Cement, Energy and Environment

storm water and offer a cooling effecting the area. vi . Reduced the need for lighting at night by virtue of its lighter colour and reflective characteristics . vii . Improve access of water and air to root systems of trees . viii . Safer for drivers and pedestrians. Because pervious concrete absorbs water rather than allowing it to puddle, it reduces hydroplaning and tire spray causing drivers to loose control by preventing standing water from poling on paved surfaces. ix. Offer excellent pathways to provide disability access for people in wheelchairs. x. Serves as water retention structures. 3 · Properties The plastic concrete mixture compared to pervious is stiff traditional concrete · Slumps when ~heasured, are gener~lly less an 20m I as h' m, a though slumps IQh as 50 mm have been USed W co · hen placed and rnpacted, the aggregates are tightly adhered to one another and e h'b't th Cha X I I e P I racteristic open matrix. In– ace den ·t· 160o k s 3 1 les of the order of c g/m to 2000 kg/m 3 are ornrnon that · The void content vary · h and den . Wit aggregate size ran Slty of the mixture can t ~e from 18 to 35° 1 (1) A YPIC I / O. ot 2 .: compressive strengths Which to 2 8 ~pa is achieved INide make 1t su itable for a ihe d/~nge of applications. con amage rate of pervious crete agg pavement vary with th re~ate size and density of e lll1xt fall . ure, but will generally lJrn~nto }he range of 81 to 730 ln/rn · (2) A moderate porosity pervious concrete pavement system will typically have a permeability of 143 liters per minute per square meter. (8534 mm/hr.) . In contrast the steady state infiltration rate of soil ranges from 25 mm/hr and 0.25 mm/hr. Because of such a high permeability of pervious concrete even if it is severely clogged up due to possibly poor maintenance it is unlikely that the perm19ability of pervious concrete is the controlling factor in estimating runoff from a pervious concrete pavement. Flexural strength in pervious concretes generally ranges between 1.0 MPa and 3.8MPa. Abrasion and raveling could be a problem. Good curing practices and appropriate w/cm is important to reduce raveling. Most parking areas, when properly constructed, will last 20 to 40 years according to the Southern California Ready Mixed Concrete Association. 4. Design considerations As each project and has geographical areas circumstances particular to it such as soil conditions or available local aggregates, which may require modifications, it is suggested to make sufficient number of trial mixes to achieve the mix proportion that fulfill . the specific needs of the proJect. The American Concrete Institute Committee 522 has blished the 522R-06 pu 'd to document, which is a QUI e the use of pervious concrete. The committee is also working to complete the 522.1 specification , whi ch will provide guidance tor specifiers who may . be incorporating the material Into their projects. In absence of desired indigenous study, these ts Ca n be referred to documen . take a start to design the miX fulfill the project requi remer.t. 5. Maintenance Maintenance of pervious concrete pavements is a highly debated issue. Proper maintenance generally consists simply of vacuum sweeping or power washing. Ongoing research shows that systems that are not maintained still perform very well over time but obviously not at their original infiltration rates. However, a good cleaning generally will improve the infiltration rate of the system. 6. Installation costs In general, initial costs for pervious concrete pavements are higher than those for conventional concrete or asphalt paving because of the thicker installed size of pervious concrete than regular concrete. The subgrade is designed for quite low strength because as the water go through pervious pavement and saturate the subgrade underneath it reduce the strength what it would have when dry or partially saturated. For a pervious parking lot, we may go 150 mm thick as compared to 100 mm for conventional concrete. But when an overall installation and life-cycle cost is compared, pervious concrete clearly stands as winner; 1. Limitations of use Though the pavement is an excellent option tor certain situations , it may not always be a viable choice. Rough-textured honeycombed surface with comparatively less compressive strength , restrict its application on heavily traveled roadways. Any site that is at risk of siltation from adjacent areas would be a poor choice for pervious concrete unless special measures are taken to protect the pavement. 65