How to determine the surface moisture in fine aggregate?

The surface moisture in fine aggregate is determined by field test. This test covers the procedure for determining the amount of surface moisture in fine aggregates by displacement in water. The accuracy of the method depends upon accurate information on the specific gravity of the material in a saturated surface dry condition.


Note: The same procedure, with appropriate changes in the size of sample and dimensions of the container may be applied to coarse aggregates.


Field Method for Determination of Surface Moisture Content of Fine Aggregate

Field Method for Determination of Surface Moisture of Fine Aggregate as per IS: 2386 Part-3 (1963)


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IS Code for Determination of Surface Moisture in Fine Aggregate by Field Method:-

IS: 2386 Part-3 (1963): Method for determination of Specific Gravity, Density, Voids, Absorption and Bulking in Aggregates


Apparatus Required for Determination of Surface Moisture in Fine Aggregate by Field Method:-

Apparatus

Description

Balance

A balance having a capacity of 2 kg or more and sensitive to 0.5 g or less.

Flask

A suitable container or flask preferably of glass or noncorrosive metal.


Specification for flask: The flask may be a pycnometer, a volumetric flask, a graduated volumetric flask or other suitable measuring device. The volume of the container shall be from 2 to 3 times the loose volume of the sample. The container shall be so designed that it can be filled up to the mark, or the volume of its contents read, within 0.5 ml or less.



Sampling and Selection of Test Specimen:

A representative sample of the fine aggregate shall be taken for the field test of surface moisture content. The weight of sample should not be less than 200 g. Note that larger samples will give more accurate results.


Temperature and Humidity:

The surface water content may be determined either by weight or by volume. In both cases the test should be conducted at a temperature range of 22°C to 32°C.



Procedure for Determination of Surface Moisture in Fine Aggregate by Field Method:-

The surface moisture content in fine aggregate may be determined either by weight or by volume.


Method 1: Determination of Surface Moisture in Fine Aggregate by Weight

  1. Fill the container up to the mark with water and determine the weight in grams.
  2. Then empty the container.
  3. Place enough water in the container to cover the sample, after which pour the sample of the fine aggregate into the container and remove the entrained air.
  4. Fill the container with the original mark and determine the weight in gram.

The amount of water displaced by the sample shall be calculated as follows:


Field Method for Determination of Surface Moisture Content of Fine Aggregate

Where;

Vs = Weight in g of water displaced’ by the sample,

Mc = Weight in g of container filled up to the mark with water,

Ms = Weight in g of the sample and

M = Weight in g of the sample and container filled to the mark with water.



Method 2: Determination of Surface Moisture in Fine Aggregate by Volume

  1. Measure the volume of water in milliliters sufficient to cover the sample and place it in a container.
  2. Pour the weighed sample of the fine aggregate into the container and remove the entrained air.
  3. Determine the combined volume of sample and water by direct readings when a graduated flask is used.
  4. Where a pycnometer or volumetric flask of known volume is used, determine the combined volume of the sample and water by filling it to the mark with the measured volume of water and subtracting this volume from the volume of the container.

The amount of water displaced by the sample shall be calculated as follows:


Field Method for Determination of Surface Moisture Content of Fine Aggregate

Where;

V = Volume in ml of water displaced by the sample,

V = Combined volume in ml of the sample and water and

V = Volume in ml of water required to cover the sample.



Calculation:-

The percentage of surface moisture in terms of the saturated surface-dry fine aggregate and in terms of the weight of wet fine aggregate shall be calculated as follows: 

Where;

P = Percentage surface moisture in terms of saturated surface dry fine aggregate,

P = Percentage surface moisture in terms of the weight of wet fine aggregate,

V = Weight in g of water displaced,

V = The weight of the sample (M) divided by the specific gravity on saturated and surface-dry basis, determined as prescribed,

M = Weight in g of the sample.


Note:- These formulae are readily derived from basic relationships. For convenience, express P in terms of the ratio r, that is, the ratio of the weight of surface moisture to the weight of the saturated surface-dry sample. It follows that:

Field Method for Determination of Surface Moisture Content of Fine Aggregate

Reporting of Results:-

The surface moisture in the fine aggregate shall be reported to the nearest one percent and also the method of determination, that is, either by weight or by volume.



Safety and Precautions While Testing:

  1. Clean the apparatus thoroughly before testing and after testing.
  2. The test should be performed away from vibrations and other disturbances.
  3. Care should be taken to maintain the specified temperature, humidity as per test requirement.


FAQs:

What is surface moisture in fine aggregate?

Surface moisture in fine aggregate is the free water retained on surfaces of aggregate particles and considered to be part of the mixing water in concrete, as distinguished from absorbed moisture.


Is any field method for determination of surface moisture in fine aggregate?

Yes, there is a field method for determination of surface moisture in fine aggregate. The full procedure with apparatus list, observations, formula and reporting are discussed below.


Value of the surface moisture in fine aggregate:

The stockpiled fine aggregate is often in a wet state with a surface humidity of 0 to 5%. More water can be placed at the intersection between particles than in coarse aggregates.


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