Expansion of CEM I and slag-blended cement mortars exposed to combined chloride-sulphate environments

Ukpata, Joseph O.; Basheer, Pam; Black, Leon

doi:10.1016/j.cemconres.2019.105794

Cited by 36 publications

(22 citation statements)

References 56 publications

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“…The accuracy of the extracted pre-edge intensity is 0.03 (a.u.). The crystalline references for XANES spectroscopy were rutile (TiO 2 ) and fresnoite (Ba 2 TiSi 2 O 8 ) for [6] Ti and [5] Ti, respectively.…”

Section: Xanes Measurementsmentioning

confidence: 99%

“…X-ray absorption near-edge structure allows determine the coordination number of Ti ( [4] -, [5] -and [6] Ti). The low-energy side of the absorption edge ( Figure 3) corresponds to the pre-edge, which is a specific feature, the intensity of which is enhanced for [4] Ti and [5] Ti sites, as compared to a [6] Ti site. The sensitivity of XANES allows investigate the proportion of Ti coordination numbers, 25,26 as shown in Figure 4.…”

Section: Ti K-edge Xanesmentioning

confidence: 99%

“…The pre-edge shows a similar shape and intensity for all ground slag samples and the [5] Ti references, KTS2 and fresnoite (Ba 2 TiOSi 2 O 7 ). Based on the energy position of this pre-edge and its intensity, Figure 4 indicates that the investigated slags do not contain measurable amounts of [6] Ti, Ti being mainly five-coordinated, with a minor contribution of tetrahedral Ti. The intensity of the pre-edge feature ( Figure S4) increases by 10%, without change in the energy position or linewidth, from the pristine slags, which contain Ti 3+ and Ti 4+ , to the remelted slags, which contain only Ti 4+ : this confirms the similar speciation of Ti 3+ and Ti 4+ .…”

Section: Ti K-edge Xanesmentioning

confidence: 99%

“…Titanium occurs in glasses under three different coordination numbers: [4] Ti, [5] Ti, [6] Ti. When Ti is four-coordinated, that is, in tetrahedral coordination, it may occur in a networkforming position, although its ionic radius is almost twice as large as that of Si (0.42 Å vs 0.26Å for [4] Ti 4+ and [4] Si 4+ , respectively).…”

Section: Speciation Of Timentioning

confidence: 99%

“…For instance, the replacement of Portland cement by GGBS increases the resistance of concrete and mortar against chloride penetration and sodium sulfate attack, with insignificant mass transfers between mortar and solution. 6,7 GGBS are calcium aluminosilicate glasses, which contain a dozen oxides including TiO 2 . 8 "Green" cements can be made with up to 95% GGBS.…”

Section: Introductionmentioning

confidence: 99%

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Structural role of titanium on slag properties

Cornec

Galoisy

Izoret³

et al. 2020

J. Am. Ceram. Soc.

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The presence of titanium in ground granulated blast-furnace slags (GGBS) has been suspected to modify cement properties. This study provides the first evidence of a relation between the TiO 2 content of slags and the mechanical properties of mortars based on slag cements. It is observed that only the slags containing less than 1%TiO 2 show a compressive strength at 28 days that remains within the 52.5 MPa norm with CEM III cements complying with the European Standard NF EN 197-1. The structural origin of this chemical dependence of the performance of cements is investigated by determining directly the titanium speciation in various European slags by spectroscopic methods. Electron paramagnetic resonance indicates that about 76% of Ti in slag occurs as Ti 4+. The atomic structure around Ti was determined by Ti K-edge X-ray absorption near edge structure, which shows that Ti is mainly five-fold coordinated in square-based pyramid geometry. Five coordinated Ti acts as networkstabilizer of the silicate network as it increases the polymerization. Requiring Ca 2+ for charge-compensation of the titanyl bond, it reduces the availability of Ca 2+ during glass alteration in a modified random model of glass structure, where Ca 2+ atoms are clustered in percolating cationic domains. As a consequence, the presence of fivecoordinated Ti results in a slower dissolution of the slag. These peculiar structural properties of titanium may explain the detrimental role of Ti above a 1% concentration, for many physical and chemical slag properties. This work provides a scientific ground for the technological acceptability of the upper limit of the Ti-content of GGBS.

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Section: Xanes Measurementsmentioning

confidence: 99%