EFFECTS OF MOISTURE ON AGGREGATE PROPERTIES

The effects of moisture on the properties of four aggregates from igneous rock quarries in the UK have been investigated. Three suspect sources were selected because premature failure of bituminous macadam wearing courses incorporating these aggregates had been reported. A fourth source of aggregate known to be of good quality was selected as a control. At each quarry faces were examined and an engineering weathering grade classification was used to assess material in situ and also when crushed. Most material was found to be of grades II and III with poorer quality material removed during processing. The general lack of fresh grade I material means that most aggregate particles exhibit some degree of alteration. For each source two sizes of aggregate, coarse and fine, were sampled and subjected to moisture content, water absorption and standard and modified aggregate impact tests in both "dry" and "wet" conditions and at a range of temperatures. Flakiness and soundness tests were also performed on each of the aggregates. Results showed there to be significant differences in the behaviour of the four aggregates with respect to moisture, strength and soundness. Considerable differences in the rate of moisture movement are considered to be related to differences in mineralogy, texture and surface area. Generally the aggregates were weakened by soaking but the amount of weakening varied greatly. Increasing temperature had no significant effect on strength. Differences in strength and behaviour of coarse and fine fractions of the same aggregate are often due to a difference in quality. Reduction in mechanical strength can be detected by comparison of standard and modified aggregate impact values, and breakdown of physical integrity by using the magnesium sulphate soundness test. (TRRL)