High-modulus asphalts

High-modulus asphalts (HiMAs) are bituminous materials with high stiffness modulus, high resistance to rutting, good spreading ability and good durability. They are used only for base or binder courses in roads, airfields or other paved areas. 

known as enrobe a module eleve (EME), were introduced in France in the early 1980s as a measure to reduce the usage of oil-derived products by reducing asphalt layers thickness. The high stiffness of this material enabled the base course material to be reduced by up to 40% when compared with conventional French asphalt, grave bitumen (Nunn and Smith 1994). 

Later on, a similar mixture such as high-stiffness road base macadam, called heavy-duty macadam, was tested on road trials (Nunn and Smith 1997) and compared with EME (Sanders and Nunn 2005). 

Over the last 10 years, various other countries carried out successful trials and evaluation of HiMAs on road pavements (Bankowski et al. 2009 Capitao and Picado-Santos 2006 Nkgapele et al. 2012 Ferret et al. 2004 Wu et al. 2011). HiMA with hard bitumen modified by an SBS additive has also been tried successfully over bridge deck pavement (Li et al. 2011). 

The aggregate grading of HiMA complies with the requirements of AC hence, they are also called HiMA concrete. Nevertheless, the French notification EME is also used, particularly in France. Hence, HiMAs are also known as AC-EME and, occasionally, EME. 

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Badkowski W, M. Tusar, and L.G. Wiman. 2009. Laboratory and field implementation of high modulus asphalt concrete. Requirements for HMAC mix design and pavement design. Sustainable Pavements for European New Member States (SPENS), Sixth Framework Programme Sustainable Surface Transport. European Commission, DG Research. 

Li Y., Y. Tan, and L. Meng. 2011. Application study on high modulus asphalt concrete in bridge pavement. Advanced Materials Research, pp. 243-249. Switzerland Trans Tech Publications. Mathews D.H. and B.W. Feme. 1970. Trials of the Manufacture and Machine Laying of Mastic Asphalt. 

Wu C., B. Jing, and X. Li. 2011. Performance evaluation of high-modulus asphalt mixtures. Advanced Materials Research, Vols. 311-313, p. 2138. Switzerland Trans Tech Publications. 

The French design guide (Delorme et al. 2007 SETRA 2008) has set limiting stiffness values for designing high stiffness asphalt concretes (AC-BBME) or high-modulus bituminous mixtures (AC-EME). The minimum values of stiffness (S or E) when the test is carried out at 15°C and 10 Hz at 0.02 s are as follows ... 

Note AC, asphalt concrete and high stiffness asphalt concrete for surface or binder course, AC 10 and AC 14, with thickness between S and 9 cm. AC-Airf, asphalt concrete for airfields for surface and binder course, AC 10 or AC 14 AC-GB, asphalt for road base, AC20, with thickness between 8 and 16 cm. AC-thin, asphalt concrete for surface or binder course, AC 10 and AC 14, with thickness between 3 and 5 cm. AC-VTL6, asphalt concrete for very thin layers with D = 6 mm. AC-VTLIO, asphalt concrete for very thin layers with D = 10 mm. EME, high stiffness modulus mixtures, AGIO, with thickness between 7 and 13 cm, or AC 14, with thickness between 9 and IS cm. 

The modulus of elasticity can also influence the adhesion lifetime. Some sealants may harden with age as a result of plasticizer loss or continued cross-linking. As a sealant hardens, the modulus increases and more stress is placed on the substrate—sealant adhesive bond. If modulus forces become too high, the bond may faH adhesively or the substrate may faH cohesively, such as in concrete or asphalt. In either case the result is a faHed joint that wHl leak. 

The asphalts produced with thermosetting polymer-modified bitumen have excellent adhesive ability, excellent resistance to deformation, excellent fatigue performance and high stiffness modulus. 

Compacted soils and aggregates generally have good compressive modulus but poor tensile modulus and hence can be readily separated when subjected to high tensile loads. Geotextiles with fibres of suitable tensile moduli can effectively be used as reinforcing tension elements when embedded in compacted soils and aggregates. Some major uses are over soft soil unpaved roads, mnways, railroads and landfills, to stabilize a temporary bunds slope, as closure systems over unstable landfills, ash ponds and to reinforce asphalt pavement layers. 

As one might expect, vulcanized rubber can also Improve elasticity (Increase the storage modulus) of the asphalt binder and strengthen the asphalt - aggregate bond at high temperatures. A comparison of G7sin 6, G", a characteristic ratio, and high temperature viscosity for a series of rubber mixtures prepared from AC-10 and... 

Permanent deformation The rutting resistance of the binder is represented by the stiffness of the binder at high temperatures that one would expect in use. This is represented by G /sin(5), where G is the complex shear modulus and 5 is the phase angle determined by the dynamic shear rheometry, DSR, measured at 10 rad s (1.59 Hz). The complex modulus can be considered as the total resistance of the binder to deformation under repeated shear, and consists of elastic modulus, G and loss modulus, G" (recoverable and non-recoverable components). The relative amounts of recoverable and non-recoverable deformation are indicated by the phase angle, 5. The asphalt binder will not recover or rebound from deformation if d = 90°. 

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