Brownmillerite hydration in the presence of gypsum: The effect of Al/Fe ratio and sulfate ions

Abstract

The brownmillerite, also known as tetracalcium aluminoferrite (C4AF), represents a solid solution series of Ca2(AlyFe(2–y))O5 (0 ≥ y ≤ 1.33), which is one of the most important components in ordinary Portland cement. The hydration of brownmillerite in the presence of gypsum attracts massive attentions, but the hydration mechanism remains controversial nowadays. In particular, the influence of Al/Fe ratio on brownmillerite hydration with gypsum is obscure and out of favor. This paper studies the hydration characteristics of a binary system containing brownmillerite and gypsum with variables including two Al/Fe ratios and gypsum contents in an attempt to interpret the retarding mechanism of sulfate ions. When the molar ratio of brownmillerite to gypsum is 1.0, the hydration process of Ca2(Al1.3Fe0.7)O5 shows five distinct stages in the conductivity test, while only two stages are observed in the case of Ca2(Al1.0Fe1.0)O5. A decrease of Al/Fe ratio in brownmillerite leads to severe stagnation of the hydration process. When the molar ratio of Ca2(Al1.0Fe1.0)O5 to gypsum is increased to 2.7, the hydration is able to proceed and also displays five stages similar to Ca2(Al1.3Fe0.7)O5. An adsorption layer of sulfate ions on the surface of brownmillerite contributes to the postponement of brownmillerite hydration. In addition, the concentration of aluminum in the solution is the key to break this adsorption layer and dominate the hydration proceeding of brownmillerite.

Formation and hydration of eco-friendly cement using industrial wastes as raw materials

“…However, the quantity of some presently mentioned formed compounds was small, thus the compounds cannot be clearly distinguished in the XRD patterns. The formation of new compounds can be described by the following reactions 54 , 58 , 59 : …”

In‐depth understanding the hydration process of Mn‐containing ferrite: A comparison with ferrite

“…Combining the conductivity with pH results, the hydration process of cement can be accurately presented with a water/cement ratio over 20, 51,52 which reflects the variation of ions concentration and pH at the same time. The experiment was conducted at a water bath equilibrated at 20°C.…”

“…Combining the conductivity with pH results, the hydration process of cement can be accurately presented with a water/cement ratio over 20, 51,52 which reflects the variation of ions concentration and pH at the same time. The experiment was conducted at a water bath equilibrated at 20 • C. Before the experiment, 250 ml deionized water was balanced at the water bath for 3 h. Note that 3.28 g ferrite and 1.72 g gypsum (with a molar ratio of S/Al = 1.5) were added, 53 and then the measurement started along with 500 r/min of magnetic stirring.…”

Preparation and Hydration of Brownmillerite-Belite-Sulfoaluminate Cement

“…The hydration products of the BBSC paste cured for different times were tested by XRD. As shown in Figure 4, the main hydration products of BBSC consisted of AFt, C 2 AS•8H 2 O, unhydrated C 2 S, and few low-sulfur AFt (AFm) [4,18,[33][34][35]. Furthermore, AFm, AH 3 , and FH 3 were also present, however, they were not obviously observed in the XRD patterns due to their gel state and poor crystal development.…”

“…High belite-sulfoaluminate cement with a relatively higher content of brownmillerite can also be named as brownmillerite-belite-sulfoaluminate cement (BBSC). Presently, the hydration of brownmillerite and the belite-sulfoaluminate containing brownmillerite has been researched [1, [7][8][9][10][11][12][13][14][15][16][17][18][19]. However, the hydration and flexural/compressive strength of BBSC have rarely been clarified.…”