Non destructive evaluation of in-situ strength of high strength concrete

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Non destructive evaluation of in-situ strength of high strength concrete

  1. 1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 21 NON- DESTRUCTIVE EVALUATION OF IN-SITU STRENGTH OF HIGH STRENGTH CONCRETE STRUCTURES Dr. K.V.Ramana Reddy Professor in Civil Engineering, Mahatma Gandhi Institute of Technology, Hyderabad- 500075, India ABSTRACT This paper deals with the evaluation of in-situ strength of high strength concrete (HSC) structures using Non Destructive Evaluation (NDE) techniques like Ultrasonic Pulse Velocity (UPV) Rebound Hammer test and combined methods. An experimental research was carried out, involving both destructive and non destructive methods applied to different concrete mixes, with compressive strength varying from 50 up to 130 MPa. Both cubic and cylindrical standard specimens and bigger blocks were cast with water cement ratio of 0.30. Just before conducting destructive test, UPV and Rebound Hammer tests were conducted on the same cubes as per IS 13311 (Part-1&2). The results of all the tests were utilized to obtain correlation curves between destructive and non-destructive parameters. For all the experimental values, design curves were drawn for correlating the compressive strength with the UPV and Rebound Number. Regression analysis was performed for assessment of in-situ strength of high strength concrete structures. Cores were also taken from the columns of the buildings for compressive strength. The results shows NDE techniques like pulse velocity, surface hardness and combined methods are suitable for evaluation of compressive strength of high strength concrete structures up to compressive strength of 130 MPa. Keywords: Concrete, HSC, Non-Destructive Evaluation Techniques, Combined methods. I. INTRODUCTION Non-Destructive Testing (NDT) is defined as one that does not damage or impair the intended performance of the structural element or member being tested. NDT methods offer simple, quick and reliable results if proper procedure and appropriate test programme are defined and implemented. NDT is a good tool to survey uniformity in quality of concrete, for damage assessment, to estimate current engineering properties of concrete-usually the compressive strength (Chandrakant B.Shah, 2002). It has been defined as comprising those test methods used to examine object, material or system without impairing its future usefulness (N.J.Carino, 1994). Strictly speaking, this definition of nondestructive testing does include noninvasive medical diagnostics. INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET) ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), pp. 21-28 © IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2013): 5.3277 (Calculated by GISI) www.jifactor.com IJCIET © IAEME
  2. 2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 22 Ultrasound, X-rays and endoscopes are used for both medical testing and industrial testing. The term is generally applied to non-medical investigations of material integrity. A number of other technologies - for instance, radio astronomy, voltage and amperage measurement and rheometry (flow measurement) - are nondestructive but are not used to evaluate material properties specifically. Of the various NDT, surface hardness method-Rebound hammer (RH) and ultrasonic pulse velocity (UPV) method are truly non-destructive and the others such as pull out test may cause some damage to the concrete. The demands on integrity assessment and life management of ageing infrastructure such as old buildings, bridges and dams are providing continuous impetus for development of reliable testing methods. These methods not only provide information on the necessity for repairs, but also frequency of future inspections/repairs as they sense damages at micro level (Francois Buyle-Bodin, 2003). However, while assessing the capabilities and limitations of various non-destructive testing (NDT) and evaluation techniques that can be applied to concrete structures, it has been fount that, in many cases, the data obtained are qualitative rather than quantitative and hence efforts are being made to overcome this limitation. The evaluation by non destructive methods of the actual compressive strength of concrete in existing structures is based on empirical relations between strength and non destructive parameters (K.V.Ramana Reddy, 2008). . The most commonly used testing methods are rebound hammer, pulse velocity, microcoring and combined methods. The validity of the above mentioned relations is actually limited to normal strength concrete, up to 50 MPa. HSC has been employed in recent years, with compressive strength up to 130 MPa and over. The relations used to evaluate the compressive strength of normal concrete by non destructive tests may be no longer valid for HSC. This experimental research is aimed to verify the possibility of applying the known NDT methods to HSC, to state the limits of the testing equipment available and to extend the existing relations, or determine new ones between no destructive parameters and compressive strength of high strength concrete. II. EXPERIMENTAL PROGRAMME Materials: The materials used in the present investigations are summarized below. Throughout the investigation, the materials have been procured from the same respective sources for maintaining uniformity in all the cubes cast. Cement: Ordinary Portland Cement of 43 grade has been procured confirming to IS:8112 and is used in the present investigation. Fine Aggregate: The locally available sand is used as fine aggregate. The local sand free from clay, silt and organic impurities and confirming to IS:383-1970 is used as fine aggregate. Coarse Aggregate: Machine crushed well graded angular granite aggregate of maximum size 20 mm free from impurities such as dust, clay particles and organic matter confirming to IS:383-1970 is used as coarse aggregate. Water: The locally available potable water, which is free from concentration of acids and organic substances, is used for mixing the concrete and curing the specimens. Admixture: A new superplasticiser based on carboxylic ether polymer with long side chains (Glenium 51 of M/s. MAC S.p.A., Treviso, Italy) was used. Flyash: Class F flyash from thermal power plants Mix Design: In the present work, mix design is carried out by Indian Standard recommended method IS 10262:1982 and also as per the procedure laid down in IS: 456: 2000. The quantities of dry materials used for the grades to obtain one cum of compacted concrete have shown in the Table.1.
  3. 3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 23 Table. 1 Quantities of materials S. No Grade of Concrete Proportion of Mix Cement (kg) Fine Aggregate (kg) Coarse Aggregate (kg) Flyash (kg) Super Plasticizer (cc) 1 M 40 1:1.22: 2.14 410 613 1135 - 1200 2 M 50 1:1.12: 2.09 430 642 1176 121 1350 3 M 60 1:1.02: 2.02 480 633 1186 164 1560 4 M 70 1:0.90: 1.82 510 426 1242 198 1852 5 M 80 1:0.78: 1.65 530 385 1341 209 1964 6 M 90 1:0.72: 1.45 540 346 1369 245 2052 7 M 100 1:1.65: 1.42 550 315 1405 269 2126 One hundred and ten cubes were cast and results obtained at ages of 7, 14, 28, and 56 days. Non- destructive tests were conducted viz rebound hammer, ultrasonic pulse velocity techniques and combined method. On the same specimens compression test was conducted on digital compression testing machine of 3000 kN capacity. III. CORRELATION CURVES The experimental work is carried out on plain concrete of various grades form 50 MPa to 130MPa. Concrete cubes of size 150x150x150mm were cast with W/C ratio of 0.3 and cured and tested for 7,14,28,56 days compressive strength. Before testing for compressive strength, Ultrasonic Pulse Velocity (UPV) Rebound Hammer and combined methods for assessment of strength of concrete. All these results used to obtain correlation curves between destructive and non-destructive parameters. For all the experimental values, correlation curves were drawn between compressive strength and NDE techniques and were presented in Figures.1, 2 and 3. Some of the photographs were also presented from plate numbers1 to 4. Regression analysis was also made to correlate the values from one another. Fig. 1 Correlation between compressive strength and UPV Values y = 83.57x - 299.3 R² = 0.990 40 50 60 70 80 90 100 110 120 130 140 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 ComprtessiveStrengthinMpa UPV Values in km/s
  4. 4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 24 Fig. 2 Correlation between compressive strength and rebound number Fig. 3 Equal strengthg lines based on linear regression analysis of data obtained from combined method of rebound hammer and ultrsonic pulse velocity y = 4.443x - 114.4 R² = 0.997 35 45 55 65 75 85 95 105 115 125 135 30 35 40 45 50 55 60 CompressivestrengthinMpa Rebound number y = 6.492x + 7.935 R² = 0.935 20 24 28 32 36 40 44 48 52 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 ReboundNumber Pulse Velocity (km/s) Fig. 3 Equal strengthg lines based on linear regression analysis of data obtained from combined method of rebound hammer and ultrsonic pulse velocity 15-24.9 MPa 25-34.9 MPa 35-44.9 MPa 45-54.9 MPa 55-64.9 MPa 65-70 MPa Linear (65-70 MPa)
  5. 5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 25 From the Design curves, mathematical equations are formulated and is shown in Table:2. Table:2 Mathematical Equations for compressive strength from NDE techniques Sl. No NDE technique Equation Regression co-efficient 1 Ultrasonic Pulse Velocity fc = 83.57V-299.3 R2 =0.990 2. Rebound Hammer fc = 4.443R-114.4 R2 =0.997 3. Combined Method fc =1.24R+0.058V4 -24.1 R2 =0.935 Note: units of V is km/s Plate 1: Rebound Hammer Test on a Bridge pier Plate 2: UPV Test on a RCC slab Plate 3: Core Extraction from Bridge PierPlate 4 : Rebound Hammer test on slabs
  6. 6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 26 IV. DISCUSSION OF TEST RESULTS To validate the above obtained mathematical equations from the Design curves, ultrasonic pulse velocity and rebound hammer tests were conducted as per the procedures laid down in IS- 13311 (Part1&2),on various bridges and flyovers in and around Hyderabad and also on the gas turbine foundations of Gautami Power Project, Samarlakota, India. Ten concrete cores of 55 mm diameter were extracted from hardened concrete (beams, columns) on which UPV and RH tests have been conducted for evaluating the actual in -situ strength of the structures. These concrete core samples were used to determine the density also. The parameters which influence the measured compressive strength are size of the specimen i.e diameter as well as length to diameter ratio, direction of drilling, method of capping, the effect of drilling operations, moisture conditions of the core at the time of testing as per IS:516. The equivalent cube strength of concrete are presented in the Table:3 for comparison. A curve was drawn between predicted strength by mathematical equations and experimental strength from cores taken in the field and is shown in Fig.4. On comparison, it is found that there is about 10% variation in these values. Table: 3 Statistically analyzed data of UPV and RH tests Item Pair of UPV spots Ultrasonic Pulse Velocity No. of Rebo- -und Num- bers Rebound Number (RN) Qualityofconc. Est.strengthfromUPV(Mpa) Est.strengthfromRH(Mpa) Avg.Est.strength (Mpa) Exp.Strengthfromcores(Mpa) Mean Velo- city (km/s) Std. Devi - ation (km/ s) Co- eff of vari-- ation Mean RN Std. Devi- ation Co- eff of Vari- ation OB1 75 3.58 161 4.6 400 27.42 4.85 17.5 G 31.23 32.2 31.71 33.5 OB2 52 3.75 213 6.7 126 28.4 4.13 14.20 G 35.25 36.5 35.88 38.45 NB1 64 4.25 375 8.10 370 32.45 4.92 17.64 G 41.1 43.2 42.15 45.95 NB2 15 4.34 392 7.90 85 31.52 5.10 16.49 G 38.8 38.2 38.5 41.9 B1 52 4.85 521 6.40 42 145 4.15 18.92 E 78.5 80.2 79.35 86.95 B2 46 4.99 463 6.87 36 151 5.12 17.98 E 86.1 85.6 85.85 93.25 F 36 4.98 502 5.8 24 148 4.86 21.40 E 85.6 87.4 86.5 93.95 GT1 15 5.25 124 5.10 40 39.5 4.90 15.20 E 109.5 110.5 110.0 119.5 GT2 10 5.15 201 8.10 60 43.2 3.70 17.15 E 102.5 100.2 101.4 110.6 OB: Old Building NB: New building GT: Gas Turbine Foundations B: Bridge F: Flyover G: Good E: Excellent
  7. 7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 27 Fig. 4 Comparison between Experimental and predicted in- situ strengths V. CONCLUSIONS 1. The in-situ strength of concrete obtained from the destructive testing is about 10% more than that predicted based on the design curves and mathematical equations presented in this paper. 2. Combined Method of UPV and Rebound Hammer technique is found to be more effective for validating the in - situ strength of high strength concrete structures. VI. ACKNOWLEDGEMENTS Vasavi College of Engineering and Civil-Aid Technoclinic Private Limited, Hyderabad, are greatly acknowledged for extending the facilities and co- operation for conducting the experiments. VII. REFERENCES [1] Chandrakant B.Shah ,2002, “NDT of earthquake-affected structures in Gujarat: Case study” The Indian Concrete Journal [2] Francois Buyle-Bodin, 2003,”Contribution of coupling non-destructive methods for diagnosis of concrete structures”, International symposium (NDTCE-2003),Japan [3] Konstantin Kovier and Isaak Schamban, 1999, “Mathematical Methods of Experimental Design in Nondestructive Testing”, International Simposium on NDT Contribution to the Infrastructure Safety Systems, Brazil [4] T.Jayakumar 2003, “Integrity assessment of concrete structures using Non Destructive Evaluatioin Techniques”, INCONTEST- 2003, India [5] Giovanni Pascale,2000, “ Evaluation of Actual Compressive Strength of High Strength Concrete by NDT” Rama2000, Italy [6] K.V.Ramana Reddy, 2007, “ Assessment of Strength of Concrete By Non-Destructive Testing Techniques” International conference on Fast track construction of Bridges (IIBE), Hyderabad, India 40 60 80 100 120 140 40 55 70 85 100 115 130 145 Estimatedstrength(Mpa) Prdicted strength (MPa) Predicted Strength (Mpa) Experimental Strength(MPa)
  8. 8. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 28 [7] Samarin.A.(1984) “Determination of in-situ concrete strength; rapidly and confidently by non- destructive testing” ACI, Detroit [8] Malhotra.V.M,(2001): Testing of in-situ concrete: Non-Destructive Methods [9] K.V.Ramana Reddy, 2008, “ Design curves and mathematical equations for in-situ strength of concrete structures by NDE Techniques” International conference on Advances in concrete construction (ICACC- 2008) VCE, Hyderabad, India [10] Giovanni Pascale ( 2000): “Evaluation of Actual Compressive Strength of High Strength Concrete by NDT” Roma 2000. [11] Dr. Debasish Basak and Bubun Das, “In-Situ Nondestructive Assessment of a Winder Rope of a Coal Mine”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 416 - 421, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [12] D.B.Mohite and S.B.Shinde, “Experimental Investigation on Effect of Different Shaped Steel Fibers on Flexural Strength of High Strength Concrete”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 2, 2013, pp. 332 - 336, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

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