Porous Concrete

2. Pervious Concrete
 A mixture of coarse aggregate, Portland cement, water
and little or no sand.
 Controlled amounts of water and cementitious materials
are used to create a paste that forms a thick coating
around aggregate particles without flowing off during
mixing and placing. Using just enough paste to coat the
particles maintains a system of interconnected voids.
The result is a very high permeability concrete that
drains quickly.
 Typical pervious concrete pavement has a 15-25% void
structure. It is consequently lightweight, with a density
of 1600 to 1900 kg/m3.

3. Pervious Concrete Pavements
 Primary use of pervious concrete is in pavements.
 The compressive strength of pervious concrete is limited since
the void content is high. However, compressive strengths of 3 to
30 MPa are typical and sufficient for many applications.
 Its low paste content and low fine aggregate content make the
mixture harsh, with a very low slump. This also leads to increased
traction for vehicles and prevents driving hazards like
hydroplaning.
 Also referred to as porous concrete, permeable concrete, no-
fines concrete, gap-graded concrete, and enhanced-porosity
concrete.
 By capturing storm water and allowing it to seep into the ground,
porous concrete is instrumental in recharging groundwater,
reducing storm water runoff, etc.

4. Asphalt Pervious Concrete
Comparison of
asphalt and pervious
concrete surfaces in
a case study from
USA.
Water stagnant on
asphalt surface while
pervious concrete
allows the water to
flow through.

5.  Other applications that take
advantage of the high flow rate
through pervious concrete
include drainage media for
hydraulic structures, parking lots,
tennis courts, greenhouses, and
pervious base layers under
heavy-duty pavements.
 Its high porosity aides it to be
used in buildings as a thermal
and sound insulator.
Summary of applications
Low-volume pavements
Residential roads, alleys and driveways
Sidewalks and pathways
Parking areas
Tennis courts
Sub-base for conventional concrete
pavements
Patios
Artificial reefs
Slope stabilization
Well linings
Tree grates in sidewalks
Foundations / floors for greenhouses,
fish hatcheries, aquatic centres, zoos
Hydraulic structures
Swimming pool decks
Pavement edge drains
Seawalls
Noise barriers
Walls (including load-bearing)

6. Engineering
Properties

7. Fresh Properties
 The plastic pervious concrete mixture is stiff compared to
traditional concrete. When placed and compacted, the
aggregates are tightly adhered to one another and exhibit
the characteristic open matrix.
 For quality control and quality assurance, unit weight or
bulk density is the preferred measurement because some
fresh concrete properties, such as slump, are not
meaningful for pervious concrete.
 Concrete working time is typically reduced for pervious
concrete mixtures. Usually, one hour between mixing and
placing is all that is recommended. This can be altered
using stabilizers & retarders.

8. Hardened Properties
Density
 The density of pervious concrete depends on the properties and
proportions of the materials used, and on the compaction
procedures used in placement. In-place densities in the order of
1600 to 2000 kg/m³are common, which is in the upper range of
lightweight concretes.
Compressive Strength
 Pervious concrete mixtures can develop compressive strengths in
the range of 3 MPa to 30 MPa, which is suitable for a wide range of
applications. Typical values are about 20 MPa.
 Drilled cores are the best measure of in-place strengths, as
compaction differences make cast cylinders/cubes less
representative of field concrete.

9. Flexural Strength
 Flexural strength in pervious concretes generally ranges between
about 1 and 4 MPa. Factors which influence the flexural strength
are the degree of compaction, porosity, and the aggregate-to-
cement (A/C) ratio.
Shrinkage
 Drying shrinkage values in the order of 0.002 have been reported,
roughly half that of conventional concrete mixtures.
 The material’s low paste and mortar content is a possible
explanation. Roughly 50% to 80% of shrinkage occurs in the first
10 days, compared to 20% to 30% in the same period for
conventional concrete. Because of this lower shrinkage and the
surface texture, many pervious concretes are made without
control joints and allowed to crack randomly.

10. Durability : Freeze-Thaw Resistance
 Freeze-thaw resistance of pervious concrete in the field
appears to depend on the saturation level of the voids in the
concrete at the time of freezing.
 In the field, it appears that the rapid draining characteristics
of pervious concrete prevent saturation from occurring.
 Anecdotal evidence also suggests that snow-covered
pervious concrete clears quicker, possibly because its voids
allow the snow to thaw more quickly than it would on
conventional pavements.
 When the large open voids are saturated, complete freezing
can cause severe damage in only a few cycles.

11. Sulfate Resistance
 The open structure of pervious concrete makes it more
susceptible to acid and sulfate attack over a larger area
than in conventional concrete.
Abrasion Resistance
 The open & rough structure of pervious concrete,
abrasion and ravelling of aggregate particles on the
surface can be a problem. Thus, highways are generally
not suitable for pervious concretes.

12. MIX DESIGN
& PLACEMENT
Samples with different Quantity of
water content – too little, medium &
too much water.
Grading
Pervious
Concrete

13. Material Proportions (kg/m3 )
Cementitious Materials 270 - 415
Narrowly graded aggregate (gravel/
crushed stone)
1190 - 1480
w/c ratio 0.25 – 0.34 ( with chemical admixtures)
0.34 - 0.40 ( without chemical
admixtures)
Cementitious materials/Aggregate ratio 1:0.21 – 0.25
Fine aggregate: Coarse aggregate ratio 0 to 1:1
Polypropylene fibres (optional when no
fine aggregate is present)
0.1% by volume or 0.9 kg/m3
Typical Mix Proportions for Pervious Concrete
 Cement may be replaced by about 10-30% of fly ash, 20-50% of
blast furnace slag and 5% of silica fume
 Addition of fine aggregate will decrease the porosity and
increase strength

14. Transportation
 A pervious pavement mixture should be discharged completely within
one hour after initial mixing. Its very low slump may make discharge from
transit mixers slower than for conventional concrete; transit mixers with
large discharge openings or paving mixers tend to provide a faster
unloading time. The use of retarding chemical admixtures or hydration-
stabilizing admixtures may extend discharge times to 1½ hours or more.
Placement and Consolidation
 Pervious concrete mixtures cannot be pumped, making site access an
important planning consideration. Prior to placement, the sub-base
preparation and forms should be double-checked.
 Placement should be continuous, and spreading should be rapid.
Mechanical vibrating, laser screeds and manual screeds are commonly
used, although manual screeds can cause tears in the surface if the
mixture is too stiff.
 Consolidation is generally accomplished by rolling over the concrete with
a steel roller, which compacts the concrete to the height of the forms.
Because of rapid hardening and high evaporation rates, delays in
consolidation can cause problems

15. Curing
As pervious concrete pavements do not bleed, they can have a
high propensity for plastic shrinkage cracking.
In fact, “curing” for pervious slabs and pavements begins before
the concrete is placed - the sub grade must be moistened to
prevent it from absorbing moisture from the concrete. After
placement, fog misting followed by plastic sheeting is the
recommended curing procedure, and sheeting should remain
in place for at least seven days.
Placement & strike-off using vibratory screed Plastic Sheeting for curing
Joints

16. Construction Inspection and Testing
 Slump and cylinder/cube strengths are not meaningful.
Strength is a function of the degree of compaction, and
compaction of pervious concrete is difficult to reproduce in
specimens.
 Instead, a unit weight test is usually done for quality
assurance, with acceptable values dependent on the mix
design, but generally between 1600 and 2000 kg/m³.
Post-Construction Inspection and Testing
 After seven days, cores can be taken and measured for
thickness and unit weight as quality assurance and
acceptance tests. A typical testing rate is three cores for
every 75m³.

17. Maintenance
 Maintenance of pervious concrete pavement consists
primarily of prevention of clogging of the void structure.
 Cleaning options may include power blowing and
pressure washing. Pressure washing of a clogged
pervious concrete pavement has restored 80% to 90% of
the permeability in some cases.
 Pervious concrete in freeze-thaw environments must not
become fully saturated. Saturation of installed pervious
concrete pavement can be prevented by placing the
concrete on a thick layer of 200 to 600 mm of open-
graded stone base.

18. REFERENCES
 Construction Specifier Magazine, http://perviouspavement.org/PDFs/
A%20NCSU%20Structural%20Design%20-%20Permeable%20Pavements.pdf
• "NC State University Permeable Pavement Research and Changes to the State of NC
Runoff Credit System", From the 8th International Conference on Concrete Block Paving,
Nov’ 2006, http://perviouspavement.org/PDFs/ncsu_study.pdf
 "Structural Design of Permeable Pavements Worksheet" North Carolina State ,
University Department of Biological and Agricultural Engineering
 "Hydraulic Design for Permeable Pavement Worksheet" North Carolina State ,
University Department of Biological and Agricultural Engineering
 “Infiltration Opportunities in Parking-Lot Designs Reduce Runoff and Pollution" By
Betty Rushton, Southwest Florida Water Management District. An analysis of the
treatment train used in the parking lot of the Florida Aquarium in Tampa. From the 7th
Biennial Stormwater Research and Watershed Management Conference in Florida.
 "Mix Design Development for Pervious Concrete in Cold Weather Climates"
National Concrete Pavement Technology Center - Final Report, February 2006.

19.  "Oil Retention and Microbial Ecology in Porous Pavement Structures" Coventry
University, School of Science and The Environment.
 "Heavy Metal Retention Within a Porous Pavement Structure"
Department of Civil Engineering, Urban Water Management - University of Essen.
 N. Subramanian, The Indian Concrete Journal, Vol. 82, Dec’2008.
E- BROCHURES :
 Concrete in Practice (CIP): Pervious Concrete
 "Concrete Parking Areas-- They're GREEN“
 "When it Rains, It Drains" (4-page Pervious Concrete brochure)
 Freeze-Thaw / Pervious Brochure (17 pages)
WEB SOURCES:
 NRMCA's ConcreteAnswers.org
 RMC Research And Education Foundation
 www.perviouspavement.org
 www.youtube.com – pervious concrete installation – 1 min 48 sec
 Video.google.com – pervious concrete – 41 sec