5/27/2020

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Trends in Modern

Concrete Floors

Kevin A. MacDonald, Ph.D.,P.E, FACI

Beton Consulting Engineers

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Changes in cement composition

Changes in concrete composition

Changes in Flatness Measurement

Changes in expectations

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Aesthetics and Slabs

When Structural Concrete is Architectural

Concrete

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Definitions

Architectural concrete : Concrete that will

be permanently exposed to view And

therefore requires special care in selection

of the concrete materials, forming, placing,

and finishing to obtain the desired

architectural appearance.

Structural concrete: Plain or Reinforced

concrete in a member that is part of a

structural system required to transfer gravity

loads, lateral loads or both along a path to

the ground.

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FF and

FL

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F-Numbers with Scans

Scanning a concrete floor with a 3D laser scanner

is an application that has great potential to

improve construction quality.

ASTM E1155, “Standard Test Method for

Determining FF Floor Flatness and FL Floor

Levelness Numbers.” updated in 2014 to allow

the use of a “laser imaging device;”

but didn’t change how results are to be reported

or the test’s limitations, such as measuring within

72 hours, having sample measurements greater

than 11 feet, and taking no measurements within

2 feet of slab edges, columns, or penetrations.

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DPR ConstructionScanning the

concrete when it’s still wet (before,

top) allows additional finishing

work to be done to improve the

profile (after, bottom).

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Green Initiative

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ASTM C1157

Performance-Based Cement

Type IL cement

Contains a larger replacement of clinker with

Limestone

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Type I L Cement

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Pozzolans, Nucleation and Size

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Thermodynamics and Kinetics

Nucleation

the first step in the formation of either a new

thermodynamic phase or a new structure via self-

assembly or self-organization.

Catalysis

The process by which a substance speeds up a

chemical reaction without being consumed or

altered in the process.

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Admixtures

Admixtures can cause uncontrolled /

unexpected air entrainment

ASCC

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Core 1

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Design Methods

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Shilstone Coarseness Chart

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25

30

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40

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020406080100

Coarseness Factor

Wo

rkab

ilit

y F

acto

r

IV

I

II

III

VCoarse

Fine

Gap Graded

Optimal ¾

max.

aggregateOptimal

for larger

aggregate

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0.45 Power Chart

0

20

40

60

80

100

Sieve (^0.45)

% R

eta

ined

Mixture

Max Density

Limits

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Gap Grading

Grading in which one or more intermediate

size fractions are omitted

Can be economical, require less sand and lower

w/c for given slump

Can create segregation prone concrete

Recommended for stiff mixes of very low

workability, compacted by vibration

Applications

Architectural concrete

Pervious concrete

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Gradation vs Paste Content

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Volumetric Problems

1 2 3 4 5 6 7

Cement Water Aggregate and Air

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Extended Floor Joint Spacing

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Why do we care?

Joints 24 to 36 times the slab thickness

Cut at the appropriate time

Load transfer devices where applicable

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Largest Cost to Owner is Joint

Maintenance

Joints are discontinuities

Stress at the edge or

Maintenance of Joint sealant

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Financial / Safety Impacts

Workplace Safety

Equipment Damage Worksite Productivity

• Reduces repair costs

associated with fork

lift, AGV equipment and robotics damage

from joints

• Reduces back injuries

• Allows for safe and faster driving

speeds• Safer for workforce – trips and falls,

less vibration to drivers and

operators

• Smoother material-handling aisles

• Perfect for high racking applications – flat and level floors that stay flat

and level• Eliminates costly maintenance and downtime associated with saw

cuts – caulking and crack repairs

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Loads

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Materials

Concrete

Fiber

Subgrade

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Concrete

Elastic (not Linearly)

Fails at defects as cracks move in plastic

process zone

Cracks propagate rapidly

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Subgrade

Westergaard Theory

Slabs on a Winkler Subgrade

“k” factor

Used in most methods of Design

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Slab on Grade Design – Who does

that?

ACI 318

ACI 360

TR34

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Reinforcement

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Subgrade Drag Theory (Ytterberg)

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Shrinkage must be low(!)

Concrete mix design is critical

Low Shrinkage

Excess paste

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Dominant Joint

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Outline

Fibers are often used to distribute cracking

due to thermal, shrinkage and load induced

strains in plain concrete

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ACK Model

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Strain Softening Behavior Ef>Ec

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Pass Stress Across the Crack

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Barzin Mobasher ASU

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Fiber addition to truck, chute &

ring

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Finishing ring

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Cylinders

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Fiber and no fiber

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Slabs

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Measuring slabs

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No fiber

Plain shrinkage charts from rings

!140%

!120%

!100%

!80%

!60%

!40%

!20%

0%

20%0% 10% 20% 30% 40% 50% 60% 70% 80% 90%

Ring%1%!%%Fiber%!%Average% Ring%2%!%%Fiber%!%Average% Ring%3%!%Fiber%!%Average% Ring%4%!%No%Fiber%!%Average% Ring%5%!%%No%Fiber%!%Average% Ring%6%!%No%Fiber%!%Average%

Crack%

A-6

53, 63, 67

Avg 61

67 68

Fiber

Fiber shrinkage charts from rings

!140%

!120%

!100%

!80%

!60%

!40%

!20%

0%

20%0% 10% 20% 30% 40% 50% 60% 70% 80% 90%

Ring%1%!%%Fiber%!%Average% Ring%2%!%%Fiber%!%Average% Ring%3%!%Fiber%!%Average% Ring%4%!%No%Fiber%!%Average% Ring%5%!%%No%Fiber%!%Average% Ring%6%!%No%Fiber%!%Average%

Crack%

A-7

64, 65, 69

Avg 66

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Shrinkage Compensating Slab

Neutral Axis moves below

the slab, using more of the slab

in compression

The Science Behind the System

Net εsh is compressive

ε

t

Fibers are in the mixture, so the steel cannot be mis-located

Test Bar Expansion

Sla

b E

xpan

sion

ρ increasing

Design: Eliminate

anticipated shrinkage

Steel chaired in each location –

limits productivity

Conventional ShCC Slab

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P

Plastic Hinge Facilitated by

Fibers

The Science Behind the System

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Rapid Drying Concrete

Water needs to go somewhere

In the pores

In the Atmosphere

In the Hydration products

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Joints

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Conclusions

Almost 1/3 of concrete is placed as soil

supported floors

Changes are occurring and there are good

and bad, intended and unintended

consequences

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Thank You

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