Early Stages Of Hydration Research Articles

Functionality of silica nanoparticles on hydration mechanism and microstructure of tricalcium aluminate

In this paper, a detailed reaction mechanism of tricalcium aluminate (C3A) in presence and absence of silica nanoparticles (SNPs) within 24 hr of hydration was studied. The effect of SNPs on an early stage of hydration was assessed through XRD (mineralogical analysis), TGA (quantification of hydrated products), FTIR (analysing chemical bonding) and FESEM (morphological study). The results indicate that SNPs promote C3A hydration at the very early stage of hydration (10 min of hydration), after that retardation in C3A hydration was observed and the pattern of reaction is consistent up to 24 hr of hydration. The retardation might be due to the surface coverage of C3A grain by calcium silicate hydrate (C-S-H) and calcium alumina silicate hydrate (C-A-S-H), thus, the reactivity of C3A decreases. This study presents a detailed inside reaction mechanism of C3A hydration with SNPs, which will help in understanding the influence of other admixtures (such as superplasticizers, accelerators and retarders) in SNPs modified cementitious system.

Synergistic use of sodium bicarbonate and aluminum sulfate to enhance the hydration and hardening properties of Portland cement paste

A novel composite admixture (N-A admixture) including sodium bicarbonate (NaHCO3) and aluminum sulfate (Al2(SO4)3) was developed for the in situ generations of calcium carbonate (CaCO3) nano-reinforced particles in Portland cement paste. The effect of N-A admixture dosage (0%, 1%, 2%, 3%, 4%, 5%) on the hydration and hardening properties of Portland cement paste such as setting time and compressive strength was systematically investigated. The enhancement mechanism of the N-A admixture was also revealed by using XRD, TGA, SEM, MIP, and ICC. The results indicated that the N-A admixture can effectively accelerate the hydration reaction process of Portland cement paste and shorten its setting time. When the N-A admixture was added at 3%, the compressive strength at 1 day was 86.9% higher than that of the control Portland cement paste, and there was no inversion of strength at 90 days. N-A admixture promoted the formation of more hydration products. At the early stage of hydration, in situ CaCO3 with a grain size ranging from 25.53 to 42.98 nm was generated, the amount of which increased with the addition of N-A admixture. Moreover, the in situ CaCO3 also reacted with the aluminum phase to form mono-carbonate (Mc) in the late stage, which effectively reduced the proportion of large pores, resulting in a dense microstructure of the hardened Portland cement paste. The results of this work provide a novel and facile method for the generation of in situ CaCO3, which can be used to greatly improve the performance of cement concrete.

Formation and hydration of eco-friendly cement using industrial wastes as raw materials

In this work, the optimal conditions of the synthesis of eco-friendly cement by using industrial wastes as well as the peculiarities of its early stage hydration were investigated. The eco-friendly cement was synthesized within the 1000–1250 °C temperature range when the targeted composition was 60% of belite, 20% of ye’elimite, and 20% of brownmillerite. It was determined that the optimal sintering temperature for eco-friendly cement is 1100 °C because the primary compounds were fully reacted, and hydraulic active compounds were dominant in the products. Microcalorimetry analysis was performed for the investigation of early stage hydration. The best results of hydration were obtained with the eco-friendly cement which was produced by using mixtures with silica gel waste: three exothermic reactions were observed in the heat evolution curve, while the cumulative heat was equal to 264 J/g after 72 h. Additionally, the sequence of compounds formation during the first day of hydration was analyzed. It was determined that the composition of the initial mixture impacts the hydration rate of synthetic eco-friendly cement; however, it did not affect the mineralogical composition of the hydration products. These results were confirmed by XRD, STA, and SEM analysis.

Turning sandstone clay into supplementary cementitious material: activation and pozzolanic reactivity evaluation

The present paper explores the methods of transforming low grade kaolinitic clay, sandstone clay, into supplementary cementitious material (SCM). The sandstone clay is the waste product in the sand manufacturing from sandstone mineral. Thermal calcination at 600–900 °C was applied to activate the initial sandstone clay. Microstructure characterization was then carried out on the obtained activated sandstone clays (ASCs) to study the microstructure and chemical changes during the thermal activation. The pozzolanic reactivity of ASCs were assessed by direct methods (isothermal calorimetry test and lime consumption test) and indirect method (strength measurement of ASC blended mortar). The compressive strength of the ASCs blended cement based mortar showed that ASCs possessed high pozzolanic reactivity through the dehydroxylation and the alternation of Al and Si coordination environments during thermal activation. Agglomeration occurred after the sandstone clay calcination, however the particle size was reduced. Even at a short time calcination for 1 h, the pozzolanic reactivity of ASCs improved as the calcination temperature increased from 600 to 900 °C. Mortar strength test results confirmed that the ASCs with a fineness similar to OPC, can be used as high quality SCMs. Further isothermal calorimetry results indicated that ASCs not only contributed to pozzolanic reaction but also had a good filler effect in the early hydration stage due to the existence of micro-quartz.

Synthesis and evaluation of a new type of oil-well cement temperature-resistant retarder

Theretardercitricacidusedinoilwellcementhasthedisadvantagesofsensitivedosageandlowearlystrength. In order to overcome this disadvantage, citric acid was used as chelating agent, metal nitrate and ethylene glycol were selected as reactant materials, and an orthogonal test was used to synthesize a new metal chelate-type retarder in this paper. The experimental results show that the optimum conditions for MCR synthesis are: mass ratio of Ca/Al/Fe nitrates of 14:3:1, reaction temperature of 60 ℃, and reaction time of 12 h. MCR is temperature resistant, and can easily control the thickening time and has less impact on the compressive strength of cement slurry. The 7 days strength of cement slurry with MCR exceeded 22 MPa, which also meets the construction requirements. In addition, combined X-ray diffraction and thermogravimetric analyses to elucidate the retardation mechanism of MCR show that MCR effectively inhibits the formation and growth of Ca(OH)2 crystals in the early stage of cement hydration.

Hydration Modification of Cement in the Presence of Diethanol-Isopropanolamine

In this investigation, calorimetry, quantitative X-ray diffraction analysis and the scanning electron microscopy were applied to explore the mechanism of hydration modification of cement with diethanol-isopropanolamine (DEIPA). It showed that the addition of DEIPA favoured the strength development on 3 and 28 days, but was undesirable for the 1d strength. The reason for this was that the dissolution of intermediate phase being promoted by DEIPA participated in the aluminate reaction interrupting the normal hydration of C3S. Appropriate adjustment on SO3 content in the cement was able to slow down the rate of aluminate reaction allowing C3S to react in a right fashion, which gave an optimum strength enhancement at early ages. The addition of DEIPA also impacted the formation of hydrates. Significant differences can be recognized in quantities, chemical compositions and the morphologies of hydrates in blank sample and the DEIPA-dosing ones. With the help of SO3 adjustment in cement with DEIPA, a great number of hydro-sulfoaluminates precipitated at the early stage of hydration to decrease the porosity of hardened cement pastes, which contributed to the strength gain of cement.

Influence of the Concentration of Seawater on the Early Hydration Properties of Calcium Sulphoaluminate (CSA) Cement: A Preliminary Study

This research investigates the effect of seawater of different concentrations on the hydration process and microstructure of calcium sulphoaluminate (CSA) cement. It studies the CSA cement pastes via experiments carried out to determine the initial and final setting times, mechanical strength and chemical shrinkage with X-ray diffraction (XRD), scanning electron microscopy (SEM) and simultaneous differential thermal-thermogravimetric (DTA-TG) analysis. The DTA-TG and XRD results showed that the main hydration products were ettringite (AFt) and aluminum hydroxide in the CSA cement paste mixed with both freshwater and seawater, while a small amount of ettringite (AFt) became monosulfate (AFm) in the freshwater-mixed CSA cement. The SEM results demonstrate that seawater can improve the microstructure of CSA cement paste in the early stage of hydration (1 d) but impairs the microstructure of the CSA cement matrix in the later stage of hydration (7 d). The experimental results also indicate that a high concentration of seawater can extend the setting time, increase the chemical shrinkage and decrease the mechanical strength of CSA cement.

Effect of pre-introduced sodium chloride on cement hydration process

Chloride-based accelerators are widely used to accelerate cement hydration; however, there is no focus on the effect of the interaction between Cl− and SO42− on cement hydration. Hence, the interaction effect between initial gypsum and sodium chloride (NaCl) in the cement hydration process was investigated. Isothermal calorimetry, scanning electron microscopy, thermogravimetric analysis, X-ray diffraction and inductively coupled plasma spectroscopy were used to evaluate the hydration process of cement paste. Moreover, a thermodynamic model and boundary nucleation and a growth model were applied to calculate the hydration products and describe the hydration process, respectively. It is clear that sodium chloride can accelerate cement hydration, but as the incorporated sodium chloride increases, the acceleration effect is weakened. The incorporation of chloride salts will promote the dissolution of minerals and increase the growth rate. In the early stage of hydration, the formation of ettringite precedes formation of Friedel's salt, owing to the fact that tricalcium aluminate (C3A) favours binding with SO42−, which can be demonstrated by the change in ion concentrations and the evolution of hydration products. The formation of Kuzel's salt depends not only on the chloride concentration but also on the hydration time.

Beneficial effect of nanomaterials on the interfacial transition zone (ITZ) of non-dispersible underwater concrete

Non-dispersible underwater concrete (NUC) is a kind of widely used construction engineering material. It has added flocculant so that concrete can have the characteristics of inhibiting dispersion of cement and aggregate in an underwater environment. However, soluble salts (such as sodium chloride and calcium sulphoaluminate) in seawater can infiltrate the interfacial transition zone (ITZ) of concrete, and then the ionic binding ability of the crystal surface will be reduced, which will cause mass loss of bonding materials in an ITZ and lead to the reduction of mechanical properties of concrete. In order to solve the problem of weak mechanical properties of ITZ, in this study, the influences of three types nanomaterials (nano-SiO2, nano-metakaolin and nano-Al2O3) were studied. These materials were added into concrete to improve the bond and hardness strength of ITZ, which could be characterized by a push-out test, nano indentation test, X-ray diffraction (XRD) and scanning electron microscope (SEM). The results indicated that the nano-SiO2 and nano-metakaolin could significantly increase the bond strength of ITZ at 3 d by 134.12% and 87.70%, respectively, and by 108.54% and 43.41%, respectively, at 28 d). When the addition of nano-SiO2 and nano-metakaolin was 3%, the modulus of ITZ was improved by 54.39% and 71.03%, respectively, compared with plain NUC. The XRD data displayed the fact that nanomaterials could promote the formation of calcium hydroxide (CH) at early stage of hydration, while they had a pozzolanic effect on the reduction of content of CH at later stage of hydration. The nano-SiO2 and nano-metakaolin could obviously improve the microscopic morphology. This study revealed that nano-SiO2 and nano-metakaolin could effectively enhance mechanical properties of NUC, thus enhancing anti-erosion and anti-scouring ability of NUC. It is believed that these findings could fulfill a better understanding of the role of nanomaterials in NUC.

Microstructural characterization of cement in the presence of alkanolamines

In order to understand the potential issues regarding the cement performance over time in the presence of alkanolamines, such as triethanolamine (TEA) and triisopropanolamine (TIPA), this investigation provided a series of quantitative phase characterization to monitor the hydration and microstructure of cement pastes. The addition of 0.02 % alkanolamines to cement promoted the strength development and altered the hydration kinetics at early ages. The aluminate reaction was greatly promoted, which resulted in the formation of hydrosulfoaluminates with a high monosulfoaluminate-to-ettringite ratio due to the facilitated dissolution of the intermediate phase. The morphology and chemical composition of the hydrates, as well as the porosity of the pastes, were also influenced by the altered hydration kinetics. Particularly, TIPA markedly reduced Si/Ca ratio (from 0.61 to 0.51) and increased Fe/Ca ratio (from 0.016 to 0.036) in the C-S-H gel at the early stage of hydration. Based on the variations in microstructural features subjected to the alkanolamines, the durability and long-term performance of the cement, including the phase variation, resistance to sulfate or chloride ingression and volume stability, were discussed.

Effect of nano-metakaolinite clay on the performance of cement-based materials at early curing age

The aim of this study is to improve the physical and mechanical properties of cement-based materials by adding nanometakaolinite clay (NKC). The results show the mechanism by which NKC modifies cement-based materials at the microscale level. A comparative experimental analysis of micromorphology and pore structure of cement specimens with NKC prepared using different NKC dispersion methods was performed to investigate the influence of the dispersion method and time on the dispersion of NKC in cement slurry. This showed that NKC can be efficiently dispersed in cement slurry by ultrasonic dispersion and stirring lasting 15 min, providing the most significant improvement to the cement pore structure. A large number of Ca(OH)2(CH) crystals in the early stage of hydration of cement are transformed into closely packed calcium silicate hydrate gel, thereby increasing the compactness of the cement matrix. After 28 days of standard curing, the CH crystal content in the hardened cements paste containing 5% of NKC by weight of cement was 12.72% lower than that of ordinary cement paste. The microscale analysis of the hardened cement paste showed that NKC can effectively fill the internal pores of cement-based materials, optimize the pore structure, and significantly improve the microscale compactness. NKC can also effectively improve the early mechanical properties of hardened cement paste. After curing for three days, the bending strength of cement paste prepared with 3% of NKC was 14.97% higher than that of ordinary cement paste. The compressive strength of hardened cement paste with 5% NKC addition was 15.13% higher than that of ordinary cement paste. During the ring test, the cracking time of cement mortar with NKC was earlier initiation and its surface stress–strain increased rapidly. Adding NKC increased the brittleness of hardened cement paste, which increased the risk of early age cracking.

Properties and hydration mechanism of cement pastes in presence of nano-ZnO

Nano-ZnO could delay the setting and the hardening of cement pastes but promote the later cement hydration, which made it an ideal inorganic retarder in cement based materials. In this research, properties and structures of fresh and hardened cement pastes containing nano-ZnO (CZ) were tested. Early hydration of CZ was greatly delayed and its early mechanical performances were decreased. However, the 28 days compressive strength of CZ with 0.1 wt% nano-ZnO was slightly higher than that of blank paste. Nano-ZnO was rapidly dissolved in alkaline environment to form the amorphous Zn(OH)2 in the early hydration stage, the deposition of Zn(OH)2 layer on the surface of clinker particles would block the early hydration. With the processing of cement hydration, as-formed Zn(OH)2 would be further reacted with Ca(OH)2 to generate intermediate Ca(Zn(OH)3)2·2H2O, which broke the Zn(OH)2 coatings and promoted the cement hydration in this period. In addition, the coarsening of capillary pores ranged from 5 nm to 50 nm in hardened CZ matrix was observed, which was presumed to be responsible for the autogenous shrinkage reduction of CZ pastes.

Direct Observation of Carbonate Formation in Partly Hydrated Tricalcium Silicate by Dynamic Nuclear Polarization Enhanced NMR Spectroscopy

Solid-state NMR combined with dynamic nuclear polarization (DNP NMR) is used to study hydration processes in tricalcium silicate (Ca3SiO5, abbreviated as C3S) samples. The studied C3S samples have experienced early stage hydration (1–30 h) and slow aging (9 years) processes. The appearance of Q3 and Q4 lines in the 29Si MAS and 1H → 29Si CP MAS NMR spectra obtained for partly hydrated C3S samples indicated the formation of amorphous silica which corresponds to their carbonation, which was corroborated by complementary FTIR data. Significant DNP signal enhancements obtained for the studied samples allowed to further investigate the C3S carbonation process in detail employing the 1H → 29Si CP MAS FSLG HETCOR technique. Finally, DNP enhanced 1H → 13C CP MAS and 1H → 13C CP MAS FSLG HETCOR techniques enabled to directly observe the formation of carbonate moieties in partly hydrated C3S samples.

The Relation between Concrete, Mortar and Paste Scale Early Age Properties.

Microstructure development of concrete, mortar, and paste scale of cement-based material (CBM) during the early hydration stage has a significant impact on CBM’s physical, mechanical, and durability characteristics at the high maturity state. The research was carried out using compositions with increased autogenous shrinkage and extended early age period, proposed within the RRT+ programme of the COST Action TU1404. The electrical conductivity method, used to follow the solidification process of CBM, is capable of determining the initial and final setting time, and the end of the solidification process acceleration stage for the paste and mortar scale. Simultaneous ultrasonic P- and S-wave transmission measurements revealed that the ratio of velocities VP/VS is highly dependent on the presence of aggregates—it is considerably higher for the paste scale compared to the mortar and concrete scale. The deviation from the otherwise roughly constant ratio VP/VS for each scale may indicate cracks in the material. The non-linear correlation between the dynamic and static elastic moduli valid over the three scales was confirmed. Additionally, it was found that the static E-modulus correlates very well with the square of the VS and that the VS is highly correlated to the cube compressive strength—but a separate trendline exists for each CBM scale.

Influence of milling of a reused FCC catalytic waste on the early hydration stages of a special class cement

This work investigates the influence of milling on the physical, chemical and mineralogical properties of a catalyst residue (Recat) after being reused in a second Fluid Catalytic Cracking process (FCC). The effect of milling this waste in a planetary ball mill for different times on the hydration process is also evaluated as partial replacement of a special cement for oil wells. Six pastes were prepared, one for reference and five others containing Recat milled for different times, replacing the cement mass by 15%. The water/solids ratio remained constant and equal to 0.5. The hydration process was evaluated by isothermal calorimetry during the first three days of hydration. The characterization of the pastes at the end of this period was done by thermogravimetric analysis (TG/DTG), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The results showed that the milling of Recat improves its reactivity in cementitious pastes, favoring not only pozzolanic activity, but also nucleating action. It was noticed that nucleating and pozzolanic effects occur simultaneously and, that thermogravimetry actually shows only the resulting effect on CH content. As a consequence, when the paste was composed by the less milled Recat, their pozzolanic action during the first three days was higher than their nucleating effect and the opposite was noticed in the pastes prepared with most milled Recat. This was only possible to detect analyzing by thermogravimetry all the pastes also after 28 days of hydration, when the pozzolanic action of the finest Recat particles overcame their early age nucleating effect.

Behaviour of nanocrystalline tricalcium silicate-based cements at early stages of hydration

Tricalcium silicate-based cements (TCS-BC) have reached great relevance in modern dentistry, where they are used in root-end filling or perforation repair treatments, and also for restoring deep and/or voluminous coronary carious lesions, among other applications. In some TCS-BC such as BiodentineTM, the physical and chemical properties, e.g. high compressive strength, have led to consider this cement as a dentine substitute. One of the drawbacks of BiodentineTM is its very high washout; which refers to the tendency of disintegrate at initial stage of hydration upon early contact with blood or other fluids, just at the moment after it is still as a freshly prepared paste. The present research was focused to compare properties related to workability and hardening at early stages of hydration of experimentally synthetized nano-sized tricalcium silicate (nTCS) and BiodentineTM (BIOD). Both pastes were tested for hardening at 0, 1, 2 and 3 h of hydration, using a penetration test adapted from standards D3441-79 and D1558-84. The hydrated products were evaluated by X-ray diffraction (XRD), thermogravimetry (TG) and 29Si NMR spectroscopy; pH measurements were taken along 28 days of hydration. The set cement pastes were evaluated for sealing ability and microleakage. Following literature reports, the CSH phase as a hydration product, was identified and modeled in both cements as defective clinotobermorite Ca11Si9O28(OH)2·8.5H2O. The CSH phases obtained differ from each other by its microstructural arrangement and packing densities, which depend on the w/c ratio of nTCS and BIOD pastes, which were 0.5 and 0.36 respectively. The hardening of BIOD is significantly influenced by its w/c ratio with a hydration fluid that presumably contains about 0.05% of polycarboxylate-based superplasticizer, which was identified by Raman spectroscopy. The washout and hardening properties were pictured by and scheme for flocculation, w/c ratio, and packing density of the CSH particles characterizing the cement pastes.

Hydration properties and kinetic characteristics of blended cement containing lithium slag powder

Lithium slag (LS) powder is a potential supplementary cementitious material due to its large content of active aluminosilicate minerals. To clarify the properties of LS powder as a supplementary cementitious material, the ionic dissolution properties of LS powder and the hydration properties and kinetic process of blended cement containing LS powder were studied in this paper. ICP was used to analyze the dissolution of Si4+, Al3+ and Ca2+ ions in LS powder in the simulated cement alkali environment, and the mineral composition of the dissolved LS powder was analyzed by XRD. The results showed that SiO2 and Al2O3 were the main active sources of LS powder and that an increase in the alkaline solution temperature promoted the dissolution of silicate in the LS powder and breaking of the Si–O and Al–O bonds. The hydration characteristics of blended cement were studied by isothermal calorimetry combined with the K-D model. The results showed that LS powder reduced the structural compactness of the hardened cement paste to varying degrees in the early stage of hydration, but in the later stage of hydration, the high content of S in the LS powder promoted the formation of rod-shaped ettringite in the hydration product. The proper amount (10%) of LS powder made the paste structure more compact. As determined by the hydration kinetic analysis, the hydration process of blended cement can be divided into crystal nucleation and growth (NG), phase boundary reaction (I) and diffusion (D) processes, and the rate of crystal nucleation is far greater than the rates of the phase boundary reaction and diffusion. According to the SEM results, the structure of blended cement is more compact when 10% LS powder was mixed in the cementitious system.

Carbonation Curing of Concretes in a Flexible Enclosure under Ambient Pressure

Early-age carbonation curing of concrete is considered an alternative curing method that efficiently utilizes carbon dioxide to improve the performance of concrete and reduce carbon emission. Carbonation curing is commonly implemented in a pressure chamber at high pressure. The application is therefore limited only to special products such as concrete masonry units. To promote wider applications of the technology for general precast concrete with any shapes and sizes, an ambient pressure carbonation system in a flexible enclosure is needed. This paper presents a study on developing a new carbonation curing system at a curing pressure of 1.4 kPa (0.014 bar), which is considered as ambient pressure. The system includes a flexible enclosure made from a plastic sheet with a pressure-resistant zipper that can accommodate any shape and size of precast concrete products and can be made either in a factory or on a job site. Compared to the traditional high-pressure carbonation at 0.5 MPa (5 bars), which generates 12% CO2 uptake, carbonation in the ambient-pressure system at 1.4 kPa (0.014 bar), can achieve a carbon dioxide uptake of 11% with a comparable strength at both the early and late ages. Besides, the ambient pressure carbonation has shown less pH reduction and smaller carbonation depth than high pressure, which would have the advantage of protecting the reinforcing steel in concrete from carbonation-induced corrosion. Furthermore, ambient pressure carbonation-cured concretes were found to have higher compressive strength, higher surface electrical resistivity, lower porosity, and faster ultrasonic pulse velocity than normal hydration concretes at both the early and late hydration stage. Microstructure analysis indicated that carbonates were intermingled with C─ S─ H, contributing to the strength gain and performance improvement of concretes subject to ambient pressure carbonation curing.

Detailed in situ ATR-FTIR spectroscopy study of the early stages of C-S-H formation during hydration of monoclinic C3S

The early stages of tricalcium silicate hydration has been studied by in situ ATR-FTIR spectroscopy. A method for data reduction based on background correction and subtraction of spectra of pure components is presented, which makes it possible to describe the kinetic evolution of the calcium silicate hydrate phase upon hydration with great detail. The results obtained are in full agreement with recently reported, detailed solid-state NMR spectroscopy measurements. As ATR-FTIR spectroscopy does not require any isotope enrichment in order to increase the signal intensities and is a widely available technique, we suggest that our study opens up an avenue towards detailed in situ characterization of hydrating cementitious systems and hydrating systems in general.

Influence of Water‐Cement Ratio and Type of Mixing Water on the Early Hydration Performance of Calcium Sulphoaluminate (CSA) Cement

The present work studies the influence of water‐cement ratio and types of mixing water on the hydration process and microstructure of calcium sulphoaluminate (CSA) cement. Experimental tests on the setting time, physical properties, compressive strength, chemical shrinkage, X‐ray diffraction (XRD), and scanning electron microscopy (SEM) of CSA cement paste were carried out. The XRD analysis confirmed that the main hydration product is ettringite in both freshwater and seawater mixed CSA cement with different w/c ratios. The SEM analysis and physical properties test show that both low w/c ratio and seawater can improve the microstructure of CSA cement. The test results also find out that the high w/c ratio can accelerate the hydration process, extend the setting time, lower the compressive strength, and increase the chemical shrinkage of CSA cement, and the seawater presents a similar influence except for the mechanical property. The seawater increases the compressive strength of CSA cement in the early stage of hydration but will increase the microcracks at the later hydration stage of CSA cement and reduce its mechanical properties.