Rheological and the Fresh State Properties of Alkali-Activated Mortars by Blast Furnace Slag

Abstract

The fresh and rheological properties of alkali mortars activated by blast furnace slag (BFS) were investigated. Consistency tests, squeeze flow, dropping ball, mass density in the hardened state, incorporated air, and water retention were performed. Mortars were produced with the ratio 1:2:0.45 (binder:sand:water), using not only ordinary Portland cement for control but also BFS, varying the sodium content of the activated alkali mortars from 2.5 to 15%. The results obtained permitted understanding that mortars containing 2.5 to 7.5% sodium present a rheological behavior similar to cementitious mortars by the Bingham model. In turn, the activated alkali mortars containing 10 to 15% sodium showed a very significant change in the properties of dynamic viscosity, which is associated with a change in the type of model, starting to behave similar to the Herschel–Bulkley model. Evaluating the properties of incorporated air and water retention, it appears that mortars containing 12.5% and 15% sodium do not have compatible properties, which is related to the occupation of sodium ions in the interstices of the material. Thus, it is concluded that the techniques used were consistent in the rheological characterization of activated alkali mortars.

Materials for Production of High and Ultra-High Performance Concrete: Review and Perspective of Possible Novel Materials

“…This is also related to the fact that the OPC industry is highly polluting. Alkali-activated precursors and cement are considered alternative and eco-friendly binders [ 232 , 236 , 237 ], usually resulting in concretes with lower CO 2 emissions than OPC-based concrete (around 10%, according to [ 238 ]). The accurate determination of the environmental impact associated with these binders—and consequently compare it with those associated with OPC—would require a detailed analysis which will not be addressed in this paper; nonetheless, further details can be found in [ 239 , 240 , 241 ].…”

“…Regarding calcium-rich precursors, the main materials used are steel residues or by-products, mainly blast furnace slag. The alkaline activation of these materials results in products similar to those obtained during the hydration of OPC such as C-S-H, but with the potential to be even stronger [ 236 , 274 ]. Regarding calcium-rich precursors, the main materials used are steel residues or by-products, mainly blast furnace slag.…”

“…The main disadvantages of the application of blast furnace slag as a precursor in alkali-activated cement are related to the loss of workability in the material in the fresh state. Marvila et al (2021) [ 236 ] evaluated the rheological aspects of HPC produced with alkali cement activated on the basis of blast furnace slag and sodium hydroxide solution. The authors observed that in smaller amounts of sodium, up to 7.5% Na 2 O, the obtained material behaved rheologically similar to materials based on OPC.…”

“… Scanning electron microscopy illustrating tobermorite obtained by activating alkali cement activated on a blast furnace slag base [ 236 ]. …”

Natural Fibers as an Alternative to Synthetic Fibers in Reinforcement of Geopolymer Matrices: A Comparative Review

“…When the load is continued, the fiber breaks, and then some connections in the fracture area are broken almost simultaneously. At this stage, the fiber breaks into two fragments, in addition to a void in the rupture region (break gap) [ 107 ]. With these connections breaking close to the fracture region, the connections closest to these end up being maintained, even if they remain tensioned, while the connection lines further away from the fiber rupture are not much affected by the applied effort, maintaining the original condition of regularity and balance [ 108 ].…”