Some Issues of Shrinkage-Reducing Admixtures Application in Alkali-Activated Slag Systems

Abstract

Significant drying shrinkage is one of the main limitations for the wider utilization of alkali-activated slag (AAS). Few previous works revealed that it is possible to reduce AAS drying shrinkage by the use of shrinkage-reducing admixtures (SRAs). However, these studies were mainly focused on SRA based on polypropylene glycol, while as it is shown in this paper, the behavior of SRA based on 2-methyl-2,4-pentanediol can be significantly different. While 0.25% and 0.50% had only a minor effect on the AAS properties, 1.0% of this SRA reduced the drying shrinkage of waterglass-activated slag mortar by more than 80%, but it greatly reduced early strengths simultaneously. This feature was further studied by isothermal calorimetry, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Calorimetric experiments showed that 1% of SRA modified the second peak of the pre-induction period and delayed the maximum of the main hydration peak by several days, which corresponds well with observed strength development as well as with the MIP and SEM results. These observations proved the certain incompatibility of SRA with the studied AAS system, because the drying shrinkage reduction was induced by the strong retardation of hydration, resulting in a coarsening of the pore structure rather than the proper function of the SRA.

Development of solutions concerning regulation of proper deformations in alkali-activated cements

“…Additional effects of such compounds are known. For example, a decrease in AASC shrinkage in presence of polypropylene glycol (polyether) is due to redistribution of the pore space through raising number of pores with diameter of 0.1-1 μm in which capillary pressure is much lower than that in smaller capillaries [25].…”

“…The presented studies [14][15][16][17][18][19][20][21][22][23][24][25] show positive influence of mineral and organic admixtures on reduction of AAC shrinkage, however there is no explanation of the mechanism of their structure formation. This fact limits understanding ways of regulating proper deformations in artificial stone.…”

Effects of Aging on the Tensile Properties of Polyethylene Fiber-Reinforced Alkali-Activated Slag-Based Composite

“…Many researchers have investigated methods to reduce the amount of cement used or even to develop cement-free concrete utilizing pozzolanic and latent hydraulic materials [11][12][13][14][15][16]. Recently, in an effort to simultaneously improve both the mechanical properties and the environmental aspect of concrete, studies have been conducted on highductility cement-free composites using alkali-activated binders and synthetic fibers.…”

Effect of a Synthetic Nano-CaO-Al2O3-SiO2-H2O Gel on the Early-Stage Shrinkage Performance of Alkali-Activated Slag Mortars

“…Kalina et al [ 15 ] discovered that polypropylene glycols reduce surface tension and seem to be suitable for shrinkage-reducing admixture (SRA), and the significant reduction of surface tension leads to effective reduction of shrinkage. Bílek et al [ 16 ] found that shrinkage-reducing admixtures (SRAs) based on 2-methyl-2,4-pentanediol exhibits good ability to reduce shrinkage, when 1.0 wt % of this SRA reduced the drying shrinkage of waterglass-activated slag mortar by more than 80%, but at the same time greatly reduced early strengths.…”