In situ X-ray Micro-Tomography (XMT) analyses with a pixel size of 0.325 mu m were conducted on slag-based blended cements containing 75% of Ground-Granulated Blast-Furnace Slags (GGBS) and 25% of Ordinary Portland Cement (OPC), with or without CaCl2 acceleration. Results show the identification of the main cementitious phases and the need to perform data repeatability tests in order to allow their quantification. Investigation of the early hydration during the first 31 h of hydration by image subtraction showed (i) the dissolution of OPC/GGBS, (ii) the precipitation of hydrates including C-S-H, (iii) the accelerating effect of CaCl2, and (iv) phase-identification based on their specific grey level.

Ground granulated blast furnace slags (GGBS) are glasses (>99%) of the CaO-Al 2 O 3-SiO 2 compositional system and are widely used as supplementary cementitious materials. Differences in reactivity of GGBS were screened by modifying the content of 11 minor elements (namely Ba, Ce, Cs, Cr, Mn, P, Sn, Sr, Ti, V, Zr). SEM observations showed that most elements entered the silicate glass matrix, only Sn was reduced to its metallic form and P accumulated in minor minerals. Mortar strength tests showed that 2d-compressive strength was reduced by > 50% for a TiO 2 content of 2.5 wt.% in the slag. At 28 days the loss in compressive strength was still > 40%. Calorimetric tests on other element additions showed that network modifiers (Ba, Cs and Sr) and GGBS reactivity are positively correlated, whereas Ce, Cr, V and Zr significantly decreased reactivity. It is shown that these effects can be well estimated by the weighted field strength of the added element.

Cements with high substitution rates of ground granulated blast furnace slags (GGBS) have the potential to significantly lower CO2 emissions of concrete, but their early age strength is often below those of traditional OPC cements. One way of mitigating this drawback is to use accelerating admixtures. In this study, the effect of CaCl2 additions on the hydration of blended cements was investigated by measuring compressive strength, porosity, heat release and propagation of ultrasound in blends containing 70 wt% of GGBS. The onset of formation of aluminate phases was monitored using in-situ XRD. The effect of CaCl2 on slag hydration was isolated by replacing GGBS by an inert quartz filler. Results showed that compressive strength values at one, two and seven days were increased by 50% by the CaCl2 addition. The increases in compressive strength corresponded to a reduction in pore space. GGBS hydration contributed to the heat development, structuration and compressive strength of the blended cements from 15 h. The addition of CaCl2 led to an earlier onset of the GGBS reaction, at around 10 h, and increased the rate of GGBS hydration during the first seven days. The time of onset of the GGBS contribution was also the moment when AFm precipitation started. In CaCl2-containing blends, Cl was incorporated in AFm.

Ground granulated blast furnace slag (GGBS) is a glassy by-product of pig iron production and is commonly used in concrete industry to replace cement and thereby lower the carbon footprint of the material. Large variations in reactivity exist depending on the GGBS physical and chemical features. Here we investigate the ability of three rapid calorimetric methods to evaluate the reactivity of GGBS. On a set of 16 industrial GGBS, we show that 24 h heat release, using the R3-protocol, correlates well with 2d compressive strength of standard mortars using 75 wt% GGBS. The correlation of R3-test results (R-2 = 0.87) is better than for traditional reactivity indices calculated from chemical composition. Furthermore, we present data on the repeatability of the test protocol and show that the R3-protocol is very sensitive to sample fineness. Finally, XRD patterns show that slight differences in phase assemblage exist between the most and least reactive GGBS.

The effect of Ti and other minor elements on the reactivity of granulated ground blast furnace slag (GGBS) in blended cements SIMON BLOTEVOGEL1, LAURENT STEGER1,2, HANSJÖRG BORNHÖFT3, JOACHIM DEUBNER3, LOLA DOUSSANG2, FRANCK FAYON4, DANIEL HART3, JUDIT KAKNICS5, VALERIE MONTOUILLOUT4, CEDRIC PATAPY1, GIUSEPPE SALDI7, JACQUES SCHOTT7, MARTIN CYR1 1 LMDC, UPS/INSA Toulouse, France 2 Ecocem Materials, Dublin, Ireland 3 Clausthal University of Technology, Germany 4 CNRS CEMHTI, Orléans, France 5ArcelorMittal Research, Maizières-les-Metz, France 6GET-CNRS-IRD, Toulouse, France

For many microstructural studies it is necessary to “stop” cement hydration—to remove free water. This paper describes the results of a round robin test on the impact of hydration stoppage methods on the composition of hydrated cements. A regular and a fly ash blended Portland cement hydrated for 90 days were selected. Ten laboratories participated in the round robin test. Four common hydration stoppage methods were studied: (1) oven drying at 105 °C, (2) solvent exchange by isopropanol, (3) vacuum drying and (4) freeze drying. After the stoppage of hydration powder samples were studied by thermogravimetry (TG) and X-ray diffraction (XRD). Bound water and Ca(OH)2 content were determined based on the TG data. Portlandite and ettringite content were quantified by Rietveld analysis of the XRD data. The goal was to establish interlaboratory reproducibility and to identify the best available protocols for research and standardization purposes. Based on the results of the round robin test three recommendations are made. (1) Oven drying at 105 °C is not recommended. This dehydrates, alters and decomposes calcium aluminate hydrates significantly more than other methods and often produced carbonation artefacts. (2) Isopropanol exchange is the most appropriate hydration stoppage method for the study of the complete hydrate assemblage of cements, including calcium aluminate hydrates such as ettringite and AFm phases. (3) For quantification of portlandite (Ca(OH)2) all tested hydration stoppage protocols are satisfactory, with the exception of oven drying.

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 R 3 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 R 3 model systems. Acceleration and improvement of the reproducibility of the IS 1727 test will be attempted as well.

This recommendation is an outcome of the work carried out by a working group within the RILEM Technical Committee 238-SCM “Supplementary Cementitious Materials”. The working group studied the effect of supplementary cementitious materials on the pore solution, the microstructure and the hydration product assemblage of hardened Portland cements blended with common supplementary cementitious materials. The recommendation reflects the results of a round robin test programme on common hydration stoppage methods in 10 participating laboratories. Among four different methods tested, solvent exchange by isopropyl alcohol (isopropanol) gave the best results in terms of preservation of the cement hydrate assemblage and overall reproducibility of the results [1]. The current protocol is developed based on best laboratory practices of the participating laboratories and literature reports [2, 3, 4]. The presented hydration stoppage protocol is recommended for the study of Portland cement-based hydrate assemblages by common material characterization techniques such as thermogravimetry and X-ray powder diffraction.

Non-reinforced precast industry is a technical sector which uses low water-to-binder ratio, specific particular size distribution of aggregates, and needs high reactivity binders to ensure high production rates. The use of Supplementary Cementitious Materials is technically challenging in this industry but has benefits of reduced environmental impact and improved durability of the final products. A solution could be the partial replacement of Portland cement by ground granulated blast-furnace slag (GGBS) activated by several chemical compounds1,2,3.

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address