Influence of Cement Type and Water-to-Cement Ratio on the Formation of Thaumasite

Ailian Zhang,Linchun Zhang

doi:10.1155/2017/7643960

Abstract

Cement mortar prisms were prepared with three different cement types and different water-to-cement ratios plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, these samples were submerged in 2% magnesium sulfate solution at 5°C and the visual appearance and strength development for every mortar were measured at intervals up to 1 year. Samples selected from the surface of prisms after 1-year immersion were examined by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results show that mortars with sulfate resisting Portland cement (SRC) or sulphoaluminate cement (SAC) underwent weaker degradation due to the thaumasite form of sulfate attack than mortars with ordinary Portland cement (OPC). A lower water-to-cement ratio leads to better resistance to the thaumasite form of sulfate attack of the cement mortar. A great deal of thaumasite or thaumasite-containing materials formed in the OPC mortar, and a trace of thaumasite can also be detected in SRC and SAC mortars. Therefore, the thaumasite form of sulfate attack can be alleviated but cannot be avoided by the use of SAC or SRC.

Highlights

In recent years, it has become a common practice to incorporate fine limestone powder as an additional constituent in the cement production [1]
It was reported that the addition of a finely ground limestone filler has a positive effect on the behavior of mortars exposed to magnesium sulfate solution due to the improved compactness [5]
It has been widely reported that cement and concrete containing limestone are subject to a special type of sulfate attack, attributed to taht elfoowrmtaetmiopneroaftuthraeus m(laoswiteer(CthaSainO31⋅5C∘CaC) O[63,⋅C7a]S.OS4i⋅n15cHe 2tOhe) formation of thaumasite involves the reaction of C-S-H in the cement paste with carbonate and sulfate ions [8], it results in severer and quicker decomposition of cement and concrete than conventional sulfate attack attributed to ettringite

Summary

Introduction

It has become a common practice to incorporate fine limestone powder as an additional constituent in the cement production [1]. The use of limestone in cement or concrete seems to have many benefits, such as reducing water demand, improving strength development, and being economical [3, 4]. It was reported that the addition of a finely ground limestone filler has a positive effect on the behavior of mortars exposed to magnesium sulfate solution due to the improved compactness [5]. The use of sulfate resisting Portland cement with low C3A content becomes ineffective to preserve cementitious materials against the thaumasite form of sulfate attack [9]. This paper presents experimental results related to the effect of cement type and water-to-cement ratio on the resistance to thaumasite sulfate attack of mortars containing a limestone filler

Experimental

Results and Discussion

Conclusions