Hydration Of Portland Cement Pastes Research Articles

Assessing hydration kinetics and rheological properties of Limestone Calcined Clay Cement (LC3): Influence of clay-mitigating and superplasticizer admixtures

Limestone calcined clay cements (LC3) signify a trend in the construction sector aimed at reducing environmental impacts. However, the fresh state behavior of these cements, especially concerning clay properties and their interaction with chemical admixtures, needs to be better understood and investigated. This study is designed to assess the impact of a polycarboxylate-based superplasticizer (ADV) and a clay-mitigating (CM) admixture, along with exploring the synergistic effects that arise from combining both admixtures on the properties of LC3 cements. Hydration kinetics were evaluated in cement pastes using isothermal calorimetry and in-situ XRD, while fresh state properties were evaluated by rotational rheometry. The calorimetry results showed that the CM admixture provides a delay in the aluminate reactions of all LC3 systems, while it does not significantly affect the hydration of Portland cement pastes, suggesting a pronounced interaction of this admixture with clay particles. The incorporation of the CM admixture did not yield favorable workability conditions in LC3 mixtures when compared to the effectiveness of the ADV. In general, the assessment indicates that the CM admixture lacks effective dispersion capabilities and exhibits a limited influence on the formation of hydrated products in LC3 cements produced with calcined kaolinitic clay.

Effect of Multiwalled Carbon Nanotube Functionalization with 3-Aminopropyltriethoxysilane on the Rheology and Early-Age Hydration of Portland Cement Pastes

Effect of Multiwalled Carbon Nanotube Functionalization with 3-Aminopropyltriethoxysilane on the Rheology and Early-Age Hydration of Portland Cement Pastes

Hydration of Portland cement paste mixed with densified silica fume: From the point of view of fineness

To be easily transported and stored, silica fume is commonly densified before using in concrete. The size of densified silica fume (DSF) agglomeration is up to several millimeters. In general, the agglomeration is hard to be dispersed into individual silica fume sphere. The properties of concrete are closely associated with the fineness of DSF. In order to explore the effects of DSF fineness on the hydration of Portland cement, four techniques, such as isothermal calorimetry, X-ray diffraction (XRD), thermogravimetry (TG) and scanning electron microscope (SEM) are carried out. In the end, the effect of the fineness of DSF on the mechanical property of cement mortar is discussed. Four series of DSF with different particle size distribution are investigated. Three dosages (0%, 10% and 20%) are considered. The results show that the screened DSF is difficult to be dispersed in the cement paste regardless of fineness. The fineness of DSF has obvious effect on the hydration of cement. With the increase of particle size, the delay action of DSF agglomeration on the hydration of cement becomes noticeable. The rate of cement hydration is decreased and the acceleration period is prolonged. The large DSF agglomeration shows less pozzolanic activity. In this binary system, calcium hydroxide cannot be consumed completely by DSF under high replacement level at 28 days of curing. Finer DSF definitely contributes to the improvement of the compressive strength of cement mortar, but only at a curing age of 28 days.

Evaluation of sample drying methods to determine the apparent porosity and estimation of degree of hydration of portland cement pastes

Evaluation of sample drying methods to determine the apparent porosity and estimation of degree of hydration of portland cement pastes

Direct in-situ observation of early age void evolution in sustainable cement paste containing fly ash or limestone

This paper uses fast X-ray Computed Tomography (fCT) to study the change in air-filled voids during hydration of portland cement pastes of different water to cement ratios and with fly ash and limestone additives between 30 min and 12 h of hydration with deionized and de-aired water. For the deionized samples, the total volume of the air-filled voids increased during the induction period and decreased as the acceleration period began and finally stayed constant. The samples with 20% replacement of fly ash and 20% replacement of limestone showed the same trends as the OPC samples but with a reduction in the observed air-filled void formation. The air-filled void distribution in these samples changed from a limited number of large voids at the beginning of the measurements to a system with a significantly greater number of uniformly distributed smaller voids. The changes in the air-filled voids were not significant in pastes made with 50% fly ash or with de-aired water in the same testing condition. This might be explained by differences in pore solution chemistry and a reduced amount of dissolved air in the mixing water. A mechanism is proposed for a change in ionic concentration in solution to cause release of the dissolved air within the mixing water.

Effect of nano-SnO2 on early-age hydration of Portland cement paste

Nanomaterial, as a new emerging material in the field of civil engineering, has been widely utilized to enhance the mechanical properties of cementitious material. Nano-SnO2 has presented high hardness characteristics, but there is little study of the application of nano-SnO2 in the cementitious materials. This study mainly investigated the hydration characteristics and strength development of Portland cement paste incorporating nano-SnO2 powders with 0%, 0.08%, and 0.20% dosage. It was found that the early-age compressive strength of cement paste could be greatly improved when nano-SnO2 was incorporated with 0.08% dosage. The hydration process and microstructure were then measured by hydraulic test machine, calorimeter, nanoindentation, X-ray diffraction, scanning electron microscope, and mercury intrusion porosimetry. It was found that the cement hydration process was promoted by the addition of nano-SnO2, and the total amount of heat released from cement hydration is also increased. In addition, the addition of nano-SnO2 can promote the generations of high density C-S-H and reduce the generations of low density C-S-H indicating the nucleation effect of nano-SnO2 in the crystal growth process. The porosity and probable pore diameter of cement paste with 0.08% nano-SnO2 were decreased, and the scanning electron microscopic results also show that the cement paste with 0.08% nano-SnO2 promotes the densification of cement microstructure, which are consistent with the strength performance.

Investigation of Blended Cement Hydration in the Reactive Powder Concrete with Increasing Levels of Silica Fume Addition

Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydration products. By the process of hydration Portland cement mixed with sand, gravel and water produces the synthetic rock we call concrete. The Therefore, the concrete properties always accompanies with the hydration degree of cement. This paper presents some experimental test results on how silica fume affects the cement hydration in cement pastes of the Reactive Powder Concrete as increasing levels of silica fume addition with the content from 0% to 30% of cement mass. The hydration process of cement/silica fume paste was followed from the estimation of heat of hydration, rate of heat evolution, of binder pastes obtained by isothermal calorimetry (TAM-Air). In addition, the portlandite content, the hydration degree of pure cement, reaction degree of binder paste as well as reaction degree of silica fume were investigated. The quantitative assessment on these characteristics are due to the simulation of the hydration of Portland cement pastes containing silica fume.

Blended cement hydration assessment by thermogravimetric analysis and isothermal calorimetry

In the present study, the hydration of Portland cement pastes containing 5%, 10%, 15% and 20% tuff, limestone filler and granodiorite was investigated by thermogravimetric analysis coupled with differential scanning calorimetry and microcalorimetry isotherm. The monitoring of the hydration kinetics by thermogravimetric analysis made it possible to quantify the quantity of water combined with the cement (nonevaporable water) and the degree of hydration. By coupling this technique to the differential scanning calorimetry, it was also possible to measure the energy absorbed or released by the material during its decomposition. The results showed that the non-evaporable water content and the degree of hydration of the mixtures containing various mineral admixtures were relatively lower with respect to the reference mixture when as the content of mineral admixture increased. The effect of the evolution of the hydration process on the mechanical properties of mortars was also monitored. The relative variation of the compressive strength to that of the flexural strength was evaluated at 7, 28 and 90 days. Results showed that all the mixtures have a greater contribution in flexion than in compression.

Unsupervised and supervised pattern recognition of acoustic emission signals during early hydration of Portland cement paste

Several studies have been conducted to investigate early age Portland cement hydration using acoustic emission technique, with different mechanisms attributed by different authors. In the proof-of-concept research presented in this paper, acoustic emission (AE) was employed to explore relationships between recorded signals associated with elastic stress waves and potential mechanisms associated with cement hydration. Ordinary Portland cement paste samples having water/cement ratio of 0.3 and 0.5 were monitored during the first 72h of curing using broadband AE sensors. The acoustic emission signals were analyzed using unsupervised and supervised pattern recognition algorithms to address limitations of acoustic emission parameter analysis. Wavelet analysis was utilized as a complementary method, which can be considered as a map for identification of patterns in the signal set. Unsupervised methods are useful when there is no history or background data concerning the pattern of a phenomenon such as the hydration process.

Blended Cement Systems with Zeolitized Silica Fume

In this paper the properties and the hydration of Portland cement pastes containing zeolitized silica fume were studied. Hydrosodalite was obtained by zeolitization of silica fume. XRD, DSC, SEM and energy-dispersive X-ray spectroscopy were used as investigation methods. The compressive strength of hardened cement paste was measured after 28 days. The levels of cement replacement by additives were 5 %, 10 % and 15 % by weight in the specimens. Changes in the strength of hardened cement paste were observed. The influence of additives on hydration rate and hydration temperature was also observed. Both 1Hs (hydrosodalite) and 2Hs (modified hydrosodalite) additives accelerate the hydration of the cement paste. The highest hydration temperature was achieved in a mixture with 5 wt. % 1Hs additive and with 10 wt. % 2Hs additive. The microstructure of hardened cement paste specimens with 1Hs and 2Hs additive is denser compared with reference specimens without the additives. The maximum compressive strength of the specimens with 10 wt. % of 2Hs reached up to 101 MPa under laboratory conditions.DOI: http://dx.doi.org/10.5755/j01.ms.22.2.7018

Cement hydration with ultrasound treated clinoptilolite

There are many cement replacement materials and one of them is zeolites. Zeolites are crystalline solids structures made of silicon, aluminum and oxygen that form a framework with cavities and channels inside where cations, water and/or small molecules may reside. In this study natural zeolite clinoptilolite was used. Clinoptilolite is the most popular natural zeolite mineral with the chemical formula (Na, K, Ca)23Al3(Al,Si)2Si13O3612H2O. The present paper shows the results of using ultrasound treated clinoptilolite as Portland cement replacement material. The duration of ultrasound treatment was 5 min, 10 min, and 20 min. Results showed that the XRD of ultrasound-treated clinoptilolite slightly differs in comparison to conventional clinoptilolite. The cement samples with 5% and 10% clinoptilolite substitute provide the strength increase, 30% significantly reduces the strength compared to control samples. The heat measurements of Portland cement paste hydration, containing clinoptilolite, showed that the clinoptilolite slightly increases the duration of hydration, but hydration temperature is lower than in the controls samples. The experimental results suggest that ultrasound-treated clinoptilolite positively influence cement hydration processes, consolidation kinetics, CSH formation; the mechanical strength of the samples is increased. Typical content of Portland cement substituting does not exceed 20% of mass of Portland cement in samples. Reducing the consumption of Portland cement with substituting it with ultrasound treated clinoptilolite is preferred for reasons of environmental protection.DOI: http://dx.doi.org/10.5755/j01.sace.11.2.12430

Modeling cement hydration by connecting a nucleation and growth mechanism with a diffusion mechanism. Part II: Portland cement paste hydration

Abstract A particle-based C3S hydration model with only three rate constants developed in Part I of this study is further developed and applied to Portland cement paste hydration. Experimental data are obtained with chemical shrinkage tests of cement pastes prepared with different water to cement (w/c) ratios (0.3–0.5), and cured at different temperatures (24°C–63°C) and pressures (0.69–51.7 MPa). The proposed model produces exceptionally good fits to test data. The fitted results indicate that the entire process of cement hydration can be modeled by connecting a nucleation and growth mechanism with a diffusion mechanism. Furthermore, the results reveal that the deceleration period of cement hydration may be due to the gradual transition of the rate-controlling mechanisms of different particles. The fitted rate constants generally follow basic chemical kinetics laws in terms of their dependencies on curing temperature and pressure, and appear to be largely independent of w/c ratio.

Dynamic mechanical thermo-analysis of Portland cement paste hydrated for 45 years

The effect of prolonged hydration of Portland cement paste on engineering behavior was investigated using dynamic mechanical thermo-analysis (DMTA) methods. Specimens ranged in age from 3 days to 45 years. Compacts of hydrated cement powders and normally hydrated paste specimens were tested. Age dependent nanostructural characteristics of C–S–H were shown to influence the mechanical response of cement paste. Evidence was provided to support the use of compacts as structural models for hydrated cement paste. Details of ageing effects on the DMTA parameters (storage modulus and internal friction) as a function of temperature and porosity are reported.

Modeling cement hydration by connecting a nucleation and growth mechanism with a diffusion mechanism. Part I: C3S hydration in dilute suspensions

Abstract A particle-based C3S hydration model, which mathematically connects a nucleation and growth controlled mechanism with a diffusion controlled mechanism, is developed in this study. The model is first formulated and fitted with C3S hydration in stirred dilute suspensions in Part I where interactions between different particles can be ignored, and further developed and fitted with Portland cement paste hydration in Part II to account for inter-particle interactions. Excellent agreement was observed between experimental and modeled results. Three critical rate-controlling parameters, including a parallel growth rate constant, a perpendicular growth rate constant and a diffusion constant, were identified from the proposed model. The dependencies of these parameters on particle size and initial quantity of nuclei are investigated in Part I while their dependencies on cement composition, water-cement ratio, and curing condition are studied in Part II.

Effect of temperature on the hydration of Portland cement blended with siliceous fly ash

The effect of temperature on the hydration of Portland cement pastes blended with 50wt.% of siliceous fly ash is investigated within a temperature range of 7 to 80°C.The elevation of temperature accelerates both the hydration of OPC and fly ash. Due to the enhanced pozzolanic reaction of the fly ash, the change of the composition of the C–S–H and the pore solution towards lower Ca and higher Al and Si concentrations is shifted towards earlier hydration times. Above 50°C, the reaction of fly ash also contributes to the formation of siliceous hydrogarnet. At 80°C, ettringite and AFm are destabilised and the released sulphate is partially incorporated into the C–S–H. The observed changes of the phase assemblage in dependence of the temperature are confirmed by thermodynamic modelling.The increasingly heterogeneous microstructure at elevated temperatures shows an increased density of the C–S–H and a higher coarse porosity.

Modeling early-age hydration kinetics of Portland cement using flexible neural tree

The early-age hydration of Portland cement paste has an important impact on the formation of microstructure and development of strength. However, manual derivation of analytic kinetic equation for hydration process is very difficult because there are multi-phased, multi-sized and interrelated complex chemical and physical reactions during cement hydration. In this paper, a flexible neural tree structure is built as the right-hand side of kinetics instead of traditional analytic expression. Two evolutionary algorithms gene expression programming and particle swarm optimization are used to evolve tree structure and rules’ parameters, respectively. In order to reduce the computing time, GPUs are used for acceleration in parallel. Studies have shown that according to the established model, simulation curve of early-age hydration is in good accordance with the observed experimental data. Furthermore, this model still has a good generalization ability even changing chemical composition, particle size and curing conditions.

Solidification/stabilization of Ni(II) by various cement pastes

The immobilization of Ni(II) in various cement matrices was investigated using the solidification/stabilization (S/S) technique. The different cement pastes used in this study were neat Portland cement in absence and presence of water reducing- and water repelling-admixtures as well as blended cement with kaolin. Two ratios of Ni(II) were used (0.5% and 1.0% by weight of the solid binder). The hydration characteristics of the used cement pastes were tested via the determination of the combined water content, phase composition and compressive strength at different time intervals from 1 up to 180 days. The results show that the presence of NiCl 2 caused retardation for the hydration of Portland cement paste in absence and presence of water-reducing agent. But NiCl 2 caused acceleration rather than retardation on the hydration of the mixes containing calcium stearate and/or clay. The degree of immobilization of the added heavy metal ions was very high in the different investigated cement pastes.

Reverse extraction of early-age hydration kinetic equation from observed data of Portland cement

The early-age hydration of Portland cement paste has an important impact on the formation of microstructure and development of strength. However, manual derivation of hydration kinetic equation is very difficult because there are multi-phased, multi-sized and interrelated complex chemical and physical reactions during cement hydration. In this paper, early-age hydration kinetic equation is reversely extracted automatically from the observed time series of hydration degree of Portland cement using evolutionary computation method that combines gene expression programming and particle swarm optimization algorithms. In order to reduce the computing time, GPUs are used for acceleration in parallel. Studies have shown that according to the extracted kinetic equation, simulation curve of early-age hydration is in good accordance with the observed experimental data. Furthermore, this equation still has a good generalization ability even changing chemical composition, particle size and curing conditions.

Alkali binding in hydrated Portland cement paste

The alkali-binding capacity of C–S–H in hydrated Portland cement pastes is addressed in this study. The amount of bound alkalis in C–S–H is computed based on the alkali partition theories firstly proposed by Taylor (1987) and later further developed by Brouwers and Van Eijk (2003). Experimental data reported in literatures concerning thirteen different recipes are analyzed and used as references. A three-dimensional computer-based cement hydration model (CEMHYD3D) is used to simulate the hydration of Portland cement pastes. These model predictions are used as inputs for deriving the alkali-binding capacity of the hydration product C–S–H in hydrated Portland cement pastes. It is found that the relation of Na + between the moles bound in C–S–H and its concentration in the pore solution is linear, while the binding of K + in C–S–H complies with the Freundlich isotherm. New models are proposed for determining the alkali-binding capacities of C–S–H in hydrated Portland cement paste. An updated method for predicting the alkali concentrations in the pore solution of hydrated Portland cement pastes is developed. It is also used to investigate the effects of various factors (such as the water to cement ratio, clinker composition and alkali types) on the alkali concentrations.

The effect of curing temperature on white cement hydration

Cement manufacture has undergone extensive change in its attempts to rise to the successive challenges posed by society. The hydration of Portland cement is a complex phenomenon that depends on both reagent characteristics and reaction conditions. It is a well-known fact that the curing temperature plays an important role on the hydration kinetics. The present study is the first to be undertaken on the effect of curing temperature on white Portland cement paste hydration over long hydration times (365 days at 20 °C and 124 days at 60 °C). The technique used, 29Si and 27Al NMR spectroscopy, is particularly well adapted to the study of cement hydration. White cement hydration generates a C–S–H gel in which the aluminium taken up forms bridge bonds. After nine days at 60 °C, the degree of reaction expressed in terms of the Al(IV)/Al(VI) ratio nearly doubles the value found after 90 days at 20 °C.