Roadways are vital to stimulating economic and social development. They are the backbone of our transportation infrastructure system that enables goods and services, essential workers and ourselves to get where we need to be. Therefore, our network of road infrastructure is considered the most important of all public assets. The portion of the road infrastructure most visible to the road-user is the “pavement” – the structure which separates vehicle tires from the underlying foundation material (naturally a sub-grade soil, but could be structural concrete or a steel bridge deck), provides traction and distributes stresses.

What are the types of pavement?

Pavements over soils consist of a multilayer construction with relatively weak materials below, and are traditionally classified into “flexible” or “rigid”. Flexible pavement consists of a bituminous (asphalt) surfacing, a base, and sub-base. Rigid pavement consists of concrete slab-surface and typically a sub-base. When an asphalt surface is placed over a rigid pavement, this is called a composite pavement. The pavement design provides the specification for the various layers that make up the pavement in terms of its thickness and constituent materials.

Approximately 95 per cent of Ontario’s roadways are comprised of asphalt concrete pavement roads and five per cent are concrete pavement. Other than roadway and highway applications, asphalt is also used on airport runways, parking structures, driveways, hydraulic structures, and other environmental applications due to its non-leaching capability.

There are two types of conventional concrete pavement – Jointed Plain Concrete Pavement (JPCP), and Continuously Reinforced Concrete Pavement (CRCP). These two types are used in roadways, bridges, airports and parking lots.

How is a road built?

Asphalt pavement designs are tied directly to traffic volume and vehicle weight, climatic environment and knowledge of soil conditions. The design, construction and maintenance over the service life (typically 15-20 years or more) must meet an acceptable ride quality and skid resistance per the roadway category. Under-designed pavements will deteriorate sooner than its properly-designed counterparts due to the inability to withstand excessive stresses. Additional factors to a pavement’s failure will include: moisture related damages from environmental actions (water entering cracks accelerates failure), and a general lack of preservative, preventive, or timely routine maintenance. It is expected that an adequately designed asphalt pavement should not experience any visible deterioration within its first 5-years in-service.

What causes potholes?

A typical challenge for many road owners with asphalt roadways are “potholes”. Potholes are unsafe to road users and can damage vehicles. Potholes often start out as faint microscopic cracks on the pavement surface. A pothole can develop from these tiny cracks if a pavement is not maintained for common distresses. Bad weather, poor drainage and heavy traffic further cause loosening and wearing of the pavement surface. While most pavement distresses are noticeable on the surface, root causes stem from the foundation structure. In such cases, prompt repairs can only delay the appearance of potholes but not prevent their occurrence. Only a combination of a solid structural pavement system and timely preservation activities can completely avoid the formation of potholes and development of other distress types.

Building roads that last.

To increase the durability of an asphalt pavement, the mix design and production of the asphalt must ensure that the end product can resist factors such as aging of the asphalt cement, disintegration of the aggregate and stripping of the asphalt film from the aggregates. These coupled with placement best practices during construction, rehabilitation and/or maintenance of the pavement structure ensures that the desired quality and material properties – such as impermeability, strength, stability, stiffness, flexibility, fatigue resistance, and workability – are maintained for long-term performance.

In Ontario, asphalt pavements and materials are designed, tested, inspected and placed in accordance with applicable versions of the Ontario Provisional Standards and Specifications (OPSS), and in conformance to individual municipal requirements. Stakeholders (owners, contractors, and any third party) are reminded and encouraged to regard roadway construction as a partnership, with each having clear understanding of their contract and professional responsibilities.

As part of its core mandate, the Ontario Asphalt Pavement Council (OAPC – Council of Ontario Road Builders’ Association (ORBA)) recognizes and fully supports the need to continually improve and enhance the quality and performance of asphalt pavements in Ontario, through several published ABC series, factsheets, informational brochures and bulletins, available on its website (www.onasphalt.org), including educational seminars and other training programs delivered throughout the year.

Dr. Doubra Ambaiowei, Ph.D., P.Eng., MCSCE, is a Professional Engineer in the Province of Ontario and Technical Director for the Ontario Road Builders’ Association and Ontario Asphalt Pavement Council (OAPC-council of ORBA).  He has developed extensive and practical experience in asphalt research and technical studies, and pavement engineering consulting services. His work specifically supports all technical requirements to promote the quality use of hot mix asphalt, and all other road building materials and construction best practices in general. He has co-authored several papers, and is involved with consultations, training and service delivery geared towards promoting the growth of Ontario’s transportation infrastructure industry. He can be reached at Doubra.Ambaiowei@orba.org