🛤️ Bulk density of compacted specimens of an asphalt mixture

Construction PN-EN 12697-6

Overview

The standard PN-EN 12697-6 describes methods of determining the bulk density of a compacted specimen of an asphalt mixture — compacted in the laboratory or taken from a pavement by coring or cutting. The four procedures are matched to the estimated content and accessibility of the voids: A — dry (specimens with a very closed surface, for example mastic asphalt), B — saturated surface-dry SSD (a closed surface; according to IBDiM asphalt concrete up to about 5 % (v/v) and SMA up to about 4 % (v/v) of voids), C — sealed specimen (an open or rough surface, up to 15 % (v/v)), D — by dimensions (specimens of regular shape, a void content above 15 % (v/v), for example porous asphalt). Annex A gives guidance on the choice of procedure. The description is based on the preview of the draft prEN 12697-6:2018 (preceding the 2020 edition) and on a study by IBDiM for GDDKiA.

The bulk density is the mass per unit volume, including the voids, at a known test temperature; the (maximum) density according to PN-EN 12697-5 is the mass per unit volume without the voids. Both parameters serve for the calculation of the void content and of the degree of compaction according to PN-EN 12697-8 — key criteria for the design of the composition and for the acceptance of asphalt layers. The result depends on the state of the specimen: an excess of moisture on the surface in procedure B leads to an underestimation of the density and an overestimation of the voids, and an excessive outflow of water to the opposite.

In WT-2 2014 of GDDKiA the bulk density of specimens for tests of water and frost sensitivity is determined according to PN-EN 12697-6 by method B (SSD) or D (geometric) — the choice depends on the range of application of the method — and the difference of the mean bulk densities of the sets must not exceed 0.015 Mg/m³. In the laboratories of GDDKiA the method is used routinely under the name „gęstość objętościowa, metoda B wg PN-EN 12697-6” [bulk density, method B according to PN-EN 12697-6].

Method principle

The bulk density of an intact compacted specimen is calculated from its mass and its volume. The mass is obtained by weighing the dry specimen in air (m1). In procedures A, B and C the volume follows from the mass in air and the mass in water: in procedure A the mass in water is determined without any preliminary treatment; in procedure B the specimen is first saturated with water and, after it has been taken out, its surface is dried with a damp chamois leather; in procedure C the specimen is sealed before immersion (paraffin wax, shrink film, latex emulsion), so that water does not penetrate the voids. In procedure D the volume is calculated from the dimensions measured according to PN-EN 12697-29. The density of the water at the test temperature is calculated to 0.0001 Mg/m³ from formula (1) of the standard; all the masses to 0.1 g, the dimensions to 0.1 mm.

Applications

• Calculation of the void content and of the degree of compaction of asphalt layers (with PN-EN 12697-5 and PN-EN 12697-8)
• Design of the composition of asphalt mixtures and type testing according to PN-EN 13108-20
• Acceptance of asphalt layers on cores from the pavement
• Preparation of sets of specimens for tests of water and frost sensitivity (WT-2 2014: method B or D, a difference of ≤ 0.015 Mg/m³)
• Testing of mastic asphalt (procedure A) and of porous asphalt (procedure D)

Key parameters

Standard

Standard number

PN-EN 12697-6:2020-07

Title (PL)

Mieszanki mineralno-asfaltowe — Metody badań — Część 6: Oznaczanie gęstości objętościowej próbek mieszanki mineralno-asfaltowej

Title (EN)

Bituminous mixtures — Test methods — Part 6: Determination of bulk density of bituminous specimens

Step-by-step procedure

1. Preparation of the specimen

   Clean the specimen by brushing or washing; it is to be dry, of known water content or dried to constant mass (successive weighings after drying at intervals of ≥ 1 h differing by ≤ 0.1 %). A thickness of ≥ 20 mm or twice the maximum particle size. Do not disturb the specimen while handling it.

2. Choice of the procedure

   Match procedure A, B, C or D to the estimated content and accessibility of the voids (Annex A of the standard; the guidance of IBDiM: B — asphalt concrete up to about 5 % and SMA up to about 4 % of voids, C — up to 15 %, D — above 15 %).

3. Density of the water

   Determine the temperature of the water in the bath and calculate its density ρw to 0.0001 Mg/m³ from formula (1) of the standard.

4. Procedure A (dry)

   Weigh the dry specimen (m1), immerse it in the bath at a known temperature and determine the mass under water immediately after the movement of the water has stopped (m2). With moist specimens, determine the dry mass at the end.

5. Procedure B (SSD)

   Weigh the dry specimen (m1), immerse it in the bath and saturate it until the mass stops changing (usually 30 min, not longer than 3 h); determine the mass of the saturated specimen under water (m2), making sure that no bubbles cling to the surface or escape from the specimen. Take it out, dry its surface with the damp chamois leather and weigh it in air at once (m3). If water is still running out — stop and use procedure C.

   ⏱ Time: 30 min – 3 h

6. Procedure C (sealed specimen)

   Weigh the dry specimen (m1) and seal it so that the internal voids are not penetrated and no additional voids are enclosed between the coating and the specimen (paraffin wax: immerse part of the specimen for < 5 s with shaking and, once it has set, repeat on the other parts until the coating is continuous). Weigh the dry sealed specimen (m2), immerse it in the bath and weigh it under water (m3) with no bubbles on the coating.

7. Procedure D (by dimensions)

   Measure the dimensions of the specimen to 0.1 mm according to PN-EN 12697-29 and weigh the dry specimen (m1); calculate the volume from the dimensions according to the shape (cylinder, cuboid).

8. Calculation

   Calculate the bulk density as the mass of the dry specimen divided by its volume, determined from the masses in air and in water (A, B), taking into account the mass and density of the sealing material (C) or from the dimensions (D), according to clause 10 of the standard; the result in Mg/m³.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Molten paraffin wax (procedure C) — a risk of burns and of ignition; heat it in a bath with temperature control, with no naked flame
• Handle the specimens and the basket for hydrostatic weighing carefully — specimens from a pavement are heavy and brittle at the edges
• Dry the specimens to constant mass only at a temperature which does not deform the binder (keep the specimens at ≤ 25 °C)

Frequently asked questions