Expert: Bryan P. Lindsey, P.E. - 6/14/2010

Question
Hi,please i will like to know the importance of carrying out moisture content test and specific gravity test on soils before use in road constructions

Answer
The moisture condition test is a method of quickly assessing the suitability of earthwork materials for use as fill, i.e. the soil / fill is at a moisture content such that it can be fully compacted by the appropriate plant.

The moisture condition test is a physical test indicating how much compactive effort is needed to compact a sample of soil at a particular moisture content.

Compactive effort is provided by dropping a captive  weight vertically a known distance on to a sample of soil in a cylindrical mould, and measuring compaction.
By counting blows to give the required compaction it will be possible to establish a Moisture Condition Value,(MCV), for a soil at a particular moisture content.

From laboratory compaction/density tests it is possible to determine an optimum moisture content at which site compaction of that soil should take place.

By performing a MCT on a soil sample at this optimum  moisture content at which it is able to be fully compacted, you are able to establish a MCV reference number. then a MCT performed on site should give a MCV  that complies, (with a small tolerance), to the MCV reference number to ensure maximum compaction of the soil is able to take place assuming correct layer thickness and compaction plant, and no change in soil type.

The MCT therefore excludes the need for a moisture content to be taken on site and allows a quick assessment of the suitability of fill material being placed.

The results obtained from this test method can be used to determine the unit weight of compacted dense bituminous mixtures and in conjunction with Test Method D 3203, to obtain percent air voids. These values in turn may be used in determining the relative degree of compaction.

Since specific gravity has no units, it must be converted to density in order to do calculations that require units. This conversion is made by multiplying the specific gravity at a given temperature by the density of water at the same temperature.