Update on concrete specifications, mix design, and the role of petrography in concrete construction. Ramón L. Carrasquillo, Ph.D., P.E.

Transcription

1 Update on concrete specifications, mix design, and the role of petrography in concrete construction by Ramón L. Carrasquillo, Ph.D., P.E. RRASQULLO ASSOCATES MATERALS, CONSTRUCTON AND STRUCTURAL CONSULTANTS SEAoT 2009 Annual Conference, Austin, TX, October 31,

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3 What is Needed? What is Specified? NEEDED? Strength Durability? SPECFED f c w/c ratio Field Quality Control QUALTY CONTROL Cylinder Strength NEEDED? Strength Durability? QUALTY CONTROL Test Results: 5500 psi 3300 psi SPECFED 3000 psi w/c = 0.45 SUBMTTAL f cr = 5800 psi w/c = 0.45 PRESCRPTVE SPECFTONS WATER-CEMENT RATO CYA GROWNG PANS PERFORMANCE PERMEABLTY KNOW WHAT YOU ARE DONG PRESCRPTVE Specifications Will (w/cm) ratio guarantee permeability? Will strength guarantee permeability? 3

4 WATER-CEMENT RATO The lower the water to cement ratio, the better the service life of the structure. True or False? Not Necessarily True! Lowering the water to cement ratio Complicates mix proportions ncreases number and dosage rate of chemical admixtures Unfriendly fresh concrete Higher concrete temperatures ncreases cracking Poor finishing Higher strengths? Durable? Performance Specifications Requirements for strength and durability Develop specification requirements Ensure compliance through quality control tests You must make sure that what you ordered is: What you needed What you received \PR-Apr01-Specs-099.jpg \PR-Scho-P1-028.jpg 4

5 \Linb-FW-082.jpg \Linb-FW-081.jpg What are we really interested in? Permeability of the concrete Protection of reinforcement against corrosion Chloride on ntrusion Quality Control Test: Resistance to Chloride ntrusion Permeability How can you predict the permeability of concrete at later ages (6 months) based on testing conducted at 28 days? Chloride Permeability Early Age Accelerated Curing for 28 days? Moist Curing at 73 F for 6 months Cement Type Class F Fly Ash None None w/cm (by wt.) day Moist Cured (Coulombs) day Accelerated Cured (Coulombs) month Moist Cured (Coulombs) d : Moist 73 F 7-28d : Moist 100 F None 20% 20% % % % %

6 w/cm: day Moist Cured 28d Accelerated Cured 6m Moist Cured Permeability, Coulombs Fly Ash Content, % PRDOT Special Provision 934 Structural Concrete Mineral Admixtures Fly Ash (equal weight basis) a) cement replacement up to 40% b) fine aggregate replacement up to 20% c) as any combination of a) and b) above Performance Based Specifications (PRDOT: SP934) 6

7 Table Portland Cement Concrete Mixtures Class of Concrete Specified Design Compressive Strength at 28 days (psi) * Permeability Maximum Charge Passed ** (Coulombs) Minimum Cementitious Content *** (lb/cy) (General Use) 3,000 See Table (934-2) 500 Compressive Strength Testing* Cylinder Size: 4 in. x 8 in. or 6 in. x 12 in. Test Age*: 28 days moist cured at 73 F V (General Use) 4,000 See Table (934-2) 550 V (Bridge Deck) 4,000 See Table (934-2) 600 * f test ages greater than 28 days are specified, acceptance of concrete could be based on 28 days accelerated test results. V (Drilled Shaft) 5,000 See Table (934-2) 650 V (Prestressed Members) 5,000 See Table (934-2) 650 V (Pavement) 5,000 See Table (934-2) days: moist cured at 73 F 7 28 days: moist cured at 105 F (PRDOT: SP934) (PRDOT: SP934) Permeability: Maximum Charge Passed** Slump (Resistance to Chloride Penetration) Classes of Concrete AASHTO T277 tested at 28 days 0 7 days: moist cured at 73 F 7 28 days: moist cured at 105 F 2. Slump of concrete for testing shall match job requirements and need not be limited to restrictions as stated in ASTM C157 Section 7.4. (PRDOT: SP934) (PRDOT: SP934) Workability Proportioning of Concrete e. The concrete mix shall be of adequate fresh concrete properties to be placed, consolidated and finished without segregation or defects that will affect the performance of the concrete in service. The Contractor is responsible to ensure that the concrete mix proportions are adequate to meet the minimum standards of practice for the concrete s intended use. (PRDOT: SP934) 7

8 GREEN BULDNG PROJECT UT Medical Sciences Complex Houston, TX Mix Designation MXTURE PROPORTONS Portland Cement Fly Ash sks pcy % pcy 6.0: : : : : Compressive Strength (psi) 12,000 10,000 8,000 6,000 4,000 2,000 0 UT MEDL SCENCES COMPLEX 6 sks / 0% FA 6 sks / 51% FA Age (days) Compressive Strength (psi) 12,000 10,000 8,000 6,000 4,000 2,000 0 UT MEDL SCENCES COMPLEX 6 sks / 0% FA 8.5 sks / 51% FA 8.5 sks / 60% FA 8.5 sks / 80% FA Age (days) RCPT (Coulombs) (564:0) UT MEDL SCENCES COMPLEX (276:278) (392:407) 6 sks / 0% FA 6 sks / 51% FA 8.5 sks / 51% FA 8.5 sks / 60% FA 8.5 sks / 80% FA Mixture Proportions (sks / % FA) (320:479) (PC, lbs / FA, lbs) Test Age: 90 days (160:639) 8

9 Typical Specifications Strength: 3000 psi Slump: 3-5 inches (w/c) max : 0.45 Cement: 5 sks. minimum Fly Ash: 20% maximum No HRWR } 470 Structural Safety Workability? Permeability? pcy What mix proportions will meet this specification? 376 pcy Cement 94 pcy Fly Ash Strength Cement Fly Ash Slump w/c No HRWR more workable? better concrete? 6.5 sks 5 sks minimum 376 pcy Cement 94 pcy Fly Ash more durable? better service life? 489 pcy Cement 122 pcy Fly Ash SPECFTONS Prescriptive 489 pcy Cement 122 pcy Fly Ash Performance 376 pcy Cement 94 pcy Fly Ash 141 pcy Fly Ash Strength 5 sks 376 pcy Cement 94 pcy Fly Ash PRESCRPTVE Durability 6.5 sks 489 pcy Cement 122 pcy Fly Ash 5 sks 376 pcy Cement 94 pcy Fly Ash 141 pcy Fly Ash as Mineral additive O.K. Strength Workability Consolidation Finishing Pumpability Durability Cracking Maintenance Service Life Quality Taxpayer s Cost O.K. Better Better Better Better Better Less Less Longer Better Lower 9

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13 Alkali-Silica Reaction TRADTONAL PETROGRAPHY nternal Sulfate Distress: DEF/LEF Fundamental Difference Between Mechanisms: ASR & DEF/LEF ASR DEF/LEF Expansion originates at the reactive aggregate particle Expansion originates at a discrete location within the cement paste - ettringite 13

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15 MUCHAS GRACAS! 15