powerpoint presentation · concrete mix design can be as simple as the time-honored 1:2:3 blend of...

3/9/2020

1

CONCRETE MIX DESIGN:

WHAT TO LOOK FORKEN HOVER, P.E.

CORNELL UNIVERSITY, ITHACA, NY

Description:

Concrete Mix Design can be as simple as the time-honored

1:2:3 blend of cement, sand, and stone. Or it can be as

complicated as 1, 2, 3, or 4 cementitious materials and up to

5 aggregate bins. But there are a few fundamental principles

that apply to all concrete mixes, and understanding those

principles can help you troubleshoot, modify, or adjust a mix

to produce the results that you need.

LEARNING OBJECTIVES

1. Understand why water-control is essential.

2. Know what to look for in aggregate size, shape, and textures

3. Recognize the advantages and disadvantages of supplementary cementitious materials and admixtures.

COPYRIGHT MATERIALS

This presentation is protected by US and International

copyright laws. Reproduction, distribution, display and

use of the presentation without permission of the

speaker is prohibited.

© Kenneth C. Hover, P.E.

THANK YOU FOR BEING HERE!

Ken Hover

Cornell University, Ithaca, New

York

[email protected]

I will be happy to say in the room afterwards

to respond to your questions and comments!

mailto:[email protected]

3/9/2020

2

• Objectives of Mix Proportioning Methods

• General Mixture Behavior

• ACI 211.1 thought process

• Caution Flags

• Performance is the goal

• Implications of phrase “Mix Design”

• Pick Any Two…

• Cannot change one parameter only

• Floyd Slate’s Rule:(“Everything affects everything else.”)

OUTLINE

Lots of ways to get there-- few basic principles for how

Proportions InfluenceConcrete Performance!




• Caution Flags



• Pick Any Two…



OUTLINE

Mix Design Objectives:

• Will meet fresh & hardened concrete specs.

• Can be consistently produced with available materials

• Can be placed, consolidated, and finished.

Generate a Trial Mixthat after testing andadjustment:

Concrete

Supplier

Designer /

Specifier

The Mix Design Process

Contractor

Sources of Mix Design Help

•Materials Suppliers

•Materials Consultants

•Test Labs

Plans, Specs, Stds., Codes→

• Max Agg size

• Max w/cm

• f’c, fr, Ec

• Exposures

Contract Documents

Concrete

Supplier

Designer /

Specifier

The Mix Design Process

Contractor

Mixture Submittal

• Materials

• Batch wts.

• w/cm

• Air

• Prob. f’c, fr, Ec

The Submittal

Mix Proportions Material Data Test Results

3/9/2020

3

Mix Submittal

From Concrete

Supplier:

•TO Contractor

•TO Architect

•TO Engineer

Green Hawaii Project

Mix Proportions

How is it done?

• Adjust from known mixes (most common)

• Local Experience

• Tradition (e.g., “Sacks”)

• Empirical methods (experience-based)

• Mathematical Computational methods

• Some combination of methods

Clairvoyance, Mysticism, Mythology

The number of concrete producers we have in the room right now…

…is the number of useful and unique methods for concrete mix designIn the room right now!

One available option: ACI 211.1




• Caution Flags



• Pick Any Two…



OUTLINE

Let’s take a look inside the concrete…

3/9/2020

4

Aggregate~5X Stiffer than Paste

Agg. Stress ~5X

Paste Stress

More Abrasion

Resistant

Denser

Stable Volume

PasteSoft, Porous,

Low Stiffness

Chemically Active,

(Sulfates, Alkalis, Acids)

Gives-off Heat

Absorbent, Freeze-thaw

Vulnerability

Shrinks

Paste Layer

Aggregates Paste

Aggregates can Move in Workable Concrete

LubricantFresh

Concrete

Cement paste as a lubricant for aggregate particles

Aggregates Paste

LubricantFresh

Concrete

Hardened

ConcreteAdhesiveHardened

ConcreteAdhesive

3/9/2020

5

Paste

Agg.

Gluing Blocks

Together…

Powdered Wood Glue

Powdered Wood Glue

Share Two Great Truths:

PowderedCement

“Just Add Water”

Start w/ fixed wt. of powdered adhesive

Flu

idity o

f G

lue

Amt. Water Added


Approximate quantity of mix water prior to adjustmentfor aggregate, air, or water reduction. First estimate based on slump and nominal max. aggregate size only. Adapted from ACI 211.1-91, Table 6.3.3

Nominal maximum aggregate size--in. (mm)

1-1

/2 in

. (3

8 m

m)

1 in

(25 m

m)

3/4

in (1

9 m

m)

1/2

in (

13 m

m)

3/8

in (

10 m

m)

2 in

(5

0 m

m)

24

0

26

0

28

0

30

0

32

0

34

0

36

0

38

0

40

0

42

0

Water Content (Lbs/CY)

0

1

2

3

4

5

6

7

8

Slu

mp (

inches)

BasWater00.grf

0

25

50

75

100

125

150

175

200

Slu

mp (

mm

)

15

0

16

0

17

0

18

0

19

0

20

0

21

0

22

0

23

0

24

0

Water Content (kg/m3)

Basic Water Requirement

Water Content

Flu

idity

3/9/2020

6

Aggregates Paste

LubricantFresh

Concrete

Hardened


ConcreteAdhesive

Bond Strength of the “Glue” or “Paste”

Glu

e B

ond S

trength

Amt. Water Added


Weight of Water

Weight of Cement + SCM

Type IType IASH

The higher the w/c or w/cm,

the more dilute the adhesive!

w/cm =

ASH

0.40 0.50 0.60 0.70 0.80

Water Cement Ratio

1000

2000

3000

4000

5000

6000

28-D

ay C

om

pre

ssiv

e S

tre

ngth

Approximate 28-Day Compressive Strengthas a function of Water/Cement Ratio.Adapted from ACI 211.1-91, Table 6.3.4(a)

Non Air-Entrained Concrete (about 2% air)

Air-entrained concrete (about 6% air)

Avg. 28-Day

Compression

Strength

ACI 211.1

Guide to

Proportioning

Amt. Water Added


Two Contrary Forces in

the Concrete Universe

Amt. Water Added

Increase powdered adhesive AND water at fixed ratio…

Strength

3/9/2020

7

0.30 0.40 0.50 0.60 0.70 0.80

1600

1200

800

400

Mic

rostr

ain

Water / cementAfter Nawy

30% Paste

20% Paste

40% Paste

Inches of shrinkage per 100 feet

2

1

1-1/2

1/2

WaterCement

AirSand

Coarse

Typical Volumetric Proportions

Paste

Paste

plus

Air

1.) Enough paste to coat all aggs. & air bubbles.

2.) Enough air to protect the paste (18% paste vol.)

3.) Paste is soft, absorbent, hot, and expensive

4.) Paste shrinks; rocks and sand usually don’t

25-30%

27-38%

Air2-8%

Mo

rtar

Co

ncre

te

1.) Need enough mortar to coat all coarse agg.

2.) Too much mortar clogs the pump

100%

50-60%

~50% ~60%RoundedGravel

Crushed Stone

Mortar Vol. Fraction

Pumping an

Over-Sanded Mix

Conc. Pump Pipe Paste Layer

Mortar Zone

Concrete/

Coarse

Aggregate

Zone

Pressure De-watering

of an Over-Sanded Mix

Leak in Pipe Joint Seal

Conc. Pump Pipe Pipe Joint

3/9/2020

8

Aggregates Paste

LubricantFresh

Concrete

Hardened


ConcreteAdhesive

How Much “Glue” or “Paste” Do We Need?

Thickness

and Viscosity

of Lubricating

Layer

Greased Bearings

Aggregates Paste

Aggregates can Move in Workable Concrete

Thickness and Viscosity

of Lubricating

Paste Layer

Thickness of Paste Layer Depends on:

Volume of Paste (Cement + Water)

And Size and Surface Area of Aggregates

How much glue

will we need?Depends on surface area

and glue thickness

Paste

Agg.

Paste Vol. FractionDepends on:

Aggregatesurface area

Thickness ofpaste layer

3/9/2020

9

How much Jam

do you need to

Jam a whole loaf

of bread?

Thick-Sliced

Thin-Sliced

Thin-Sliced Bread @ 3/8 inch

Thick-Sliced Bread @ 5/8 inch

Texas Toast @ ~ 1-1/2 inches

Jam-Thickness @ 3/16 inches

0%

10%

20%

30%

40%

50%

60%

Texas Toast Thick SlicedSandwich

Thin SlicedSandwich

Jam Volume / Toast Volume

Smaller Aggregate:

More paste required/CY conc.

Aggregates Paste

LubricantFresh

Concrete

Hardened


ConcreteAdhesive

Thicker paste layer promotes workability

Thicker paste layer may not increase strength

Smaller Aggregate:

More paste required/CY conc.(Cement wt. )

Less room for aggregate/CY conc.(Agg wt. )

Neville’s Cement Triangle

Hydration

HeatShrinkage

• Slump Loss• Setting• Strength• Stiffness

• Thermal Cracking• Strength Effects

• Curling• Cracking• Complaining

3/9/2020

10

0.30 0.40 0.50 0.60 0.70 0.80

1600

1200

800

400

Mic

rostr

ain

Water / cementAfter Nawy

30% Paste

20% Paste

40% Paste

Inches per 100 feet

2

1

1-1/2

1/2

Smaller AGG

Hig

he

r A

ir

Mo

re P

aste




• Caution Flags



• Pick Any Two…



OUTLINE

Proportioning by Principles

ACI 211.1

One of several combinations of fundamentals,

experience, tradition,and common sense

Not Code, Not Specification, Not Specifiable Document

Water

Cement

Air

SandCoarse

Designing for fixed volume ( 1 CY or 1 m3)

Backbone of the ACI 211.1 Thought Process:

Water

Cement

Air

SandCoarse

Start with Nominal Coarse Agg. Size:1

3/9/2020

11

About ¼ min.

pipe inside dia.

AGG-SIZE Rules

ARE

Code Provisions

AGG-SIZE Rules

ARE

Code Provisions

Cracking in Thin Concrete Overlays:

Small Aggregate → High Paste → High ShrinkageLarge Drying Surface / Concrete Volume Ratio

AGG-SIZE Rules

ARE

Code Provisions

Reality v. FantasyClosely-Spaced Reinforing: “Rebar Sieve”Small Aggregate → High Paste → High ShrinkageVibrator Clearance?

Water

Cement

Air

SandCoarse


Water req’d for Workability = f(slump,agg )2 Aggregate Size

and Surface Area

3/9/2020

12


Nominal maximum aggregate size--in. (mm)1-1

/2 in

. (3

8 m

m)

1 in

(25 m

m)

3/4

in (1

9 m

m)

1/2

in (

13 m

m)

3/8

in (

10 m

m)

2 in

(5

0 m

m)

24

0

26

0

28

0

30

0

32

0

34

0

36

0

38

0

40

0

42

0


0

1

2

3

4

5

6

7

8

Slu

mp (

inches)

BasWater00.grf

0

25

50

75

100

125

150

175

200

Slu

mp (

mm

)

15

0

16

0

17

0

18

0

19

0

20

0

21

0

22

0

23

0

24

0





1-1

/2 in

. (3

8 m

m)

1 in

(25 m

m)

3/4

in (1

9 m

m)

1/2

in (

13 m

m)

3/8

in (

10 m

m)

2 in

(5

0 m

m)

24

0

260

280

30

0

32

0

34

0

360

38

0

40

0

42

0


0

1

2

3

4

5

6

7

8

Slu

mp (

inches)

BasWater00.grf

0

25

50

75

100

125

150

175

200

Slu

mp (

mm

)

15

0

160

170

180

190

20

0

21

0

22

0

23

0

24

0



1-inch stone at 4-inch slump

“About 1-inch slump gain for 1 gallon per yard”



1-1

/2 in

. (3

8 m

m)

1 in

(25 m

m)

3/4

in (1

9 m

m)

1/2

in (

13 m

m)

3/8

in (

10 m

m)

2 in

(5

0 m

m)

24

0

260

280

30

0

32

0

34

0

360

38

0

40

0

42

0


0

1

2

3

4

5

6

7

8

Slu

mp (

inches)

BasWater00.grf

0

25

50

75

100

125

150

175

200

Slu

mp (

mm

)

15

0

160

170

180

190

20

0

21

0

22

0

23

0

24

0



3/4-inch stone at 2-inch slump

About 1-inch slump gain for 2 gallons per yard



1-1

/2 in

. (3

8 m

m)

1 in

(25 m

m)

3/4

in (1

9 m

m)

1/2

in (

13 m

m)

3/8

in (

10 m

m)

2 in

(5

0 m

m)

24

0

260

28

0

30

0

32

0

34

0

36

0

38

0

40

0

42

0


0

1

2

3

4

5

6

7

8

Slu

mp (

inches)

BasWater00.grf

0

25

50

75

100

125

150

175

200

Slu

mp (

mm

)

15

0

16

0

17

0

18

0

19

0

20

0

21

0

22

0

23

0

24

0



Gallons Water Added/CY to DOUBLE the slump

2.2 2.2 2.2 2.6 2.8 3.4

Increasing Water Content is not the only way to increase slump

But, adding water is the:

Cheapest wayQuickest way

Most readily available waySometimes the only way on-site

Most effective way to: lower strength & durability, and increase shrinkage

-30% -25% -20% -15% -10% -5% 0% 5% 10% 15% 20% 25% 30%

Percentage Adjustment in Water Content

Aggregate Shape and Texture (-5 to +5%)

Combined Aggregate Grading (-10 to + 10%)

Air Entrainment (-10 to 0%)

Normal Range Water Reducer (-10 to -5%)

Mid-Range Water Reducer (-15 to -8%)

High-Range Water Reducer (-30 to -12%)

Mineral Admixtures (-10 to +15%)

Other Factors (-10 to +10%)

-30% -25% -20% -15% -10% -5% 0% 5% 10% 15% 20% 25% 30%

Decreased Water Demand Increased Water Demand

fly ash silica fume

round, smooth flat, elongated, rough

well-graded gap-graded

6-10% air 1-3% air

coarse cement, high w/cm, cold conc. fine cement, low w/cm, hot conc.

high dose low dose

high dose low dose

high dose low dose

Additional

Factors

Influencing

Workability

Suggesting %

increase or

decrease in

Water Demand

(relative to data

on previous

graphs)

3/9/2020

13

Water-Addition

Nature’s Own Plasticizer!

Strength-Reducer

Durability-Reducer

Surface-Softener

Shrinkage-Increaser

Is there a

way to

gain

workability,

and maintain

quality?Fabric

Softener

Technology

Water

Reducing

Admixtures

•Normal

•Mid-Range

•High-Range

Cement grains dispersed in water

Mutual attraction of charged particles

3/9/2020

14

Water-Reducer Molecule

No water

reduction

5% water

reduction

10% water

reduction

Same Benefit: Mid-Range Water-Reducer or Changing agg. from 19 to 38 mm

3/9/2020

15

15% water

reduction

10% Effective Mid-Range Water as a Slump Increasing Admixture

Effective as

10% water

Addition

-30% -25% -20% -15% -10% -5% 0% 5% 10% 15% 20% 25% 30%

Percentage Adjustment in Water Content

Aggregate Shape and Texture (-5 to +5%)

Combined Aggregate Grading (-10 to + 10%)

Air Entrainment (-10 to 0%)

Normal Range Water Reducer (-10 to -5%)

Mid-Range Water Reducer (-15 to -8%)

High-Range Water Reducer (-30 to -12%)

Mineral Admixtures (-10 to +15%)

Other Factors (-10 to +10%)

-30% -25% -20% -15% -10% -5% 0% 5% 10% 15% 20% 25% 30%

Decreased Water Demand Increased Water Demand

fly ash silica fume

round, smooth flat, elongated, rough

well-graded gap-graded

6-10% air 1-3% air

coarse cement, high w/cm, cold conc. fine cement, low w/cm, hot conc.

high dose low dose

high dose low dose

high dose low dose

Reasons that

slump is not a

consistent or

reliable indicator

of water content.

At a constant

water content, a

change in any

one or more of

these factors will

produce a

different slump.

Water

Cement

Air

SandCoarse

Water Wt. / Density = Water Vol. /CY or /m3)

Batch Wt. of Water = f(slump, agg size)2

Water

Cement,CM

Air

SandCoarse


Required Total Cementitious Materials3

Find required w/cm3aA Deeper

LookInside the concrete:

3/9/2020

16

Velcro

Water / Cement Ratio

W / C = 0.70


W / C = 0.54


W / C = 0.42


W / C = 0.33

3/9/2020

17

3-Point Curve

0.30 0.40 0.50 0.60 0.70 0.80 0.90

w/cm Ratio

2000

3000

4000

5000

6000

7000

Ave

rag

e 2

8-d

ay C

om

pre

ssiv

e S

tre

ng

th (

psi)

0.40 0.60 0.80

2000

3000

4000

5000

6000

7000

ACI 211 Data, Air 2% or less

For 6-Sack

Mix lose

150 psi per

gallon/CY

ACI 211 Data, Air 2% or less

0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8

Water / Cement

0

1E-010

2E-010

3E-010

4E-010

5E-010

Pe

rme

ab

ility

m/s

ec/u

nit g

rad

ien

t

10

20

30

40

50

Ave

rag

e 2

8-D

ay C

om

pre

ssiv

e S

tre

ng

th (

MP

a)

Estim

ated Strength, N

on-Air E

ntrained

Estimated Strength, Air-Entrained

38 mm

Agg.

AC

I 3

18

Co

de

Lim

its

for

Co

rro

sio

n P

rote

ctio

n

AC

I 3

18

Co

de

Lim

its

for

Fre

eze

-Th

aw

Pro

tectio

n

Range of Values

U.S.B.R.

Building Code Requirements

All 50 States and

All U.S. Territories

Water

Cement,CM

Air

SandCoarse


Required Total Cementitious Materials3a

3/9/2020

18

Water

Cement,CM

Air

SandCoarse

(CM Wt./CY) / Density = CM Vol. /CY (or /m3)

CM Wt.= Water Wt. / (w/cm)

Definition: (w/cm) = (wt. water) / (wt. cm)

Pick Any Two!Somebody

has to pay Extrafor the Third One

This DeterminesWorkability

This DeterminesStrength and Durability

This DeterminesCost, Shrinkage, Heat, Carbon

Footprint, & Chemical Reactivity

160

180

200

220

240

260

280

300

320

340

360

380

400

420

440

460

480

500

Adjusted Water Content (lb/CY)

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

Ce

me

nt

Co

nte

nt

(lb

/CY

)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

Ce

me

nt

Co

nte

nt

(Sa

ck

s/C

Y)

0.40

0.50

0.60

0.70

Water/Cement Ratio

Cement

Wt.

=Water Wt.

w/c

A

Great

Truth!

Incr.

Workability

Dec

rea

se

w/c

m

Off-set with WRA,

Air, Grad., SCM

Incr

ease

to

tal

cm

16

0

18

0

20

0

22

0

24

0

26

0

28

0

30

0

32

0

34

0

36

0

38

0

40

0

42

0

44

0

46

0

48

0

50

0


3

4

5

6

7

8

9

10

11

12

13

14

Pa

ste

Vo

lum

e (

ft3/C

Y)

10

15

20

25

30

35

40

45

50

55

Pa

ste

Vo

lum

e F

rac

tio

n (

% o

f C

on

c. V

ol.)

0.70

0.40

0.50

0.60

Low Shrinkage Zone

High Shrinkage Zone

Water/Cement Ratio

Incr.

Workability

Dec

rea

se

w/c

m

Off-set with WRA,

Air, Grad., SCM

Off-set

with SRA

Incr

ease

Pa

ste

& S

hri

nk

ag

e

Water

Cement,CM

Air

SandCoarse


Cement + Supplementary Cementitious Materials3b

Supplementary Cementitious Materials: “Reactive Silica”

•Fly ash

•Ground Granulated

Blast Furnace Slag

•Silica Fume

•Metakaolin

•Natural Pozzolans

3/9/2020

19

Volcanic Ash

(Rapid Cooling)

Liquid Drops of

melted Silicon

Dioxide Solidify to

Glass

Pozzolan Production (Schematic)

Pozzolans are

“Reactive Silica”

• Glass

• React with Calcium Hydroxide

• Given:

HEAT

WATER

TIME

Active Ingredients:

Portland Cement

Silicon Dioxide

Calcium Oxide

Aluminum Oxide

Iron Oxide

Portland Cement

TYPE I / IIActive ingredients: SiO2, CaO, Al2O3, Fe2O3

Ithaca

Cement Co.

Active Ingredients:

Flyash

Silicon Dioxide

Calcium Oxide

Aluminum Oxide

Iron Oxide

Flyash

TYPE FActive ingredients: SiO2, CaO, Al2O3, Fe2O3

Ithaca

Flyash Co.

3/9/2020

20

Portland Cement Coal Fly Ash Silica Fume

Water

Cement

Air

SandCoarse


Required Air Content

Table 19.3.3.1—Total air content for concrete exposed to cycles of freezing and thawing

Nominal maximum

aggregate size, in.

Target air content, percent

F1 F2 and F3

3/8 6 7.5

1/2 5.5 7

3/4 5 6

1 4.5 6

1-1/2 4.5 5.5

2 4 5

3 3.5 4.5

4

Smaller AGG

Hig

he

r A

ir

250 260 270 280 290 300 310 320 330 340 350

Water Content lb/CY

1

2

3

4

5

6

7

8

9

10

11

Re

qu

ire

d A

ir C

on

ten

t in

Co

ncre

te (

%)

90 95 100 105 110 115 120

Water Content kg/m3

Average Bubble Radius = 7 mils





= 430 in2 / in

3

= 500 in2/in

3

= 600 in2/in3

= 750 in2/in3

= 1000 in2/in3

w/c = 0.45

Ave

rag

e B

ub

ble

Ra

diu

s

w/c = 0.45

270 lb/CY

= 750 in2/in3

3.0% air OK!

Water

Cement

Air

SandCoarse

Air Vol. = Air% x Concrete Vol. / CY or /m3

Required Air Volume

Since aggregate is less expensive, less-porous, less reactive *ASR, harder, higher modulus, and less shrinkable…

How much can we use?

3/9/2020

21

Water

Cement

Air

FineCoarse

Volagg = Total Vol- Volw – Volcm - Volair

Required Aggregate Volume-Typical

Concrete producer usually knows

best blend of local agg sizes.

5




• Caution Flags



• Pick Any Two…



OUTLINE




• Caution Flags



• Pick Any Two…



OUTLINE

Trial & Error Process: Batch / Evaluate / Adjust / Batch Again…

Field experience with job-materials ALWAYS BEATS

Graphs, charts, and tables


1-1

/2 in

. (3

8 m

m)

1 in

(25 m

m)

3/4

in (1

9 m

m)

1/2

in (1

3 m

m)

3/8

in (

10 m

m)

2 in

(5

0 m

m)

24

0

26

0

28

0

30

0

32

0

34

0

36

0

38

0

40

0

42

0

Basic Water Content (lb/CY)

0

1

2

3

4

5

6

7

8

Slu

mp

(in

che

s)

160

200

240

280

320

360

400A

dju

ste

d W

ate

r C

on

ten

t (l

b/C

Y)

24

0

26

0

28

0

30

0

32

0

34

0

36

0

38

0

40

0

42

0

Basic Water Content (lb/CY)

15.00 20.00 25.00 30.00 35.00 40.00 45.00

Paste Volume (% of Total Concrete Volume)for OPC Mixture

160

200

240

280

320

360

400

Adju

ste

d W

ate

r C

onte

nt

(lb

/CY

)

4 5 6 7 8 9 10

11

12

Paste Volume (ft3/CY) for OPC


Adjusted Water Requirement

1.2

Water Reduction Factor

1.1

1.0

0.9

0.8

0.7

0.70w/c 0.60 0.50 0.40

Paste Vol. for OPC

High Shrinkage Zone

16

0

18

0

20

0

22

0

24

0

26

0

28

0

30

0

32

0

34

0

36

0

38

0

40

0

42

0

44

0

46

0

48

0

50

0


3

4

5

6

7

8

9

10

11

12

13

14

Pa

ste

Vo

lum

e (

ft3/C

Y)

10

15

20

25

30

35

40

45

50

55

Pa

ste

Vo

lum

e F

rac

tio

n (

% o

f C

on

c. V

ol.)

0.70

0.40

0.50

0.60

Low Shrinkage Zone

High Shrinkage Zone

Water/Cement Ratio




• Caution Flags



• Pick Any Two…



OUTLINE

“…intended for guidance… Reference…shall not be made in the Project Documents.”

“…methods provide a first approximation of proportions intended to be checked by trial batches… and adjusted, as necessary.”

3/9/2020

22

We call this “Mix Design” But is it really “Design?”

YES—IN the sense of a creative, decision-making process with clearly defined input and output.

YES—IT can be a challenging intellectual activity, requiring training in industrial guidelines.

No--in the sense of codified procedures with analytically demonstrated, appropriate solutions.

It is still primarily a trial-and-error process. Predicted outcomes have to be verified with test results. No Guaranteed Methods!

We do not have to Load-Test

every structure we design.

Trial and Error Process:Batch / Evaluate /Adjust / Batch Again…

We do have to test

every single “Trial Batch”




• Caution Flags



• Pick Any Two…



OUTLINE

Workability w/cm Total cm

Dictates water content &

admixtures

Dictates strength& durability

Dictates shrinkage, heat, alkalis, CO2 and

Cost

“Higher is Better” “Lower is Better” “Lower is Better”

High Low High cm

Low Slump Low Low

High High w/c Low

Slump w/cmTotalcm

Pick Any Two…

But somebody has to pay extra for the third!

3/9/2020

23




• Caution Flags



• Pick Any Two…



OUTLINE Fixed Volume

System

Cannot Change only

one component




• Caution Flags



• Pick Any Two…



OUTLINE

Everything

Affects

Everything

Else!--F.O. Slate



1-1

/2 in

. (3

8 m

m)

1 in

(25 m

m)

3/4

in (1

9 m

m)

1/2

in (

13 m

m)

3/8

in (

10 m

m)

2 in

(5

0 m

m)

24

0

260

28

0

30

0

32

0

34

0

36

0

38

0

40

0

42

0


0

1

2

3

4

5

6

7

8

Slu

mp (

inches)

BasWater00.grf

0

25

50

75

100

125

150

175

200

Slu

mp (

mm

)

15

0

16

0

17

0

18

0

19

0

20

0

21

0

22

0

23

0

24

0



Water, cm, CO2, Air, Shrinkage, Cost

Source: ACI 211.1

Smaller Aggregate

• Principles govern performance

• Mixes based on Unique Characteristicsof Local Materials

• When you know what to look for, youcan:

• Track behavior of your mixes andmaterials

• Calibrate general relationships

• Make predictions

CONCLUSIONS

3/9/2020

24

THANK YOU FOR BEING HERE!

Ken Hover

Cornell University, Ithaca, New

York

[email protected]

I will be happy to say in the room afterwards

to respond to your questions and comments!

Questions?

Please complete the session evaluation on the CONEXPO –CON/AGG Mobile App. This is the same place you can log Professional Development Hours (PDH).

mailto:[email protected]