Control de Calidad de los

Pavimentos de Hormigón

Mark Snyder

Quality Control of

Concrete Paving

International Seminar on Concrete Pavements:Improving the Quality of Concrete Pavements

Viña del Mar, ChileSeptember 3-4, 2013

Mark B. Snyder, Ph.D., P.E.

International Society for Concrete Pavements

3

• Achieving quality equates to conformance to

requirements

• Requirements need to be well-defined,

measurable, and not arbitrary

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

“hit-or-miss” proposition.

What is Construction Quality?

How Do The Following People

Affect “Quality”?

o Designer/Specifier

o Agency Inspector

o QC Technician

o Loader Operator at the concrete plant

o Truck Driver

o Paver Operator

o Concrete Finisher

o Texture/Cure Machine Operator

Quality Measurement Tools

• Two principal tools used to measure

conformance with requirements:

� Inspection

�Testing

Inspection

• Equipment

• Environmental

Conditions

• Materials

• Product

Workmanship

Testing

• Three criteria:

�Quality Characteristics

(What do we want?)

�Quality Measures

(How do I measure it?)

�Quality Limits

(How much is enough?)

How Much Quality Is Enough?

• Is 99.9% “good enough”?

� 45 minutes of unsafe drinking water every month

� 2 long or short landings at many American

airport each day

� 500 incorrect surgical operations each week

� 3,000 newborns accidentally falling from the

hands of nurses or doctors each year

� 22,000 checks deducted from the wrong bank

account each hour

QA Principles

• Types of Tests

�Process Control Test

�Not Random

�Contractors use when needed

–Change in process or material

� Independent Assurance

�Not the project personnel

�Random Samples

�For compliance with specifications

�No others count for compliance

Basis for Testing

• Random testing assumes that the results

are normally distributed

• The mean and standard deviation of test

results are used to determine if the

samples are within specified limits

• Variability is due to the operator (and

equipment), the test procedure, and the

material being tested

Quality vs. Construction Variability

• Variability is an inherent part of construction.

�Many sources

• 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 requires control over all

sources of variability.

Source: Shiraz Tayabji, Fugro Consultants, Inc.

QA Principles

N = 1

• Sources of Variability

�Material

�Sampling

�Tester

�Equipment

�Procedures

Material Process Sampling Testing

Composite

Variability

Sources of Variability

Precision and Bias

• Established test procedures (ASTM,

AASHTO) have accounted for test

variability through precision and bias

statements

• All physical tests have built in variability

that must be accounted for in some

manner

• The following slide illustrates the problem

in determining a “right answer”

Precision and Bias

16

REASONABLE LEVELS OF VARIABILITY

(In terms of acceptable standard deviation)

• Subgrade Density: 1 to 3 lb/cu. ft

• Concrete Thickness: 0.25 to 0.50 in.

• Concrete Flex Strength: 40 to 60 psi

• Concrete f’c: 300 to 500 psi

17

Higher levels of variability =>> construction process is not under control and/or testing procedures are

marginal

Quality Control (QC)

• QC generally refers to testing by the

contractor for the purpose of process

control and to ensure meeting or exceeding

specifications

• A comprehensive QC program is much more

involved than QA because all aspects of the

project must be proactively monitored

(materials, batching, placement, etc.)

Quality Control

• Contractor’s QC system should address:

�Materials production processes

�Materials transportation and handling

�Field placement procedures

�Calibration and maintenance of

equipment

�Watching the process

�Fixing the process

Quality Control Charts

• Quality control charts (QCC) are statistically based and used primarily for process control

• Graphical format of QCC provides a simple and effective means to determine when a specific process is trending out of limits

Statistical Process Control

Concrete Batching QC

• Uniformity between concrete batches is critical in producing a smooth and long-lasting pavement

• The following parameters are routinely checked during batching:

� Aggregate moisture

� Water content

� Water/cementitious materials ratio

• Plant calibration and continuous monitoring are required

ASTM Batching Tolerances

Construction Operations QC

Construction operations require many varied types of QC measures, including the following:

• Concrete temperature at time of placement

• Entrained air content

• Consolidation (internal vibration)

• Dowel bar placement

• Potential for many others depending on specification requirements

Testing – Temperature

• ASTM C1064• EASY, just place thermometer in

concrete• Results help verify conformance to

requirements

Testing – Slump

• ASTM C143 / AASHTO T119

• Measures consistency; NOT QUALITY!

• Typical values:�Slipform: 0.5-1.5 in.�Fixed form: 3-4 in.

• Slump is dependent on mixture and also on time of testing

Testing – Density (Unit Weight)

• ASTM C138 / AASHTO T121

• Measures known volume

• Typically 130 to 150 lb/ft3

• Indicates batch-to-batch variability

• Reduction in density may indicate:

�Higher air content, higher water

content, lower cement content, change

in proportions of ingredients, or change

in aggregate specific gravity or

moisture

• One of the most valuable tests for process

control

Testing – Air Content

• ASTM C231 / AASHTO T152

• Target air depends on agg size

• Testing at plant or in front of

paver doesn’t account for air

loss of up to 2% in paver

• Quality critical to durability

• AVA and petrography are other

means to measure

Max AggSize

Target Air

9.5mm 7 ½%

13mm. 7%

19mm 6%

25mm 6%

38mm 5 ½%

Testing – Air Content (continued)

• Affected in the field by:

�Cement

�SCMs

�Chemical admixtures

�Gradation of aggregates

�w/cm ratio

�Temperature

�Delays

�Placement/consolidation

Air Content

• Why important?• Does not address

aggregate durability problems

• Typically specified as a target value and range (e.g., 5.0% 1.0%)�Nonfreeze states: 1-6%�Freeze states: 4-8%

Quality Assurance (QA)

• QA typically involves testing by the

agency or its representative to determine

compliance with specifications

• The most frequently used QA criteria for

paving jobs include

� Slab thickness

� Concrete strength

� Entrained air content

� Ride quality

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

Source: Shiraz Tayabji, Fugro Consultants, Inc.

Qualifications

• QC/QA personnel must be adequately

trained (and, often, certified)

• Repeatability and reproducibility of results

are critical for both QC and QA functions

Key Concrete Pavement

Acceptance Items

• Air content • Slab thickness• Concrete strength• Initial

smoothness

Thickness

• Probe

• Probe

• Probe

Slab Thickness

• Why important?• Traditional method:

�Cores at prescribed locations

�Governed by ASTM C174

• NDT methods:�GPR (limitations)�Impact echo

Slab Thickness Measuring:

Magnetic Imaging Tomography

Concrete Strength

• Why important?• Traditional measurement methods

�Flexural strength of beams�Compressive strength of cylinders

or cores�Split tensile testing of cylinders or

cores

Flexural, Compressive Strength

• Strength testing of concrete is one of the most common tests performed

• It is usually a combination of field preparation and laboratory (or mobile laboratory) testing

• Relatively simple, but variability in results can often be attributed to slight variations in procedure

Testing – Comp & Flex Strength

• ASTM C39 / AASHTO T22 for cylinders• ASTM C78 / AASHTO T97 for beams• Typical strength requirements (low / avg / high)

�Compressive: 21 / 24.5 / 28 MPa�Flexural: 3.8 / 4.2 / 4.5 MPa

Concrete Strength Testing:

Traditional Measurement Methods

Beams

Cylinders

Cores

Concrete Strength:

Type Used for Acceptance

0

5

10

15

20

Nu

mb

er

of

Sta

tes

Compressive Flexural

3-day

7-day

14-day

28-day

Unknown

Concrete Strength:

Specifying Strength

• Strength type (flex, comp, split tensile)• Time of measurement (3, 7, 14, 28 days)• Strength value (average or minimum)

• Typical*:�Avg f’c = 28 MPa at 28 days �Min f’c = 24 MPa at 28 days

*ACPA Database of State Practices (2007)

Concrete Strength:

Alternative Methods

• Maturity (ASTM C1074)�Monitoring in-place concrete pavement

temperatures to estimate strength• Pulse velocity (ASTM C597)

�Measuring speed at which ultrasonic waves travel through concrete

• Seismic pavement analyzer�Measuring resonant frequency of stress

waves imparted in concrete

• Strength of concrete = f(time, temp) • Laboratory-derived correlation curve• Monitoring of field

pavement temps• Precision to

cylinders: ±5%• Governed by

ASTM C 1074

Concrete Strength:

Maturity

Temperature-Time Factor, M(t)

Co

mp

ressiv

e S

tren

gth

(M

Pa)

Co

mp

ressiv

e S

tren

gth

(p

si)

0 100 200 300 400 5000

5

10

15

20

25

30

35

40

0

1000

2000

3000

4000

5000

Testing – Maturity

Testing – MaturityASTM C1074 / AASHTO T325

Testing – Maturity

Maturity Testing

• Early sawing• Surface texturing• Compatible equipment• Equipment condition

Initial Smoothness

• Why important?• Measurement methods

�Straight edge�Profilograph (California)�Lightweight profilers

• Typically expressed in terms of:�Profile Index

� 5-mm blanking band (typ. 0.08 – 0.16 m/km)

� 0-mm blanking band: (typ. 0.32 – 0.47 m/km)

�IRI (typ. 0.95 – 1.10 m/km)

Initial Smoothness:

Measurement Methods

California Profilograph

Lightweight Profiler

Current Smoothness Issues

• Accuracy

�Wavelengths (profilograph)

�Tining, joints, cracks

• Repeatability of device

�Tining, joints, cracks

�Coarse textured pavements

These are current topics of research…

Specification

Incentives/Disincentives

0

5

10

15

20

25

30

Strength Thickness Smoothness

Nu

mb

er

of

Sta

tes

Incentives

Disincentives

None

Summary

• Key specification acceptance items

�Strength

�Thickness

�Air content

�Smoothness

• Conventional test methods well established

• New and innovative test methods evolving

�Rapid

�Nondestructive

�More test points

Acknowledgments

• U.S. Federal Highway Administration Concrete

Pavement Technology Program

• CTL Group, Inc.

• U.S. National Highway Institute

• American Association of State Highway and

Transportation Officials (AASHTO)

• American Concrete Pavement Association

• Iowa State University National Concrete

Pavement Technology Center

Questions?