Hydration Time Research Articles

Optical Sensing of pH and O2 in the Evaluation of Bioactive Self-Healing Cement.

Leakage from cementitious structures with a retaining function can have devastating environmental consequences. Leaks can originate from cracks within the hardened cementitious material that is supposed to seal the structure off from the surrounding environment. Bioactive self-healing concretes containing bacteria capable of microbially inducing CaCO3 precipitation have been suggested to mitigate the healing of such cracks before leaking occurs. An important parameter determining the biocompatibility of concretes and cements is the pH environment. Therefore, a novel ratiometric pH optode imaging system based on an inexpensive single-lens reflex (SLR) camera was used to characterize the pH of porewater within cracks of submerged hydrated oil and gas well cement. This enabled the imaging of pH with a spatial distribution in high resolution (50 μm per pixel) and a gradient of 1.4 pH units per 1 mm. The effect of fly ash substitution and hydration time on the pH of the cement surface was evaluated by this approach. The results show that pH is significantly reduced from pH >11 to below 10 with increasing fly ash content as well as hydration time. The assessment of bioactivity in the cement was evaluated by introducing superabsorbent polymers with encapsulated Bacillus alkalinitrilicus endospores into the cracks. The bacterial activity was measured using oxygen optodes, which showed the highest bacterial activity with increasing amounts of fly ash substitution in the cement, correlating with the decrease in the pH. Overall, our results demonstrate that the pH of well cements can be reliably measured and modified to sustain the microbial activity.

Color tracing in the hydration process of α-Ca3(PO4)2:Eu

Eu-doped tricalcium phosphate (α-TCP:Eu) powders were obtained via solid-state reaction under air. The phase and microstructures of as-recieved samples and the hydration products soaked in 0.25 M K2HPO4 solution for different time was investigated using X-ray diffraction, SEM and Rietveld refinement method. The photoluminescence results of powders were changed with prolonged hydration time, not only the luminescence intensity of the products gradually depressed, but also the CIE chromaticity coordinates moved from bluish-green region of α-TCP phase to orange region of hydroxyapatite phase. The light emission change was confirmed by the color under the UV lamp. Therefore, results of this study suggested that the photoluminescence color of hydration products can be used as an obvious qualitative feature to trace the hydration process of α-TCP: Eu.

The Behavior of Superabsorbent Polymers (SAPs) in Cement Mixtures with Glass Powders as Supplementary Cementitious Materials.

The absorption and desorption of superabsorbent polymers (SAPs) in cement mixtures containing two different glass powders as supplementary cementitious materials are examined in this paper. Two SAPs with different chemical compositions were synthesized in-house and used in the experiments. SAP absorption was investigated directly through the mass change of SAPs in cement slurries, as well as indirectly using the flow test. Scanning electron microscopy was used to monitor the desorption of SAPs using samples prepared with freeze-drying. Hydration and setting time were evaluated to explain the desorption behavior of SAPs. SAP absorption generally increased in pastes with glass powders. The desorption rate of SAPs in different pastes was shown to correlate with the onset of solid skeleton development in the pastes. The addition of SAPs reduced autogenous shrinkage in neat cement paste more than in pastes with glass powders.

Thermodynamic data for magnesium (potassium) phosphates

Magnesium potassium phosphate (MKP) cements show fast setting and high early strength. MKP cements harden in the presence of water due to the reaction of potassium dihydrogen phosphate (KH2PO4) with magnesia (MgO) resulting in the formation of mainly K-struvite (MgKPO4⋅6H2O). Other hydrates, newberyite, phosphorrösslerite, cattiite and Mg2KH(PO4)2⋅15H2O are formed as intermediate phases during hydration. This paper presents a consistent thermodynamic database for magnesium phosphate hydrates based on solubility measurements for newberyite, phosphorrösslerite, farringtonite, Mg3(PO4)2⋅4H2O, bobierrite, cattiite, K-struvite, KMgPO4⋅H2O, and Mg2KH(PO4)2⋅15H2O carried at different temperature.It was found that the formation of the different hydrates is strongly influenced by pH. Newberyite, phosphorrösslerite and Mg2KH(PO4)2⋅15H2O are intermediate phases, which form at low pH as typical at very early hydration times. As pH rises, bobierrite and cattiite may be stabilised, while at high pH K-struvite forms. The phases formed are also strongly influenced by the temperature.

Combining Ionizing Irradiation and Ultrasound Technologies: Effect on Beans Hydration and Germination.

The present work studied, for the first time, the effect of two technologies on the hydration and germination process of beans: ionizing irradiation and ultrasound. In addition, this work proposed a possible biological effect of ultrasound to describe its effect on grain hydration. Carioca beans were irradiated at doses of 2.3 and 3.8 kGy using γ-rays, establishing different metabolic activities for the beans. Then, they were hydrated with and without the ultrasound technology (91 W/L and 25 kHz) at 25°C. Both the hydration and germination kinetics were evaluated considering the application of both technologies alone and in combination. As results, irradiation did not significantly affect (P>0.05) the hydration rate, the equilibrium moisture, or the lag phase time, but ultrasound affected them, reducing 50% of the processing time. On the other hand, only the equilibrium moisture was slightly reduced by the interactive effect of irradiation and ultrasound technology, which was discussed based on different metabolism levels. Furthermore, the germination process of carioca bean was hindered by both the studied variables, reducing its germination capacity to 0% in some cases. Therefore, by studying the effect of ultrasound on beans with different active metabolism (due to different irradiation doses), it was suggested that both physical and biological mechanisms are involved during hydration process and that both can be affected by ultrasound. Further, irradiation could be used on carioca beans with objectives such as avoid germination, insects, and microorganism's growth, without an important effect on the hydration kinetics. PRACTICAL APPLICATION: Ultrasound technology has demonstrated to accelerate the soaking process of several legume grains. However, sometimes, grains are irradiated for disinfestation purpose to improve their shelf life. Indeed, irradiation can change the grain properties as the cooking time, hydration time, and germination capacity. Therefore, this work verified if irradiation changes the desirable effect of ultrasound on grain processing: soaking and germination. Moreover, this work novelty is also based on describing the phenomena: by proposing a possible biological effect, further approaches to improve the grain processing can be achieved.

Novel low-cost shrinkage-compensating admixture for ordinary Portland cement

This work proposes a low-cost and eco-friendly shrinkage-compensating admixture (SCA) composed of an Al-rich waste and calcium sulfate for cement-based binders. The hydration process and microstructural changes of cement pastes with the proposed SCA were investigated by means of isothermal conduction calorimetry, X-ray diffraction, differential thermal and thermogravimetry analysis, elastic modulus and compressive strength tests for several hydration times. Length changes were also followed for 7 days. The main results revealed that the cement pastes with the proposed SCA expand between the first and third day of hydration enough to mitigate the shrinkage of cement pastes. SEM micrographs and X-ray patterns suggest that the expansion is managed through the nucleation and growth of needle-like crystals of ettringite.

Portland limestone cement for reduced shrinkage and enhanced durability of concrete

In this work, different cementitious systems were used to investigate the shrinkage of concrete under plastic and drying conditions. Emphasis was placed on Portland limestone cement (type IL) with replacement amounts of 10% of Portland cement. Comparisons were made with a cement type with low Blaine fineness (i.e. coarse ground cement). The results indicated that type IL cement has good shrinkage results without adversely affecting other engineering properties of concrete such as strength, resistivity, degree of hydration and setting time. This is probably due to improved particle packing, access to more nucleation sites for the hydration products and the formation of calcium carbo-aluminate hydrates. Scanning electron micrographs of coarse ground cement paste also indicate a retarded degree of hydration compared to type I/II Portland cement paste.

Effects of microstructure and pore water on electrical conductivity of cement slurry during early hydration

In this study, inductance-type electrical conductivity measurement (IECM) was performed to study the electrical conductivity of different formulations of cement slurry. Low-field nuclear magnetic resonance, in situ X-ray micro-tomography, and environmental scanning electron microscopy were used to investigate the effects of the microstructure, pore characteristics, and pore water of cement slurry on its electrical conductivity. Experimental results showed that the pore characteristics and ion concentration governed the initial electrical conductivity of fresh cement slurries. The sedimentation stability of fresh cement slurries increased the number of interconnected pores, and the initial electrical conductivity increased from 16.8 mS/cm to 19.4 mS/cm. When the CaCl2 accelerator content was 2 wt%, the initial electrical conductivity of the fresh cement slurry increased to 26.9 mS/cm, while the electrical conductivity rapidly decreased with the formation of hydration products. With increasing hydration time, large amounts of hydration products were formed in the pores, which changed the microstructure and pores of the cement slurry from connected large volume pores to many small volume pores and subsequently changed the distribution of pore water. The experimental results revealed that the connected porosity of the cement slurry was proportional to the electrical conductivity. An exponential relationship was found between the electrical conductivity and the evaporable water content, whereas a linear relationship was found between the electrical conductivity and the free water content.

Heat Emission Kinetics and Hydration Behavior of Modified Polymer–Cement Mixtures for 3D Printing Construction

Abstract—The process of heat emission is investigated during the hydration of the binder in polymer–cement mixtures and mixtures modified by phloroglucinol–furfural superplasticizer. The specific binder hydration enthalpy in the presence of a polyvinyl acetate dispersion and redispersible polymer powder is determined. It is established that the specific enthalpy of polyvinyl acetate polymer–cement systems is positive, which indicates the endothermic nature of the overall process. The dependence of the absolute heat emission values in the initial periods of material hardening on the binder hydration time in the presence of organic mixture components (polyvinyl acetate and phloroglucinol–furfural modifier) is studied. It is proved that, when modifying polymer–cement systems, there is a decrease in the heat emission peak, a reduction in the timing of the initial hydration period, and an increase in the duration of the second (induction) period. The heat emission kinetic curves of the modified polyvinyl acetate–cement mixtures are presented, and the hydration behavior of the studied systems is considered. It is established that, in the initial period of hardening, polyvinyl acetate increases and phloroglucinol–furfural superplasticizer reduces the heat emission rate, while when modifying the polymer–cement system with a polymer in the form of a polymer dispersion, this process is partially balanced.

Investigating the application of reactive polymers in fluid loss control

Water reactive polymers are rapid setting fluids that exhibit high viscosity after being exposed to water to control severe fluid loss. In this study, the performance of a water reactive polymer is studied through a series of fluid loss experiments. Various unconsolidated and permeable formations were simulated using different sand size grades, with the change in permeability being recorded after applying the reactive polymer under different operating conditions. The results showed 62–100% permeability reductions depending on the initial value of permeability and operating conditions. In addition, the setting time of the reactive polymer was obtained at different water concentrations and temperatures by monitoring the viscosity of the reactive polymer using a Brookfield viscometer. The results indicate that a hydration time of 30 min is satisfactory to reach an acceptable viscosity for all hydration volumes tested. At lower hydration volumes, the viscosity increased rapidly at the same rate and reached the same maximum viscosity. As hydration volume increased, both the rate of increase and maximum viscosity were reduced.

Influence of Nano-SiO2, Nano-CaCO3 and Nano-Al2O3 on Rheological Properties of Cement-Fly Ash Paste.

Rheological curves of cement–fly ash (C–FA) paste incorporating nanomaterials including nano-SiO2 (NS), nano-CaCO3 (NC) and nano-Al2O3 (NA) at different resting times (hydration time of 5 min, 60 min, and 120 min) were tested with a rheometer. The rheological behaviors were described by the Herschel–Bulkley (H–B) model, and the influences of these nanomaterials on rheological properties of C–FA paste were compared. Results show that the types, content of nanomaterials and resting time have great influences on the rheological properties of C–FA paste. Incorporating NS and NA increases yield stress and plastic viscosity, and decreases the rheological index of C–FA paste. When the content of NS and NA were 2 wt%, the rheological index of C–FA paste was less than 1, indicating rheological behavior changes from shear thickening to shear thinning. Meanwhile, with rising resting time, yield stress and plastic viscosity increased significantly, but the rheological index decreased evidently, showing paste takes on shear thinning due to the rise of resting time. However, incorporating 3 wt% NC and the rising of resting time did not change the rheological properties of C–FA paste. These differences are mainly that the specific surface area (SSA) of NS (150 m2/g) and NA (120 m2/g) are much larger than that of NC (40 m2/g). The huge SSA of NS and NA consume lots of free water and these tiny particles accelerate the hydration process during resting time.

Insights on ions migration in the nanometer channel of calcium silicate hydrate under external electric field

In this study, molecular dynamics is utilized to investigate on the migration of NaCl solution in the nanochannel of calcium silicate hydrate under external electric field ranging from 0 to 0.05 V/Å. The generated ionic current and flux are linearly related with the electric field intensity. While the directional movement of Cl− ions accounts for more than 85% of the ion currents, the migration of Na+ ions and Ca2+ contributes little percentage to the ionic current. The little contribution from cations is attributed to that the silicate chains near the C–S–H surface provide plenty of the oxygen sites to associate with the cations by forming Na–Os and Ca–Os bond, immobilizing the migration of the cations. However, the external electric field can weaken the bond stability of the Na-Osand Ca-Osbond, which can be proved from the hydration time of the ion-water cluster and the resident time of ions in the silicate chains. Furthermore, the ions accelerating effect induced by the external field is dramatically retarded by the nanoconfinement. The diffusion coefficient of ions ultra-confined in 3.4 nm and 5.6 nm pores is 3 magnitudes lower than the mobility of ions in the bulk solution. Due to the different H-bond and ionic bond restriction from the C–S–H substrate, the mobility of Na, Cl and Ow ranks in the following order: Cl > Ow > Na, unlike the same transport rate of solution species in the bulk solution. The results obtained from this work may help clarify the diffusion mechanism of ions in concrete structures during the electrochemical desalination processes and is helpful for the design to improve durability of materials.

Expedited Resolution of 5-Fluorouracil-Induced Erythema and Barrier Dysfunction with White Petrolatum

Actinic keratoses (AK) are precancerous lesions that develop on chronically sun-exposed skin. They frequently require prophylactic field treatment due to the risk of progression to squamous cell carcinoma. Topical treatment with 5-fluorouracil (5-FU) yields near complete AK resolution, yet leaves a patient with an exuberant erythematous treatment site, which may be embarrassing and/or uncomfortable. We report a case of a patient with diffuse facial AK who was treated with 5-FU twice daily for 2 weeks, resulting in fiery-red erythema and disrupted barrier indices. Application of pure ultra white petroleum jelly, an emollient preferred by dermatologists for post-operative wound healing, resulted in drastic decreased erythema and recovery time of post-treatment transepidermal water loss and hydration, compared to the contralateral, non-petrolatum-treated side. Additionally, petrolatum use did not disrupt the AK resolution endpoint. We suggest that petroleum jelly be used for the repair of 5-FU-induced barrier disruption and erythema to promote greater patient adherence.

Effects of graphene oxide on the hydration behavior of ye’elimite

The research on the cement hydration with graphene oxide (GO) can provide a guidance for designing GO-modified cement-based materials. Ye’elimite is the dominant mineralogical phase in calcium sulfoaluminate cement. However, an in-depth understanding of GO on the hydration behavior of ye’elimite is still lacking. Here, we demonstrate the influences of GO on the hydration process and products of ye’elimite. Firstly, GO was successfully coated on the surface of ye’elimite and then the hydration development of ye’elimite was investigated by iso-thermal calorimetry and X-ray diffraction. The results revealed that the hydration time of ye’elimite moved up at first and delayed later with the increasing amounts of GO. The addition of GO could enhance the hydration degree of ye’elimite and promote the formation of monosulfate. The complexation effect of Ca2+ and –COOH group played a negative role in the formation of ettringite. This study provides a promising way for employing GO to regulate the hydration of ye’elimite.

Voids effect on the swelling behaviour of compacted bentonite

This paper investigates the swelling behaviour of compacted MX80 bentonite under hydration with the presence of initial voids that simulate the technological voids in real nuclear waste repositories. With water introduced into samples from the initial voids, the swollen bentonite first filled up the initial voids, and then swelling pressure was generated. At different hydration times, the microstructure was investigated at different heights (initial void, top, middle and bottom) using mercury intrusion porosimetry, together with the determination of dry density, water content and suction. It was observed that the microstructure was characterised by the presence of a large- and a small-pore families at bottom and middle layers, but by the creation of a new medium-pore family with dominant pore mode around 0·04–2 μm at the top and initial void layers after the void space was filled by swollen bentonite. From bottom to void, the significant increase in medium pores was accompanied by an increase in inaccessible pores and a decrease in large and small pores. Further examination showed that the sample could be divided into compression and swelling zones based on the variation of void ratio with swelling pressure: at the compression zone, the soil was compressed over time, characterised by a significant reduction of medium and large pores; whereas at the swelling zone, the soil was still undergoing swelling, represented by the increase of inaccessible pores and medium pores. In addition, the changes in microstructure along the sample were found to be well correlated with changes in dry density and water content: the water content was decreasing and the dry density was increasing from the initial void to the bottom positions; over time the dry density of the upper part was increasing due to compression, while the dry density of the lower part was decreasing due to swelling. This provided evidence for the main mechanism of compacted bentonite swelling with the presence of technological voids: the swollen bentonite fills the initial voids first and then undergoes compression by the swelling of the bentonite behind.

A study on effect of silica fume and surface penetrant on bonding strength for overlaying

Currently, concrete structures are at risk of deteriorating conditions due to their exposure to various severe environments. Repairing and strengthening these structures is a better solution than replacing them by new constructions. As a retrofitting method, the top/bottom surface overlaying or jacketing method is commonly used around the world. In this method, polymer cement mortar (PCM) is sprayed/troweled onto the surfaces of concrete, and PCM adhesive strengthens the concrete structures. However, the concrete-PCM interface is considered to be the weakest part of a structure, and it may cause brittle fracture. This study focused on how this interface can be strengthened more effectively to prevent brittle fractures and investigated the effects of applying surface penetrant and silica fume from the perspective of chemical reactions. In addition, the reaction time relationship between PCM hydration and surface penetrant application time is also investigated based on a preliminary experiment. Mixing silica fume into PCM was conclusively found to strengthen the interface bonding strength in some conditions. Applying surface penetrant to an interface could decrease the interface strength if the application time was inappropriate. However, the results of an application time experiment indicated that it is possible to strengthen the interface via the surface penetrant.

Spectroscopic Determination of Optimal Hydration Time of Zircon Surface

When a mineral surface is immersed in an aqueous solution, it develops an electric charge produced by the amphoteric dissociation of hydroxyl groups created by the hydration of the solid surface. This is one influential surface property. The complete hydration process takes a time which is specific for each mineral species. The knowledge of the aqueous solution contact time for complete surface hydration is mandatory for further surface phenomena studies. This study deals with the optimal hydration time of the raw zircon (ZrSiO4) surface comparing the classical potentiometric titrations with a fluorescence spectroscopy technique. The latter is easy and reliable as it demands only one sample batch to determine the optimal time to ensure a total hydration of the zircon surface. The analytical results of neutron activation analysis (NAA) showed the presence of trace quantities of Dy3+, Eu3+ and Er3 in the bulk of zircon. The Dy3+ is structured in the zircon crystalline lattice and undergoes the same chemical reactions as zircon. Furthermore, the Dy3+ has a good fluorescent response whose intensity is enhanced by hydration molecules. The results show that, according to the potentiometric analysis, the hydration process for each batch (at least 8 sample batches) takes around 2 h, while the spectrometric method indicates only 5 min from only one batch. Both methods showed that the zircon surface have a 16h optimal hydration time.

Molecular dynamics study onwater and ions on the surface of graphene oxide sheet: Effects of functional groups

Water and ions in the vicinity of grapheme oxide (GO) sheet has achieved much interest recently because of its great potential applications in building grapheme nanocomposites. In this study, molecular dynamics was utilized to study the structural, dynamical and interfacial behavior of calcium and sulfate ions in the vicinity of GO sheet. To better understand the effects of surface properties on the behavior of ions, four surface types were modeled, including graphene sheet (G), GO with carboxylate (GOCOO−, deprotonated carboxyl), GO with carboxyl (GOCOOH) and GO with hydroxyl (GOOH). We found that the presence of oxygen-containing functional groups restrained the layered packing of water molecules, reduced the water density and changed the dipolar angle distribution in the vicinity of graphene sheet. The OH bond of water molecules preferred to orientate toward the graphene sheet due to the surface hydrophilicity. With increasing polarity of the functional groups, more surface water molecules donated their H to the oxygen sites provided by the COO−, COOH and COH. Moreover, the adsorption properties of calcium and sulfate ions were greatly depended on the polarity of GO surface. The adsorption ratios of ions were arranged in the following order: GOCOO− > GOCOOH > GOH > G. The GO sheets immobilized the calcium ions by forming the Ca-O ionic bond with the functional oxygen atoms. The strength of CaO interaction was increased with the increasing polarity of functional groups, which was characterized by the time correlation function. The adsorbed surface calcium ions can further immobilize the sulfate ions by forming CaSO4 ionic pair. Comparing with the water and ions near the graphene sheet, the diffusivity of solution on the GOCOO− surface decreased by 73%. The dramactical reduction of the mobility was attributed to longer resident time of ions on the GO surface and longer hydration time of the ions. Hopefully, this study can provide valuable insights on the functional GO sheet design. This study can contribute to the molecular understanding of the immobilization mechanism of GO sheets.

Fringing Field Impedance Sensor for Hydration Monitoring and Setting Time Determination of Concrete Material

This paper deals with the development of a simple, low-cost, fringing field impedance sensor suitable for early age hydration monitoring and setting time determination of hydraulic cement paste. An impedance technique using a double-sided copper-cladded printed circuit board substrate as a sensor is proposed. Different batches of sensors with different probe sizes and substrate thickness have been fabricated and tested for hydraulic cement paste. The cement samples having different water-to-cement ratios (w:c) by weight are considered to study the effectiveness of the sensor. The purpose of this study is to develop a simple yet effective measurement system to determine the change in impedance of the cement paste with hydration time and thus to correlate the impedance change to determine the critical initial and final setting times. Initial and final hydration times of different cement samples are compared with the results of the commercial Vicat apparatus (VA). The values of the setting times closely match the Vicat values (the average value at 100 kHz differs by 4 m). Therefore, the proposed sensor-based system can be used in place of conventional VA to determine the hydration condition. The output of the sensor can be electronically processed further to develop a prototype system.

Kinetic modelling of polyphenol degradation during common beans soaking and cooking

Phenolic compounds are phytonutrients with anti-inflammatory attributes that are significant for brain, heart and gut health. Losses of natural phenolic compounds in foods occur due to degradation during processing. The extent of degradation depends on the processing conditions applied. In this study, the degradation of total phenolic compounds during the processing of common beans (Phaseolus vulgaris L.) cultivars was investigated. The effects of soaking time, soaking water temperature and cooking conditions on polyphenol degradation were examined. The total phenolic compounds were determined as gallic acid equivalents. The result shows that increase of hydration time and process water temperature significantly (p < 0.05) increased polyphenol degradation. There was a strong positive Pearson correlation (r > 0. 85) between the rate of water uptake and polyphenol degradation regardless of the water temperature and cultivar. The rate of degradation varied from 0.041 – 0.098 and 0.014–0.069 mg/g per hour for Kabulangeti and Maine cultivar, respectively. The addition sodium chloride (NaCl) and potassium carbonate (K2CO3) during cooking to soften the beans significantly increased the degree of degradation. The activation energy for degradation was estimated as 45.4 and 26.3 kJ/mol for Kabulangeti and Maine cultivar, respectively.