Chemical Composition Of Cement Research Articles

Development of cement slurries with additives of nanoclay particles for the construction of oil wells at elevated temperatures

Relevance. Strength decrease is a phenomenon that becomes more pronounced as the temperature rises above 110°C. It is characterized by significant chemical and microstructural changes that Portland cement undergoes at high temperatures. Adding silica particles (SiO2) to cement can significantly increase cement resistance to strength reduction when the temperature exceeds 110°C. Nanoclays are currently used in the cement industry to increase the strength of the cement matrix due to their ability to fill capillary micropores and due to their relatively small particle size. Aim. To investigate the effect of adding nanoparticles (nanoclay) to Saudi grade G cement on compressive and tensile strength, and cement stone permeability under high temperature conditions (300°С). Objects. Six samples of cement mortars with different concentrations of nanoclay, cement stones from, tested after 7 and 28 days of hardening at 25 and 300°C. Methods. Cement chemical composition was evaluated by the X-ray fluorescence method with the WORKSTN-V Olympus Vanta X-ray fluorescence analyzer. Cement physical composition was evaluated by the method of ray diffraction on the Mastersizer 2000 laser particle size analyzer. The test of the grouting stone samples was carried out in accordance with ISO 10426-2:2003 on a hydraulic press 65-L1132. The tensile strength of the samples by the Brazilian method was tested in accordance with ASTM D 3967-08 standard on a hydraulic press 65-L1132. The permeability of the samples was determined by single-phase stationary filtration at a facility for studying the filtration and capacitance properties of the PIK-OFP-UCH core in accordance with ISO 10426-2:2003. Results. The data obtained showed that cement destruction at extremely high temperatures can be avoided by using nanoclay (up to 3% by weight of cement). The microstructure of the cement matrix was significantly affected due to the aggregation of nanoparticles when more than 3% of nanoclay was added. All rheological characteristics of the cement slurry were improved by the addition of nanoclay particles.

From risk study to field evidence: an unprecedented and isolated case of delayed ettringite formation in Brazil

This paper describes the first ever reported case in Brazil where delayed ettringite formation (DEF) has been confirmed as the sole cause of deterioration in field concrete. Still under construction and less than 2 years old, numerous cracks were observed in the foundation structures of a building located in Recife, a city known for its history of alkali–aggregate reaction (AAR) cases. In addition to a field survey of cracks, microstructural analyses, tests for residual expansion and compressive strength, a review of the structural design, determination of sulfate content in the groundwater and simplified thermal analysis were carried out. The results confirmed that DEF was the sole cause of the damage present in cast-in-place concrete structures, with no evidence of AAR or any other deterioration process. This work corroborates previously published studies on the high risk of the occurrence of DEF in the region, demonstrating the urgent need for a preventive technical standard in the country, considering the chemical composition of cements and prior thermal analyses to adopt possible preventive measures to limit the maximum internal temperature of concrete.

Study Regarding the Micro Filler Effect of Sludge Resulting from Steel Pickling

The management of waste, resulting in high amounts from different production processes, often raises special problems. This is also the case for sludge, generated in increasing amounts from the chemical pickling of steel pipes. This article presents the results of laboratory experiments regarding the micro filler effect of sludge generated by chemical pickling of steel pipes and analyzes its capacity to be a pozzolanic material. The study involved the performance of mechanical tests (specific surface of the powder; compressive mechanical strengths) and chemical tests (determination of the general chemical composition of cement and sludge using the X-ray fluorescence (XRF) method; determination of oxides in the chemical composition of sludge by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES); X-ray diffraction (XRD) analysis of the sludge and cement used). This topic was addressed because recycling of sludge, by using it for the manufacture of new building materials, takes advantage of the waste resulting from the pickling of steel pipes that-until now-has generated large volumes without a specific use.

A stoichiometric approach to find optimum amount of fly ash needed in cement concrete

This study aimed to find the optimum amount of fly ash that can be replaced with cement using a stoichiometric approach. For this purpose, the balanced chemical reactions between cement, water and fly ash were studied. This new proposed methodology uses information like chemical composition of cement, elemental composition and crystallinity in fly ash sample, and can easily find the optimum amount of fly ash that can replace cement. Considering the chemical composition analysis and percentage crystallinity in fly ash sample, the quantity of fly ash that can replace cement came out to be 30%. To assess the performance of control group and partially replaced cement (PRC) samples, specimens were casted and different tests like compressive strength, split-tensile strength, density and sorption were conducted. The experimental results showed that PRC samples gained almost 95% compressive strength as that of control group at 90 days. The resistance to water intrusion as measured with sorption test showed that PRC samples had almost 50% less depth as compared to control group. The improvement in mechanical and durability properties of PRC samples supports the outcome of studied chemical reactions. The fly ash consumed the cement hydration product i.e. calcium hydroxide for producing binder gel; which enhanced the strength, lowered permeability and made the concrete denser. The development of compressive strength and density with time shows good agreement with an R2 value of 0.96.

A study on the effect of the salt content on the solidification of sulfate saline soil solidified with an alkali-activated geopolymer

The salt content has a significant effect on the hydration reactions of alkali-activated geopolymers, thereby influencing the curing effect. The main objective of this paper is to study the changes that occur in the mechanical properties of sulfate saline soil solidified with an alkali-activated geopolymer due to varying the sulfate salt content. Sodium silicate, lime-fly ash, and the combination of lime-fly ash and sodium silicate were selected to solidify sulfate saline soils with different salt contents. An unconfined compressive strength test was conducted to study the variation in the compressive strength of the solidified soil at different salt contents. Moreover, the consistency characteristics, phase characteristics, chemical composition and microstructure of the solidified soil were evaluated. The results showed that as the salt content increased, the unconfined compressive strength of the three curing agents first increased and then decreased. Additionally, the peak strength occurred at a salt content of approximately 1.8%. Analyses of the phase characteristics, chemical composition and microstructure of the solidified soil indicated that the influence of the salt content on curing is reflected by changes in the cement chemical composition and the pore structure.

Influence of Cement Chemistry on the Performance of Cement Stabilized Tropical Lateritic Soil

Chemical composition affects overall performance of cement on other materials such as when used in concrete or for stabilization of lateritic soil. This research studied the influence of chemical composition of three Portland cement types represented as samples A, B and C on engineering performance when mixed with laterite under tropical environmental conditions.The Lateritic soil sample classified according to AASHTO as A-5(4) was collected from a typical tropical region. Performances of these cements were considered at different cement-laterite proportions, varying from 2-14%. Parameters determined include chemical and metallic contents of the cements as well as Maximum Dry Density (MDD), California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) of cement-laterite mixat a temperature range of 26-28°C. One-way Anova test was used to validate the significant variation in the chemical composition of cements and the unconfined compressive strength. Results indicate that the bearing capacity and unconfined compressive strength of laterite – cement mix depend on the quantity of lime (CaO) and silicon dioxide (SiO2) content in the cement; results also confirm the influence of Aluminium Oxide (Al2O3) and sulphur trioxide (SO3) content on the setting time of cement.

Incorporating reaction-rate dependence in reaction-front models of wellbore-cement/carbonated-brine systems

Contact between wellbore cement and carbonated brine produces reaction zones that alter the cement's chemical composition and its mechanical properties. The reaction zones have profound implications on the ability of wellbore cement to serve as a seal to prevent the flow of carbonated brine. Under certain circumstances, the reactions may cause resealing of leakage pathways within the cement or at cement-interfaces; either due to fracture closure in response to mechanical weakening or due to the precipitation of calcium carbonate within the fracture.In prior work, we showed how mechanical sealing can be simulated using a diffusion-controlled reaction-front model that links the growth of the cement reaction zones to the mechanical response of the fracture. Here, we describe how such models may be extended to account for the effects of the calcite reaction-rate. We discuss how the relative rates of reaction and diffusion within the cement affect the precipitation of calcium carbonate within narrow leakage pathways, and how such behavior relates to the formation of characteristic reaction modes in the direction of flow. In addition, we compare the relative impact of precipitation and mechanical deformation on fracture sealing for a range of flow conditions and fracture apertures. We conclude by considering how the prior leaching of calcium from cement may influence the sealing behavior of fractures, and the implication of prior leaching on the ability of laboratory tests to predict long-term sealing.

Models for Prediction of 28-Day Concrete Compressive Strength

Abstract The design codes usually specify 28-day concrete compressive strength as design strength for reinforced concrete (RC) structures. Concrete specimens are cast and tested at 28 days to ensure compliance of concrete strength with the design requirements. Prediction of concrete strength can help in reducing waiting time and can result in speeding up construction activities. This paper presents prediction models for concrete compressive strength up to 28 days. The data of experimentally tested concrete cylinders were employed in the development of these models. The effects of cement chemical composition and fineness were included by defining two parameters in the models. The predictions are based on 7-day concrete strength. The proposed models provided good correlation with the observed concrete strength data. The models were also validated using the strength results of concrete mixes in the available literature. Generalized forms of the models have been suggested for cement brands available in Pakistan.

Soil Pollution by the Cement Industry in the Bazian Vicinity, Kurdistan Region

The three most significant things in our life are air, water, and soil which are essential for life and any imbalance of these three cause a big problem in nature. Soil is one of the most common agents in life and supplies us with all the basic necessities. Portland cement is one of the common types of cement which is used in construction nowadays. But soil can be polluted by cement plants, where cement industries are established. The chemical composition of cement is a mixture of calcium aluminum silicate also, a trace amount of Cd, Pb, Fe, Ti and silica. According to several chemical analyses the area surrounding industries show that the further the area is from the factory, the better as soil pollution decreases. In this research paper, we checked the physiochemical pH, electrical conductivity, nitrate ions, sulphate ions, Lead ions and calcium ions content in soil in the Bazian area. The area is far from the surrounding industries and this shows that the further the area is from the factory, the better as soil pollution decreases. There is positive correlation between the calcium ions and electrical conductivity. There is negative correlation between pH and concentration of lead ions. There is also weak correlation between sulphate and nitrate ions concentrations in soil samples.

Probabilistic Design for Concrete Durability in Marine Environment

A probabilistic method to durability is proposed for the design of reinforced cover of a concrete immersed in marine environment. It uses a non-linear chloride diffusion model for a saturated medium. Parameter variability is estimated and used by the probabilistic method to assess the probability of reaching a critical chloride concentration near the reinforcement for a given service life. Based on the concrete formulation and the cement chemical composition, the model parameters are evaluated with their associated random distribution.

Slagment Cement Improve the Cement Resistance Toward Acids Attack During Acidizing Treatment

Acidizing treatment in past experience shows several zonal isolation problems after the treatment. This study presents the effect of the acid treatment toward class G cement and slagment cement as the improvement method to improve the cement resistance toward the acid. Lab experiments were conducted by immerge the respective cement cubes into 12% HCl/3% HF solution for 40 min before several analysis were conducted. Based on the result, the mass loss and compressive strength loss of the cement cubes decrease as the curing temperature and pressure increase due to more evenly distributed cement chemical composition crystal in high curing condition as shown in Scanning Electron Microscopy (SEM) analysis. From X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) analysis, only the first layer of the cement cubes shows chemical component change due to the reaction between the acid. This study found that, replacing class G cement to slagment cement can reduce the mass loss and compressive strength loss up to 72% and 82%, respectively.

Influence of various parameters on heat-induced internal sulphate attack

The work presented in this article studies the effects of some parameters that can be considered, a priori, as important in the appearance of delayed ettringite formation (DEF). The parameters studied are the nature of the binder, the water/cement (W/C) ratio, the preliminary microcracking (wetting–drying cycles) and the curing conditions. The results presented show that the chemical composition of cement is one of the main parameters controlling the appearance of DEF. The other parameters studied, (W/C ratio, wetting–drying cycles and temperature of curing water) principally modify the kinetics of the expansion: it seems that, the more favourable the conditions are to ionic and hydrous transfers, the sooner the expansion starts. Finally, the renewal of the curing water strongly affects the start of DEF. In one case of the study, the renewal of the curing water only accelerated the start of the expansion. In the second, it led to late starting of DEF (four years) whereas the same mixture cured continuously in water that was not renewed still had not expanded after more than five years. L’étude présentée dans cet article a pour objectif d’observer les effets de certains paramètres que l’on peut qualifier a priori d’importants vis-à-vis de l’apparition de la DEF. Les paramètres étudiés sont la nature du liant, le rapport E/C des mélanges, le préendommagement des éprouvettes (cycles d’humidification-séchage) et, enfin, les conditions de conservation des échantillons. Les résultats présentés montrent que la composition chimique du ciment est l’un des principaux paramètres contrôlant l’apparition de la DEF. Les autres paramètres étudiés (rapport E/C, cycles d’humidification-séchage et la température de l’eau de conservation des échantillons), modifient principalement la cinétique de l’expansion: il semble que plus les conditions sont favorables pour améliorer les transferts ioniques et hydriques, plus l’apparition des expansions est accélérée. Enfin, le renouvellement de l’eau de conservation affecte fortement le début de l’apparition de la DEF. Dans un cas d’étude, il n’a fait qu’accélérer le début de l’expansion. Dans un second cas, le renouvellement de l’eau de conservation a permis le déclenchement de la DEF au bout de 4 ans, alors que le même mélange conservé en permanence dans l’eau qui n’a pas été renouvelé n’avait pas encore montré de gonflement après plus de 5 ans.

Robust Statistics Analysis of Proficiency Test Result of Cement Chemical Composition

Test result of cement chemical composition was obtained from the participating laboratory through organizing and performing the cement proficiency test plan. After performing the robust statistical analysis to the result, the test proficiency of the laboratory is evaluated, the proficiency of each laboratory on chemical composition analysis and test is objectively reflected.

Relating Compressive Strength to Heat Release in Mortars

Conventionally, isothermal calorimetry and ASTM C186 heat of hydration results are reported on the basis of heat per mass of cement (powder), with typical units being Joules per gram (of cement), for example. Given that it is the filling of porosity with hydration products that is chiefly responsible for strength development in cement-based materials, there might be merit in instead reporting these results in terms of the unit volume of (initial) water. This paper examines a database of well over 200 mortar mixtures to investigate the relationship between heat release and mortar cube compressive strength development. For reasonably low water-to-cementitious-materials ratios (w/cm) (w/cm < 0.43), a single universal straight line relationship with some scatter is obtained. Based on numerous experimental data sets and the accompanying theoretical computations, the effects of the w/cm, sand volume fraction, cement chemical composition, sulfate content, cement fineness, incorporation of a high range water reducing admixture, and curing conditions on this universal relationship are all considered. Fifty data points from the Cement and Concrete Reference Laboratory proficiency sample program were analyzed in order to develop a linear relationship between ASTM C109 mortar cube compressive strengths and ASTM C186 heats of hydration at 7 d and 28 d. The application of this relationship for virtual testing is also evaluated. In this case, computer simulations would be employed to predict the heat of hydration versus time for a particular cement, and the developed equations would be employed to convert this heat release to a strength prediction at the age(s) of interest. In general, it appears that these relationships can be used to predict mortar cube compressive strengths based on measured heats of hydration, within about ±10 % of the experimentally measured strengths. A preliminary analysis of a single dataset for concretes with and without limestone replacement for cement indicates that the linear relationship between strength and heat release likely holds for concretes as well as for mortars.

Effects of alkaline and alkaline-earth ions on the rheological behavior and zetametric study of two cement pastes (artificial cement portland-CEMI and cement resistant to the sulfates-CRS) with the polynaphthalene sulfonate (PNS)

The use of admixtures which tends to be generalized in the formulation of self-compacting concrete (SCC), requires taking into account the chemical composition of cement, particularly its content of SO3, which can inhibit or restrain the effect of these admixtures (superplasticizers). For more information of the compatibility problem of cement-superplasticizer, the rheological tests with a rheometer-AR2000 and measurements of zeta potential with a Zetasiser-2000 were used in this study. In order to understand this phenomenon due to the presence of SO3 in cement, we propose to evaluate the action of alkaline and alkaline-earth ions, incorporating different types of additions (K+, Na+, and Ca2+) to the cement pastes. To achieve this, our work will concern the study of rheological properties and physical characteristics of the pastes obtained using two types of cement (C1: Cement Resistant to the Sulfates (CRS) and C2: CEMI). This experiment will focus on two reports: Water/Cement (W/C) = 0.30 for which the polynaphthalene sulfonate (PNS) is used as superplasticizer and W/C = 0.50 (without superplasticizer). The results show that the presence of sulfate leads to different rheological behaviors which are function of sulfates and the cements used. Key words: Cement, rheology, superplasticizer, yield stress, plastic viscosity, self-compacting concrete, sulfates.

ESTIMATION THE 7 AND 28- DAY NORMAL COMPRESSIVE STRENGTH BY ACCELERATED TEST METHODS IN CONCRETE

Curing of concrete is the maintenance of a satisfactory moisture content and temperature for aperiod of time immediately following placing so the desired properties are developed. Acceleratedcuring is advantages where early strength gain in concrete is important. The expose of concretespecimens to the accelerated curing conditions which permit the specimens to develop a significantportion of their ultimate strength within a period of time (1-2 days), depends on the method of thecuring cycle.Three accelerated curing test methods are adopted in this study. These are warm water,autogenous and proposed test methods. The results of this study has shown good correlationbetween the accelerated strength especially for the proposal curing test method and normal strengthusing normal curing method at ages 7 and 28 day for the five different chemical composition ofcement with different water to cement ratios equal to 0.45, 0.55, 0.65 and 0.75. Linear andnonlinear regression analysis show high correlation for the different types of the accelerated curingmethods with coefficient of correlation (R2) more than 0.9.

Prediction of Thermal Decomposition of Hardened Cement Paste

When exposed to elevated temperatures, various constituents in hardened cement paste will undergo decomposition, resulting in thermal damage of concrete. To better understand the thermal damage mechanism, it is essential to investigate the whole decomposition process of hardened cement paste. Based on the kinetic and stoichiometric analysis, a numerical method is presented in this paper for predicting the thermal decomposition of hardened cement paste. In this method, the initial volume fractions of various constituents in hardened cement paste are expressed as a function of the water-to-cement ratio, degree of hydration, and the chemical composition of cement. By analyzing the kinetics of decomposition, the volume fraction evolution of each constituent is then formulated in terms of the heating rate and temperature. When silica fume is added, the pozzolanic reaction is also considered. Finally, the validity of the proposed numerical method is verified with three sets of experimental data collected from the literature. The effect of the heating rate on the thermal decomposition of hardened cement paste is evaluated in a quantitative manner.

Cement Hydration Kinetics Research Based on the Multi-Phase Hydration Model

Based on the multi-phase hydration dynamic model, taking into account the factors such as chemical composition of cement, curing temperature, water-cement ratio, the final hydration degree and fineness of cement, a theoretical hydration kinetics equation is established in this paper. It can be used to predict the hydration rate increases with the change of hydration degree. The results showed that: water-cement ratio will accelerate the phase boundary reaction, while not influence the early crystallization of nucleation and crystal growth; temperature can accelerate the hydration process, while it can not change the ultimate hydration degree.

Dependency of C–S–H carbonation rate on CO 2 pressure to explain transition from accelerated tests to natural carbonation

The use of normalized accelerated carbonation tests is currently limited to the classification of concretes in terms of carbonation resistance and the results are not easily transposable to forecasting concrete carbonation in natural conditions. Common models assume that the kinetics of the carbonation front ingress in concrete is a square root function of the CO 2 pressure but observations in the field generally invalidate this assumption. Based on an experimental program including carbonation tests at several CO 2 pressures, this paper shows that the amount of carbonated product depends largely on the CO 2 pressure. Several experimental analyses of carbonated concrete under different pressures are confronted, to finally propose a new analytical model able to predict carbonation ingress in natural conditions using the results of accelerated tests. The model takes both the cement chemical composition and its amount in concrete into account. The carbonation kinetics dependence on CO 2 pressure is considered through two underlying functions including, for the first, the dependence of the CSH carbonation rate on the pressure and, for the second, the effect of this additional carbonation on the reduction of the CO 2 diffusion coefficient.

Probabilistic approach for durability design of reinforced concrete in marine environment

A probabilistic approach to durability is proposed for the design of reinforced cover of a concrete immersed in sea water. It uses a non-linear chloride diffusion model for a saturated medium, which is first exposed with its physical parameters. Parameter variability is estimated and used through the probabilistic approach to assess the probability of reaching a critical chloride concentration near the reinforcement for a given service life. Based on the concrete formulation and the cement chemical composition, the model parameters are evaluated with their associated random distribution. The corrosion risk is then estimated through the Hasofer–Lind reliability index. Currently, the methodology is available for Ordinary Portland Cement (OPC) and for saturated media. A practical application is proposed to underline the applicability of the methodology. The decrease in the reliability index with time is computed for a cover depth coming from actual design rules. The probabilistic sensitivity factors are also assessed and show the importance of some model parameters called “durability indicators”.