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Determination of fractured faces of aggregates

References:   ASTM D 5821           AASHTO T-85               FLH Designation T 507-94

Definition:

A fractured face is defined as being caused either by mechanical means or by nature and should have sharp or slightly blunted edges. A gravel which  was previously fractured by hand  or by machine and then weathered by water or time is not accepted as fractured.

Natural fractures, to be accepted, must be similar to fractures produced by a crusher. A broken surface constituting an area equal to at least 25% of the projected area of the particle, as viewed perpendicular to (looking directly at) the fractured face, is considered an acceptable fractured face.

Apparatus (Instruments):

1.Mecahnical Splitter             2. Balance             3.Sieve 4.75(No 4)

Sampling:

The sampling is Follows Instructions in Sampling Page, but the sample must be as much as get the desired amount of sample retained on sieve No 4( test samples must just retained on sieve No 4) .Table below is showing the minimum amount of requirement of sample according to the maximum nominal size of aggregate.

Maximum Nominal Particle Size Minimum Weight Retained on Sieve No 4
37.5mm 2500   Grams
25mm 1500  Grams
19 mm 1000   Grams
9.5 mm 700     Grams
4.75 mm 500     Grams

            Table No 1 required sample sizes

Note: the (maximum nominal size) expression is  to a sample which pass at least 90% of total amount from  the same sieve  size. for example  when we say nominal gradation of  a sample is 25 mm ,it mean that at least 90% of total aggregate has passed from sieve 25 mm .

Procedure

         First split the sample to obtain enough amount according the table No 1.Wash the sample and dry it until reaching to a constant mass ,and Weight the sample and called it Test sample weight.

        By visual inspection separate the particles first by two category: 1.Crushed  2. Non Crushed ,then separate the Crushed Particles into two category: 1. one surface crushed  2. Two Surface Crushed, that have fractured faces, either one or two fractured faces. separate the particles which have one or two faces individually. then weigh the particles individually and record that .by a simple formula simply found the percentage of Crushed aggregate. Below is a preliminary explanation of Fractured Faces

Picture No ((1))

Picture No((2))

 

Picture No ((3))

Calculation

Percentage of  total Fractured faces   

W3=Two Faces F

Percentage of One Face Fractured Faces

Report the result to nearest percent (minimum two digit )

For Picture of Procedure Click Here