Influence of C[sub(3)]A content on frost and scaling resistance

Abstract The effects of chemical transformation processes on the frost and frost-deicing salt resistance of concrete are by far not of the same order as the physical effects, but they are nevertheless significant. Our investigations showed that monosulphate (AFm phase) is particularly instable and will transform to ettringite (AFt phase) under frost and also under frost-deicing salt attack. This formation of secondary ettringite, which is supported by thermodynamic conditions at low temperatures, may reduce considerably the frost and frost-deicing salt resistance of concretes without airentrainment. Keywords: C3A content, ettringite, frost attack, frost-deicing salt attack, monosulphate, portland cement, phase transformation

1 Introduction

Practical experience of many years has shown that it is possible to produce Portland cement with a high frost and scaling resistance - independent of the types of phases of the cement -, if favourable air void parameters are created by air-entraining agents, if the water-cement ratio is kept low, and if frost and deicing-salt resistant aggregates are employed. On the other hand, however, it is well-known that Portland cement concretes and mortars without air-entrainment which differ only in the type of Portland cement used may vary considerably in their frost and scaling resistance. This is the reason why already for decades attempts have been made to discover a relationship between the types of phases in Portland cements and the frost and scaling resistance of the respective concretes. In the discussions on the influence of cement

on frost and scaling resistance the evaluation of the clinker phases of Portland cements is of particular interest.