The Effect of Hydrometer Type on the Influence of the Phosphate Dispersants on Particle Size Distribution of Soil Fines

Abstract

Hydrometer method is used to determine the particle size distribution of fine portion of soils. Despite the introduction of new method SANS (2014), the national laboratories in South Africa still follow the guidelines laid down by the old method, TMH1 (1986). TMH1 (1986) does not make the provision for the effect of dispersant in the solution on the readings recorded during the test, thus incorrectly yielding inflated fines content. It also recommends the use of an old hydrometer (152H) which was replaced by hydrometer 152H: E100 as per SANS (2014). In this study, hydrometer analyses by using the hydrometer 152H: E100 are conducted to investigate the effect of dispersants (Calgon, sodium pyrophosphate decahydrate, and sodium tetra pyrophosphate) in various concentrations on the hydrometer readings when applying TMH1 (1986) method. The results showed an anomalous increase in the hydrometer readings with the use of dispersants in higher concentrations, thus indicating the importance of understanding the effect of dispersants on the particle size analyses of the fine soils, therefore, making it necessary to correct the fines content. These results when compared with results obtained by the old hydrometer 152H indicated that hydrometer 152H: E100 generally yields lower results in comparison to hydrometer 152H.