Cement Agent Research Articles

Microstructure characteristics of cement-stabilized sandy soil using nanosilica

An experimental program was conducted to explore the impact of nanosilica on the microstructure and mechanical characteristics of cemented sandy soil. Cement agent included Portland cement type II. Cement content was 6% by weight of the sandy soil. Nanosilica was added in percentages of 0%, 4%, 8% and 12% by weight of cement. Cylindrical samples were prepared with relative density of 80% and optimum water content and cured for 7 d, 28 d and 90 d. Microstructure characteristics of cement-nanosilica-sand mixtures after 90 d of curing have been explored using atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. Effects of curing time on microstructure properties of cemented sandy soil samples with 0% and 8% nanosilica have been investigated using SEM test. Unconfined compression test (for all curing times) and compaction test were also performed. The SEM and AFM tests results showed that nanosilica contributes to enhancement of cemented sandy soil through yielding denser, more uniform structure. The XRD test demonstrated that the inclusion of nanosilica in the cemented soil increases the intensity of the calcium silicate hydrate (CSH) peak and decreases the intensity of the calcium hydroxide (CH) peak. The results showed that adding optimum percentages of nanosilica to cement-stabilized sandy soil enhances its mechanical and microstructure properties.

Water reducing agent effects on the engineering performance of cement stabilized aggregates

Water reducing agents (WRAs) are usually utilized in cement concretes to reduce the water-cement ration, increasing mechanical strength and improving the durability of concrete structures. As a kind of widely used construction materials in pavement structures, i.e., base or subbase course, cement stabilized aggregates (CSAs) have to face their own problems, e.g., drying shrinkage at early ages. To evaluate the feasibility of water reducing agent in cement stabilized aggregates, and its effects on engineering performance, six groups of cement stabilized aggregates were prepared (water reducing content = 0, 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%). Engineering performances including density-water relationships, unconfined compressive strength (UCS), tensile splitting strength (TSS), compressive resilience modulus (CRM) and drying shrinkage strain(DSS) were measured. Result indicates that water reducing agents used in this study can significantly benefit the engineering performances of cement stabilized aggregates. The function or role of water reducing agent in cement stabilized aggregates were summarized, which would be beneficial to guide the water reducing agent utilization in cement stabilized aggregates.

The lack of true cohesion in hydrate-bearing sands

The mechanical behavior of hydrate-bearing sands is affected by the hydrate quantity, hydrate morphology in the pores, soil skeleton characteristics, stress confinement and more. It has been traditionally assumed that bonding exists between hydrate and sand particles, which affects the global sediment strength. However, this paper shows, extending previous work, that the mechanical effect of hydrate in the sediment has kinematic rather than cohesive nature, based on comparison of mechanical and visual evidences with cemented sand. The visual analysis includes comparison between micro-scale X-ray images of sand containing either hydrate or cement agent. The mechanical analysis includes examining drained triaxial test results of hydrate-bearing sands with cemented sand results, using investigation through stress-dilatancy theories. The paper concludes that all mentioned hydrate-related effects should be interpreted by their influence on the sediment kinematics, rather than on strength characteristics. For a given kinematic response of hydrate-bearing sand, it is shown that the full mechanical behavior can be described using a single friction parameter.

Effect of Type of Cement and Expansive Agent on the Hardening of Steam-Cured Concrete

Pre-cast concrete products are sometimes manufactured in two cycles daily. It is ensured that they have the required strength at an early stage of demolding by increasing the steam curing temperature to reduce cost or increase productivity. However, the reduction in durability because of cracking due to thermal stress is a topic of concern. On the other hand, it has been known that fine blast-furnace-slag powder and expansive agents show high temperature dependence. Although they are used even in precast concrete products, the effect of steam curing on these materials is not known. Thus, in this study, the expression of compressive strength and expansion that are critical in improving the quality and productivity of precast concrete products was investigated, using high early-strength cement and two types of expansive agents, namely, ettringite-based and lime-based agents. Consequently, the strength expression was accelerated by the addition of expansive agent to ordinary cement and high early-strength cement. The extent of restrained expansion is greater for the lime-based expansive agent than for the ettringite-based expansive agent, and when an expansive agent is added to high early-strength cement, the extent of restrained expansion falls to a level lower than that in the case of ordinary cement.

Characterization of the Microbial Induced Carbonate Precipitation Technique as a Biological Cementing Agent for Sand Deposits

Characterization of the Microbial Induced Carbonate Precipitation Technique as a Biological Cementing Agent for Sand Deposits

Cement mortar reinforced with reclaimed carbon fibres, CFRP waste or prepreg carbon waste

This experimental investigation deals with the effects of reclaimed carbon fibres (RCF), carbon fibre reinforced polymer (CFRP) waste, and prepreg carbon waste (PW) of different contents on the mechanical properties of Portland cement mortar. The mechanical properties of reinforced cement mortars were measured by bending, compression and fracture toughness tests. Moreover, the shrinkage behaviour was observed by restrained drying shrinkage test. The influences of dispersing agent and additives for cement, including mineral and chemical admixtures, were evaluated for a total of 18 different combinations.

Designing gravel pack for uranium ISL wells

The paper describes the improvement of gravel packing technique applied for the production wells. The authors have suggested new design of gravel pack for gravel packing of productive formations. The issue is currently topical because gravel packing at drillhole ISL is less time- and money-consuming. The subject of the research is gravel pack design and content. The purpose defined by the authors is to design the gravel pack and to suggest the composition of gravel cement agent. As a result of the research, the authors have described different designs of the gravel pack, its optimal shape, as well as a choice and justification of cement agents, a hold cover of the gravel pack, and suggested the methods of experimental research.

Influences of bacteria-based self-healing agents on cementitious materials hydration kinetics and compressive strength

Bacterially induced calcium carbonate precipitation has been proposed as an alternative and environmental technique to develop self-healing cementitious materials system in recent years. This study investigated the influences of bacteria-based self-healing agents on the rheology, hydration kinetics and compressive strength of cementitious materials to further verify the feasibility of bacteria-based self-healing agents for crack repairing. The results showed that the rheology of cement mortar was significantly improved by the addition of bacteria-based self-healing agents. Incorporation of bacteria-based self-healing agents in cement greatly influenced the hydration kinetics. The self-healing agent RB could delay the hydration of cement resulting in final setting time increase, however the self-healing agents JB and NB accelerated the hydration resulting in initial and final setting time decrease. In addition, compressive strength test results showed that incorporation of RB in cement mortar resulted in early age compressive strength decrease, but the 28d compressive strength increased compared to control. Incorporation of JB in cement mortar enhanced compressive strength, however incorporation of NB in cement mortar could result in unwanted compressive strength loss. Furthermore, MIP test results indicated that the pore size distributions were different between cement paste samples with and without bacteria-based self-healing agents. The addition of bacteria-based self-healing agents increased the porosity between 100 and 1000nm. The porosity between 100 and 1000nm of the sample with NB increased the most compared to the samples with RB and JB. The incorporation of JB increased the porosity between 100 and 1000nm, but at the same time the small pores with a diameter under 10nm increased. These results could be used to explain the compressive strength development.

Effect of different stress path regimes on borehole instability in poorly cemented granular formations

Boreholes are drilled for different purposes such as discovering potential new deposits of underground minerals, extraction of petroleum, underground strata investigation, etc. Although no specific significant problems have been reported on drilling through hard rocks and strong formations, considerable problems have been observed in areas consisting of a sandy formation where particles are not strongly cemented by natural cement agents such as clay, iron oxide or calcite. In this study, a series of the thick-walled hollow cylinder (TWHC) laboratory tests was conducted on synthetic poorly cemented sand specimens in which the applied stresses were at levels of generating breakout on the borehole wall. Five different stress paths were designed and applied to the specimens to investigate the effect of stress paths on the borehole failure. Two borehole diameter sizes (10mm and 20mm) and three different cement contents (6%, 7% and 8%) were considered to evaluate the effect of the borehole size and grain bonding strength on the borehole failure in poorly cemented sandy formations. The results showed that in these weak formations the confining pressure has a more significant effect on the instability of the borehole than the cement agent content. It was found that for any stress path the effect of the supporting stress on ε1 was more significant for 10mm borehole sizes. In addition, based on the applied stress paths a new failure quadrilateral was determined for poorly cemented sands. Results showed that with increasing the cement content, similar quadrilaterals with almost parallel sides will be established. These outcomes can contribute to improving the design of the supporting systems and can be utilised to predict the borehole instability prior to drilling.

Delivery of Antifungal Agents from Bone Cement

Fungal osteoarticular infections, including prosthetic joint infections and osteomyelitis, are rare yet present a therapeutic challenge with no guidelines to direct optimal treatment. When these infections occur, the majority are due to Candida species. In addition to systemic therapy, adjunctive antifungal-loaded bone cement has been utilized to successfully treat these infections. Amphotericin B is used most commonly, but cases utilizing voriconazole, fluconazole, and itraconazole have been reported as well. In vitro data suggest better elution of voriconazole from bone cement while there is minimal elution of amphotericin B. Unfortunately, a lack of consistency in the methods of both in vitro studies and case reports makes it difficult to determine if the addition of an antifungal agent in bone cement improves outcomes in fungal osteoarticular infections. This article provides an overview of bone cement as a delivery system for antifungal agents in vitro and in clinical reports.

Factors Affecting the Mechanical Properties of Cement-Mixed Gravel

A study has been conducted to investigate the mechanical properties of cement-mixed gravel using the unconfined compression test and the tensile test. Basic factors including the curing period, the water-binder ratio, the cement content, and the strain rate were evaluated. Ordinary Portland cement with fly ash was employed as the cementation agent for preparing cemented samples. The results indicate that the unconfined compressive strength, the deformation modulus, and the tensile strength increase with the increase in the curing period. The ratio of tensile strength to unconfined compressive strength has no distinct change after 7 days. An optimum water-binder ratio can be obtained. The unconfined compressive strength and deformation modulus decrease as the water-binder ratio decreases and increase from the optimum water-binder ratio. With the increasing of the cement content, the unconfined compressive strength increases distinctly, the deformation modulus increases significantly when the cement content is less than 4% and then increased slowly, and the failure strain increases to a peak value and then decreases. With the increasing of the strain rate, the unconfined compressive strength increases slightly and the deformation modulus increases slowly. The failure strain decreases with an increase in the strain rate.

Experimental Comparison of Air Pore Content of Concrete with Different Dosage of Cement by Microscopic Analysis

The pore structure of concrete is a very important material property influencing the durability of concrete. Concrete pore structure is influenced, among others, by the composition of concrete, water/cement ratio, aeration or cracking [1]. The experiment described in this paper understands concrete cover to be 40 – 60 mm from the surface of the specimen.The paper focuses on the determination of air void content in different concrete mixtures by means of microscopic analysis. Mixtures differ in the amount of cement and plastifying agent added while maintaining the consistency of the fresh concrete. In order to determine the air void characteristics, the experiment used manual and automated microscopic analysis.

Shear stiffness modeling of cemented clay

The shear modulus and damping of cemented clay are investigated using ultrasound transducers, bender elements, and a resonant column device. The model SimSoil-CC, based on the Pestana and Salvati (published in 2006) model SimSoil, is proposed to represent the maximum shear modulus and stress–strain behavior (under cyclic loading conditions) at small strains for the cemented clay. The model can also be used for uncemented clay when the cementation parameter is set to zero. Model parameters are determined for three types of clay (kaolinite, bentonite, and the equal mix of kaolinite and bentonite) and two types of cementation agents (type III Portland cement and gypsum). The model SimSoil-CC is validated using the laboratory test data of this study and data from other studies in literature. The SimSoil-CC model can be very useful for performing earthquake site response analysis for naturally cemented clay sites or sites that have been improved by cementation. In addition, a relationship between the cementation parameter acc(CC)2(acc, cement material constant; CC, dry cement content) and the unconfined compression strength is proposed. The relationship simplified modeling for naturally cemented clay soil or cemented clay whose cement contents and cementation type are otherwise difficult to determine. This research advances the understanding of cemented clay by providing a database of test results and creation of a model that can be used to predict the response of cemented clay soils to dynamic loads.

Effective solidification/stabilisation of mercury-contaminated wastes using zeolites and chemically bonded phosphate ceramics.

In this study, two kinds of zeolites materials (natural zeolite and thiol-functionalised zeolite) were added to the chemically bonded phosphate ceramic processes to treat mercury-contaminated wastes. Strong promotion effects of zeolites (natural zeolite and thiol-functionalised zeolite) on the stability of mercury in the wastes were obtained and these technologies showed promising advantages toward the traditional Portland cement process, i.e. using Portland cement as a solidification agent and natural or thiol-functionalised zeolite as a stabilisation agent. Not only is a high stabilisation efficiency (lowered the Toxicity Characteristic Leaching Procedure Hg by above 10%) obtained, but also a lower dosage of solidification (for thiol-functionalised zeolite as stabilisation agent, 0.5 g g(-1) and 0.7 g g(-1) for chemically bonded phosphate ceramic and Portland cement, respectively) and stabilisation agents (for natural zeolite as stabilisation agent, 0.35 g g(-1) and 0.4 g g(-1) for chemically bonded phosphate ceramic and Portland cement, respectively) were used compared with the Portland cement process. Treated by thiol-functionalised zeolite and chemically bonded phosphate ceramic under optimum parameters, the waste containing 1500 mg Hg kg(-1) passed the Toxicity Characteristic Leaching Procedure test. Moreover, stabilisation/solidification technology using natural zeolite and chemically bonded phosphate ceramic also passed the Toxicity Characteristic Leaching Procedure test (the mercury waste containing 625 mg Hg kg(-1)). Moreover, the presence of chloride and phosphate did not have a negative effect on the chemically bonded phosphate ceramic/thiol-functionalised zeolite treatment process; thus, showing potential for future application in treatment of 'difficult-to-manage' mercury-contaminated wastes or landfill disposal with high phosphate and chloride content.

A soft matter in construction – Statistical physics approach to formation and mechanics of C–S–H gels in cement

Calcium-silicate hydrate (C–S–H) is the main binding agent in cement and concrete. It forms at the beginning of cement hydration, it progressively densifies as cement hardens and is ultimately responsible of concrete performances. This hydration product is a cohesive nano-scale gel, whose structure and mechanics are still poorly understood, in spite of its practical importance. Here we review some of the open questions for this fascinating material and a statistical physics approach recently developed, which allows us to investigate the gel formation under the out-of-equilibrium conditions typical of cement hydration and the role of the nano-scale structure in C–S–H mechanics upon hardening. Our approach unveils how some distinctive features of the kinetics of cement hydration can be related to changes in the morphology of the gels and elucidates the role of nano-scale mechanical heterogeneities in the hardened C–S–H.

The effect of magnesium and zinc on indium cementation kinetics and deposit morphology in the presence of and without nonylphenylpolyethylene glycol

Indium cementation on magnesium and zinc at 60 °C and pH 1.2 in the presence and absence of nonylphenylpolyethylene glycol (D1) is investigated. Indium cementation follows first-order kinetics in all experiments. The cementation agent affects indium cementation rate, a side reaction of hydrogen evolution and the morphology of the obtained deposit. Both highest cementation rate and most intensive hydrogen evolution accompanied with the highest dissolution of the cementation agent are found during indium cementation on magnesium. Surfactant D1 substantially inhibits all these processes. The rate of indium cementation on zinc in the presence and absence of D1 is 1.5 or 1.8 times lower compared with that on magnesium. The variation of the fraction of deposited indium with time was examined according to the shrinking core model. A combination of ash diffusion model and chemical reaction model controls indium cementation on magnesium, while the chemical reaction model dominates during indium cementation by zinc. Indium deposit morphology depends strongly on the cementation agent. A thick layer of indium (with large or small cracks as well as with formations of bubbles and flakes) is observed on the magnesium surface. A compact smooth deposit of fine crystallites is found on zinc. The presence of D1 causes deposition of more compact and refined deposits on both cementation agents. The obtained results show two alternatives: using zinc-magnesium alloy and temperature higher than 60 °C to increase indium cementation rate on zinc or using low temperature and magnesium as a cementation agent of indium in the presence of surfactant D1. • The cementation agent affects indium cementation rate, a side reaction of hydrogen evolution and deposit morphology. • The highest cementation rate and dissolution of the cementation agent are found during indium deposition on magnesium. Surfactant D1 substantially inhibits these processes. • The indium cementation rate on zinc in the presence of and without D1 is 1.5 or 1.8 times lower compared with that on magnesium.

Evaluation of Compressive Strength and Stiffness of Grouted Soils by Using Elastic Waves

Cement grouted soils, which consist of particulate soil media and cementation agents, have been widely used for the improvement of the strength and stiffness of weak ground and for the prevention of the leakage of ground water. The strength, elastic modulus, and Poisson's ratio of grouted soils have been determined by classical destructive methods. However, the performance of grouted soils depends on several parameters such as the distribution of particle size of the particulate soil media, grouting pressure, curing time, curing method, and ground water flow. In this study, elastic wave velocities are used to estimate the strength and elastic modulus, which are generally obtained by classical strength tests. Nondestructive tests by using elastic waves at small strain are conducted before and during classical strength tests at large strain. The test results are compared to identify correlations between the elastic wave velocity measured at small strain and strength and stiffness measured at large strain. The test results show that the strength and stiffness have exponential relationship with elastic wave velocities. This study demonstrates that nondestructive methods by using elastic waves may significantly improve the strength and stiffness evaluation processes of grouted soils.

Mechanical Properties and Microstructure Analysis of Copper Tailings Solidifying with Different Cementitious Materials

With new type steel slag-blast furnace slag-fluorgypsum-based cemented material, P O42.5 cement, commonly used cementation agent in China, mechanical properties and microstructure of tailings solidification bodies are studied. The hydration products and morphology tailings concretion body in 60 days are analyzed by SEM and XRD test, which reveals the tailings cementation mechanism solidifying with different cementitious material. Furthermore, a large number of slender bar-like ettringite crystals and filamentous network-like calcium-silicate-hydrate gels bond firmly each other, which is the most important reason why steel slag-blast furnace slag-fluorgypsum base cemented material has the best tailings cementation mechanical properties.

A method proposed for the assessment of failure envelopes of cemented sandy soils

This study aims at quantifying the influence of the amount of cement (C), the porosity (η) and the porosity/cement ratio (η/Civ) in the assessment of the Mohr–Coulomb failure envelope of artificially cemented sands centered on splitting tensile strength (σt) and unconfined compressive strength (σc). Based on the concept previously established by Consoli et al. that the σt/σu relationship is unique for each specific sandy soil and cement agent, it is shown that the effective angle of shearing resistance of a given cemented sandy soil (Ø′) is independent of the porosity and the amount of cement of the specimen and that effective cohesion intercept (c′) is a direct function of the unconfined compressive strength (σc) [or splitting tensile strength (σt)] of the improved granular material, which depends on the porosity/cement ratio (η/Civ) of the soil–cement blends. These concepts are tested with success for a uniform fine sand treated with early strength Portland cement and a silty sand treated with ordinary Portland cement, considering weak, moderate and strong cementation levels, as well as for a volcaniclastic formation deposit composed of moderately cemented fine sand and silt-size particles (naturally cemented soil). The methodology developed herein allows estimating c′ and Ø′ for any specific condition comprised inside the range of porosity and amount of cement employed during basic testing, without the necessity of carrying out triaxial testing or any other complex and time consuming tests.

Reactive transport modelling of organic complexing agents in cement stabilized low and intermediate level waste

The Swedish final repository for short-lived radioactive waste (SFR 1) is located at Forsmark in Sweden. It holds low and intermediate-level operational waste from the Swedish nuclear power plants, as well as industrial, research-related, and medical waste. A variety of low molecular weight organic compounds are present in the waste or in its matrix. Such compounds can also be formed by chemical degradation of organic macromolecules. These organics can ligate to metal atoms forming stable complexes and also adsorb to the surface of cement, thereby influencing the net release of radionuclides from the repository. This motivates the study of the concentration distribution of complexing agents in the repository as a function of time. The following paper reports the results of mass transport modelling, describing the transport of complexing agents through the cementitous matrix in the rock vault for intermediate-level waste in the SFR 1 repository. Nitrilotriacetate (NTA) and isosaccharinate (ISA) have been investigated, where the former is considered to be non-sorbing and non-reacting, while the latter is produced from cellulose degradation and adsorbs strongly to cement. The 3D model considers advection, diffusion, and sorption of solvated species in cement pore water over a time period of 20,000years. The model accounts for the spatial distribution of the flow field in the repository structure and also considers changing groundwater flow during the investigated time period. It is found that 99% of the NTA is removed after approximately 4000years, while 90% of the ISA is retained in the rock vault after 20,000years. The maximum pore water concentration of ISA is found to be 8.6mol/m3 after approximately 2300years, based on the degradation of the deposited amounts of cellulose. Over the investigated time scale, the ligands retained in the repository can redistribute across several waste compartments where the organic compounds were not originally deposited. In the case of ISA this effect is dampened due the influence of sorption.