechanical properties of cement-clay admixtures on the influencing parameters on the basis of the results of unconfined compression, oedometer, and triaxial tests. The proposed parameter tends to capture the mechanical characteristics of cement-clay admixtures under different test conditions.

Microstructure and Chemical Properties of Cement Treated Soft Bangladesh Clays

This paper examines the relationship between the microstructure and chemical properties of soft Bangladesh clays due to cementation. The microstructure was investigated using X-ray diffraction, scanning electron microscopy, pH measurement, specific surface area and soil chemical tests. The results indicate that a multitude of changes occurred in the properties and behavior of cement-treated clays that can be explained by the interaction between four underlying microstructural mechanisms. That is, it is suggested that the hydrated lime is formed by hydration, which causes the flocculation of the little clay particles, by the preferential attack of the calcium ions on kaolinite rather than on illite and monmorillinite in the pozzolanic reaction, by surface deposition and shallow infilling by cementitious products such as calcium silicate hydrate and calcium alumino silicate hydrate (CSH and CASH) on clay clusters, and finally, by the presence of water trapped within the clay clusters. The chemical properties of the cement-treated clays were found to depend on the plasticity of soil.

Cyclic deformation characteristics of cement-treated clay in hollow cylindrical torsional shear tests

Cyclic deformation characteristics of cement-treated clay in hollow cylindrical torsional shear tests

Small-Strain Shear Modulus and Strength Increase of Cement-Treated Clay

AbstractA simple nondestructive technique was used as an alternative method to monitor the hardening of cement-treated clay as a function of time. The principle of this monitoring technique is based on the use of bender elements to measure the small-strain shear modulus (G0) at various time intervals. The strength increase was monitored by conventional unconfined compression testing. Experimental work was carried out on Kaolin clay treated with Portland cement and blast furnace slag cement at different dosages. The results showed that G0, as well as strength, of cement-treated samples increases logarithmically with time. However, blast furnace slag cement produces a slower hardening rate early after mixing. It was found that for each binder type, the G0 increase and the strength increase, when normalized, follow a common trend. Such a hardening function may be used as the basis of a strength prediction rule. The functions obtained are in good agreement with data on other cement-treated inorganic clays published in the literature.

Multifaceted potentials of tire-derived three dimensional geosynthetics in geotechnical applications and their evaluation

Scrapped tire-derived materials, such as tire chips and tire shreds, can be categorized as three dimensional geosynthetics. This paper introduces recent Japanese experience in geotechnical related applications of geosynthetics that focus mainly on tire chips and tire shreds. Three specific applications of tire chips and tire shreds are introduced here. They are: (1) tire shreds to improve drainage; (2) sand-mixed tire chips to mitigate earthquake damage; and (3) tire chips mixed with cement-treated clay to improve toughness and ductility. The developed techniques related to these applications, verification through model testing, as well as element testing and the field applications are presented. It was observed that tire shreds can maintain high permeability even under a high compressive load. When tire chips and/or sand-mixed tire chips are used as a compressible cushion, not only the dynamic load against a structure but also the dynamically induced permanent structural displacement could also be significantly reduced. On the other hand, mixing tire chips with cement-treated clay gives toughness to the geomaterial, and thus provides resistance against the development of cracks during deformation. In addition, an X-ray CT investigation of deformation behavior of such materials demonstrated the success of using cement-treated clay with tire chips as a sealing material to protect leakage of contaminated materials at a waste disposal site in Tokyo bay area.

Influence of salts on strength of cement-treated clays

This paper discusses the influence of salts on cement-treated clays. Three types of soil were studied: Bangkok Clay, bentonite and kaolinite. Two experimental methods were used. In the first method, homoionic clay was made with different concentrations of sodium and calcium to simulate the influence of naturally occurring salts on cement-treated clay. In the second method the clay was mixed with different quantities of sodium chloride (NaCl) and calcium chloride (CaCl2) to evaluate the influence of additional salt on cement-treated clay. All samples were investigated by using unconfined compression tests to determine the strengths of the cement-treated clays. Finally, the samples were evaluated by chemical analysis to study the changes in chemical properties. According to the experimental investigation, the influences of salts on cement-treated Bangkok Clay, bentonite and kaolinite varied as a result of the soil structure and chemical reactions. The mechanisms of the homoionic clay and the clay mixed with salt admixture were different. In the natural clay, the existence of Na+ is beneficial in dissolving the soil silica and alumina, which induces higher strength than that of Ca2+. For practical soil stabilisation, Ca admixture is more beneficial in improving the strength of cement-treated clay than Na admixture because of the high Ca2+ content, which promotes increased cementation.

High-Strengthening of Cement-Treated Clay by Mechanical Dehydration

A technique called the cement-mixing and mechanical dehydration method (CMD) as one of recycling techniques for soft clay slurry is developed. In order to evaluate the effectiveness of the CMD for increasing the strength of soft clay, a series of unconfined compression tests and several durability tests were performed together with the literature review of unconfined compressive strength in cement-treated soils. Moreover, a series of constant strain rate consolidation tests were also performed to evaluate the effects of cement content and dehydration speed on the permeability of cement-treated clay. The following conclusions are obtained: 1) Literature review and theoretical considerations on the shear strength of cement-treated soils show that an additional treatment for the purpose of increasing the density of cement-treated specimen is effective for increasing the shear strength of cement-treated soil. 2) The mechanical dehydration of soft clay with high pressure is accelerated by cement mixing, where the coefficient of consolidation of cement-treated clay increases as the cement content increases. 3) The high-strength specimen having the unconfined compressive strength of more than 20 MPa can be created from soft clay treated by the CMD with the cement content of over 20% and the dehydration pressure of 20 MPa.

Stress-Deformation Behavior Under Anisotropic Drained Triaxial Consolidation of Cement-Treated Soft Bangkok Clay

ABSTRACT In this study the compression behavior of high water content cement-treated soft Bangkok clay is further investigated by conducting a constant stress ratio (CSR) test at various stress ratios (η). The test utilized cement-treated clay specimens with cement contents (Aw) of 10% and 15%, each of which was in combination with 100% and 130% total clay water contents. The test results confirmed that the ratio of after-curing void ratio to cement content (eot/Aw) can effectively characterize the compression behavior of cement-treated clay. The specimens with higher values of eot/Aw yielded higher volumetric and shear strains at the same stress ratio. While those with lower values of eot/Aw resulted in lower shear strains, with consequent higher values of strain increment ratios (dɛv/dɛs) both before and after transitional yield points. Significantly, the eot/Aw ratio has described the relationship of the compression yield loci of cement-treated clay at various stress ratios and mixing conditions.

Microstructure of cement-treated Singapore marine clay

This paper examines the microstructural behaviour of cement-treated soft Singapore marine clay. The microstructure was investigated using X-ray diffraction, (XRD) scanning electron microscopy, (SEM) mercury intrusion porosimetry, and laser diffractometric measurement of particle size distribution. The XRD analysis of cement-treated clay enables the identification of the formation of cementitious products, namely calcium silicate hydrate (CSH) and calcium aluminium silicate hydrate (CASH). The relative amount of cementitious products (CSH + CASH) is found to increase with increase of the cement content. The fabric of the treated clay changes to flocculated type, comprising clay-cement clusters separated by large intercluster voids with smaller intra-cluster pores, as can be seen from the SEM images of treated clay. This change is more pronounced with higher cement content and prolonged curing time. The flocculation of the clay particles also causes water to be trapped within the clay-cement cluster and increases both the effective size of the particles or cluster and the entrance pore diameter. This understanding clearly helps to explain the observed engineering behaviour of cement-treated clays commonly found in deep cement mixing or jet grouting techniques. Cet exposé examine le comportement microstructural d'une argile marine tendre de Singapour traitée au ciment. Nous avons étudié sa microstructure en utilisant une diffraction de rayons X, une microscopie électronique à balayage, une porosimétrie à intrusion de mercure et des mesures de diffractométrie laser pour la répartition de dimensions de particules. L'analyse XRD de l'argile traitée au ciment permet d'identifier la formation de produits cimenteux, nommément d'hydrate de silicate de calcium (CHS) et d'hydrate de silicate d'aluminium calcium (CASH). Il est apparu que la quantité relative de produits cimenteux (CSH + CASH) augmentait en même temps que la teneur en ciment. La structure de l'argile traitée devient floculée et comporte des noyaux d'argile-ciment séparés par de grands vides entre les noyaux et avec de pores plus petits à l'intérieur des noyaux. Ce changement est plus prononcé lorsque le contenu de ciment est plus élevé et que le temps de cuisson est plus long. La floculation des particules d'argile a pour effet de piéger l'eau à l'intérieur des noyaux argile-ciment et augmente à la fois la dimension effective des particules ou du noyau et le diamètre de pore d'entrée. Cette constatation aide clairement à expliquer le comportement mécanique observé des argiles traitées au ciment utilisées couramment dans les techniques de mixage profond ou d'injection de ciment.

Laboratory Evaluation of the Geogauge and Light Falling Weight Deflectometer as Construction Control Tools

The objective of this paper is to assess the potential use of the geogauge and the light falling weight deflectometer (LFWD) as quality control/quality assurance ( QC ∕ QA ) devices for testing subgrades, base courses, and compacted soil layers. A comprehensive laboratory experimental program was conducted on compacted layers of silty clay, clayey silt, cement-treated clay, sand, gravel, recycled asphalt pavement, and limestone aggregates. The geogauge, LFWD, static plate load test (PLT), and the dynamic cone penetration (DCP) measurements were acquired for the constructed layers. The geogauge elastic modulus and the LFWD dynamic modulus were correlated with the PLT initial and reloading elastic moduli and with the DCP penetration rates. The results of this study show that the geogauge and the LFWD can be used to calculate the elastic modulus/stiffness characteristics of compacted layers. Whereas the geogauge and the LFWD determined the initial modulus of the cement-treated clay, they did not yield accura...