Fines quality assessment in all-in aggregates for pavement layers related to different standard procedures

Abstract

During the construction of the unbound pavement layers of Corridors X and XI in Serbia, a problem was detected regarding the evaluation of cleanliness of the available materials. The European standard for the sand equivalent from 1999 to 2015 had significant changes related to the test procedure. A mass correction has been taken into account. It consists of replacing a part of the fines with rinsed material (0.063/2 mm) when the percentage of fines exceeds 10% in a tested fraction. Thus, the test sample usually yields high values of the sand equivalent, which often exceeds the limits of 50% and 60%. From the standpoint of the technical specifications, aggregates are considered clean, while using other methods like methylene blue or a plasticity index, the presence of clay particles above the limits can be confirmed. This paper presents the results of research on 63 laboratory-prepared test samples of limestone aggregate with small quantities of the smectite group of clay minerals, where the fines content in the unbound aggregate, 0/31.5 mm, gradually increased up to 20%. It was found that the sand equivalent values are continuously decreasing from 84 to 14% in the fraction 0/2 mm and from 87 to 18% in the 0/4 mm fraction, with increasing of the methylene blue value of the all-in aggregate (MBA) from 0.4 to 4.5 g/kg. Correlations of different methods and fractions, as well as with the content of fines were found. There are no correlations with SE10 because of grouping the test data around one point.