Concrete Materials Information for
Construction Academy
MICHAEL (MIKE) BERGIN, P.E.,
STATE STRUCTURAL MATERIALS ENGINEER
FDOT, STATE MATERIALS RESEARCH PARK
AUGUST 20, 2014
MICHAEL.BERGIN@DOT.STATE.FL.US
Topics
 Fundamentals of Good Concrete
 A better understanding of w/c ratio
 Slump of Concrete
Water added at the site
 Penalties
 Available water for hydration

 Drilled shaft concrete and slump loss
 Mass concrete
 Specification changes
Topics




346 changes based on 1/15 lettings
Performance Based Concrete Pavement, Section 350
Slab Replacement Concrete, Section 353 (proposed changes)
Sampling Steel
 New Ideas, Concepts and Research
 Internal Curing
 Roller compacted concrete (RCC)
 Self consolidating concrete (SCC)
 Ground Glass in Concrete
 GTR in Concrete
Water Cementitious Materials Ratio and
the Velcro Approach
What is the w/c ratio ?
Cementitious Materials
 Includes:
◦
Cement


◦
Pozzolans,






◦
Type I, II, III
Particle size; ∼ 25 to 40 microns
Fly ash, Class F and C
Ground glass
Rice hull ash
Sugar Cane Ash
Highly reactive pozzolans
Particle size, ∼ 0.1 to 50 microns
Slag


GGBFS, grade 100 or 120
Particle size, ∼ 20 to 40 microns
Pozzolans and ‘Particle Packing’
 Straight cement and high w/c (>0.41)
◦
◦
◦
Particles separated by high water content
Shrinkage
Excessive bleed water
 Straight cement and low w/c (≤0.41)
◦
◦
Particles closer together, tighter bond
A little more durable
 Cement and pozzolans with low w/c
◦
Particles



◦
closer together,
size more distributed,
very tight bond
Durability has arrived
High w/c Ratio
 Water
 Increases initial volume
 Collects in lens under the surface
 Lens is a problem when traffic is placed on it
 Lens may be under reinforcement
 Increase in ‘bleed water’
 Delays finish work
 Unwanted surface conditions and less durable concrete
Shrinkage
 Surface cracking
 Scaling

High w/c Ratio
 Fines help reduce bleed water
 Cementitious plus fine aggregate
 60% coarse/40 fines is a good ratio.
 Rate of bleed water evaporating is regulated by
external conditions (weather)

A need for curing
Low w/c Ratio
 How much water is needed to hydrate cement?
 Concrete maintains its volume
 A little more is needed for pozzolans or slag
 Reduces the pathways for bleed water
 Still need some bleed water
 More durable concrete
Increase in density
 Less surface problems on finished concrete

Add Fly Ash or Slag
 We have additional fine particles for packing and to
provide pozzolanic activity


Particle packing helps minimize voids in the paste
Pozzolanic activity -concrete continues to hydrate (react)
continues as long as there is calcium, silica and moisture in the
matrix.
 Cement and fly ash both provide calcium and silica.
 Moisture already available in mix and moist curing ???
 Some method of curing.

Add a low w/c ratio
 Best particle packing
 Less water between particles
 Additional moisture (if needed) comes with wet
curing or covering the surface to prevent moisture
loss.



Wind
Heat
Dry conditions and low humidity
Water/Cement Ratio
Cement particle
Cement particle
High W/C
Low W/C
Hydration
Hydration
High w/c ratio equates to lots of shrinkage cracking
Shrinkage Cracking
Water Added at the Job and Slump of Concrete
Sect. 346
 Target Slump and Tolerance Range
 Here’s a helpful graphic to clarify the issue (346,
Table 6)

Graphic illustrates target slump value
Slump Range
TOLERANCE SLUMP RANGE (3”)
REJECT
1-1/2” DRY
1-1/2” WET
ACCEPT – WATER MAY
BE ADDED
TARGET
SLUMP
REJECT
When the Contractor adds water…
 Determine the slump
 If within the Target Slump Value
 Perform other plastic properties;
 Air
 Temperature
 Determine w/c ratio
346-6: Control of Quality
 346-6.4 Tolerances: When slump is outside the
tolerance range,




Make cylinders
Contractor rejects concrete
He notifies the concrete production facility to adjust the
concrete mixture
He tests each subsequent load and the first adjusted load from
the plant
346-12: Penalty occurs…
 If contractor places concrete when any of the plastic
properties are outside the limits of the approved mix
design
 He not only assumes risk of placing non compliant
concrete, the contractor is penalized the invoice price
of concrete, unless the Engineer approves.



On-going drilled shaft placement
Large footer (don’t want a cold joint)
Disposition of defective materials (DDM) is required
The discussion of w/c ratios,
slump, slump loss, and elapse time
are a major concerns for drilled
shafts.
Slump Loss? Elapsed Time?
 Time it takes to loose slump - drops from 10” to 5”
 Indicates how long the contractor has to place the
concrete, set bolts, remove temporary casing.
 to get slump, producer uses water reducing
admixtures and water.
Drilled Shaft Concrete should not look like this!
Or this!
Q: What is the minimum clear cover (in inches) over steel?
Some Probable Causes?
 Concrete not workable?

Slump loss not accurate for this placement? Need new
slump loss?
 Contractor not ready for concrete?
 Rebar spacing too tight?
Engineers increasing capacity
 Second truck delayed?
 How was the deficiency determined?

High Slump Concrete
 high slump concrete (≥7.5 ”) may have lumps
and balls.
 Use a grate with max opening size of 2.5” in
either direction
 Placement continues but,




Lumps and balls are removed
Contractor still responsible for strength
Engineer can make cylinders anytime
Department personnel to monitor

Notify DMO if balls and lumps are present
High Slump Concrete
 If you see lumps and balls,…
 DMO will evaluate the plant to ensure
compliance with QC plan


Plan indicates how they are to batch high slump concrete
DMO can verify if the plant was producing in compliance
with their plan
 If problems persist, the DMO may revoke the
plants QC plan
346 Changes
FOR LETTINGS BEGINNING JAN 2015
Section 346-2 Materials
 346-2.2 Type II cement replaced with Type II (MH),
moderate heat

Required for mass (v/sa ≥ 1.0) concrete placements
 346-2.3
 Fly ash or slag is required for all concrete.




Not required for dri-cast precast elements.
New cement type is added, Type IP
Ternary blends allowed in all classes of concrete
Highly reactive pozzolans (HRP) are identified (SF, Metak,
UFFA)
346-3.1 General
 Substituting higher strength for lower strength
 Can be used in two applications if approved by the
Engineer


1. For Structural Concrete a Higher Strength can be used in
lieu of Lower Strength
2. Structural Concrete can be used in lieu of Non-Structural
Concrete
346-3.1 General
 Acceptance of concrete is based on contract
requirements.

Say contract requires C-II, 3400 psi
A higher strength (C-IV, 5500 psi) is substituted
 Compressive strength results are 5,100 psi

 Does the concrete pass or fail?
346-3.1 General
 5,100 psi meets contract requirements
 Concrete is accepted at FULL PAY
 But wait a minute !!!!
346-3.1 General
 The minimum required for the C-IV was 5,500
psi - only achieved 5,100


Notify DMO that concrete did not meet mix design target
strength
DMO will investigate concrete producer
 QC Program issue, not acceptance issue
346-3.1 General
 Section 347 governs non-structural concrete
 Do not test concrete based on 346
 Acceptance based on delivery ticket, signed by
batcher and QC certifying minimum 2,500 psi
346-3.2 Drilled Shaft Concrete
 Allows for slump loss test to be performed in the lab
 Less than 30 cubic yards, or
 Less than an maximum elapsed time of 5 hours
 Concrete used during the summer, temp > 85F, perform slump
loss test at hot weather conditions.
346-3.3 Mass Concrete
 Mass concrete is indicated on the plans (v / sa ≥ 1.0)
 Control concrete temperature
Max 180F (> 180F, what happens?)
 ΔT≤ 35F (interior to exterior)
 Interior stays hot, exterior cools
 If exceeded, contractor must take action
 How would contractor control temp???

346-3.3 Mass Concrete


New language is added;
Same size elements
One plan can be used
 2 elements could be placed at one time
 2nd needs to be started within 1 hour of the first.
 Both need to be instrumented
 Why would we want both instrumented???

346-5: Sampling and Testing Methods
 Table 5
 Added testing requirements for self consolidating concrete
(SCC)
 Also indicates that QC will use the same type of air meter as V.
346-5: Sampling and Testing Methods
 Table 5 –
 If pressure meter is used, must have an aggregate
correction factor on mix design
 Curing facilities have capacity to hold all QC and V
cylinders
 V will use same air meter and cylinder size as QC
 Can take entire concrete sample at one time from middle
of load, ASTM C172
346-7 Mixing and Delivering
 Transit time, reject trucks exceeding the maximum
transit time

Typically 90 minutes (agitator truck, HRWR)
 Construction personnel need to notify the District
Materials Office of concrete placements

To witness complicated placements
Mass concrete
 Structural Drilled Shaft


To IA QC or V technicians
346-7 Mixing and Delivering
•
•
346- 7.3 Mixing at the Site: This is indicated in the Contractors
QC plan.
346-7.7 Adding Water:

Any water missing from the saddle tanks is;
 Assumed to be in the batch and
•
is added to the jobsite water on the delivery ticket and included in
the w/c ratio.
346-7 Mixing and Delivering
 Changes
 No water added to truck after 130 revs
 Truck has started to place within 90 min.


has 15 additional min to complete the placement
If 120 min haul time already approved, no additional time
allowed.
346-7 Mixing and Delivering
 346-7.8 Sample Location: Sample Correlation
required when contractor can’t sample at the point of
final placement.

Need 5 samples, one sample per load


What is a sample?
DMO will help with this process
Bottom Up Pumping
346-8 Plastic Concrete Sampling and
Testing
 Truck Mixer Identification Card?
 Inspector should request to see this.
 If no card, truck cannot deliver for FDOT, reject concrete
 Contractor is responsible to remove this if there are
deficiencies with the truck that cannot be repaired
immediately.
 He is to forward id card to DMO
 When any 5 loads within 2 days are outside the specified
tolerances- notify DMO, they will suspend production from the
plant!
346-9: Acceptance Sampling and Testing
 When a mix is used for a different application, the
LOT is defined by that application.

Class II concrete is placed for use as Class I Pavement.

Lot size for this Class II concrete is defined as 2000 sy, or 1 days
production, its placed as pavement
346-9: Acceptance Sampling and Testing
 Acceptance is typically a 50 cyd lot size
 346-9.2.1 Acceptance Tests can be reduced to 100
yd3 if there is consistency in strength tests (same
mix, same plant, same contract)
 Need 2 Sdev (95% of data) above the minimum
required strength based on the class of concrete
346-9: Acceptance Sampling and Testing
 For Class IV or higher, need ten consecutive strength
tests to determine reduced frequency
 For Class III or lower, need five consecutive
strength tests to determine reduced frequency
 Data must come from an approved lab (Section 105)
346-9: Acceptance Sampling and Testing
 Need prior approval of the Engineer
 Provide data prior to approval
 CPAM has instructions on the process
 Usually includes the DMO to help verify data.
Why would a concrete producer not want the
contractor to use the “reduced frequency”
option?
346-10 Investigate Low Strength Concrete
 The 10% (below minimum) was removed and is now
500 psi only.

If the strength of the concrete is within 500 psi below the
minimum required;
the contractor cannot core to determine strength
 a pay penalty is applied .


Why do we have this caveat??
Performance Based Spec. for Pavement
 Complete rewrite of Section 350
 PB 350 Pilot Projects
 I-4, from SR 44 to I-95, Deland
 I-275, area north of I-4, Tampa
 9B, Jacksonville
PB 350 Mix Design
 Compressive strength (4000 psi)
 W/cm not to exceed 0.50
•
Material sources must be approved
◦ Can use a commercial mix
◦ Mix will be approved by DMO;

Requires LIMs entry
PB 350 Mix Design
 Plant approval
 Central batch plant
Develop Sdev for plant with 30 data points
 Previous data - OK
 Provides the overdesign needed for mix approval


Ready mix plant

Overdesign still required – Why??
PB 350 Equipment
 Slip form paver;
◦
On board vibrators


frequency is calibrated
recording device used to monitor frequency
 Forms may be used where needed;
◦
Must be steel, straight and designed for concrete.
◦
Curing compound spraying equipment, must be mechanically
driven.
PB 350 Placing Concrete
 Place concrete by single lane width or full width of the
combined travel lanes
 Thickness cannot deviate by more than ½ inch
 Delivery ticket


Still required (modified tix) for contractors using central batch
plant, unit price/syd
Required for each load of ready mix
 Addition of water does not apply unless concrete is
delivered by ready mix truck
PB 350 Sampling and Testing
 QC is temperature control of the concrete and
making and curing cylinders

Cylinders may need to be vibrated
 A LOT is 2000 syd or 1 days production
 Partial LOTs (<500 syd) are combined with previous LOT
for acceptance purposes.
 Testing may be reduced to 4000 syd, with
consistent strength data
PB 350 Finishing and Curing
 Finish the concrete with a burlap drag.
 Curing will be with white pigmented curing
compound


1 gal/ 200 ft2
If forms are used, apply curing compound to the sides of the
concrete when forms are removed.
 Saw the joints when the sheen has left the concrete
surface.

We want to control where the concrete cracks!
Add some other pics of
shrinkage and other cracking
Stress Crack
PB 350 Thickness
 Core the pavement to determine thickness of
concrete (ASTM C174), need 2 cores
 The department will trial the use of the Probe
Method (FM) to verify the thickness


Use 12 points to verify thickness by the probe method.
The hope is to use this to verify thickness, instead of coring
Concrete Probe (thickness)
350 Opening to Traffic
 Concrete strength ≥ 2200 psi
 Cylinders cured similar to the slab concrete.
 Maturity Method can be used to indicate concrete
strength


For opening to traffic
Not for acceptance
Changes to Section 353
 What is 353 Concrete?
 Revising this specification to address current
problems


In some cases- high rate of cracked slabs in new concrete
Slab replacement projects are on-going or scheduled to start in
almost every district
353 Concrete is almost ready to be placed.
What’s missing?
353 Issues
 Opening to traffic, contractor’s major goal (usually
night work)

If he places concrete until 4 AM
Does not provide curing time for concrete
 Can’t limit truck traffic
 Can we limit contractor?
 Limit means and methods of contractor?
 Require a minimum curing time?

353 Issues
 Mixes are extremely “hot”
 Initial set, 15 to 30 min.
 Accelerators are used and are typically placed
outside of recommended dosage rates
 Revisions needed to ‘cool’ the concrete
Now this is HOT!!
353 Revision
 We’re revising Section 353 to;
 Provide construction personnel with guidance on the
placement and curing of 353 concrete
 Ensure a low percent of failures.
 Record admixture dosage

limit dosage to max dosage on tech data sheet.
Sampling Steel on the project
How is reinforcement steel sampled?
How is post tensioning strand sampled?
How are stressing bars sampled?
Sampling Steel
 Project personnel need to collect;
 3 pieces, at random by you.
 Mill certificate w/ Buy America clause


Cert should identify the steel
 Place in envelope, firmly attached to steel
Do not cut sample with a torch!
 Send 1 bar, hold 2 (a check may be needed)
 Any bar not selected by you is not random!

No ‘test bars’, ‘splice bars’, or ‘FDOT test samples’
Sampling Steel
 Job Guide Schedule indicates amount of steel on the
job




Look for total quantity (usually in lbs)
Take the total ÷ 2000 lbs to get tons
Divide that number by 80 to get the samples needed
Randomly sample during project

Not while project is being certified!
Sampling Steel
 Rebars (#3 to #18)
 A sample is 3 bars – 7’ long –
Mill cert in an envelope attached to the sample
 1 per 80 tons


Submit 1 bar to SMO, hold 2

Sample most frequently used bar size
If bar passes, give the other 2 bars to contractor, or
discard.
 Foreign bars indicate country of origin

Sampling Steel
 Post tension 7 wire strand
 A sample is 3 strands, 5’ long
Mill cert in an envelope attached to the sample
 1/ shipment

Send 1, hold 2 (may need a check sample)
 Again, must be a random sample

Sampling Steel
 Threaded stressing bars
 A sample is 3 bars, 4’ long
Mill cert in an envelope attached to the sample
 1/ heat/ shipment/ job or JGS



Send 1, hold 2
Random, selected by you
Sampling Steel - Review
 Take 3 pieces of steel from project at a frequency
indicated in JGS.

No torching of bars
 Send 1 to SMO, hold 2
 Send mill cert in envelope attached to steel
 Sample to match mill cert
Internal Curing of Concrete
 Use light weight aggregate
 About 20% of the total fines in mix
 Provides additional moisture in the mix
 Does not “bleed” out during normal curing
 Remains to provide the additional moisture needed to provide
long term hydration
 Used by pozzolans long after 28 day strength is determined
Roller Compacted Concrete
 Use cement, good blend of coarse aggregate and a






little water
Batch materials in a pug mill
Delivered in a dump truck
Placed into a spreader or a high density asphalt
paver.
Rolled to a specific density with a steel wheel roller.
Can be smoothed with a rubber tire roller if needed
Finished surface may be rough.
Self Consolidating Concrete
 Very fluid
 Self levels
 Very finicky
 Sensitive to temperature
 Changes to water
Water additions to load
 Changes to aggregate moisture

Lab Test Methods for SCC
 To verify and approve the mix;
 ASTM C 1610 - Static Segregation of SCC using Column
Techniques
 ASTM C 1712 – Dynamic Segregation of SCC (new
device)
Static Segregation Test
(ASTM C1610)
Dynamic Segregation Test
Field Test Methods for SCC
 To accept concrete at the project;
 ASTM C 1611 - Slump Flow of SCC
 ASTM C 1621 - Passing Ability of SCC by J-Ring
 Conventional tests;
Percent air, Air or pressure meter
 Temperature

Slump Flow of SCC
(ASTM C1611)
Passing Ability of SCC through
the J Ring (ASTM C1621)
Chap.8.4 of Materials Manual
 Prestressed and Precast concrete
 A revision to 8.4 allows a change in the slump
flow of SCC from 25” to 27” ± 2.5”
 Provides a more fluid concrete to reduce bug
holes and voids in highly reinforced prestressed
elements
Ground Glass in Concrete
 Glass not used in the past- due to ASR
 What is ASR?
 New research indicates if ground small enough, no
ASR
 The ground glass actually reacts like fly ash
 Can use any color glass, except for Pyrex (very
reactive)
 Glass has to be cleaned before use
Ground Tire Rubber in Concrete
 Several particle sizes were used
 The best size is a crumb rubber similar to the size




used in asphalt.
Use about 20% maximum replacement of fine
aggregate.
Provides a reduction in strength (less brittle)
The MOE is lower, so slabs are able to move a little
The effort helps to reduce the amount of rubber tires
going into landfills.
LIMS Updates
 MAC is the new system, and its coming!
 But if you have any questions about how to enter a
sample in LIMs,….
LIMS
 Look up the information at; “Instructions for
Samples for Structural Materials” on the SMO
website
 http://www.dot.state.fl.us/statematerialsoffice/
laboratory/lims/resources/tutorials.shtm
My Request from You
 In my evaluation, tell me:
 About concrete topics that should be discussed in this session
 Are there portions of 346 that are confusing and need
clarification?
 Is there additional concrete training or information that are of
special interest to you or others?
Thanks for your time!