Hello, I'm Yves Brosseaud from IFSTTAR. I am a senior researcher of MIT Laboratory, materials for Transport infrastructures, in charge of research and application activities for pavement material testing, design and modelling. The objective of this video is to present surface treatments to improve the performances and durability of roads. This video describes the principles, the main structures and composition, the advantages and disadvantages, and also the limits and the field of uses of these techniques. With traffic, weather conditions, and aging effects, road surfaces show signs of stress: stripping, bleeding, cracking, and also wear of aggregates which reduces skid resistance. Maintenance of the wearing course is necessary to keep the two main functions of this layer, to protect the road base (by imperviousness of the road structure) and to ensure good surface characteristics (evenness, skid resistance, evacuation of water) for better safety conditions for users. When there is no structural trouble, or for low traffic roads with no significant deformations, the application of a simple surface treatments is sufficient. There are two main processes: surface dressing and microsurfacing. Surface dressing: the simplest wearing course is one layer of bitumen plus one layer of gravel, (no sand), The requirements are found in NF EN 12271. Micro surfacing, the laying of cold asphalt mix, ( D maximum size up to 4 millimeters) at low spreading rate, (about 15 to 20 kilograms per meter), without compaction in many cases, the requirements are found in NF EN 12273. Note, the generic term used for "cold-cast bituminous materials" is the slurry seal, but in France this designates the fine aggregates Dmaximum size four millimeters, not used for wearing course due to poor skid resistance. These surface pavements are prepared and applied directly at the work site with specific equipment, binder sprayer, chipping spreader, (self-propelled,or put on a truck), bi-spreader, micro surfacing machine. The thickness is very small, only one centimeter, so there is no additional work. The binder is a bituminous emulsion, potentially with polymer modified bitumen when the stresses increase or for better durability. For surface dressing, fluxed bitumen is also used sometimes with polymers added. The proportions of the hot bitumen and emulsion are fifty-fifty, with about 15% with modification. In France, the use of cutback has been forbidden for many years due to safety and environmental concerns. The choice of components is essential. Tests in laboratory are applied to assess the performances of micro surfacing and to define the mix composition. ( European method adapted from ISSA procedures), and to determine the adhesion quality between the aggregates and the binder for surface dressing (with vialit test, and passive adhesion). Different structures can be used according to the main topic: Surface dressing: Mono layer, simple gravelling, the most common aggregate range is 6 to 10, or 10 to 14 millimeter maximum size. Mono layer double gravelling, the most common is 10 to 14 and 4 to 6 millimeters. Bi-layer, it is twice mono layer single gravelling, the most common is 10 to 14 + 6 to 10 millimeters. Pre-graveled, thickener. Micro surfacing: mono layer, generally 0 to 6 millimeters, sometimes 0 to 8 or 0 to 10 millimeters. Double layer, one layer to improve the profile with slurry seal, 0 to 4, plus second layer, 0 to 6. The advantages are: low-cost maintenance (especially for surface dressing). Low thickness for wearing course, so low consumption of raw materials, Quick to apply, so low inconvenience to traffic (Order of magnitude for the the daily output 25,000 and 8,000 square meters for surface dressing and micro surfacing), Rapid reopening to traffic, Excellent macrotexture and skid resistance by using aggregates with high polishing resistance, Very good seal efficiency, especially for bi-layer surface dressing. The disadvantages are : insufficient resistance under shear stresses, like small radius turning, turnabout, Sensitive to poor quality of the support, cracking, debonding, bleeding,... These deteriorations appear rapidly if the preparation of the support is not sufficient, or if the structure is not well adapted. And exclusively for surface dressing: - stripping at an early age, (first week in service), due to the process of chipping, Very high rolling pavement noise, resulting from high roughness. The limits of these techniques are: - the quality of the support, which must be: sufficiently homogeneous, good profile, without rutting or deformation: less than one or two centimeters for micro surfacing and two or three centimeters for surface dressing. Low deformability, the deflection must be under a range of 50 to 150 hundredths of a millimeter, depending of the class of traffic, for the macro-surfacing, There is no limitation for surface dressing, The intensity of traffic, less than 750 trucks (load up to 3.5 tons)
per day per lane. The weather conditions, (temperature up to 10°C, dry support) and the period of laying (before winter) must be respected for curing, Surface dressings are generally too noisy in dense, urban areas. Micro surfacing is commonly applied in city areas because it offer a good compromise for all of the surface characteristics. (For instance, the annual surface laid in France is approximately 30 million square meters). Surface dressing is the most common technique for wearing courses especially for the economical maintenance of rural roads for moderate traffic. It accounts for than more 150 million square meters. A new technique has appeared on national roads, the CAPESEAL which combines ESU (surface dressing) plus ECF ( cold micro asphalt
concrete surfacing). It increases the efficiency to reflective cracking and maintains the advantages of these two techniques, without the disadvantages of surface dressing. Thank you for your attention...
