Abstract
This study is about the mechanical and microstructural properties of alkali-activated slag (AAS) paste using magnesium sulfate (MS) as an activator. MS is 2%, 4%, 6%, 8% and 10% contents of binder weight and water-binder ratio is 0.35. Compressive strength, X-ray diffraction, mercury-intrusion porosimetry, and thermal analysis were performed for analysis. The MS contents at which the maximum compressive strength appeared varied according to the measurement age. Hydration products affecting compressive strength and pore structure were ettringite and gypsum. As a result, the changes of ettringite and gypsum depending on the contents of MS have a great influence on the pore structure, which causes the change of compressive strength. The high MS contents increases the amount of gypsum in the hydration products, and the excess gypsum causes high expansion, which increases the diameter and amount of pores, thereby reducing the compressive strength.
Highlights
Eco-friendly cement has attracted much research interest
Regardless of the amount of magnesium sulfate (MS), the compressive strength increased with age from 3 to 28 days
The highest compressive strengths at 3 days, 7 days, and 28 days were observed in the contents of a particular MS. These results indicate that the compressive strength does not increase linearly with increasing MS contents
Summary
Eco-friendly cement has attracted much research interest. In particular, alkali-activated slag cement (AASC) is a blend of ground granulated blast-furnace slag (GGBFS) and activators [1,2]. Some researchers have reported that the silica modulus of sodium silicate influences the properties of alkali-activated slag [12]. Mobasher et al [15] studied how the sodium sulfate content and curing duration affect the binder structure of sodium-sulfate-activated slag cement; they prepared activating solutions containing 5, 10 and 25 wt% Na2 SO4 by dissolving solid anhydrous Na2 SO4 in distilled water. Rashad [18] reported the effect of five additives (silica fume, fly ash, limestone, hydrated lime and Portland cement) on the workability, compressive strength and drying shrinkage of 1% Na2 O equivalent of Na2 SO4 activated slag. Studied how gypsum (CaSO4 ·2H2 O) and phosphoric acid affect the properties of sodium-silicate-based alkali-activated slag (AAS) paste. Investigated how the slag fineness and Na2 SO4 dosage affect the strength, pH, hydration products and microstructure properties, compared with those of ordinary Portland cement. In order to do so, we present data of compressive strength measurements, X-ray diffraction (XRD), thermal analysis and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS)
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