🛤️ Void characteristics of specimens of an asphalt mixture (Va, VFB)

Construction PN-EN 12697-8

Overview

The standard PN-EN 12697-8 describes the procedure for calculating the void characteristics of a compacted specimen of an asphalt mixture: the void content (Va), the voids in the mineral aggregate filled with binder (VFB) and — for mixtures with additives — filled with binder and additives (VFBad). The method applies to specimens compacted in the laboratory and to specimens cut from a pavement after laying and compaction or from slabs compacted in the laboratory, by coring or cutting. These characteristics serve as criteria for the design of the composition and as parameters for assessing the mixture after it has been laid and compacted in the road.

The 2018 edition (PN-EN 12697-8:2019-01) replaced PN-EN 12697-8:2003: the title no longer restricts the method to hot mixtures, PN-EN 12697-7 (bulk density by gamma rays) was added as a source of ρb, the concepts of VMAad and VFBad were introduced for mixtures with additives, the units were changed from kg/m³ to Mg/m³, and for mixtures with water in their composition (emulsion, foamed bitumen) it was specified that the bulk density refers to the dry state.

The void content and the degree of compaction are the basic parameters for assessing a mixture at the stage of design and of acceptance of the layers; both are calculated from the density and the bulk density. In WT-2 2014 of GDDKiA the requirements for mixtures are given with reference to PN-EN 12697-8 clause 4 (Va, for example Vmin/Vmax) and clause 5 (VFB, VMAmin), and according to IBDiM the assessment of the compaction of a layer is sometimes the decisive, and often the disqualifying, factor at the acceptance of the works.

Method principle

The void content of a specimen is calculated from the (maximum) density of the mixture (ρm — the mass per unit volume without voids) and the bulk density of the specimen (ρb — the mass per unit volume including the voids): Va = (ρm − ρb)/ρm · 100, to 0.1 % (v/v), both densities in Mg/m³. For mixtures with water in their composition, ρb refers to the dry bulk density. The VFB (mixtures without additives) is calculated from the binder content, the voids in the mineral aggregate (VMA — the intergranular space comprising the voids and the volume of the binder), the bulk density of the specimen and the density of the binder; the VFBad additionally from the content and density of the additives. The absorption of binder by the aggregate may lead to an overestimation of Va — depending on the porosity of the aggregate.

Applications

• Design of the composition of asphalt mixtures (Va, VFB, VMA as criteria in WT-2 2014 and PN-EN 13108)
• Assessment of the compaction of asphalt layers after laying (cores from the pavement)
• Type testing of mixtures according to PN-EN 13108-20 (the volumetric properties of Marshall specimens)
• Assessment of mixtures with additives (VFBad) and with emulsion or foamed bitumen (the dry bulk density)
• Production control in the plant (laboratory specimens)

Key parameters

Standard

Standard number

PN-EN 12697-8:2019-01

Title (PL)

Mieszanki mineralno-asfaltowe — Metody badań — Część 8: Oznaczanie zawartości wolnej przestrzeni próbek mineralno-asfaltowych

Title (EN)

Bituminous mixtures — Test methods — Part 8: Determination of void characteristics of bituminous specimens

Step-by-step procedure

1. Specimen

   Use a specimen compacted in the laboratory or cored or cut from a pavement after compaction or from a laboratory slab; record its origin, the type of mixture and any additives.

2. Density of the mixture ρm

   Determine the (maximum) density of the mixture according to PN-EN 12697-5 in Mg/m³.

3. Bulk density ρb

   Determine the bulk density of the specimen according to PN-EN 12697-6 (the procedure matched to the void content) or PN-EN 12697-7; for mixtures with water in their composition use the dry bulk density. If the dimensions were measured, record them to 0.1 mm.

4. Calculation of Va

   Va = (ρm − ρb)/ρm · 100, to 0.1 % (v/v).

5. Calculation of VFB or VFBad

   Without additives: the VFB from the binder content, the VMA, the bulk density of the specimen and the density of the binder (5.2.1). With additives of known content and density: the VFBad additionally from the content and density of the additives (5.2.2).

6. Test report

   Give: the origin of the specimen, the type of mixture and the additives, the dimensions of the specimen to 0.1 mm (if measured), the methods used for the density and the bulk density, both densities in Mg/m³ and Va to 0.1 % (v/v); likewise for VFB/VFBad.

Required equipment and apparatus

Health and safety (OHS)

• The method is one of calculation; the hazards concern the constituent tests: hot mixture when compacting specimens, the noise of the Marshall compactor, the drilling and cutting of specimens from a pavement (dust, cooling water)
• With bulk density by gamma rays (PN-EN 12697-7) the regulations on radiation protection apply

Frequently asked questions