The hydration phase and pore structure formation in the blends of sulfoaluminate-belite cement with Portland cement

Sulfoaluminate-belite (SAB) cements are an attractive class of low-energy cements from the viewpoint of saving energy and releasing less CO₂ into the atmosphere during their production. Their hydraulic activity, however, does not match that of the ordinary Portland cement (PC) and needs improvement before they can be used on their own. However, SAB cements when blended with PC have the potential to be used effectively in traditional applications as shown by this study. Mortars made with blends of SAB cements and PC, and a cement-to-sand ratio of 1:3 by weight and a water-to-cement ratio of 0.5, indicate a superior protection against corrosion of steel to those made with blends of PC and blast-furnace slag (BFSPC). The prepared mortars were stored at 20 °C for 90 days under either a 60% relative humidity (RH)-dry air, or 100% RH-wet air conditions. With further improvement in the SAB cement quality through better understanding of their characteristics, a genuine competition between SAB/PC and BFSPC can be expected in practice.     

Quantitative study of Portland cement hydration by X-ray diffraction/Rietveld analysis and independent methods

X-ray diffraction (XRD) is a powerful technique for the study of crystalline materials. The technique of Rietveld refinement now enables the amounts of different phases in anhydrous cementitious materials to be determined to a good degree of precision. This paper describes the extension of this technique to a pilot study of the hydration of a typical Portland cement. To validate this XRD-Rietveld analysis technique, its results were compared with independent measures of the same materials by the analysis of backscattered electron images (BSE/IA) and thermogravimetric analysis (TGA). In addition, the internal consistency of the measurements was studied by comparing the XRD estimates of the amounts of hydrates formed with the amounts expected to form from the XRD estimates of the amounts of anhydrous materials reacted.     

A model investigation of the influence of particle shape on portland cement hydration

The NIST Virtual Cement and Concrete Testing Laboratory (VCCTL) is used to simulate the influence of particle shape on the hydration kinetics and setting of portland cement. Building on previous work in reconstructing particle shapes from real cements, real-shape particles are used to produce three-dimensional digitized cement paste microstructures, and the hydration of these microstructures is tracked using VCCTL. The degree of hydration and percolation of solids is monitored and compared to experimental data at several water-cement ratios. The simulations predict that shapes of particles influence cement hydration in two ways: the additional surface / volume ratio relative to spherical particles results in greater rates of hydration, and the anisometry in shape influences the degree of hydration at which the particles and hydration products percolate to form a stiff three-dimensional network.     

Acid neutralisation capacity and hydration behaviour of incineration bottom ash-Portland cement mixtures

The present paper deals with the use of incineration bottom ash in cementitious systems. The results of the physical-mechanical characterisation of the solidified products were discussed elsewhere, while the present work focuses on the acid neutralisation capacity (ANC) of the investigated mixtures as a means to evaluate the type of hydration products and their relative amounts in the solid matrix. The approach consists of differential acid neutralisation analysis, which was validated using traditional X-ray diffraction (XRD) methods.     

Porosity study on free mineral addition cement paste

A study of the hydration process and the porosity evolution in a cement paste is presented. The analysis of porosity was made in samples with water to cement ratios (w/c) of 0.24, 0.40 and 0.60 at age of 3, 7, 28 and 365 days, respectively. Information on the evolution of total porosity and on the strength of the paste were obtained using positron annihilation lifetime spectroscopy (PALS), scanning electron microscopy (SEM), X-ray diffraction (XRD), mechanical tests (compression and flexion) and water absorption techniques. Specifically, positron lifetime technique allowed us to analyze the evolution of gel and capillary porosity during the hydration process. Using a simple function proposed, reasonable fits to the experimental data of the porosity evolution as a function of the compression strength were obtained.     

Early hydration of portland cement — effects of water/cement ratio

The water/cement ratio at which Portland cement is hydrated is shown to influence the early hydration behaviour. Results have been obtained with both an ordinary Portland cement and a white Portland cement. As the water/cement ratio was progressively raised from 0.3 through 0.4 to 0.5, increased quantities of ettringite were formed at all the hydration times studied up to two hours. The results have been interpreted on the basis of a through solution mechanism for the formation of ettringite.     

Thermal behavior of cement matrix with high-volume mineral admixtures at early hydration age

Thermal cracks that usually occur in mass concrete are closely related to the thermal behavior of cement matrix, such as heat liberation, temperature rise and thermal shrinkage. Cement pastes added with large-volume mineral admixtures that are usually used for thermal controlling were cast into well-sealed plastic cylinder and covered by heat insulation materials to simulate the pseudo-adiabatic condition of mass concrete. The deformation and temperature rise of cement specimens under the heat insulation condition have been examined at early hydration age. Results show that with addition of fly ash, coal gangue and blast furnace slag the heat liberation and peak temperature of cement paste decrease, while its total shrinkage increases.There is no shrinkage but expansion of the pastes during the temperature rise process, which may be ascribed to the complete compensation of the shrinkage by thermal dilation of the pastes. The thermal dilation coefficient (TDC) of cement paste changes drastically with the hydration duration, and it is also related to the addition of mineral admixtures.     

Insights into early hydration of Portland limestone cement from infrared spectroscopy and isothermal calorimetry

Isothermal calorimetry and diffuse reflectance infrared DR-FTIR spectroscopy are combined to correlate evolutions of spectroscopic signatures with rates of chemical reactions as reflected in the rate of heat emitted during the first 38 h of cement hydration. Portland limestone cement mortar is employed and the analysis is repeated for two different mixing procedures. Intensive blender mixing with quartz sand is found to cause activation of the cement resulting in a faster hydration process. At early stages of hydration, two types of C-S-H are formed. The spectral intensity of the earlier C-S-H is found to saturate, while that of the later form continues to acquire intensity throughout the 38 h of the experiment. Evidences are presented which support the interpretation that the two forms differ mainly in morphology and water content. Simultaneously with the saturation of the early C-S-H, a transient species is observed with DR-FTIR. This species correlates with the observed thermogram fine-structure.     

Early hydration behaviour of portland cement containing tartaro- and titanogypsum

Portland cements containing tartaro- and titanogypsum were respectively hydrated for up to two hours at a water: cement ratio of 0.5. They were compared with a Portland cement containing high grade natural gypsum hydrated similarly. The cement containing tartarogypsum produced much more ettringite than those with titanogypsum and natural gypsum. Comparisons were made with previous examinations of the hydration of Portland cements containing other by-product gypsums. Reasons for the observed hydration behaviour of the Portland cements with tartaro- and titanogypsum are discussed.     

Class H cement hydration at 180 °C and high pressure in the presence of added silica

Under deep oil-well conditions of elevated temperature and pressure, crystalline calcium silicate hydrates are formed during Portland cement hydration. The use of silica rich mineral additives leads to the formation of crystalline hydrates with better mechanical properties than those formed without the additive. The effects of silica flour, silica fume (amorphous silica), and a natural zeolite mixture on the hydration of Class H cement slurries at 180 °C under externally applied pressures of 7 and 52 MPa are examined in real time using in-situ synchrotron X-ray diffraction. For some compositions examined, but not all, pressure was found to have a large effect on the kinetics of crystalline hydrate formation. The use of silica fume delayed both C₃S hydration and the formation of crystalline silicate hydrates compared to what was seen with other silica sources.     

Early age hydration of rice hull ash cement examined by transmission soft X-ray microscopy

Early age hydration of barium-doped β-Ca₂SiO₄ cement, produced from rice hull ash (RHA), is examined by transmission soft X-ray microscopy. Use of low-energy cements produced from by-product materials, such as the cement considered here, may be economically and environmentally advantageous. However, the hydration kinetics and morphology and composition of the products of RHA-based β-Ca₂SiO₄ cements have not been investigated. Observation of the early age cement hydration shows evidence of cement dissolution and hydration product formation, including the formation of Hadley grains. The rates of the reaction and amount product formed appear to be related to the hydrothermal processing temperature and the chemical composition of the cement. That is, more rapid hydration is observed for barium-doped RHA cements produced at higher temperatures and for cements produced with higher barium contents, within the ranges examined.     

Effect of lignosulfonate, calcium chloride and their mixture on the hydration of RHA-blended portland cement

Hydration of 10 wt.% rice husk ash (RHA)-blended Portland cement has been studied in the presence of 2 wt.% CaCl₂, 1 wt.% lignosulfonate (LS) and a mixture of the two admixtures by using different methods. Free lime determinations and differential thermal analysis have shown that CaCl₂ accelerates the pozzolanic reaction of Ca(OH)₂ and RHA. In the presence of mixture of two admixtures, lower amount of water is required for consistency of the paste. IR spectral studies have supported that the mixture of the two admixtures act as a strong accelerator for cement hydration. The compressive strength is highest in the presence of a mixture of the two admixtures at 28 days of hydration. The admixtures did not prevent the deterioration of the blended cement in corrosive atmosphere.     

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.     

The hydration products of Portland cement in the presence of tin(II) chloride

The hydration products of Portland cement pastes cured using water containing tin(II) chloride have been compared with those using distilled water. In the latter case, the expected products—portlandite, ettringite and calcite—were observed. The X-ray diffraction patterns of the cement pastes cured in the presence of tin(II) chloride showed several additional peaks that have been attributed to the formation of calcium hydroxo-stannate, CaSn(OH)₆, and Friedel's salt (tetracalcium aluminate dichloride-10-hydrate), Ca₃Al₂O₆·CaCl₂·10H₂O. The amount of portlandite formed was reduced in the presence of tin(II) chloride. Calcium hydroxo-stannate contains tin in the +IV oxidation state and equations are presented to account for the oxidation of Sn(II) to Sn(IV) preceding the formation of CaSn(OH)₆ and Friedel's salt.     

Early hydration and setting of oil well cement

A broad experimental study has been performed to characterize the early hydration and setting of cement pastes prepared with Class H oil well cement at water-to-cement ratios (w/c) from 0.25 to 0.40, cured at temperatures from 10 to 60 °C, and mixed with chemical additives. Chemical shrinkage during hydration was measured by a newly developed system, degree of hydration was determined by thermogravimetric analysis, and setting time was tested by Vicat and ultrasonic velocity measurements. A Boundary Nucleation and Growth model provides a good fit to the chemical shrinkage data.Temperature increase and accelerator additions expedite the rate of cement hydration by causing more rapid nucleation of hydration products, leading to earlier setting; conversely, retarder and viscosity modifying agents delay cement nucleation, causing later setting times. Lower w/c paste needs less hydration product to form a percolating solid network (i.e., to reach the initial setting point). However, for the systems evaluated, at a given w/c, the degree of hydration at setting is a constant, regardless of the effects of ambient temperature or the presence of additives.     

矿物掺合料对氯氧镁水泥早期水化行为的影响

研究了矿物改性氯氧镁水泥前期水化行为,绘制了各矿物掺合料氯氧镁水泥水化电阻率-时间曲线,测试终凝时间以及1 d抗弯与抗压强度。结果表明,矿物掺合料能够延缓氯氧镁水泥水化速度,并随着矿物掺合料掺量的提高,其水化速度逐渐变慢。同等掺量下硅灰延缓反应时间的作用最为明显,其次是石粉与粉煤灰。硅灰的掺入延缓氯氧镁水泥水化速度,大幅度提高其初终凝时间,降低早期强度,其掺量不宜超过20%。粉煤灰与石粉氯氧镁水泥初终凝时间均在规范要求以内,对早期抗弯拉强度与抗压强度影响幅度相对较小。添加粉煤灰与石粉试样晶体较掺硅灰试样结晶程度更高。     

纳米α-Ni(OH)_2膜的合成及其超级电容性质研究

采用化学沉淀法在室温下合成了一种α-Ni(OH)_2纳米薄膜,探讨了合成温度及表面活性剂的影响。采用XRD、SEM、TEM和BET对材料进行表征。结果表明,合成温度及表面活性剂的种类对产物组成和形貌有较大影响,室温下,样品为厚度约2 nm的薄膜,带有较多的褶皱,比表面积206.8 m²/g;50℃下合成的产物表面褶皱开始消失,且不均匀,有颗粒状物质生成,80℃下的产物褶皱状结构消失,主要为团聚在一起的颗粒组成。同时,将α-Ni(OH)_2纳米膜制成单电极,循环伏安和恒电流充放电测试表明,α-Ni(OH)_2纳米膜具有较好的电化学性质,当充放电电流密度为1 A/g时,电极材料的比容量达到539.6 F/g。     

Suspended hydration and loss of freezable water in cement pastes exposed to 90% relative humidity

Degree of hydration (DOH) and differential scanning calorimetry (DSC) measurements are used to characterize the effect of early exposure to a 90% relative humidity (RH) environment on cement paste hydration. Early exposure to a 90% RH environment can lead to the consumption of freezable water and altered microstructural development. The minimum duration of 100% RH curing required to eliminate the effects of an unsaturated environment on microstructural development coincides with the appearance of a DSC peak near −30 °C that occurs in the range 1-14 days for the pastes studied. The Jennings colloidal microstructural model is used to argue that the −30 °C peak coincides with the cessation of capillary pore percolation. Alternatively, all samples cured under 100% RH conditions for 7 days prior to 90% RH exposure hydrated at the same rate as those continuously exposed to 100% RH. The application of these results to the formulation of separate curing practices for durability and strength is discussed.     

An in situ synchrotron energy-dispersive diffraction study of the hydration of oilwell cement systems under high temperature/autoclave conditions up to 130 °C

The technique of synchrotron energy dispersive diffraction has been developed for in situ studies of cement hydration under autoclave conditions. This has been applied to oilwell cements hydrating at typical oilwell temperatures up to 130 °C. The results show clearly the detailed interplay between 11 detectable phases, from which a phase transformation scheme has been derived; this illustrates the progression of hydration up to 130 °C for two extreme cases, with and without conservation of water content and autoclave pressure. The monosulphate hydrate phases are found to exhibit different stability bounds, with a surprising sequence of the 14-water, 10-water then 12-water monosulphate as temperature/time increases; the latter form is particularly associated with conditions of water/pressure loss. The effect of retarders on C₃S dissolution and CH formation is negligible above 70 °C, whereas the effect on the calcium sulphoaluminate hydrates is more complex, and possible reasons for this are discussed.     

Early hydration behaviour of portland cement containing boro-, citro- and desulphogypsum

Portland cements containing boro-, citro- and desulphogypsum, respectively, were hydrated at water:cement ratio 0.5 for up to two hours and compared with a Portland cement containing high grade natural gypsum hydrated similarly. It was found that the cements containing boro- and citrogypsum produced considerably more ettringite than those with desulpho- and natural gypsum. Comparisons were made with previous investigations of Portland cements containing fluoro-, formo- and phosphogypsum, respectively, hydrated under analogous conditions. Reasons for the observed hydration behaviour of the Portland cements containing the aforementioned chemical gypsums are discussed.