Sabita information sheet #12 - HiMA

High Modulus Asphalt (HiMA)WHAT IS HiMAHigh Modulus Asphalt (HiMA) is a distinct type of hot mix asphalt and many of the matters covered in Sabita Information Sheet #4 – HMA apply to HiMA. The technology associated with HiMA is based on the French technology Enrobé à Module Élevé (EME). In essence, HiMA consists of hard, unmodified bitumen blended at high concentrations (up to 6.5% by mass) with good quality aggregate to produce a mix with low air voids content.

Key features of this type of asphalt are:• High elastic stiffness, hence excellent load spreading capability;• Superior resistance to permanent (plastic) deformation;• Extended fatigue life; • Resistance to moisture damage; and• Good workability.

This product is recycle-friendly and has proved itself as a viable alternative to concrete base pavements in accelerated road pavement testing at the Laboratoire Central des Ponts et Chaussées (LCPC) in France. Extensive studies in the UK carried out by Transport Research Laboratory have led to the transfer of the French Technology to that country.Transfer of the French technology to South Africa commenced in 2006 and has now reached a stage where its implementation can proceed. For this purpose design guidelines have been developed by Sabita.

USE AND APPLICATIONSPavements comprising HiMA as the principle structural layer can be employed for design traffic well in excess of 50 million ESALs with due consideration and selection of supporting pavement materials and structure. Structural analyses performed in France and SA show that asphalt base thickness reductions in the order of 30 % can be achieved using HiMA. The ability to reduce layer thicknesses makes HiMA also ideally suited for application in urban areas where the need for relocation and/or disruption of subsurface services can be significantly reduced. Potential application zones of HiMA include:• Pavements subjected to severe loading, such as dedicated bus and truck routes, loading bays

and container terminals; • Long life pavements for major freeways and expressways where interventions need to be

limited to avoid excessive disruption to traffic; and• Airport runways and taxiways.There are two classes of HiMA – Class 1 and Class 2, with the Class 2 material having significantly higher binder content and, hence, improved fatigue resistance.

Did you know?

Following the Sabita sponsored research the first full-scale high modulus asphalt (HiMA) trials to be conducted in South Africa began in September 2010 on a section of the heavily trafficked old South Coast Road near Durban’s harbour. Reference: http://nationalasphalt.co.za/?page_id=567

Sabita information sheet #12 - HiMA

Tel: + 27 21 531 2718 • Fax: +27 21 531 2606 • email: info@sabita.co.zaSouthern African Bitumen Association

DESIGN OF HiMA

The two main constituents of HiMA are high quality, fully crushed aggregates and hard, unmodified bitumen of either 10/20 and 15/25 penetration. There are no prescribed aggregate gradings for HiMA, although guidelines are given as a point of departure of the design process. The main objective of determining a suitable grading for HiMA in a particular application is to meet performance related criteria for adequate workability, durability, resistance to permanent deformation, fatigue strength and stiffness.As with conventional asphalt, filler is used to meet the grading requirements. When active fillers such as cement and hydrated lime are used care should be taken not to increase the viscosity of the hot mastic beyond values that will adversely affect workability during mixing and paving. Where hydrated lime is used the quantity should be limited to 1% by mass of the total aggregate.In the design process the binder content of HiMA is defined by a “Richness Modulus”, which is a measure of the thickness of the binder film surrounding the aggregate and is related to the specific surface area and the density of the aggregate used. This is a critical requirement which requires strict compliance. The table below summarises the recommended performance related requirements adopted in the design of HiMA for each of Classes 1 and 2.

CONSTRUCTIONWhile all the usual precautions pertaining to the manufacture and laying of hot mix asphalt apply to HiMA, special precautions are :• As the HiMA layer is the principal structural component of the pavement, it is essential that

minimum specified thicknesses are met;• Where HiMA is constructed in more than one layer, care should be taken to ensure good bonding

between these layers; • Due to the high viscosity of the bitumen used, the mixing and compaction temperatures are

elevated. During compaction HiMA characteristically “stiffens up” quite suddenly upon cooling of the mat. Once this occurs, further rolling has very little effect on compaction; and

• Upon completion in-situ voids should not exceed 6%.

Property Test Requirements

HiMA class

Class 1 Class 2

Workability Gyratory compactor, air voids after 45 gyrations

≤ 10% ≤ 6%

Durability Modified Lottman, TSR ≥ 0.80 ≥ 0,80

Resistance to permanent deformation

RSST-CH, 55 ⁰C, 5 000 reps ≤ 1,1% strain ≤ 1,1% strain

Dynamic Modulus Dynamic modulus at 10 Hz, 15 ⁰C ≥ 14 GPa ≥ 14 GPa

Fatigue Beam fatigue test at 10 Hz, 10 ⁰C, to 50% stiffness reduction

≥ 106 reps @ 300 ε

≥ 106 reps @ 390 ε