43552 Tusker, C.G.; Milne, J.M.; Smith, R.L Recent work at the National NDT Centre on concrete inspection Impact o f Non-Dest ruc t ive Testing, Proceedings o f the 28th Annua l Brit ish Conference on Non-Dest ruct ive Testing, Sheff ield (United Kingdom) , 18-21 Sop. 1989. pp. 271-284. Edi ted by C Brook and P.D Hanstead. Pe rgamon Press, (1990)

The work carried out at the National NDT Centre at Harwell during the past year on the non-destructive inspection of concrete is presented. Described are two new advances in concrete inspection - Laser generation and detection of ultrasound in concrete and the application of Pulse Video Thermography to concrete inspection. Both techniques are at a nascent stage of development but show considerable promise. Some early results are presented together with discussions on how well these techniques stand against some presently accepted methods for inspecting concrete.

43408 Tusker, C.G.; Smith, R.L. Ultrasonic techniques for the non-destructive testing of concrete Reliabili ty in Non-Dest ruct ive Testing, Proceedings o f the 27th Annua l British Conference on Non-Dest ruc t ive Testing, Por tsmouth (United Kingdom), 12-15 Sep. 1988. pp. 299-307. Edited by C. Brook and P.D. Hanstead. Pergamon Press, 1989.

The use of ultrasonic resonance, pulse velocity measurement and surface wave scanning for the non-destructive inspection of concrete and the recent development at the National NDT Centre of two concrete inspection systems based on these techniques are described. Results obtained during laboratory trials are also presented.

43290 Marl, A.K.; Ouyang, C.; Shah, S.P. Fracture mechanisms of quasi-brittle m a t e r i a l s b a s e d on acoustic emission Journal o f Materials Research, Vol. 5, No. 1, pp. 206-217 (Jan. 1990)

In this study, piezoelectric transducers were calibrated using displacement transducers. The validity of an elastodynamic Green's function approach was examined for cement-based materials. The acoustic emission source was characterized using moment tensor analysis. Acoustic emission measurements were analyzed for center- cracked-plate specimens of mortar and concrete. It was observed that, as expected, the dominant mode of cracking was mode I (tensile). However, mode II (shear) and mixed mode cracks also occurred, perhaps due to grain boundary sliding and interface debonding. Microfractures appear to localize prior to critical crack propagation. Mode I cracks generally required more energy release than mode II and a smaller inclusion provided a stronger interface bond than the larger ones.

43277 Cent Sviluppo Mat Small-size, highly sensitive ultrasonic shock-wave testing device in- cludes shock-wave ultrasonic generator, detector transducer and signal synchroniser between generator and detector European Patent No. 325,093 (26 Jnl. 1989)

43075 Smith, R,L.; Crook, M.J. The non-destructive detection and mapping of ASR cracking in concrete Transport and Road Research Labora tory , Crowthorne (United Kingdom), TRRL-CR-156 , ISSN-0266-7045 , 38pp. (1989)

This report considers which nondestructive testing (NDT) techniques may be appropriate to the detection and mapping of cracking in concrete bridge sections due to the alkali-silica reaction (ASR). An NDT method was needed which could determine the extent of internal cracking and the orientation and depth of cracks in reinforced concrete. The system chosen had to be robust and portable and distinguish between cracks, reinforcement and other embedded materials. A literature search using in NDT database revealed a number of possible NDT techniques. Four ultrasonic techniques and an acoustic emission (AE) method were assessed experimentally using standard concrete building block. The ultrasonic techniques met with limited success and the AE tests were useful for source location. Three further NDT techniques were considered for the task, but no experimental assessment was made, namely radar, thermography and electrical continuity.

42866 Andrews, D.R.; Turner, C.W. Investigation using visualizing methods of the critical tolerances in a mechanically steered ultrasonic transmitter with application to con- crete t es t ing Proceedings of Ultrasonics International 89, Madr id (Spain), 3-7 July 1989, pp. 1075-1082, But terwor th Scientific Ltd. ISBN 0408054182 (1989)

The objective was to devise a steerable transmitter design with good energy transfer and negligible distortion. A glass block containing a rotating cylinder was built which models the beam steering design of the transmitter. A PZT transmitter disc was attached to the cylinder and tone-burst signals of 500 V peak at frequencies of approximately 1.7 MHz were used to excite it into resonance. Images of individual wavefronts were rendered visible using a commercial visualizing system which generates light flashes of 50 ns duration. Images showed that whilst good energy transfer can be achieved at gaps of the order of 1/20th wavelength, mode-conversion and reverberation still result in significant pulse distortion.

42865 Turner, C. W.; Andrews, D.R.; Bolorfbrosh, M.S.S.; Conway, B,; Uzoegbo, H. A rev iew of ultrasonic research projects in progress at King's College, London Proceedings o f Ultrasonics International 89, Madr id (Spain), 3-7 July 1989, pp. 1095-1103, But terworth Scientific Ltd. ISBN 0408054182 (1989)

Several novel ultrasonic techniques are under development in this Department. All

of them can be described as visualization techniques. There are three principle areas of interest: improvements to the working range of the optically scanned transducer (OST), ultrasonic robot sensors and development of methods for imaging inside ultrasonic scattering materials -with application to concrete. It h~s also become interesting to investigate methods for characterising materials from their dispersion curves, two techniques are being studied: Kramers- Kronig relation and the Wigner distribution.

42807 Hoddinott, D. Inspecting the HarweH r e a c t o r s Atom, No. 399, pp. 10-15 (Jan. 1990)

This article outline the the protocol of safety inspections of the United Kingdom Atomic Energy Authority's reactors Dido and Pluto at Harweli laboratory. The nuclear installations made a number of recommendations in its safety audit of these thirty years old reactors, which are used as neutron sources, for neutron beam studies and for isotope production. The organisation and management of the inspection is described. Not only the reactors themselves, but also the surrounding concrete blocks and steelwork, were subject to a variety of nondestructive testing techniques. The tests were completed with satisfactory results within the timescale allotted.

42791 Lira, M.K.; Koo, T.K. Acoustic emission from reinforced concrete beams Magazine o f Concre te Research, Vol. 41, No. 149, pp. 229-234 (Dec. 1989)

The acoustic emission behaviour of reinforced concrete beams under flexure load was studied. Useful correlation was established between the acoustic emission activity under loading state and crack growth in the reinforced concrete beams. Three different acoustic emission rate regions were observed during the flexural loading. Crack initiation and crack propagation were detected by monitoring the acoustic emission.

42643 Keating, J.; Hannant, D.J.; Hibbert, A.P. Correlation between cube strength, u l t r a s o n i c pu l se velocity and volume change for oil well cement slurries Cement and Concre te Research, Vol. 19, No. 5, pp. 715-726 (1989)

Four types of cement slurries used in cement oil well casings have been examined to determine whether strength bnild-up during the first 24 hours after mixing can be predicted from measurements of ultrasonic pulse velocity and volume change. The pulse velocity method was found to be a useful predictive technique but there was no general correlation between bulk volume change and cube strength.

42390 Muravljov, M.; Zivkovic, S. The effect of curing temperature on strength-velocity relationship for ultrasonic assessment of concrete strength at early ages Durabi l i ty of Construct ion Materials , Vol. 3. Proceedings o f the 1st International Congress held by RILEM and organised by A F R E M , Palais des Congres , Versailles, France, 7-11 September 1987, pp. 943-950. Edited by J.C. Maso. C h a p m a n & Hail, 1988

This paper deals with the effect of curing temperature on strength- velocity relationship, used for the assessment of concrete strength at early ages. The work is based on a recent experimental investigation on concrete with pure Portland cement and Portland cement with blast- furnace slag. Experimental results have shown that the effect of curing temperature on strength-velocity relationship cannot be neglected when Portland cement with slag is used. In addition, the authors explain a procedure for mathematical modeling of curing temperature effect on this relationship. For this purpose, the temperature of 20°C is chosen as a referent curing temperature; the pulse velocity measured on the same concrete, but cured on different temperatures, has to be corrected with regard to the curing temperature. Thus, all results of testing pulse velocity are reduced on the same curing condition and a generalized correlation equation can be used for the assessment of concrete compressive strength.

42373 Pessiki, S.P.; Carino, N.J. Setting time and strength of concrete using the impact-echo method ACI Materials Journal , Vol. 85, No. 5, pp. 389-399 (Sep . -Oct . 1988)

Tests were performed to evaluate the feasibility of using the impact- echo method to determine setting time and to monitor strength development of concrete. In the impact-echo method, the test object is subjected to point impact and the surface displacement is monitored at a point adjacent to the impact. From the measured displacement waveform and the thickness of the object, the P-wave velocity is determined. Changes in the P-wave velocity with time reveal information about the development of mechanical properties as the concrete matures. Tests were performed to examine the relationship between P-wave velocity, as determined by the impact-echo method, and the compressive strength of concrete. It is concluded that the impact- echo method is a promising nondestructive technique for monitoring the development of mechanical properties in concrete from initial setting to ages of several days.

42372 Keating, J.; Hannant, D.J.; Hibbert, A.P. Comparison of shear modulus and pulse velocity techniques to measure the build-up of structure in fresh cement pastes used in oil well cementing Cement and Concre te Research, VoL 19, No. 4, pp. 554-566 (1989)

Fresh cement slurries typical of those used in the oil industry during drilling operations are assessed for the growth of structure in the first few hours after mixing by the use of shear modulus and ultrasonic pulse velocity measurements. It is shown that during the first two hours, the shear modulus technique is a much more sensitive measure of the developing physical structures but after initial set the ultrasonic pulse velocity is an effective method of differentiating between different mix formulations.

42355 Bungey, J.H. The testing of concrete in structures Surrey Univers i ty Press, 225 pp. Second edition. (1989)

270 N DT & E International October 1991