🏗️ Thickness of a bituminous pavement and of its layers — measurement on drilled cores and the electromagnetic method
In short
The standard describes two methods. The first, destructive, consists in measuring cores drilled through the full depth of the pavement: four measurements distributed evenly round the circumference of the core, each to an accuracy of 1 mm. The test is performed according to PN-EN 12697-36:2022-09; Accredited range in practice: Up to 500 mm for the destructive measurement (list of tests of a road laboratory). The procedure comprises 9 steps; it is used for: Acceptance of layers of a bituminous pavement after construction, Checking the conformity of the thickness of the layers with the design documentation, Accredited tests of road laboratories (range up to 500 mm, point 6.1 of the standard).
At a glance
- Standard: PN-EN 12697-36:2022-09
- Category: Construction
- Procedure steps: 9
- Two methods: Destructive — measurement on drilled cores (point 6.1); non-destructive — electromagnetic measurement
- Accuracy of measurement: To 1 mm; a metal rule and a calliper with a permissible error of at most 1 mm
- Number of measurements per core: Four, distributed evenly round the circumference; the places of measurement marked on the core
Overview
The standard describes two methods of testing the thickness of a bituminous pavement. The first is based on measurements made on one or several cores drilled through the full depth of the slab or of the road structure and is a destructive method. The second uses an electromagnetic measurement and is non-destructive. The standard has neither normative references nor a list of terms and definitions.
The destructive method is in Polish road practice an accredited test: road laboratories declare it in their lists of tests with a measuring range up to 500 mm, naming point 6.1 of the standard, that is precisely the measurement on cores.
With the electromagnetic method the apparatus consists of a foil or aluminium sheet glued to the bituminous layer or fixed to the unbound aggregate of the substrate. The quality of such a counter-pole must be the same all the time, and within a radius of 1 m of it there must be no other metal object, because this affects the measurement.
Method principle
In the destructive method, cores representative of the slab from which they are taken are cut from the pavement, drilled through its full depth. The thickness of each core or of each layer is measured to an accuracy of 1 mm, perpendicularly to the upper plane of the core, between the upper and the lower surface or between clearly marked layer boundary lines. Four measurements distributed evenly round the circumference of each core are made, and the places of measurement are clearly marked on the core. When the core has a single layer, or when only the total thickness matters, the mean of the four measurements is taken as the result. When the core has more layers and their individual thicknesses matter, at each of the four points a line is drawn to the lower surface of the core, perpendicularly to the upper one, the layer boundary lines are marked on it and the thicknesses are measured cumulatively, beginning with the upper layer; the thickness of a single layer is calculated as the difference of two successive cumulative measurements, to an accuracy of 1 mm.
Applications
- Acceptance of layers of a bituminous pavement after construction
- Checking the conformity of the thickness of the layers with the design documentation
- Accredited tests of road laboratories (range up to 500 mm, point 6.1 of the standard)
- Assessment of the structure of an existing pavement before rehabilitation
- Non-destructive thickness measurements by the electromagnetic method where cores are undesirable
Key parameters
| Parameter | Value |
|---|---|
| Two methods | Destructive — measurement on drilled cores (point 6.1); non-destructive — electromagnetic measurement |
| Accuracy of measurement | To 1 mm; a metal rule and a calliper with a permissible error of at most 1 mm |
| Number of measurements per core | Four, distributed evenly round the circumference; the places of measurement marked on the core |
| Recommended diameter of the core | 100 mm or 150 mm |
| Axis of the core | Preferably within 5° of the normal to the surface of the pavement |
| Requirements for the cores | Drilled through the full depth; the ends free from features untypical of the pavement surface; cores damaged during drilling — fragmented, delaminated, bent — are rejected |
| Multi-layer cores | Cumulative measurement at the points where the four perpendicular lines cross the layer boundary lines; the thickness of a layer as the difference of successive measurements |
| Making the boundaries easier to read | Where the boundary lines are difficult to distinguish, the core may be rolled along the floor or wetted; where this does not suffice and the core is not needed for other purposes — cut lengthwise in half |
| Electromagnetic method | A counter-pole of foil or aluminium sheet of constantly uniform quality; within a radius of 1 m there must be no other metal object |
| Accredited range in practice | Up to 500 mm for the destructive measurement (list of tests of a road laboratory) |
Standard
- Standard number
- PN-EN 12697-36:2022-09
- Title (PL)
- Mieszanki mineralno-asfaltowe — Metody badań — Część 36: Określanie grubości nawierzchni asfaltowej
- Title (EN)
- Bituminous mixtures — Test methods — Part 36: Determination of the thickness of bituminous pavement
Step-by-step procedure
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Taking the cores
Drill cores representative of the slab of pavement from which they are taken, through the full depth of the pavement. The axis of the core should lie within 5° of the normal to the surface. The recommended diameter is 100 mm or 150 mm.
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Assessing the suitability of the cores
Check whether the ends of the cores are free from features untypical of the pavement surface. Do not use cores with defects affecting the measurement or damaged during drilling — fragmented, delaminated or bent.
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Marking the measuring points
Establish four points distributed evenly round the circumference of the core and mark their position clearly along the core.
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Measuring a single-layer core
Measure the thickness at the four points to an accuracy of 1 mm, perpendicularly to the upper plane of the core, between the upper and the lower surface. Record the mean of the four measurements as the thickness of the pavement.
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Preparing a multi-layer core
At each of the four points draw a line to the lower surface of the core, perpendicularly to the upper surface, and mark the layer boundary lines on it. Where the boundaries are difficult to distinguish, the core may be rolled along the floor or wetted; where this does not suffice and the core is not needed for other purposes, cut it lengthwise in half.
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Measuring the layers
Beginning with the upper layer, measure the thicknesses cumulatively at the points where the four perpendicular lines cross the layer boundary lines.
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Calculating the thicknesses of the layers
Calculate the thickness of each layer as the difference of two successive cumulative measurements, to an accuracy of 1 mm.
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A core inclined from the vertical
If the angle between the wall of the core and the vertical plane exceeds 5°, place the core with its upper surface on a horizontal base and measure the total thickness and the thicknesses of the individual layers with respect to the VERTICAL, and not parallel to the axis of the core — otherwise proceed as in steps 3–7.
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Non-destructive measurement and test report
With the electromagnetic method ensure a constant quality of the counter-pole and the absence of other metal objects within a radius of 1 m of it. The requirements concerning the test report are given in clause 7 of the standard, which is NOT in the preview — we do not reproduce its content here; read the scope of the report from the text of the standard.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Metal rule or tape | Permissible error at most 1 mm | — |
| Calliper | Permissible error at most 1 mm; with multi-layer cores a calliper with one extended jaw is convenient | — |
| Positioning device | Approved rig or another device assisting the measurement | — |
| Core drilling rig | For taking cores of the recommended diameter 100 mm or 150 mm through the full depth of the pavement | — |
| Apparatus for the electromagnetic measurement | With a counter-pole of foil or aluminium sheet glued to the bituminous layer or fixed to the unbound aggregate of the substrate | — |
| Saw for cutting cores | For cutting the core lengthwise where the layer boundary lines are illegible and the core is not needed for other tests | — |
Health and safety (OHS)
- Drilling cores in the carriageway takes place within the road reserve — traffic management, signing and protection of the working place
- A core drill with water cooling — a risk of electric shock when supplied in a damp environment, residual-current protection
- Silica dust when cutting and drilling dry — wet working or extraction, a dust mask
- Sharp edges of the cores and of fragments of asphalt — gloves when carrying and cutting them
- Holes left in the carriageway after coring — immediate protection and reinstatement
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN 12697-36:2022-09 — “Bituminous mixtures — Test methods — Part 36: Determination of the thickness of bituminous pavement”.
How does this method work?
In the destructive method, cores representative of the slab from which they are taken are cut from the pavement, drilled through its full depth. The thickness of each core or of each layer is measured to an accuracy of 1 mm, perpendicularly to the upper plane of the core, between the upper and the lower surface or between clearly marked layer boundary lines.
What is the measuring range and accuracy?
Two methods: Destructive — measurement on drilled cores (point 6.1); non-destructive — electromagnetic measurement; Accuracy of measurement: To 1 mm; a metal rule and a calliper with a permissible error of at most 1 mm; Number of measurements per core: Four, distributed evenly round the circumference; the places of measurement marked on the core; Recommended diameter of the core: 100 mm or 150 mm.
How long does the test take?
The procedure comprises 9 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Metal rule or tape, Calliper, Positioning device, Core drilling rig, Apparatus for the electromagnetic measurement, Saw for cutting cores.
Where is this test used?
Acceptance of layers of a bituminous pavement after construction; Checking the conformity of the thickness of the layers with the design documentation; Accredited tests of road laboratories (range up to 500 mm, point 6.1 of the standard); Assessment of the structure of an existing pavement before rehabilitation; Non-destructive thickness measurements by the electromagnetic method where cores are undesirable.
What safety precautions apply?
Drilling cores in the carriageway takes place within the road reserve — traffic management, signing and protection of the working place; A core drill with water cooling — a risk of electric shock when supplied in a damp environment, residual-current protection; Silica dust when cutting and drilling dry — wet working or extraction, a dust mask; Sharp edges of the cores and of fragments of asphalt — gloves when carrying and cutting them; Holes left in the carriageway after coring — immediate protection and reinstatement.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN 12697-36.