Hydration Characteristics Of Cement Pastes Research Articles

Influence of Molybdenum Tailings Powder on the Hydration Characteristics of Cement Paste

Influence of Molybdenum Tailings Powder on the Hydration Characteristics of Cement Paste

Insight into the early hydration characteristics of Portland cement with hydroxyethyl methyl cellulose highlighted by 1H low-field NMR

1H low-field nuclear magnetic resonance (1H NMR) as a non-destructive test method can effectively capture the water state changes in cement pastes. The water changes can in turn reflect the early hydration characteristics of cement pastes. Hydroxyethyl methyl cellulose (HEMC) with different viscosities affects the hydration characteristics of cement by acting on the water in different states. The following experimental results are obtained by testing hydration of cement pastes with HEMC by using 1H NMR test. Incorporating 0.1–3% HEMC with different viscosities all can effectively control the bleeding water phenomenon. HEMC can absorb a part of the water in the cement pastes. Incorporating 2–3% HEMC significantly delays the enrichment of the gel pores water and interlayer water. When the content of HEMC increases from 0% to 3%, the hydration degree of cement pastes tends to decrease. Besides, HEMC with higher viscosity of 15000–40000 mPa·s obviously delays the hydration process of cement pastes compared to HEMC with lower viscosity of 400 mPa·s.

Ultrasonic monitoring of hydration behavior of cement paste doped with triethanolamine using novel piezoelectric ultrasonic transducer

The propagation of ultrasonic wave in cement paste is closely related to its physical properties, and therefore shows a potential application in fields of online monitoring of hydration and hardening properties of the cementitious materials. Here, the hydration characteristics of cement paste doped with triethanolamine were studied based on the ultrasonic transmission method using the tailor-made horizontal omnidirectional piezoelectric ultrasonic transducer. The results show that clear ultrasonic waveforms can be observed at hydration age of 2 h. The dominant frequency of the reception wave is low at early hydration age and shifts towards the high frequency direction with hydration. The amplitude of the head wave increases sharply before hydration of 24 h, and the increasing extent decreases gradually until hydration of 166 h. The hydration process of cement at early hydration age can be classified into three stages based on amplitude changes of the head wave, that is, the induction period before 4 h, the acceleration period during 4–12 h, and the deceleration period after 12 h. The acoustic parameters of cement paste at early hydration age conform well to the logistic function distribution. The research finding might provide a new method to estimate hydration and hardening properties of cementitious materials, especially on large construction sites.

Early hydration characteristics and kinetics model of cement pastes containing internal curing materials with different absorption behaviors

Internal curing with superabsorbent polymer (SAP) has potential effect on the early deformation and hydration of cementitious material. However, there are few studies on the hydration kinetics and hydration characteristics of internal curing cementitious material. Here, the effects of microgel, composite microgel and commercial SAP with different dosage and absorption behaviors on the hydration characteristics of cement paste were studied by the hydration model proposed by Krstulović-Dabić and hydration heat. Results showed that the hydration reaction of paste containing internal curing materials increased as function of the dosage. When nano-silica(NS) incorporated into microgel, 24.5% and 5.6% increase in value of exothermic peak and cumulative heat were observed for paste. The hydration kinetic model showed that the composite microgel promoted the crystal growth and phase boundary reaction process, thus extending the transition point to the diffusion process. For commercial SAP with premature desorption behavior, the hydration rate of cement paste decreases and the appearance of conversion point at each process is delayed. Hydration characteristics are in good agreement with the kinetic model, suggesting that portlandite consumed by pozzolanic reaction promoted the development of hydration reaction and further refined the microstructure of paste.

Pore structure formation and hydration characteristics of cement paste with temperature rising inhibitor

Pore structure formation and hydration characteristics of cement paste with temperature rising inhibitor

Effect of a specific PCE superplasticizer on the initial dissolution and early hydration of Portland cement

The existence of polycarboxylate ether superplasticizer (PCE) affects cement dissolution and usually retards cement hydration. It is still unclear how the adsorbed PCE retard the cement hydration process at dissolution stage or at generation of the hydration products stage. Herein, a new method to simulate the initial dissolution reaction between cement and PCE by using water instead of lime saturated solution as a solvent is proposed. In addition, this work analyzes the early hydration characteristics of cement paste with the PCE, using the techniques of calorimetric, adsorption measurement, zeta potential, XRD, thermogravimetry, ICP−OES and dynamic light scatting. It was found that the PCE can improve the initial dissolution rate of cement and then retard cement hydration by its dispersing effect. The complexation between the PCE and Ca2+ ions, the increase in Al3+ ions, and the reduction of hydration products are responsible for the retardation effect of cement hydration.

Effect of TEA·H3PO4 and TEA·C18H30O3S on the mechanical properties and hydration characteristics of cement paste

In this study, TEA·H3PO4 (TP) and TEA·C18H30O3S (TDS) have been used as organic admixtures in cementitious materials. Mortar specimens with different TP and TDS dosages were subjected to mechanical, setting time, hydration degree, isothermal calorimeter tests, as well as to XRD, TG, SEM and MIP analyses. Results show that less than 0.10% TP and 0.05% TDS shorten the initial setting time, while more than 0.50% TDS can lead to a retarding effect in mortar specimens. TP is beneficial to increase the early age strength, but a sharp decrease in both compressive and flexural strengths is found when TDS is introduced. The XRD and TG analyses indicate that the introduction of TDS brings more generation of the portlandite (CH), ettringite (AFt), and monosulfate (AFm), whereas TP leads to the reduction of CH content in the cement pastes. Moreover, the SEM observations reveal that the decline in strength may result from the air-entraining effect caused by the incorporation of TDS which increase the amount and size of hydration pores, and the variation of mechanical properties of mortar specimens with TP is closely linked to the size of CH generated in mortar specimens.

Effects of slag on cement hydration by electrical resistivity characterization

Non-contact resistivity measurement was used to characterize the early hydration characteristics of cement paste with different contents of slag, combined with other traditional methods such as hydration heat, compressive strength. The results show that the maximum compressive strength of sample P0.4SL20 was 34.4 MPa and 45.2 MPa at 3 d and 7 d, respectively. The addition of slag could reduce the hydration heat of slurry, which makes the second hydration exothermic peak shift to the left. The characteristic points on electrical resistivity differential curve with different slag contents had good correspondence with the corresponding characteristic points on hydration heat release curve of samples with different slag contents. A good linear relationship between electrical resistivity and compressive strength was shown as f c(3d) = 5.23992P(3d)-12.31066. The electrical resistivity method can be used to characterize the influence of slag on the hydration process of cement paste and predict its compressive strength.

Effects of PCEs with various carboxylic densities and functional groups on the fluidity and hydration performances of cement paste

In this research, effects of polycarboxylate superplasticizers (PCEs) with various carboxylic densities and functional groups on the adsorption behavior, dispersing performance as well as hydration characteristics of cement paste were systematically investigated. PCEs with different architectures were synthesized through substituting acrylic groups with sulfonic groups, ester groups, acylamino group, and changing the molar ratio between HPEG and acrylic groups in the PCE backbones under free radical solution polymerization. The molecular structures of different PCEs were characterized by size exclusion chromatography (SEC). The adsorption isotherms and the dispersing properties of different molecular PCEs were measured by total organic carbon measurement (TOC), mini-slump cone and shear rheometer, respectively. Cement hydration characteristics in the function of various molecular PCEs were investigated through X-ray diffraction (XRD), differential thermal analysis-thermogravimetric analysis (DTA-TG) as well as isothermal calorimetry. Results show that carboxylic density and the functional groups in PCE molecules significantly influence the adsorption behavior and the dispersing performance of PCEs. The increase in carboxylic density and integrating sulfonic groups into PCE backbone can enhance the adsorption capability of PCEs onto cement grain surface, which hence generate higher initial dispersing property. PCEs with higher carboxylic density hinder the cement hydration during the induction period, but promote the maximum hydration degree during the acceleration period. Integrating sulfonic group into PCEs backbone significantly promotes the cement hydration, while integrating amide groups or ester groups into the backbone of PCEs depresses the cement hydration process. The variation in cement hydration caused by the addition of different molecular PCEs is almost diminished at 28 d.

Use of Algerian Natural Mineral Deposit as Supplementary Cementitious Materials

Much of the current research on concrete engineering has been focused on including siliceous additions as supplementary cementitious materials (SCMs). Silica reacts with Calcium hydroxide release during cement hydration, and produces more C-S-H. The latter contributes to increase compactness, mechanical strengths and sustainability of concrete. This paper explores the hydration characteristics of cement paste based on various natural mineral additions, that are very abundant in Algeria and present a high silica content (ground natural pozzolana “PZ” and ground dune sand “DS”). For this purpose, several analyses were carried out on modified cement pastes and mortars. TheseSCMswere introduced by replacement levels of 15, 20 and 25 by weight of cement. We first, studied the effect of these SCMs on the heat of hydration and mechanical strength of mortars at different ages. The evolution of hydration of modified paste was studied, by using Thermal analysis (TG/TDA) at different ages, to analyze the Calcium Hydroxide (CH) content of the modified pastes. It is shown that the CH content of the mixes including SCMs is lower than that of the plain cement paste, indicating that silica reacts with the cement paste through a pozzolanic reaction. Increased pozzolanic activity results in higher amounts of Calcium Silicate Hydrate in the paste, which in turn results in higher compressive strength for modified cement mortars. Due to its crystalline morphology, the ground DS particles present a partial pozzolanic effect, compared to PZ which is semi-crystalline. Modified mortars by 20% DS can be the optimal composition. It presents satisfactory results: good mechanical strength and low heat of hydration. It can lead to an economic and sustainable concrete. Ground DS is very abounded in Africa and free of any impurities and can be a good alternativeSCMsin cement industry.

The Early Hydration Characteristics of Portland Cements with Superplasticizer Using Electrical Measurements

In this paper, an electrical measurement was applied to investigate the early hydration characteristics of cement paste with different dosages of superplasticizer. The bulk electrical resistivity development curves and the derivative curves were studied. It is found that there are two main peaks and four critical points on the derivative curves. The critical points are used to divide the hydration process into dissolution, setting, acceleration, deceleration and diffusion-controlled periods. The physical meanings of the critical points are identified by the penetration measurement of Vicat device and the heat evolution test. The setting occurred in the second period which provides an alternative method to determine the setting time by the electrical measurement. The results of the bulk electrical resistivity have a positive relation with that of the compression strength. The retardation effect of the superplasticizer is demonstrated by the delayed time for the critical points occurrence and confirmed by the setting time. A rapid method for selecting a suitable dosage of the chemical admixture for construction requirements is proposed.

Influence of lignosulfonate on the early age rheology and hydration characteristics of cement pastes

Four different cements made from gypsum mixed with clinkers possessing varying amounts of clinker phases were employed to investigate the influence of lignosulfonate on the early age rheological and hydration properties of cement pastes. Two test methods were employed; the parallel plate rheometry and isothermal calorimetry. Here, lignosulfonate was quantitatively shown to impact the early age hydration of cement pastes depending on the C3A and C3S compositions, in the respective order. A threshold amount of ~4.6% C3A is needed to sufficiently impair the performance of lignosulfonate at normal working dosages (0.4% bwoc). When high amounts of C3A was present (~10%), flash set of the cement paste occurred even at the low dosage of 0.2% bwoc of lignosulfonate. When cement possessed low amount of C3A, lignosulfonate mainly retarded the hydration of C3S, but this effect decreased when the C3S was doped with Al.

Hydration Characteristics of Cement Paste Containing Supplementary Cementitious Materials

An experimental investigation was carried out to evaluate the hydration characteristics and compressive strength development of cement paste containing various supplementary cementitious materials (SCMs), viz. pulverised fuel ash (PFA), ground granulated blast-furnace slag (GGBS) and microsilica (MS). Cement pastes were prepared in two series (A and B). Mixes of series A were manufactured with a fixed water–binder ratio of 0.30 and a superplasticiser, whereas the water–binder ratios of mixes in series B were equivalent to those needed for standard consistencies. The XRD and TG data showed that the addition of PFA, GGBS and MS reduced the intensity of Ca(OH)2 peaks at test ages of 3, 7, 28 and 91 days. The incorporation of PFA and GGBS in the cement paste mixes produced a lower strength value at early age. However, at later ages, the strength was either greater or comparable to the control specimen. Although the compressive strength of cement paste containing 15% MS was greater than that of the PFA and GGBS pastes at all ages, from a cost point of view, it can be suggested that combinations of 40% PFA and 7.5% MS or 50% GGBS and 7.5% MS may be best to improve the hydration properties and compressive strength of cement paste.

The mechanical properties and hydration characteristics of cement pastes containing added-calcium coal gangue

The mechanical properties of several kinds of coal gangue calcined with limestone were Researched so as to find the optimum way of calcinations with limestone. Microstructure and property of hydration process of cement pastes containing added-calcium coal gangue were analyzed by means of scanning electron microscope (SEM) and method of mercury in trusion poremeasurement (MIP), etc. The experiment can approve those results: when proper amounst of gypsum and fluorite were taken as mineralizers in the course of calcinations of added-calcium coal gangue, activity of coal gangue can be effectively improved. The results of mechanical property and structural characteristic such as hydration process, hydration product and microstructure etc. of cement pastes containing added-calcium coal gangue are consistent.

Hyperbolic method to analyze the electrical resistivity curve of Portland cements with superplasticizer

Electrical measurement was employed to investigate the early hydration characteristics of cement pastes with different dosages of superplasticizer in the same W/C ratio. The hyperbolic method was applied to analyze the electrical resistivity development. The peak point (Ph) on the hyperbolic curve could be easily read. The time (th) to reach the point Ph had strong relations with the setting time. th was delayed with the increment of the dosage of superplasticizer. The time th was used to plot the relationship between the initial setting time and fi nal setting time. The hyperbolic equation was established to predict the ultimate resistivity. The retardation effect of the superplasticizer was confirmed in the same W/C ratio by setting time and isothermal heat evolution.

Study of the influence of superplasticizers on the hydration of cement paste using nuclear magnetic resonance and X-ray diffraction techniques

Melamine and naphthalene-based superplasticizers have been used, over the past few decades, in order to improve the workability of concrete. Recently, more efficient copolymer formulations have been introduced for the same purpose. However, the influence of these chemical admixtures on the microstructure of the hardened concrete and, consequently, on its properties still needs to be extensively evaluated. Accordingly, the present work analyzes the hydration characteristics of cement pastes with naphthalene, melamine and copolymer-based superplasticizers, using the techniques of X-ray diffraction (XRD) and nuclear magnetic resonance (NMR), up to the age of 28 days. The results indicate a significant influence of the superplasticizer on the growth rates of the hydrates and on the state of polymerization of the silicates.