Moisture content measurement is mainly used to perform weight-volume calculations in soils. Also, moisture content is a measure of the shrink-swell and strength characteristics of cohesive soils.
Test applied: ASTM D2216: Standard Test Method for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass.
Equipment and Materials:
- Oven-safe containers
- Disturbed sample of moist soil
- Scale capable of measuring to the nearest 0.01 g
- Soil drying oven set at 110o ± 5 oC
Procedure:
Three measurements are taken in order to calculate the moisture content:
1) Mass of container, Mc;
2) mass of moist soil plus container before drying, M1; and
3) mass of dry soil plus container after drying, M2.
Moist soil is placed in an oven-safe container and dried for 12-16 hours in a soil drying oven. The soil-filled container is weighed before and after drying to obtain M1 and M2, respectively.
The moisture content, w is calculated as the mass of water in the soil, Mw divided by the sum of the mass of soil solids, Ms
Precautions:
- Avoid inadequate drying, or excessive drying beyond the recommended 12-16 hour drying period.
- For soils containing a significant amount of organic material or hydrous minerals such as gypsum, the oven temperature should be reduced to 60 oC instead of 110 oC as in these cases, some of the water is bound by the soil solids, so excessive drying will effectively drive some of the soil solids away and produce erroneous results.