pavement - road science

Background

In a New Zealand first Road Science can now manufacture EME2 structural asphalt mixes.

EME2 is a very stiff, high rut resistant structural asphalt mix that was developed in France over 30 years ago. The high bitumen content of this mix provides superior fatigue resistance, this combined with the high modulus used in design results in around a 30% to 50% reduction in thickness compared with a standard AC20 mix. EME2 gives around 100 times more rut resistance at intersections with slow moving and stationary heavy vehicles compared with a standard AC20 mix.

This technical note gives EME2 mix pavement design criteria for experienced pavement designers who use CIRCLY for pavement design. The design criteria given complies with current Austroads and NZTA Pavement Design Guidelines. For further information on the benefits and background to this mix please refer to the EME2 product brochure.

PLEASE NOTE:

This document provides a pavement design criteria derived from resilient modulus tests on a RS mix from test results for a Wellington mix. This is considered a starting point for a desktop design to check the viability of using RS EME in your project.

It is the designer’s responsibility to seek and use current resilient modulus test data relevant to their project and to conduct their own interpretation and use of this data in their own pavement design. Therefore the ownership and liability of the design rests with the pavement designer and their client.

Figure 1 - Pavement model for mechanistic design procedure (Ausroads 2012)

Pavement Design

Helps to resolve these problems:

Habitat

roadscience.co.nz 0800 180 200

PAVEMENT DESIGN CRITERIA EME2

The Austroads Pavement Design Guide requires a modulus specific to the design temperature and loading speed, along with tensile fatigue criteria from the Shell equation for input into CIRCLY. Modulus is determined from resilient MATTA modulus tests at 25 degrees Celsius as per AS/NZS 2891.13.1 – 13 and using Shell and Austroads rules (Section 6.5 Asphalt from 2012 Austroads Guide to Pavement Technology Part 2: Pavement Structural Design https://www.onlinepublications.austroads.com.au/items/AGPT02-12) is converted for the design temperature (weighted mean annual pavement temperature) and vehicle speed.

Pavement design criteria derived in this way for the Wellington Asphalt (RS EME B15 KP16) mix is shown in the tables 1 and 2.

It has been found that minor variations of binder and binder content within the allowable limits of the specification can affect the very sensitive measure of resilient modulus (AS/NZS 2891.13.1 – 13). The pavement designer can consider variations in resilient modulus by ensuring the design is compliant for the lowest expected modulus value shown in the table 2. The design criteria can be used for a desktop design using RS EME but the design will need to be checked using mix design properties for the RS EME mix that will be used on the specific project.

Table 1 – Data from Matta Resilient Modulus from AS/NZS 2891.13.1 - 13

Asphalt TypeMatta Resilient Modulus (MPa):

SpecificationBulk Specific Gravity @ 25°C:

Air Voids (%):

Total Bitumen Volume (%):

RS EME Mix average 13600 6.40% 2.326 4.9% 14.59

RS EME Mix lowest 8000 6.40% 2.326 4.9% 14.59

Table 2 – Pavement Design Criteria for use in CIRCLY mechanistic design using Matta Resilient Modulus (Table 1)

Asphalt Type

Design Speed (km/hr)

Temp (WMAPT)

Speed Adjust-ment

Temp Adjust-ment

Air voids Adjust-ment

Total Adjust-ment

Design Modulus (Mpa)

CIRCLY K Value

CIR-CLY b Value

RS EME Mix Average

30 23 0.66 1.17 1.01 0.78 10559 0.003343 5

RS EME Mix Lowest

30 23 0.66 1.17 1.01 0.78 6211 0.004047 5

RS EME Mix Average

80 23 0.94 1.17 1.01 1.11 15105 0.002939* 5

RS EME Mix Lowest

80 23 0.94 1.17 1.01 1.11 8885 0.003557 5

* Use in CIRCLY Pavement Design Software


Pavement Design Criteria - queensland tmr EME2

The Queensland Transport Main Roads have developed recommended design criteria for initial desktop analysis as detailed in their document (http://www.tmr.qld.gov.au/-/media/busind/techstdpubs/Technical-notes/Pavements-materials-geotechnical/TN142.pdf?la=en ):

Design criteria for EME2 from this technical note is summarised in the table 3 but it is for Queensland temperatures of 32 degrees celcius. Using the Austroads conversions these design criteria have been adjusted for a design temperature of 23 degrees as used in Auckland shown in table 4 and 5.

Table 3 – Table 2 from Queensland Technical Note for Design of EME2

Asphalt mix type Binder typeVolume of binder (%)

Asphalt modulus at heavy vehicle operating speed

10 km/h

30 km/h

50 km/h

80 km/h

EME 2EME Binder (15/25

PEN)13.5 2000 3000 3600 4200

The design values below can be used for a desktop design using RS EME but the design will need to be checked using mix design properties for the RS EME mix that will be used on the project. It should be noted that experience with using RS EME mixes in New Zealand has found that the modulus and bitumen content is higher than that used for the Queensland presumptive values and therefore if used the design would be considered conservative.

Table 4 – Estimate of Matta Resilient Modulus Test Result at 250C Used to Generate Queensland Presumptive Values (Table 3)

Asphalt Type

MATTA RESILIENT MODULUS (MPa):

Total bitumen content

(%)

Bulk specific gravity @ 25 *C:

AIR VOIDS (%):

Total bitumen volume (%):

EME2 QUEENSLAND PRESUMPTIVE

7769 5.92% 2.326 4.9% 13.50


Table 5 – Pavement Deisgn Criteria for use in CIRCLY mechanistic design using Queensland Matta Resilient Modulus

Design Speed (km/hr)

Temp (WMAPT)

Speed Ad-justment

Temp Ad-justment

Air voids Adjust-ment

Total Ad-justment

Design Modulus (Mpa)

CIRCLY K Value

CIR-CLY b Value

10 23 0.44 1.17 1.01 0.52 4039 0.004399 5

30 23 0.66 1.17 1.01 0.78 6032 0.003808 5

50 23 0.79 1.17 1.01 0.94 7268 0.003561 5

80 23 0.94 1.17 1.01 1.11 8629 0.003347 5

RUT Resistance

One of the main advantages of using RS EME mix is to prevent rutting in locations that are prone to failure when traditional asphalt mixes are used. RS EME is ideal at intersections, bus stops, ports and airports where there are high loads and when the load is slow moving or stopped.

The current method to ensure the asphalt mix is rut resistance is to comply with NZTA M10 (https://www.nzta.govt.nz/resources/dense-graded-and-stone-mastic-asphalt/ ) where rutting is measured in a wheel tracker for 10 thousand load cycles at 60 degrees Celsius as per the test method AGPT /T232, the maximum allowed is 6mm. This criteria is considered not sufficient to prevent rutting at areas where there are slow moving loads like bus stops and traffic lights. RS EME mix has significantly higher rut resistance with a rut depth of only 1.7mm after 60,000 passes in the same wheel tracker at 60 degrees Celsius as per AGPT/T232 as shown below for a RS EME mix used at Wellington airport (Test # T16/2669).

Figure 1 - EME2 mix wheel tracking result at 60 degrees celsius for 60,000 wheel passes

To ensure EME2 mix has sufficient rut resistance at intersections where heavy vehicles are stopped Road Science undertook Repeated Load Triaxial tests to simulate slow loading times up to 30 seconds at temperatures of 30, 40 and 60 degrees to measure rutting/permanent deformation and vertical compressive modulus/stiffness. Initial results show EME2 has 94 times more rut resistance for a 30 second load duration at 40 degrees celcius than a standard heavy duty AC20 mix with 40/50 binder complying with NZTA M10. The AC20 mix failed when tested at 40 degrees and a 30 second load duration and could not be tested at 60 degrees while EME2 mix performed well with low rutting at both 40 and 60 degree test temperatures for a 30 second load duration.

More testing is planned by Road Science to more accurately predict the rutting life of RS EME mix. Initial results clearly show superior rut resistance and modulus/stiffness at 40 degrees for long loading times when compared with a heavy duty AC20 mix as shown in the figures 1 and 2.


Figure 1 - RS EME and AC20 Vertical Compressive Modulus Results at 40 degrees for different load durations.

Figure 2 - RS EME and AC20 Estimates of Rutting Life at 40 degrees for different load durations.

An analysis of the rutting results at 40 degrees for an intersection where 5% of the time the asphalt is at 40 degrees and the load duration is for 10 seconds is shown in the table 6.

Table 6 - Estimated load passes at a 10 second duration at 40 degrees Celsius until rutting failure in asphalt (10mm rut).

AC Mix (40 degrees 10 second load duration)

Estimated Actual load passes to 10mm rut from RLT test

Total allowable wheel load passes estimated based on time @ 40 degrees (5% of loading time)

Life (years - assuming failure @ 30mm rut and 200,000 ESAs per year)

EMac20 40/50 binder PTIVE

4,780 95,600 1.4

EME2 298,238 5,964,754 89.5


Specification

To ensure long term durability, fatigue life and rut resistance RS EME mix is designed to comply with the Queensland Transport Main Roads Specification PSTS107 High Modulus Asphalt (EME2) (http://www.aapaqtmr.org/docs/EME/2015-05-16_PSTS107_EME2.pdf ). A similar AAPA specification for EME2 is also currently being developed.

For construction quality control NZTA M10 specification is used for the job mix formula for RS EME mix. Queensland Transport Main Roads also has a construction specification that could be used and is available for download from: http://www.aapaqtmr.org/docs/EME/2014_07_25_PSS107_EME2.pdf

Further Information

Please refer to the EME2 brochure for more details on the benefits and for technical design help contact Dr Greg Arnold of the Road Science Team.

Te Rapa Wairere Drive EME2 site

Before After

Images show SMA surface on top of EME2 structural asphalt.

The information contained in this document is, to the best of our knowledge, true and accurate, but since the conditions of use are beyond our control, any recommendations or suggestions which may be

made are without guarantee and no warranty, expressed or implied, is given. We reserve the right to change this document at any time.

[email protected]

IF YOU WOULD LIKE TO TALK

Greg has over 22 years’ experience in research, pavement design and project management, with a comprehensive understanding of aggregate testing methodologies. He uses an array of test methods including Repeated Load Tri-axial (RLT) and flexural beam tests to ensure his pavement designs produce best value results for customers.

021 032 3117

DR GREG ARNOLD Principal

Pavement Engineer


pavement - road science

Documents