Measurement of crack depths in concrete

composition is compared with model predictions based on modified plane-wave theory. 41606 Domone, P.L.; Casson, R.B.J. Ultrasonic testing of concrete Mathematical Modelling in Non-Destructive Testing, Cambridge (United K i n g d o m ) Sop. 1986, pp. 347-356. Edited by M. B l a k e m o r e and G . A . Georgiou. Clarendon Press (1988) Time-of-flight ultrasonic testing through hardened concrete is a standard and widely used technique. The stainless steel transducers have lead zirconate titanate ceramic piezoelectric elements. A commercial instrument, the PUND IT, is used for testing. Pulse velocity (UPV) through the concrete can be measured using PUND IT and recent experimental work is described. The implications of mathematical modelling using UPV is also discussed. 41520 Amoco Corporation Method and apparatus for determining cement conditions U.S. Patent No. 4,800,537 (24 Jan. 1989) This patent describes an acoustic method for determining the condition of cement next to casings in wellbores. Transducers are positioned internally and externally to the casing. Ultrasonic velocity measurements for transmission through the concrete casing are compared to known standard values and the results used to determine whether any foreign bodies or voids are present. 41286 Clemena, G.G.; Steele, R.E. Measurements of the thickness of in-place concrete with microwave reflection Virginia Transportation Research Council, Charlottesville (United States) PB88-232830/GAR, 40 pp. (Apr. 1989) Previous microwave reflection measurements made on simple, unreinforced concrete blocks have shown that the transit time of a microwave through concrete is linearly related to its thickness. In the study measurements were conducted on concrete slabs that were built to simulate pavements and on an actual continuouly reinforced concrete pavement to determine whether this type of rapid nondestructive measurement could be used in lieu of coring in the inspection of newly built concrete pavements for compliance with slab thickness specifications. 41199 Kabir, M.H.; Das, M.K. Non destructive testing in evaluation of quality of concrete of a muitistoried building in Dhaka City Proceedings of the 12th W o r l d Conference on Non-Destructive Testing, A m s t e r d a m (Netherlands), 23-28 Apr. 1989, Vol. 2, pp. 1596-1598. Edited by J. Boogaard and G . M . van Dijk, Elsevier, 1989. This paper reports a comparative study of results from cylinder tests and non destructive tests (NDT), using the ultrasonic pulse techniques, conducted on concrete of a 25 storied office building in Dhaka City. Statistical comparisons performed on strength values and their variations on global and local bases show reasonable degrees of agreement. 41197 Ohm, K.; Watanabe, T.; Jinzhong, Y.; Daft, T.; Henghui, C. Low frequency ultrasonic probe for testing concrete structure Proceedings of the 12th World Conference on Non-Destructive Testing, A m s t e r d a m (Netherlands), 23-28 Apr. 1989, Vol. 2, pp. 1582-1585. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989. In order to design a low frequency probe for testing concrete, a multi- layer piezo-electric transducer has been prepared and its characteristics have been analyzed by means of Mason's equivalent circuit. The resonator's material and its thickness must be selected according to the analysis. The frequency and impulse response of probe are shown. The probe must be matched acoustically to the specimen and also matched electrically to the equipment. 41196 Di Maio, A.A.; Traversa, L.P. Estimation of concrete strength in situ using nondestructive testing Proceedings of the 12th World Conference on Non-Destructive Testing, A m s t e r d a m (Netherlands), 23-28 Apr. 1989, Vol. 2, pp. 1579-1581. Edited by J. Boogaard and G . M . van Dijk, Elsevier, 1989. In this paper studies are presented about the evaluation of concrete quality in a wall corresponding to a two years old structure. The effective strength was realized using the ultrasonic method, the hammer rebound and the Break-Off test. Correlation equations were used which had previously been obtained in concrete elaborated with materials of similar characteristics, Correction factors for moisture content, carbonation and path length of the wave were also employed. The verification of the effective strength was done by means of compressive tests of cores drilled out of the structural element. 41135 Amoco Corporation Method for acoustic reverberation removal U.S. Patent No. 4,796,237 (3 Jan. 1989) Defects in cement in wellbores can be determined using this downhole tool. A transducer within the tool transmits pulses of acoustic energy. The time delay (DELTA t) between transmission of a pulse and the reception of the first acoustic reverberation is measured. Positive and negative pulses of energy are used to establish a reverberation pattern. 41041 Koo, J.; Lee, S.; Kim, Y.; Lew, H.S. Quantitative spectral analysis of the flaw detection in concrete Proceedings of the 12th World Conference on Non-Destructive

NDT International April 1990

Testing, Amsterdam (Netherlands), 23-28 Apr. 1989, Vol. 2, pp. 1255-1260. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989. For nondestructive detection of the flaws in concrete, the resonance method of transient stress waves is useful in high power and low attenuation. Quantitative spectral analysis of the spectrums for 2- dimensional scanning identifies the main peaks unambiguously and provides information about the depth and shape of the flaws. The test results from concrete blocks containing several types of artificial flaws are presented. 41040

Ogura, Y.; Miyajima, T.; Takishita, T.; Ohtake, K.; Akutsu,

Y. Measurement of crack depths in concrete Proceedings of the 12th World Conference on Non-Destructive Testing, A m s t e r d a m (Netherlands), 23-28 Apr. 1989, Vol. 2, pp. 1249-1254. Edited by J. Boogaard and G . M . van Dijk, Elsevier, 1989. A study was made on the low-frequency ultrasonic measurement of depths of surface opening cracks in concrete structures. Basic tests were conducted to obtain the relationship between crack depth and ultrasonic propagation time/reception frequency by varying the ultrasonic mode, frequency and distance between probe, revealing that with a suitable ultrasonic mode selected, there were correlations between crack depth and propagation time/reception frequency. The standard deviations with these methods were below 9.0 ram. 41039 Teodoru, G. V.M. A new answer to an old question: the non-destructive testing of concrete Proceedings of the 12th World Conference on Non-Destructive Testing, A m s t e r d a m (Netherlands), 23-28 Apr. 1989, Vol. 2, pp. 1237-1242. Edited by J. Boogaard and G . M . van Dijk, Elsevier, 1989. Details are presented about this method of multiple correlation. The method is based on simultaneous non-destructive tests (NDT): both ultrasonic pulse velocity (UPV) and attenuation and rebound indices of Schmidt Hammer type N are used. The utility of this concept for multiple correlation in the control of the concrete quality, especially in a plant for precast elements, is evident both directly for the assessment of the compressive strength of concrete, as well as from statistical quality analysis. Even when mathematically the degree of accuracy of predicted strength increases, the possibility of errors in this assessment is greatly reduced. 40955 Bungey, J.H. Monitoring concrete early age strength development Proceedings of the 12th World Conference on Non-Destructive Testing, A m s t e r d a m (Netherlands), 23-28 Apr. 1989, Vol. 2, pp. 1243-1248. Edited by J. Boogaard and G . M . van Dijk, Elsevier, 1989. A range of non-destructive techniques are examined to assess their reliability and practicability for on-site concrete strength estimation within the first 24 hours from casting. Some commonly used methods are found to be unsuitable for the low strength levels sometimes encountered. Laboratory and site trials related to cooling tower construction are reported with particular attention to strength correlations and early age variability of concrete properties. Proposals relating to planning, interpretation and economic advantages are also provided with reference to other applications within civil engineering construction. 40736 Naish, C.C.; O'Brien, T.M. Acoustic monitoring techniques for corrosion degradation in cemented waste canisters United K i n g d o m Atomic Energy Authority, Harwell, A E R E - G - 5 0 1 1 , 5 pp. (Feb. 1989) There is a requirement for radioactive waste producers to ensure the integrity of the cemented wasteform canisters that they produce. Presently available corrosion monitoring and NDT techniques are not readily applicable to cemented canisters. A technique that offers promise in monitoring degradation of a cement wasteform from the outside of a canister is acoustic emission. This report describes the progress of work being carded out to investigate acoustic emission as a monitor of corrosion and degradation of such wasteforms.

Mizunuma, M.; Hanada, H., Takagi, I.; Kadomatsu, Y.; Kitagawa, T. Sato, K.

40682

Experiments on the detection limit of iron reinforcement rods a n d various types of defects in X-rays and gamma ray radiographic test of concrete. (In Japanese) Journal of Japanese Society for Non-Destructive Inspection, Vol. 37, No. 9A, pp. 871-872 (Sop. 1988) 40654 Miyajima, T.; Ogura, Y.; Takishita, T. Trial for spectroscopy in ultrasonic testing of concrete (In Japanese) Journal of Japanese Society for Non-Destructive Inspection, Vol. 37, No. 9A, pp. 869-870 (Sep. 1988) 40559 Koido, J.; Hoshikawa, H.; lshibashi, Y. Basic characteristics of test coil for reinforcement of concrete (In Japanese) Journal of Japanese Society for Non-Destructive Inspection, Voi. 37, No. 9A, pp. 837-838 (Sep. 1988) 40348 Yokota, 0.; lshii, Y. Detection of reinforcing b a r in concrete constructions by electromagnetic induction testing

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