Types Of Cement Paste Research Articles

Chloride binding behavior of calcium silicate hydrates and Friedel's salt of pastes

Understanding the chloride binding capacity of cement pastes is crucial to investigating the concrete durability. To characterize the chloride binding behavior of calcium silicate hydrates (C–S–H) and Friedel's salt (Fs), this study investigates the chloride binding capacity of four types of cement paste using chloride binding isotherms, analyzes the correlation between phase composition and chloride binding capacity, and discusses the evolution law of the chloride binding capacity of Fs and C–S–H. The results indicate that the influence of mineral admixtures on the chloride binding capacity of C–S–H is basically the same as that of pastes. Slag (SL) has a significant positive effect, while silica fume (SF) generally plays a negative role, and the effect of fly ash (FA) depends on the concentration of NaCl solution. As to the influence of chloride concentration, the chloride combined by per unit mass of C–S–H and Fs presents different evolution trends, and a concentration break-even point exists between C–S–H and Fs combined chloride. Notably, this point provides the insight into which substance occupies the majority of the total bounded chloride. Moreover, the impact of chloride concentration on the chloride binding capacity of pastes cannot be solely determined by the content of C–S–H and Fs, and the chloride combined by per unit mass of C–S–H and Fs at different chloride concentrations offers more relevance.

Phase development of hydrated cement pastes with SCMs under delayed heating conditions below 100 °C

This paper focuses on studying the effect of the delayed heating of cementitious materials on the phase assemblage variations in three types of cement paste. Two heating temperatures of the order of 65 °C and 80 °C were used to thermal treat the samples. Our results show that the thermal treatment induces the modification of the phase assemblage(particularly degradation of AFt and AFm phases) as well as the polymerization of the C-(A)-S-H. The observed variations depend mainly on the initial sulfate, aluminate and carbonate content in each cement. Finally, it is shown that the thermal treatment-related phenomena such as adsorption of aluminates on C-(A)-S-H are almost completely reversible after the temperature drop and re-immersion in water for 3 months, meanwhile other phenomena such as the formation of the hydrogarnet and hydrotalcite are only partially reversible. This modifies the free elements proportion and influences the probability of the DEF occurrence.

Coupling of chemical kinetics and thermodynamics for simulations of leaching of cement paste in ammonium nitrate solution

A novel numerical method is proposed in this paper to model the leaching of various types of cement pastes in the ammonium nitrate solution by coupling chemical kinetics with chemical thermodynamics. Arrhenius equation and Eyring equation are applied to predict the rate constant of fast dissolution of portlandite in the ammonium nitrate, and a modified rate law is developed by incorporating the saturation ratio of the reaction. The estimations of leached depths from the proposed method comply with the well-known square root-time relationship and they also agree well with the reported experimental results. Moreover, the evolutions of porosity and major hydrate compositions during leaching are obtained. It is found that a simple linear relation exists for the acceleration factor of leaching in 6M of ammonium nitrate with respect to leaching in pure water regardless of the type of the cement clinker.

Monitoring hydration of UHPC and conventional paste by quantitative analysis on Raman patterns

Cement hydration governs physical, chemical and mechanical properties of cement pastes. Therefore, tracing hydration progress in different types of cement pastes can help to understand different hydration mechanisms and paste behaviours. In the present research, a quantitative analysis on Raman spectroscopy (RS) patterns for conventional cement paste and ultra-high performance concrete (UHPC) matrix at different hydration ages has been applied. It has been found that quantitative analysis on peak area of Raman patterns is fully capable to differentiate between conventional cement hydration and pozzolanic reaction in UHPC. The result also showed that silica fume included in the UHPC matrix was more reactive at early ages, which was completely in agreement with reduction of calcium hydroxide (CH) content at the same hydration period.

A new method to determine initial setting time of cement and concrete using plate test

The present study developed a new method for determination of cement and concrete setting times. The disadvantage of current methods is that most only determine setting time of either cement or concrete and cannot determine the setting time of all types of concrete and cement, especially those containing mineral admixtures. In the proposed method, a plate with a rough surface is rigidly attached to the bottom of a precision balance in a PVC cylinder and immersed in fresh mixture poured into the side of the cylinder opposite the balance. The shear force exerted on the plate increases over time and the value recorded by the balance increases moment-by-moment. The difference between the sequential weights recorded at specific intervals was maximized at the setting time moment. Three types of cement paste and three types of self-compacting concrete were evaluated using the new method. The initial setting time obtained by this method was confirmed using the results of existing test methods. The results show the feasibility and accuracy of the proposed plate test method to determine initial setting times of cement and concrete.

Erosion Phases in Two Types of Cement Pastes Containing Limestone Exposed to Sulfate Attack

Limestone filler and aggregates are used widely in cement production and concrete mixing nowadays, which could be connected with thaumasite formation, and lead to a lack of durability further. This work deals with the sulfate minerals including of thaumasite, ettringite and gypsum in two types of cement pastes containing 35% w/w limestone powder immersed in MgSO4 solution at 5°C±2°C for 15 weeks by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD). Two types of cements were used: (i) ordinary Portland cement (P·O), (ii) typeII Portland cement (P·II). Test results show that thaumasite is present in two types of cement pastes, amount of thaumasite as well as amount of portlandite reacted with external SO42- in P·II cement paste are more than those in P·O cement paste. It indicates that P·II cement is more susceptible to thaumasite formation than P·O cement containing the same amount of limestone powder, and more gypsum formation could contribute to thaumasite formation possibly during the external MgSO4 attack at low temperature.

Experimental Study of Thermal Conductivity for Different Types of Cement Paste in Iraqi Markets

In this study practical tests for thermal conductivity are done on twenty one specimens for seven types of cement mortar contains different types of cement available in local markets for Kirkuk city in the same standard conditions. Heat flow amounts within the specimens are calculated using Fourier law for conduction. Comparison between practical results and theoretical values depended in references for calculating thermal loads in concrete walls gave good agreement. Test results for specimen No. (7) for cement of Al-Sulaimanya company gave minimum value for thermal conductivity, which was (1.162 W/m.oC), and maximum value was for specimen No. (4) for Iranian cement, which was (1.55 W/m.oC) and for specimen No. (3) for cement of Bazian company, which was (1.52 W/m.oC). Results of thermal conductivity for all the other specimens were within the depended theoretical value. Minimum heat flow within the material was for specimen No. (7) for cement of Al-Sulaimanya company, while maximum value was for specimen No. (4) for Iranian cement. Key words: thermal conductivity test, cement, mortar, heat flow, Fourier law for conduction.

Chemo-Micro-Dilatation Modeling of Carbonation Shrinkage Phenomenon of the Porous Mortars

In this paper, we investigate the CO2 carbonation on porous materials such as the cement paste mortar. Our scientific goal is to model the CO2 carbonation effect on the porous cement mortar by the micro-dilatation theory and to determine the chemo-mechanical stress development due to the chemical reactions. In fact, this phenomenon will modify not only the pH value of the cement paste but also the micro-structure due to collapsing pore-network. Based upon the micro-dilatation theory originally proposed by Cowin and Nunziato, four unknown parameters related to the micro-structure will be determined for the cement mortar using the semi-empirical method and numerical modeling. The experimental carbonation tests on two different types of cement paste (CEMI and CEMIII) have been realized to capture carbonated affected zones and to measure their shrinkage deformations.

Interaction of bentonite with supercritically carbonated concrete

Bentonite and concrete are essential components in construction of a geological high level nuclear waste (HLNW) repository. Conventional Ordinary Portland Cement (OPC) used for concretes gives a pore water leachate with a pH as high as 13.5 in contact with ground water. This alkaline plume of leaching waters might perturb the engineered barrier system, which might include bentonite buffer, backfill material or the near-field host rock. The accepted solution to maintain the bentonite stability, which is controlled by the pH, is to develop cementitious materials with pore water pH around 11. Four lixiviation experiments representative of long-term interaction of solids and pore fluids at the concrete/bentonite interface were performed with two types of cement paste, Portland and calcium aluminate cement, before and after being carbonated under supercritical conditions, with granite water at 80 °C. The evolution of the pH indicates that the supercritical carbonation reduced the alkalinity of the cement pastes and calcite likely controls the equilibrium of Ca at the end of the experiments. The bentonite helps to buffer the alkalinity of concrete leachates through several reactions such as dissolution of montmorillonite and precipitation of secondary products as trioctahedral smectite, zeolites (gismondine), and presumably Mg hydroxides and amorphous gels. Carbonation may reduce propagation of the alkaline plume and enhance the barrier performance.

The fragmentation of cementitious composites in a jaw breaker

The paper reports about the fragmentation of cementitious composites in a laboratory jaw breaker. Two types of cement paste and six different concrete materials were investigated. Specific fragmentation energy and size distributions of the generated fragments were estimated. A microscopic inspection of the debris was also performed. Specific energy has values between 5 and 10 J/g. It is highest for a concrete with high porosity and lowest for a mortar. It is also found that the specific fragmentation energy depends on the amount of coarse aggregates in the material. Based on these findings, the specific fragmentation energy is linked to a brittleness parameter of the concrete materials derived from non-linear fracture mechanics. A detailed SEM-study showed features of non-linear fracture, namely crack branching, aggregate bridging, and pore–crack interaction. It was further found that a Rosin–Rammler–Sperling distribution best describes the size distribution of the generated fragments, except the mortar. An approximate estimation of the strain rate during the fragmentation was performed, and a value of ε ̇ =1.41×10 3 s −1 was calculated for concrete.

Numerical simulation of hydration-driven moisture transport in bulk and interface paste in hardening concrete

In real concrete two types of cement paste can be distinguished, i.e., bulk paste and interface paste. Initially the paste in the interface zone will generally contain more water than the bulk paste and will therefore hydrate differently. Differences in relative humidity and associated differences in pore water pressure will result as well. If the interface paste and the bulk paste could hydrate individually, a situation will result where a relatively porous water-rich interfacial zone coexists with a relatively dry bulk paste. However, due to gradients in porosity, permeability, relative humidity and pore water pressure, a flow of moisture will start from the water-rich interfacial zone to the bulk paste. It will be shown how the moisture transport can be simulated numerically and how this transport phenomenon influences the overall rate of hydration of cement in concrete. Numerical results are compared with experimental data presented in literature. The relevance of modelling of this kind of transport phenomena is briefly dealt with.