An Introduction to the science and art of road building
by Theuns Eloff
(Leading Equipment, October 2009)

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INTRODUCTION
Roads came into existence to answer to the needs of transportation, but like all other innovations and developments, this seemingly simple invention catapulted military performance, political, social and economical developments to where it is today, and continues to be the yardstick of how far a country/area has developed. In a nutshell, the cornerstones of a prosperous society are well-maintained roads and infrastructure.

Where roads are built, economic and social improvements follow. This growth will in turn cause the roads to require upgrades and redesigns, feeding the continuous cycle for economic growth.

Depending on the volume and types of traffic, roads have different design criteria to be able to withstand/carry these loads. Over the past 100 years, transportation has changed immensely, with traffic increasing, heavier and bigger trucks and faster cars. So, the road surface and pavement layers and safety structures also need to change continuously to keep up with and carry these loads.

Where roads used to be a basic flat stretch, covered in cobblestones or planks in the Roman era, today we build roads with many layers and specific materials, for each layer, compacted to standard specifications and densities according to the design criteria for every required road.

THE PROCESS
The road building process starts with clearing the area of all unwanted material by hand, or using backhoe loaders (BHLs), graders, skid-steer loaders and dozers. If a road goes through a very uneven area, certain parts need to be 'cut' away from the landscape, and other areas need to be 'filled up', to rise to the elevation of the future travelled way. While these cut-to-fill operations are performed, the material that is removed is checked to see if it can be used at a later stage or in a fill.

Often the ground material of an area does not have the required characteristics to be used in the layer works, and the correct materials need to be imported from quarries or borrow pits to meet the required specifications. The civil engineer and contractor need to have a thorough understanding of material mechanics and specifications in order to build a strong and durable road.

As the layers are placed according to standard specifications, the material is tipped, levelled using graders according to predetermined levels under the watchful eyes of surveyors, and compacted. These operations are done with dozers, BHLs, dumpers and tippers running back and forth like huge working ants.

Water is essential for achieving the correct density and is added with a water cart before, during and after compaction. The main piece of plant used for compaction - the roller comes into play in this phase and is available in many different types and sizes, from vibrator to oscillating rollers. Obtaining optimum density is one of the most important elements of a good, strong road, with the lower layers weaker and increasing in quality and density as you advance to the top.

MAINTAINING STANDARDS
Lately, in South Africa, we find ourselves where standards cannot quite keep up with technological developments. Layers are still placed and compacted in 100-200 mm thickness, while the latest rollers can easily compact up to 600-1 000 mm at once. These rollers also reduce the compaction effort immensely and reduce the amount of moisture that would otherwise be required to place materials at its optimum moisture content. However, this is not always taken into consideration and compacting on 'old' standards and methods is still performed on site.

The Average Joe understands road building as the final surface layer being placed and painted, ready for traffic; and is not at all aware of the immaculate planning, multiple variables and preparation that goes into the development in order to get to the final product. Safety specifications on site; traffic regulations during construction; continuous testing of standards; availability of materials and water; local labour, political and community issues; weather influences; water drainage; plant availability; environmental impact and budget constraints are just a few.

This makes an experienced road builder a very valuable and scarce commodity to any civil construction company, to be able to function effectively and 'maintain sanity' in a continuously demanding and highly, stressful environment.

Getting to the placing of a final surface layer is only a small part of the whole process. Roads must be strong enough to handle a specific load; smooth enough to create a comfortable ride and; coarse enough to create enough friction for control of stopping and moving traffic. The final layer/wearing course which is exposed to traffic, can consist of different materials, ranging from ordinary gravel roads, to premix layers, single seal, double seal, to concrete.

The material is often determined by the traffic it will need to carry as well as the costs involved. Concrete surfaces, for example, are much more costly, but will also last much longer and need much less maintenance in the future. Specialised equipment, such as asphalt pavers, chip spreaders and concrete pavers are used in placing these surface layers and requires a lot of experience in order to achieve the correct outcome. The material is then compacted using PTRs, tandem rollers or three wheel rollers.

RECYCLING
With resources becoming scarce and more difficult to come by, due to environmental factors, modern equipment used for the recycling of materials is becoming increasingly in demand and popular. Recyclers/deep millers for instance can mill up, add water and bitumen (emulsion or cement), mix and place the product in situ at a much lower cost and much faster than rebuilding it from new raw material. The versatility of the recycler is what makes it such a sought after piece of plant. It is not just successful with the recycling of old road layers; it is also very effective with the construction of certain new pavement layers. Stabilising of sub-base layers is performed very productively with the use of a deep miller.

The inventions of planers and mobile crushers have considerably changed the way roads are built and maintained today. Material taken from existing road layers or widened cuttings can now be successfully utilised in pavement layers after crushing and proper blending. Mobile crushers are seen more and more on site, assisting with the breaking down of coarse materials such as rocks and concrete slabs, alleviating the problem of material shortage.

GETTING ATTACHED
Plant has also become more versatile with the additional developments of all kinds of attachments and many of them can be used for a variety of functions depending on the attachment used. A BHL or excavator, for example, can be equipped with a hydraulic pecker, auger, or broom. This machine is therefore much more in demand and readily available than a more specialised machine with only a single function, such as a PTR, would be.

GOING COMPACT
Another innovation that has improved road building recently was the arrival of several items of compact or 'mini' plant. Miniature versions of excavators, BHLs and loaders including miniature attachments, has made working in small and restricted areas much easier and faster. With the widening of a road, for example, the area might be too narrow to do layer works using conventional machines and manual labour may take too long. Enter mini plant and the job is done!

GETTING A LIFT
Yet another development - mobile cranes are also seen around a lot more these days. These cranes are a lot stronger and more stable than in the past and are considered a valuable asset to construction companies, making the placement of precast concrete structures and other materials at specific sites seem effortless and more feasible.

CONCLUSION
These exciting times, in terms of the development of new machines and technologies, stand in deep contrast to the present unemployment situation in our country. While more jobs need to be created and consequently more work needs to be done by hand versus machines, this leads to longer construction periods, lowering of standards and lower productivity with higher labour costs.

However, in some cases, labour intensive methods might be more viable, for example, when it may be too costly or impractical to get machines to far away/smaller places. A delicate balance needs to be found between the 'developing' social circumstances and the 'developed' available technology in order to move forward to the maximum benefit of all role-players, while simultaneously keeping up with the rest of the world.

ABOUT THE AUTHOR
Theuns Eloff has a BSc. Eng and a CElTS Diploma in soil stabilisation, coupled with 11 years experience working in the construction sector and two years as an independent construction consultant and training provider. His experience and expertise is diverse across the realms of road building and infrastructural development and he regularly provides seminars and training courses on this subject matter.

Download PDF article here (1.8 MB)