Concrete Mix Design - precast.orgconcrete placement on long term concrete durability in Japan, particularly in complex, thin walled sections in heavily reinforced buildings where achieving

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Marcus Barnett, Hamilton Kent

Concrete Mix Design


CONCRETE MIX DESIGN

• Wet Cast (Slump)

• Dry Cast (no Slump)

• SCC (Spread)(Flowable)


WATER, CEMENT, & AGGREGATE

• As the water to cement ratio increases, the strength of a concrete mix decreases.

• As the surface area of the aggregate increases the more water will be needed to maintain a given slump.

• Coarser Surface Texture

• Particle Shape

• Particle Size Distribution

• As the air content increases, the strength of the concrete decreases.

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It’s a calculation:

• w/c ~ lbs. of water / lbs. of cement• w/cm ~ lbs. of water / lbs. of cementitious

WATER / CEMENTITIOUS RATIO

Often when w/c is discussed its really

w/cm that is intended as the reference

= Water cement ratio

Water needs to be drinkable or meet ASTM 1602

0.45 expressed as decimal45 lbs of

water

100 lbs of

cement


• Specific Gravity

• The relative density of a material compared to water

• The ratio of a material’s weight to the weight of an equal volume of water

• Bulk specific gravity (SSD):

• Used to determine the “solid volume” (absolute volume) of a material going into concrete

• It is determined by submerging the material in water for 24 hours in order to fill any permeable voids

TERMINOLOGY


SPECIFIC GRAVITY

Stone: Specific Gravity = 2.70

Water: Specific Gravity = 1.00

Same Volume, but 2.70 Times More Mass

Cement – 3.15

Steel – 7.85

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CALCULATIONS FOR SSD BULK SPECIFIC GRAVITY

Coarse Aggregate Using Basket Suspended in water:

B / (B - C) = SSD Bulk Specific Gravity

where:B = weight of SSD sample in airC = weight of SSD sample in water

Field Calculation of SSD Bulk Specific Gravity:

Weight of Aggregate @ SSD

Weight of equal volume of water displaced= Specific Gravity

1245 grams of SSD aggregate=

469.81 grams of water displaced2.65


Concrete Mix Design

• It’s always about volume!

• What is absolute volume?


Relationship of Materials to Volume

• specific gravity of Type I Cement = 3.15

• specific gravity of water = 1.0

• 1 gallon of water weights 8.33 pounds

• water weights 62.4 pounds / cubic foot

WHAT IS ABSOLUTE VOLUME?

Pounds of Material

S.G. X 62.4

= Absolute Volume


BASIC CONCRETE MIX DESIGN

MaterialsPounds of

materialS.G.

Abs

Volume

Cement 667 3.15 3.39

-

Total Cementious 667

Miller Stone 1590 2.6 9.80

Evert Sand 1242 2.65 7.51

Water 300 1 4.81

Air 5.5% 1.485

Total 3799 27.00

w / cm 0.45 Unit Wt. 140.72



MaterialsPounds of

materialS.G.

Abs

Volume

Cement 667 3.15 3.39

-



Evert Sand 1242 2.65 7.51

Water 300 1 4.81

Air 5.5% 1.485

Total 3799 27.00

w / cm 0.45 Unit Wt. 140.72

667

3.15 X 62.4

1590

2.60 X 62.4

1242

2.65 X 62.4



MaterialsPounds of

materialS.G.

Abs

Volume

Cement 667 3.15 3.39

-



Evert Sand 1242 2.65 7.51

Water 300 1 4.81

Air 5.5% 1.485

Total 3799 27.00

w / cm 0.45 Unit Wt. 140.72

300

1.0 X 62.4

0.055 X 27

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WATER / CEMENT RATIO = W/C

MaterialsPounds of

materialS.G.

Abs

Volume

Cement 667 3.15 3.39

-



Evert Sand 1242 2.65 7.51

Water 300 1 4.81

Air 5.5% 1.485

Total 3799 27.00

w / cm 0.45 Unit Wt. 140.72

Water / Cement

300

667 Weight

(mass)


DENSITY (UNIT WEIGHT)

MaterialsPounds of

materialS.G.

Abs

Volume

Cement 667 3.15 3.39

-



Evert Sand 1242 2.65 7.51

Water 300 1 4.81

Air 5.5% 1.485

Total 3799 27.00

w / cm 0.45 Unit Wt. 140.72

Design (unit weight)

3799

27.0

@ 1.5% air, unit weight (density) = 147.26


MIX DESIGN WITH CEMENT & FLY ASH

133 lbs. fly ash

667 Total lbs. Cm

= 20% ash

It’s about volume!

Note: lower water

demand due to fly ash

- for same slump



Proportion the mix to

yield 27 ft3 … but how

much sand, stone …

what ratio?

Sand / Aggregate

ratio is by volume





Volume without

aggregate = 8.72

27.00 - 8.72 =

18.28 ft3 required


SAND TO AGGREGATE RATIO

Volume of Sand

Volume of Total Aggregate =

Manufactured Concrete Pipe

60-80% Packerhead Mix

45-65% Dry Cast

Rules of thumb ?

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CALCULATING SAND & STONE TO YIELD 27FT3 OF CONCRETE

•Assume this concrete needs to have Sand / Aggregate ratio of 0.42

Volume of Sand = 7.68 ft3

Volume of Sand

18.28 ft3= 0.42

Total Volume of Aggregate

= 0.42Volume of Sand


CALCULATING POUNDS OF SAND

Pounds of Material

S.G. X 62.4

= Absolute Volume

Evert Sand S.G. = 2.65

Pounds of Material (sand)

2.65 X 62.4

= 7.68 ft3

Sand = 1270 lbs


CALCULATING POUNDS OF STONE

Pounds of Material

S.G. X 62.4

= Absolute Volume

Miller Stone S.G. = 2.60

Pounds of Material (stone)

2.60 X 62.4

= 18.28 - 7.68 = 10.60 ft3

Stone = 1720 lbs

Total Aggregate Volume

Sand Volume


SSD MIX DESIGN


AGGREGATE MOISTURE

Bone Dryor

Oven Dry

Air Dry

Saturatedand

Surface Dry

Moist

Absorbed moisture

(absorption)

Free moisture(moisture content)

SSD (ideal)

Add Water

Subtract

Water


MOISTURE ADJUSTMENTS

Moisture Management is Critical (How much free water)

Total aggregate moisture = aggregate absorption + free water

(TM = absorption + free water)

3.0% = 1.5% + free water, (% free water = 1.5%)

0.015 X 1720 = 26 pounds of free water on the Stone

STONE

Sand

5.5% = 0.85% + free water, (% free water = 4.65%)

0.0465 X 1270 = 59 pounds of free water on the Sand

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WATER ADJUSTMENT

If 26 + 59 pounds of water rides in on the aggregates you must take that amount of water out of the BATCH water.

Design water

Water on aggregates

Batch water

295

-85

210


MOISTURE ADJUSTMENT

Total moisture = Free moisture + Aggregate absorption

SSD & batch totals

will be the same


Weight (LBS) MIX COMPONENT

SPECIFIC GRAVITY

VOLUME (CU FT)

CEMENT

POZZOLON

WATER

AIR

COARSE AGG (CA)

FINE AGG (FA)

TOTALS

W/C RATIO UNIT WEIGHT


6 Bag Cement Mix

25% flyash Type F / SG 2.45

.45 w/c ratio

6 % Air

45 % sand ratio

Sand SG. 2.65

Stone SG 2.70


• Portland Cement Association (PCA)

5420 Old Orchard Road

Skokie, IL 60077-1083

847 966-6700 PH

847 966-8389 FX

Info @ cement.org


ADMIXTURES

Admixtures is defined as a material, other than,

• Cement

• Water

• Aggregate

• That is used as an ingredient of concrete and is added to the batch immediately before or during mixing.

• Admixtures are used to modify the properties of ordinary concrete so as to make it more suitable for any situation.

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COMPRESSIVE STRENGTH

0

1500

3000

4500

6000

7500

9000

0 1 3 7 14 21 28

TIME (DAYS)

CO

MP

RE

SS

IV

E

ST

RE

NG

TH

(P

SI)

HIGH SLUMP

CONCRETE

W/WATER

NO-SLUMP

CONCRETE

SUPERPLASTICIZED

CONCRETE


“Self Consolidating Concrete”

Let it Flow..............


Self Consolidating Concrete(SCC)

• SCC - what is it, where did it come from

• SCC Mix Design- Applications- Raw materials

• Benefits of SCC- Properties- SCC Test Methods- Producing SCC – examples- Case Studies


Self Consolidating Concrete(SCC)

“ A highly flowable, yet stable concrete that can spreadreadily into place and fill the formwork withoutundergoing any consolidation and without undergoingsignificant separation”

Khayat, Hu and Monty


SCC has unique benefits over flowing concrete:

Self Placement: the need for vibration can be eliminated because

SCC is highly flowable concrete that will change shape under its

own weight to self-level and self consolidate within formwork

No Segregation: SCC is a flowable, yet highly cohesive material

with no segregation and significantly reduced bleeding

No Blocking: SCC can pass freely through narrow openings and

congested reinforcement without aggregates “blocking” behind obstructions and stopping the flow of concrete

Self Consolidating Concrete


SCC History

Japan

• SCC was developed from technologies used in underwater concreteplacement in 1988 by Prof. Okamura at the University of Tokyo.

• In Japan, use of viscosity modifiers as a cohesive aid to enable SCCproduction was researched by academics in conjunction with majorcontractors, who then further developed their own systems and testmethods for SCC.

• The initial driver for SCC was concern over the effect of poorconcrete placement on long term concrete durability in Japan,particularly in complex, thin walled sections in heavily reinforcedbuildings where achieving proper consolidation was a major difficulty

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SCC History

Europe

• SCC has also been adopted in Europe, particularly Scandinavia which is now widely regarded as being the most advanced in SCC adoption.

• In Europe the availability of fine powder materials, such as limestone powder and pozzolans, led to the development of SCC based on the “powder method”. Viscosity modifiers are also used to produce consistent, reliable SCC.

• European motivations for using SCC include increased potential for reduced vibration, and automation in precast factories, thus increasing worker productivity and limiting vibration health and safety issues


Self Consolidating ConcreteMix Design


Raw Materials

• Cementitious Types and Volumes

– High fine powder content is required for most SCC mixes (these can include inert powders such as limestone powder)

– Cementitious contents can be reduced for less demanding applications

– Use of pozzolans (GGBF slag or flyash) is highly recommended


Raw Materials

• Water/Cementitious Ratio

–Water content is determined by flow requirements, and not by strength (SCC mixes are overdesigned for most applications)

– Typically under 0.40 w/c ratio is recommended for high performance SCC mixes. W/C ratio can be increased where appropriate


Raw Materials

• Aggregates (Combined)

– Use non gap-graded materials

– Moisture contents must be known and controlled


MOISTURE ADJUSTMENT

Total moisture = Free moisture + Aggregate absorption

SSD & batch totals

will be the same

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8 Bag Cement Mix

25% flyash Type F / SG 2.45

.40 w/c ratio

5 % Air

50 % sand ratio

Sand SG. 2.65

Stone SG 2.70


Self Consolidating ConcreteBenefits


Benefits

• Eliminate vibration

– Reduce noise levels and improve the plant environment for employees and neighbors

– Improve labor safety and productivity with self leveling, self consolidating concrete that requires less manpower to place and finish

– Reduce capital cost and maintenance on formwork and vibration equipment


• Improve concrete consolidation

– Improve consolidation around dense reinforcement– Fill areas impossible to reach with internal poker vibrators

• Improve concrete finish

– Reduce repairs and sack rubbing required

• Increase flexibility in design and orientation of formwork

– Place concrete in unique shaped molds that could not be used for conventional concrete

Benefits


Added Productivity

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Self Consolidating Concrete

Applications:

• Horizontal elements

• PC/PS elements - Dense Reinforcement - Spacingless than 1.5 inches (40 mm)

• Highly reinforced PC/PS elements - ReinforcementSpacing greater than 1.5 inches (40 mm)

• Architectural Concrete


Self Consolidating ConcreteProperties


Hardened Properties• Compressive and Tensile Strength

– Early strength (1 day) similar to slightly higher than a mix with the same cement content and water to cement ratio

– 28 day strength similar to higher than a mix with the same cement content and water to cement ratio

• Durability (Freeze/Thaw testing ASTM C666)

– Similar to conventional super plasticized concrete– Despite high flow ability SCC concrete can be air entrained and meet

requirements for freeze-thaw durability.

• Shrinkage (Length Change ASTM C157)

– Numbers range from 0.02 to 0.05, similar to other high cementitious mixes


Self Consolidating ConcreteTest Methods


Testing

• Visual Stability Index (VSI)

- Based on slump flow test – ASTM C 1611

- Provides a means for assessing segregation prior to placement

- A qualitative & a highly subjective parameter

• Column Segregation Test - ASTM C1610

• Penetration Test – ASTM C 1712

Current Test Methods for Segregation Resistance of SCC

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Testing

• Provides a means for assessingsegregation prior to placement

• A qualitative & a highly subjectiveparameter

Visual Stability Index (ASTM C1611)


Visual Stability Index (VSI)

0 0.5 - 1

31.5 - 2

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CONCRETE MIX DESIGN WEIGHT / VOLUME CALCULATIONS


SPECIFIC GRAVITY

VOLUME (CU FT)

CEMENT

POZZOLON

WATER

AIR

COARSE AGG (CA)

FINE AGG (FA)

TOTALS


CONCRETE MIX DESIGN WEIGHT / VOLUME CALCULATIONS


SPECIFIC GRAVITY

VOLUME (CU FT)

CEMENT

POZZOLON

WATER

AIR

COARSE AGG (CA)

FINE AGG (FA)

TOTALS


Documents

Concrete Mix Design - precast.orgconcrete placement on long term concrete durability in Japan, particularly in complex, thin walled sections in heavily reinforced buildings where achieving