Characterisation of magnesium potassium phosphate cements blended with fly ash and ground granulated blast furnace slag

Abstract

Magnesium potassium phosphate cements (MKPCs), blended with 50 wt.% fly ash (FA) or ground granulated blast furnace slag (GBFS) to reduce heat evolution, water demand and cost, were assessed using compressive strength, X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) spectroscopy on 25 Mg, 27 Al, 29 Si, 31 P and 39 K nuclei. We present the first definitive evidence that dissolution of the glassy aluminosilicate phases of both FA and GBFS occurred under the pH conditions of MKPC. In addition to the main binder phase, struvite-K, an amorphous orthophosphate phase was detected in FA/MKPC and GBFS/MKPC systems. It was postulated that an aluminium phosphate phase was formed, however, no significant Al-O-P interactions were identified. High-field NMR analysis of the GBFS/MKPC system indicated the potential formation of a potassium-aluminosilicate phase. This study demonstrates the need for further research on these binders, as both FA and GBFS are generally regarded as inert fillers within MKPC.

Production and Compression Strength of Mortars Containing Unprocessed Waste Powdered Steel Slag

“…It can be observed that the fayalite and magnetite contents are almost constant in the four batches, while the amount of other compounds can significantly change. In particular, the amount of glaucochroite and calcium iron oxide decrease with increasing the maximum particle size of the powders whereas that of aluminum calcium oxide and periclase tend to increase in agreement with literature data [31]. The variability of the content of these compounds can affect workability as well as durability of the mortars with a negative effect on their performance.…”

Evolution of phase assemblage of blended magnesium potassium phosphate cement binders at 200° and 1000°C

“…4); again, no crystalline reflections were identified that could be associated with a dehydrated KMgPO 4 phase. As discussed above, it is postulated that KMgPO 4 is non-crystalline between 200 °C -700 °C [25][26][27] , as a result of dehydration of struvite-K. Diffuse scattering associated with the glassy slag fraction is reported between 24 , however the diffuse scattering in the 200 °C diffraction pattern was evident over a wider range (between ), suggesting that more than one amorphous phase could be present. The quartz identified at 200 °C is believed to be contamination from the cleaning media (sand) used during grinding.…”

“…Backscattered electron micrographs of FA/MKPC and GBFS/MKPC binders are shown in for these binders as reported in the literature 12,24 . It was observed in both systems that the main binding phase, struvite-K, formed a continuous phase that was interspersed with embedded large struvite-K crystallites.…”

“…This density difference between the supplementary cementitious materials (SCMs) could also explain the disparity observed in Figure 3, as the slightly denser GBFS would occupy a smaller volumetric contribution (in a 20 mg TG sample) than the FA and, as such, it would appear that additional struvite-K had formed in the GBFS/MKPC binder. The authors have recently reported that FA and GBFS do not behave as inert fillers within the MKPC system but rather that incongruent dissolution results in the formation of secondary reaction products 24 , which makes it difficult to accurately quantify the proportion of the volumetric composition.…”

Orthogonal Experimental Studies on Preparation of Mine-Filling Materials from Carbide Slag, Granulated Blast-Furnace Slag, Fly Ash, and Flue-Gas Desulphurisation Gypsum

“…e major component of FGD gypsum is calcium sulphate dihydrate. At present, these industrial wastes are primarily utilised for the production of cement [1,2], concrete [3][4][5][6][7], geopolymers [8][9][10], and cementitious materials for mine filling [11,12]. For example, Ma et al [13] prepared sulphoaluminate cement that was capable of meeting special structural requirements from fly ash and FGD gypsum.…”