Briefly explain Los Angles test.
Answers
Answered by
0
The Los Angeles (L.A.) abrasion test (Figure 1) is a common test method used to indicate aggregate toughness and abrasion characteristics. Aggregateabrasion characteristics are important because the constituent aggregate in HMA must resist crushing, degradation and disintegration in order to produce a high quality HMA
The standard L.A. abrasion test subjects a coarse aggregate sample (retained on the No. 12 (1.70 mm) sieve) to abrasion, impact, and grinding in a rotating steel drum containing a specified number of steel spheres.
After being subjected to the rotating drum, the weight of aggregate that is retained on a No. 12 (1.70 mm) sieve is subtracted from the original weight to obtain a percentage of the total aggregate weight that has broken down and passed through the No. 12 (1.70 mm) sieve. Therefore, an L.A. abrasion loss value of 40 indicates that 40% of the original sample passed through the No. 12 (1.70 mm) sieve.
The standard Los Angeles abrasion test is:
AASHTO T 96 or ASTM C 131: Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine
Background
Aggregates undergo substantial wear and tear throughout their life. In general, they should be hard and tough enough to resist crushing, degradation and disintegration from any associated activities including manufacturing (Figure 2), stockpiling (Figure 3), production (Figure 4), placing (Figure 5) and compaction (Figure 6) (Roberts et al., 1996[1]). Furthermore, they must be able to adequately transmit loads from the pavement surface to the underlying layers and eventually the subgrade. These properties are especially critical for open or gap graded HMA, which do not benefit from the cushioning effect of the fine aggregate and where coarse particles are subjected to high contact stresses (Wu et al., 1998[2]). Aggregates not adequately resistant to abrasion and polishing may cause premature structural failure and/or a loss of skid resistance. Furthermore, poor resistance to abrasion can produce excessive dust during HMA production resulting in possible environmental problems as well as mixture control problems.
Because of the preceding issues, a test to predict aggregate toughness and abrasion resistance is valuable. The L.A. abrasion test is the predominant test in the U.S.; it is used by 47 States (Wu et al., 1998[2]).
Test Concept
The L.A. abrasion test measures the degradation of a coarse aggregate sample that is placed in a rotating drum with steel spheres (Figure 7). As the drum rotates the aggregate degrades by abrasion and impact with other aggregate particles and the steel spheres (called the “charge”). Once the test is complete, the calculated mass of aggregate that has broken apart to smaller sizes is expressed as a percentage of the total mass of aggregate. Therefore, lower L.A. abrasion loss values indicate aggregate that is tougher and more resistant to abrasion.
The standard L.A. abrasion test subjects a coarse aggregate sample (retained on the No. 12 (1.70 mm) sieve) to abrasion, impact, and grinding in a rotating steel drum containing a specified number of steel spheres.
After being subjected to the rotating drum, the weight of aggregate that is retained on a No. 12 (1.70 mm) sieve is subtracted from the original weight to obtain a percentage of the total aggregate weight that has broken down and passed through the No. 12 (1.70 mm) sieve. Therefore, an L.A. abrasion loss value of 40 indicates that 40% of the original sample passed through the No. 12 (1.70 mm) sieve.
The standard Los Angeles abrasion test is:
AASHTO T 96 or ASTM C 131: Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine
Background
Aggregates undergo substantial wear and tear throughout their life. In general, they should be hard and tough enough to resist crushing, degradation and disintegration from any associated activities including manufacturing (Figure 2), stockpiling (Figure 3), production (Figure 4), placing (Figure 5) and compaction (Figure 6) (Roberts et al., 1996[1]). Furthermore, they must be able to adequately transmit loads from the pavement surface to the underlying layers and eventually the subgrade. These properties are especially critical for open or gap graded HMA, which do not benefit from the cushioning effect of the fine aggregate and where coarse particles are subjected to high contact stresses (Wu et al., 1998[2]). Aggregates not adequately resistant to abrasion and polishing may cause premature structural failure and/or a loss of skid resistance. Furthermore, poor resistance to abrasion can produce excessive dust during HMA production resulting in possible environmental problems as well as mixture control problems.
Because of the preceding issues, a test to predict aggregate toughness and abrasion resistance is valuable. The L.A. abrasion test is the predominant test in the U.S.; it is used by 47 States (Wu et al., 1998[2]).
Test Concept
The L.A. abrasion test measures the degradation of a coarse aggregate sample that is placed in a rotating drum with steel spheres (Figure 7). As the drum rotates the aggregate degrades by abrasion and impact with other aggregate particles and the steel spheres (called the “charge”). Once the test is complete, the calculated mass of aggregate that has broken apart to smaller sizes is expressed as a percentage of the total mass of aggregate. Therefore, lower L.A. abrasion loss values indicate aggregate that is tougher and more resistant to abrasion.
Similar questions