GGBS composition and the choice of the activation systems have a large impact on the reactivity of GGBS-based binders. Here, the reactivity of 16 artificially-modified GGBSs was investigated in blended cements, alkali-activated binders and supersulfated cements, using isothermal calorimetry for hydration times between 24 h and 120 h. Lower glass network polymerization by addition of CaO or MgO increased the reactivity at all ages and in all activation systems. Increased Al2O3 content mainly resulted in higher early reactivity. This effect was more pronounced in blended and supersulfated cements. TiO2 addition decreased GGBS reactivity in all activation systems but the negative effect was reduced at high Al2O3 contents, especially at later ages in supersulfated cements. In alkali-activation, the hydration was delayed by several hours for some compositions. In summary, the results suggest that it is possible to increase the reactivity of GGBS by choosing an activation system optimized for a given GGBS composition.

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.

Small TiO2 contents in the slag-glass significantly reduce their cementitious reactivity. We investigated the role of Ti in the glass network and its influence on slag-glass dissolution. XANES and EPR analysis showed that 67% of Ti was present as Ti(IV) with about 70% in Ti-[5] and 30% in Ti-[4] coordination, and 33% as Ti(III). The presence of Ti had only a minor impact on initial dissolution rates at pH 11 (R asymptotic to 10(-6) molglass.s(-1).m(-2)). During dissolution, Ti accumulated in an amorphous layer at the glass-surface. Ti-coordination in this layer was 50% Ti-[5] and 50% Ti-[6]. At pH 11, the layer was mainly composed of TiO2 (66 wt%), but intermixed with a hydrotalcite-like phase at pH 13. The loss of cementitious reactivity in the presence of Ti appears to be not only due to stabilization of the glass structure but also to the formation of a Ti-rich surface-layer, that may become passivating.

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.

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