Raising the Quality Bar- Everyone Wins!

Quality in the Concrete Paving Process

Introduction Introduction - 1

Raising the Quality Bar- Everyone Wins!

Virginia Concrete Conference March 8, 2013 Richmond, VA


Jim Grove, PE Federal Highway Administration/Global Consulting Inc.

Office of Infrastructure


Introduction - 2

What?

• Quality Assurance – We test and inspect to insure pavement meets

specifications – We have quality procedures to insure long life

pavements – These are not the same!


Introduction - 3

Testing vs. Quality

• Testing does not insure quality • Testing is a tool to achieve quality • Testing and inspection allow us to anticipate

and avoid problems • We use test results to

achieve quality


Introduction - 4

Quality in the Concrete Paving Process Workshops

Upcoming Workshops

Alaska Hawaii Workshops to

date


Introduction - 5

Agenda • Workshop Introduction • Module 1: Quality Assurance Concepts • Module 2: Materials and Characteristics for Quality

Pavement • Module 3: Pre-Paving and Mix Production • Module 4: Paving • Module 5: Utilizing Quality Concepts • Module 6: Quality in Field Practice

What

Why

How

Both contractors and agency personnel!


Introduction - 6

Reference Materials

• Participant Workbook – All the presentation slides – Class exercises


Richmond, Virginia 2013


Introduction - 7

Reference Materials

• Testing Guide – Identified concrete tests

for critical concrete properties

– What to test – Purpose – How to test – What does it mean? – Implication


Introduction - 8

Reference Materials

• Quality Manual – What to inspect – How to inspect – Format of the Workshop – QC Plan – Checklists – Both contractors and

agency


Introduction - 9

Reference Materials • Flash Drive

– National Concrete Pavement Technology Center: Integrated Materials and Construction Practices for Concrete Pavement Manual (IMCP Manual)

– ACPA : Concrete Pavement Field Reference: Pre-Paving

– ACPA : Concrete Pavement Field Reference: Paving – NHI Course 134064: Transportation Construction

Quality Assurance – Example QC Plan – Example spreadsheets for control charts


Introduction - 10

Contractor Benefits • Contractors who consistently meet specifications

have an advantage at the bidding table – Reduce Penalties

• Done right the first time • Reduced Re-Work • QC costs are typically a fraction

of re-work costs

– Increase Incentives • Know you will get full incentive • Use incentive to reduce bid amount

• Allows energy for monitoring the process, not wasting it on fixing problems


Introduction - 11

Agency Benefits

• Agency receives improved quality without additional cost

• Finish project sooner – Frees up personnel sooner – Open to the public sooner

• Avoids time needed to assess re-work and determine penalty

• Creates a better working environment

• Public gets a longer lasting pavement


Introduction - 12

Core Elements of a QA Program

Quality Assurance

Quality Control

Agency Acceptance

Independent Assurance Dispute Resolution

Qualified Labs Qualified Personnel


Introduction - 13

Acceptance Plans that Recognize Inherent Variability

• Based on proven mathematical probability (MIL 414)

• Take into account the sources of inherent variability

• Provide a more realistic assessment of degree of conformance


Introduction - 14

Quality Measurement Tools

• Two principal tools used to measure conformance with requirements: – Inspection

– Testing


Introduction - 15

Inspection Components

• Equipment

• Materials

• Workmanship

• Environmental Conditions


Introduction - 16

Measuring Quality with Testing

• Three criteria must be identified to assess Quality through testing: – Quality Characteristics

– Quality Measures

– Quality Limits


Introduction - 17

Sampling

• “The process of selecting one or more samples from a population (Lot).”

• Key elements of sampling system: – Lots

– Statistical Samples

Minimum of 3 samples

Ideally 8 to 20 random samples

– Sublots

– Samples


Introduction - 18

Random Sampling • Removes bias • All materials have an equal probability of being

sampled • Appropriate for acceptance testing • Appropriate for statistical

process control


Introduction - 19

Material Process Sampling Testing

Composite Variability

Sources of Variability


Introduction - 20

Validity of Sampling Data

• The principles associated with Normal Distribution can be applied to determine the Quality of a Lot of Material, assuming:

1) “Multiple” (n > 3) samples are used 2) All samples are “Randomly” obtained 3) Samples are obtained from the same Lot under “Controlled Conditions”


Introduction - 21 II - 21

Re-Sampling vs. Re-Testing

• Re-sampling – Take a new material sample – Replace the original sample with the new

• Re-testing – Perform another, separate test – Perform the test on the split from the original sample


Introduction - 22

Analysis and Application of QC Test Results

• Control charts – Used to plot and monitor consecutive QC test results

– Results can be tracked against a process target/limits

– Can help to identify whether the process is in control

– May indicate that adjustments process is necessary

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1-1 1-2 2-1 2-2 2-3 3-1 3-2 3-3 4-1 5-1 5-2 6-1 6-2 7-1 7-2

Uni

t Wei

ght,

pcf

Unit Weight Mixture Design Upper Limit Lower Limit


Introduction - 23

Control Charts

• Control charts do not – Eliminate variability

– Tell you where your problem lies

– Tell you how to correct the problem

• Some control charts – Help distinguish between the inherent

chance causes of variability and assignable causes


Introduction - 24

Acceptance Function

• Acceptance is not focused on directing the methods used to achieve conformance

• The primary objectives of agency acceptance are: – Measure the Quality of all materials produced

and placed by the contractor

– Determine the corresponding payment the contractor should receive


Introduction - 25

Acceptance Function

• Quality measurement is achieved through three general acceptance activities: – Monitoring the adequacy of contractor QC activity

– Performing acceptance inspection to identify visually deficient work

– Performing Acceptance sampling and testing for key quality characteristics

• Agency is obtaining information to confirm that all products meet the specified quality level



Module 2: Materials and Characteristics for

Quality Pavement


Introduction - 27

Concrete Materials

• Cements / Supplementary cementitious materials • Aggregates • Water • (Admixtures)


Introduction - 28

How SCM’s Work

Supplemental Cementitious

Material CSH CH +

Secondary Reaction

Water +

Calcium Silicates + Water CSH CH +

Calcium Hydroxide Cement

Fly Ash / Slag Begins after the cement reaction

Calcium Silicate Hydrate

Causes Stuff to Harden =>

Calcium Carbonate


Introduction - 29

Chemical Admixtures • Air entraining admixtures (AEA)

• Water reducers

• Set modifying admixtures

To make good concrete better, not to fix bad concrete!!


Introduction - 30

Strength

• Affects fatigue cycles • Controlled by w/cm

– Other factors are indirect – Strength and durability are not the same


Introduction - 31

Permeability

– Rapid Chloride Permeability Test (Indirectly)

– Wenner Probe/Surface Resistivity Test

(Indirectly)

Rapid Chloride Permeability Test Surface Resistivity Test

• Test (Surrogate tests for durability)


Introduction - 32

Unit Weight

• Test – Unit Weight

• Quality Indicator for: – Uniformity

• Batching tolerances – Air Content


Introduction - 33

Calorimetry

• Test – Calorimetry (heat signature)

• Quality Indicator for: – Cementitious system – Strength development – Time of set – Sawing window – Uniformity


Introduction - 34

Air Content

• Test – Air Content

• Quality Indicator for: – Freeze-thaw damage – Strength

Air 1% Strength 5%


Introduction - 35

Air Void System

• Why? – Water expands when it freezes

• What are we looking for? – Small bubbles close together – Air void system is more important than total air content

Expansion of 9%


Introduction - 36

Quality Control Stage

• Monitor mixture quality during production and react to changes – Gradation – Slump – Unit weight – Air content – Microwave water content – Strength – Permeability


Introduction - 37

Incompatibility

• All materials meet specification, yet the mixture is unsatisfactory – Early stiffening – Air entrainment – Strength development

• Due to chemical reactions between materials • Change mix temperature, SCM dose and/or

admixture type • Refer to page 9 of the “Testing Guide”


Introduction - 38

Volume Shrinkage



Pre-Paving Activities


Introduction - 40

Dowel Basket Placement • Load transfer • Why?

Dowel Basket Placement


Introduction - 41

Paver Preparation • Extrusion process

• Check slab dimensions and cross-slopes


Introduction - 42

Aggregate Stockpile Management • Minimize segregation

– Build long and wide-NOT high! – Build stockpiles in tiers to avoid

segregation

Fines at the top

Coarse at the bottom

Picture courtesy of Martin Marietta Materials


Introduction - 43

Aggregate Stockpile Management • Uniform Moisture

– Stable and well drained foundation underneath stockpiles – Place a separation layer on top of soil – Draw from areas of known moisture content


Introduction - 44

Aggregate Stockpile Management • Mud balls


Introduction - 45

Recommended Practices • Adequate mixing time

– Uniformity – Air entrainment – Strength – Workability


Introduction - 46

Transporting Concrete • Maintain haul route



Paving Activities Refer to the “Field Reference Manual for Quality Concrete

Pavements” for details on steps shown in italics



Spreading Concrete • Continuous supply of concrete to the paver • Consistent head => smoothness



Consolidation • Match vibrator frequency to workability and paver speed • Electronic vibrator monitor



Key Inspection Items • One contactor example • Tape QC Inspection list on the paver

• Stringline – constant • Edge slump – every 50’ • Offset alignment – every 50’ • Slab width – every 50’



Key Inspection Items • Check dowel location

• Real-time • NDT

• Core verification after first day − Depth − Alignment − Position relative to sawn joint



QC Measurements • Verify dowel bar location behind the paver


Introduction - 53

Key Inspection Items • Periodically verify steel location behind the paver

– Cover meter (pachometer) – GPR after hardened – MIT-SCAN-2

Pachometer

GPR


Introduction - 54

Key Inspection Items • MIT-SCAN-2

• Cut the tie wires



Recommended Practices • Identify bumps and dips – overlap straightedge by 1/2 • Correct bumps and dips


Introduction - 56

Texturing • Macro Texture

– Wet weather skid resistance – Reduce hydroplaning


Introduction - 57

Group Activity

Why do we Cure?



Recommended Practices • Adequate number of saws on the project



Module 6: Quality in Field Practice


Introduction - 60

Slump • Measure of consistency • Quick and easy


Introduction - 61

Air Void Analyzer • Air void system • Initially to verify a good air void system • For QC, not for specification compliance • Higher total air => lower spacing factor

0.000

0.004

0.008

0.012

0.016

0.020

3-1 3-2 3-3 4-1 5-1 6-1

Spac

ing

Fact

or, i

n

Spacing Factor, in 0.01 in Limit 0.015 in Limit

5.2% 6.5% 6.0% 6.5% 5.0% 5.3% Total Air

At the plant


Introduction - 62

Heat Signature • Cementitious system • Strength development

– Time of set – Sawing window

• Incompatibilities • Uniformity


Introduction - 63

Permeability • Surface Resistivity Test

– Easy and quick test

• Rapid Chloride Permeability Test – Takes more time and effort- old stand by

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5

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15

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Surf

ace

Resi

stiv

ity, K

Ohm

-cm

Sample ID

56 DaysLow

Moderate

High


Introduction - 64

Heat Signature vs. Surface Resistivity

y = 1351.9e-0.046x

R² = 0.9141

5.0

7.0

9.0

11.0

13.0

15.0

17.0

19.0

21.0

23.0

25.0

90 92 94 96 98 100 102 104 106

56 D

ay S

urfa

ce R

esis

tivity

, Ohm

-cm

Maximum Temperature of the Heat Signature Curve, F


Introduction - 65

HIPERPAV [Example]

• Software tool for assessing cracking risk

Tensile Strength

Critical Tensile Stresses - Top

Critical Tensile Stresses - Bottom


Introduction - 66

@ 9:00 P.M.

HIPERPAV • Software tool for assessing cracking risk

@ 1:00 A.M. @ 5:00 A.M. Placement on the night of 5/21/12


Introduction - 67

HIPERPAV • Software tool for assessing cracking risk

@ 8:00 P.M. @ 12:00 A.M. @ 4:00 A.M. Placement on the night of 5/22/12


Introduction - 68

Maturity • Maturity curve

– Temperature and time factor can be used to determine in-place pavement strength

Opening strength= 550 psi MOR

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ural

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engt

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SI

Maturity, °C-Hrs

Maturity Curve - Standard Cured Beams

Specimens Caston 5/16/12

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Maturity, °C-Hrs



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Maturity, °C-Hrs



820 C-Hrs


Introduction - 69

Maturity • Maturity curve

– Temperature and time factor can be used to determine in-place pavement strength

Maturity number = 820 ○C-Hrs

Opening strength= 550 psi MOR

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0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48

Mat

urity

(°C-

Hrs)

Time(hrs)

Field Maturity (5/18/12)Field Maturity (5/21/12)

22 hrs


Introduction - 70

MIT-SCAN-T2 • Thickness example

– Design thickness = 11” – Average thickness (T2)= 12.3”

10.010.511.011.512.012.513.013.514.0

294+

05

296+

00

297+

00

299+

00

301+

00

697+

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698+

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700+

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702+

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00

708+

00

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00

713+

00

715+

00

T2 P

avem

ent T

hick

ness

, in

Thickness Design Average


Introduction - 71

Air/Unit Weight • Normally they will run parallel

– Unit weight changes if air content changes – Unit weight changes if water (slump) changes

• When they diverge – Change in materials or proportions

5%

6%

7%

8%

9%

10%137

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1-1 2-1 2-2 2-3 3-1 3-2 3-3 3-4

Air C

onte

nt, %

Uni

t Wei

ght,

pcf

Sample ID

Unit WeightAir Content

??


Introduction - 72

Agenda • Workshop Introduction • Module 1: Quality Assurance Concepts • Module 2: Materials and Characteristics for Quality

Pavement • Module 3: Pre-Paving and Mix Production • Module 4: Paving • Module 5: Utilizing Quality Concepts • Module 6: Quality in Field Practice

What

Why

How

Both contractors and agency personnel!


Introduction - 73

Jim Grove Federal Highway Administration/Global Consulting Inc.

Office of Infrastructure

2711 South Loop Drive Suite 4502

Ames, Iowa 50010 Phone: 515-294-5988 Mobile: 515-450-3399

[email protected]

Documents

Raising the Quality Bar- Everyone Wins!