CTQP Materials Sampling and Testing 2 — Questions and Answers
Question 1: What are the two key values determined by the Standard Proctor compaction test (AASHTO T 99)?
- Bearing capacity and shear strength of the compacted soil
- Maximum dry density and optimum moisture content of a soil (Correct answer)
- Permeability and consolidation rate of the soil
- Liquid limit and plastic limit of fine-grained soil
Correct answer: Maximum dry density and optimum moisture content of a soil
The Standard Proctor test establishes the maximum dry density and the optimum moisture content, which serve as the compaction standard against which field results are compared.
Question 2: What property does the Limerock Bearing Ratio (LBR) test measure for base course materials in Florida?
- The weight of limerock material per cubic yard at standard moisture
- The bearing strength or load-bearing capacity of limerock and similar base course materials (Correct answer)
- The moisture absorption capacity of limerock under saturation conditions
- The unconfined compressive strength of limerock core samples
Correct answer: The bearing strength or load-bearing capacity of limerock and similar base course materials
The LBR test measures the bearing strength of limerock and stabilized materials used as base course, and the result is expressed as a percentage relative to a standard crushed stone.
Question 3: What does the Los Angeles Abrasion test (AASHTO T 96) measure for coarse aggregates?
- The specific gravity and absorption of coarse aggregate particles
- The moisture content of aggregate at the time of sampling
- The resistance of coarse aggregate to degradation by abrasion and impact (Correct answer)
- The gradation and particle size distribution of coarse aggregate
Correct answer: The resistance of coarse aggregate to degradation by abrasion and impact
The LA Abrasion test tumbles aggregate with steel balls in a rotating drum to measure the percent loss due to abrasion and impact, indicating aggregate hardness and durability.
Question 4: What information does a sieve analysis (gradation test) provide about an aggregate sample?
- The moisture content retained by the aggregate particles
- The particle size distribution (gradation) of the aggregate (Correct answer)
- The hardness and abrasion resistance of aggregate particles
- The bulk specific gravity and absorption capacity of the aggregate
Correct answer: The particle size distribution (gradation) of the aggregate
A sieve analysis separates aggregate particles by size using a series of nested sieves, producing a gradation curve that shows the percentage of material passing each sieve size.
Question 5: When performing a concrete slump test per AASHTO T 119, what does a higher slump value indicate about the fresh concrete?
- Higher compressive strength at 28 days
- A lower water-to-cement ratio and stiffer mix
- Greater workability and more fluid consistency of the fresh concrete (Correct answer)
- Better freeze-thaw durability and air entrainment
Correct answer: Greater workability and more fluid consistency of the fresh concrete
A higher slump indicates more workable, fluid concrete; this is usually due to higher water content, but can also result from water-reducing admixtures.
Question 6: The Atterberg Limits test is used to determine which characteristics of fine-grained soils?
- Compressive strength and bearing capacity of cohesive soils
- The Liquid Limit and Plastic Limit, which define the plasticity of fine-grained soils (Correct answer)
- The permeability and consolidation properties of clay soils
- The unit weight and void ratio of silty and clayey soils
Correct answer: The Liquid Limit and Plastic Limit, which define the plasticity of fine-grained soils
Atterberg Limits define the moisture content boundaries between soil behavior states; the Liquid Limit and Plastic Limit are used to calculate the Plasticity Index, indicating expansive potential.
Question 7: Why is it important to measure the air content of fresh concrete on Florida highway projects?
- To determine the water-to-cement ratio before placing concrete
- To measure the compressive strength early before cylinder breaks
- To verify that adequate air entrainment is present to ensure durability and resistance to distress (Correct answer)
- To check that concrete temperature is within specification limits
Correct answer: To verify that adequate air entrainment is present to ensure durability and resistance to distress
Air entrainment creates microscopic bubbles that improve concrete durability, workability, and resistance to distress; FDOT specifications require air content within defined limits.
CTQP Materials Sampling and Testing 2
What are the two key values determined by the Standard Proctor compaction test (AASHTO T 99)?