# Research on Performance of a Dense Graded Ultra-Thin Wearing Course Mixture
## 1 Introduction  
An ultra-thin paving technique, usually with 1.5 to 2.5 centimetres pavement thickness, namely Novachip, originated from France in the late 1970s [1]. It has several advantages like short construction time, good anti-skid performance and good water permeability [1; 2; 3; 4]. These distinctive features have been gradually gaining popularity, as ultra-thin wearing layers are being frequently applied in old highway maintenance as well as serving as wearing layers in new constructed highways [2; 3; 5; 6]. Apart from the excellent functional performance, the ultra-thin paving technique is also cost-effective, environmental-friendly and a sustainable construction method [7; 8; 9], which is attracting more and more attention from researchers. [PERSON] and [PERSON] [8] examined the road performance of two Novachip projects in Alabama, USA. After 4.5 years of service, both two Novachip projects showed no significant ravelling, concluding that the cohesion between the ultra-thin wearing layer and underlying asphalt layer is good. However, the ultra-thin wearing layer presents more surface friction than the hot mixture asphalt (HMA) wearing layer. In order to identify appropriate evaluation indexes for ultra-thin wearing layers, [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [5] conducted several experiments (thermal stress restrained sample tests,permeability tests, skid resistance tests, and indoor abrasion tests) on asphalt mixture with three different surface layers--stone mastic asphalt mixture with a nominal maximum aggregate size of 10 mm (SMA10), ultra-thin asphalt concrete with a nominal maximum aggregate size of 10 mm (UTAC10) and Novachip Type C. The result shows that frozen broken temperature and frozen broken strength could be regarded as appropriate evaluation indexes for low temperature performance of ultra-thin surface layers. Moreover, sliding attenuation degree and initial British Pendulum Number (BPN) value are proposed to measure the anti-skid performance of the ultra-thin surface layer. Furthermore, the author indicates that the freeze-thaw splitting strength ratio and freeze-thaw splitting strength should be combined to evaluate resistance of water damage performance. [PERSON] et al. [10] studied the anti-skid performance, permeability and texture depth of three different asphalt mixtures--dense-graded asphalt mixture with a nominal maximum aggregate size of 13.2 mm (AC13), open graded friction course with a nominal maximum aggregate size of 13.2 mm (OGFC13) and semi-open gradation Novachip Type C. Results show that Novachip Type C as an ultra-thin wearing layer has better overall performance in terms of skid resistance, permeability and texture depth. Furthermore, Novachip Type C was proven to have better shear capability than other types of asphalt mixture, under the same tack coat material and dosage. Moreover, [PERSON], et al. [11] investigated the moisture stability, high temperature stability and low temperature cracking resistance of the same three types of asphalt mixture (AC-13, OGFC-13 and semi-open gradation Novachip Type C). The result shows that Novachip Type C has better high temperature stability than the other two types of asphalt mixture. However, the low temperature cracking resistance and moisture stability performance of Novachip Type C is worse than the AC-13 asphalt mixture but better than the OGFC-13 asphalt mixture. [PERSON], [PERSON] and [PERSON] [4] argue that the current design specification in China [12] does not take temperature into consideration and the interlayer contact is presumed as completely continuous. The actual environmental condition subjected to pavement structure is not sufficiently considered in the specification. Thus, the author conducted an experiment to investigate the shear stress between the ultra-thin wearing layer and the underlying asphalt layer under different temperatures and interlayer contact situations.