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Some countries require special finishing techniques for SMA surfaces. Those requirements are described here. 10.7.1 G ritting Applying a layer of grit to the finished surface is often specified. Why has gritting been applied? Soon after placement, the SMA layer is characterized by relatively low friction (the so-called postconstruction slipperiness) caused by a thick film […]

In some countries, particularly where surface properties are high priorities for a wearing course, in addition to other parameters, requirements for macrotexture are also laid down. The British requirements (HA MCHW, 2008) for mixtures with an upper (D) aggregate size of 14 mm or less, stipulate a minimum 1.3-mm macrotex­ture depth[64] (measured using the volumetric […]

Calculating the quotient of the bulk and maximum (the so-called theoretical maxi­mum density [TMD] or the Rice density after ASTM 2041) densities is a popular method of determining the compaction factor. The requirement for compaction of an SMA layer is a minimum 94% (of the maximum density) according to the NAPA SMA Guidelines QIS 122; […]

Almost all documents on SMA reviewed for the purposes of this book contain the compaction factor as a specified requirement. As in many other cases, the differ­ences between European and U. S. specifications are clear. That factor has been defined differently in different countries. The differences are grounded in the different reference density used related […]

A series of acceptance tests are carried out after finishing the placement of a mix­ture. They usually comprise measuring the content of air voids and the compaction factor, conducted on specimens of cores taken from the finished pavement. In many countries, nuclear density gauges are used for testing the homogeneity of compac­tion. When this is […]

The layer edge should be rolled with a machine fitted with a side-roll; this will enable suitable compaction of the area close to the edge. The drums of a roller should be moistened with water, which should protect them against mastic adhesion and drag­ging particles out. 10.5 pLAcEMENT of sMA IN KOMPAKTASPHALT TEcHNIQuE The Kompaktasphalt […]

The time available for compacting the layer depends mainly on the following condi­tions during placement: • The mixture temperature behind the paver • The air and surface temperatures and wind velocity • The layer thickness The matters of temperature are elaborated on in Section 10.3.2. In extremely adverse weather conditions, the time for compacting is […]

Usually six to nine roller passes are enough to compact an SMA mixture. Moreover, compaction should not cause squeezing of the mastic onto the surface. The number of passes with vibrations should be limited to the indispensable minimum (most frequently, three). On many construction sites or at the start of a new SMA mixture, it […]

The speed of the rollers should be controlled and should be slow. According to the NAPA SMA handbook QIS 122, the speed of a roller during rolling must not exceed 5 km/h. In one of the British guidelines, the speed of the rollers should normally be between 4 and 6 km/h (SEHAUC, 2009). Rolling with […]

Various compaction sequences are adhered to. Generally speaking, every road-en­gineering company works out its own procedure after some time. By and large, the standard rule states that the paver is followed by static rollers first and then by vibra­tory rollers. Final passes are always carried out by static rollers, which finally level the surface, removing […]