concrete Mixture Optimization - Contek Shilstone Mixes... · Concrete Mixture Optimization ......

Concrete Mix Design-The New Technology

Systech 2008 Customer Conference

Presented by James M. Shilstone, Jr.

Shilstone/Day Technologies, Inc. 1 http://www.shilstone.com

Concrete

Mixture

Optimization

2010 Concrete Optimization Technology Conference

Concrete mixtures fit a need

� Structural needs

� Service life conditions

� Aesthetics

� Construction requirements

� Locally available materials

� Cost effective

� Environmental considerations

Specs as a laundry list

� Low slump

� Low w/cm

� Low shrinkage

� High strength

� Low permeability

� Non-segregating

� Freeze-thaw resistant

√

√

√





Specs in balance

Low w/cm

Low permeablilty

No cracks

Higher cement

More heat

Greater shrinkage

Higher cost

Blind Men & the Elephant

Duff AbramsSelecting Mixture Proportions

� Select max agg

� (Choose air content)

� Determine best blend of coarse and fine agg for minimum water

� Determine water

� Determine cement

� Proportion pozzolans

� Determine combined aggregate





Paste & Aggregate

� Paste

� Strength, durability

� Cost

� Aggregate

� Need for paste

� Concrete “infrastructure”

� Combined concrete

� All the parts work together

Optimizing Aggregate

� Grading approaches� Coarseness Factor, Mortar Factor

� Individual % retained, % passing, .45 Power

� Combined Fineness Modulus

� Mix Suitability Factor and Specific Surface

� Minimum voids� Particle packing / ternary diagram

� Dewar minimum voids

� Rheology� Viscosity and shear

� deLarrard

Optimum aggregate combination

2500

3000

3500

4000

4500

5000

Percent coarse aggregate

PS

I

0.45

0.5

0.55

0.6

0.65

0.7

W/C

Ra

tio





Coarseness Factor Chart

Coarseness Factor

1990’s Aggregate Distribution





WATER DEMAND

RESULTS OF GAP GRADING

HAYSTACK - “Optimum”





C33 - 1923 Graded Mix

Colorado Bridge Deck

Wisconsin Univ/DOT ResearchOptimized Aggregate Conclusion

� Compressive strength - plus 10 to 20%

� Air entraining agent - minus 20 to 30%

� Potential water demand - minus 20 to 30%

� Potential high spacing factor for air voids

� Reduced segregation and higher densityfollowing extended vibration





Wisconsin DOT/UnivEffects of particle distribution on segregation

8/18 Grading Spec

Air Force Findings





Workability Zones

Mortar Requirements

MORTAR NEEDS(Approximate)

� 52.0 for a 5” diameter high pressure pump with a long stroke (gravel).

� 54.0 to 55.5% for 5” diameter high pressure pump with long stroke (cubical crushed).

� 55.5 to 57% for lighter, but good, pumps (crushed stone).

� 60% for 1/2” sharp edged crushed stone with a 2” line.

� 63.3 to 63.8% for topping mixes.





.45 Power Chart

Specific Surface

33.5846SS

3.60153.431050.69#200

7.80039.63814.12#100

9.169815.815813.75#50

5.900715.133929.56#30

4.808717.812744.69#16

0.925.751662.5#8

0.66488.31868.25#4

0.22525.63476.563/8"

0.27486.87482.191/2"

0.210289.063/4"

0.01880.94299.061"

0011001-1/2"

SS value%rtdFactor% PassingSieve

Mix Suitability Factor

� MSF = f(SS, % air, cement)� MSF Targets

� < 16 – Too harsh� 16-20 – Harsh, zero slump mixes� 20-22 – Industrial slabs� 22-25 – Structural concrete� 25-27 – Pumpable concrete� 26-28 – Pumpable lightweight� 27-31 – Flowing concrete





Use a variety of methods

The Problem

None of these methods address particle shape and texture.

Proportion coarse agg –ACI 211







Developed in 1938 for concrete placed without vibrators

Particle packing





Concrete Rheology

Optimizing paste

Minimize the paste, but make it high quality

Lower w/c = less permeable concrete?

3000

3500

4000

4500

5000

5500

6000

0.35 0.4 0.45 0.5 0.55 0.6 0.65

� Lower w/c means more cement

� More cement means more heat

� More heat causes thermal shrinkage

� More cement causes more autogenous shrinkage

� More shrinkage means more cracks





High w/c Ratio

High w/c Ratio

Low w/c Ratio





Low w/c Ratio

Very Low w/c Ratio





Real-life concrete

0

0.5

1

1.5

2

2.5

0 0.2 0.4 0.6

w/c ratio

paste volume

Unhydrated Hydrated Cement

Cement efficiency

400 450 500 550 600 650 700

Plain cement Cement + AdmixCement + Ash Cement + Admix + Ash

Cementitious particle size

� Fly ash – 1–200 µm

� Cement – 10-50 µm

� GGBFS – 5-30 µm

� Silica Fume – 0.1-0.3 µm

� Particle size distribution matters





Hydration of Portland Cement

Cement + Water

C-S-H + Ca(OH)2 + Other

C

C

C

C

C

C

C

Hydration of Portland Cement

Pozzolanic Reaction in Concrete

Ca(OH)2 + Pozzolan

more….. C-S-H





C C

CC

C

Effect of Pozzolanic Reaction

Marin Airport - PR

500

1500

2500

3500

4500

5500

6500

7500

8500

5 sk 6 sk 7.5 sk

Cement Cem + ash

Determining cement-ACI 318

•Best – use historical test data and determine

appropriate overdesign,

then determine cement

content

•Alternate – produce lab

batches to develop w/c vs

strength curve and select

appropriate cement content

•If no data available, use

“expertise”





ACI 318 Overdesign Criteria

�Moving average of 3fcr = (f’c + 2.33s)/√3 = f’c + 1.28s

� Individual <= 5000 psifcr = (f’c – 500 psi) + 2.33s

� Individual > 5000 psifcr = (0.90 *f’c) + 2.33s

Paste Content

Paste = everything passing the #200 sieve

Mortar = everything passing the #8 sieve

Air = 1.35 cftPaste = 9.2 cft%AirPaste= 14.7%

There is NO perfect way





Admixtures

� Air entraining agents

� Water Reducers

� Retarders

� Superplasticizers

� Accelerators

� VMA, set inhibitors

� No way to predict effect of admix

� Admix performance depends on other materials

Heat signature of paste

“Developing a Simple and Rapid Test for Monitoring the

Heat Evolution of Concrete Mixtures for Both Laboratory and Field Applications” –

Center for Transportation Research and Education

Self-consolidating concrete

� Fluidity without segregation

� Ways to achieve

� Well-graded aggregate blend

� Viscosity modifiers

� Admixtures

� Finely divided powders

� Very difficult to achieve on a production basis





High fines manufactured sand

� Proposed revision to ASTM C-33

� Allow up to 18% passing #200

� Dust of fracture only

� Can increase strength, decrease permeability

� Requires increased Super-P dosage

� Particle shape critical

Challenges to mix design

� Impact of particle shape and texture on water demand and rheology

� Interaction between cement, mineral additives, admixtures and water

� Effect of ambient conditions on concrete performance

� Effect of processing variables on concrete performance

� Tests that reflect performance

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