PAVESCAPE Concrete – Which is a modified pervious concrete developed at R&D Centre of AHLCON Engineering Services, is a special type of concrete obtained by a combination of specially formulated mixture of cement, water and open graded coarse aggregate. Typically, it has little to no fine aggregate content and has just enough cementitious paste to coat the aggregate particles while maintaining the interconnectivity of the voids. The void content in the pervious concrete is in the range of 15 to 22% compared to three to five percent in conventional concrete pavements. It has the ability to percolate the water underneath. It also reduces the runoff from paved areas, which reduce the need for separate drainage for storm water. PAVESCAPE concrete is highly suitable for warm weather climates and areas with native permeable subgrades.
PAVESCAPE concrete is also known as porous concrete, permeable concrete, gap-graded concrete, enhanced-porosity concrete, no-fines concrete and zero-fines concrete. While PAVESCAPE concrete can be used for a surprising number of applications, its primary use is in pavement construction. It is used mainly for low traffic areas such as parking lots, residential roads, driveways and footpaths.
The history of PAVESCAPE concrete dates back to 1852 in England with the construction of residential houses and it became considerably more widespread during the material shortages after World War II, for cast in place load bearing walls of single & multistoried buildings. The use of PERVIOUS concrete in pavement applications had started in US and Japan since 1980s. Since then a lot of research has been done on pervious concretes in developed countries like US and Japan and it has been extensively used in field.
PAVESCAPE Concrete & Environment
The key advantage of PAVESCAPE concrete is that it allows the surface water to enter the pavement structure quickly so that the ground water resources can renew on time. The relative high permeability provides for almost complete percolation of surface water into the pavement, with little to no resulting runoff from the paved surface. It improves the environment of road surface. PAVESCAPE concrete can also reduce the impact of development on trees. It allows the transfer of air and water to root system allowing trees to flourish even in highly developed areas.
It also saves construction materials like fine aggregates resulting in saving our natural resources. The quantity of cement can also be reduced, which results in less emission of CO2produced during cement production.
Applications of PAVESCAPE ConcreteFollowing are the areas where PAVESCAPE concrete can be successfully used:
- Low volume pavements
- Residential roads, alleys & driveways
- Sidewalks & pathways
- Parking areas
- Low water crossings
- Tennis courts
- Slope stabilization
- Well linings
- Foundation/Floors for green houses, fish hatcheries, zoos, etc.
- Pavement edge drain base
- Noise barriers
- Walls (including load-bearing)
- Architectural & Sculpture objects
Materials and Mixture ProportioningThe aggregate generally used in PAVESCAPE concrete applications usually ranges from 10mm to 20mm. The PAVESCAPE concrete specimens tested had aggregate-cement ratios varying from 6:1 to 10:1. Mix proportions of PAVESCAPE concrete depend on the final application. For pavement applications the concrete strength is more critical and aggregate-cement mixes as low as 4:1 is generally used.
The cement paste is only a thin layer and does not contain air bubbles, so the voids are obtained mostly through the interconnected spaces of the aggregate particles. The void content is dependent upon the aggregate-cement ratio and thus varies greatly. The air content of PAVESCAPE concrete ranges from 13 to 28 percent for aggregate-cement ratios between 4:1 and 6:1. Table-1 provides typical ranges of materials proportion in PAVESCAPE concrete.
The density of PAVESCAPE concrete is dependent upon the void content in the concrete. Due to the high air content it is a lightweight concrete with a density of about two-thirds of conventional concrete. The density of pervious concrete normally ranges between 1600 and 1900 kg/m3. This is dependent upon the shape, size and density of the aggregate, the aggregate-cement-water ratio and the compaction exerted on the concrete.
The structure of the PAVESCAPE concrete is like a rice bubble bonded together to form a porous structure. The close look at the PAVESCAPE concrete is shown in the Figure 2.
Typical PAVESCAPE Concrete Pavement
Placing and CuringPAVESCAPE concrete should be discharged as close as to its final position to avoid raveling and shoveling for a large distance. The concrete can be vibrated using a roller compactor or vibratory screeder. The use of mechanical vibrators and ramming is generally not recommended with PAVESCAPE concrete. A light rodding should be adequate and used to ensure that the concrete reaches all sections of the formwork. A steel roller can be used for compaction. Curing should be done and surface should be covered with polyethylene sheets immediately after placing of PAVESCAPE concrete, preferably within 20 minutes. Curing should be continued at least upto 7 days. Also, for situations where normal conditions are not achieved during placement and curing, the formwork should not be removed after 24 hours as with conventional concrete. PAVESCAPE concrete has very low cohesiveness and formwork should remain until the cement paste has hardened sufficiently to hold the aggregate particles together.
Scope of Use of PAVESCAPE ConcreteIn Indian cities, we are facing three serious problems:
- Lowering of water table in most of the cities.
- Flooding of areas during rains, virtually converting our roads/ Pathways/ Parking lots into lakes.
- Paucity of good quality fine aggregates & increase in environment pollution due to CO2 emission during cement production.
As a part of Infrastructure development activity, huge areas like pedestrian paths, school approaches, backyard pavements, are required to be constructed. By installing pervious concrete, their cost, construction time and environmental impacts can be greatly reduced.
R&D work on PAVESCAPE Concrete at AHLCON Engineering Services (AES)Extensive R&D work has been taken up by AES, which is a subsidiary of AHLCON Ready Mix Concrete (P) Limited. Trial mixes have been developed and their performance has been evaluated at AES laboratory. The aggregate cement ratio of the trail mixes has been kept around 6:1 and the w/c as 0.40. The specimens were demoulded at the end of 24 hours itself and cured in the curing tank, as well by water spray, like normal concrete. At the end of 7 days, compressive strength obtained was of 3 MPa to 5 MPa. Figure 6 shows the samples casted at AES laboratory, which is a NABL acredited Laboratory. The perviousness of the concrete has been tested by pouring water through the top of the sample. Figure 7 shows the PAVESCAPE concrete tested for its perviousness. To add to AES laboratory investigations, a parking lot has been constructed in AHLCON RMC plant to validate the results. The parking lot installed in AHLCON RMC plant is shown in Figure 8. Further research has been in progress to optimize the strength, void content and the durability of the PAVESCAPE concrete.
Availability of PAVESCAPE ConcreteProduction of PAVESCAPE concrete at site may be a very difficult job as it needs a high level control during its production, tight water-cement ratio and accurate dosage of admixtures for ensuring strength & durability. The proper coating of cement slurry over each piece of aggregate can only generate proper bond between no fines matrix. This can only be achieved in RMC plants having special facilities for producing pavescape concrete which include selection of proper materials and good R&D back up, highly experienced and qualified manpower. PAVESCAPE concrete for different applications is available from AHLCON RMC, one of the largest producer of R.M. concrete in Delhi and NCR Region.
- Schaefer, V. R., K. Wang, M.T. Suleiman, and J.T. Kevern (2006) Mix design development for pervious concrete in cold climates, Technical report, IOWA Department of Transportation.
- Park, S., and M. Tia (2004) An Experimental Study on the water-Purification properties of porous Concrete. Cement and Concrete Research 34: 177–184.
- Malhotra, V.M. (1976) No-Fines Concrete-Its Properties and Applications ACI Jaurnal 73.11:628-644.
- Harber, P.J.(2005) Applicability of no-fines concrete as a road pavement, Dissertation, University of Southern Queensland.
- Mississippi Concrete Industries Association (MCIA). (2002) Pervious concrete: The pavement that drinks http://www.mississippiconcrete.com.
- Necille, A.M.(1997) Properties of Concrete, Longman Publications.
- Beeldens, A. (2001) Behavior of porous PCC under freeze-thaw cycling. Paper presented at the Tenth International Congress on polymers in Concrete, Honolulu, HI.
- Olek, J., W.J. Weiss, N. Neithalath, A. Marolf, E. Sell, and W.D. TAHRONTON. (2003) Development of quiet and durable porous Portlant cement concrete paving materials, final Report SQDH 2003-5. West Lafayette, IN: Purdue Ubiversity.
- Tennis, P., M. Leming and D. Akers (2004) Previous Concrete Pavements, Partland Cement Association.
- P.C. SHARMA-Pervious concrete for low volume Traffic Pavements-National Seminar on Highway Development-Design, const, operation and Repairs-Lucknow-16thNov, 08
- SERC Roorkee Technical Report No. CTD/1/85- studies on No. Fine concrete and its Performance-March 1985.
- K.B. Prakash, B.R. Patagundi, P.G. Kulkarni-An evaluation of the No Fine concrete short columns with glass Fibre Reinforced plastic (GRRP) Casings, New Building. Material & Construction World-Sept, 2002. Page 24.
- Shivkumar M. etal ‘No Fines concrete’, KSCST Projects-Dept of Civil Engg. SLN College of Engg. Raichur.