Resistance to permanent deformation

The resistance to permanent deformation is determined with respect to maximum wheeltracking rate and maximum rut depth, using a small device and procedure A of CEN EN 

The maximum wheel-tracking rate should range from 5.0 to 20.0 pm/cycle, assigned to seven categories, WTS airS-o to WTSAairzo.o- 

The maximum rut depth should range from 3.0 to 16.0 mm, assigned to categories from 

The stiffness should lie between the minimum and maximum values specified or declared. The minimum stiffness should range between 1500 and 21,000 MPa, assigned to 13 cat-CgOrieS, to 5a,ia2l,000  

The maximum stiffness should range between 7000 and 30,000 MPa, assigned to eight categories, S, 

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PBT is easily made into fiber and monofilament and has been used in some fiber applications. For example, PBT fibers are used commercially as toothbrush bristles. Compared to PET, PBT fiber is more resistant to permanent deformation. Compared to nylon, PBT shows almost no change when exposed to moisture. PBT shows much more resistance to staining than nylon and can be colored by the use of pigments. However, PBT is more difficult to color by solution dying than nylon. PBT is not typically used in textile applications due to its perceived high price. 

Plastics of the second sort are insoluble in the asphalt and have little effect on the properties of the asphalt, but they may have some effects on the mechanical properties of the asphalt mixture. The particles of the plastics become soft and plastic at hot-mixing for making the asphalt mixture and deform at compaction, in between the aggregate particles. They become back to hard and elastic upon cooling. The elastic particles in between the aggregate particles will restrict the movement of the aggregate particles, and consequently the resistance to permanent deformation of the asphalt mixture will become higher. 

Hypalon, when properly compoimded, also exhibits good resistance to wear and abrasion, good flex life, high impact resistance, and good resistance to permanent deformation imder heavy loading. 

The role of modified bitumen in paving is mainly fourfold to increase asphalt s resistance to permanent deformation, to improve asphalt s fatigue life, to increase asphalt s stiffness modulus and to improve adhesion between bitumen and aggregate particles. All the above tasks are to be fulfilled without affecting, if possible, the workability of the mixture. Only certain modifiers are able to fully accomplish these rather complicated and difficult tasks. 

Mixtures to which fibres are added are the SMA and porous asphalt and occasionally in micro-surfacing. Dense asphalt mixtures with fibres were also found to have high resistance to fatigue (Samanos and Serfass 1993). The addition of plastic or iron fibres was found to increase the resistance to permanent deformation (Courard and Rigo 1993). The percentage of iron fibres added was 0.4% to 1.5%, while for the plastic fibres, it was 0.1 to 0.7%, by mass of bitumen. 

Bitumens for filling joints and cracks in pavements of roads, airports, parking places and other trafficked areas are specially modified bitumens, so as to resist thermal tensile and compressive stresses developed as a result of temperature changes. At the same time, they possess excellent resistance to permanent deformation. Depending on the additives incorporated in the bitumen, these modified bitumens can also be fuel resistant. 

At the target mixture, the following should be determined the composition, the grading of aggregates, the void content, the resistance to permanent deformation and the water... 

When the large-sized wheel-tracking device is used, the resistance to permanent deformation is expressed in reference to proportional rut depth (P), expressed in per cent. The maximum values of the proportional rut depth range from 5% to 20%, assigned to five categories, P5, P7.5, F15 and P20. 

When the target composition is determined by fundamental requirements, the AC should fulfil the general requirements, as outlined in Section 5.4.1.3, plus the fundamental requirements, which are grading, binder content, stiffness, resistance to permanent deformation in the triaxial compression test and resistance to fatigue. 

Resistance to permanent deformation in the triaxial compression test... 

The resistance to permanent deformation under the triaxial compression test of cylindrical specimens is expressed in reference to creep rate (fj and should be less than the maximum value specified. 

The use of modified bitumen (polymers and sulfur) or Trinidad lake asphalt improves HRA s resistance to permanent deformation and its weathering properties (Carswell 1987 Denning and Carswell 1981a,b, 1983 Jacobs 1980). 

SMA was developed in Germany and Scandinavian countries in the mid-1960s. The prime reason for the development of this mixture was the demand to produce a mixture that can sustain the destructive action of studded tyres, to have good resistance to permanent deformation and long service life. 

At the target mixture, the following empirical properties should be determined void content, voids filled with bitumen, binder drainage, water sensitivity, resistance to permanent deformation and, when required, resistance to abrasion by studded tyres. 

The resistance to permanent deformation of MA is determined by the indentation test conducted in accordance to CEN EN 12697-20 (using cube or Marshall specimens), CEN EN 12697-21, Test W or Test B (using plate specimens) or CEN EN 12697-25 (2005) (cyclic... 

Recent laboratory and field evaluation of HWMA proved that their mechanical properties, such as stiffness, resistance to permanent deformation and resistance to water damage, were considered adequate and similar to those of the equivalent hot mix materials. Additionally, less hardening of the binders recovered from HWMA was found when compared to those recovered from the hot mixtures (Artamendi et al. 2011). 

The mechanical behaviour of asphalts is determined by resistance to tensile forces, known as resistance to fatigue cracking, and resistance to compressive forces, known as resistance to permanent deformation. The first is expressed by the relationship between tensile strain and number of loadings, known as the fatigue equation. The second is expressed by the relationship between compressive strain and number of loadings, known as the creep equation. 

The wheel-tracking test and the cyclic compression tests, apart from determining the resistance to permanent deformation of a bituminous mixture, also make it possible to rank various mixes or to check on the acceptability of a given mix. 

The assessment of the asphalt performance in resistance to permanent deformation is determined with reference to either creep rate and creep modulus or creep rate and cumulative strain after n load applications, or permanent shear strain, depending on the test employed. 

According to the American practice, the resistance to permanent deformation, or resistance to rutting as it is called, of the bituminous mixtures is determined with the recently introduced flow number test. The test is a uniaxial repeated (dynamic or cyclic) compression test executed with a test device specially developed for Superpave mix design procedure. The test device is known as AMPT, which is also capable of determining the dynamic modulus of the mixture. The test is carried out at an elevated temperature determined from the average 7-day maximum pavement temperature 20 mm below the surface (see Section 7.6.23). The test is carried out in accordance to AASHTO TP 79 (2013). 

The bituminous mixture s resistance to permanent deformation is assessed in terms of creep rate, (Method 1, Section 7.6.2.2.1), or in terms of parameters B and eiooo.cak (Method 2, Section 7.6.2.2.2). 

The relevant creep parameters obtained to determine AC 20 mm resistance to permanent deformation using both calculations are given in Table 7.4. The results were obtained from tests carried out at the Highway Engineering Laboratory of the Aristotle University of Thessaloniki. 

The resistance to permanent deformation of the bituminous mixture is assessed in terms of creep stiffness modulus, determined using the following equation ... 

In mix design calculations, the mix with the lowest value of slope coefficient, b, and the highest creep stiffness modulus, is more resistant to permanent deformation and should be selected as the target mix. 

The development and use of the wheel-tracking test are relatively recent in the United States. The wheel-tracking test procedures used in the United States for the determination of the resistance to permanent deformation, or susceptibility to rutting, of the bituminous mixtures are (a) the asphalt pavement analyser (APA) test and (b) the Hamburg wheel track (HWT) test. 

The test can determine not only the bituminous mixture s resistance to permanent deformation but also its moisture susceptibility. 

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