1. AASHTO T90 (2020) Standard method of test for determining the plastic limit and plasticity index of soils. American Association of State Highway and Transportation Officials, Washington, DC, USA
2. AS 1289.3.2.1 (2009) Methods of testing soils for engineering purposes: soil classification tests — determination of the plastic limit of a soil — standard method. Standards Australia, Sydney, NSW, Australia
3. ASTM D4318 (2008) Standard test methods for liquid limit, plastic limit, and plasticity index of soils. ASTM International, West Conshohocken, PA, USA
4. BS 1377–2 (1990) Methods of test for soils for civil engineering purposes — part 2: classification tests. British Standards Institution, London, UK
5. BS EN ISO 17892–12 (2018) Geotechnical investigation and testing – Laboratory testing of soil. Part 12: Determination of liquid and plastic limits. British Standards Institution, London, UK