Anhydrite/hemihydrate-blast furnace slag cementitious composites: Strength development and reactivity

Hemihydrate or waste anhydrite in composite binders with blast-furnace slag: Hydration products, microstructures and dimensional stability

“…The pastes with 20%PFA and 0% pozzolan denoted peaks of portlandite after 24 h as result of the Portland cement hydration, such peaks disappeared after 7 days after its consumption by the pozzolanic reaction to form C-S-H, and possibly ettringite as the PFA can dissolve Al 2 O 3 under the activating environment, which in turn favored the initial strength development. This can be seen in Table 2 with the representative results of strength and non-evaporable water (NEW) of the binders of this study from a previous report [14]. The main reflection of ettringite at 9.65°2h was observed from 7 days onwards in the composites with PFA and 0% pozzolan; the intensity grew slightly with time indicating increased ettringite contents from early ages, similar to reports on supersulphated cements [19].…”

“…However, when comparing the NEW losses at 60°C for the pure commercial gypsum paste (100%CG) in Table 2 with those of the 70%CG binder, it is noted that this effect is delayed till after 28 days for the latter, instead of the drastic drop after 7 days suffered for former. It is possible that the hydration products from the GGBFS protected the gypsum crystals bearing the high temperature for longer periods, as is reported elsewhere [14]. Ettringite was not identified in the patterns of Fig.…”

“…This work is a complement of a previous contribution that deals with the strength development and reactivity of the same composite binders, in which a detailed description of the state of the art and characterization of the raw materials was presented [14]. Some of the conclusions of such work highlighted the marked differences in compressive strength between both types of calcium sulphate binders: the use of anhydrite was better over the use of hemihydrate in terms of strength; however, a notable gain in the rate of heat evolution was registered by the former during the initial minutes of curing.…”

“…Ground granulated blastfurnace slag from Altos Hornos de Mexico (GGBFS) was ball milled to a Blaine fineness of 4300 cm 2 / g. Two pozzolanic materials were used as complements to the binders: type-F pulverized fly-ash (PFA) from a local thermoelectric plant and a silica fume (SF) from BASF. Details of the mineralogical composition of the raw materials was reported previously [14], where the main phases of CG and FG where hemihydrate and anhydrite, respectively, while traces of calcite and anhydrite were detected for the latter and quartz for the former. The GGBFS denoted a large fraction of vitreous network with crystalline phases such as melilite, merwinite and diopside.…”

“…Compressive strength and non-evaporable water (NEW) for the studies binders cured under water; adapted from[14]. Standard deviation for NEW < 0.18% for all cases.…”