Compaction and Material Requirements for Subbase

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Questions and Answers

What is the maximum allowable Plasticity Index for the fraction passing the 0.425 mm sieve?

6 (correct)

What should be the maximum mass percent wear of coarse aggregates as per the abrasion test?

50 (correct)

What is the minimum soaked CBR value required for the material passing the 19 mm sieve?

85%

80% (correct)

70%

75%

The thickness of the layer can vary by what maximum value allowed above the design?

+10 mm Signup and view all the answers

What is the maximum allowable surface irregularity measured by a 3-m straight edge?

5 mm Signup and view all the answers

What is the maximum permitted variation for longitudinal grade over a 25 m length?

+0.2 % Signup and view all the answers

Which test method is used to determine the Liquid Limit?

AASHTO T 89 Signup and view all the answers

What is the maximum Liquid Limit for the fraction passing the 0.425 mm sieve?

25 Signup and view all the answers

What is the maximum compacted thickness allowed per layer for aggregate base and subbase courses?

200 mm Signup and view all the answers

What moisture adjustments are permitted prior to compaction of subbase materials?

Adjusting moisture content as needed by watering or drying out. Signup and view all the answers

What is the required field density for each layer after compaction?

100% of the maximum dry density Signup and view all the answers

How should layers be constructed if thickness exceeds 200 mm?

Spread and compact into two or more layers not exceeding 200 mm each. Signup and view all the answers

What is the maximum allowable fraction passing the 0.075 mm sieve in relation to the 0.425 mm sieve?

0.66 of the fraction passing the 0.425 mm sieve Signup and view all the answers

What must be done before starting sub-base construction?

Conduct a trial section to check materials and methods. Signup and view all the answers

Which grading requirement specifies a mass percentage passing the 25.0 mm sieve?

Grading A allows 60–85% passing Signup and view all the answers

What equipment is necessary to compact layers effectively?

Vibratory roller equipment with at least 10 metric tons capacity. Signup and view all the answers

What is the significance of the larger particles in the gradations of base materials?

They provide load bearing support. Signup and view all the answers

What must happen before laying succeeding layers of materials?

The previously compacted layer must undergo field density tests. Signup and view all the answers

What percentage of material retained on the 4.75 mm sieve is allowed in the filler?

Not more than 15 percent Signup and view all the answers

What is the requirement for liquid limit of fines in engineering materials?

Not more than 25 Signup and view all the answers

What is the purpose of conducting a trial section?

To verify the suitability of materials and efficiency of equipment. Signup and view all the answers

What is the required percentage passing the 0.075 mm sieve for Grading B?

2–14 % Signup and view all the answers

What materials are allowed for aggregates in base construction?

Any durable particles or fragments Signup and view all the answers

In base course materials, which sieve designation should ideally allow 20-50% mass passing under Grading A?

4.75 mm Signup and view all the answers

What is the Liquid Limit in soil mechanics?

The lowest moisture content at which soil will flow upon application of a very small shearing force Signup and view all the answers

What does the Plasticity Index indicate about a soil?

It indicates the soil's compressibility and permeability Signup and view all the answers

Which material is allowed to be blended with crushed stones for the base course according to Department Order No. 95?

Weathered limestone Signup and view all the answers

What is the main purpose of sieve analysis in soil mechanics?

To determine the grain size distribution in soils Signup and view all the answers

What does the California Bearing Ratio (CBR) evaluate?

The bearing capacity of soil in its worst condition Signup and view all the answers

What test is used to evaluate the structural strength of coarse aggregate?

Abrasion Test Signup and view all the answers

Which of the following statements about trial sections is correct?

They are considered in the quantity of aggregate base course Signup and view all the answers

Which factor contributes to the scarcity of conventional base course materials in some areas?

Environmental restrictions on mining Signup and view all the answers

What is the maximum allowable percentage of material passing through a 0.075 mm (No. 200) sieve for mineral filler?

100% Signup and view all the answers

Which type of hydrated lime is expected to enhance the resistance of pavements to water damage?

Type N Signup and view all the answers

What is the minimum percentage of calcium and magnesium oxides required in hydrated lime?

60% Signup and view all the answers

For hydrated lime, what is the maximum allowable residue retained on a 0.600 mm (No. 30) sieve?

0.57% Signup and view all the answers

What is the range of percentage passing through a 0.075 mm (No. 200) sieve for hydrated lime?

85-100% Signup and view all the answers

What is the maximum percentage of unhydrated oxides allowed for Type S hydrated lime?

8% Signup and view all the answers

What is the required plasticity figure for putty from Type S, Special Hydrate when tested promptly after mixing with water?

200 Signup and view all the answers

Where should samples of hydrated lime be taken for testing?

At the place of manufacture or an agreed destination Signup and view all the answers

Study Notes

Spreading and Compacting Requirements

Maximum compacted thickness per layer for aggregate subbase and base courses is 200 mm.
Use vibratory roller equipment with a minimum capacity of 10 metric tons to achieve at least 100% of the prescribed maximum dry density.
If thickness exceeds 200 mm, spread and compact in two or more layers, ensuring each layer does not exceed 200 mm.
Adjust moisture content of subbase material through watering or drying before compaction to ensure required density.
Areas inaccessible to rollers, such as curbs and walls, must be compacted with approved tampers.
Each layer must achieve field density of at least 100% of maximum dry density as per AASHTO T-180, Method D.
No new layer may be placed until previous layers pass field density tests.
A trial section of 500 m² is required for each material type and proposed construction method before starting actual work.

Material Requirements

Base course materials must meet specific grading requirements concerning sieve size distribution.
Grading A and B incorporate a specified percentage of mass passing various sieve sizes, including 100% at 50 mm.
Aggregate must consist of durable materials such as crushed stone or gravel; maximum allowable wear from abrasion tests is 50%.
Liquid Limit for fines passing the No. 40 sieve should not exceed 25; Plasticity Index should be under 6.
Soaked CBR value must be at least 80% for materials passing through 19 mm sieve.
The fraction passing the 0.075 mm sieve must not exceed two-thirds of the fraction passing the 0.425 mm sieve.

Allowable Tolerances

Thickness of layer may vary by +10 mm from design; surface level by +5 mm or -10 mm.
Surface irregularity must not exceed 5 mm, and crossfall or camber may increase by +0.2%.
Longitudinal grade variation allowed is +0.1% over 25 m length.

Method of Measurement

Aggregate Base Course is measured by cubic meter; payment is based on design volume compacted in place.
Trial sections are included in the quantity and not measured separately.

Definition of Terms

Liquid Limit: Lowest moisture content allowing soil flow under minimal sheer force.
Plastic Limit: Minimum moisture content for soil to be readily molded.
Plasticity Index: Difference between Liquid Limit and Plastic Limit, indicating soil compressibility.
California Bearing Ratio (CBR): Measure of soil bearing capacity under adverse conditions.
Sieve Analysis: Evaluates grain size distribution in soils for classification.
Abrasion Test: Assesses structural strength of coarse aggregate against wear.

Department Order No. 95

Encourages the use of 40% weathered limestone blended with 60% crushed stones or gravel for base course applications.
The blended materials must meet the existing standards for Aggregate Base Course.

Hydrated Lime Requirements

Type N or S lime is recommended for use in bituminous plant mixtures to enhance water resistance.
Chemical requirements mandate a minimum of 60% Calcium and Magnesium Oxides.
Physical criteria include a maximum residue of 0.57% on the 0.600 mm sieve and not more than 15% on the 0.075 mm sieve.
Grading standards dictate that 100% must pass through the 0.850 mm sieve and 85-100% through the 0.075 mm sieve.
Samples should be collected either at the manufacturing site or at an agreed destination.

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Description

This quiz covers the essential requirements for spreading and compacting aggregate subbase and base courses. It includes guidelines on layer thickness, equipment capacities, moisture content adjustments, and density testing standards. Ideal for construction and civil engineering students.