Bryan Perrie, Managing Director-The Concrete Institute in South Africa and former ISCP Vice-President and Board Director explains that concrete roads suffer from an image problem because many very old concrete pavements still in existence were designed long ago to very different design criteria than modern concrete pavements. Decades ago, concrete roads were constructed using what are now regarded as obsolete equipment and techniques that have negatively affected ride comfort. “Although safety has always been a major concern, ride and acoustic comfort were barely considered 40 years ago. Modernized designs, new construction methods, better surface finishing, and high-tech machines mean that nowadays, it is perfectly possible to realize high-quality concrete pavement surfaces that do indeed satisfy the needs and objectives of road users, communities who live near the pavements, as well as road managers.”
Characterized by longitudinal evenness and mega-texture as well as rut formation, surface evenness significantly impacts the ride comfort of vehicle passengers. “Early concrete pavements were perceived as being uncomfortable to ride on because of the widths of the joints, faulting at the joints due to a lack or loss of load transfer, or localized damage to supporting layers that contained material susceptible to erosion. But, since the early 1970s, ride problems have been significantly reduced due to modified concrete pavement design.”
Perrie says these solutions included: Shorter slabs of concrete (minimum 4m long) that make the pavement less prone to cracking; Narrow contraction joints that limit the joint nuisance to a minimum; and Dowels in the transverse joints and cement-bound bases that ensure excellent load transfer and no longer allow any level differences at the joints. “Continuously reinforced concrete (CRC) is often chosen for motorways and primary roads as this form of construction does not feature transverse joints. The shrinkage of the concrete is absorbed by a pattern of narrow, closely spaced cracks that have no impact whatsoever on the pavement’s evenness or ride comfort.”
Smooth concrete roads can now be built thanks to:
- Optimized concrete mixes with constant workability—prepared in modern computer-controlled mixing plants often set up on the site
- New generations of slipform pavers equipped with automatic vibrator control systems
- Properly installed guide wires for controlling the machine or wireless systems that make use of total stations
- Use of longitudinal leveling beams behind the finishing machine (“super-smoothers”)
- New types of evenness measurement set up immediately behind the paver, thus allowing the correction of the construction process
“Apart from countries where studded tires are allowed, concrete pavements are immune to rut formation. An important property of concrete pavements is that the longitudinal and transverse evenness obtained after construction is retained for many years,” Perrie adds.
When it comes to safety threats such as skidding, aquaplaning and visibility, accidents can be prevented in both dry and wet weather by providing a good surface texture with sufficient surface friction. Concrete pavements’ capacity to counter skidding have been improved in recent years through fine exposed aggregate surfaces that show no significant decrease in skid resistance over time.
“The texture of the pavement, combined with the transverse profile, has a major influence on the potential danger of aquaplaning which happens when vehicle tires lose all contact with the pavement surface. As concrete surfaces do not form ruts, the likelihood of this is virtually non-existent if the transverse profile is given the correct super-elevation.
Transverse textures or exposed aggregate surfaces with sufficient texture depth will also substantially limit splash and spray coming from behind vehicles. The color and texture of concrete pavements can also be varied to warn motorists of impending hazardous situations.”
Concrete pavements’ traffic noise can be controlled through various means that include:
- The use of barrier walls that are particularly effective on pavements with heavy truck traffic
- Building the roads an adequate distance away from people living in the vicinity
- Controlling the noise at source- at the pavement surface
“In recent years, numerous noise-abating wearing courses have been developed and research and testing are still ongoing in many countries,” Perrie adds.
To read the full Creamer Media’s Engineering News online article, please go to: http://www.engineeringnews.co.za/article/modern-concrete-roads-now-offer-ride-comfort-and-safety-2018-06-04/rep_id:4136
For the PDF of the press release from Jan de Beer, please go to:
http://us-cdn.creamermedia.co.za/assets/articles/attachments/74666_safety.pdf
For more information, please contact:
Bryan Perrie | T: 011 315 0300 | W: www.theconcreteinstitute.org.za