7 Technical Advantages of Precast Concrete Smart Pavement Over Ashphalt Roads

The 7 Advantages of Precast Concrete Smart Pavements Over Ashphalt Roads are listed below. But before we delve into the topic of removable precast concrete roadworks, let us see what makes precast concrete pavement much supirior to conventional ashphalt pavement in roadworks:

Economic Advantages:

• Higher Durability: Concrete roads can be designed for 50 years or more, and they last around three to five times longer than asphalt roads before a first major rehabilitation is required.The superior durability of concrete over asphalt ensures minimum and predictable maintenance costs. USA and Germany are the front runners in using concrete pavements over ashphalt pavements.
• Less Maintenance: While asphalt requires regular maintenance and frequent reconstruction, concrete will last for decades with relatively minor repair. Every time you need to repair a pavement you need to close at least one lane, causing traffic congestion, lost time, and an additional danger of accidents.
• Competetive Initial Cost: Increased experience with concrete pavements and modern design methods have brought down the initial cost of concrete to levels comparable to asphalt. New constructive solutions such as removable precast pavements, roller compacted concrete, short slabs or soil cement offer additional reduction potential over conventional concrete.
• Lower Operational Cost: Heavy-duty applications such as roads in industrial plants and logistics yards with their high loads and moderate requirements for surface finish can be very cost-efficiently paved with precast concrete pavement, and roller compacted concrete.The bigger and more challenging the project, the higher the advantage of concrete pavements in initial cost.
• Predictable Inflation adjusted Price: The price of asphalt is closely tied to that of international oil prices - it is volatile and rises faster than the overall inflation rate. Concrete, on the other hand, follows local dynamics. Recent MIT study confirms the significant risks related to the volatility and increases in asphalt prices due to dependency on oil price.
• Lower Life Cycle Cost for Project: In the full life cycle of the project, concrete has significantly lower cost versus asphalt despite its slightly higher initial cost.

Environmental Advantages 

• Reduced Urban Heat Island Effect: Cities are warmer than their surroundings, which in summer leads to discomfort, medical conditions, and higher air conditioning use. Light-colored surfaces such as concrete reduce this so called Urban Heat Island Effect. Concrete reflects up to three times more sunlight than asphalt, reducing surface temperature on sunny days by 8 to 15°C or more.
• Reduced Fuel Consumption: On the rigid surface of a concrete pavement the wheels do not sink in as much as they do on flexible, i.e. asphalt pavements. This effect, called deflection, is invisible to the naked eye, but has a noticeable impact on fuel efficiency. As per MIT study, concrete pavement can reduce fuel comsumption by 3% than ashphalt pavement
• Lower Environtal Impact over Full life Cycle: A Life-Cycle Assessment (LCA) analyzes the total environmental impact from cradle to grave, including different dimensions such as global warming, use of non-renewable energy or the Ecological Scarcity indicator. Concrete offers ignificant advantages in a number of impact categories; even in global warming concrete performs better if the effect on the fuel consumption of vehicles is accounted for.
• Recycling to Save Natural Resources: A well-designed concrete pavement can be used as the basis for the road for generations to come. In the case the pavement is demolished the concrete can be recycled and used as a valuable building material. Some cement-based solutions can recycle worn-out asphalt pavements as part of a new, stabilized base, effectively solving the problem of removal and disposal of a potential waste with high content of hydrocarbons, and reducing other environmental impacts.

Social Advantages

• Safety: Concrete road pavement is the only solution for tunnels, Fires in tunnels can ignite asphalt. The burning asphalt does notonly contribute to the heat, but also to the formation of smoke, andeven outside the actual combustion area melting asphalt will makefirefighting and evacuation of victims more difficult. Concrete does not burn,nor emit toxic gases This means a significant advantage over asphalt in case of fires, particularly in tunnels. A number of countrieslike Austria now mandate that all pavements in tunnels shall be made of concrete.
• Reduction of Braking Distance and Noise: The higher skid resistance of concrete reduces braking distances by 12 -15% in both dry and wet conditions, compared to new asphalt surfaces. As concrete surfaces are very stable the advantage over asphalt increases over time; in addition, as concrete pavements do not rut the risk of hydroplaning is effectively eliminated. The noise level of concrete roads can be significantly reduced without sacrificing durability or safety by choosing an adequate surface texture, e.g. broom finish, diamond-ground surface or exposed aggregates. An Austrian study unveils that concrete pavements offer far better long-term behavior in terms of noise reduction
• Versality: Concrete is good material for every pavement project like national highways, urban roads, major district roads, dedicated truck/bus lane, airport runways taxiways aprons, industrial floors, vehicular parking etc.
• Aesthetics: Concrete is the maintenance-free solution that offers great options for distinctive road aesthetics. Whether you want a particular color or a certain surface finish – concrete is the right material for it.Can be built very economically with a number of cement-based solutions such as roller-compacted concrete or soil cement.

Precast Concrete Hexagonal Slabs for Smart Pavements

The removable precast concrete pavement is conceptualised as precast reinforced concrete hexagonal blocks that are laid to match the required roadwidth between the curbs as schematically shown in following sketches for a pilot road project executed at Saint Aubin, France.

Plan of Pilot Project Road, Saint Aubin, Normandi, France

Hexagonal Precast Slabs with combinations at edges and corners

Placing Hexagonal Precast Slab with Vacuum Liftng Crane

Hexagonal Slab and Base/Sub Base Detail

Slab Details around Opening/Manhole

Precast Hexagonal Slab laying in progress

Slab Removal for running Utilities

Area A = 2.6R^2, Perimeter P = 6R

Geometry of Hexagonal Precast Slab

Precast Full Hex Slab Approx. Dimension for different Road Widths between Curbs

1. 1- Lane: Road width 3.5 m, R =  775mm,  2 full slabs + 2 half slabs

2. 2- Lane: Road width 7.0 m, R =  775 mm, 4 full slabs + 2 half slabs

3. 3- Lane: Road width 10.5m R =  1165mm, 4 full slabs + 2 half slabs

4. 4- Lane: Road width  14m   R =  1075mm, 6 full slabs + 2 half slabs

Design Specifications for Precast Concrete Smart Pavement Slab Units

A. Removable Precast Slabs

• Hexagonal Slab Units: Grade shall be minimum M30 to M40, thickness 200mm plus 10mm extra thickness for 100 mm wide band around periphery at bottom to create void for better grip, use top and bottom mesh reinforcement fabric  8Y@150c/c bothways (IS:1566) with clear cover not less than 65mm both at top and bottom. OPC of Grade 53, Cement content ~ 400kg/m^3, water cement ratio 0.36 See IRC:44
• Joint Fillers: A soft, cold, waterproofed, polymetric/polysulphide material: easy to remove manually when nedded for utility positioning or maintenance. Refer IRC:57 for more.
• Granular Base: This comprises of 30mm thick coarse grain sand of 6/10mm size
• SECTM: Structurally Excavable Cement Trated Material shall be easy to dig out to remove precast slabs in urban setting to run utility maintenance. Cement dose of 1.1% by mass would give a 28-day compressive strength of less than 2.5 MPa, and a 28-day splitting tensile strength above 0.16 MPa. Suggested to be done in two layers in 300mm each layer consolidated and compacted to 98% proctor density. This SETCM is very much essential in case of removable precast pavements.
• Subbase/SubGrade: This must conform to the requirement of minimum 8% CBR value

B. Non-Removable Precast Slab

• Hexagonal Slab Units: Grade shall be minimum M30 to M40, thickness 200mm  directly laid over Direct Lean Concrete (DLC) layer, use top and bottom mesh reinforcement fabric  8Y@150c/c bothways (IS:1566) with clear cover not less than 65mm both at top and bottom. OPC of Grade 53, Cement content ~ 400kg/m^3, water cement ratio 0.36 See IRC:44
• Joint Fillers: The joint sealing compound shall be of hot poured, elastomeric type or cold type chemical based polysulphide or single chemical based silicone, or polyurethane having flexibility, durability and resistance to age hardening. If the sealant is of hot poured type, it shall be of rubberized bitumen and shall conform to AASHTO M 282 or ASTM: D 3406 and cold applied sealant shall be in accordance with BS: 5212 (Part 2) and IS 11433.
• Dry Lean Concrete (DLC): Thickness of DLC sub-base should be minimum 150 mm in case of , National highways, StateHighways and Urban Roads. For others it can be 100 mm, the surface finish of the sub-base shall be smooth. The cement content (OPC or blended) in the DLC shall be at least 150 kg/m^3. See IRC:SP:49 for more.
• Granular Sub Base (GSB): Minimum compacted thickness of this well graded layer nelow DLC at locations where drainage requirements are predominant shall not be less than 300 mm. See IRC:SP:42 and IRC:58
• Subbase/SubGrade: This must conform to the requirement of minimum 8% CBR value

7 Technical Advantages of Precast Concrete Smart Pavements

1. Excellent quality control on finished precast products fabricated at plant. Reduces material westage, water wastage, plant work does not suffer during monsoon season. Limited site work involved with less labour requirement and logistics at site. Reduction of nuisances to both users and neighbours caused by maintenance works. Least maintenance required even in 50 years time.
2. Ease of access to underground networks in urban setting because the hex slabs can be removed in no time with least interruption to ongoing traffic. Saves fuel and waiting time for drivers.
3. Sustainable management of the pavement (possibility of repairing or modifying pavement functions, streamlined reuse/recycling of the modular elements)
4. Fast track building of smart pavements during night hours at no obstruction to traffic
5. Possibility of adding utility networks and instrumentation into the removable pavement itself;
6. Possibility of building permeable, noise-absorbing pavements offering easy maintenance (in a factory setting)
7. More environment friendly in conserving natural resources, reduced pollution, increased aesthetics. Life Cycle Cost favours smart pavement over ashphalt pavement for least maintanance

Credits

• Francois De Larrard: Removable Urban Pavements: An Innovative and Sustainable Technology
• Shiraj Tayabji: Precast Concrete pavements: Current Technology and Future Directions

Recommendation

The above writing is meant to inspire Precast Concrete Manufacturers/Contractors and Precast Concrete Design Engineers who are fearless to explore the application opportunities of  precast concrete roads (with removable and non-removable hex slabs) as a possible diversification and addition to precast building elements at a small fraction of a price because the plant is there for you. Simply create a precast smart pavement on some segments of inroads in the plant and this would sell itself to visitors/clients. Hope this information would serve as an aid to highway engineers and decision makers to explore feasibility of Precast Concrete Smart Pavements in roadworks with more zeal and confidence. The author has no conflict of interest and the opinions are of his own.

Disclaimer

The contents of this article is for informational purpose only and proper professional guidence must be sought before implementation of design and construction of Removable Precast Concrete Pavement.