practical application of pervious concrete - mix designs that are workable

8/12/2019 Practical Application of Pervious Concrete - Mix Designs That Are Workable

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Pervious Concrete

Practical Application of PerviousConcrete: Mix Designs that are

workable

NRMCA ConferenceRick Blackburn, May, 06

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What is Pervious ConcreteIt is a free drainage

concrete with little or nosand:

Designed for zero slump

Has air void system of 13-30%

Can drain up to 3 gallonof water/hour

Used in Florida for pasttwo decades

Definition


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Why use Pervious?

EPA / LEED legislation Helps storm water systems by slowing

water during rain and melt times

Recharges local aquifers

Helps improve ground water in local area

Goals


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How is it designed?

Mix Design

ACI design guide 211, Appendix 6

- Porosity calculation method related tocomponents properties

- Porosity to strength correlation

- Paste to porosity correlation (compaction

dependent)

- Sand addition


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Usual Mix Design:

HRWR, Retarder, VMAAdmixture

0.27 to 0.38Water / Cement Ratio

2400 - 2800 lbs.(1431-1670kg)Coarse Aggregate

375 - 650 lbs.(224 388 kg)Cement (Any Type)

Mix Design

How is it designed?


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RecommendationsUse quality clean aggregates, testsperformed with dirty stones are poor

Moisture Content and absorption of coarse

aggregate is crucial

Sand addition sometime act reversely,increasing porosity instead of reducing it

Increased cement content makes mix less

workable, promotes meat balls and makes

the mix stick in drums

Mix Design


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Water Cement Ratio should remain as low as

possible, use higher ratio only if concrete islightly compacted

Mixing time should be 5 minutes in yard or

longer, to allow aggregate coating After batching pervious should look glossy and

should hold together in hand with simple

gripping

Mix Design

Recommendations


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Mixing Procedure No ACI 211 recommendations

Our experience:

Water, admixtures and aggregates

(Duraflux line, 2000 Ni, Stop Set L) Mix for 1 minute

Add cement

Mix drum for 100 revolutions beforeleaving plant (~ 2 minutes wet batch)

Application


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Placement Working time depends on admixtures mix

design (Stop set L)

Material once truck arrives cannot be

dosed with more HRWR or water, will

cause paste separation and plug thepervious bottom

Keep surface from drying out (sensitive)

Compaction, Compaction, Compaction

Application


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Placement Notes

Pre Placement- Base should be compacted stone 6

- Lifts designed for no greater than 6

or do multiple lifts

- If only one lift, make sure lift allows

for compaction of pervious

Placement


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Durability of pervious If pervious was placed and compacted

properly the material will allow water todrain away

With little or no water, freeze thaw is

minimum Loading areas with heavy trucks still not

advised

Properties


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Strength of the Mix

Since this is pavement, flexural strengths

is recommended

Once paste is hardened, durability of

aggregate influences final strength Proper compaction improves strength

Properties


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Calculated for 20 % voids

Actual porosity is higher

Allows for optimum drainage

Still have good strength

Porosity of Pervious

Properties


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Mix Designs Used

332VMA

335Stop Set L

462548600Cement

Mix 3Mix 2Mix 1

7.157.0013.00Setting time

345Duraflux 33

0.350.350.3W/C Ratio

2580258025803/8 Limestone

Case Study


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Flexural Strength ResultsMix 3Mix 2Mix 1

513 psi641 psi735 psiFlexural Strength

462 lbs.548 lbs.600 lbs.Cement Content

Slow set time helped mix one

All three mixes tacky

Strength of mix two was acceptable forpavement usage

Case Study


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Improper Compaction Old concrete

techniques used Small lawn roller only

compaction

Single lift is over 6inches

Mix not level with

concrete drive area

Placement


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Common Compaction Vibration skree

used for compaction

Lawn roller filled with

fluid

Extra material worked

into surface

Placement


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Good Compaction Weighted hydraulic

roller Secondary weighted

roller

Manual compactionaround Edges

Tool joints every 20

Placement


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Conclusions

Follow ACI 211 formula Try to purchase clean aggregates

Keep accurate moisture log on aggregate

No addition of any admix or water once

truck leaves yard


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Conclusions contd.

600 psi flexural is attained

Surface is durable

With proper monitoring, pervious concrete

is a quality ready mix product that can beproduced by any supplier

practical application of pervious concrete - mix designs that are workable

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