Quantitative Phase Analysis of Laboratory‐Active Belite Clinkers by Synchrotron Powder Diffraction

Abstract

Several active belite laboratory clinkers with a theoretical composition of 60 wt% of C2S have been synthesized. The activation process has been carried out by adding variable amounts of alkaline salts, K2CO3, or Na2CO3 to the raw materials. In addition to an ordinary Portland clinker and a nonactive belite clinker, four active belite clinkers have been prepared with 1.0 and 2.0 wt% of K2O or 0.5 and 1.5 wt% of Na2O. Phase‐enriched residues, silicate, and aluminate fractions have also been prepared in order to identify the most suitable structural description for each phase. High‐resolution synchrotron X‐ray powder diffraction patterns have been collected for the residues and for the laboratory clinkers. Quantitative phase analyses were performed by the Rietveld method using the synchrotron patterns. The reference belite laboratory clinker has a large amount of β‐C2S but the addition of alkaline salts to raw mixtures promotes the stabilization at room temperature of the highest temperature polymorphs: α′H‐C2S and α‐C2S. As an example, the active belite clinker with 2.0 wt% nominal content of K2O contains 4.5(2) wt% of β‐C2S, 19.2(1) wt% of α′H‐C2S, 35.9(2) wt% of α‐C2S, 17.6(1) wt% of C3S, 13.2(1) wt% of total C3A, and 9.6(1) wt% of C4AF. The role of K2O and Na2O, which stabilize different polymorphs, will be discussed. The partial volatilization of the alkaline metals will also be addressed. Finally, a calorimetric study has been undertaken in order to correlate the phase assemblage determined in the powder diffraction study with the hydration behavior.

Aluminum-rich belite sulfoaluminate cements: Clinkering and early age hydration

“…This behavior is probably mainly due to the reduction in the content of anhydrous cement phases if more gypsum is added. On the other hand, all of these cements show higher hydration enthalpies than a typical belite-rich cement (with no C 4 A 3 $ but with some C 3 S) which was slightly lower than 190 J/g at 6 days (144 hours) [10].…”

“…We have performed a SEM study of pieces of clinker pellets (without milling) in order to examine the texture of the clinkers. Figure 4 shows the SEM photographs of (a) a belite-rich clinker [10] and (b) BSA_50:30, prepared under the conditions detailed in this work. From these images, it is clear than BSA clinkers are more porous than belite-rich clinkers, which should favor their grindability, as already reported [68,69].…”

“…These disadvantages can be overcome in two complementary ways: i) producing BSA cements, with C 4 A 3 $ [also named as Klein´s salt] [6,7] and ii) stabilizing high temperature belite polymorphs ( -forms) [8][9][10][11]. Recently, a class of iron-rich BSA cements has been proposed by Lafarge [12], in which activation is promoted by both strategies already mentioned.…”

Preparación y caracterización de cementos belíticos blancos activados con dopantes alcalinos

“…La adición de los alcalinos a los crudos ha favorecido la estabilización de α' H -C 2 S en todos los clínkeres. Al aumentar el contenido de Na 2 O y/o de K 2 O, el porcentaje de α' H -C 2 S aumenta, con la disminución del contenido en β-C 2 S. La estabilización de la forma α (de más alta temperatura) se ha conseguido únicamente con la adición a los crudos de un 2,0% (en peso) de Na 2 O o K 2 O. Esta fase se ha estabilizado en cantidades menores a las obtenidas en clínkeres belíticos grises con las mismas cantidades de alcalinos añadidas (9). Esto es debido principalmente al aumento de la tasa de volatilización de los alcalinos con el aumento de la temperatura, ya que los clínkeres belíticos blancos han sido preparados a 1.450 ºC, mientras que los clínkeres belíticos grises se prepararon a 1.365 ºC.…”

Rietveld quantification of γ-C2S conversion rate supported by synchrotron X-ray diffraction images

“…Belite cement (BC), which contains more than 50% (in weight) of Ca 2 SiO 4 (C 2 S), has such advantages as lower calcination temperature, less calcium content, and lower heat of hydration. Therefore, it draws wide attention of many researchers (Chatterjee, 1996;Fukuda and Ito., 1999;Morsli et al, 2007;García-Díaz et al, 2011). However, BC has a chief disadvantage of low mechanical strength at its early age.…”