Effect of particle size on the measurement of the apparent contact angle in sand of varying wettability under air-dried conditions

Yunesh Saulick,Sergio Lourenço,Béatrice Baudet,P Delage,A.-M Tang,Y.-J Cui,J.-M Pereira,S Ghabezloo

doi:10.1051/e3sconf/20160909003

Yunesh Saulick, Sergio Lourenço + Show 6 more

Open Access

https://doi.org/10.1051/e3sconf/20160909003

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Abstract

Changes in the wettability of soil are known to affect several processes such as infiltration and the shear strength of soil. In this study, the wettability of a medium to fine sand was chemically modified by using different concentrations of dimethyldichlorosilane (DMDCS). The sessile drop method (SDM) was used for the assessment of wettability of hydrophobised Leighton Buzzard Sand (LBS). The results demonstrate that beyond a concentration of 2 g per kg of LBS, the finer fraction had its apparent contact angle (ACA) increased up to 115° while the maximum ACA attained by the coarser fractions was 100°. At such high concentration of DMDCS, the effect of trapped air, which is known to increase the ACA, was found to be either small or insignificant. The standard deviations of the ACAs agreed well with past studies. The most important factors contributing to the water-repellent behaviour of chemically synthesised sand were attributed to the characteristics of the particles; these include surface area and particle shape.

Highlights

The wettability of natural soils is known to alter significantly with time due to numerous reasons such as organic matter and soil texture [1, 2, 3]
A decrease in particle size due to crushing will cause a significant increase in the surface area of the particles, which will in turn require more organic matter for coating
The difference in the maximum apparent contact angle (ACA) between the two sieve-fractions in Figure 2 demonstrates that the assumption of a larger fraction of air being trapped in the coarser particles compared to the finer ones is not justified for the relative higher ACA in fine sand

Summary

Introduction

The wettability of natural soils is known to alter significantly with time due to numerous reasons such as organic matter and soil texture [1, 2, 3]. A decrease in particle size due to crushing will cause a significant increase in the surface area of the particles, which will in turn require more organic matter for coating. A decrease in the wettability of soils causes increased surface runoff and enhance preferential flow in soils [3,4]. Shear strength of non-wettable soils as evaluated by direct shear tests performed by Bardet et al [6] using soils coated by wax demonstrated that there was no change in the angle of shear resistance compared to wettable samples. Lee et al [7] showed that a decrease in the peak friction angle (tests carried out with samples having same initial void ratios) could be observed when their samples were made less wettable by means of a silane coating

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