The concepts of "Sustainability" and "Sustainable development" are of much importance and receiving much attention from all walks of life as the causes of global warming and climate changes are debated world over. Concrete White topping Technology is sustainable because of its long life (over 30 years). Concrete overlay is in thinner section, hence consumes minimal raw materials, easy to construct. It requires minimum maintenance and rehabilitation over its lifetime. G Sreenivasa, General Manager – Business Development, UltraTech Cement, makes his case.What is White Topping and Why?

White topping is the covering of an existing asphalt pavement with a layer of Portland cement concreteUsing concrete overlays (against asphalt overlays) provide desirable life, performance against heavy loading & rain, offers safety, friction and skid resistance properties. In addition, concrete overlay offers cost effective and environmental benefits:

• Non- rutting, ing surface that doesn’t trap water
• Excellent surface drainage
• Better light reflectance
• Fewer repairs,- Fewer work-zone accidents over life of overlays
• Comparable initial cost to asphalt
• Lower ownership cost to asphalt (life cycle cost)
• Cement is available locally where as bitumen has to be imported
• Price of cement is consistent and predictable where as bitumen price is highly volatile.
• Cement is available in plenty where as bitumen is scarce material in future.

The many advantages elaborated LongevityThe longevity of concrete roads & concrete overlays (or white topping) is well demonstrated and documented. In this context, the concrete paved Marine Drive in Mumbai is an outstanding example. The concrete pavement was done as far back as in 1939 and the road even now, 71 years later, is still giving satisfactory performance.Life cycle cost of concrete pavement against asphalt pavement

• An asphalt road requires maintenance every 2 to 4 years and resurfacing every 8 to 10 years
• The concrete road requires relatively very little maintenance. Depending upon usage, it may require some minor repairs to joints and surface texture, but won’t need to be resurfaced for 30, 40 or even 50 years.
• Hence, the maintenance cost of concrete overlays is 1/8th to 1/10th of asphalt overlays results in smooth traffic flow over longer period.

Long life concrete overlays have demonstrated economic advantages in terms of life cycle costs (see picture). In addition, they contribute directly to the system’s sustainability in several important ways.Fuel saving (During its Lifecycle time)Properly designed, constructed, grooved, textured concrete overlays have much lesser pavement deflection, which results in reduced vehicle fuel consumption (see picture below). Fuel Consumption on Asphalt and Concrete Pavement (By CRRI & Dr Kadiyali associates) – After construction;The above table shows how the savings progressively increased as the vehicle weight increases. This is a very significant finding for Indian conditions where overloading is common. Hence concrete overlays are not only more capable of resisting heavy loads but also achieve fuel savings.Emission Reduction due to White topping;Assuming, a 10MT truck/bus travel 24000kms in urban areas per annum and (assume fuel consumption as 2.5kms/ltr) Fuel savings of 9.8 per cent (30.24cc/km) achieved on concrete overlay, Thus, total fuel saved in a year will be 800 litres or Rs 33600 per vehicle(Rs 42/ltr), Approx 2MT of CO2 will be reduced per trip.Energy saving due to White Toppinga) The cost of lighting streets in urban areas2Lighting fixtures are important elements of most urban streets. Enhanced night time visibility is related to improved traffic safety. A report comparing environmental impacts of concrete & asphalt overlays indicates that asphalt overlays require more lights per unit length to achieve the same illumination (Gajda and VanGeem 1997).To overcome the lack of light reflectance, during nights, an asphalt overlay requires either1) More street lights per mile than a concrete overlay, or 2) Higher watt light bulbs at the same light pole spacing as used on Concrete overlay.In either case, more energy is consumed to illuminate the asphalt roads. Where more poles are installed, initial costs are more.Visibility during nights – in cityConcrete’s superior reflectance improves night visibility, saves money on street lighting and reduces power consumption.Surface reflectance readings on concrete overlays are 4-5 times higher than asphalt overlays, which means drivers can see the road, other vehicles and pedestrians clearer and sooner, thus helps in reducing accidentsSafety: How Quickly Can You Stop?From a study, it has been noticed that breaking distance for concrete overlays are less compared to asphalt overlay, hence concrete overlays are safe on both dry and wet surface condition. The breaking distance even increases with rutted asphalt surface. This clearly shows that the concrete overlays are more sustainable in reducing the wear and tear of tyres, brake drum, and reduces the consumption of brake oil.Heat Island Effect – Concrete v/s Asphalt overlayIn Urban areas, the Heat Island Effect can contribute significantly to energy consumption for air conditioning to cool the urban building. This also costs money, in-turn leads to emissions at power generation units. One estimate that the increase in temperature due to Heat island effect accounts for 5-10 per cent of peak urban electric demand for air conditioningLower Energy Footprint

Embodied primary energy is a measure of all energy use associated with the production, delivery and maintenance of a facility over predetermined time period. It includes both feedback energy and primary energy.The study here shows that asphalt surface require 2 to 5 times more energy than equivalent concrete surface. Fig shows illustrates, the embodied primary energy associated with concrete pavement is only about 33 per cent of the embodied primary energy of asphalt pavements.Graph shows comparison of embodied primary energy for asphalt and concrete pavementsRecyclability /reusability and Natural resourcesConcrete pavement is a 100 per cent recyclable material and at its ultimate end of fatigue, concrete pavement can be crushed and reused as granular fill, sub base/ base material for new pavement. This leads to reduced demand on non-renewable natural resources. Based on the analysis, on equivalent pavement designs for asphalt and concrete pavements for an arterial road on a low- strength sub grade, approximately twice as much granular material is needed for an asphalt pavement structure than for concrete pavement.ConclusionsConcrete overlays / pavements are sustainable, economical, long- lasting and truly green roads in more than many ways against asphalt overlays;

• Technical reasons clearly show that concrete overlays are long lasting (over 30 years), require little or no repair or replacement as is in case of asphalt overlays
• Concrete overlays cost little maintenance or 1/8th to 1/10th of asphalt overlays and thus no frequent repair of road results in traffic jam and fuel emissions
• Saving in fuel consumption up to 20 per cent has been noticed. However, in urban areas the saving will be about 10 per cent for (10MT) buses and trucks. This results reduction in CO2, NO2 and SO2 emission over life cycle period of 30 years
• Use of fly ash, GGBS and silica fume, improves the performance of concrete, saves money, reduces the need for disposal in landfills greatly, reduces energy use and generation of green house gases
• Concrete overlays are light coloured and lead to improved visibility, reduced lighting requirement and reduce accidents in cities
• Cool surface of concrete overlay reduces heat island effects in cities
• Concrete overlay’s overall energy footprint means tremendous savings in energy over the lifecycle of concrete overlay
• Concrete overlays renewability and 100 per cent recyclability lead to reduced demand on non renewable resources and save the quantity of sub base materials