Los Angeles abrasion value of rock

Lab No. 7 Objective: To determine Los Angeles abrasion value of rock using loss Angeles abrasion testing apparatus. Required Apparatus: • Los Angeles Machine • Standard Sieves • Digital balance • Drying Oven • Steel Charge • No.10 Sieve Los Angeles Machine: Drum • Hollow steel cylinder, closed at both ends • Inside diameter of 28 ± 0.2 in. • Length =20±0.2in. • Rotates on horizontal axis • Dust‐tight cover Abrasion: Abrasion is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion. After friction, the moving particles dislodge loose and weak debris from the side of the rock. The intensity of abrasion depends on the hardness, concentration, velocity and mass of the moving particles. Los Angeles Abrasion Test: The L.A. abrasion test measures the degradation of a coarse aggregate sample that is placed in a rotating drum with steel spheres .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. . The %age wear due to rubbing with steel balls is determined and is known as abrasion value Therefore , lower L.A. abrasion loss values indicate aggregate that is tougher and more resistant to abrasion. Typical L.A. Abrasion Loss Values Rock Type L.A. Abrasion Loss (by percent weight) General Values Hard, igneous rocks

10

Soft limestones and sandstones 60 Ranges for specific rocks

Basalt

10 – 17

Dolomite

18 – 30

Gneiss

33 – 57

Granite

27 – 49

Limestone

19 – 30

Quartzite

20 – 35

Procedure of the LA Abrasion Test:  Prepared sample is placed in the abrasion-testing machine.  A specified number of steel spheres are then placed in the machine and the drum is rotated for 500 revolutions at a speed of 30 - 33 revolutions per minute (RPM) for hard rock and 25rpm for soft rock.  The material is then separated into material passing the 1.70 mm (No. 12) sieve and material retained on the 1.70 mm (No. 12) sieve.  Dry the sample in an oven.  Calculate %age loss due to Abrasion by calculating the difference between the retained material (larger particles) compared to the original sample weight. The difference in weight is reported as a percent of the original weight and called the "percent loss". Los Angeles Abrasion Hardness: • Mass (weight) placed in abrasion machine • Mass (weight) of intact particles left after test • L.A Abrasion value % = ((Initial Mass – Final Intact Mass)/(Initial Mass)))×100% Criteria L.A.A >50% L.A.A 40-50% L.A.A< 40%

Descriptors Intermediate rock Normal rock Hard rock

Observation and calculation: Given sample =limestone Mass (weight) placed in abrasion machine=5kg Rotation of drum = 31rpm Time of rotation =9 mints 45 seconds Mass (weight) of intact particles retain on No.10 sieve after test =3.565kg L.A Abrasion value % = (

=( =28.7%

–

)×100% )

Results: Limestone has Los Angeles Abrasion value 28.7 %, this shows that limestone perform satisfactory in pavement, dam construction, slop stability; it is sufficiently hard to resist the abrasive effect and quite resistant to crushing effect of traffic over long period of time. Common Errors: • Incorrect number of spheres • Total charge mass outside tolerances • Not setting (or resetting) counter • Drum not rotated at constant speed– slip and backlash • Not removing all material from drum • Sample not dried to constant mass • Improper seal between hatch and drum Test Adequacy / Suitability: The L.A. Abrasion test is an empirical test; it is not directly related to field performance of aggregates. Field observations generally do not show a good relationship between L.A. abrasion values and field performance. L.A. abrasion loss is unable to predict field performance. Specifically, the test may not be satisfactory for some types of aggregates. Some aggregates, such as slag and some lime-stones, tend to have high LA. Abrasion loss but perform adequately in the field. L.A. abrasion loss seems to be reasonable well correlated with dust formation during handling and HMA production in that aggregates with higher LA. Abrasion loss values typically generate more of dust. Uses & Significance of LA Abrasion Test:  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. 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. Reference: http://www.aboutcivil.org/to-perform-los-angeles-abrasion-test.html http://www.pavementinteractive.org/article/los-angeles-abrasion/