ACI - Aggregate Base Testing Technician 2026 - 69 Questions and
Answers Already Graded A+ Premium Exam Tested And
Verified
Subject Area Civil Engineering - Construction Materials Testing
Description This exam covers advanced principles and practices for aggregate base testing,
including sampling, gradation, compaction, moisture-density relationships, and
quality control per ACI and ASTM standards. Designed for technicians seeking
certification in aggregate base testing at the level of a senior laboratory or field
technician.
Expected Grade A+
Total Questions 69
Duration 3 hours
Learning Outcomes 1. Apply ASTM and AASHTO standards to aggregate sampling and testing
2. Analyze gradation curves and interpret fineness modulus and uniformity
coefficient
3. Evaluate compaction characteristics using Proctor and CBR tests
4. Troubleshoot common test discrepancies and equipment errors
5. Integrate statistical quality control methods for aggregate base acceptance
Accreditation This exam aligns with ACI Certification Program requirements and ASTM
D2940/D75 standards for aggregate base testing. It reflects the rigor expected of
an R1 university graduate-level course.
Page 1
,1. A technician performs a sieve analysis on a crushed stone sample and obtains the
following cumulative percent passing: 100% at 50 mm, 95% at 37.5 mm, 70% at 19
mm, 45% at 9.5 mm, 25% at 4.75 mm, 10% at 2.36 mm, and 2% at 0.075 mm.
According to ASTM D2940, which of the following best characterizes this material?
A. The material is well-graded with a uniformity coefficient (Cu) exceeding 4 and a
coefficient of curvature (Cc) between 1 and 3.
B. The material is gap-graded, missing the intermediate sizes between 9.5 mm and 19 mm.
C. The material is uniformly graded with Cu less than 4, indicating poor drainage.
D. The material is open-graded with less than 5% passing the No. 200 sieve, suitable for
drainage applications.
Answer: B. The material is gap-graded, missing the intermediate sizes between 9.5
mm and 19 mm.
The gradation shows a plateau between 9.5 mm and 19 mm (45% to 70% passing),
indicating a gap. Well-graded materials have smooth curves with Cu > 4 and Cc
between 1-3, but here the missing sizes create a gap. Uniformly graded would show a
steep slope around one size. Open-graded typically has very little fines (<5% passing
No. 200), but here 2% is low, yet the gap is the defining feature.
Page 2
,2. During a Modified Proctor compaction test (ASTM D1557) on a granular base
material, the technician observes that the optimum moisture content (OMC) is 6.2%
and the maximum dry density (MDD) is 2.24 g/cm³. A field nuclear density gauge
reading at a compacted lift shows a wet density of 2.35 g/cm³ and a moisture content
of 7.5%. The contractor claims the compaction meets the 98% of MDD specification.
Which of the following is the most appropriate conclusion?
A. The compaction is acceptable because the dry density is 2.19 g/cm³, which is 97.8% of
MDD, within acceptable tolerance.
B. The compaction is unacceptable because the dry density is 2.19 g/cm³, which is 97.8% of
MDD, below the 98% requirement.
C. The compaction is acceptable because the wet density exceeds the MDD, indicating
overcompaction.
D. The compaction is unacceptable because the moisture content exceeds OMC by more than
1%, weakening the base.
Answer: B. The compaction is unacceptable because the dry density is 2.19 g/cm³,
which is 97.8% of MDD, below the 98% requirement.
Dry density = wet density / (1 + moisture content/100) = 2..075 = 2.186 g/cm³ 2.19
g/cm³. Percent compaction = (2..24) * 100 = 97.8%. Since 97.8% < 98%, it fails
the specification. Option A incorrectly rounds up. Option C confuses wet density with
dry. Option D is not a standard rejection criterion; moisture above OMC is allowed if
density meets spec, but here it doesn't.
3. A technician is performing the California Bearing Ratio (CBR) test on a soaked
aggregate base sample. After soaking for 96 hours, the penetration load at 2.54 mm
(0.1 in) is 12.5 kN, and at 5.08 mm (0.2 in) is 18.0 kN. The standard load for 2.54 mm
is 13.24 kN (3000 psi) and for 5.08 mm is 19.96 kN (4500 psi). What is the reported
CBR value?
A. 94%
B. 90%
C. 92%
D. 88%
Answer: A. 94%
CBR = (test load / standard load) * 100. At 2.54 mm: (12..24)*100 = 94.4%. At
5.08 mm: (18..96)*100 = 90.2%. The reported CBR is typically the higher value if
the curve is concave upward, but per ASTM D1883, if the test at 2.54 mm gives a higher
value, that value is reported. So 94% is correct. Option B is the 5.08 mm value. Option
C is an average. Option D is incorrect.
Page 3
, 4. A technician is tasked with sampling a stockpile of crushed limestone base
material according to ASTM D75. The stockpile is approximately 10 m in diameter
and 4 m high. Which of the following sampling plans minimizes bias and ensures a
representative sample?
A. Collect one sample from the top of the stockpile using a shovel, then split the sample in
the lab.
B. Use a front-end loader to dig into the stockpile at three random locations, combine the
material, and then quarter to test size.
C. Sample only from the base of the stockpile where segregation is least likely, then reduce
by riffle splitting.
D. Take multiple increments from the conveyor belt during loading, but only during the first
10 minutes of operation.
Answer: B. Use a front-end loader to dig into the stockpile at three random
locations, combine the material, and then quarter to test size.
Stockpiles often segregate; sampling from multiple locations (especially from the
interior) reduces bias. Option A only samples the top, which may be finer. Option C
focuses only on the base, which may be coarser. Option D is time-dependent and may
miss variations. Option B uses a loader to access interior material at multiple points,
then combines and quarters, which is standard practice.
Page 4
Answers Already Graded A+ Premium Exam Tested And
Verified
Subject Area Civil Engineering - Construction Materials Testing
Description This exam covers advanced principles and practices for aggregate base testing,
including sampling, gradation, compaction, moisture-density relationships, and
quality control per ACI and ASTM standards. Designed for technicians seeking
certification in aggregate base testing at the level of a senior laboratory or field
technician.
Expected Grade A+
Total Questions 69
Duration 3 hours
Learning Outcomes 1. Apply ASTM and AASHTO standards to aggregate sampling and testing
2. Analyze gradation curves and interpret fineness modulus and uniformity
coefficient
3. Evaluate compaction characteristics using Proctor and CBR tests
4. Troubleshoot common test discrepancies and equipment errors
5. Integrate statistical quality control methods for aggregate base acceptance
Accreditation This exam aligns with ACI Certification Program requirements and ASTM
D2940/D75 standards for aggregate base testing. It reflects the rigor expected of
an R1 university graduate-level course.
Page 1
,1. A technician performs a sieve analysis on a crushed stone sample and obtains the
following cumulative percent passing: 100% at 50 mm, 95% at 37.5 mm, 70% at 19
mm, 45% at 9.5 mm, 25% at 4.75 mm, 10% at 2.36 mm, and 2% at 0.075 mm.
According to ASTM D2940, which of the following best characterizes this material?
A. The material is well-graded with a uniformity coefficient (Cu) exceeding 4 and a
coefficient of curvature (Cc) between 1 and 3.
B. The material is gap-graded, missing the intermediate sizes between 9.5 mm and 19 mm.
C. The material is uniformly graded with Cu less than 4, indicating poor drainage.
D. The material is open-graded with less than 5% passing the No. 200 sieve, suitable for
drainage applications.
Answer: B. The material is gap-graded, missing the intermediate sizes between 9.5
mm and 19 mm.
The gradation shows a plateau between 9.5 mm and 19 mm (45% to 70% passing),
indicating a gap. Well-graded materials have smooth curves with Cu > 4 and Cc
between 1-3, but here the missing sizes create a gap. Uniformly graded would show a
steep slope around one size. Open-graded typically has very little fines (<5% passing
No. 200), but here 2% is low, yet the gap is the defining feature.
Page 2
,2. During a Modified Proctor compaction test (ASTM D1557) on a granular base
material, the technician observes that the optimum moisture content (OMC) is 6.2%
and the maximum dry density (MDD) is 2.24 g/cm³. A field nuclear density gauge
reading at a compacted lift shows a wet density of 2.35 g/cm³ and a moisture content
of 7.5%. The contractor claims the compaction meets the 98% of MDD specification.
Which of the following is the most appropriate conclusion?
A. The compaction is acceptable because the dry density is 2.19 g/cm³, which is 97.8% of
MDD, within acceptable tolerance.
B. The compaction is unacceptable because the dry density is 2.19 g/cm³, which is 97.8% of
MDD, below the 98% requirement.
C. The compaction is acceptable because the wet density exceeds the MDD, indicating
overcompaction.
D. The compaction is unacceptable because the moisture content exceeds OMC by more than
1%, weakening the base.
Answer: B. The compaction is unacceptable because the dry density is 2.19 g/cm³,
which is 97.8% of MDD, below the 98% requirement.
Dry density = wet density / (1 + moisture content/100) = 2..075 = 2.186 g/cm³ 2.19
g/cm³. Percent compaction = (2..24) * 100 = 97.8%. Since 97.8% < 98%, it fails
the specification. Option A incorrectly rounds up. Option C confuses wet density with
dry. Option D is not a standard rejection criterion; moisture above OMC is allowed if
density meets spec, but here it doesn't.
3. A technician is performing the California Bearing Ratio (CBR) test on a soaked
aggregate base sample. After soaking for 96 hours, the penetration load at 2.54 mm
(0.1 in) is 12.5 kN, and at 5.08 mm (0.2 in) is 18.0 kN. The standard load for 2.54 mm
is 13.24 kN (3000 psi) and for 5.08 mm is 19.96 kN (4500 psi). What is the reported
CBR value?
A. 94%
B. 90%
C. 92%
D. 88%
Answer: A. 94%
CBR = (test load / standard load) * 100. At 2.54 mm: (12..24)*100 = 94.4%. At
5.08 mm: (18..96)*100 = 90.2%. The reported CBR is typically the higher value if
the curve is concave upward, but per ASTM D1883, if the test at 2.54 mm gives a higher
value, that value is reported. So 94% is correct. Option B is the 5.08 mm value. Option
C is an average. Option D is incorrect.
Page 3
, 4. A technician is tasked with sampling a stockpile of crushed limestone base
material according to ASTM D75. The stockpile is approximately 10 m in diameter
and 4 m high. Which of the following sampling plans minimizes bias and ensures a
representative sample?
A. Collect one sample from the top of the stockpile using a shovel, then split the sample in
the lab.
B. Use a front-end loader to dig into the stockpile at three random locations, combine the
material, and then quarter to test size.
C. Sample only from the base of the stockpile where segregation is least likely, then reduce
by riffle splitting.
D. Take multiple increments from the conveyor belt during loading, but only during the first
10 minutes of operation.
Answer: B. Use a front-end loader to dig into the stockpile at three random
locations, combine the material, and then quarter to test size.
Stockpiles often segregate; sampling from multiple locations (especially from the
interior) reduces bias. Option A only samples the top, which may be finer. Option C
focuses only on the base, which may be coarser. Option D is time-dependent and may
miss variations. Option B uses a loader to access interior material at multiple points,
then combines and quarters, which is standard practice.
Page 4
