🏗️ Density of a bituminous mixture — volumetric, hydrostatic and mathematical methods, PN-EN 12697-5

Construction PN-EN 12697-5

Overview

THE SCOPE FROM THE PKN CATALOGUE CARD, THE OPENING QUOTED VERBATIM: "This document specifies a test method for the density of a bituminous mixture. A volumetric, a hydrostatic and a mathematical method are specified. The test methods described apply to bituminous mixture in the loose state containing paving grade bitumen, modified bitumen or other bituminous binders used for mixtures [...]. Samples may be supplied as material in the loose state or as compacted material; it is recommended that the latter be broken up first. The methods are suitable for fresh and aged bituminous materials."

THE SENTENCE ABOUT COMPACTED MATERIAL CHANGES THE REACH OF THE STANDARD. The test concerns material in the loose state, but the sample NEED NOT reach the laboratory in that state: compacted material may be broken up and tested. This is therefore not a boundary of materials but a requirement as to the state of the sample at the moment of measurement. The scope also covers AGED materials, which means the methods apply not only to freshly produced mixture but to material taken from an existing pavement.

THE LOOSE STATE — THE WORD THAT SETTLES WHAT THE STANDARD IS ABOUT. The scope speaks of a mixture "in the loose state", that is uncompacted. The quantity determined here is often called the maximum density: it describes the material without voids, as the sum of its constituents. A discrepancy of titles in the catalogue follows this distinction: the Polish title reads "Determination of density", the English one "Determination of the maximum density"; it is the same quantity, named differently in the two languages. The bulk density of COMPACTED SPECIMENS — measured without breaking them up, and hence including the voids — is determined by another part of the series, PN-EN 12697-6, which has its own entry in this knowledge base. Confusing them leads to an error in the void calculation, for it is precisely the difference between the two densities that gives the void content.

THREE METHODS, AND WHY THERE ARE THREE. The volumetric method rests on measuring the volume of liquid displaced in a pyknometer; the hydrostatic one on weighing in air and in liquid; the mathematical one on calculating the density from the known densities and proportions of the constituents, without any measurement on the mixture. The third is therefore a calculation, not a test: its result is worth as much as the input data about the constituents, and it will not detect an error in the composition of the mixture. The report must state by which method the density was determined — three different routes give results that may differ, and the recipient has no way of reconstructing this from the figure alone.

WHY DENSITY IS DETERMINED AT ALL. In itself it is rarely the subject of a requirement. It is a reference quantity: the void content of a compacted specimen is calculated by comparing the bulk density of the specimen with the density of the mixture determined under this standard. An error in the density therefore carries straight over into the void content, and that is one of the basic criteria in assessing a pavement — it governs durability, water-tightness and resistance to rutting.

THE SCOPE COVERS MODIFIED BINDERS. The sentence about "paving grade bitumen, modified bitumen or other bituminous binders" matters in practice: the method is not confined to mixtures with ordinary bitumen, as is sometimes assumed on the basis of older commentaries.

WHAT WE DO NOT GIVE. We do not have the text of the standard — PKN supplies it for a fee (TC 212, Road Construction and Maintenance). We therefore DO NOT GIVE sample masses, test temperatures, de-aeration times, the kind of liquid or the calculation formulae for any of the three methods.

Method principle

The density of a mixture in the loose state is determined as the ratio of mass to the volume of the material without voids. Two of the three methods are measurements and differ in how the volume is found: the volumetric one measures the volume of liquid displaced by the sample in a pyknometer, the hydrostatic one uses the difference between masses weighed in air and in liquid. The third method is a calculation: the density is derived from the densities and proportions of the constituents of the mixture, without testing the material itself.

Applications

• Determining the density of a bituminous mixture as the reference quantity for calculating the void content
• Production control of mixtures in asphalt plants
• Type testing and factory production control under the PN-EN 13108 series
• Assessment of road pavements — durability, water-tightness and resistance to rutting depend on the void content

Key parameters

Standard

Standard number

PN-EN 12697-5:2019-01 (wersja angielska; wprowadza EN 12697-5:2018 [IDT])

Title (PL)

Mieszanki mineralno-asfaltowe -- Metody badań -- Część 5: Oznaczanie gęstości

Title (EN)

Bituminous mixtures — Test methods — Part 5: Determination of the maximum density

Step-by-step procedure

1. Choose the method

   Volumetric, hydrostatic or mathematical. Remember that the third is a calculation from the composition, not a test of the material.

2. Bring the sample to the loose state

   Break up material supplied compacted — the card recommends this expressly. For the bulk density of compacted specimens, determined without breaking up, PN-EN 12697-6 applies.

3. De-aerate

   Air bubbles trapped between the grains overstate the volume and hence understate the density — and thereby overstate the calculated void content.

4. Measure

   By the chosen method, under the conditions set by the standard. WE DO NOT GIVE TEMPERATURES OR MASSES — they are in its text.

5. Calculate

   The formulae are in the standard. With the mathematical method the result depends solely on the data assumed for the constituents.

6. Record in the report

   Give the METHOD APPLIED and the full designation of the standard with its year — three methods may give different results, and the figure alone does not reveal which was chosen.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Bituminous mixtures are tested at elevated temperature — risk of burns when taking and preparing samples
• Fumes from hot bitumen contain polycyclic aromatic hydrocarbons — extract ventilation is required
• In variants using a solvent — fire and toxic hazard; work under a fume hood, away from sources of ignition

Frequently asked questions