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Pervious concrete

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Pervious concrete is known as No fines, gap graded

Pervious concrete is known as No fines, gap graded
or porous concrete. This concrete is a mixture of Cement, Corse Aggregate and with or without sand.

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Pervious concrete Pervious concrete Presentation Transcript

  • Pervious Concrete Also known as No fines, gap graded or porous concrete Abhishek gupta
  • Introduction Definition : • Pervious Concrete is a special type of concrete with a high porosity used for concrete flatwork applications that allows water from precipitation and other sources to pass directly through, thereby reducing the runoff from a site and allowing groundwater recharge • The high porosity is attained by a highly interconnected void content. Recognized as the best management practice by US Environment Protection agency (EPA)
  • • It is a mixture of Cement, Corse aggregate and with or without sand (Fine aggregate) and has enough cementitious paste to coat the coarse aggregate while preserving the interconnectivity of the voids. • This concrete is being used as paving material to solve or reduce the storm water runoff to the drainage system and minimize water logging problems • It is an important application for sustainable construction and is one of many low impact development techniques used by builders to protect water quality.
  • Pervious Concrete when it rains, it drains
  • Difference between Pervious and Impervious concrete
  • Pervious concrete pavements • A mixture of Cement, Corse aggregate and with or without sand. • Controlled amounts of water and cementitious material are used to create a paste that forms a thick coating around aggregate particles without flowing off during mixing and placing. • Typical pervious concrete pavements has a 15-20% void structures. It is consequently lightweight, with density of 1600 to 1900 kg/m³
  • Properties Density • It depends on the properties and proportions of the materials used, and on the compaction procedures used in placement. In place densities on the order of 1600 kg/m³ to 2000 kg/m³ are common, which is in the upper range of lightweight concretes. Permeability • It depends on the materials and placing operations. Typical flow rates for water through pervious concrete are 120 L /m^2/min, or • 0.2 cm/s to 320 L /m^2/min, or 0.54 cm/s. Compressive strength • Pervious concrete mixtures can develop compressive strengths in the range 3.5 MPa to 28 MPa, which is suitable for a wide range of applications. Typical values are about 17 MPa.
  • Flexural strength • It generally ranges between about 1 MPa and 3.8 MPa • factors influence the flexural strength are • degree of compaction, • Porosity, • the aggregate: cement (A/C) ratio. Shrinkage • Drying shrinkage of pervious concrete develops sooner, but is much less than conventional concrete. (0.002, roughly half to that of conventional concrete mixtures) • 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.
  • Durability Freeze-thaw resistance: It depends on the saturation level of the voids in the concrete at the time of freezing. deterioration of concrete exposed to freeze-thaw 1) random cracking 2) surface scaling 3) joint deterioration due to cracking Snow-covered pervious concrete clears quicker, possibly because its voids allow the snow to thaw more quickly that it would on conventional pavements.
  • Sulphate resistance: The open structure of pervious concrete makes it more susceptible to acid and sulphate attack over a larger area than in conventional concrete.
  • Abrasion resistance: Because of the rougher surface texture and open structure of pervious concrete, abrasion and raveling of aggregate particles can be a problem. This is one reason why applications such as highways generally are not suitable for pervious concretes.
  • Mix design and placement different surface textures can be obtained through the use of different maximum sizes Samples of pervious concrete with different water contents, formed into a ball: too little water, proper amount of water, and too much water.
  • Typical Ranges of Materials Proportions in Pervious Concrete 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
  • Transportation • A pervious pavement mixture should be discharge completely within one hour after initial mixing. • The use of retarding chemicals admixtures or hydrationstabilizing admixtures may extend discharge time to 1 ½ hours or more. • Cement may be replaced by about 10-30% of fly ash, 20-50% blast furnace slag and 5% of silica fume. • Addition of the fine aggregate will decrease the porosity and increase strength.
  • Placement and Consolidation • Sub-base preparation and forms should be double checked, prior to placement. • 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 mixtures 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.
  • Placement and strike off using vibrating screed
  • 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 7 days. Plastic sheets for curing
  • Construction Inspection and Testing • Slump and cylinder strengths are not meaningful for pervious concrete. Strength is a function of the degree of compaction, and compaction of pervious concrete is difficult to reproduce in cylinders. • A unit weight test is usually used for quality assurance, with acceptable values dependent on the mix design, but generally between 1600 kg/m³ and 2000 kg/m³
  • Post-Construction Inspection and Testing • After seven days, core samples can be taken and measured for thickness and unit weight as quality assurance and acceptance tests. A typical testing rate is three cores for each 75 m³. • Compression testing for strength is not recommended, because of the dependence of compressive strength on compaction.
  • 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.
  • Environmental Benefits • Reduces storm water runoff. • Eliminates need for detention ponds and other costly storm water management practices. • Replenishes water tables and aquifers. • Allows for more efficient land development. • Minimizes flash flooding and standing water. • Prevents warm and polluted water from entering streams. • Mitigates surface pollutants. • Light reflectivity is higher than with asphalt surfaces, reducing any heat island effect. etc…
  • Disadvantages • Runoff from adjacent areas onto pervious concrete needs to be prevented. • The parking areas are generally limited to auto parking and occasional trucks. • If reinforcement is required, epoxy coated bars should be used. • Concrete is variable in permeability; over vibration significantly reduces permeability. • It is still a new material that requires acceptance from cities and states.
  • Applications • Pervious pavement for parking lots. • Alleys and driveways. • Trees gates in sidewalk . • Swimming pool decks. • Tennis court. • Greenhouse floors.
  • Thank you!