Hydration Reactions and Mechanical Strength Developments of Iron-Rich Sulfobelite Eco-cements

Abstract

Belite calcium sulfoaluminate (BCSA) cements are low-CO 2 building materials. However, their hydration behavior and its effect on mechanical properties have still to be clarified. Here, we report a full multitechnique study of the hydration behavior up to 120 days of nonactivated and activated BCSA laboratory-prepared clinkers, with βor α H -belite as main phase, respectively. The effects of the amount of gypsum added were also studied. The hydration and crystallization processes are reported and discussed in detail. Finally, shrinkage/expansion data are also given. The optimum amount of gypsum was close to 10 wt %. Our study has demonstrated that β-belite reacts at a higher pace than α′ H -belite, irrespective of the gypsum content. The hydration mechanism of belite determines the development of the mechanical strengths. These are much higher for activated BCSA cement, ∼65 MPa at 120 days, against ∼20 MPa for nonactivated BCSA cement, with the latter having larger amounts of stratlingite.

Structure of stratlingite and effect of hydration methodology on microstructure

“…Preparation of belite calcium sulfoaluminate cement pastes Laboratory BCSA clinker (Álvarez-Pinazo et al, 2012) and pastes (Álvarez-Pinazo et al, 2013) were prepared as previously reported. The as-prepared BCSA paste was gathered in two groups and treated as follows: (a) transferred into a methacrylate sample holder covered with plastic wrap and statically stored in a humidity chamber at 99% relative humidity (RH); (b) cast in a hermetically closed polytetrafluoroethylene (PTFE) cylinder shape mould rotated at 15 r/min for 24 h. After that time, this sample was kept in deionised water.…”

“…In the last few years, belite calcium sulfo-aluminate (BCSA) cements, also known as sulfobelite cements, have been developed as OPC substitutes (Cuberos et al, 2010;Gartner and Li, 2006;Morin et al, 2011). Although they have been proposed as a sustainable alternative to OPC, some technological challenges (Álvarez-Pinazo et al, 2013), such as relatively low mechanical strengths and durability, need to be improved. The understanding of the hydration processes (Klaus et al, 2013;Le Saoût et al, 2013;Winnefeld and Lothenbach, 2010) should lead to an improved design of the clinker composition (activation) and better performances after setting and hardening.…”

In-situ early-age hydration study of sulfobelite cements by synchrotron powder diffraction

“…Thus, the key issue seems to be the hydration products and not the polymorphism of the dicalcium silicate. According to a related study [46], BCSA pastes with higher percentages of stratlingite develop lower mechanical strengths. The precipitation of stratlingite requires an oversaturated pore solution in silicon and aluminum hydroxides [16], thus it is obvious that G10B2 paste will present less stratlingite as less ye'elimite is dissolved.…”

“…Thus, in G10B0 the reactivity of β-C 2 S is hastened by this fact. Active belite-rich [45] and active BCSA [19,46] cements develop higher mechanical strengths (at any hydration age) when compared with non-active materials. Thus, the key issue seems to be the hydration products and not the polymorphism of the dicalcium silicate.…”

Pseudocubic Crystal Structure and Phase Transition in Doped Ye’elimite

“…In addition, the interest in the ye'elimite structure has recently increased because it is the major component in calcium sulfoaluminate cements (CSA) [14][15][16] , and the second most relevant phases in sulfobelite cements, BCSA, (~25 wt%) [17][18][19] . CSA and BCSA cements are environmentally-friendly materials as they allow decreasing the CO 2 footprint in cement fabrication.…”