Concrete

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Concrete

2009 Concrete Pavement Workshop

Atlanta, Georgia – November 5, 2009

Best Practices for

Construction of

Airfield PCC

C Pavements

By: Shiraz Tayabji

Fugro Consultants, Inc., Columbia, Maryland, USA.


‣Jointed

Airfield Concrete Pavements

• As-designed service life ~ 20 years; anticipated

service life ~ 25 to 30+

years

• 12 to 25 ft joint spacing

• t=8in(GA)to16-20 to in (Hub) to 20+ in (Military)

• Less than 20 by 20 ft;

old about 25 by 25 ft

• Dowel bars at longitudinal joints

• And, at transverse joints for wide body aircraft

• Stabilized base common at hub airports


Airport Concrete Pavement

Performance

Requirements

‣ Structural performance

e – low level of cracking

(BY DESIGN)

‣ Material performance

– concrete durability –

minimize joint & crack spalling

‣ Safety – maintain frictio

on properties & minimize

hydroplaning potential

‣ Smoothness – minimize

dynamic forces (g

forces) in the aircraft

‣ Reduce/eliminate i FOD

(foreign object damage)


Airfield Pavement Performance

Service

eability

(PCI)

Deficient

Materials and/or

Construction

10 yrs

Threshold

Level

As-designed

Time

Owner

Expectation

20+ yrs 30+ yrs

UGRO


How do Airfield Concrete Pavements Fail

Early age failures (within

few days)

•Cracking

•Spalling

In-service failures (20 to

30 years)

•Cracking g - aircraft loading

•Spalling

•Materials related distress (ASR, Deicer)

•Roughness

•Safety y needs


Spec Role - Avoiding Future Problems

Pavement failure should be a result of structural distress

(repeated aircraft loadings)

and not due to concrete

material, support or construction related defects


Outline

Recent IPRF Construction Related Findings

Specificat

tion Intent

End Product Requirements

Quality in Construction

Construction Best Practices (Selected)


Over-riding Assumptions

for IPRF

Studies

‣The constructed pavem

ent will be durable for all

concrete mixtures, placement and finishing

techniques, project size

or climatic conditions.

‣The pavement will exhib

bit failure due to

anticipated aircraft loadings over the design

period and not due to material deficiencies.

Thus, durable concrete is that concrete that will

not exhibit materials rela

ated failures during the

service life of the pavement.


Over-riding Assumptions

for IPRF

Studies

‣Thus, s primary focus of I

PRF studies has been on

improving concrete materials technology and

improving ing construction ction process, including process

control and acceptance testing procedures

‣Addressing hot/current issues to meet stakeholder

needs


Gaps in Construction Technology

Addressedd by IPRF

‣ Best practices guide

‣ Early age strength

determination (maturity)

‣ Stabilized base interface

‣ Rapid rehabilitation

‣ Proposed construction

spec (P-501X)

‣ Deicer related materials

requirements

Concrete flexural strength

‣ Deleterious materials limits

‣ Flyash in concrete

‣ Airfield pavement

smoothness

‣ Recycled materials for base

‣ Use of highway DOT specs

‣ Other


Gaps Addressed

Best Pract

tices Guide

‣ Basis: Even if a paveme

ent is

designed to the highest

standards, it will not perf

form

well if It is not constructed well.

‣A compendium of constr

ruction

and inspection practices

that

lead to long-term perform

mance

of airfield concrete

‣A must read!!

by IPRF Studies


Gaps Addressed

by IPRF Studies

Early age strength requirements & determination

(maturity)

‣Maturity testing is a reliable predictor of

early age strength

‣For early opening to construction traffic &

for repair opening to airc

craft traffic

‣Need project specific correlation & daily

mix verification

‣Variety of systems available


Maturity Testing


Opening to Construction Traffic

(IPRF study Recommendation – Item P-50X)

‣ Joints are sealed/prote

ected

‣ Minimum in-place concrete flexural strength is:

• 450 psi, or

• Larger of 300 psi or calculated max pavement edge

stress due to the critica

al construction equipment

multiplied by 2.5

• Precludes early fatigue related damage to the pavement

Thicker slabs require less strength

Thinner slabs require higher strength


Opening to Construction Traffic

(For slab thickness = 16

in.) (IPRF STUDY)


Gaps Addressed

by IPRF Studies

Stabilized base interface

‣Basis: Concrete paveme

ents constructed over

certain types of stabilized (rigid) and permeable

bases may have a highe

er risk of early-age

age

cracking (even when constructed in accordance

with standard specificati

ions).

‣Need for better guidance for slab/base interface


Stabilized Base

(CTB) Interface

Typical US- asphalt emulsion, two coats of curing compound

More positive methods – choke

layer (IPRF), ~2 in. AC layer,

mm thick geotextile (Germany), Geo-fabric (e.g., Denver)

Fabric nailed

in-place

Geo-fabric bond-breaker

over CTB at Denver Airport

5 mm geotextile over

CTB (German practice)

17


Slab/CTB Interfa

ace – Choke Layer

‣A new recommendation (IPRF) – use of a choke layer


Gaps Addressed

by IPRF Studies

Concrete flexural strength

‣ Basis: The numerous varia

bles encountered in the process

of determining flexural strength of concrete, using ASTM

C-78, are well documented as sources of error.

‣ No documented attempt to measure a precision statement

for field cured specimens; or, what is the impact of the

initial steps in determining the flexural strength of batch

concrete


Gaps Addressed

‣ Status:

• IPRF study in progress

by IPRF Studies

Concrete flexural strength

‣Item P-50X – recommends an option – use of

splitting tensile strength testing & use of project

specific correlation

‣Military – allows use of compressive strength with

project specific correlation


Gaps Addressed

Airfield pavement smoothness

‣ Basis: Smoothness is critica

al to

aircraft operation. Rough runway

pavements may result in more frequent

need for aircraft maintenance and

accelerate the damage to pavements

under aircraft loadings. Also, reduce

potential for hydroplaning

‣ But, what is the correct wayto

measure smoothness as it impacts

aircraft operations

‣ FAA staying with straightedge testing

by IPRF Studies


Gaps Addressed

Proposed construction spec (P-501X)

‣ Emphasis on the need to pro

oduce a

durable concrete pavement.

‣ Requirements are a combination of

prescriptive and end product

requirements

‣ Less emphasis on methods.

‣ Allows contractor reasonable flexibility

to use innovative construction methods

that result in cost savings without

sacrificing i the quality of the product.

by IPRF Studies


Construction Specification Objectives

‣To identify and accommodate or minimize

variability in the concr

rete pavement

construction process to reduce the risk of

early failure

• To deliver an end product that is durable

• To minimize risk of FOD & premature failures

• To minimize owner’s risk of accepting marginal

product

• To minimize contractor’s risk of rejecting

acceptable product

Specs should always be based on CURRENT knowledge


What is the End Product

‣A concrete pavement

that meets the intent

of the plans & specific

cation

• Geometric requirements

• Grade

• Smoothness

• Structural section require

ements

e • Layer thickness

• Joint layout

• jointing

• Materials requirements

• As-delivered

• As-placed & hardened


Quality in Construction

‣ For construction projects, achieving quality

equates to conformanc

ce to requirements

• Requirements need to be well defined, can be

measured, ed, and are aenot

arbitrary abtay

‣ Quality must be built into a project. It is not a

hit or miss proposition.

p

•Owner should not

expect more than

what is specified

•Contractor may

not deliver more

than what is

specified


End Product Requirements vs.

Perfor

rmance

‣ Material requirements -> Material distresses -> Durability

‣ Air -> Freeze-Thaw Damage -> Durability

‣ Dowel alignment –> Early Cracking & Load Transfer at

Joints -> Structural Performance (20+ year life)

‣ Thickness/Strength –> Structural/Fatigue Cracking ->

Structural Performance (20+

year life)

‣ Grade -> Aircraft Operation

‣ Smoothness -> Functional Performance -> Aircraft

Operation/Aircraft maintenance

• ARE WE MEASURING THE RIGHT PARAMETERS

‣ Texture/Grooving -> Functional Performance -> Safety


Quality vs. Construction Variability

‣Variability is an inherent part of construction.

• Material, Process, and Testing (precision and bias)

‣ All sources of variability

have a negative impact

on the property being measured.

‣Need to understand the

magnitude of the

different sources of variability

‣Quality construction ti requires control over all

sources of variability.

27


Getting Ready for Paving

‣Subgrade, subbase & base construction very

important

‣Qualifying construction materials

• Consider lead time for aggregate testing ti (ASR, F/T)

Concrete plant setup and management

Concrete consistency testing

• Aggregate stockpile management


Typical Concrete Requirements (Design)

‣Flexural strength – 600 to

650 psi at 28 days

‣Min. cementitious conten

~ 500 pcy

‣Water cementitious ratio

‣SCM use

• FA (CaO < 13%) - < 25%

• GGBFS - < 50% of total

• Total SCM < 50% of total

– > 0.38 & < 0.50

of total

• Governed by reactive aggregate mitigation plan

‣Air content – ASTM C 94

– based on maximum

aggregate size & exposure conditions


Concrete Mixture Issues

‣Quality of concrete depends on quality of

aggregates & paste and

the bond between the

two

• Paste quality ==> amou

unt of water & admixtures &

AGGREGATE CLEANLINESS

‣Key properties of concr

rete

• Workability – easily placed, consolidated, finished

• Durability – long term du

urability under service

conditions

• Strength – required stre

ength at desired time


Concrete Aggregates Gradation

‣Require gradation evaluation

of the proposed aggregates

• To minimize segregation and

promote consistency in the

concrete mixture – produce a

workable mixture for slipf

form

paving application

• Test for optimized combin

ned

aggregate gradation should be

required


Gradation Evaluation

Wor rkability Fa actor

45

40

35

30

25

IV

Too sandy

I

Optimized

II

Too coarse

V

III

20

100

80

60

40

20

0

Coarseness ase essFactor


Critical Factors for Concrete Paving

‣Test section verification

‣A good concrete mixture

‣A good grade & trackline for paving

‣Stringline management (Future => stringless

paving)

‣Continuous supply of concrete to paver

‣Consistent concrete workability

‣Controlled density of concrete – just the

right vibration & finish

ing


Concrete Placement Highlights

‣Test section

• Contractor t expected

dt to adjust this

process and concrete mixture, so when

test t section is starte

ted, the specified end

product is attained


Test Section

‣Used to evaluate concrete batching, transporting,

placement, finishing, curi

ng & QA/QC

‣First day of paving – min. 500 ft, max. one lot

• Testing equal to production paving testing

Concrete mixture used is designated the approved

mixture for production paving

• TEST SECTION REJECTED IF PAVEMENT IS

DEFICIENT / DEFECTIVE

E & IF THICKNESS NOT

RIGHT

• Pre-test section paving &

rejected test section

considered defective – removed & replaced


Adjustments to the

Concrete Mixture

Proportions

‣Mixture u e can be adjusted

• Achieve uniformity in properties of fresh concrete &

concrete workability

• Provide the specified properties of the fresh &

hardened concrete

‣Adjustmentst t

• Aggregate proportions (within limits)

• Cementitious i materials +

10%

• Cement/SCM replacement – upto 10% of cement

• Admixture as warranted (within limits) it to


Paving Equipment Requirements

‣Machine Paving

• Heavy machines – slipfor

rm pavers

• Lighter machines – not

recommended for produc

ction

paving

‣Paving equipment

• Capable of placing and

consolidating concrete

uniformly

across the width of placement &

shaping concrete to specified

cross-section


Paving Requirement

The Contractor shall place,

spread, consolidate, and finish the

concrete to meet the end product

requirements – dense concrete

that does not exhibit segregation

• Internal vibrators are require

ed, as is

use of vibrator monitoring device

• Hand-finishing operations behind the

paver to be kept to a minimum to

correct minor surface defects.

NO NEED FOR PRESCRIPTIVE SPECIFICATION


Concrete Placement Options

‣ Method 1 - Place pilot lanes

Then, place the fill-in i lanes.

first.

• Sufficient delay between the placement

of a pilot lane and the placeme

ent of the

adjacent filler lane

‣ Method 2 - Place the most central

lane first. Then, place a lane

on each

side of the central lane and continue

placing new lanes on alterna

ate sides.

• This is an efficient process, minimizes

equipment turnaround time.


Concrete Placement

‣ Deposit concrete as close to

paver as possible

‣ Avoid stop & go operation

‣ Maintain uniform speed

‣ Maintain uniform head

‣ Manage/monitor vibration

• Check for vibrator trails

‣ Maintain steady concrete delivery

‣ No front end loaders or backhoes

to distribute concrete


Water Addition at Site

‣W/cm ratio control is important

• Do not add water to conc

crete in front of paver

• Do not add water to ready mix concrete, over the

approved w/cm ratio

‣What is the consequence of extra water

addition

• DURABILITY SUFFERS

• STRENGTH IMPACT


Concrete Placement Issues

‣Proper vibration effort

• Control of consolidatio

n across paving width

• Provide just enough fines at surface for a tight finish

Concrete dumping

• In front of paver – better – can control concrete head

better

• MILITARY: Side loading belt placer or spreader

‣Do o not add water to co

oncrete

in front of paver

‣Check for voids along

slipformed sides


Filler Lane

Placement

‣Reasonably easy to place

‣Protect pilot lane concret

te edges

from paver track

• Check for over-consolidation along

edges

‣Understand potential for

filler lane

• Doweled longitudinal joints

• Friction from pilot lane joint faces

• Possible use of higher slump concrete

• Shorter joint sawing window

‣Seal pilot lane joint openings

cracking in


Dowel Bar Installation

‣Transverse joints

•Pre-positioned using bask

kets

•Placed using DBIs

‣Longitudinal g

joints

•Drilled & grouted in hardened

concrete

•DO NOT USE INJECTORS


1

Inject Grout

to Back of Hole

2

Twist one turn

while pushing

in dowel

3

Place grout

Place grout

retention disk to

hold in grout


Dowel Bar

Alignment


Dowel Bar Ali

ignment Testing

German MIT

SCAN Device

47


Signal intensity

Contour plot

Horizontal

alignment

Vertical

alignment


Concrete Consolidation

‣Proper consolidation very

important

‣Inadequate d t consolidation

n results in

•Lower in-place concrete strength

•Honey-combing

‣Over-consolidation results in

•Poor air void system

•Less durable concrete

‣Need to regularly monitor

vibration

effort

•Use of vibrator smart system

recommended – continuous

monitoring


Poor

Consolidation

Should we check for

consolidation behind the paver

How


Finishing Operations

‣Minimal hand finishing – do not over-finish

•Surface does not have to be super-smooth

‣Longer straight edges produce smoother surface

‣Do not add water to facilitate finishing – if used, it

should be fogged, not sp

rayed

‣Finishers have final say on PCCP smoothness &

surface durability


Headers

– End & Beginning i of day Construction

What are some of the concerns

Consolidation

Dowel alignment

Finishing (over-finishing)

Runout – no header

(full-depth sawcut & remove)

52


Concrete

e Curing

‣Need to maintain adequate

moisture regime

‣Inadequate curing leads

• Excessive moisture loss at surface

=> plastic shrinkage cracking

• Weak surface => durability

problems

to

‣Must assure timely curing

behind paver - begins soon after

concrete finishing

Curing compounds

(CRD C300/ASTM

C309)

53


‣Ponding/continuous

sprinkling

‣Burlap/cotton mats

Curing Methods

‣Plastic sheeting

‣Curing g compounds (CRD

C300/ASTM C309)

54


Curing Compou

und Application

‣Time of application

• Apply as soon as surfac

ce sheen has disappearedd

‣Use automated equipment for uniform coverage

‣Cover all exposed surfaces (incl. Sides)

• Re-apply at joints after sawcutting

‣Typical application rate: 150-200 ft 2 /gal

‣Curing time: Typically 72 to 96 hours

55


Nozzle

Height

8-in PC

CCP

Check nozzles regularly for uniform spray

(clogging)

10-in PC

CCP

56


Protection of Concrete Against Rain

‣ Contractor must establish procedures to

follow in case of impending

rain

• Stop paving operation ASAP

• Cover freshly placed concretee

• Do not remove excess water before

covering

‣ Damage due to rain

• Surface damage – wash away of paste

• Rapid cooling - potential for cracking due to

high built-in stresses & greater slab curling

‣ Evaluate rain damage age by examining &

testing core samples – effect on durability


Joint Sawing

Critical element

• Too soon: raveling

• Too late: random cracking

Sawcutting “window”

depends on mix design,

climatic factors, curing

techniques, and base

friction

Set

oncrete

C

Too

Early

Sawcutting

“Window”

Time

Too

Late


Factors that Shorten Window

‣Sudden temperature drop

‣High wind, low humidity

‣High friction base

‣Bonding between base & slab

‣Porous base (PATB)

‣Retarded set

‣Delay in curing applicatio

on

60


Joint Sawing

QA/QC Issues

‣Check planned vs. actual

locations

‣Inspect joint raveling/spalling

‣Check sawcut depth

‣Check excessive water use and

slurry containment

‣Check sawcut carried through

vertical edge

61


Contractor Process Control

‣Provides necessary safeguards to ensure that

owner receives an end product with the specified

characteristics

‣Material is rejected or process is stopped when

testing indicates that the

end product

requirements are not being met

‣Minimizes placement of

acceptable concrete

marginal or non-


Process Control Testing

‣Aggregate quality tests – deleterious, flat/elongated

• Reject aggregate when tw

wo consecutive tests fail

‣Combined aggregate gradation

• Adjust aggregate proport

ions when tests t fail

• Reject aggregate if adjustment not possible

‣Air content & concrete temperature

• Test every truck load if two tests for a truckload fails

‣Hand-finishing at edges

• Limited to 25% of the edge per slab panel


Acceptance Testing

‣Intent of testing is not to discriminate absolutely

between good and bad end product

• Otherwise, we would be testing every cy of concrete

and every sy of the pavement

‣Intent is to discriminate sufficiently to minimize

• Contractor’s risk of good end product being rejected

• Owner’s risk of a bad end

product being accepted

‣Balance is maintained by

type & extent of testing

and rules used to accept

test results

64


Typical End Product Testing

‣Vertical grade, edge slump, joint face deformation

(defective or deficient)

‣Smoothness (straight edge/profilograph)

‣Dowel bar alignment (defective)

‣Cracking, g sliver and joint

spalling (defective or

deficient)

‣Slab thickness (PWL – pay factor)

Concrete flexural strength (PWL – pay factor)

NO Arbitrary

Requirements!!


Concrete

Strength

‣Strength Method 1 – Beams

• As before (Item P-501) –

sublots/lot)

2t tests t per sublot t(5

‣Strength th Method 2 – Compressive or Splitting

Tensile Strength

• Develop correlation in the

lab – flexural vs. splitting

tensile strengths

• In the field, 3 tests t per sublot (5 sublots/lot)

t)

• Use correlation factor to determine lot flexural strength

Note: For cylinders, 15 tests per lot – statistically more

robust that current 8 tests per lot


Deficient Pavement

(can be corrected/treated)

td/t td)

‣Deficient pavement

• Shallow cracking (< 2 in.

• High spots (< ½ in.)

deep) – minor repair

• Correct by grinding; Evaluate surface drainage

• Joint spalls (


Plastic Shrinkage Cracking

‣Typically, cracking is shallow

(1/2 to 3 in. deep) & clo

osely

spaced – due to poor curing

‣Obtain i cores over a few

cracks to verify depth

‣Treatment:

• Do nothing

• Inject low viscosity epoxy or

high molecular methacrylate

• Extensive or deeper cracking

slab removal & replacement

68


Profiling and Grinding

(to correct for bumps –smoothness is very important)

Grinding too Deep

69


Defective Pavement

‣Full-depth p cracking

‣Excessive grade issues

‣Excessive spalling

‣Other

All deficient pavement

areas are removed

and replaced


Full-Depth Cracking

Early age full-depth cracking may

result from

• Late or shallow sawing

• Excessive curling/warping

g

• Rapid surface cooling

• Misaligned dowel bars

• Early age loading

• Excessive drying shrinkage

• Excessive e base

frictional

restraint/bonding

Treatment

• Replace panel


Future Considerations

‣More end product driven – less prescriptive

‣Definitive tests for con

ncrete durability

• ASR testing & mitigation

• Other – minimize joint

spalling

‣More behind-the paver testing of concrete

• Less testing of as-deliv

vered concrete; more of asplaced

concrete (rapid/NDT)

• Air system characterization

Concrete consolidation

Concrete segregation/surface mortar depth

• Strength

• Dowel bar alignment


Summary - Cost

of Poor Quality

‣ For airport owner

• Operational delays & los

ss of

revenues

• Cost of claims (litigation)

• Reduced service life

‣ For contractor

• Corrective measures

• artial a payments

• Cost of claims (litigation)

• Liquidated damagesP


Greetings from

Washington

Thank

You!

Contact: SHIR

RAZ TAYABJI

Fugro Consultants, Inc.

Columbia,

Maryland

Phone: 410-997-9020

STAYABJI@F

FUGRO.COM

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