International Symposium (NDTCE 2003) NonDestructive Testing in Civil Engineering 2003  
Start > Contributions >Posters > Ultrasonic: 
Reference concrete for ultrasonictesting and its creation by components with preanalysed propertiesDipl.Ing. André Glaubitt, Universität Dortmund, Dortmund (Germany)Dipl.Geophys. Sascha Bussat, Universität Dortmund, Dortmund (Germany) Prof. Dr.Ing. Jürgen Neisecke, Universität Dortmund, Dortmund (Germany) 1.IntroductionThe aim of the project is to give prediction about the dynamic Emodulus of concrete by the use of the elastic properties (dynamic Emodulus, Poisson´s ratio and density) of its components (cementmatrix, aggregate). These predictions should be made by inclusion of the aggregate (e.g. basalt, granite and sandstone), water/cementratio and different kinds of cement. However, in the past the acoustic properties could not be measured so exactly like it is possible nowadays by using new measuring methods. Elastic properties of aggregate and cementmatrix are now defined by measuring of longitudinal and surface waves (Rayleigh wave) with an accuracy of +/ 0,5%. By this it should be possible to examine existing predictionmodels for dynamic Emodulus referring to their accuracy or if necessary create a new model. Using such models it even should be possible to predict ultrasonic wave speed V_{T}, V_{L }(transverse and longitudinalwavevelocity) in concrete with a required reliability by measuring of V_{T}, V_{L} of concrete´s separate components. As a conclusion, it is absolutely necessary to know as much as possible about each component of cement concerning factors having influence on their elastic properties. Otherwise a creation of reference concrete with reproducibility will not be possible. The predictions can be used for targeted production of reference concrete for ultrasonictesting to compare measuring of different testers and testing methods. By this it is possible to give statements for example about their accuracy. 2.Determination of elastic properties (dynamic Emodulus E_{dyn}, Poisson´s ratio m_{dyn})To determine elastic properties (dynamic Emodulus E_{dyn}, Poisson´s ratio m _{dyn}) as exactly as possible, it is necessary to determine ultrasonicwavevelocity of longitudinal and transverse wave (V_{L},V_{T}) and density r. 2.1 Determination of longitudinalwavevelocity By this method a very exact determination of V_{L} is possible, because several separate measurings are analysed for one result. The accuracy of this method is at least about +/ 0,5% and the determination of the delay is more exactly than by the "facetoface"method.
2.2Determination of transversewavevelocity To determine the transversewavevelocity exactly, the phase velocity V_{R} of the surface wave is measured. If a material is homogeneous, phase velocity is equal to group velocity. A precondition is, that wave velocities V_{T}, V_{L} and density of the sample do not vary by depth. Otherwise an analysis of dispersion has to be made [1]. The measuring of Rayleighwavevelocity is done with two compressional probes. While the transmitter is fixed on the sample, the transceiver is placed in different distances to the transmitter. For both probes glycerin is used as couplant. Depending on the distance between transmitter and transceiver different Ascans are recorded, which are placed in parallel over the offset (distance between transmitter and transceiver). The last step to get the Rayleighwavevelocity is to define the increase of the straight line through the onsets of regististrated Rayleigh waves.
2.3Determination of modulus E_{dyn} and Poisson´s ratio m
_{dyn} Because of knowing V_{P} and V_{R} the formula can be written as followed: By determing f(V_{T})=0 the velocity of transversewave V_{T} is been given. For further determination of E_{dyn} and m _{dyn} the system of equations with has to be solved. 2.4 Example
As a result of the troughtransmission, there is a longitudinalwavespeed V_{L} = 4440 m/s. The configuration for determination of Rayleighwavevelocity can be seen in figure 3., the recorded Ascans with different distances to the transmitter are shown in figure 4. For V_{R} the velocity was determined to 2500 m/s. The result of the subsequent determination of transversewavevelocity was V_{T} = 2655 m/s. The dynamic Emodulus was calculated to E_{dyn} = 35,3 N/mm² and Poisson´s ratio to m _{dyn} = 0,22.
2.5 Advantages of determination of Rayleighwaves
3.PredictionmodelsThe exact determination of longitudinal and transversewavevelocities V_{L} and V_{T} gives the possibility to determine E_{dyn} and m _{dyn} . The dynamic Emoduli and Poisson´s ratios m _{dyn} are input data of several predictionmodels. With these models the Emodulus of for example concrete should be calculated by the Emoduli and Poisson´s ratios of its components (cement, aggregate). These ideas of models are based upon the assumption that concrete is a twomaterialsystem. Extensive analyses of different ideas of models were made in the past. There is a differentiation between basicmodels and complexmodels. The basic models do not include the influence of transverse elongation or it is disregarded. The complex models do exist with the influence of transverse elongation and also without [3]. Because of the exact determination of V_{L} and V_{T} and by this E_{dyn} and m _{dyn} , these predictionmodels have to be controlled belonging to their accuracy. Therefore concrete´s two components cement and aggregate have to be examined in matters of E_{dyn} and m _{dyn} . Using predictionmodels these results lead to a statement of the Emodulus and Poisson´s ratio of concrete produced with these two components. As a conclusion, it is strongly necessary to examine the influence of different parameters of concrete´s production. By this it should be avoided that the mixing of the two components to one material will have influence on their Emoduli and Poisson´s ratios. If it is not possible to avoid such effects, at least it should be known in which dimension there is an influence. Therefore one first step is the examination of cementmatrix. Prisms of cement made of CEM I 32,5 R and varying w/cratio under vacuum showed a linear variation of longitudinalwavevelocity V_{L }dependent on w/cratio. By the production under vacuum the air and compactionpores should be eliminated, so that concerning the pores only capillary pores should have an influence on longitudinalwavevelocity V_{L} . Theoretically there should not be any capillarypores in cementstone with an w/cratio less than " 0,4. Therefore, if capillarypores have a great influence on ultrasonicwavevelocity, the linear dependence of V_{L} on w/cratio should be different between w/cratio less than 0,4 and more than 0,4. However, this effect can not be seen in the examined test series (see fig. 5).
An examination of cementstone with a mercury porosimetry analysis will give more detailed information about porestructure. 4.OutlookIf all important factors that have influence on ultrasonicwavevelocity of cementstone are known, it is possible to produce one or if necessary several "StandardUltrasonicCementstone(s)", which is (are) reproducible. Afterwards there will be a further examination with diverse test series to discover the influence of aggregate in a modeltestblock of "StandardUltrasonicCementstone". First the aggregate will be, concerning to the idea of a twomaterialsystem, monomineral and later even a mixture of several minerals. These aggregates will vary in proportion to cementstone, particle shape, maximum particle size and grading curve. With these results existing predictionmodels will be controlled and tested concerning their accuracy. In the past the examination of such predictionmodels was not so accurate, because it was not possible to give detailed information about the accuracy of measured ultrasonicwavevelocities (there was no calibration of the equipment), nor the Poisson´s ratio was considered in the calculation of the Emoduli. If need be, a new predictionmodel has to be developed with the extracted information of the test series. With the abovenamed basic steps it is possible to develop one or several reference concrete(s), because fixed specifications about recipe and creation can be made, which will ensure a reproducibility. With these reference concretes it is possible to develop referencesamples for ultrasonictesting. Such referencesamples are a precondition for comparability, transferability and reliability of measuring results, testingmethods and equipment for the nondestructive testing of cementbonded mortar and concrete. References

