A new model for the C-S-H phase formed during the hydration of Portland cements

Gartner, E.M.; Maruyama, Isao; Chen, Jeffrey

doi:10.1016/j.cemconres.2017.03.001

Cited by 160 publications

(82 citation statements)

References 35 publications

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“…One way to reconcile all of the observations is to suppose that the microstructure of the C-S-H gel, arising from the hydration of alite, is a fine intermixing of tobermorite with amorphous Ca(OH) 2 plus the water in the small and large gel pores [6,13,16]. An updated mechanism of growth of the C-S-H gel, and consequently, the evolution and nature of the gel water, have been very recently proposed [17].…”

Section: Cementsmentioning

confidence: 99%

Synchrotron Radiation Pair Distribution Function Analysis of Gels in Cements

et al. 2017

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Abstract:The analysis of atomic ordering in a nanocrystalline phase with small particle sizes, below ≈5 nm, is intrinsically complicated because of the lack of long-range order. Furthermore, the presence of additional crystalline phase(s) may exacerbate the problem, as is the case in cement pastes. Here, we use the synchrotron pair distribution function (PDF) chiefly to characterize the local atomic order of the nanocrystalline phases, gels, in cement pastes. We have used a multi r-range analysis approach, where the~4-7 nm r-range allows determining the crystalline phase contents; the~1-2.5 nm r-range is used to characterize the atomic ordering in the nanocrystalline component; and the~0.2-1.0 nm r-range gives insights about additional amorphous components. Specifically, we have prepared four alite pastes with variable water contents, and the analyses showed that a defective tobermorite, Ca 11 Si 9 O 28 (OH) 2 ·8.5H 2 O, gave the best fit. Furthermore, the PDF analyses suggest that the calcium silicate hydrate gel is composed of this tobermorite and amorphous calcium hydroxide. Finally, this approach has been used to study alternative cements. The hydration of monocalcium aluminate and ye'elimite pastes yield aluminum hydroxide gels. PDF analyses show that these gels are constituted of nanocrystalline gibbsite, and the particle size can be as small as 2.5 nm.

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Section: Cementsmentioning

confidence: 99%

Synchrotron Radiation Pair Distribution Function Analysis of Gels in Cements

et al. 2017

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“…It is in this LD C-S-H that irreversible processes occur during the first drying process. The mechanism can be explained by Gartner, Maruyama, Chen (GMC) model (Gartner et al 2017). The GMC model presumes that dehydration of initially wet C-S-H occurs in discrete steps, in which oxygen atoms associated with water or OH ligands around the charge-balancing Ca cations are replaced by oxygen atoms bound to silicon in the silicate groups attached to the basal CaO layer.…”

Section: Hcpmentioning

confidence: 99%

“…84 represents a reduction of water adsorption sites in the stable C-S-H layers due to drying. This is due to the dehydration of water molecules hydrated with Ca ions on the surface of C-S-H and the generation of Si-O-Ca-O-Si bonds that stabilize the interlayer between mono-C-S-H layers (Gartner et al 2017). This mechanism is considered to be an irreversible process involving C-S-H during the first drying step.…”

Section: Hcpmentioning

confidence: 99%

Development of Soundness Assessment Procedure for Concrete Members Affected by Neutron and Gamma-Ray Irradiation

Maruyama

Kontani

Takizawa

et al. 2017

ACT

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In 2008, Nuclear and Industrial Safety Agency (NISA) (currently integrated to the Nuclear Regulatory Authority) launched a project to develop a soundness assessment method for concrete members subject to a radiation environment. Presently, the soundness of concrete members subject to radiation is evaluated based on whether the predicted fast neutron fluence and gamma-ray dose values are lower than specific reference values in Japan, which are 1×10 20 n/cm 2 and 2×10 5 kGy, respectively. These reference values were determined based on report by Hilsdorf et al. This project begins by reviewing Hilsdorf et al.'s report, and we find that the scientific evidence for the current reference values is weak. We thus conclude that new experimental research is required to assess the current reference values and to propose a new alternative soundness assessment procedure if needed. We quantitatively evaluated the influence of neutrons, gammarays, and the resultant heating and drying processes on the strength of concrete as well as their underlying mechanisms. The irradiation experiments confirmed the degradation mechanism of concrete due to neutron irradiation. The main reason for this degradation is the metamictization of rock-forming minerals, which, in turn, leads to aggregate expansion. Due to aggregate expansion, cracks around aggregates form, which reduce the compressive strength and Young's modulus of concrete. Among the rock-forming minerals, α-quartz is the most sensitive to neutron radiation.60 Co gamma-ray irradiation experiments demonstrated that concrete strength increased as the gamma-ray dose and gammaray flux does not have a dose-rate impact on the first radiolysis of evaporable water in cement paste within the present study. The effect of gamma-ray irradiation on the properties of concrete is equivalent to that of heating and drying. Concrete strength alteration due to heating and drying is attributed to the colloidal and porous nature of hardened cement paste and crack formation around the aggregate due to a mismatch in the volume changes of the mortar and aggregate. In addition, a numerical analysis code called DEVICE (Damage EValuation for Irradiated ConcretE) is developed to harness knowledge obtained from concrete samples to predict the distribution of the physical properties in concrete members and their changes over time. From these fundamental studies, we propose a new soundness assessment procedure for concrete members subject to radiation. We also recommend a new radiation-induced strength-degradation reference value of 1×10 19 n/cm 2 for fast neutron.

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“…e second major dehydration peak between 400°C and 500°C in each of the DTG curves (Figure 8(b)) was attributed to the decomposition of calcium hydroxide [33]. Tricalcium silicate and dicalcium silicate reacted with water to form C-S-H gels and calcium hydroxide [34]. e intensities of the C-SS and C-GTs paste samples at the curing age of 28 days were stronger than those at the curing age of 3 days, which indicated that the hydration degree was also further deepened with the extension of the curing age.…”

Section: Tg-dtg Analysismentioning

confidence: 99%

Preparation of Portland Cement with Gold Ore Tailings

Wang

Yao

Zhu

et al. 2019

Advances in Materials Science and Engineering

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e disposal of gold ore tailings (GTs) has been a very difficult problem for a long time. us, this study explored a new approach to the management of GTs by preparing Portland cement. Physical properties, reaction mechanisms, and hydration product types of cement prepared with GTs (C-GTs) and ordinary Portland cement (C-SS) were compared. X-ray diffraction (XRD), thermogravimetric (TG), and scanning electron microscope energy-dispersive spectroscopy (SEM-EDS) analysis techniques were used to study the mineralogical phases of the clinker and raw materials, hydration product types, and microtopography. e consistency, setting time, flexural strength and compressive strength values of the cement samples (C-GTs and C-SS), and burnability of the raw materials were also studied. e burnability analysis indicated that GTs provided a higher reactivity. e XRD results showed that the clinker phases of the C-GTs were C 3 S, C 2 S, C 3 A, and C 4 AF. e XRD, TG, and SEM-EDS results showed that the hydration products were flaky calcium hydroxide, rod-shaped ettringite, and granular C-S-H gels. Its compressive strength and flexural strength were, respectively, 30.4 MPa and 6.1 MPa at the curing age of 3 days and 59.1 MPa and 9.8 MPa at the curing age of 28 days, which were slightly higher than those of the C-SS. Furthermore, the results showed that the consistency, initial setting time, and final setting time for the two kinds of cement were similar, which further suggested that GTs could be used to prepare Portland cement.

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A new model for the C-S-H phase formed during the hydration of Portland cements

Abstract: 4A model is developed to explain why the C-S-H phase that grows during the hydration of Portland 5Cements initially requires a high water content, much of which is lost by gentle drying. It is proposed 6 that the rapid growth of C-S-H during the hydration of alite (C3S)

Cited by 160 publications

References 35 publications

Synchrotron Radiation Pair Distribution Function Analysis of Gels in Cements

Synchrotron Radiation Pair Distribution Function Analysis of Gels in Cements

Development of Soundness Assessment Procedure for Concrete Members Affected by Neutron and Gamma-Ray Irradiation

Preparation of Portland Cement with Gold Ore Tailings

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