5/27/2020
1
Trends in Modern
Concrete Floors
Kevin A. MacDonald, Ph.D.,P.E, FACI
Beton Consulting Engineers
2
Changes in cement composition
Changes in concrete composition
Changes in Flatness Measurement
Changes in expectations
3
Aesthetics and Slabs
When Structural Concrete is Architectural
Concrete
4
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.
6
5/27/2020
2
7 8
9 10
11 12
5/27/2020
3
FF and
FL
14
15 16
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.
17
DPR ConstructionScanning the
concrete when it’s still wet (before,
top) allows additional finishing
work to be done to improve the
profile (after, bottom).
18
5/27/2020
4
Green Initiative
20
ASTM C1157
Performance-Based Cement
Type IL cement
Contains a larger replacement of clinker with
Limestone
21
Type I L Cement
22
23 24
5/27/2020
5
Pozzolans, Nucleation and Size
25
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.
26
Admixtures
Admixtures can cause uncontrolled /
unexpected air entrainment
ASCC
27
Core 1
28
Design Methods
29
5/27/2020
6
Shilstone Coarseness Chart
20
25
30
35
40
45
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
33
0.45 Power Chart
0
20
40
60
80
100
Sieve (^0.45)
% R
eta
ined
Mixture
Max Density
Limits
34
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
35
Gradation vs Paste Content
36
5/27/2020
7
Volumetric Problems
1 2 3 4 5 6 7
Cement Water Aggregate and Air
37
Extended Floor Joint Spacing
38
Why do we care?
Joints 24 to 36 times the slab thickness
Cut at the appropriate time
Load transfer devices where applicable
39
Largest Cost to Owner is Joint
Maintenance
Joints are discontinuities
Stress at the edge or
Maintenance of Joint sealant
40
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
41
Loads
42
5/27/2020
8
43
Materials
Concrete
Fiber
Subgrade
44
Concrete
Elastic (not Linearly)
Fails at defects as cracks move in plastic
process zone
Cracks propagate rapidly
45
Subgrade
Westergaard Theory
Slabs on a Winkler Subgrade
“k” factor
Used in most methods of Design
46
Slab on Grade Design – Who does
that?
ACI 318
ACI 360
TR34
47
Reinforcement
48
5/27/2020
9
Subgrade Drag Theory (Ytterberg)
49
Shrinkage must be low(!)
Concrete mix design is critical
Low Shrinkage
Excess paste
50
51 52
53
Dominant Joint
54
5/27/2020
10
Outline
Fibers are often used to distribute cracking
due to thermal, shrinkage and load induced
strains in plain concrete
55
ACK Model
56
Strain Softening Behavior Ef>Ec
57 58
Pass Stress Across the Crack
59
Barzin Mobasher ASU
60
5/27/2020
11
Fiber addition to truck, chute &
ring
61
Finishing ring
62
Cylinders
63
Fiber and no fiber
64
Slabs
65
Measuring slabs
66
5/27/2020
12
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
69 70
71 72
5/27/2020
13
73 74
75 76
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
5/27/2020
14
P
Plastic Hinge Facilitated by
Fibers
The Science Behind the System
80
81
Rapid Drying Concrete
Water needs to go somewhere
In the pores
In the Atmosphere
In the Hydration products
82
Joints
83 84
5/27/2020
15
85
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
86
Thank You
87