Effect of Boron and Water-to-Cement Ratio on the Performances of Laboratory Prepared Belite-Ye’elimite-Ferrite (BYF) Cements

Materials

卷:14

Raquel Pérez-Bravo¹  Isabel Santacruz¹  Alejandro Morales-Cantero¹  Miguel A. G. Aranda¹  Angeles G. De la Torre¹  Margherita Bruscolini² 

[1] Departamento de Química Inorgánica, Cristalografía y Mineralogía, Facultad de Ciencias, Campus Teatinos, Universidad de Málaga, 29010 Málaga, Spain;

[2] Dipartimento di Scienze Della Terra, Università Degli Studi di Milano, Via Botticelli 23, I20133 Milano, Italy;

关键词: belite;    calcium sulphoaluminate;    rheology;    superplasticisers;    Rietveld method;    degree of hydration;   

DOI  :  10.3390/ma14174862

来源: DOAJ

【 摘 要 】

The effect of superplasticiser, borax and the water-to-cement ratio on BYF hydration and mechanical strengths has been studied. Two laboratory-scale BYF cements—st-BYF (with β-C₂S and orthorhombic C₄A₃$\overline{\mathrm{S}}$) and borax-activated B-BYF (with α’_H-C₂S and pseudo-cubic C₄A₃$\overline{\mathrm{S}}$)—have been used, and both show similar particle size distribution. The addition of superplasticiser and externally added borax to BYF pastes has been optimised through rheological measurements. Optimised superplasticiser contents (0.3, 0.4 and 0.1 wt % for st-BYF, B-BYF and st-BYF with externally added 0.25 wt % B₂O₃, respectively) result in low viscosities yielding homogeneous mortars. The calorimetric study revealed that st-BYF is more reactive than B-BYF, as the values of heat released are 300–370 J/g and 190–210 J/g, respectively, after 7 days of hydration; this fact is independent of the water-to-cement ratio. These findings agree with the higher degree of hydration at 28 days of β-C₂S in st-BYF (from 45 to 60%) than α’_H-C₂S in B-BYF (~20 to 30%). The phase assemblage evolution has been determined by LXRPD coupled with the Rietveld method and MAS-NMR. The formation of stratlingite is favoured by increasing the w/c ratio in both systems. Finally, the optimisation of fresh BYF pastes jointly with the reduction of water-to-cement ratio to 0.40 have allowed the achieving of mortars with compressive strengths over 40 MPa at 7 days in all systems. Moreover, the st-BYF mortar, where borax was externally added, achieved more than 70 MPa after 28 days. The main conclusion of this work does not support Lafarge’s approach of adding boron/borax to the raw meal of BYF cements. This procedure stabilises the alpha belite polymorph, but its reactivity, in these systems, is lower and the associated mechanical strengths poorer.

【 授权许可】

Unknown