Density, Yield and Air Content of Fresh Mix Concrete (ASTM C-138)

 Density, Yield, and Air Content of Fresh Mix Concrete

(ASTM C-138)

Introduction

In this test, we have to determine the density of fresh-mix concrete and give formulas for calculating the yield, cement content and air content of the concrete,

Control the quality of concrete the density test is very important

A lower density may indicate

Material has changed lower specific gravity
Change in the proportion of ingredients
Higher air content
Higher water content
Lower cement content

A higher density would be indicated the reverse of the above mentioned 

Yield

Yield is defined as the volume of the concrete produced from a mixture of known quantities of the component's materials

Apparatus

Measuring cylindrical container

Temping rod, diameter 16 + 2 mm
Internal vibrator, diameter 19 to 38 mm, frequency 7000 per min.
Strike off Plate, Thick 12 mm, length, and width 50 mm greater than the measure 
Mallet, 600 + 200 grams

Internal Vibrator or Temping Rod

If the slump is greater than 75 mm, using a rod 
If the slump is 25 to 75 mm, using the rod or vibrator
If the slump is less than 25 mm, using a vibrator 

Procedure of Temping Rod

Fill the concrete in a cylindrical container with three layers of equal volume 

A first layer, rodding 25 times through its depth, tap the container 10 to 15 times with a mallet
A second layer, rodding 25 times through the previous layer approximately 25 mm, tap the container 10 to 15 times with a mallet
A third layer, rodding 25 times through the previous layer approximately 25 mm, tap the container 10 to 15 times with a mallet

Procedure of Internal Vibrator

Fill the concrete in a cylindrical container with two layers of equal volume 

Insert the vibrator at three different points in each layer

Ensure the vibrator does not rest or touch the bottom or sides of the container

Compacting the final layer insert the vibrator through the previous layer approximately 25 mm

Vibrate in the concrete until the depression is left from the surface of the concrete, Over vibration may cause segregation

Surface Leveling

Remove all excess concrete from the top of the container with a trowel or other tools

Strike off the surface of the concrete and finish it smoothly with a strike-off plate

Clean the exterior of the container and determine the mass


Calculation

Density = Net Mass of Concrete / Volume of Container

Yield = Total Mass of All Material / Density of Concrete

Relative Yield = Volume of Concrete Produce Per Batch / Volume of Concrete Design to Produce




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