ACI Aggregate Properties and Testing Questions and Answers 1 — Questions and Answers
Question 1: According to ASTM C136/C136M, what is the primary reason for performing a sieve analysis on fine and coarse aggregates?
- To determine the moisture content of the aggregate
- To measure the resistance of the aggregate to abrasion
- To determine the particle size distribution (grading) of the aggregate (Correct answer)
- To calculate the specific gravity of the aggregate
Correct answer: To determine the particle size distribution (grading) of the aggregate
ASTM C136/C136M is the standard test method for determining the particle size distribution, also known as grading, of fine and coarse aggregates. The results are used to check for compliance with specification requirements and for quality control in the production of aggregates and concrete.
Question 2: A technician is tasked with determining the bulk density (unit weight) of a coarse aggregate sample by rodding, in accordance with ASTM C29/C29M. The procedure involves placing the aggregate into a calibrated measure in how many approximately equal layers?
- One continuous layer
- Two layers
- Three layers (Correct answer)
- Four layers
Correct answer: Three layers
The rodding procedure described in ASTM C29/C29M requires the calibrated measure to be filled in three approximately equal layers. Each layer is then rodded 25 times with a tamping rod to achieve a standard compacted state before the next layer is added.
Question 3: Which of the following properties is determined using the Los Angeles (L.A.) abrasion test (ASTM C131)?
- The percentage of voids in an aggregate sample
- The resistance of coarse aggregate to degradation by abrasion and impact (Correct answer)
- The amount of material finer than the 75-µm (No. 200) sieve
- The absorption capacity of fine aggregate
Correct answer: The resistance of coarse aggregate to degradation by abrasion and impact
The L.A. abrasion test (ASTM C131) is used to measure the toughness of coarse aggregate, specifically its resistance to degradation from a combination of abrasion, impact, and grinding in a rotating steel drum with a specified charge of steel spheres.
Question 4: A laboratory is testing a coarse aggregate sample for specific gravity and absorption according to ASTM C127. The aggregate is soaked for a prescribed period and then dried to a saturated-surface-dry (SSD) condition. What does the SSD condition signify?
- The aggregate has been oven-dried to a constant mass.
- The aggregate's permeable pores are filled with water, but the surfaces of the particles are dry. (Correct answer)
- The aggregate is completely submerged in water.
- The aggregate contains no moisture in its pores or on its surface.
Correct answer: The aggregate's permeable pores are filled with water, but the surfaces of the particles are dry.
The saturated-surface-dry (SSD) condition, as defined in ASTM C127, is a state where the aggregate's internal pores are filled with water, but the outer surfaces are dry. This is a critical reference point for calculating bulk specific gravity (SSD) and absorption.
Question 5: When an accurate determination of the material finer than the 75-µm (No. 200) sieve is required for an aggregate sample, ASTM C136 states that dry sieving alone is insufficient. Which test method should be performed prior to the dry sieve analysis?
- ASTM C29 (Unit Weight)
- ASTM C127 (Specific Gravity and Absorption of Coarse Aggregate)
- ASTM C131 (L.A. Abrasion)
- ASTM C117 (Materials Finer than 75-µm Sieve by Washing) (Correct answer)
Correct answer: ASTM C117 (Materials Finer than 75-µm Sieve by Washing)
ASTM C136 explicitly states that for an accurate determination of material finer than the 75-µm (No. 200) sieve, Test Method C117 should be used. This method uses washing to separate fine particles more completely than dry sieving alone can achieve. The results from C117 are then used in the C136 calculations.
Question 6: A technician performing a bulk density test on a dry coarse aggregate sample according to ASTM C29 obtains the mass of the aggregate in the measure and knows the volume of the measure. To calculate the voids in the aggregate, what additional property of the aggregate must be known?
- The absorption of the aggregate
- The L.A. abrasion loss value
- The bulk specific gravity (dry basis) of the aggregate (Correct answer)
- The fineness modulus of the aggregate
Correct answer: The bulk specific gravity (dry basis) of the aggregate
To calculate the percentage of voids in an aggregate sample, both the bulk density (unit weight) from ASTM C29 and the bulk specific gravity (on a dry basis) are required. The voids content is calculated using these two values, representing the volume of spaces between particles.
ACI Aggregate Properties and Testing Questions and Answers 1
According to ASTM C136/C136M, what is the primary reason for performing a sieve analysis on fine and coarse aggregates?