2.5
Objective
Elongation is a means of classifying coarse aggregates.
Aggregate particles are classified as elongated when they have a length (greatest dimension) of more than 1.8 of their mean sieve size.
The objective of the test is to determine the Elongation Index of coarse aggregates.
For base course and wearing course aggregates the presence of elongated particles are considered undesirable as they may cause inherent weakness with possibilities of breaking down under heavy loads.
Main Principles
The Elongation Index of an aggregate sample is found by separating the elongated particles and expressing their mass as a percentage of the mass of the sample. The test is applicable to material passing a 50 mm sieve and retained on a 6.3 mm sieve.
References
BS 812 : Section 105.2 : 1990
Required equipment
· A sample divider, e.g. a riffle box
· Drying oven - with temperature of 105 ± 5 °C.
· Balance - readable to 1.0 g.
· Test sieves Ref. Table 1
· A sieve shaker (optional)
· Metal trays
· A Metal Length Gauge, of a pattern shown in Figure 3.
Nominal aperture size
(square hole perforated plate 450 mm or 300 mm) mm
37.550 2820 1410 6.3
Table 5. Particulars of sieves Example: Aggregates passing 14 mm and
retained on 10 mm are classified as elongated when:
L > ½ (14 + 10) x 1.8 = 21.6 mm
CML Central Materials Laboratory
Ministry of Works
Notes
2 Aggregates and Concrete
TEST NO.
Sample preparation
Step 1: Reduce the sample to produce a test portion complying with Table 2 below.
Step 2: The test sample shall be washed, if necessary, and oven-dried at 105 ± 5 °C to substantially constant weight.
Step 3: Allow the sample to cool and weigh the sample to the nearest 1g.
Nominal size of material Minimum mass of test portion after rejection of oversize and undersize particles
Table 6. Minimum mass of test portion
Test Procedure
Step 1: Carry out a sieve analysis using the sieves given in Table 1.
Step 2: Discard all aggregates retained on the 50 mm sieve and all aggregate passing the 6.3 mm sieve.
Step 3: Weigh each of the individual size-fractions retained on the sieves, and store them in trays with their size marked on the trays.
Step 4: From the sums of masses of the fractions in the trays (M1), calculate the individual percentage retained on each of the various sieves. Discard any fraction whose mass is 5 % or less of mass M1. Record the mass remaining (M2).
Step 5: Gauge each fraction using the length gauge. Select the gauge appropriate to the size-fraction under test (see Table 3) and gauge each particle of that size-fraction separately by hand. Elongated particles are those whose greatest dimension prevents them from passing through the gauge, and these are placed to one side.
Step 6: Combine and weigh all the elongated particles. (M3).
Aggregate size fraction Gap between pins Minimum
Test sieve of length gauge mass for
100 % passing 100% retained subdivision
mm mm mm kg
Table 7. Data for determination of Elongation Index
Elongation Index
2.5
If required, an Elongation Index may be determined separately for individual size fractions by recording separately the masses of each of the individual size-fractions and the masses of elongated particles in each size-fraction.
Notes
CML Central Materials Laboratory
Ministry of Works
2 Aggregates and Concrete
TEST NO.
Calculations
The value of the Elongation Index is calculated from the expression:
Elongation Index, EI = x 100 where
M2 is the sum of the masses of fractions that have a mass greater than 5 % of the total mass.
M3 is the mass of all the elongated particles
Report
The test report shall include the following:
a) Type of material and sample identification b) Reference to this procedure
c) Test result, i.e. the Elongation Index of the test sample.
The Elongation Index shall be expressed to the nearest whole number.
d) Whether the material was tested in the natural state or after sieving e) Sieve analysis obtained from this test.
Form for the test
The enclosed form shall be used.
M 3
M 2
Elongation Index
2.5
Figure 3 Lenght gauge
CML Central Materials Laboratory
Ministry of Works
Notes
2 Aggregates and Concrete
TEST NO.
Objective
Aggregates used in road construction should be strong enough to resist crushing under traffic wheel loads. If the aggregates are weak, the integrity of the pavement structure is likely to be adversely affected. The strength of coarse aggregates may be measured by the Aggregate Crushing test.
The Aggregate Crushing Value (ACV) gives a relative measure of the resistance of an aggregate to crushing under a gradually applied load.
Main Principles
The Aggregate Crushing Value (ACV) is determined by measuring the material passing a specified sieve after crushing under a load of 400 kN.
The test is applicable to a standard fraction aggregates passing a 14 mm sieve and retained on a 10 mm sieve.
The method is not suitable for testing soft aggregates with an ACV higher than 30. In such cases the method for Ten Percent Fines Value (TFV) is applicable, ref. CML Test no. 2.7.
References
BS 812 : Part 110 : 1990
Required equipment
· A Steel Cylinder, open ended of nominal 150 mm internal diameter with Plunger and Baseplate, ref. figure 1.
· Test sieves square-hole perforated-plate type of sizes 14 mm and 10 mm, and a woven wire 2.36 mm sieve.
· Tamping rod, steel bar 16 mm diameter and 600 mm long with both ends hemispherical
· Compression Testing Machine, 500 kN capacity
· Cylindrical Metal Measure, with internal diameter of 115 mm and internal depth of 180 mm
· A sample divider, e.g. a riffle box
· Drying oven - with temperature of 105 °C ± 5 °C.
· Balance min. 3 kg capacity readable to 1 g.
· Rubber mallet
· Metal tray of known mass
· Brush with stiff bristles.
Sample preparation
Step 1: Reduce the sample to produce a test portion of sufficient mass to produce three test specimens of 14 mm to 10 mm size fraction, ref. Table 1 below.
If the standard size fraction 14 - 10 mm is not available, tests may be performed on other size fractions between 2.36 mm and 28 mm, ref. BS 812, and table below:
For the sizes smaller than 10mm a smaller apparatus may be used, i.e. cylinder diameter 75 mm, mould size 57 mm x 90 mm, tamping rod diameter 8 mm, and applied force 100 kN.
If the material is dusty, it should be washed before testing. It is not to be washed after testing.