Delivering Concrete to Survive the...

Delivering Concrete to Survive

the Environment

Dr. Peter Taylor

Outline

• What can go wrong?

• How do we prevent it?

2

What Can Go Wrong?

• Internal Expansion• External attack

Durability

• Ability of the concrete to survive the

environment to which it is exposed

Aggressive fluids

Cold weather

Unstable aggregates

Slab deformation

Overload

Aggressive fluids

• Sulfates

• External sulfates (eg soil)

• C3A in the cement

• Softening

• Complex chemistry

Aggressive fluids

• Salt crystallization

• Transported in solution

• Water evaporates leaving solid salt

• Not necessarily cold related

6

Aggressive fluids

• Soft water or acids

• Dissolves calcium compounds

• Problem in:

• Pure water reservoirs

• Some streets

(Bourbon St., New Orleans)

• Industrial settings

7

Cold Weather

• Saturated Freezing and Thawing

• Thin flakes in paste

• Or deep cracks

8

Cold Weather

• De-icing salts

• Calcium oxychloride (MgCl2)

• Friedel’s Salt – Calcium-chloro-aluminate

• Ettringite

9

Cold Weather

• Deicing salts

• Oxychloride

• Causes paste expansion at ~40°F

• Separates aggregate from paste

10

Cold Weather

• Deicing salts

• Ettringite

• Accelerates saturation

11

Stark and Bollmann 2000

Moulzolf

Unstable Aggregates

• Alkali Aggregate Reaction• Chemical reaction with some aggregates,

paste alkali hydroxides and water• Expansion

Unstable Aggregates

• D-Cracking

• Some limestone aggregates hold water

• Freezes

13Marks and Dubberke 1982

Unstable Aggregates

• Popouts

• Porous aggregates

• Freezing

• Surface phenomenon

• May accelerate other

distresses

Slab deformation

• Shrinkage

• Cracking

• Warping

• Expansion

Overload

• Strength

• Support

Slabs on GradeWhat's critical Name What is the

cause

What does it look

like

Where does it

occur

Where does it start How far does it go Prevention Repair Photo Deteriratio

n Type

D-Cracking Water freezing in

coarse

calcareous

aggregate

containing clays

and or with a

pore system that

holds water

Cracks near joints,

often an a curve at

intersection of

joints

Full depth, cracks

are parallel to

free surface, mm

part

Bottom of a joint Up to ~18" from joint Avoid

deleterious

aggregates.

Reducing

maximum size

delays damage

As per ASR

Physical

Freeze thaw Water freezing in

saturated cement

paste with

inadeqaute air

void system

Thin flakes parallel

to free surfaces at

joints

Joints Where water is trapped A few mm Adequate air

void system,

low

permeability

Partial depth repair

Physical

Oxychloride MgCl2 reacts

with some paste

systems at about

40F to form

expansive

oxychloride

compounds

Cracks parallel to

joint faces,

sometimes up to 1"

from previous cut

or crack

Joints Tops of saw cuts or in the kerf Up to ~9" from joint High SiO2

cementitious

systems, low

permeability,

adequate air,

limit use of

MgCl2

Partial depth repair, Full

depth repair

Chemical

Salt Scaling Salts or ice

crystallizing

below the

surface, often

related to poor

surface finishing

Flakes peeling off

the surface of the

slab

Surface only Surface Can cover the whole slab Good finishing

procedures,

curing,

adequate air

void system,

low alkali

cement

Grind

Not sure

Popout Water freezing in

low density

aggregate

Divot above

aggregate particle

At the surface Joints Whole slab surface Avoid

deleterious

aggregates

None

Physical

Checial Reaction

Alkali silica reaction Reaction

between some

silicates in

aggregate, alkali

hydroxides in

pore solution

and water

Cracks mostly

parallel to

longitudinal joint

Full depth Near edges Whole slab surface Avoid

deleterious

aggregates,

low calcium

SCM, Lithium

comounds

Remove and replace, rubblize

and overlay, unbonded

overlay

Chemical

Joint Related

Only Surface

What do we measure now?

•Slump

•Strength

•Air

•Thickness

Performance Engineered Mixtures

• Seeking to:

Understand what makes concrete “good”

Specify the critical properties and test for them

Prepare the mixtures to meet those

specifications

Delivering concrete to

survive the environment

PEM

• A program to make

everyone’s life miserable

The Perfect Specification

You get paid after […] years

Or we do a test that predicts life

Slump?

Strength?

Why bother?

• Currently:

Focused on strength

Struggling to get durability

Wrestling with unintended

consequences

Why bother?

1967 2017

No. of ingredients Cement, water,

rock, sand, AEA

Add SCMs,

admixtures, int.

aggregates,

limestone…

Opening Weeks Days (or hours)

Curing Weeks Days

De-icing Sand, NaCl Other chlorides,

formates, acetates

Design life 20 years 100 years

Knowledge base In house Contracted out

What Really Matters?

• Transport properties (everywhere)

Resistivity / Formation Factor

• Aggregate stability (everywhere)

ASR AASHTO R80

D-Cracking IPA

• Strength (everywhere)

Flex or compression

What Really Matters?

• Cold weather resistance (cold locations)

Air

SAM

LTDSC

• Shrinkage (dry locations)

Prism

Ring

• Workability (everywhere)

VKelly

Box

A Better Specification

Measure the right things at the right time

Prequalification

–This is what will be delivered

Process control

–What was delivered will make it

Acceptance

–Delivered

as promised…

A Better Specification

A buffet of approaches (for the Agency)

Prescriptive: w/cm, paste volume

Performance: Formation factor

Equivalency?

A Better Specification

AASHTO PP84 published in March 2017

Guide Specification / Standard Practice

“Deemed to satisfy”

Avoids bonus discussion – that is local

Provisional = meaning we can

modify as we learn things

Construction

• QC should include

Unit weight

Calorimetry

Maturity

Strength development

Air void stability

And a response…

• Risk management

Test Methods

• Tests for those critical properties

VKelly / Box

SAM

Resistivity / Formation factor

Sorptivity

Ring / Dual ring

30

VKelly

• Measure initial slump (initial penetration)

• Start vibrator for 36 seconds at 8000 vpm

• Record depth every 6 seconds

• Repeat

• Plot on root time

• Calculate slope = VKelly Index

31

Box Test

• A test that examines:

Response to vibration

Filling ability of the grout (avoid internal voids)

Ability of the concrete to

hold an edge

Ley

Box Test

• The edges of the box are then removed and

inspected for honey combing and edge slump

Ley

Super Air Meter

• Reports air content and SAM number

• SAM number correlates well with freeze thaw

testing

Ley

Formation Factor

•F = Resistivity (bulk)

Resistivity (solution)

•Sample is fully saturated

•Solution resistivity = ~0.01 kΩ•cm

ASTM C1202 Classification Charge Passed (Coulombs) Resistivity (kΩ ∙ cm)a Formation Factor

High >4,000 <5.2 520

Moderate 2,000–4,000 5.2–10.4 520–1,040

Low 1,000–2,000 10.4–20.8 1,040–2,080

Very low 100–1,000 20.8–207 2,080–20,700

Negligible <100 >207 20,700

Sorptivity

•Assess capillary absorption (ASTM C 1585)

Condition sample for moisture content

Seal the sides and top

Measure mass increase over time with open

face immersed in water

Ring Test

•Assesses cracking risk

•Starts immediately

37

How do we proportion to achieve

design goals?

Workability Transport Strength Cold

weather

Shrinkage Aggregate

stability

Aggregate System Type, gradation - - - -

Paste qualityAir, w/cm, SCM

type and dose

Paste quantity Vp/Vv - - - -

Doing the Sums

The wonders of

a spreadsheet and a

solver function…

Aggregate System

Project Effect of gradation 9/29/2016

Materials Blue= Input Data

Red = Calculation Don’t touch!

Cementitious 472 Yellow = Output Don’t touch!

Coarse Agg 1" Black = Working Don’t touch!

Fine Agg Sand

Intermediate 3/8"

Sieve Analysis Data

Max nominal aggregate size 1.00 inch (0.75, 1.0 or 1.5)

Coarse 1" Fine Sand Intermediate 3/8" Combined Fineness

Percent Cum. Sieve Modulus

Percent mass 100.0 44.9 45.7 9.4 Passing Retained Retained

Sieve: % Pass % Mix % Pass % Mix % Pass % Mix % % %

2" 100.0 44.9 100.0 45.7 100.0 9.4 100.0 0.0 0.0

1 1/2" 100.0 44.9 100.0 45.7 100.0 9.4 100.0 0.0 0.0

1" 99.0 44.4 100.0 45.7 100.0 9.4 99.6 0.4 0.4

3/4" 73.9 33.2 100.0 45.7 100.0 9.4 88.3 11.7 11.3

1/2" 37.5 16.8 100.0 45.7 100.0 9.4 71.9 28.1 16.3

3/8" 19.7 8.8 100.0 45.7 90.2 8.5 63.0 37.0 8.9 0.0

# 4 3.5 1.6 98.6 45.1 21.6 2.0 48.7 51.3 14.4 1.4

# 8 0.8 0.4 88.3 40.3 2.0 0.2 40.9 59.1 7.8 11.7

# 16 0.4 0.2 68.9 31.5 0.6 0.1 31.7 68.3 9.2 31.1

# 30 0.4 0.2 37.0 16.9 0.4 0.0 17.1 82.9 14.6 63.0

# 50 0.3 0.1 9.7 4.4 0.4 0.0 4.6 95.4 12.5 90.3

# 100 0.3 0.1 0.8 0.4 0.3 0.0 0.5 99.5 4.1 99.2

# 200 0.3 0.1 0.2 0.1 0.3 0.0 0.3 99.7 0.3

2.97

Coarsness Factor 62.55 Power 45 least difference 31.0 Tarantula error 0.0 4.5

Workability Factor 40.89 Power 45 error 350.2 113.7

Adjustments 0.00

Adjusted Workability Factor 40.89 Fine 31.5 24-34 23.9 34.1

Coarse 31.5 >15 15

0

5

10

15

20

25

2"

1 1

/2"

1"

3/4

"

1/2

"

3/8

"

# 4

# 8

# 1

6

# 3

0

# 5

0

# 1

00

# 2

00

Perc

en

t R

eta

ined

Sieve

Tarantula

Greater than 15% on the sum of #8, #16 and #3024-34% of fine sand (#30-200)

0

20

40

60

80

100

2"11/2"

1"3/4"1/2"3/8"# 4# 8# 16# 30# 50# 100# 200

Perc

en

t P

assin

g

Sieve

Individual and Combined Gradations

C33

Sand

3/8"

1"

Combined

0

20

40

60

80

100

% P

assin

g

Sieve (^0.45)

Power 45

Mixture

Max Density

Limits

#50 #16 1" 2"1/2"#4#200

20

25

30

35

40

45

020406080100

Wo

rkab

ilit

y F

acto

r

Coarseness Factor

Shilstone Chart

IVSandy

IGap

II

IIISmall Agg

VCoarse

Measure Va

Does it Work?

• West Des Moines specification

• WI using the proportioning tool

• Other states looking at shadow evaluations in

2018

Are we there yet?

• A framework is in place

• The details need work

Ruggedness

Limits

Correlation with life

Training