Timely maintenance using proven cost-effective methods can extend the life of a highway by many years as Patrick smith reports
Highways are expensive assets to construct, and the wear and tear of modern traffic means that regular maintenance will delay costly repairs or in extreme cases reconstruction.There are a number of methods of carrying out such maintenance, and these include the use of slurry seals and micro-surfacing, which are cold mixed asphalt which is a mixture of graded aggregate, asphalt emulsion, water and additives that is applied over existing pavement as one smooth layer. It offers a hard wearing surfacing for pavement preservation.
Italian company Socotherm Infraviab, part of the Socotherm Group, points to slurry seal a good solution, which it is said can extend the life of a pavement by seven years or more.
"Existing distresses in older pavements such as surface cracking, ravelling, loss of matrix, increased water and air permeability, and slipperiness due to flushing and aggregate polishing, can be corrected through a slurry application. Waterproofing is also achieved, preventing further deterioration. An all-weather, long-lasting surface is created that offers skid resistance and improved handling characteristics for drivers," says the company.
"With one simple application, the existing pavement receives a new wearing surface of uniform black colour and texture.
"By undertaking a programme of planned pavement maintenance, considerable savings in rehabilitation costs may be achieved. The pavement surface will remain sound, usable, and safe. Extensive downtime repairing deep cracks and potholes will be reduced or eliminated.
"The application of slurry seal will significantly extend the life of existing pavements by protecting the under surface from damage caused by water seepage. Improved surface performance is an added bonus.
"A pavement maintenance programme using slurry seal will not only help to protect the pavement, it will help to protect the paving investment." And the company points to a project where slurry seal was chosen.
Since January, 2003, Strada dei Parchi has been concessionaire for the Rome-L'Aquila-Teramo and Torano-Pescara motorways, and is part of the
Autostrade per l'Italia is a leading European concessionaire for toll motorway construction and management, and for related transport services, and its motorways cover 3,413.5km offering an effective transport system and services in, and between, urban areas.
The Strada dei Parchi highways takes in 281.4km (A24 A25 from Rome to L'Aquila and Pescara) and are some of the most interesting highways in Italy, linking Rome and the mountains (Appennini), crossing beautiful canyons and natural parks including the Gran Sasso Natural Parc.
This year, Strada dei Parchi extended its maintenance intervention in the field of slurry seal treatment in order to maintain the road and to keep the highway safer.
The ongoing work is managed by a joint venture between Socotherm Infraviab and Krause Italia, among the Italian leaders in this type of work with some 20 million m² laid in Italy and overseas.
Socotherm Infraviab's asphalt road maintenance offers advanced systems including hot in place recycling, cold slurry micro-surfacing, macro-roughening by shot peening, bridge decks waterproofing, expansion joints and sound barriers for roads and railways. Bologna, Italy-based Krause Italia operates in the slurry seal field and was established in 1999 by C.I.S.E. and Krause Technology.
"The constant research on aggregate mix composition and the experience in adaptation of the emulsion formula to weather conditions has allowed Krause Italia during past years to complete slurry seal treatments in difficult situations such as tunnels, night jobsites, and low temperatures," says Socotherm Infraviab.
The complete works for Strada dei Parchi will be approximately 300,000m², and the first part of this (15km of the A24 highway) covering 160,000m² was done in about nine days, with a very high daily production rate.
"It [slurry seal] is economical to install, highly cost-effective to use, and the new surface is ready for use just hours after application.
"Used over newly laid pavements, slurry seal will prevent surface distresses such as the effects of weathering from occurring. Oxidation, loss of oils, loss of matrix, and embrittlement of the mix are minimised. It also provides special durability and texture not available in the underlying mix."
Aesthetic appeal
According to
Slurry seals can be polymer modified for longer wear and better resistance to traffic and cracking: the modification includes latex rubber, crumb rubber and other polymers, and VSS Macropaver, together with its sister company International Surfacing, offers many binders including its mobile asphalt rubber blending system. Asphalt rubber is said to be a premier modified binder material that significantly improves fatigue crack resistance; low temperature cracking resistance; rut resistance; resistance to bleeding; aging resistance, and stone retention.
"Slurry is mixed in a travelling paver truck. The exact proportions, determined in a laboratory mix design, are mixed in a pugmill controlled by the advanced electronics and hydraulics of the VSS Macropaver, the machine we design and build ourselves. It is laid through a specially designed spreader box, and it is fast and efficient as well as cost effective," says VSS Macropaver (see also panel).
Innovative spray bars
An innovative concept is being offered by
The Italian company, which produces bitumen handling equipment, says the control on the new system can be made manually from the cab or the nozzles can be controlled automatically, depending on the speed of the truck to allow a more consistent finish quality. The spray bars generally operate at pressures of 0.8-1.5bars and the system will vary the pressure automatically, depending on the application and the material being sprayed. The prototype machine is being tested at present and will be made available later this year.
Because the truck chassis designs vary widely from one manufacturer to another, Massenza has to design the tank and spray system to suit the vehicle. As a result, the sprayer systems effectively have to be custom built: when an order is placed, Massenza asks the customer detailed questions about the truck model that will be used as well as the specifications of the machine. However Diego Massenza, assistant general manager said: "Sometimes it goes the other way and the customer asks us what truck is best." Because of this high degree of customisation, Massenza has tried to simplify the sprayer designs as much as possible using a modular layout. There are six basic emulsion sprayer designs and Massenza said: "We work on the basis that we have some standard components." The firm can build sprayers with single or twin tanks, with the latter offering storage for water and emulsion.
Meanwhile,
The M2 series consists of the M206, which can carry 4.5m3 of aggregate and 1,135litres of asphalt emulsion and water, and the M210 (7.7m3 of aggregate and 2,250litres of asphalt emulsion and water).
Both models feature a 200litre additive tank, and the pugmill, conveyor and all liquid material tanks are removable.
"Aggregate is delivered to the pugmill by a belt-over-chain conveyor that eliminates slippage, and the asphalt emulsion ratio is regulated as it is pumped by the gear pump into the pugmill, where it is mixed with the aggregate. The variable speed, dual-shaft, multi-paddle pugmill has a dual hydraulic drive, which provides even mixture and coating of the aggregate," says Bergkamp.
Micro-surfacing technology speeds Namibian project
The main road MR100 from the MR67 junction to Opuwo in the north-western part of Namibia is 56km long.
For the final wearing layer, RCC used a
The grading of the aggregate depends on the targeted surface quality and the condition of the primary road surface and its damages.
Micro-asphalt is mixed in the machine in a continuous working pugmill and applied directly by means of a spreader box linked to the mixing machine.
"It is highly important that the correct formulation of the mix is kept throughout the complete mixing time. On the other hand has to have the possibility to delicately change some of the mixing parameters in order to ensure the surface quality," says WEIRO.
The mix is introduced into the spreader box and, as the machine moves slowly forward, it is placed in a thin layer over the working width, usually a single traffic lane.
For this purpose, WEIRO provides spreader boxes with a fixed working width or a spreader box with continuously adjustable working width.
"The micro-surfacing machine operator plays a critical role in implementing a correct application of the slurry mix." Two men working with squeegees behind the machine repair all defects.
WEIRO basically provides two types of micro-surfacing machines: the manually operated SOM type and the MAP with computer-controlled surveying and monitoring of the formulation and mixing process.
Export award for VSS
Export Assistance Center recognised VSS Macropaver with an Export Achievement Certificate for recent accomplishments in the Global Marketplace, and this was presented by Congressmen George Radanovich to company vice president Doug Hogue at the Craigs School of Business at California State University, Fresno.
The award follows its success over the past year during which it has exported to over ten countries: China, Canada, Chile, the Philippines, Nicaragua, Ecuador, Russia, Zambia, Colombia and Mexico. Boasting a sales increase of 35% compared to 2007, over 50% of VSS Macropaver's sales are from exports.
