EXPERIMENT ON AGGREGATE ABRASION TEST

EXPERIMENT ON THE DETERMINATION OF AGGREGATE ABRASION TEST OF A COARSE AGGREGATE

AIM

•      To determine that Abrasion value of a coarse aggregate.     
•     To assess its durability in pavement surfacing.

APPARATUS

·        Abrasion machine

·        Abrasive charges

·        Oven

·        Weighing Balance

·        B.S. Test Sieves of sizes 20mm, 14mm, 10mm and 1.70mm.

THEORY

The Los Angeles test is a measure of degradation of mineral aggregates of standard gradings resulting from a combination of actions including abrasion or attrition, impact, and grinding in a rotating steel drum containing a specified number of steel spheres. The Los Angeles (L.A.) abrasion test is a common test method used to indicate aggregate toughness and abrasion characteristics. Aggregate abrasion characteristics are important because the constituent aggregate in HMA must resist crushing, degradation and disintegration in order to produce a high quality HMA.
 For an aggregate to perform satisfactory in pavement, it must be sufficiently hard to resist the abrasive effect of traffic over long period of time. Furthermore, they must be able to adequately transmit loads from the pavement surface to the underlying layers and eventually the sub grade. The soft aggregates will be quickly ground to dust, whilst the hard aggregates are quite resistant to crushing effect.

The test also will determine the quality of the aggregate.

The L.A. Abrasion test is widely used as an indicator of the relative quality or competence of mineral aggregates.

Classification of aggregate using Aggregate Impact Value is given by :

< 10%	Exceptionally Strong
10 - 20%	Strong
20 - 30%	Satisfactory
> 35%	Very weak

SAMPLE PREPARATION

ü We placed the sample in an oven at a temperature not exceeding 110°C and for a period of 4 hours

ü We then allowed it to cool off at room temperature.

ü We then passed the sample through sieve sizes of 20mm,14mm and 10mm respectively over each other.

ü We weighed 2500g of sample passing sieve size 20mm but retained on the 14mm sieve (Sample X)

ü We weighed 2500g of sample passing through the sieve size 14mm but retained on the 10mm sieve (sample Y)

PROCEDURE

·        We opened the machine by removing its cover and then poured samples X and Y into the machine

·        We poured in abrasive charges and fix the cover back on firmly

·        We switched on the machine and allowed it 500 revolutions at 30 revolutions per minutes

·        After the revolution was complete, we switched off the machine and emptied its content in to the tray below the machine.

·        We then passed the sample collected in the tray through the 1.7mm sieve until no significant amount is passed through it in one minute.

·        We measured both the fraction retained (A) and fraction that passed through (B) the 1.7mm sieve.

DATA AND CALCULATIONS

Total mass of Prepared Samples X & Y = 5000g

Mass of portion passing through the Sieve Size 1.7mm (B) = 1611g

Therefore, the % fines formed to the total sample mass is

% Fines = B/(X + Y)

% Fines = (1611/5000) x 100

          = 32.22 %

OBSERVATION

ü The aggregate abrasion value is a little less than 35%

PRECAUTION

• ü We ensured the sample was properly prepared for the test.
• ü We ensured that samples X and Y were poured completely into the machine.
• ü We ensured that we poured the abrasive charges immediately after the sample was poured.
• ü We ensured the machine was covered before switching on the machine.
• ü We ensured that the timer was set before starting the machine.
• ü While the machine was revolving there was no form of horse play around it.
• ü When the revolution was complete, the machine was switched off and allowed to stop by itself before it was opened.

ERROR

• Human Error
•  Parallax error

CONCLUSIONS

After the test has been carried out and proper calculations done, it was observed that the Aggregate Abrasion value to be above 30%.

RECOMMENDATION

From the classification given in the theory of this report, it can only be concluded that the sample only satisfies the standard for concrete works hence cannot be used for Pavement works. It is weak and has a poor durability in pavement surfacing when traversed by many repetitions of truck wheel loads.