Pérez-Bravo Raquel, Morales-Cantero Alejandro, Bruscolini Margherita, Aranda Miguel A G, Santacruz Isabel, De la Torre Angeles G
Departamento de Química Inorgánica, Cristalografía y Mineralogía, Facultad de Ciencias, Campus Teatinos, Universidad de Málaga, 29010 Málaga, Spain.
Dipartimento di Scienze Della Terra, Università Degli Studi di Milano, Via Botticelli 23, I20133 Milano, Italy.
Materials (Basel). 2021 Aug 26;14(17):4862. doi: 10.3390/ma14174862.
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-CS and orthorhombic CAS¯) and borax-activated B-BYF (with α'-CS and pseudo-cubic CAS¯)-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 % BO, 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-CS in st-BYF (from 45 to 60%) than α'-CS 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.
研究了高效减水剂、硼砂以及水灰比对碱激发粉煤灰（BYF）水化和力学强度的影响。使用了两种实验室规模的BYF水泥——st-BYF（含β-CS和正交晶系CAS¯）和硼砂激发的B-BYF（含α'-CS和假立方晶系CAS¯），二者粒径分布相似。通过流变学测量对向BYF浆体中添加高效减水剂和外加硼砂进行了优化。优化后的高效减水剂含量（st-BYF为0.3 wt%、B-BYF为0.4 wt%、外加0.25 wt% BO的st-BYF为0.1 wt%）可使粘度降低，从而得到均匀的砂浆。量热研究表明，st-BYF比B-BYF反应活性更高，水化7天后的放热值分别为300 - 370 J/g和190 - 210 J/g；这一事实与水灰比无关。这些发现与st-BYF中β-CS在28天时的水化程度（45%至60%）高于B-BYF中α'-CS（约20%至30%）一致。通过结合Rietveld方法的LXRPD和MAS-NMR确定了相组成演变。在两个体系中，硅钙石的形成均因水灰比的增加而更有利。最后，对新鲜BYF浆体进行优化并将水灰比降至0.40，使得所有体系的砂浆在7天时抗压强度超过40 MPa。此外，外加硼砂的st-BYF砂浆在28天后抗压强度超过70 MPa。这项工作的主要结论不支持拉法基在BYF水泥生料中添加硼/硼砂的方法。该方法可使α型贝利特多晶型稳定，但在这些体系中其反应活性较低，相关力学强度也较差。
