Durability of Cement and Ash Mortars with Fluidized and Siliceous Fly Ashes Exposed to HCl Acid Environment over a Period of 2 Years.

Elżbieta Janowska-Renkas,Grzegorz Janus,Jolanta Kowalska,Agnieszka Kaliciak

doi:10.3390/ma14123229

Abstract

The paper presents results of research on the impact of fly ash from fluidized bed combustion (FBC) of lignite, used in quantities of 30 and 45% by mass, and the mixture of FBC and silicious fly ash in amount of 45% by mass, on properties of cement–ash mortars. Mortars were exposed to aggressive environment of 1, 3, and 5% HCl solutions for 2 years. Mortars containing 45% FBC exposed to 1% HCl solution (pH = 2) showed the highest durability from among other mortars. The growth of their strength observed after 90 days of testing in 1% HCl environment, as well as the lowest drop of strength after 730 days of exposure to this environment, resulted from the reduced amount of large pores from 20 to 200 nm in mortars containing fly ash, with simultaneous growth of smaller pores of <20 nm during testing. A beneficial effect has been demonstrated of FBC addition to cement on properties of cement–ash mortars exposed to the aggressive impact of the HCl. Mortars with FBC fly-ash content increased to 45% by mass showed higher strength values, smaller differences in linear and mass changes, and increased durability in an aggressive environment observed during 730 days of testing.

Highlights

Durability of materials based on cement binders may be at risk in the presence of an aggressive environment of chloride ions
This was shown by the results of tests conducted by Rovnanikova [1], based on which the authors demonstrated that durability of cement-based composites was more endangered in the presence of chloride ions originating from MgCl2 and NaCl salts than in the presence of Cl- ions originating from hydrochloric acid (HCl)
A reduction in the specimens’ dimensions occurred; this was observed during a two-year conditioning of the mortars, irrespective of the type and content of fly ash applied, either fluidized bed combustion (FBC) or cement with siliceous fly ash (CFA)

Summary

Introduction

Durability of materials based on cement binders may be at risk in the presence of an aggressive environment of chloride ions. CFA) into the cement the formation of additional products in the cementitious mortars containing fly ash confirmed the possibility for wide application of such mortars, and indicated an (ZII–ZIV), the presence of which was a consequence of the reduced content of larger pores effective method regarding how the FBC fly ash could be improved, which was confirmed (>20nm) (Figure 30), which may be associated with a bonding reaction of chlorides with by the results presented and in the works of other authors [10,13]. The results of porosity testing presented were a proof of the formation of additional products in the cementitious mortars containing FBC fly ash (ZII–ZIV), the presence of which was a consequence of the reduced content of larger pores (>20nm) (Figure 30), which may be associated with a bonding reaction of chlorides with aluminum oxides [54]. Application of FBC ash in the cements tested did not allow us to make such a statement

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Results

Discussion

Conclusion