Reactivity tests for supplementary cementitious materials: RILEM TC 267-TRM phase 1

A primary aim of RILEM TC 267-TRM: “Tests for Reactivity of Supplementary Cementitious Materials (SCMs)” is to compare and evaluate the performance of conventional and novel SCM reactivity test methods across a wide range of SCMs. To this purpose, a round robin campaign was organized to investigate 10 different tests for reactivity and 11 SCMs covering the main classes of materials in use, such as granulated blast furnace slag, fly ash, natural pozzolan and calcined clays. The methods were evaluated based on the correlation to the 28 days relative compressive strength of standard mortar bars containing 30% of SCM as cement replacement and the interlaboratory reproducibility of the test results. It was found that only a few test methods showed acceptable correlation to the 28 days relative strength over the whole range of SCMs. The methods that showed the best reproducibility and gave good correlations used the R3 model system of the SCM and Ca(OH)2, supplemented with alkali sulfate/carbonate. The use of this simplified model system isolates the reaction of the SCM and the reactivity can be easily quantified from the heat release or bound water content. Later age (90 days) strength results also correlated well with the results of the IS 1727 (Indian standard) reactivity test, an accelerated strength test using an SCM/Ca(OH)2-based model system. The current standardized tests did not show acceptable correlations across all SCMs, although they performed better when latently hydraulic materials (blast furnace slag) were excluded. However, the Frattini test, Chapelle and modified Chapelle test showed poor interlaboratory reproducibility, demonstrating experimental difficulties. The TC 267-TRM will pursue the development of test protocols based on the R3 model systems. Acceleration and improvement of the reproducibility of the IS 1727 test will be attempted as well

Preparation and accelerated carbonation of low temperature sintered clinker with low Ca/Si ratio

A novel clinker with low Ca/Si ratio and low sintering temperature was synthesized, and the property of the clinker was tested. A clinker sintered from industrial raw materials mainly contains rankinite (Ca3Si2O7), pseudowollastonite (Ca-3(Si3O9)) and ferrosilite ((Ca,Mg,Fe,Al)(2)Si2O6). Quantitative analysis of the mineral composition was performed via X-ray powder diffraction using the Rietveld method. Results showed that the optimal formation region of the clinker was at 1300 degrees C for 4 h, resulting in a Ca/Si ratio of 1.27 and 72.7% rankinite, 24.6% pseudowollastonite and 2.7% ferrosilite. The hardening of the clinker occurred mainly due to the carbonation of rankinite and pseudowollastonite yielding CaCO3 and SiO2. Carbonation depth was determined using confocal laser scanning microscopy (CLSM). Experiments indicated that the carbonation depths of the clinker in accelerated carbonation conditions were 659 +/- 20 mu m, 787 +/- 18 mu m and 1118 +/- 98 mu m for 1, 3, and 28 days of carbonation, respectively. Moreover, well-developed calcite crystals could form a network-like and interconnected structure, further enhancing its performance. (C) 2016 Elsevier Ltd. All rights reserved

Kinetics of calcium sulfoaluminate with 1% iron oxide by isothermal and isoconversional methods

The influence of iron oxide (Fe2O3) on the formation and decomposition kinetics of calcium sulfoaluminate (C(4)A(3)$) formed from tricalcium aluminate and calcium sulfate was investigated by both isothermal and isoconversional methods. Rietveld quantitative analysis was used to determine the mineral compositions. The results showed that the addition of 1 wt$ at a given temperature. The formation and decomposition activation energies obtained by the isothermal method using the Jander diffusion model were 184 +/- 25 kJ/mol and 523 +/- 17 kJ/mol, respectively. The isoconversional methods yielded formation and decomposition activation energies of 191 kJ/mol and 509 kJ/mol, respectively. The isoconversional results were thus in agreement with the isothermal results. This confirmed the validity of the diffusion model, which revealed that both reactions were diffusion mechanisms. With 1 wt% iron oxide, the optimal region for the formation of C4A3$ was found to be in the temperature range 1150-1300 degrees C for sintering times of 8 h to 1 h

Kinetic model for calcium sulfate alpha-hemihydrate produced hydrothermally from gypsum formed by flue gas desulfurization

Modeling of the kinetics of the synthesis process for calcium sulfate alpha-hemihydrate from gypsum formed by flue gas desulfurization (FGD) is important to produce high-performance products with minimal costs and production cycles under hydrothermal conditions. In this study, a model was established by horizontally translating the obtained crystal size distribution (CSD) to the CSD of the stable phase during the transformation process. A simple method was used to obtain the nucleation and growth rates. A nonlinear optimization algorithm method was employed to determine the kinetic parameters. The model can be successfully used to analyze the transformation kinetics of FGD gypsum to alpha-hemihydrate in an isothermal batch crystallizer. The results showed that the transformation temperature and stirring speed exhibit a significant influence on the crystal growth and nucleation rates of alpha-hemihydrate, thus altering the transformation time and CSD of the final products. The characteristics obtained by the proposed model can potentially be used in the production of alpha-hemihydrate

Rapid, Robust, and Relevant (R3) Reactivity Test for Supplementary Cementitious Materials

Although supplementary cementitious materials (SCMs) are now commonly accepted and widely used, consensus has not been reached for methods to test their chemical reactivity. A multitude of test methods exist but often fall short on one or more of the key features of a proper test-that is, width of scope, practicability, reproducibility, and relevance of the result. A rapid, robust, and relevant chemical reactivity test applicable to a wide range of SCMs would therefore not only serve as global benchmark but it would also remove present ambiguities in regards to classification.In response, a new, so-called "R3" test was conceived at Ecole Polytechnique Federale de Lausanne and is now being further developed and tested in RILEM TC 267 TRM, The test method was initially based on a screening of calcined clays in portlanditealkali-sulfate systems by isothermal calorimetry. Subsequently, the system formulation was more systematically studied and compared to strength development of blended cement mortar bars for a wide range of calcined kaolinitic clays. Remarkably good correlations between strength development and heat release were found. This was confirmed for other Sells and other measurable system properties. In particular; bound water content and chemical shrinkage correlated remarkably well to the isothermal calorimetry results. The origin of this correspondence can be traced back to the hydration reaction. Indeed, it is the solidification of water that directly links heat release; chemical shrinkage; and, obviously, bound water content.This contribution traces back the origins and the first inroads leading up to the present state of development of the test method and concludes on future perspectives

SYNTHESIS AND CHARACTERIZATION OF HIGH BELITE SULFOALUMINATE CEMENT THROUGH RICH ALUMINA FLY ASH AND DESULFURIZATION GYPSUM

The objective of this study was the preparation and characterization of high belite sulfoaluminate cement (HBSC) from industrial residues. HBSC promises eco-friendly building materials with great mechanical performance at earlier ages than Ordinary Portland Cement (OPC). Preliminary results show the formation of main phase dicalcium silicate (C2S) and ye’elimite (C4A3$) at 1250°C, as determined by X-ray diffraction (XRD), are promising. The formation of minerals in the clinker was analyzed by differential scanning calorimetry-thermogravimetry (DSC–TG). Likewise, Scanning electron microscope (SEM) and XRD were used to carry out the analysis of the micro-structural and hydration products. The main HBSC hydration products, Ettringite and amorphous Al(OH)3, were formed in the early stages; however, during the later stages, monosulfate and Strätlingite were formed. Isothermal conduction calorimetry measurements indicate that hydration properties of the cements are comparable to OPC; the total hydration heat after 3 days was 438 J/g. The optimum compressive strength values of the mortars after 1-, 3-, 7-, and 28-days were 24.9 MPa, 33.2 MPa, 35.6 MPa and 52.8 MPa which can meet the requirement of special structures

Effect of welan gum on the hydration and hardening of Portland cement

This paper reports the effects of welan gum on the hydration and hardening behaviors of Portland cement (PC) by using X-ray diffractometry, mercury instruction porosimetry, thermogravimetry, differential scanning calorimetry and scanning electron microscopy. Results show that welan gum has notable influence on the setting time of PC paste and the formation of calcium hydroxide (Ca(OH)2); welan gum has little impact on the total hydration heat, AFt content and/or the morphologies of hydration products even though it delays the induction period of hydration and the second reaction of the aluminate phase. Welan gum retards the early hydration of C3S and accelerates the early hydration of C4AF. The compressive strength is improved, and pore size of hardened cement paste is reduced with at the studied period when welan gum is no more than 0.05%. In this research, the cement paste with 0.05% welan gum exhibits the highest long-term (90 d) compressive strength and lowest porosity

Alite-ye'elimite clinker: Hydration kinetics, products and microstructure

This paper presents the hydration kinetics, products and microstructure of an alite-ye'elimite clinker containing 4 wt% of ye'elimite to boost the early strength development. Isothermal calorimetry, X-ray diffraction, backscattered scanning electron microscopy and mercury intrusion porosimetry were used to study the hydration processes. The results showed that the ye'elimite phase hydrated very rapidly, before the main hydration of alite, forming ettringite as main hydration product. The ye'elimite hydration products precipitated throughout the pore space and reduced the microporosity of the hardened paste at early age. The presence of ye'elimite strongly affected the early hydration before 24 h of hydration, but did not show a significant effect on the hydration kinetics or products at later ages. (C) 2020 Elsevier Ltd. All rights reserved

Stability of Tricalcium Silicate and Other Primary Phases in Portland Cement Clinker

The decomposition of alite (C₃S) in Portland cement clinker was investigated by isothermal annealing, aiming to provide more fundamentals for the cooling process of cement clinker so as to search for potential chance for modification of the ongoing cooling process. Clinker phases were analyzed with quantitative X-ray diffraction technique. Scanning electron microscope and microscopy were used to investigate the microstructure. The fastest decomposition rate appeared at 1125–1150 °C in a temperature–time–transformation diagram. The decomposition of alite primarily occurred at the cracks, edges, and defects of the clinker. The resultant f-CaO segregated, which mainly controlled the decomposition rate of alite. The three-dimensional diffusion model (Jander) was suitable for the decomposition kinetics of alite with a non-Arrhenius behavior for the activation energy which was a piecewise linear function with temperature. Interstitial phases recrystallized during the annealing process, accompanied by an increase of the C₃A and C₄AF contents. The recrystallization of C₃A was temperature-dependent, especially above 1000 °C

Report of RILEM TC 267-TRM phase 2: Optimization and testing of the robustness of the R3 reactivity tests for supplementary cementitious materials

The results of phase 1 of an interlaboratory test, coordinated by the RILEM TC 267-TRM “Tests for Reactivity of Supplementary Cementitious Materials” showed that the R3 (rapid, relevant, reliable) test method, by measurement of heat release or bound water, provided the most reliable and relevant determination of the chemical reactivity of supplementary cementitious materials (SCMs), compared to other test methods. The phase 2 work, described in this paper aimed to improve the robustness of the test procedure and to develop precision statements for the consolidated test procedure. The effect of the pre-mixing and mixing conditions, and the impact of the mix design on the test method robustness were assessed and fixed for optimal conditions to carry out the R3 heat release test. The effect of the drying step was evaluated to define the R3 bound water test procedure in more detail. Finally, the robustness of the consolidated final test methods was determined by an interlaboratory study to define the precision statements.</p