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

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LPC Bituminous Mixtures Design Guide- Mix Design Procedure -Table 21– Suggested bitumen grade by mix typeType of mix Loading Suggested gradeMixes for wearing courses AC-BBSG,AC-BBM, BBTM, PA-BBDr and AC-BBA materialsMixes for wearing courses AC-BBSG,AC-BBM, BBTM and AC-BBA materialsMixes for base courses /foundation layersHeavyLight35/5050/70 (airfield pavement NS3)20/30 may be used for class 3 of AC-BBSGand AC-BBME50/7070/100 at higher altitudes, and in continentalzones and airfield zones submitted to lighterloads (NS1, NS2)35/50Lower thermal susceptibility bitumenThis category of pure bitumen has been specially produced and features apenetration at 25°C that corresponds with the standardized grade (e.g. 35/50 or50/70), yet whose ring and ball temperature typically exceeds the standardized limitfor the corresponding grade. The Fraass temperature is also lower than that ofsimilarly-graded pure bitumen samples (≤ -15°C). They are used in particular forimproving the rutting resistance properties of materials."Hard" bitumenThis category of pure bitumen is obtained by means of a direct refining process anddisplays a penetration of less than 25 1/10 mm. Two categories 10/20 and 15/25 aredefined according to EN 13924. The French recommendation for the ring and balltemperature is between 60°C and 76°C for 10/20 and between 55°C and 71°C for15/25. The Fraass temperature (out of the French recommendation) lies near 0°C(from +3°C to -8°C). The mixing temperature exceeds by approximately 20°C thatassociated with conventional bitumen mixes. The primary application of this type ofbinder relates to the EME high-modulus materials. The hardness of this type ofbitumen can induce brittleness at low temperature; it would thus be advised to usesuch mixes along with thermal protection when employed in harsher climates.Modified bitumenModified bitumen materials are bituminous binders whose properties have beenaltered by the introduction of a chemical agent that, added to the basic bitumen, actsto modify both the chemical structure and physical and mechanical properties. In allcases for such materials, precautions must be taken to avoid the risk of instability,creaming and sensitivity to thermal loading history.Section 1.4.2.2 provides a description of the main types of modified bitumen. Theshortfall in performance-based specifications on these materials necessitates thesystematic assurance that use of such a binder serves to obtain the desired mixperformance, hence the quality of modified bitumen and, consequently, the resultantmix properties are not solely dependent upon polymer content. Moreover, it shouldbe pointed out that for modified binders, the ring and ball temperature does not- 80 -
LPC Bituminous Mixtures Design Guide- Mix Design Procedure -constitute a relevant criterion when it comes to evaluating asphalt mix behavior athigh service temperatures.Modified binders are basically used in surface layers in both BBTM and BBDrmaterials. The ultimate application is what distinguishes the various modified binderfamilies for individual supplier-specific uses. Some products have been the topic ofTechnical Guidelines, published by the SETRA Highway Engineering Agency, whichsets forth use conditions and performance levels obtained on reference jobsites.Pigmentable bitumenThis category of bitumen and the resultant mixes show greater susceptibility totemperature than materials containing "normal" bitumen. Such components arereserved for more urban type applications or one-off uses intended to render laneindications more easily legible.Synthetic bindersSynthetic binders display a number of behavioral differences in comparison withconventional bitumen, namely:- their susceptibility to temperature may be very different from that of a similarlygradedstandardized bitumen; and- their mixing temperature must be indicated by the supplier; it may vary on theorder of 15°C with respect to that of a pure bitumen of the same consistency.Their range of application overlaps with that of pigmentable bitumen.Bituminous binders with mineral loadsThese ready-to-use binders are obtained from plant mixtures of pure bitumen andmineral loads, e.g. lime. Binder content differs from bitumen content, and theobjective herein tends to focus on "stiffening" the mix.Agrochemical bindersThese binders are made from vegetal matter without any petrochemical byproduct.The result is transparent and may be colored. Its applicability is currently beingassessed.3.1.3 AdditivesSection 1.4.3 provides a comprehensive description of the primary additives.3.1.3.1 Effect of type of additivePolyethyleneThis additive is intended to improve the level of rutting resistance and increase thestiffness modulus; it partially associates with the bitumen.The concentration level typically lies between 0,4% and 1%, with respect toaggregate quantity. It should be remarked that polyethylene at the melting point playsthe same role as bitumen. A standard concentration of polyethylene thus serves todecrease the binder concentration of the reference material by some 0,15%.- 81 -
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Table of ContentsPREFACE ..........
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