Which are the Ideal conditions for opting Cement Concrete Road?
Cement Concrete Road is the preferred choice on locations having poor sub-grade soil, Heavy rainfall areas/water logged areas, High Traffic Volume, expensive aggregates, availability of Industrial waste like fly ash in close proximity of cement plants.
HOW TO MAINTAIN & UPKEEP CEMENT CONCRETE BUILDINGS -Wear and tear losses - a heavy toll on resources
This escalating shortage in housing from 30 million in 1999 to 37 million in 2008 will obviously continue, if we do not take care of the problem of maintenance and upkeep of civil constructions and structures. The estimates by Central Electro Chemicals Research Institute (CECRI), one of the R&D institutions, under the Council for Scientific and Industrial Research (CSIR) record that India loses around 10% of GDP each year due to deterioration and decay of existing infrastructure and assets. These losses are attributed to several reasons, such as, a) wear and tear, b) corrosion, c) deterioration, d) natural calamity, e) accidents, etc.
The severest victims of the loss of GDP are the civil and construction sectors, which are also the second largest contributor to GDP of the country. The Construction, Maintenance and Upkeep of concrete buildings has, therefore, a major significance and an important role in the growth of our national economy.
Key properties of cement - a key to Durability of Concrete
Apparently, concrete is a simple composite material; but its behaviour is quite complex. With a view to achieving the final objective of producing quality concrete, it is essential to understand its various properties ? both in the fresh and hardened states. Amongst these, there are three important properties, namely, workability of fresh concrete, strength and durability of hardened concrete, which are of prime importance. Some salient aspects of these properties are described in the CMA Publication - "Building Lasting Homes".
Are not concrete roads costly?
Not really. The common perception among the Engineers and decision makers is that concrete pavements are costly to build. This might-have been true in the past when bitumen was available at cheap rate. The cost equation has drastically changed in recent times, with the steep rise in bitumen prices. Concrete roads (Highways) are cheaper even initially in case when heavy volume and heavy axle load traffic ply on them.
In case of village roads and city roads the initial cost of concrete road would be somewhat higher. However, for all categories of roads considering the very long life with negligible maintenance, concrete roads are much cheaper on life-cycle-cost.
What are the guidelines of Indian Roads Congress (IRC) for design of pavement?
• IRC:37-2012 is followed for design of bituminous pavements on highways.
• IRC:58-2011 is followed for design of concrete pavements on highways.
• IRC:SP-62-2014 is followed for design of concrete pavements for rural roads.
• IRC:SP-20-2002 is Rural Roads Manual.
What is White-Topping ?
White-Topping (Concrete Overlay ) is a cement concrete layer of suitable thickness provided on top of an existing bitumen pavement to improve its structural adequacy and riding quality. It is an ideal solution when existing road is not too badly damaged and road level can be raised. Existing surface is levelled with Profile Correction layer and tested for bearing capacity.
There are following three types of White-topping :
(i) Conventional White-topping
It consists of a plain cement concrete (PCC) overlay of thickness 200 mm or more (on the top of existing bituminous layer). Conventional White-topping is designed and constructed like a new rigid pavement without assuming any composite action. Conventional White-topping treats the exiting bituminous surface as a sub-base like Dry Lean Concrete (DLC) and to this extent the condition of existing bituminous surface does not matter significantly, except that bituminous surface should not suffer from any isolated damages like subsidence or material related problems.
(ii) Thin White-topping (TWT)
Plain Cement Concrete (PCC) overlay of thickness greater than 100 mm and less than 200 mm is classified as Thin White-topping (TWT). The bond between the overlaid PCC and underlying bituminous layer is often a consideration but it is not mandatory. High strength concrete with fibres are commonly used. Joints are at shorter spacing of 0.6 to 1.25m.
Indore Municipal Corporation (IMC) & Pimpri – Chinchwad Municipal Corporation (PCMC) have constructed roads in cement concrete. Initially, IMC decided to reconstruct/strengthen the existing city roads with bituminous overlays and concrete overlays with 50:50 funding provisions. Later on, looking to the better performance of cement concrete pavement over, bituminous pavement, IMC decided to construct all remaining roads with cement concrete overlays. With good experience PCMC have further plans to go ahead with White Topping.
(iii) Ultra-Thin White-Topping (UTWT)
To minimize the raising of existing bituminous surface on city roads for concrete overlay construction, UTWT can be adopted. This consists high strength concrete reinforced with Fibre, having longitudinal/transverse joints very closely spaced at about 0.6 to 1.25 m and thickness of overlay may be 75 – 100 mm. This type of overlay can be laid on urban streets, parking areas intersections, roads with low volume traffic.
In the year 2003 Pune Municipal Corporation (PMC) and in the year 2007, the Municipal Corporation of Greater Mumbai (MCGM) and Thane Municipal Corporation (TMC) have successfully implemented White Topping projects in their areas.
Technology Demonstration Projects :
CMA and Cement companies having major presence have successfully completed Three Technology Demo Projects of White Topping; one is in Bengaluru (August 2010) – Hosur Road from Kendriya Sadan Junction (Ayyappa Temple Junction) to Madiwala, Second in Jaipur (May 2011) – Tonk Road : Ghandinagar Mod to Laxmi Mandir Cinema Circle and Third in Chennai ( August 2012) – Velachery Main Road.
Concrete Overlay works have been successfully Implemented in cities i.e. Indore (Madhya Pradesh), Pune, Pimpri-Chinchwad, Thane, Mumbai, Nagpur (Maharashtra), Chennai and Bengaluru.
Is there any fuel saving on concrete roads?
Yes. One factor not well appreciated, but deserving notice, is fuel economy. Experiments in the USA showed a fuel economy of 20 per cent on rigid pavement. In India similar study undertaken by Central Road Research Institute on Delhi-Mathura Road revealed 14 per cent fuel saving for commercial vehicles.
Fuel Saving per truck annually (330 days running) would be Rs. 2.0 lakhs if we assume a truck to run 300 km, per day with an average consumption of fuel as 1 ltr per 4 km.
Note: Cost of Crude oil which is imported is going up. Study anticipated the shortage of bitumen, if entire road net work in the country is maintained properly.
Is it advisable to construct cement concrete roads in rural areas?
Yes. Due to poor drainage system in villages and inadequate budget provisions for maintenance of rural roads by State Govts. concrete roads will perform much better as compared to bituminous roads.
Concrete Rural Roads under PMGSY
Ministry of Rural Development (MORD) has informed all State Governments that the construction of cement concrete roads is expected to save resources of States in the long run. The difference in cost between Cement concrete roads and Bitumen road would be shared by Centre and State concerned on 50:50 basis.
Does Concrete road construction requires equipments like slipform pavers?
Not necessarily. City Roads in Mumbai, Thane, Pune, Nagpur, and Stand Road of Kolkata have, however, been successfully constructed without these pavers. A semi-mechanised process using only basic equipments can do. Of course, use of Ready Mix Concrete and modern pavers ensures good quality and speed in construction. Rural roads do not require use of slipform paver.
Is there enough cement for the purpose of constructing concrete roads?
Yes. India ranks second among the World Cement Producing countries. Production in 2013-14 was 255.74 Mt. (source- DIPP, MOI, Govt. of India). Cement is in surplus presently and would remain so for years to come. 43 Grade OPC and fly ash based PPC of Good Quality are available in plenty. Quality of cement is comparable with best quality available in the World.
What Special care for City Roads should be taken?
Planning for laying of future utilities along/across the road to be concretized is to be done before construction of concrete roads. Besides this traffic diversion plan is to be prepared and implemented.
Once constructed, concrete roads entail breaking for laying future utilities : RCC ducts can be laid at regular intervals for this purpose during construction thus avoiding the breaking of roads for laying future utilities. Now a days, Trenchless Technology for underground digging for laying services is also available for unforeseen works.
Bitumen pavements or concrete paver blocks can be provided at junctions and on either side of the concretized pavements to allow longitudinal excavation for laying underground utilities/services for the new development along the roads.
Cracks develop near manholes : To prevent cracking, the concrete slab around manholes should be cast separately with the necessary reinforcement. Now a days Concrete Paving Blocks are provided near manhole chamber, which can be replaced easily when got shrunk.
What is the best solution for a concrete road when it becomes very rough?
When a concrete road gets damaged and becomes very rough, the best solution for making its surface even would be to lay a coat of Polymer Concrete, of the required thickness, over the damaged portion. The existing surface must be thoroughly cleaned and dried, and all loose material removed. The Polymer Concrete must then be spread on it, to match the height of the rest of the road. This new surface must then be cured as per normal concrete. If the road has to be opened quickly, use of quick-setting cement along with super plasticizer, can allow re-opening within 24 hours. Polymer concrete bonds well with the old surface. Ordinary concrete, poured on top of an existing concrete surface, is likely to produce a ‘cold’ joint, which may give way under the stresses produced by fast moving traffic.
For badly damaged small portions on roads subject to very heavy traffic (e.g. expressways) repairs can be done using epoxy-concrete.
What is to be done if Cement Concrete Road surfaces become too smooth?
For road surfaces which have become too smooth, it would be best to use mechanically operated hard-wire brushes to roughen the surface. If required, an acid-water solution can be sprayed on to the road surface, a short while before the wire brushes are used. Alternatively, diamond grooving machines can be used for imparting fresh texture.
What is to be done on Black Cotton Soil?
It would be best to remove 60 cm soil for the entire road length and replace it by non-Black Cotton soil from outside.
An alternate method is to mix 2-3 per cent lime and 3 to 4 per cent cement with the existing soil. Mix thoroughly, adding desired quantity of water and compact to the required density.
What precaution should be taken to avoid any surface cracks?
The cement concrete slabs may develop cracks if proper care is not taken either during construction stage or during post-construction period.
Cracks can appear generally due to following reasons :
(a) Plastic shrinkage of concrete surface due to rapid loss of moisture.
(b) Drying Shrinkage
(c) High wind velocity associated with low humidity.
(d) High ambient temperature
(e) Delayed sawing of joints
(f) Rough and uneven surface of the base on which concrete slabs are constructed.
(g) Combination of the above factors.
To avoid surface cracks over concrete slabs main precautions are :
I. Protecting green concrete by covering with wet hessian.
II. Adequate curing of concrete.
III. Cutting of joints as early as after 6-10 hours in summer months.
IV. Concreting in nights in summers.
V. Finishing smooth surface of base course.
VI. Protect the fresh laid surface from wind and sun by a portable tent
To avoid any superficial or surface cracks, whether any nominal reinforcement at surface is recommended or otherwise.
Jointed Plain cement concrete pavements do not require reinforcement and it is not recommended as per the present practice.
What will be the remedial measure if any hair cracks occur?
The remedial measures, for repair of hair cracks of width less than 0.2 mm, are to seal without delay with low viscosity epoxy resins.
• To clean surface with wire brush
• Blow off loose particles with compressed air
• Apply low viscosity resins mixtures of resin and hardner as per IRC:77 by gravity dropped from end of long blunt na
• Reapply to fill the cracks in case required.
Please refer to IRC:SP:83-2008 “Guidelines for maintenance, repair and rehabilitation of cement concrete pavements”.
What shall be the maximum permissible spacing of Expansion joints with respect to the various thicknesses of the pavements?
In case of Jointed Plain cement concrete pavements, where transverse joints are provided @ 4.00 to 5.00 m c/c with dowel bars on these joints, the present practice is to omit expansion joints altogether and provide them at culverts and bridge abutments.