Pobierz pełny numer 1/2010 S&E - Structure and Environment - Kielce

Marek Iwański, Grzegorz MazurekThe tests of static creep were done to verify thetest results from Marshall method. The static creepmodulus is determined at the temperature of 40 o Cunder loading of 0,1 MPa for 2, 3, 5, 10, 15, 20,30, 40, 50, 60 min with the 0.0001 mm/mm readingresolution of the deformation. From the results thefollowing parameters are determined:– deformation ε from the formulae:ε max= Δh / h [mm/mm] (1)where: Δh = the difference between the initial heightand the height after the loading period, and h = theinitial height:– the static creep modulus from the formulae(measurement error up to 0.1 MPa)M s=δ s/ ε max(2)where: δ s= compressive stress, which equalls 0.1MPa; and ε max= deformation after 1 h of loading.Changes of static creep of asphalt concrete afteraging (with regard to the kind of bitumen andaggregate) are similar to the results of Marshallstability after aging. However, the dynamics of thechanges of the static creep of asphalt concrete withthe low – viscosity bitumen is lower than in the casewhen the stability change of asphalt concrete afteraging was tested. During the STOA and LTOA agingthe static creep of asphalt concrete with the Olexobit30 NV bitumen was at most 10% lower (when thequarzite aggregate was used) than the static creep ofasphalt concrete with the 35/50 bitumen.The intensity of changes of the static creep ofasphalt concrete with both the low – viscosity andtraditional bitumen during the STOA and LTOAaging (STOA/LTOA) is similar. It implies that therate of change of static creep modulus of asphaltconcrete does not depend on the kind of bitumen.From the analyses of test results after aging wemay state that the aggregate used in its productionhas a significant impact on its mechanical properties.Quarzite aggregate is least suited, especially whenthe traditional 35/50 bitumen is applied. In this casethe stability and static creep change is highest ascompared to diabase and garbo aggregate.To assess resistance to water and frost the testswere performed to determine:- indirect tensile strength before and after curingcycles, simulating weathering on roads accordingto the American procedures – the AASHTO T283method. Its detailed description can be found in [2].Indirect tensile strength after curing, simulatingthe impact of temperatures below 0 o C, according tothe PANK 4302 standard is described in [2] and [5].An assessment of aging on water and frost resistancewas also made. The tests were focused only on thethe short – term aging due to its significant influenceon mechanical properties. The results are presentedin Table 4.Table 4. The impact of aging on water and frost resistanceof asphalt concreteNo.1.Property ofasphalt concreteIndirect tensilestrength at -2ºCaccording toPANK 4302 [MPa]Thekind ofagingThe kind of asphalt concreteBA-D BA-G BA-KZ O Z O Z ONS 4.0 3.9 3.7 3.2 4.1 3.9STOA 4.5 4.3 4.0 3.5 4.5 4.2LTOA 4.6 4.5 4.2 3.7 4.7 4.42. Indirect tensile strength ratio at 20ºC according to AASHTO T283 [%]After curing in NS 76.1 79.9 78.0 81.9 77.4 79.2W WMLTOA 70.5 75.4 71.5 76.4 67.9 75.22a. water and frost STOA 74.1 76.2 74.9 78.6 73.8 76.1There is a significant impact of the aging on waterresistance and combined water and frost resistance aswell as resistance to low – temperature cracking. Theaging has the worst effect in case of asphalt concretewith quarzite aggregate. In this case the binder wasthe 35/50 bitumen with the adhesive agent. Indirecttensile strength after aging (according to PANK4302) at 2 o C was 4.7 MPa (i.e. close to the criticalvalue of 4.8 MPa). Aging, especially short – termaging, did not cause excessive stiffening in the caseof asphalt concrete with the low – viscosity bitumen.Consequently, if the road surface is made from asphaltconcrete with quarzite aggregate it can experience low– temperature cracking during winter. However, this ismuch more likely to happen for asphalt concrete withthe traditional bitumen. The aging process has alsoan unfavourable impact on water and frost resistanceaccording to AASHTO T283 methododology. Theindirect tensile strength ratios after aging of asphaltconcrete produced from quarzite, diabase and gabbroaggregate with the 35/50 bitumen were below 75%.That is the limiting value of proper water and frostresistance. In the case of asphalt concrete producedfrom quarzite aggregate and the 35/50 bitumen, itlost its resistance in low temperatures as a result ofaging (the ratio was below the critical value of 70%).The indirect tensile strength ratios after aging processaccording to AASHTO and indirect tensile strengthaccording to PANK are presented in Figure 5.28