Optimized Mixtures Will Save You Headaches and Money

The DFW Connector Experience4 December 2015

ACPA Annual Meeting

J. Mauricio Ruiz, P.E. (TX)The Transtec Group, Inc.

David SantinNorthGate Constructors

OUTLINE

•The Concept

•The DFW Connector Experience

• Impact of Optimized Aggregate Gradation on PCCP

Performance

•Final Thoughts

Optimized Aggregate Gradation (OAG) Concept

• Reduce paste content by use of an intermediate aggregate

• Sufficient paste volume to fill voids and provide workability

• Many states now allow/encourage optimized aggregate blending

• Benefits reported:

• Reduced shrinkage

• Lower cost

• Greater strengths

• Improved workability

OAG Tools

• Workability-Coarseness Factor Chart

• 8-18 Chart

• Power 0.45

• TARANTULA Curve

Aggregate Texture Matters!

OAG is not a fix-all

Coarse Sand Fine Sand

OAG for ND paving

Improved uniformity and workability

How to Achieve Concrete Uniformity?

1. Eliminate gap graded concrete mixtures

2. Control gradation

3. Avoid poor quality aggregate

4. Ensure sufficient pre-blending and mixing

5. Focus on good process control and

stockpile management

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• Owner: TxDOT

• D-B Firm: NorthGateConstructors

• Lead Design: PB Americas

• Pavement Design: Transtec

• Cost: Over $1.0 billion

• Construction Schedule: 4 years (2010-2014)

• 226 lane miles of CRCP (600,000 yd3)

www.dfwconnector.com

DFW Connector

Logistics of 3rd Aggregate

•Find intermediate aggregate source

• Material cost and haul cost

•Plant set up to handle a 3rd aggregate

•Extra room at the plant site

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DFWC Gradation

TEX-470-A

Sieve analysis before each production day

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DFWC Gradation

TEX-470-A

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DFWC Gradation

TEX-470-A

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Mixture Optimization with COMPASS

COMPASS (Concrete Mixture Performance Analysis System)

1. A system that guides the user through the mix design

process

2. Considers job-specific conditions and materials

3. Assists in optimizing mix gradations and proportions

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0.38 0.45

30

20

w/c

Paste

Vol.

Optimal mixture

Mix Optimization

Optimization Criteria• Strength• Workability• Cost

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DFWC Mix Optimization

Top Ten Optimum Mixtures

Mixture Proportioning Process

• Materials

• Round intermediate and natural

• Manufactured sand discarded

• Seasonal changes – 20% and 35% Fly ash replacement

• Mixture proportioning

• Computer proportioning : COMPASS and TEX-470-A

• Lab trial batches – small quantity

• Batch plant adjustments

Mix Proportions (4.8 sack)

• Cement 293 lb/cy

• Fly Ash 159 lb/cy

• #57 Stone 1,620 lb/cy

• 3/8” Pea Gravel 337 lb/cy

• Natural Sand 1,477 lb/cy

• Water 191 lb/cy

Uniform Concrete Mixture

Uniform Concrete Surface Requiring Minimum Finishing

DFW Connector Realized Benefits

• Strength

• Avg. 7-day breaks – 4,748 psi (specified 3,500 psi)

• Avg. 28-day breaks – 6,731 psi (specified 4,400 psi)

• Cost savings

• $500k to $600k in savings for every 20 lbs cement content reduction per

cu. yd.

• Average IRI numbers in the low 60’s ( spec is 75 in/mi for PCCP)

• Low end of cementitious content with good workability

• Mix remained very consistent compared to other concrete mixtures

in the past (consistent air and slump)

HIPERPAV Analysis of Aggregate Blending

• HIgh PERformance Concrete PAVing

– FHWA-sponsored software

– Systems Approach simulation

• Environment,

• Materials,

• Pavement Design, and

• Construction Factors

Str

ess

/ Str

engt

h

Time since Construction

Cracking

HIPERPAV Early-Age Cracking Analysis(6 sack Mix) – Cold Front

Stress-Strength ratio: 100%

Higher heat of hydration and shrinkage

HIPERPAV Early-Age Cracking Analysis(5 sack Mix) – Cold Front

Stress-Strength ratio: 97%

Sensitivity of Cement Paste Volume on Cracking Risk

Final Thoughts

•Optimized Aggregate Blending Benefits:

• Reduced cement paste – Lower shrinkage/Cost

• More consistent mixture: Less edge slump and

segregation

• Less Rework

• Savings in production time, labor, and materials

• Increased performance

END

Q&A