Abstract
Stone matrix asphalt (SMA) is a gap-graded bituminous mixture which can be used in surface layer of high volume pavements. The mixture has higher concentrations of coarse aggregates, providing strength and rut resistance to the mixture, and higher asphalt content giving durability. There must be a proper stone-to-stone contact between the coarse aggregates of SMA, and hence aggregate gradation is an important factor in this mixture. In the current study, two aggregate gradations, with nominal maximum aggregate sizes (NMAS) 16 and 13 mm were adopted to prepare SMA mixtures and their laboratory performances were compared. Polymer-modified bitumen (PMB) was used as the binder material and no stabilising additive was used, since drain down was within permissible limits for both mixtures with PMB. Conventional cylindrical specimens were prepared in superpave gyratory compactor with bitumen contents 5.0 %, 5.5 %, 6.0 %, 6.5 % and 7.0 % by weight of aggregates, and volumetric and Marshall properties were determined. Tensile strength, behaviour to repeated loading etc. were checked for cylindrical specimens prepared at optimum bitumen content, whereas specially prepared slab specimens were used to check the rutting resistance of SMA mixtures. From the laboratory study, it was observed that, out of the two SMA mixtures, the one with NMAS 16 mm performed better compared to the other. These improved properties may be attributed towards the larger coarse aggregate sizes in the mixture.
Highlights
Stone matrix asphalt (SMA) is a gap-graded HMA developed in Germany in the 1960’s, to resist the wear and tear on pavements caused by studded tyres
For all tests other than rutting test, minimum three specimens were prepared for each SMA mixture and the average of the three values was considered, whereas two SMA slabs were prepared for each mixture to evaluate rutting
The main difference between these gradations were in the nominal maximum aggregate sizes (NMAS) and in the coarse aggregate sizes, but other important factors of gradation affecting the mixture performance were kept as uniform
Summary
Stone matrix asphalt (SMA) is a gap-graded HMA developed in Germany in the 1960’s, to resist the wear and tear on pavements caused by studded tyres. Some transportation agencies from USA conducted a study tour to Europe in 1990 and they were impressed with the performance of SMA [2]. Stone matrix asphalt has higher proportion of coarse aggregates and binder mortar compared to conventional mixtures. The rich binder mortar consisting of fine aggregates, bituminous binder, mineral filler and generally a stabilising additive provides durability to the mixture due to higher binder and filler content. Laboratory performance of stone matrix asphalt mixtures with two aggregate gradations in gap-graded mixtures with higher bitumen and filler content like SMA, where a portion of bitumen and fines may be separated and flow down from the mixture during the elevated temperatures of production, transport, laying and compaction
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