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Durability Index Of  Aggregates

References:           AASHTO   T 210-91                 ASTM   D 3744-94   

Definition:  

This method describes the procedure for determining the durability of aggregates, the durability index is a value which represent the relative resistance of an aggregate to produce detrimental claylike fines when subjected to the prescribed mechanical methods of degradation.

Although this test is a little hard to do but its result is more useful. There are 4  procedure method, but here we just describe two of them which called  Method A  and  Method B.

Apparatus:

1. Mechanical Washing Machine

2.Mechanical shaker.  

3. Sieves & Timer                 

4. Collection pan               

5. A graduated cylinder with 1000 mL capacity  

6. Balance & Oven

NOTE:  All materials and samples using this test should be at 22±3° during the performance of the test.

Sampling

the sampling is as described in Sampling page.

Because the method of this  test is too long ,we divide it into several parts for better understanding for users.

Initial Sample Preparation

  1. Dry the sample sufficiently to permit a complete separation on the 4.75 mm sieve. drying must be at a normal temperature not exceed than 60° .the most used methods is air drying, warm fan drying and sunlight drying.
  2. if the sample has more clay ,try to turn an aggregate the sample during the drying to avoid formation of hard clays objects. if so break up any clay particles and if it is much remove them to avoid to affect the size gradation of sample.
  3. Determine the Gradation of the sample using the serial sieves(19,12.5,9.5,4.75,2.36 and 1.18 mm). throw out the materials retained on 19 mm sieve.
  4. Determine the method of test according the size of gradations which found in part three as follow:
  5. if less than 10 percent of total amount of sample ,passes from sieve No 4( 4.75 mm) ,use the procedure(( A )). and if less than 10 percent of sample ,retained on sieve No 4 (4.75 mm), use Procedure (( B )). But if both of the conditions satisfied or the percentages be equal must use both test methods to provide a good result.

Procedure ((A)):

 

Aggregate size Air Dry* Mass (Gr)
19.0-12.5 mm 1070±10
12.5-9.5 mm 570±10
9.5-4.75 mm 910±05
Total 2250±25 Gr.

          *[Drying the sample at constant mass of 110±5°is after gradation and is independent of the conditions described in part (1) ].

       Prepare a new sample using the table below ,( Note: this step will reviewed if 10% or more than 10 % of aggregate from 19.0 to 4.75 be loss).

Aggregate size Oven-dry mass (Gr)
19.0-12.5 mm 1050±10
12.5-9.5 mm 550±10
9.5-4.75 mm 900±05
Total 2500±25° Gr.

 

 After preparing the samples ,now it is time to do the test. and as described before we just only do the two common methods 1.(A) Method For Coarse aggregate   and  2. (B) Method for Fine aggregate .

Procedure for coarse aggregates

  1.  place the plastic  cylinder in a work table which  will not be subjected to vibration during the test. Pour (7) mL of Stock solution (Calcium Chloride) into the cylinder.

  2. place a 4.75 mm and 75 Um sieves  in the pan to collect the crossing water after washing the test.

  3. put the sample into the machine and add the water(1000 mL) to that. completely close the machine door and agitate that for 600±15 Seconds.

  4. Immediately after finishing the time remove the sample from machine and open the door, then shake that by hand horizontally to suspend the fines into water.

  5. pour the sample from machine into 4.75 mm and 75 Um sieves which are placed on a pan before, take out the materials retained on 4.75 mm and collect all materials and water finer than 75 Um.

  6. Add the  water in to dirty water to obtain 1000 mL of liquid. then transfer that into a vessel or a pan to be suitable  for pouring and moving.

  7. Place a funnel on the graduated cylinder which have Stock solution before. stir the  wash water  by hand  to bring the fines in suspension. then pour the liquid into the cylinder to bring the level of liquid into 381 mm mark.

  8. remove the funnel  ,place the stopper  in the end of the cylinder and prepare to mix the contents immediately.

  9. Mix them by turning  the cylinder up ,down, right and left ,allow the bubbles to traverse the length of the cylinder 20 times in 35 seconds.

  10. place  the cylinder  in  a work table without the shake. and let that for 1200±15 seconds.

  11. immediately after finishing the time read the height of the  sample in cylinder at nearest 2.5 mm .

Procedure (B)

Sample Preparation:

  1. Split or quarter  a representative portion from the material passing the 4.75 mm sieve to obtain about 500 grams suitable sample. Dry the sample in constant temperature of 110±5 ,and cool that in room air.

  2. place the sample in washing machine and add 1000 mL of water and close the machine door and agitate it for 120 second just after 600 seconds time after pouring water to  machine.

  3. after this two minute remove the pan (vessel) from the shaker and open it, and carefully pour it on a 75 Um which is placed on a pan. complete wash the sample until the out going water become clear and obvious.

  4.  after washing transfer the materials from sieve into a drying pan and dry it in natural temperature (110).leave the pan in a slanting surface to drain the water from bottom of the sieve ,then pour off this water. use large shallow  pan and spread the sample as thin as  possible to drying.

  5. after drying material, split it until obtain an amount of 85 mL measuring tin to overflow, after filling the tin, tap the bottom of the tin to allow consolidation of the material .after filing well the tin ,strike off  to level using the straight edge. be care  to obtain a truly good sample for this test .

Procedure for Fine aggregate

Just do the Sand Equivalent test. for this method ,except  using the shaker to shake continuously  for 600 seconds.(( For description of SAND EQUIVALENT TEST click Here))