Development of soil-water characteristic curve for flexible base materials using the methylene blue test

Hakan Sahin*, Fan Gu, Robert L. Lytton

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


This study describes an experimental investigation of the methylene blue test to determine the methylene blue value (MBV) and quantitatively generate the soil-water characteristic curve (SWCC) for unbound aggregate material based on the predicted percent fines content (PFC). The traditional methylene blue test has been improved significantly in terms of time, sample size, and method for analyzing the results. These improvements enable the methylene blue test to be not only a laboratory test but also a field test. This improved methylene blue test methodology is used to generate the SWCC for unbound aggregate material. The relationship between the MBV and the PFC value is established. The principles of unsaturated soil mechanics are taken into account to develop regression models for determining the four fitting parameters in a previously developed SWCC equation by using the predicted PFC value, which are then used to generate the SWCC for the unbound aggregates. The proposed method is validated by a comparison between the measured and predicted suction values for various unbound aggregate materials. This method is capable of generating the SWCC far more efficiently than any previous laboratory method, and it can even be used in field investigations because the methylene blue test requires limited portable test equipment. These improvements widen methylene blue test applications and allow for the development of the SWCC without requiring difficult laboratory experiments. Finally, the slope parameter, bf, in the SWCC equations is found to be associated with the moisture susceptibility of flexible base materials. A higher bf value indicates that the material is more moisture susceptible. This finding is successfully validated by the results from the permanent deformation test.

Original languageEnglish
Article number04014175
JournalJournal of Materials in Civil Engineering
Issue number5
Publication statusPublished - 1 May 2015


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