Testing the soundness of aggregates using different methodologies

Abstract

This paper compares the European (EN) and US (ASTM) standard tests for the soundness of aggregates. The main purpose of the paper is to identify the differences between these two methods and to investigate the extent of weathering inflicted on aggregates by sodium and magnesium sulphate salt solutions. The results show that both tests (using weighted average) produce similar mass losses with magnesium sulphate. They also suggest that the EN test (Annex B) is unsuitable for fine aggregates. The loss in mass for coarse aggregates tested with magnesium sulphate increases as the fraction size is reduced.

Introduction

Aggregates used in the construction industry for the manufacture of portland cement concrete and asphalt concrete must be durable in order to perform well in structures or pavements. Several durability tests are available to quantify the weathering resistance of aggregates. In EU member states, the magnesium sulphate heptahydrate soundness test (EN 1367-2) [1] is used, whereas in most of the US and some other countries in the world, the ASTM C88 [2] sodium/magnesium sulphate soundness test is used. Both tests are geared towards providing information related to aggregates’ ability to withstand environmental effects such as wetting–drying and temperature changes. They involve repeated cycles of immersion of aggregate samples in a saturated salt solution and subsequent drying to constant weight. This process causes salt crystals to form in aggregate pores; the formation of these crystals leads to the development of internal stresses, which tend to break the aggregate.

The sodium sulphate soundness test’s validity and repeatability have been questioned by researchers across the US [3], [4], [5]. According to Kline et al. [5], the test has poor repeatability not only among laboratories, but also between samples in the same laboratory. As a result of the poor repeatability of the sodium sulphate soundness test, when samples fail to meet minimum criteria, contractors tend to contest the results. Furthermore, the sodium sulphate test has mostly received poor ratings from researchers in terms of correlation to field performance [5], [6], [7], [8] despite some evidence pointing towards the opposite direction [9]. Better correlation with field performance has been reported for the magnesium sulphate test in a study carried out in Hawaii [9]. It is worth noting that Hawaiian aggregates have distinctively high water absorption (WA) values, as opposed to the rest of the world where WA ⩽ 1.5%. Similarly high WA values have recently been reported for calcareous aggregates from Cyprus [10].

The objective of this paper is to investigate whether the magnesium sulphate heptahydrate test provides more reliable and repeatable information about the quality of an aggregate than the sodium sulphate test. The major differences between the two tests are highlighted and experimental results on a variety of coarse and fine aggregate samples from different geological formations are presented. The tests have been carried out using both the EN and ASTM methodologies.