Frequently Asked Question
Ans: In field quality control of Wet Mix Macadam (WMM) layers, determining in-situ density is essential to ensure proper compaction and performance. Two standard methods are used: the sand replacement method and the core cutter method, as per IS: 2720 (Part 28 & Part 29) and MoRTH Section 900.
For WMM, which consists of coarse aggregates and fines bound by water, the sand replacement method is the more suitable and widely accepted approach. A small pit is excavated, the excavated material is weighed, and calibrated dry sand is poured into the hole to determine its volume. The field density is then computed and compared with the laboratory Modified Proctor density (IS: 2720 Part 8) to assess compaction efficiency (usually ≥98%).
The core cutter method, while simpler, is applicable mainly to fine-grained cohesive soils like subgrade or sub-base layers. It is not recommended for granular layers such as WMM because coarse particles cause inaccurate volume measurement and poor sample recovery.
Thus, for WMM verification, the sand replacement method remains the standard and most reliable procedure to validate compaction levels in line with MoRTH 5th Revision Clause 406 & 900.
Ans: The Optimum Moisture Content (OMC) for subgrade soil is the moisture level at which the soil attains maximum dry density (MDD) during compaction. Determining and maintaining this condition in the field is critical to achieve desired strength, stability, and load-bearing capacity of the pavement foundation.
In practice, OMC is first determined in the laboratory using the Standard or Modified Proctor Test (IS: 2720 Part 7 or Part 8). The dry density–moisture content curve obtained identifies the OMC corresponding to the peak dry density.
At site, field compaction is verified by:
· Moisture control: The soil is adjusted near its OMC by adding or drying water and thoroughly mixing.
· Trial compaction: A few test sections are compacted at different moisture levels (±1–2% of lab OMC) to observe density results and roller efficiency.
· Field density checks: Using the sand replacement or nuclear density gauge methods, in-situ density is compared with MDD to ensure ≥97% (as per MoRTH).
Thus, the optimum moisture content in field is achieved by correlating lab OMC with actual site conditions, soil type, and roller performance to ensure maximum compaction and uniform subgrade strength.
Ans: The Acceptable Specification Limits of DBM is 27 and 24 for BC layers.
Ans. The acceptable specification limit of FSI – IS:2720 (Part-40) should not be greater than 50%.
Ans. The Los Angeles Abrasion (LAA) and Aggregate Impact Value (AIV) tests both evaluate the durability and toughness of aggregates, but they differ in loading type, purpose, and mechanism of degradation. Here are the key differences:
Aspect | Los Angeles Abrasion Test (LAA) | Aggregate Impact Value Test (AIV) |
Purpose | Measures resistance of aggregates to abrasion and attrition (wear due to friction). | Measures resistance of aggregates to sudden impact or shock loads. |
Test Standard | IS: 2386 (Part IV) – Abrasion test | IS: 2386 (Part IV) – Impact test |
Equipment Used | Los Angeles Abrasion machine with steel balls | Impact testing machine with a dropping hammer |
Type of Load Applied | Rotational impact and rubbing (abrasion) | Vertical impact (shock) |
Simulates Field Condition | Traffic wear and rolling of vehicle tyres | Sudden impact loads from moving traffic or compaction |
Nature of Breakdown | Gradual wearing and grinding of particles | Fracturing or breaking of aggregates |
Result Expressed As | % Los Angeles Abrasion Value (weight loss) | % Aggregate Impact Value (weight of fines) |
Acceptable Limits (MoRTH) | ≤ 35% for surface courses | ≤ 30% for surface courses |
In summary:
LAA assesses wear resistance under abrasion, while AIV measures toughness under impact. Both tests complement each other in evaluating aggregate quality for road construction.
As per MoRTH Specifications, Section 900 (Table 900-3), the frequency of testing for Bituminous Mix (DBM/BC) is established to ensure consistent quality control during production and laying operations. The testing regime covers both constituent materials and finished mix properties at prescribed minimum frequencies.
For constituent materials, the following tests are specified:
Aggregate Impact Value / Los Angeles Abrasion Value – one test per 350 m³ of aggregate or whenever there is a change in source or quality.
Flakiness and Elongation Indices – one test per 350 m³ of aggregate.
Soundness (Sodium/Magnesium Sulphate) and Water Absorption – one test per source or when quality changes.
Sand Equivalent, Plasticity Index, and Polished Stone Value – one test per source or change in aggregate quality.
For the bituminous mix, the key tests and frequencies are:
Mix grading – one set per 400 tonnes of mix, with a minimum of two tests per day per plant.
Stability and Voids analysis (Marshall test) – three tests for each 400 tonnes of mix, minimum two sets per day.
Moisture susceptibility (AASHTO T283) – one test per mix type or when material source changes.
Binder content – one test per 400 tonnes, minimum two per day per plant.
Temperature control (binder, aggregate, mix) – checked at regular intervals.
Rate of spread – verified every 5th truckload.
Field density of compacted layer – one test per 700 m² area.
Ans: In field quality control of Wet Mix Macadam (WMM) layers, determining in-situ density is essential to ensure proper compaction and performance. Two standard methods are used: the sand replacement method and the core cutter method, as per IS: 2720 (Part 28 & Part 29) and MoRTH Section 900.
For WMM, which consists of coarse aggregates and fines bound by water, the sand replacement method is the more suitable and widely accepted approach. A small pit is excavated, the excavated material is weighed, and calibrated dry sand is poured into the hole to determine its volume. The field density is then computed and compared with the laboratory Modified Proctor density (IS: 2720 Part 8) to assess compaction efficiency (usually ≥98%).
The core cutter method, while simpler, is applicable mainly to fine-grained cohesive soils like subgrade or sub-base layers. It is not recommended for granular layers such as WMM because coarse particles cause inaccurate volume measurement and poor sample recovery.
Thus, for WMM verification, the sand replacement method remains the standard and most reliable procedure to validate compaction levels in line with MoRTH 5th Revision Clause 406 & 900.
Ans: The Optimum Moisture Content (OMC) for subgrade soil is the moisture level at which the soil attains maximum dry density (MDD) during compaction. Determining and maintaining this condition in the field is critical to achieve desired strength, stability, and load-bearing capacity of the pavement foundation.
In practice, OMC is first determined in the laboratory using the Standard or Modified Proctor Test (IS: 2720 Part 7 or Part 8). The dry density–moisture content curve obtained identifies the OMC corresponding to the peak dry density.
At site, field compaction is verified by:
· Moisture control: The soil is adjusted near its OMC by adding or drying water and thoroughly mixing.
· Trial compaction: A few test sections are compacted at different moisture levels (±1–2% of lab OMC) to observe density results and roller efficiency.
· Field density checks: Using the sand replacement or nuclear density gauge methods, in-situ density is compared with MDD to ensure ≥97% (as per MoRTH).
Thus, the optimum moisture content in field is achieved by correlating lab OMC with actual site conditions, soil type, and roller performance to ensure maximum compaction and uniform subgrade strength.
Ans: The Acceptable Specification Limits of DBM is 27 and 24 for BC layers.
Ans. The acceptable specification limit of FSI – IS:2720 (Part-40) should not be greater than 50%.
Ans. The Los Angeles Abrasion (LAA) and Aggregate Impact Value (AIV) tests both evaluate the durability and toughness of aggregates, but they differ in loading type, purpose, and mechanism of degradation. Here are the key differences:
Aspect | Los Angeles Abrasion Test (LAA) | Aggregate Impact Value Test (AIV) |
Purpose | Measures resistance of aggregates to abrasion and attrition (wear due to friction). | Measures resistance of aggregates to sudden impact or shock loads. |
Test Standard | IS: 2386 (Part IV) – Abrasion test | IS: 2386 (Part IV) – Impact test |
Equipment Used | Los Angeles Abrasion machine with steel balls | Impact testing machine with a dropping hammer |
Type of Load Applied | Rotational impact and rubbing (abrasion) | Vertical impact (shock) |
Simulates Field Condition | Traffic wear and rolling of vehicle tyres | Sudden impact loads from moving traffic or compaction |
Nature of Breakdown | Gradual wearing and grinding of particles | Fracturing or breaking of aggregates |
Result Expressed As | % Los Angeles Abrasion Value (weight loss) | % Aggregate Impact Value (weight of fines) |
Acceptable Limits (MoRTH) | ≤ 35% for surface courses | ≤ 30% for surface courses |
In summary:
LAA assesses wear resistance under abrasion, while AIV measures toughness under impact. Both tests complement each other in evaluating aggregate quality for road construction.
As per MoRTH Specifications, Section 900 (Table 900-3), the frequency of testing for Bituminous Mix (DBM/BC) is established to ensure consistent quality control during production and laying operations. The testing regime covers both constituent materials and finished mix properties at prescribed minimum frequencies.
For constituent materials, the following tests are specified:
Aggregate Impact Value / Los Angeles Abrasion Value – one test per 350 m³ of aggregate or whenever there is a change in source or quality.
Flakiness and Elongation Indices – one test per 350 m³ of aggregate.
Soundness (Sodium/Magnesium Sulphate) and Water Absorption – one test per source or when quality changes.
Sand Equivalent, Plasticity Index, and Polished Stone Value – one test per source or change in aggregate quality.
For the bituminous mix, the key tests and frequencies are:
Mix grading – one set per 400 tonnes of mix, with a minimum of two tests per day per plant.
Stability and Voids analysis (Marshall test) – three tests for each 400 tonnes of mix, minimum two sets per day.
Moisture susceptibility (AASHTO T283) – one test per mix type or when material source changes.
Binder content – one test per 400 tonnes, minimum two per day per plant.
Temperature control (binder, aggregate, mix) – checked at regular intervals.
Rate of spread – verified every 5th truckload.
Field density of compacted layer – one test per 700 m² area.