6. LPC Bituminous Mixtures Design Guide, Sept 2007. - Aapaq.org

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LPC Bituminous Mixtures Design Guide- Mix Design Procedure -Similarly, the increase in fatigue characteristics observed when adding polyethyleneis solely correlated with the corresponding rise in binder quantity.Example – Effect of polyethylene concentration (from cable waste) on rutting resistanceTest conducted on a AC14-BBSG mix containing 32% finely-crushed aggregate,initially leading to 15% rutting after 3000 cyclesNOTE: The mix's bitumen content has been lowered by 0,15%, in comparison with the reference mix,to account for the addition of polyethylene.Polyethylene concentration(%, with respect to the dry aggregate)Rut depth after 30,000 cycles(mm)0,5 90,8 51,1 4[Experiment conducted on aggressive loads, No. 3, Fatigue Carrousel]PolymersThese additives are intended to decrease the effect of binder susceptibility.Fine rubber crumb fraction and 2/6 rubber aggregatesThese additives contribute to improved cracking resistance, in addition to dampingthe impact from tires.New and recycling fibersIncorporated at the time of mixing, these fibers act like a bitumen reservoir once inthe mix; they can either increase bitumen content, without raising the risk of rutting(added to BBTM and SMA mixtures), or avoid drainage problems (for PA-BBDr).Depending on the type of fibers added, the mode of laboratory preparation must beadapted while continuing to respect the mode selected for including this additive in anindustrial setting.The fibers may be mixed to the binder either as a preliminary step or introduced intothe dry mix or perhaps after incorporation of the bitumen.3.1.3.2 Natural bitumen and asphaltsThis category of additives is to be used as a substitution for directly-distilled bitumenin order to obtain a stiffer mix by means of a combined binder hardness and addedfiller effect.3.1.3.3 PigmentsThe concentration of pigments depends on the desired effect, aggregate color andtype of bitumen. For a light-colored synthetic binder, this concentration lies on theorder of 0,5% and can rise as high as 2%. With a pigmentable bitumen, theconcentrations are higher, reaching the neighborhood of 2,5% to 4%. This case isgenerally limited to use of the color red.It would be necessary to consider the pigment concentration like fines within the mix.- 82 -
LPC Bituminous Mixtures Design Guide- Mix Design Procedure -The product is then incorporated into the dry mixture prior to adding the bitumen.The mix's mechanical characteristics, especially water resistance and if applicablerutting resistance, are to be verified. Oxides can actually influence binder-aggregateadhesion and the choice of associated bitumen (either pigmentable or synthetic) caninfluence rutting resistance.3.2 Relationships between binder properties and mix properties3.2.1 Penetrability and ring and ball temperatureThe test of penetrability at 25°C is correlated with stiffness of the mix at servicetemperatures. The stiffness modulus of bitumen may be deduced from both thepenetration test at 25°C and the ring and ball temperature, by means of the Van derPoel abacus (see Fig. 29).Ring and ball temperature is an effective indicator of the binder's contribution torutting resistance. This criterion loses its relevance however for modified binders.Example – Effect of ring and ball temperatureOn 3 types of asphalt mixes, a 7°C rise in the ring and ball temperature of a bitumen allowsincreasing tenfold the number of cycles leading to a given rutting depth.3.2.2 The SHRP criteriaThe Strategic Highway Research Program (SHRP) set up in the United States hassought to define the relationships between binder characteristics and mixcharacteristics. The tests conducted on binders have been aimed at ascertainingrheological aspects. The binder performance – mix performance relationships are thecurrent focus of research efforts. A few of these relationships have already beenpublished, yet their pertinence for French mixes still needs to be verified.SHRP criteria and tests conducted on asphalt mixesAccording to the SHRP, rutting resistance is effective if G*/sin δ > 1 kPa (for new binder) and> 2,2 kPa (for binder having undergone RTFOT).This relationship is not always verified with the LPC rutting tester.In contrast, the criterion G*/sin δ > 3.8 kPa leads to low rutting rates [RGRA 730].The SHRP criterion relative to fatigue resistance is expressed as: G*sin δ < 5 kPa (RTFOT + PAV).A verification on AC10-BBSG mixes serves to confirm this trend, although the correlation is not verystrong. Sin δ does not contribute any more than G*, and ε 6 is not directly correlated. The slope of thefatigue line enters into consideration.Cold resistance: The SHRP criteria are: S(60) < 300 MPa and m > 0,3 (with the doubt over whethereither of the two criteria is being met: a tensile deformation test at failure > 1% is thus conducted).The criteria selected in France are: temperature isomodulus I G*I = 300 MPa for a 1000 s loadingtime and slope m. Correlation with the theoretical brittleness temperature proves to be strong.- 83 -
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6. LPC Bituminous Mixtures Design Guide, Sept 2007. - Aapaq.org

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