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