Shape characteristics of coarse aggregates are important when determining the performance of materials or mixes. Units are constructed of durable plated steel, precision tooled for accuracy. For shape determination of flat particle sizing, set the width of a particle in the larger end of the Caliper, then tighten the pivot screw. Without adjusting the Caliper, check the same particle in the smaller measuring end of the Caliper. If the particle fits within the smaller gap, it is considered flat. Elongated particle determination follows the same steps.
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Flat and Elongated Particles Overview The flat and elongated particle test is used to determine the dimensional ratios for aggregate particles of specific sieve sizes. This characterization is used in the Superpave specification to identify aggregate that may have a tendency to impede compaction or have difficulty meeting VMA specifications due to aggregate degradation.
Flat or elongated particles Figure 1 tend to lock up more readily rather than reorient during compaction making compaction more difficult. They also have a tendency to fracture during compaction along their weak, narrow dimension, which can effectively make aggregate gradation finer and possibly cause lower-than-expected VMA.
Figure 1: Flat particles left and elongated particles right. This flat and elongated particle test uses a proportional caliper Figure 2 to help measure dimensional ratios. The specified ratio is set on the caliper and then about particles are tested for each specified sieve size.
Figure 2: Calipers for the flat and elongated particle test. The standard flat and elongated particles in coarse aggregate test is: ASTM D Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregates Background Flat or elongated aggregate particles can, if present in sufficient number, 1 impede compaction or 2 affect HMA behavior by fracturing during compaction.
Compaction Difficulties As compared to cubic shaped particles ones with relatively equal diminsions in all directions flat or elongated particles tend to impede compaction. These particles tend to lock up with adjacent aggregate particles more readily than cubic particles and resist reorientation into a more dense configuration. Therefore, significant numbers of flat or elongated particles can increase the compactive effort required to achieve a given density for a given HMA mixture.
In other words, flat and elongated particles make HMA compaction more difficult. Effect on HMA Behavior Flat or elongated particles also have a tendancy to fracture along their weak, narrow dimension when subjected to compaction loading. If they are present in large enough quantity, this fracturing can effectively change the aggregate gradation as larger flat and elongated particles are broken into smaller, more cubic particles Figure 3. The resulting greater number of fine particles will fill existing void spaces and reduce the VMA.
This reduction in VMA can result in too little room available for the asphalt binder to coat the aggregate particles, which can result in mixture instability rutting and shoving. Also, the resulting lower VMA may make the HMA mixture highly sensitive to small variations in asphalt binder content.
Thus, a small increase in asphalt binder content associated with typical manufacturing tolerances that would normally be absorbed in an HMA with adequate VMA, may result in low stability in a low VMA mixture. Also, the fracturing of flat and elongated particles within the HMA will create aggregate faces that are uncoated with asphalt binder, which can increase durability problems. Typical Definition The dimensional ratio at which an aggregate particle is considered too flat or too elongated can vary from specification to specification.
Typical ratios are , , and Figure 4. Superpave mix design specifies a ratio of and tests particles for flatness and elongation. Other agencies have used different ratios. Figure 4: Range of flat and elongated particle ratios.
The particle is very flat, giving a length:height ration of The height:width dimensions seen in the photo are about Test Description The following description is a brief summary of the test.
It is not a complete procedure and should not be used to perform the test. The complete flat and elongated particle test procedure can be found in: ASTM D Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregates Summary Individual aggregate particles of specific sieve sizes are tested for ratios of width to thickness, length to width, or length to thickness.
The test is performed on a sample of coarse aggregate reduced from a representative field sample. The sample is sieved to separate each size larger than the 0. Each size is then tested in a proportional caliper device Figure 5. Particles are weighed or counted to determine a percentage of flat, elongated, or flat and elongated particles in a sample. Figure 5: Flat and elongated particle test equipment. Approximate Test Time 30 minutes. If particle mass rather than particle count is to be used, sample preparation will take at least 12 hours or overnight because the aggregate needs to be oven dry before it is weighed to ensure accuracy.
Basic Procedure 1. Sieve a sample of coarse aggregate and collect those particles retained on the specified sieve size s ; usually the 0.
Reduce each specified size fraction until approximately particles are obtained for each specified size fraction. Checking for flatness OR elongation. Test each of the particles in each of the size fractions and place them into one of three groups: flat, elongated, or neither flat nor elongated. Testing for flatness Figure 6. Set the larger opening of the proportional caliper equal to the particle width.
The particle is flat if the thickness fits in the smaller opening. Figure 6: Testing for flatness. Testing for elongation Figure 7. Set the larger opening of the proportional caliper equal to the particle length. The particle is elongated if the width fits in the smaller opening. Figure 7: Testing for elongation. After all particles are tested, determine the proportion of the sample in each group by either count or mass.
Checking for flatness AND elongation Video 1. Use the proportional caliper device to check flat and elongation of the particles. Video 1: Flat and elongated particle test. Set the larger opening of the caliper equal to the length of the particle. The particle is considered flat and elongated if the particle, when oriented to measure its thickness, can pass completely through the smaller opening of the caliper.
Results Parameters Measured Percentage or coarse aggregate particles of a specified size or sizes that are considered flat, elongated or flat and elongated according to a specified ratio. Specifications A maximum percentage of flat and elongated particles is usually specified. The actual definition of flat, elongated and flat and elongated varies from specification to specification but is typically a dimensional ratio of , or
Flat and Elongated Particles
Zulkinris A pressuremeter test is an in-situ stress-strain test performed on the wall of a borehole using a cylindrical probe that is expanded radially. Note 2—Strain-controlled tests also can be performed, whereby the probe volume is increased at a constant rate and corresponding pressures are measured. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Note 1—A standard for the self-boring pressuremeter is scheduled to be developed separately.
Tegrel The standard flat and elongated particles in coarse aggregate test is: Flat and elongated requirements do not apply. The mass of all flaky particles passing appropriate slots as percent of the sample is the flakiness index. Particle d elongated when its length longest dimension is more than 1. This characterization is used in the Superpave specification to identify aggregate that may have a tendency to impede compaction or have difficulty meeting VMA specifications due to aggregate degradation. Periodically, inspect to width greater than a specific value. Comments to this Manuals Your Name.
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