Effect of sulphate corrosion on the durability of air-entrained cement mortars

Monika Knap,Wojciech Piasta,D Beben,A Rak,Z Perkowski

doi:10.1051/matecconf/201817402012

Monika Knap, Wojciech Piasta + Show 3 more

Open Access

https://doi.org/10.1051/matecconf/201817402012

Copy DOI

Abstract

Sulphate corrosion is a complex sequence of chemical and physical processes that, when the aqueous sulphate solutions are exposed for a sufficiently long time, irreversibly destroys the microstructure of cement paste. In order to determine the durability of Portland cement mortars, mortar resistance tests were carried out on a 5% solution of sodium sulphate by measuring linear deformations. The tests included 1 series of non air-entrained mortars and 3 series of air-entrained mortars with air content: 7%, 10% and 13%. The biggest deformations were observed for non air-entrained samples, the smallest for mortar with an air content of 13%. Compressive strength tests of mortars after 28 days and 80 weeks of residence in a solution of sodium sulphate were also carried out. For all mortars, the strength measured after 80 weeks immersion in Na2SO4 increased in relation to the strength after 28 days of maturation. Observations of the cement mortar microstructure using a scanning electron microscope (SEM-EDS) showed that ettringite was present in both the C-S-H structure and the air pores. By means of XRD analysis, the occurrence of crystalline materials was detected. Based on the research, it was found that air-entrained cement mortars showed greater durability in the context of sulphate corrosion.

Highlights

The durability of the building material, including cement composites, is most often referred to as the ability to preserve the original properties of the material throughout the assumed lifetime, without significantly reducing the usefulness and without the need for excessive maintenance [1]
The term sulphate corrosion is understood as destroying cement composites, which is caused by the physicochemical interaction of aqueous sulphate solutions with cement hydration products [3]
In the case of air entrained mortars (AE), the air content increases by 3% and amounts to 7%, 10% and 13%, respectively

Summary

Introduction

The durability of the building material, including cement composites (concrete, mortar, paste), is most often referred to as the ability to preserve the original properties of the material throughout the assumed lifetime, without significantly reducing the usefulness and without the need for excessive maintenance [1]. Sulphate corrosion is associated with the emergence of new minerals (gypsum, ettringite) through chemical reactions They can increase in volume and cause the expansion of cement paste. Ping and others [5] found that the reason for the expansion is the crystallization pressure, which is caused by the formation of ettringite from a supersaturated solution in small pores. This theory was the subject of the Scrivener study [6], which is of the opinion that expansion is not dependent on the amount of ettringite formed, but on where it is created. If the monosulphate and gypsum are locally in the same place, the formation of ettringite inside the small pores of the structure can induce expansive forces due to the crystallization pressure generated [7]

Methods

Findings

Discussion

Conclusion