Tests to Verify Low Strength Concrete ACI Georgia Chapter Virgil D. Skipper Seminar June 2009 Robert Jenkins, P. E

Tests to Verify Tests to Verify Low Strength ConcreteLow Strength Concrete

ACI Georgia ChapterACI Georgia ChapterVirgil D. Skipper SeminarVirgil D. Skipper Seminar

June 2009June 2009

Robert Jenkins, P. E.Robert Jenkins, P. E.

Available Testing ProceduresAvailable Testing Procedures

CoresCores Nondestructive EvaluationNondestructive Evaluation Load TestsLoad Tests

Core Strength TestsCore Strength Tests SPECIFICATIONS FOR STRUCTURAL CONCRETE

ACI 301-05

1.6.5.3.a Where required by the Architect/Engineer, obtain cores in accordance with ASTM C 42/C42 M.

1.6.7.3 Core tests—Strength level of concrete in the area represented by core tests will be considered adequate when the average compressive strength of the cores is equal to at least 85% of fc′ , and if no single core is less than 75% of the specified compressive strength fc′ .

Nondestructive EvaluationNondestructive Evaluation

Unanticipated testing of Unanticipated testing of hardened concrete hardened concrete• Rebound Hammer ASTM C805Rebound Hammer ASTM C805• Penetrating Probe ASTM C803Penetrating Probe ASTM C803• Ultrasonic Wave Velocity Ultrasonic Wave Velocity

Through transmission testing ASTM C597Through transmission testing ASTM C597 Impact Echo testing ASTM C1383Impact Echo testing ASTM C1383

• Pullout Test ASTM C900Pullout Test ASTM C900

Nondestructive TestsSPECIFICATIONS FOR STRUCTURAL CONCRETE

ACI 301-05

1.6.6.2 Nondestructive tests—Test results will be evaluated by the Architect/Engineer and will be valid only if tests have been conducted using properly calibrated equipment in accordance with recognized standard procedures and an acceptable correlation between test results and concrete compressive strength has been established and is submitted.

* * *1.6.7.2 Nondestructive tests—Nondestructive tests shall not be used as the sole basis for accepting or rejecting concrete, but may be used, when permitted, to evaluate concrete where standard molded and cured cylinders have yielded results not meeting the criteria in 1.6.7.1.

Load Test EvaluationLoad Test EvaluationACI 318-08ACI 318-08

20.1.3 — If the effect of the strength deficiency is not well understood or if it is not feasible to establish the required dimensions and material properties by measurement, a load test shall be required if the structure is to remain in service.

Available NondestructiveAvailable NondestructiveTest MethodsTest Methods

• Rebound Hammer ASTM C805Rebound Hammer ASTM C805• Penetrating Probe ASTM C803Penetrating Probe ASTM C803• Ultrasonic Wave Velocity Ultrasonic Wave Velocity

Through transmission testing ASTM C597Through transmission testing ASTM C597 Impact Echo testing ASTM C1383Impact Echo testing ASTM C1383

• Pullout Test ASTM C900Pullout Test ASTM C900

Rebound Hammer Rebound Hammer ASTM C805ASTM C805

Rebound Number CorrelationsRebound Number Correlations

Penetrating Probe Penetrating Probe ASTM C803ASTM C803

Penetrating Probe Penetrating Probe ASTM C803ASTM C803

Penetrating Probe CorrelationsPenetrating Probe Correlations

Ultrasonic Wave EvaluationUltrasonic Wave Evaluation

UltrasonicUltrasonicPulsePulseVelocityVelocity

ASTMASTMC597C597

Ultrasonic Pulse Velocity Ultrasonic Pulse Velocity CorrelationCorrelation

Impact - Echo Testing Impact - Echo Testing ASTM C1383ASTM C1383

T=CT=Cpp/2*f/2*f

CCpp=T*2*f=T*2*f

PulloutPulloutTestTest

ASTMASTM

C900C900

Pullout Test - CAPOPullout Test - CAPO

Pullout TestPullout Testcracking patternscracking patterns

Pullout Test – CAPO correlationPullout Test – CAPO correlation

In-Place Methods to Estimate In-Place Methods to Estimate Concrete StrengthConcrete Strength

ACI Report 228.1-03ACI Report 228.1-03• Review of Test MethodsReview of Test Methods• Statistical Characteristics of Test ResultsStatistical Characteristics of Test Results• Development of Strength RelationshipDevelopment of Strength Relationship• Implementation of In-Place TestingImplementation of In-Place Testing• Interpretation and Reporting of ResultsInterpretation and Reporting of Results• In-Place Tests for Acceptance of ConcreteIn-Place Tests for Acceptance of Concrete

Construction Project ScenarioConstruction Project Scenario

High Rise Construction – Office TowerHigh Rise Construction – Office Tower

Concrete PlacementConcrete Placement Columns – 7000 psi @ 28 days 60 yardsColumns – 7000 psi @ 28 days 60 yards Floor slab – 3500 psi @ 28 days 240 yardsFloor slab – 3500 psi @ 28 days 240 yards

Cylinder Test ReportsCylinder Test Reports

7 day strengths7 day strengths Set 1 (slab) - 2880 psiSet 1 (slab) - 2880 psi Set 2 (slab) - 2780 psiSet 2 (slab) - 2780 psi Set 3 (slab) – 2865 psiSet 3 (slab) – 2865 psi Set 4 (column) – 3580 psiSet 4 (column) – 3580 psi

Ultrasonic TestingUltrasonic Testingat 12 days ageat 12 days age

ColumnsColumns

TopTop 11500 fps11500 fps

MiddleMiddle 12000 fps12000 fps

BottomBottom 12500 fps12500 fps

SlabsSlabs 12000 fps12000 fps

Validity of Ultrasonic Wave VelocityValidity of Ultrasonic Wave Velocity

Water content of concrete can have an Water content of concrete can have an effect on the wave velocity.effect on the wave velocity.

At higher strengths the spread of wave At higher strengths the spread of wave velocity verses compressive strength is velocity verses compressive strength is less.less.

The tests of vertical elements must The tests of vertical elements must consider the top to bottom effect.consider the top to bottom effect.

Ultrasonic wave tests are affected by Ultrasonic wave tests are affected by discontinuities in the concrete.discontinuities in the concrete.






Ultrasonic Pulse VelocityUltrasonic Pulse Velocity






Ultrasonic Ultrasonic PulsePulse Velocity Velocity

Top to Bottom EffectTop to Bottom EffectWhen concrete is placed in a tall When concrete is placed in a tall vertical placement such as a vertical placement such as a column or a wall; there is a column or a wall; there is a difference in the concrete difference in the concrete strengths from top to bottom with strengths from top to bottom with greater strengths at the bottom of greater strengths at the bottom of the placement.the placement.






Travel time of wave through concreteTravel time of wave through concrete


7 day strengths7 day strengths Set 1 (slab) - 2880 psiSet 1 (slab) - 2880 psi Set 2 (slab) - 2780 psiSet 2 (slab) - 2780 psi Set 3 (slab) – 2865 psiSet 3 (slab) – 2865 psi Set 4 (column) – 3580 psiSet 4 (column) – 3580 psi

28 day strengths28 day strengths Set 1 (slab) – 4120 psiSet 1 (slab) – 4120 psi Set 2 (slab) – 4280 psiSet 2 (slab) – 4280 psi Set 3 (slab) – 3820 psiSet 3 (slab) – 3820 psi Set 4 (column) – 4480 psiSet 4 (column) – 4480 psi

Rebound HammerRebound Hammerat 35 days ageat 35 days age

Columns Columns Average Rn = 29Average Rn = 29Range Rn 26 to 35Range Rn 26 to 35

SlabsSlabsAverage Rn = 26Average Rn = 26Range Rn 20 to 31Range Rn 20 to 31

Validity of Rebound TestingValidity of Rebound Testing

Testing the hardness (stiffness) of the Testing the hardness (stiffness) of the concrete surface and shallow depth into concrete surface and shallow depth into concrete.concrete. Affected by:Affected by:

Form material and type and smoothnessForm material and type and smoothness Aggregates, closeness to surfaceAggregates, closeness to surface Reinforcing steel, closeness to surfaceReinforcing steel, closeness to surface Moisture contentMoisture content Surface finishSurface finish Hammer orientation Hammer orientation

Rebound Number CorrelationsRebound Number Correlations

Variation of Rebound NumbersVariation of Rebound Numbers


28 day strengths28 day strengths Set 1 (slab) – 4120 psiSet 1 (slab) – 4120 psi Set 2 (slab) – 4280 psiSet 2 (slab) – 4280 psi Set 3 (slab) – 3820 psiSet 3 (slab) – 3820 psi Set 4 (column) – 4480 psiSet 4 (column) – 4480 psi

56 day strengths56 day strengths Set 4 (column) – 4930 Set 4 (column) – 4930

psipsi

Coring - PROBLEMSCoring - PROBLEMS

Where to core?Where to core? Columns have No. 8 vertical reinforcing Columns have No. 8 vertical reinforcing

bars at 3 inches on center. Clear distance bars at 3 inches on center. Clear distance between bars is 2 inches.between bars is 2 inches.

ASTM C42 – cores for load bearing ASTM C42 – cores for load bearing elements minimum 3.70 inch diameter.elements minimum 3.70 inch diameter.

Core between bars yields 1.75 inch Core between bars yields 1.75 inch diameter – less than 2 times nominal diameter – less than 2 times nominal maximum aggregate sizemaximum aggregate size

WHAT TO DO???WHAT TO DO???

Other Nondestructive TestsOther Nondestructive Tests

Penetration ProbePenetration Probe• Interference from rebarInterference from rebar

Pullout Test – CAPOPullout Test – CAPO

ProblemsProblems Number of tests required and Number of tests required and

correlation to concrete strength.correlation to concrete strength.

Load TestsLoad Tests

How do you load test a How do you load test a column?column?

Or 15 columns?Or 15 columns?

Load Tests of ConcreteLoad Tests of Concrete

Usual area load of slabUsual area load of slab Pattern loading of slabs and beamsPattern loading of slabs and beams Concentrated loading of beam haunchConcentrated loading of beam haunch Special jacks and tension rods for Special jacks and tension rods for

punching shear around column.punching shear around column. Cyclic load testing using closed loop Cyclic load testing using closed loop

controllers and hydraulic jacks.controllers and hydraulic jacks.

Discussion of load testsDiscussion of load tests

Strength Evaluation of Existing Strength Evaluation of Existing Concrete BuildingsConcrete Buildings

ACI Report 437R-03ACI Report 437R-03

• Redo ultrasonic tests – concrete has dried sufficiently.

• Take small diameter cores where lower wave velocities are noted.

• Engineers determine that 5000 psi is sufficient strength for these columns.

Questions

Documents

Tests to Verify Low Strength Concrete ACI Georgia Chapter Virgil D. Skipper Seminar June 2009 Robert Jenkins, P. E