Strength Development in Phosphate‐Bonded Calcium Aluminate Cements

Abstract

The chemical reaction at room temperature between calcium aluminate cement (CAC) and NH&PO,-based fertilizer solution causes the formation of ammonium calcium pyrophosphate (AmCPP) as an amorphous cementitious phase.This phase was responsible for the development of strength in rapid-setting phosphate-bonded cement (PBC) specimens. Hydrothermal treatment of PBC at 200°C led to phase transformations of AmCPP and CAC into crystalline hydroxyapatite as the major phase and anorthite as the minor one. The moderate growth of these interlocked crystals in the interspaces of amorphous phases played an important role in creating a dense microstructure, thereby conferring a very high strength to the PBC. In contrast, an excessive crystal growth, which caused the formation of porous microstructure, resulted in a reduction in strength. [

Treatment of toxic metal aqueous solutions: Encapsulation in a phosphate-calcium aluminate matrix

“…These two facts enhanced the mechanical strength of the matrix. These findings were in line with those reported by Sugama and Carciello (1991) for hydrothermally cured phosphate-bonded calcium aluminate cements.…”

A safer disposal of hazardous phosphate coating sludge by formation of an amorphous calcium phosphate matrix

“…The control mortar showed a very short setting time (6 min), which echoed the values reported for the phosphate-bonded calcium aluminate cements (Sugama and Carciello, 1991;Sugama and Carciello, 1995;Swift et al, 2013b). The presence of either WS or BS induced a delay in the setting time (Table 4).…”

“…Hardening of CAC is primarily due to hydration of anhydrous phases such as CA, CA 2 and C 12 A 7 , yielding the metastable hexagonal phases CAH 10 , C 2 AH 8 and amorphous aluminium hydroxide, which is followed by the formation of the stable cubic phases C 3 AH 6 and AH 3 , in a highly temperature dependant process (Ukrainczyk et al, 2012). A variant of CAC binder is that derived from acidbase reaction between acidic phosphate solutions and base reactant CAC, forming polyphosphate-CAC matrices, which show some advantages in comparison with unmodified CAC specimens (Sugama and Carciello, 1991;Sugama and Carciello, 1995;Swift at al., 2013a;Swift et al, 2013b;Fernández et al, 2014).…”

Identification of the hydrate gel phases present in phosphate-modified calcium aluminate binders

“…Early studies conducted by Sugama et al [21] suggested that the mechanism of reaction in ammonium phosphate-modified CAC takes place via an acid-base reaction, between the acidic phosphate solution and the basic calcium aluminate cement. This system has been reported to favour the In the case of CAC blended with sodium monophosphate (NaH 2 PO 4 ) and sodium polyphosphate ((NaPO 3 ) n ), the phase identification is still under discussion: formation of a sodium calcium orthophosphate hydrate (NaCaPO 4 •xH 2 O) and alumina gel was originally proposed [20], while later work suggested instead the formation of a calcium hydrogen phosphate hydrate (Ca(HPO 4 )•xH 2 O) and a hydrated alumina gel [24].…”