Update on End Result Specifications Celik Ozyildirim, Ph.D., P.E.

transcript

Update on End Result Specifications

Celik Ozyildirim, Ph.D., P.E.

ACKNOWLEDGMENTS

Close cooperation between• Research Council• Materials Division• Structure and Bridge Division• Districts• FHWA• Industry

• Shared responsibility• Contractor/producer has the authority to

prepare concrete mixtures and are expected to take responsibility for performance.

• Agency accepts, rejects, or applies a pay adjustment depending on the degree of compliance.

Special Provision has three parts:

1. Process control measures

QC Plan by the contractor applicable to preconstruction and during construction

2. Mix design approval

3. Acceptance

1. Process Control MeasuresQC Plan by the Contractor

• Personnel, equipment, supplies and facilities

• Ingredients• Mix designs• Sampling, type of test and frequency• Certified technicians• Complete record of tests

2. Mix Design Approval

• Contractor submits mix designs for various classes of concrete

• Documentation showing requirements are met– past experience– trial batches

• Mix designs, ingredients, target w/cm, target fresh and hardened concrete properties

3. Acceptance

• Screening tests, contractor• Pay factor tests, VDOT• For structural, paving, and

miscellaneous concrete • Accepted on a lot-by-lot basis• Lot is limited to 500 yd3 and

consists of sublots. Sublot has maximum of 100 yd3 and at least one sublot for each day’s placement.

Differences in Specifications

Item Current ERS

Mix Design Prescriptive Performance measures

Testing VDOT Contractor and

Basis of Pay Minimum PWL (percent within limits)

First Phase Pilot Projects

Salem: • Route 11 over the New River and

Norfolk Southern Railroad tracks near Radford University, deck concrete

Culpeper: • Route 28 near Manassas, deck

and substructure

Salem Mix Proportions

Material Amount (lb/yd3)

Cement Type I/II 318

Fly ash Class F 159

Slag 159

Fine aggregate 1101

Coarse aggregate 1755

w/cm 0.45

Salem Strength and Permeability at 28 days

Property Average Std Dev

Strength (psi) 5016 305

Permeability (coul)

391 72

N=31Minimum strength = 4,000 psi, Maximum permeability = 2,500 coulombs

Second Phase Pilot Projects

• Aggregate and admixture selection• Combined aggregates• Curing boxes• Mixture proportions• Control charts

Aggregate and Admixture SelectionRoute 624 over Cat Point Creek

In the same mixture• Crushed stone and

gravel• Water reducing

admixture and retarding admixture

Combined AggregatesRoute 5 over Chickahominy River

Quality coarse aggregate did not meet #57

Combined AggregatesRoute 5 over Chickahominy River

8 #8 #30

#100 Pan

Sieve Size

Noncompliant #57 with sand

Noncompliant #57 with #78 and sand

Curing BoxesRoute 95 Widening Project

Curing Box with continuous recording (printout)

Mixture ProportionsChincoteague Bridge Bascule Footing

83.5 ft by 51 ft and 7 ft deep

Mixture ProportionsChincoteague Bridge Bascule Footing

• In A3 Mass Concrete minimum cementitious material content is 588 lb/yd3.

• In this project used 539 lb/cy3 of cementitious material content with 30% Class F fly ash.

Mixture Proportions Route 5 over Chickahominy River

Three trial batches with different cementitious material and w/cm

Mixture proportions – Route 5

Ingredient A3 Concrete A4 Concrete

Portland cement 385 438

Fly ash 165 188

Total cementitious 550 626

Coarse agg #57 1340 1340

Coarse agg #78 460 460

Fine aggregate 1208 1137

w/cm 0.44 0.39

Strength and Permeability – Route 5

A3 Str.(psi)

A3 Perm.(coul)

A4 Str.(psi)

A4 Perm.(coul)

Average 4570 456 4820 430

Std dev = SD 560 140 680 1155

Sublots 46 46 161 160

Over tidal water: USL=1700 coulombs

Control Charts Fresh Concrete

Slump Results

01234567

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Test Number

Air Content

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Test Number

Unit Weight

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Test Number

Temperature

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Test Number

Compressive Strength (Avg)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Test Number

Air content

Unit weight

Temperature

Control Charts Hardened Concrete

Compressive Strength (Avg)

20003000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Test Number

Coulombs (Avg)

200300400500600700800900

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Test Number

Compressive Strength Moving Average (psi)

41004200430044004500460047004800

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Test Number

Coulombs Moving Average

200300400500600700800900

1 2 3 4 5 6 7 8 9 10 11 12 13 14Test Number

Compressive strength

Permeability

Str. moving average of 3

Perm. moving average of 3

Control Charts

Pay Factor

• Pay factor based on PWL• Compressive strength• Permeability

• Pay as in the current spec• Rideability • Thickness (pavements)

Estimating PWL• Compressive strength• QL = (Average – LSL)/s• Permeability

QU = (USL – Average)/s Q is the Quality Index, used to estimate

PWL (percent within limits) from TablesLSL: lower specification limitUSL: upper specification limits: sample standard deviation

Pay FactorPWL for strength and permeability:

• PF = 82 + 0.2 (PWL)

PF IS NOT ENFORCED IN PILOT PROJECTS.

• 100% pay for PWL = 90%

Average pay factor:

• C1(Perm)+C2(Str)/(C1+C2)

• C is a weighting factor

• Total pay factor = Average pay factor times unit bid price plus the additional price adjustment for deficient thickness (pavement) and incentive or disincentive for the ride quality.

A3 StrengthDistrict Mean Std Dev n sublots AVG PF

Richmond 4570 560 46 100.2

Fredericksburg 3850 600 19 92.40

Lynchburg 4010 460 7 95.40

Culpeper 4870 570 9 101.90

Bristol 4890 460 24 102.00

Staunton 4940 630 15 101.90

Hampton Roads 4760 550 82 101.20

NoVa 5230 800 54 101.30

Weighted average 4759 100.42

LSL = 3800 psi

A3 PermeabilityDistrict Mean Std Dev n USL AVG PF

Richmond 456 140 46 1700 102.00

Fredericksburg 1953 670 19 3200 101.00

Fredericksburg 1236 335 18 3200 102.00

Lynchburg 2670 1150 7 3200 95.40

Culpeper 1388 475 9 3200 102.00

Bristol 742 215 24 3200 102.00

Staunton 2080 430 15 3200 102.00

Hampton Roads 460 173 82 1700 102.00

NoVa 1075 345 26 3200 102.00

Wt avg USL1700 459 102.00

Wt avg USL 3200 1419 101.45

A4 StrengthDistrict Mean Std Dev n AVG PF

Richmond 4820 680 161 94.90

Culpeper 5540 810 6 99.90

Bristol 5080 860 10 82.57

Staunton 6790 1400 8 101.60

Staunton 5030 535 16 97.40

Salem 5010 300 29 101.30

Hampton Roads 5670 743 80 101.00

NoVa 5660 680 23 100.60

NoVa 6000 760 30 101.70

Wt average 5288 98.04

LSL = 4500 psi

A4 PermeabilityDistrict Mean Std Dev n USL AVG PF

Richmond 430 155 160 1700 102.00

Fredericksburg 1090 160 6 2200 102.00

Fredericksburg 1060 48 4 2200 102.00

Fredericksburg 870 180 24 2200 102.00

Bristol 1080 300 7 2200 102.00

Staunton 1695 190 8 2200 102.00

Staunton 3150 1020 16 2200 84.80

Salem 390 72 29 2200 102.00

Hampton Roads 440 174 57 1700 102.00

NoVa 940 200 19 2200 102.00

NoVa 840 200 6 2200 102.00

Wt avg USL 1700 433 102.00

Wt avg USL 2200 1155 99.69

Summary

Class Property Average Mean n PF

A3 Strength Weighted (Wt) 4759 274 100.42

Perm Wt (USL 1700) 459 128 102.00

Wt (USL 3200) 1419 118 101.45

A4 Strength Wt 5288 98.04

Perm Wt (USL 1700) 433 217 102.00

Wt (USL 2200) 1155 119 99.69

INDUSTRY CONCERNS

• Pay adjustment: Bonus is for the contractor, penalty for the producer.

• Sublot’s include day’s production, which is usually a small amount of concrete. Small amounts: not economical and affects analysis

• Concrete classes: not enough samples• Introduce one class concrete for the bridge structures:

high quality concrete is needed throughout the structure• No bonus if any lot has less than 90% PWL (“death

clause”). Ensure no major maintenance to any section during service life.

DISCUSSION AND CONCLUSIONS

• Innovation possible: contractors/producers design mixtures

• Performance parameters specified• Emphasize QC testing by the contractor • Prequalification• Cement reduction possible• Includes standard deviation: reduced

variability• Allow mix design approval process from ERS

as an option

Thank you.

Celik Ozyildirim, Ph.D., P.E.

Update on End Result Specifications Celik Ozyildirim, Ph.D., P.E.

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