no fine concrete. or pervious concrete

Student Name : Patel Digant

Department : Civil

Div : B

Roll NO : 130170106036

Subject : Concrete Technology

Email id : digant481996@gmail.com

No fines concrete is a special typeof concrete with a high porosity used forconcrete flatwork applications thatallows water from precipitation and other sourcesto pass directly through, thereby reducing therunoff from a site and allowing groundwaterrecharge.

No fine concrete also called porous concrete,permeable concrete, and porous pavement.

The high porosity is attain by a highlyinterconnected void content

When it rains, it drains

No fine concrete was first used in the 1800sin Europe as pavement surfacing and loadbearing walls. Cost efficiency was the mainmotive due to a decreased amount ofcement. It became popular again in the 1920sfor two story homes in Scotland and England.It became increasingly viable in Europe afterthe Second World War due to the scarcity ofcement. It did not become as popular in theUS until the 1970s. In India it became popularin 2000.

No fines concrete is obtained by omitting fineaggregate fraction from the conventional concrete. Itconsist of cement, coarse aggregate and water only.Very often only single size of coarse aggregate ,ofsize passing through 20mm and retain on 10mm isused. By using single size aggregate , voids can beincreased. The actual void content may vary between30 to 40% depending upon the degree ofconsolidation of concrete.

No fine concrete is generally made with theaggregate/cement ratio from 6 : 1 to 10 : 1. Thewater/cement ratio for satisfactory consistency willvary between 0.38 to 0.50.

The strength of no fine concrete is depended onwater/cement ratio , aggregate/cement ratio andunit weight of concrete.

Cement + Pozzoluna (Fly Ash)

100% Coarse Aggregate with maximum size of 12.5 mm

0 % Fine Aggregate

Voids-15% to 35%

Water and Admixture

Density It depends on the properties and proportion of the

material used, and on the compaction proceduresused in placement. In place density on the order of1600kg/m^3 to 2000kg/m^3 are common. whichis in upper range of lightweight concretes.

• Permeability

It depends on the materials and placing operation.Typical flow rates for water through previous concreteare 120L/m^2/min to 320L/m^2/min.

Compressive strength Pervious concrete mixture develop compressive

strength in the range 3.5 MPa to 28 Mpa, which issuitable for a wide range of application .Typical Valuesare about 17 Mpa.

• Shrinkage Drying shrinkage of previous concrete develops sooner,

but is much less than conventional concrete. Roughly50% to 80% of shrinkage occurs in first 10 days,compared to 20 to 30% in the same period forconventional concrete. Because of this lower shrinkageand the surface texture, many pervious concrete aremade without control joints and allowed to crackrandomly.

A No fine concrete mixture should bedischarge completely within one hour afterinitial mixing.

The use of retarding chemicals admixtures orhydration-stabilizing admixtures may extenddischarge time to 1'/2 hours or more.

Cement may be replaced by about 10-30% offly ash, 20-50% blast furnace slag and 5% ofsilica fume.

Addition of the fine aggregate will decreasethe porosity and increase strength.

Sub-base preparation and forms should be doublechecked, prior to placement.

Placement should be continuous and spreadingshould be rapid.

Mechanical vibrating, laser screeds and manualscreeds are commonly used, although manualscreeds can cause tears in the surface if the mixtureis too stiff.

Consolidation is generally accomplished by rollingover the concrete with a steel roller, which compactsthe concrete to the height of the forms.

Because of rapid hardening and high evaporationrates, delays in consolidation can cause problem.

To prevent reduction in permeability,pervious concrete needs to be cleanedregularly. Cleaning can be accomplishedthrough wetting the surface of the concreteand vacuum sweeping.

Walkways

Parking Lots

Pavements

Green Houses

Reduces storm water runoff.

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.

Runoff from adjacent areas onto perviousconcrete needs to be prevented.

The parking areas are generally limited toauto parking and occasional trucks.

If reinforcement is required, epoxy coatedbars should be used.

Concrete is variable in permeability; overvibration significantly reduces permeability.

It is still a new material that requiresacceptance from cities and states.

Thank you