Microstructure of CEM II/B-S Pastes Modified with Set Accelerating Admixtures

Abstract

The presented paper aims to describe the influence of accelerating admixtures on the properties and microstructure of cement pastes and mortars. Blended slag cement CEM II/B-S containing two different clinkers (differing amounts of siliceous and aluminous phases) and four types of accelerators (calcium nitrate, sodium hydroxide, cement kiln dust, and crystal seeds) were used in research. Compressive strength tests (after 12, 24, 48 h of curing), Scanning Electron Microscope (SEM) observations together with an Energy Dispersive Spectroscopy (EDS) analysis, Mercury Intrusion Porosimetry (MIP) tests, and X-ray diffraction (XRD) analysis were conducted. Results have shown that SEM and EDS examination of the microstructure of cement pastes modified with accelerating admixtures at the observed points did not reveal differences that would be sufficient to explain the changes in compressive strength. Still, the increase in amorphous phase content indicates a faster hydration reaction rate for all pastes modified with accelerating admixture. It is backed up also by lower non-hydrated compounds content. All admixtures accelerate the hydration reaction of calcium silicate phases of cement, but only NaOH and cement kiln dust (CKD) influence the aluminate phase reaction rate. The pore volume is independent of the clinker type, while the pore size distribution is not.

Interactions between C-steel and blended cement in concrete under radwaste repository conditions at 80 °C

“…The recipe of the PURAM concrete detailed in Table 1 was considered for the modelling. The oxide composition of the CEM II-B-S 42.5 N was taken from Lubloy et al 21 and Pizon et al 22 . The proportions of the CEM II-B components were set at 73.5 wt.% CEM I clinker, 24.5 wt.% blast furnace slag and 2 wt.% anhydrite (CaSO 4 ) 21 .…”

“…The proportions of the CEM II-B components were set at 73.5 wt.% CEM I clinker, 24.5 wt.% blast furnace slag and 2 wt.% anhydrite (CaSO 4 ) 21 . The oxide compositions of the clinker and blast furnace slag 22 are detailed in Table SI-1 . The hydration of the CEM I clinker was assumed to be completed.…”

Influence of Accelerating Admixtures on the Reactivity of Synthetic Aluminosilicate Glasses

“…The impact of accelerating admixtures on SCMs has been generally investigated on blended cements [9][10][11][12]. CaCl 2 has been shown to increase the reactivity of blast furnace slag after 10 h of hydration in slag-blended cements [13].…”