In-Place Strength by Pullout

Transcription

1 In-Place Strength by Pullout The Concrete Industry Board of NYC (CIB) NYC Chapter of ACI New York January 8th, 2013 Claus Germann Petersen GERMANN INSTRUMENTS, Inc. In-Place Strength by Pullout Acknowledgement Dr. Nicholas J. Carino Concrete Technology Consultant & Dr.Andrzej Tadeusz Moczko Professor, Wroclaw University

2 In-Place Strength Evaluation by Testing cores Rebound hammer UPV Pullout test Pull-off test Maturity method Pullout Test ASTM C 900 Measure force to pullout an insert anchored in concrete. Cast-in-place (CIP): LOK-Test Post-installed (PI): CAPO-Test

3 LOK-TEST CAPO-TEST 25 mm 25 mm 25 mm 55 mm F 25 mm 55 mm F Instrument 1972 and today 0-40 kn, 43 kg kn, 4 kg Automatic registration of data and peak value

4 Birth of CAPO-TEST 1976 Drilling from the bottom of a 75 cm thick slab in preparation for LOK- TEST at the top of the slab 1st CAPO-TEST in the world performed adjacent to LOK-TEST LOK-Test Pullout Failure COMA-Meter for maturity Apply Pullout Load Conical Fragment

5 Capo-Test Pullout LOK-TEST Insert Hardware Attached to formwork cutouts Nailed to formwork Floated into surface

6 LOK-Test Pullout 25 mm Insert Insert Steel Plate 25 mm Formwork LOK-TEST Pullout Insert Insert Reaction Ring Pullout Force

7 LOK-Test Pullout Insert Insert Reaction Ring Pullout Force Cut hole in formwork

8 Attach backing plate and fasten insert Insert Plate Sealant Attach insert support assembly to form Apply sealant Place concrete

9 Remove backing plate Attach loading system Apply load Measure pullout strength Pressure gage Ultimate Pullout Load At peak load, 0.5 mm surface displacement Gradual decrease in load with continued displacement P u Surface Displacement

10 Estimate Concrete Strength 100 Compressive Strength, MPa f cube = 0.76 F Pullout Load, kn f cyl = 0.69 F 1.12 General Correlations for Cylinder and Cube Strength Strength indication by maturity Requires pre-established strength-maturity relationship in the lab, and: Same concrete quality on-site as in the lab Same curing conditions Same compaction

11 Maturity + Pullout Testing Use the maturity method to determine when the required strength should have been achieved in the structure Verify by using pullout tests to estimate inplace strength Combination of maturity and pullout testing can lead to rapid and safe concrete construction Pullout timed by Maturity 50 Compressive Sterngth, MPa Mixture A Mixture B Mixture C M 20, days at 20 o C

12 Caution! Tensioning of anchors in bridge girders was made at sufficient maturity, including a safety factor The concrete failed anyhow at one of the anchors destroying one girder Subsequent testing by impact-echo (left) and ultrasound echo (right) revealed a large honeycomb in the anchor s trumphet zone

13 Insert Hardware Floated into surface Floated Surface Inserts Does not require cutting holes into formwork Training for proper placement Good consolidation around insert head Minimum of surface voids Ensure representative aggregates in failure zone Requires workable concrete

14 Push insert into concrete Move sideward for aggregates to flow into the failure zone Tilt for air to escape below the insert plate Correctly installed floating inserts

15 Sharp 55 mm dia.edge from the reaction ring No surface voids Correctly performed LOK-Test using floating inserts Clearance Requirements ASTM C900 Insert clearance >200 mm >100 mm 25 mm d b d b or NMSA Reinforcement clearance Edge distance

16 Post-Installed Tests CAPO-Test Does not require pre-planning test locations Can perform test at any accessible location Permits testing of existing structures CAPO-Test Pullout

17 Prepare Concrete Core hole 18 mm dia. Plane surface 25 mm 18 mm 25 mm Cut slot 25 mm Core Hole

18 Surface Planing

19 Cut Slot 25 mm Cut Slot

20 Cut Slot Insert Expansion Cone and Coiled Split-Ring Coiled ring Cone

21 Ring Expansion Hardware Nut Coiled ring Cone Expand Ring Nut

22 Expand Ring Pullout the Expanded Ring

23 Apply Pullout Force Acceptable Test Complete failure ring

24 Unacceptable Test Incomplete failure ring General Approach to In-Place Testing Pre-construction meeting to plan the in-place testing program Develop a correlation (strength relationship) for the concrete to be used in construction Perform in-place tests on the structure Apply statistical methods to estimate in-place strength (ACI 228.1R)

25 Correlation Testing Prepare cylinders (or cubes) Prepare cubes with inserts Cure under same conditions 2 x LOK-Test 2 x CAPO-Test Correlation Testing Test 2 cylinders (cubes) and perform 8 pullout tests at each test age: 1, 2, 3, 7, 14 and 28 days 200 mm 200 mm

26 Example of Correlation Cylinder Strength, MPa Cylinder Strength, MPa Upper 95 % CL Lower 95 % CL Manufacturer Pullout Force, kn CAPO-Test vs LOK-Test 70 CAPO-Test, kn Line of Equality LOK -Test, kn

27 Cylinder strength relations Cylinder Strength, MPa Cylinder Strength Correlations Cylinder Stength Correlations Pullout Load, kn Cube Strength Correlations Cube Cube Strength Strength Correlations Cube Strength, MPa Pullout Load, kn

28 LOK- / CAPO-TEST General Correlations 100 Compressive Strength, MPa f cube = 0.76 F Pullout Load, kn f cyl = 0.69 F 1.12 General Correlations for Cylinder and Cube Strength Robust Correlation Not affected by: Cementitious materials Water-cement ratio SCC mixtures Fibers Age Air entrainment Admixtures Curing conditions Shape, type or size of aggregate < 40 mm Lightweight aggregate, however, produces significantly Test different smart Build correlation right

29 Correlation Pullout strength is related fundamentally to concrete strength Studies of test have been done Finite element study (Ottosen, 1981) Compression strut theory (Krenchel, 1987) Pullout Failure Mechanism Compression strut theory

30 Pullout Failure Mechanism Compression strut theory Compression Strut

31 Variation and duration of test Variation on homogeneous concrete is 6-8%, lower for shotcrete 3-5% In-place variabilty depends on the type of structure and the position of the test Duration of test: LOK-Test 3-4 minutes, CAPO-Test minutes Results are immediately available on-site Examples Pullout Testing

32 COMA-Meter for maturity

33 Comparative study Polish bridges for increased loading Cores, sawcut, capped, tested after 5 days drying in lab conditions (100 mm dia x 100 mm cores) CAPO-Test in-situ, double amount of cores Schmidt Hammer in-situ, up to 20 locations, each 6 tests Schmidt Hammer on side of cores prior to compression tests Age of structures: years Depth of carbonation: 4-35 mm Bridge No. Cores from structure Capo-Test on structure Schmidt Hammer on structure Schmidt Hammer on cores MPa Av. of MPa α(ct) MPa α(l) MPa α(lm) % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % Avg % % Comparative testing, Polish experience, bridges years old, ref. A. Mozcko,, Wroclaw University

34 Capo-Test on shotcrete, Cigar Lake Mining Project, Saskatchewan, Canada Compressive Strength fc (MPa) CYL, 150 x 300mm, <8 mm max aggregate size Cores, 150 x 300mm, mortar Capo-Test Pullout Load F (kn) Correlations on mortar (Yun, 1988) and concrete with < 8 mm maximum aggregate size (Krenchel, 1984)

35 CAPO Equipment Preparation Kit Pullmachine Kit DSV Kit Capo Inserts

36 Summary Pullout test is a reliable method for estimating in-place compressive strength of the cover layer Can be used for new construction and existing construction General correlations according to EN : 2005 Following ASTM C confirm general correlations for LOK-Test For CAPO-Test cores can be drilled out for comparison to the general correlation When correlating to cores Pullout test is testing the outer 25 mm cover layer of the structure, cores the interior Moisture conditioning of cores affects core strength (as well as other factors)

37 Moisture conditioning of cores In the past, cores were tested after a period of air drying or after being submerged for at least 40 h In high w/c concrete, storage under water for 40 h resulted in saturation With modern concrete and lower w/c, storage under water leads to moisture gradient Research Findings

38 Moisture Gradients Immediately After Wet Drilling Moistened concrete tends to swell Swelling is restrained by dry interior Results in internal stresses; outer region in compression Measured strength is reduced Tension Compression CT003 Joint Industry Study

39 Effect of Core Conditioning on Strength CT003 Moisture Conditioning ASTM C42/C42M Wipe off drilling water, surface dry Place in watertight containers Wait at least 5 days between wetting due to drilling or sawing and testing Other procedure permitted when required by the specifier of tests

40 ACI 214.4R for coring In-place strength Correction for L/D Correction for D Correction for moisture content Core strength Correction for damage due to coring Equivalent specified strength f ' c, eq = Kf c Average in-place strength Statistical factor Other systems correlations Rebound Hammer UPV

41 Rebound number to cores, mix specific Core Strength, MPa Ward, M.A. and Langan, B.W., Cement Concrete and Aggregates, 16(2), Dec. 1994, Rebound Number n = 13 Core Strength Upper 95 % CL Lower 95 % CL Factors Affecting Rebound Number Strength and elastic modulus of concrete near to surface Aggregate type dependence Thickness of carbonation zone Surface texture Surface moisture condition Rigidity of test object

42 Comparison of Relationships 50 Core Strength, MPa Case 1 Case Rebound Number Strength Relationship UPV Physics: V E Empirically: f c E ( V) 4 f c f c For mature concrete, large increase in strength is accompanied by small increase in velocity. Velocity

43 Relationship for a specific mix Compressive Strength, MPa day day 15 1 day Pulse Velocity, m/s Factors Affecting UPV for Given Concrete Strength Aggregate type Aggregate content Moisture content Saturated concrete 5 % greater UPV than dry Presence of reinforcement Perpendicular to pulse path Parallel to pulse path

44 Example Aggregate Type Ref: Bungey, 1982 Why is cube strength higher than cylinder strength?

45 Cube and cylinder strength correlations 100 Compressive Strength, MPa f cube = 0.76 F x 150 cubes Pullout Load, kn f cyl = 0.69 F x 300 cylinders General Correlations for Cylinder and Cube Strength Effect of End Friction Triaxial Compression Frictional Stresses Zones of triaxial compress ion

46 As L/D Decreases Strength Increases Evaluation techniques by Testing cores Rebound hammer UPV Pullout test Pull-off test Maturity method are dealt with in detail at our NDT Workshops

47 Thank you for your attention