Saving Money Without Compromising Durability

Ryan Barborak, P.E.

2012 Transportation Short Course

Specification Limiting the Coefficient of Thermal Expansion (COTE) for CRCP

Spalled cracks and

delamination at the steel mat are common distresses observed in CRCP

Distressed CRCP pavements tend to have a common feature High COTE coarse aggregate

Determined the COTE of the

concrete can be measured accurately Implement a specification Limit the COTE to a

maximum of 5.5 microstrains/F

Figure 1. E xample of Distresses Observed on TxDOT’s CRCP (Top Photo Taken 7/21/09 by Dr. Moon Won, Texas Tech University)

(Bottom Left Photo Taken by Dr. Dan Zollinger, Texas A&M University) (Bottom Right Photo Taken 2/20/10 by Dr. Moon Won, Texas Tech University)

Specification Limiting the Coefficient of Thermal Expansion (COTE) for CRCP

CST M&P is in the process of testing every coarse aggregate in the state 3 times

Use a standard mix design with a standard gradation

Using a value of 5.5 microstrain/F and considering mineralogy Nearly all purely siliceous

aggregates are above limit

About 25% of total aggregate sources exceed limit

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

0% 25% 50% 75%

CoTE

(m

icro

stra

in/d

egF)

CoTE Testing (All Data)

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

0% 25% 50% 75% 100%

CoTE

(m

icro

stra

in/D

egF)

CoTE by Matl Type: Frequency Distribution

Limestone

LS + Sil

Sil + LS

Rhyolite

Granite

Dolomite

Sil iceous

Sandstone

Limestone

LS + Sil

Sil + LS

Dol

Sil

SanGrn

Specification Limiting the Coefficient of Thermal Expansion (COTE) for CRCP CST M&P is also evaluating

potential methods to reduce COTE to allow aggregates that currently do not meet the specification

1) Blending of high COTE aggregates with low COTE aggregate

2) Optimized grading where high COTE aggregate is used as intermediate size fraction

3) Replace top size of high COTE aggregates with low COTE aggregate

4) Houston District – Using alternating loads of concrete with high and low COTE during placement

5) Use of lightweight as a replacement of the sand fraction

Conclusion

• Cost Savings – Reduction in Repairs

• Estimated that repairs in Houston District alone has cost over $500 million over the past 20 years

– Still many coarse aggregate sources available

• Cost impact for most areas should be minimal

• Alternative includes jointed reinforced concrete pavement

• Durability/Serviceability – Extended service life

without repairs • Better ride quality and

safer • Minimize traffic delays • More aesthetically pleasing • Durability is same or better

than current practice

DMS-4550 Fibers for Concrete CST M&P developed the

specification about 2 years ago

Uses ASTM C 1399 to measure average residual strength

Fibers used to replace steel reinforcement in miscellaneous concrete applications (Class A and B concrete)

Since development many producers/products have been added to list

List is now beginning to include steel fibers

Conclusion

• Cost Savings – Possibly material

• May be cheaper than wire mesh

– Construction • Should reduce time of

construction – Avoid placement of

wire mesh or rebar

• Durability/Serviceability – Same or better than

current practice

Decant Study

Evaluate the current specification limits for the decant and sand equivalent values

Changing the limits will impact the cost by either washing the material more or less (production cost) or using more or less water reducer (material cost)

Goal is to determine if the cost of the overall product can be reduced while maintaining the same or increasing the quality

Decant Study – Test Methods

Workability using Slump Using water reducers to accommodate increase

in water demand from additional fines

Also looking at substituting water for water reducer

Compressive strength

Flexural strength

Permeability (ASTM C 1202)

Shrinkage (ASTM C 157)

Modulus of Elasticity

Coefficient of Thermal Expansion

Decant Study Findings so far…

Coarse Aggregates

Limestone example Clean Decant = 0.4% Extra Dirty Decant = 5.8%

The water demand increased as the material was dirtier (e.g. higher decant value) In this case 2 cwt of

superplasticizer or 15 lb/cy or water was needed to obtain comparable slump to clean

Water addition increased w-c ratio from 0.45 to 0.48

May be more significant for lower w-c ratios

No effect on strength, CTE, MOE, and permeability as measured by ASTM C 1202. Slight increase in shrinkage in accordance with ASTM C 157

Decant Study Findings so far…

Fine Aggregates

Field sand example Clean SE = 91

Dirty Admixture = 45

Dirty Water = 39

Water demand increased significantly

Substantial effect on flexural and compressive strength at 28 days, even though w-c ratio remained the same and cement content increased.

6415 6168 6075

4790 4843 5315

4093 4730

4775

0

1000

2000

3000

4000

5000

6000

7000

517 611 705

Com

pres

sive

Str

engt

h (p

si)

Cement Content (lb/cy)

Clean Dirty Add Dirty Water

792 801 780

602 641

595 587 618

635

0

100

200

300

400

500

600

700

800

900

517 611 705

Flex

ural

Str

engt

h (p

si)

Cement Content (lb/cy)

Clean Dirty Add Dirty Water

Clean w/cSuper P Super P Water

2.75" - 12oz 2.50" - 28oz 2.75" - 1.10lb 0.4736.00" - 6oz 7.50" - 16oz 6.50" - 3.52lb 0.5157.00" - 3oz 6.50" - 8oz 7.00" - 4.00lb 0.514

DirtySlump (in.)

Conclusion

• Cost Savings – Coarse aggregate

• Allow higher decant values based on CaCO3 content of fines

• Effect on workability appears minimal, addition of water to compensate for workability produces results comparable to clean

• Save money by reduced washing (e.g. disposal of wash water, fewer rejected stockpiles, availability of water available for washing, etc.)

• Cost Savings – Fine aggregates

• Still under investigation, but initial results suggest there needs to be a minimal SE content which in some cases will require washing.

• Seems to have more effect on workability than coarse aggregates

• It is a must that a clean sand is used for low w-c ratios to obtain high strengths

• Goal going forward is to determine how low SE value can be decreased without significantly affecting strength

Verifi Concrete Management System

Currently being evaluated in the DFW Connector Project

System measures slump, temperature, drum speed, and water and admixture added

Adds water and superplasticizer for adjustment of the slump

Notifies the driver of when the concrete is fully mixed

Records all information that can be transferred to usable reports

(Koehler and Deadrick, 2012)

(Koehler and Deadrick, 2012)

Conclusion

• Cost Savings/Benefits – Reduction of rejected loads – Helpful for the inspector

• Real-time assessment of slump, temperature, and water added

– Consistent monitor of concrete properties

• Consistent slump and air • Automated slump control

– Detailed information about every load of concrete

– Monitoring of all water additions

• Stopping all water additions when the max allowable water content is reached

• Ensures water additions are fully mixed prior to discharge

• Durability/Serviceability – Same or better than current

practice

Honorable Mentions

TxDOT ASR/DEF Exposure Site Determine the cause of

early age cracking of pre-stressed beams in Central Texas

Determine feasibility of using Option 7 - alkali loading limit of 3.5 pcy as a function of aggregate mineralogy

What time/temperature is needed for several cements to initiate DEF

Lithium nitrate as a viable ASR mitigation method

Research Project 0-6255 Use more manufactured

sands in Class P concrete How mineralogy affects

the dosage (e.g limestone versus dolomites)

Questions?