Properties of Phosphate-based Cements with High Fly Ash Content

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Title: Properties of Phosphate-based Cements with High Fly Ash Content

Author(s): Samson T. Tassew and Adam S. Lubell

Publication: Special Publication

Volume: 294

Issue:

Appears on pages(s): 1-16

Keywords: magnesium potassium phosphate cement, fly ash, sand mortar, compressive strength, flexural strength, elastic modulus.

Date: 10/4/2013

Abstract:
Compared to the hydration process of traditional Portland cements, phosphate-based cements rely on an acid/base reaction process to quickly achieve strong, lightweight and durable binders with lower embodied energy. Since the binding action relies on the chemical composition of the initial components, the rheological and mechanical properties of the resulting ceramic concretes can also be influenced by other mix components including fly ash, fillers and aggregates. This paper reports on an ongoing study examining properties of concretes produced with magnesium potassium phosphate cement binders that incorporate fly ash contents of up to 80% of the total binder mass. Highly flowable mixes were developed with setting times that could be controlled through use of commonly available admixtures. The highest compressive strength of the binders and mortars were achieved when the fly ash content was 50% of the total binder mass. The produced binders and sand mortars had densities of 1800 kg/m3 [3034 lb/yd3] and 2100 kg/m3 [3540 lb/yd3] and compressive strengths of 35 MPa [5.0 ksi] and 60 MPa [8.7 ksi] after 28 days of simple ambient curing. Decreases in both strength and density were observed as the fly ash content was increased further, but remained within practical ranges for common construction applications with high fly ash contents.