Hydration Development Research Articles

Physico-chemical and mechanical characterization of hydraulic mortars containing nano-titania for restoration applications

In this work nano-titania of anatase and routile form has been added in mortars containing: (a) binders of either hydrated lime and metakaolin, or natural hydraulic lime and, (b) fine aggregates of carbonate nature. Mortar composition was tailored to ensure adhesion of fragments of porous limestones from the Acropolis monuments. The aim was to study the effect of nano-titania in the hydration and carbonation of the above binders, as well as the mechanical properties and the adhesive capability of the designed mortars, where the nano-titania proportion was 4.5–6% w/w of binder. The physico-chemical and mechanical properties of the nano-titania mortars were studied and compared to the respective ones, without the nano-titania addition. DTA-TG, FTIR, SEM and XRD analyses indicated the evolution of carbonation, hydration and hydraulic compound formation during a 1 year curing. Results indicate enhanced carbonation, hydration and modulus of elasticity of mortar mixtures with nano-titania. A specifically designed experimental procedure for measuring the direct tensile strength of the mortar–stone system proved that nano-titania mortars can be used as adhesive materials for porous limestones.

E-modulus evolution and its relation to solids formation of pastes from commercial cements

Models for early age E-modulus evolution of cement pastes are available in the literature, but their validation is limited. This paper provides correlated measurements of early age evolution of E-modulus and hydration of pastes from five commercial cements differing in limestone content. A recently developed methodology allowed continuous monitoring of E-modulus from the time of casting. The methodology is a variant of classic resonant frequency methods, which are based on determination of the first resonant frequency of a composite beam containing the material. The hydration kinetics — and thus the rate of formation of solids — was determined using chemical shrinkage measurements. For the cements studied similar relationships between E-modulus and chemical shrinkage were observed for comparable water-to-binder ratio. For commercial cements it is suggested to model the E-modulus evolution based on the amount of binder reacted, instead of the degree of hydration.

Use of clay as a cement replacement in mortar and its chemical activation to reduce the cost and emission of greenhouse gases

The effect of industrially produced quicklime on the strength development and pozzolanic reaction rates of Clay-Cementitious systems was investigated. The compressive strength development of mortars containing Quicklime–Clay–Cement (C–C–L) was studied and presented. New efficiency factors were calculated in order to find out the optimum amount of quicklime to be added. The addition of quicklime increased both the early and later strengths of the cement–clay specimens. Hydration evolution and pozzolanic reaction rates of the Quicklime–Clay–Cement (C–C–L) system were monitored. To know the quantity of hydration products, Non-evaporable water content of the produced pastes was determined. A 3% addition of quicklime was found as optimum dosage both for short and longer curing periods. The increase in the strength could be due to the fact that the lime fully employed the available silica from the clay to form additional cementitious compounds, prevailing pozzolanic calcium silicate hydrate with increase in the amount of quicklime, no accelerating effect was detected due to the diminished proportion of soluble silica in the pore solution.

SIMULATION OF HYDRATION AND CRACKING PROPAGATION WITH TEMPERATURE EFFECT BAWSED ON FUZZY LOGIC THEORY

This paper deals with the influence of temperature and temperature history on the development of hydration heat in concrete structures and on evaluation of temperature distribution in earlyage concrete. The main objective of this work is estimation of temperature influence on hydration progress in concrete during hydration reaction, then the evaluation of hydration rate, cumulative hydration heat and evolution of actual material strength. Further, the risk of cracking in concrete structure due to shrinkage and linear thermal expansion is estimated and based on results of crack risk analysis, the depth and geometry of the crack is obtained.http://dx.doi.org/10.5755/j01.mech.17.4.561

Isothermal and solution calorimetry to assess the effect of superplasticizers and mineral admixtures on cement hydration

The heat of hydration evolution of eight paste mixtures of various water to binder ratio and containing various pozzolanic (silica fume, fly ash) and latent hydraulic (granulated blast furnace slag) admixtures have been studied by means of isothermal calorimetry during the first 7 days of the hydration process and by means of solution calorimetry for up to 120 days. The results of early heat of hydration values obtained by both methods are comparable in case of the samples without mineral admixtures; the values obtained for samples containing fly ash and granulated blast furnace slag differ though. The results from isothermal calorimetry show an acceleration of the hydration process by the presence of the fine particles of silica fume and retarding action of other mineral admixtures and superplasticizer. The influence of the presence of mineral admixtures on higher heat development (expressed as joules per gram of cement in mixture) becomes apparent after 20 h in case of fly ash without superplasticizer and after 48 h for sample containing fly ash and superplasticizer. In case of samples containing slag and superplasticizer the delay observed was 40 h. The results obtained by solution calorimetry provide a good complement to the ones of isothermal calorimetry, as the solution calorimetry enables to study the contribution of the mineral admixtures to the hydration heat development at later ages of the hydration process, which is otherwise hard to obtain by different methods

Interactions in Calcium Aluminate Cement (CAC)‐Based Castables Containing Magnesia—Part II: Hydration–Dehydration Behavior of CAC and their Mixtures with Dead‐Burned and Reactive‐Grade MgO

A priori several technological problems arise on adding MgO to castable systems, due to its high tendency to react with water and the subsequent great volumetric expansion promoted by this reaction. This is detrimental to the volume stability and accordingly, the strength of the self‐forming spinel‐containing refractory castables. Nevertheless, very few basic researches have been systematically performed related to these castables behavior during the hydration and the dehydration process. In the current work, the hydration of a neat paste of a commercial ∼70 wt% Al2O3calcium aluminate cement (CAC) with and without two varieties of MgO additions (dead burned and reactive grade) was continuously followed at 24°±2°C by monitoring the exothermic heat evolution and the changes in pH. Additionally,in situtime‐resolved laboratory X‐ray diffraction (in situ‐LXRD) was continuously registered from 0 to 62 h during the dissolution of the anhydrous pastes and subsequent precipitation of hydrates. Further, the evolution of hydration and dehydration was studied from room temperature up to 1200°C by dilatometry, thermogravimetry, and differential thermal analyses to establish volumetric changes and reaction process, respectively. Also, isothermal treatments were carried out at selected temperatures, ranging from room temperature to 1200°C, and subsequently analyzed by conventional LXRD. Finally, the change of the modulus of rupture and the Young's modulus at room temperature, of the neat paste of the CAC with and without dead‐burned MgO, was measured and analyzed as a function of temperature, employing treated samples between 110° and 1400°C.

XRD investigations of hydrated homoionic montmorillonite saturated by several heavy metal cations

This paper aims at characterizing hydration behaviour and structural properties of a dioctahedral smectite (i.e. Wyoming montmorillonite), used in the context of naturel barrier for municipal waste disposal sites, and which is saturated by heavy metals cations coming from wastewater solution. Hydration of the <2μm size fraction of SWy-2 source clay has been studied by modelling XRD patterns recorded under room and controlled relative humidity (%RH) conditions on Cu2+, Pb2+, Zn2+, Co2+, Cd2+ and Ni2+ saturated specimens. There are heavy metal cations that are characterized by high natural abundance. The qualitative XRD investigation under room conditions (~35%RH) showed a similar hydration behaviour characterized by presence of three principal hydration states: 1W, 2W and 1W-2W (i.e. One, two and intermediate water layers hydration state, respectively). In order to highlight the specific hydration properties of each complex, we have studied by quantitative XRD analysis the hydration evolution under controlled relative humidity. Obtained result showed the possibility to distinguish between sample saturated with Na, Cu and Pb for high RH values (≈75%). For Ni, Zn, Cd and Co we have shown similar hydration behavior in all explored RH's range except the Ni2+ cation which presents a homogeneous 3W hydration state for 75%RH.

Reactivity of Fine Quartz in Presence of Silica Fume and Slag

Dune sand is a very abundant material in south of Algeria. Its high silica content gives a partial pozzolanic reactivity due to its crystalline state. This paper investigates the evolution of cement hydration based on a binary addition particularly the reactivity of dune sand finely ground in the presence of an amorphous addition: silica fume or blast furnace slag. Thus, four combinations of binary additions by substitution have been chosen. The X-ray diffraction analyses performed on cement pastes containing additions have shown the importance of the mineralogy and silica content of additions on their pozzolanic reactivity. Dune sand becomes reactive at long term, especially when associated up to 10% of amorphous addition (blast furnace slag or silica fume). It results an increasing in mechanical strength of Ultra High Performance Concrete (UHPC) and an improvement of the microstructure.

Cement Chemical Shrinkage Prediction Model Research Based on the Mineral Composition Content of Each Phase at Early Age

Based on the microstructure evolution of cement hydration, using the relationship between the hydration rate and hydration degree, chemical shrinkage prediction model of cementitious materials are proposed. This model can simulate chemical shrinkage curve of cement-based material well. In the early period, increasing water-cement ratio can increase chemical shrinkage. While in the middle period, its influence on chemical shrinkage is negligible. Increasing temperature accelerates the hydration process significantly, therefore, increases the chemical shrinkage.

Molecular dynamics study of ion hydration under pressure

We present results of a molecular dynamics simulation of pressure influence on ion hydration. Four different electrolyte aqueous solutions are considered: NaF, NaCl NaBr, NaI. These systems were modeled at two /pressure,temperature/ regimes: “normal” — 10 5 Pa, 298 K and “high” — 4 · 10 9 Pa, 500 K. Structural properties of the considered systems are shown in the form of instantaneous configurations of ionic hydration shells and distributions between the various atoms and/or ions. Dynamic properties are discussed in terms of the self-diffusion coefficients of the ions. We were interested in the pressure effect revealed in evolution of ionic hydration along the transition from “normal” to “high” regime. The results indicate strong changes in the hydration of considered ions as well as their ion-specific behavior.

Influencia de la temperatura de curado: hidratación y resistencia de pastas de cemento con escoria

Actualmente son muy conocidos los beneficios tecnológicos, económicos y el menor impacto medioambiental que produce el empleo de adiciones minerales como reemplazo del cemento portland. Estas razones, han consolidado el uso de muchas adiciones como: escoria granulada de alto horno, ceniza volante, material calcáreo, humo de sílice, etc. En los últimos años, los cementos presentan un importante aumento en el contenido de las adiciones; el cual influye sobre la distribución de partículas, sobre la velocidad y naturaleza de las reacciones de hidratación y en consecuencia en su ganancia de resistencia. El presente trabajo evalúa la influencia de la temperatura en el curado (20, 40 y 60 ºC) de pastas con contenido variable de escoria granulada de alto horno (0 a 80 %) elaboradas con relación agua/material cementante de 0,40, sobre la resistencia mecánica. La evolución de la hidratación se estudió a través del análisis de los compuestos de hidratación por DRX y el contenido de agua no evaporable. La resistencia mecánica se evaluó empleando un diseño de experimentos central compuesto centrado. Los resultados obtenidos indican que a medida que la temperatura de curado aumenta con el incremento del contenido de escoria en el cemento mezcla, se aumentan la resistencia y el contenido de agua no evaporable, y disminuye la cantidad de hidróxido de calcio de la pasta.

Moisture content and strain relation in wood by Bragg grating sensor and unilateral NMR

The paper describes a low-invasive experimental apparatus designed for the accurate determination of mechanical deformation and moisture content (MC) relationship on macroscopic wood samples. The device is particularly indicated for monitoring wooden handwork whose mechanical deformation is especially critical in relation to its role such as, for example, works of art or architectural works. The MC of wood is measured with a portable single-sided NMR probe and mechanical deformation by a fiber Bragg grating optical sensor. The data obtained are of high accuracy, despite the dimensions of the sample. The methodology provides an effective tool for investigating the dynamic relation between environmental relative humidity, MC, and shrinking-swelling of wood. Adsorption results collected for longitudinal deformation in silver fir (Abies alba Mill.) are presented to show the sensitivity of the optical sensor. Interesting findings include the detection of two different mechanisms of elongation and the time evolution of water mobility versus hydration and strain.

Characterization of ceramic roof tile wastes as pozzolanic admixture

The aim of this work is to study the recycling of tile wastes in the manufacture of blended cements. Cracked or broken ceramic bodies are not accepted as commercial products and, therefore, the unsold waste of the ceramic industry becomes an environment problem. The use of powdered roof tile in cement production, as pozzolanic addition, is reported. The wastes were classified as nonglazed, natural and black glazed tiles. The mineralogy of the powders was controlled by SEM-EDX microscopy, XRD analysis and FTIR spectroscopy. Particle size was checked by laser granulometry. Once the materials were fully characterized, pozzolanic lime consumption tests and Fratini tests were carried out. Different formulations of cement-tile blends were prepared by incorporation of up to 30% weight ratios of recycled waste. The compressive strength of the resulting specimens was measured. The evolution of hydration of the cement-tile blends was analyzed by XRD and FTIR techniques. Vibrational spectroscopy presented accurate evidence of pozzolanic activity. The results of the investigation confirmed the potential use of these waste materials to produce pozzolanic cement.

Structure characterization of hydration products generated by alkaline activation of granulated blast furnace slag

The hydration mechanism and mineral phase structures by waterglass activation of granulated blast furnace slag (GBFS) are investigated in detail by means of XRD and FTIR. The results show that the network structures of glassy phases are disintegrated and there is not any new material phase formed in the early stage of hydration processes. With evolution of hydration, the polycondensation reaction takes place between [SiO4]4− and [AlO4]5− species and some new mineral phases are produced. A hydration mechanism for the formation of geopolymer by waterglass activation of GBFS is proposed in detail.

In situ dynamic SEM imaging of hydration of cement using WETSEM technology

This paper presents an in situ study of the hydration of cement pastes in the SEM, made possible by the development of a radical new technology for the investigation of wet samples: the QX capsule from QuantomiX, based on the WETSEM technology, consists of an electron transparent but water and air tight membrane, which allows the examination of cement/water suspensions without any further preparation. In this way the evolution of hydration can be followed dynamically – in the same sample – over time. Results obtained with this technique are described. In addition to plain water/cement pastes the impact of additives on the early formation of phases has been studied. The strengths and limitations of this technology were identified and discussed.

Multiphasic finite element modeling of concrete hydration

This paper presents a model predicting the development of hydration and its consequences on temperature and water content. As it considers the effects of climatic conditions, the proposed model is a promising tool to evaluate the temperature, hydric and hydration fields of structures in situ. The hydration model predicts the hydration evolution of several main species (not only clinker but also mineral additions like fly ash or silica fume for instance). For each component, the modeling considers hydration development and chemical interaction between reactions. It also takes into account temperature and water content effects on reaction kinetics through thermal and hydric activation. Hydration development in turn modifies the thermal and hydric states of material. The result is a numerical model coupling hydration, and the thermal and hydric states of cement-based material. The model was tested on a 27 m 3 concrete block in situ equipped with temperature sensors situated in the core and close to the face exposed to solar radiation.

Evolution of ordinary Portland cement hydration with admixtures by spectroscopic techniques

The various waterproofing admixtures may prevent water from penetrating concrete in different ways, but primarily by rendering it hydrophobic. Spectroscopic techniques have proved to be the appropriate tools for studying cement hydration in the presence of different admixtures. A combination of Fourier Transform-Raman and 29 Si nuclear magnetic resonance (NMR) spectroscopy were used here to monitor OPC hydration and C-S-H gel formation with two different waterproofing admixtures. The Q1/Q0 ratio was determined with the former technique to evaluate the influence of the waterproofing substances on C-S-H gel formation rate and intensity, whereas 29Si NMR was employed to establish the relative amount of C-S-H gel formed at different hydration times as well as to calculate the main chain length.

Modelling the coupled evolution of hydration and porosity of cement-based materials

A modelling of the relationship between the evolution of endogenous hydration and that of porosity of cement-based materials was carried out. The mass balance equations of anhydrous and hydrates were written in molecular scale, then, transposed in macroscopic scale by using the volume averaging technique. The combined system of obtained equations (porosity equation and macroscopic mass balances) was solved numerically. The model validation was done in two steps in the case of two mortars cured during 2, 7 and 21 days. Simulation results of hydration rates were compared to the experimental results obtained by SEM images analysis and the theoretical evolution in time of the porosity was checked against MIP results. Globally, a good correlation between simulation results and experimental ones was noticed. However, to less disturbing the hydration process of the material, it seems desirable to improve the drying mode of the samples before SEM analyses or MIP tests.

Hydration evolution of C 3S–EVA composites analyzed by soft X-ray microscopy

The effect of poly(ethylene- co-vinyl acetate) or EVA on the hydration of a pure C 3S was investigated by transmission soft X-ray microscopy in highly diluted systems. EVA particles are readily recognizable by their spherical shape and semitransparency to soft X-rays. Polymeric particles adsorb on the surface of hydrating C 3S grains, and act as nucleation agents in the development of the composite microstructure. The formation of a polymeric film was observed after a few hours of hydration. Fourier-transform infrared spectroscopy supported the conclusions that a highly soluble phase is formed as a result of EVA-hydrating C 3S chemical interactions.

Hydration process and rheological properties of cement pastes modified by orthophosphate addition

The use of cement by nuclear industry for confining low radioactive waste knows a constant increase. The interest bore to this material is due to its mechanical and chemical properties. However, these properties may be modified by the nature and the amount of wastes introduced with the mixing solution especially with large amount of phosphate. Precipitation of hydroxylapatite in the cement paste at the very beginning after mixing was emphasized from a particular concentration of orthophosphate. It was also found that this phenomenon leads to an early rigidification of the cement paste. From a kinetics point of view, the evolution of hydration was both delayed and slowed down according to a pessimum of phosphate concentration. These results indicate a competition between a adsorption process of phosphate on the cement phases which delay the hydration of the cement pastes and a process of precipitation of hydroxylapatite which does not.