ULTRASONIC PULSE METHOD THE CEMENT STRENGTH EVALUATION TOOL

Transcription

1 ULTRASONIC PULSE METHOD THE CEMENT STRENGTH EVALUATION TOOL Jiri BROZOVSKY (1), Jiri ZACH (1) (1) TIBME, FCE, Brno University of Technology,and Czech Republic Abstract The spectrum of control and laboratory strength tests in the production and research of cements is possible to reduce by using of an ultrasonic pulse method. Condition is to have calibration relationships between the parameter of non-destructive testing and strength of cement. In the article there are presented testing results of blended cements with various types waste addition using the ultrasonic pulse method. Described methodology respects the specifics of used method and tested material. There are also shown calibration relations for cements compressive and tensile strength computation from the ultrasonic pulse velocity and from the dynamic modulus of elasticity. Calibration relations correlation coefficient is higher than 0,. The proposed testing methodology and calibration relations are practically applicable. 1. INTRODUCTION Non-destructive testing methods in construction practice have currently been used most widely in examination of concrete and reinforced concrete structures above all. Procedures for their use in concrete and reinforced concrete structures are listed in various standards (both in Czech technical standards and foreign or international ones). This is essentially about rebound methods, semidestructive methods and there are also some dynamic methods used here in limited range (such as ultrasonic pulse method, resonance method etc). Another area in which the dynamic methods of testing are used is about monitoring durability of building materials (frost resistance, resistance to aggressive environment). As for some types of building materials (e.g. concrete, natural stone), these methods are listed directly in technical standards. Still undervalued area of using the non-destructive testing methods lies in their use in inspection tests performed by the manufacturer of building materials. Non-destructive testing methods allow quick identification of a parameter from non-destructive testing and purchase cost of these equipments is much lower than that cost of equipment used for destructive tests. The main reason why non-destructive testing methods are not used also for other building materials lies in lack of necessary calibrating relations with sufficient correlation between monitored characteristics (compactness) and a paramater taken from non-destructive testing. 314

2 Another area in which the non-destructive testing methods have so far been used in rather low range belongs to experimental research works, although the qualified use of these methods may rationalize this situation e.g. minimize the number of testing components produced. Published here in the article, there are results of tests aimed at two types of cement CEM I 2. and CEM II 32. produced in Cement Mill of Mokra by using the ultrasonic pulse method for measuring compressive and flexural (binding) strength. The results presented here are linked to author elaborations which were aimed at using the ultrasonic pulse method for rationalisation of experimental works which were done during development research of blended cement [1] and gypsumfree cement [2] 2. ULTRASONIC PULSE METHOD AND CONDITIONS FOR ITS USE When testing the building materials by using the method of ultrasound, there is the ultrasonic pulse through-way method mostly used here. This method is based on transmitting the ultrasonic pulses, which are repeated by an energizer, into the target material and consequent monitoring the pulses passed through the tested material. To be monitored here, there is period of time spent by transitting of its front part from the energizer to sensor, e.g. time period needed to overcome a certain distance. On the basis of transit time and previously known length of measuring base, there will be calculation of ultrasonic pulse velocity according to relation (1) of EN : L V = T Where : V ultrasonic pulse velocity [km/s] L length of measuring base [mm] T transit time [µs] On the basis of ultrasonic pulse velocity and density of hardened concrete, there will be calculation of dynamic modulus of elasticity related to the tested material according to relation (2) from CSN 3131: 1 E U = V 2. D. k Where : E U dynamic modulus of elasticity [MPa] V ultrasonic pulse velocity [km/s] D density of hardened concrete [kg/m 3 ] k ambient dimensionality ratio. For use of the ultrasonic pulse method in order to determinate physical-mechanical characteristics of the material, it is necessary to create a calibration relation between ultrasonic pulse s velocity (resp. dynamic modulus of elasticity) and a monitored parameter (like for example compressive strength or flexural strength). Measuring by ultrasonic pulse method is influenced by many factors, above all it is moisture of tested material, form and dimensions of test specimen, energizer s frequency, composition and ingredients of tested material and defects in its structure. (1) (2) 31

3 The only influencing factor that should be eliminated when testing cement materials by using the ultrasonic pulse method for determination of cement s strength is modification of specimen moisture. The elimination should be done by determining requirements for test performance. There are strict requirements given for tests of cement strength according to EN 16-1, e.g. requirements for ingredients and composition of cement mortar. There is standardized sand of accurately given granulometry and chemical composition used as filling material. Composition of standardized mortar is constant: 1 portion of cement to 3 portions of aggregate. Value of water-cement ratio is w=0.. Procedure of production including requirements for parameters of production equipment (mortar mixer, jolting apparatus) are accurately specified. There are conditions for storage of test specimens, which are stored until the day of testing, strictly defined here. There are also conditions for storage until the day of un-forming the storage material in the area where relative humidity is % and temperature ±2 0 C and after un-forming the testing specimens of storage in water where the temperature is ±2 0 C. There is strict definition of form and dimensions of test specimen-cement mortar prism - xx1mm. As arising from the above mentioned facts, the essential factor which may influence measuring by using the ultrasonic pulse method when testing cement materials is question of test specimen s moisture. This phenomenon may be eliminated by determining some strict conditions of testing aimed at the target of avoiding unwanted water evaporation out of the test specimen before the own measuring procedure is done. The own measuring by using the ultrasonic pulse method is very quick (one test specimen, including measuring the density of 2 transit time measurements, can be done within - 80 seconds-if the measurement is well organised). 3. CEMENT MATERIAL CHARACTERISTICS AND TESTING PROCEDURE 3.1 Tested Cement The tests were performed with two types of industrial cement in Cement Mill of Mokrá - marked according to EN 1-1: CEM I 2.N (portland cement) CEM II/B-S 32.,R (portland slag cement) - containing granulated blastfurnace slag (21-3% ) In the tests, there were cements which were produced in the period of 2 months (6 specimens for CEM I and 4 specimens for CEM II). 3.2 Test Procedure There are some test specimens of standardized mortar for the purpose of doing tests and processing the calibration relations. The procedure which is followed here is stated in EN Cement materials which tested here were 1, 2, 3,, 14, 21, 28 and 6 (or also 0) days old. Here is the procedure used during testing with ultrasonic pulse method: Test specimens were removed from standardized placement shortly before the test. They were also dried with a damp towel, cleaned and weighed. Measuring on test specimens were performed by using the method of direct throughsounding (see Figure 1), using probes with frequency of 82 khz. In order to achieve good 316

4 acoustic relation between probes of ultrasonic device and testing surface, there was an EKG equipment used here, the equipment which is used in medical treatment too. Transit time measurement was repeated twice on each test specimen. If the measured values did not deviate from each other by more than % (due to smaller value measured), the results were considered as satisfactory ones. If the deviation was more than %, there had to be performed another measurement and calculation of average specimen s transit time was performed by using values which did not deviate from each other by more than %. If this condition was not met, then the test specimen should have been excluded from the evaluated group. After measuring by the ultrasonic pulse method, there were dimensions of test specimens found here. There were also destructive tests of flexural and compressive strength on fragments of cement mortar prism, done by using procedures according to EN 1-1. Figure 1: Measuring with ultrasonic device of cement mortar prism 4. RESULTS OF THE TESTS AND CALIBRATION RELATIONS 4.1 Results of the Tests There were testing specimens made of standardized mortar for purpose of tests and processing the calibration relations. They were made by using the procedure of EN They were 10 couples of results available for processing the calibration relations in CEM I cement (strength parameter taken from non-destructive tests). Then for CEM II, there were 2 couples of results available. Results of the tests including dependences between non-destructive test parameter (ultrasonic pulse velocity; dynamic modulus of elasticity) and compressive strength (or also flexural strength) are shown in figures 2 to

5 y = 0,034e1,x 8 6 y = 0,0881e1,0428x 3,8 4,0 4,2 4,4 4,6 4 3,8 4,0 4,2 4,4 4,6 Figure 2: CEM I 2. V x R c Figure 3: CEM I 2. V x R f y = 0,0003x3,16 y = 0,0028x2, Figure 4: CEM I 2. E cu x R c Figure : CEM I 2. E cu x R f 318

6 0 y = 0,036e1,828x y = 0,0264e1,23x 3 0 3,2 3, 3,8 4,1 4,4 4, 1 3,2 3, 3,8 4,1 4,4 4, Figure 6: CEM II 32. V x R c Figure : CEM II 32. V x R f 0 y = 0,0003x3,3 3 y= 0,000x2, Figure 8: CEM II 32. E cu x R c Figure : CEM II 32. E cu x R f 31

7 80 0 y = 0,03e1,6634x 3 y = 0,004x, ,2 3, 3,8 4,1 4,4 4, 1 3,2 3, 3,8 4,1 4,4 4, Figure : CEM V x R c Figure : CEM V x R f 80 0 y = 0,0002x3,4 3 y = 0,000x2, Figure12: CEM E cu x R c Figure 13: CEM E cu x R f 3

8 4.2 Calibration Relations On the basis of test results there were calibration relations (3) to (8) processed in order to determine cement s compressive and flexural strength taken from ultrasonic pulse velocity (resp. dynamic modulus of elasticity). The corelation relations are practically useful if the corelation coefficient is higher than 0.. Comparison of processed calibration relations for determination of compressive strength taken from ultrasonic pulse velocity for cement CEM I 2. (portland cement) and CEM II 32. (portland slag cement content of granulated blastfurnace slag 21-3%) is shown in figure 14. a) Compessive strength CEM I 2.N 1.V R c = 0.034e r = 0.88 (3) 3.16 R c = E r = 0.84 cu CEM II/B-S 32.R 1.828V R c = 0.036e r = 0.2 (4) 3.3 R c = Ecu r = 0.8 CEM I 2.N + CEM II/B-S 32.R V R c = 0.03e r = 0. () 3.4 R c = Ecu r = 0.2 b) Flexural strength CEM I 2.N V R f = e r = 0.43 (6) R = r = 0.42 f Ecu CEM II/B-S 32.R 1.23V R f = e r = 0.88 () R = r = 0.86 f Ecu CEM I 2.N + CEM II/B-S 32.R,083 R f = 0.004V. r = 0.6 (8) R = r = 0.63 c Ecu 321

9 Compressive strength [MPa] ,3 3, 3, 3, 4,1 4,3 4, 4, CEM II 32. R (4) CEM I 2.N (3) Figure14: Comparison of processed calibration relations for cement CEM I 2. and CEM II 32.. CONCLUSIONS Practical usefulness of ultrasonic pulse method for cement compressive as well as flexural strength has been demonstrated here. Processed calibration relations (3) (8) for determination of cement s compressive and flexural strength taken from parameters of ultrasonic pulse method (ultrasonic pulse velocity, resp. dynamic modulus) have got high corelation coefficient e.g. from 0,2 to 0.2 for compressive strength and 0,42 0,88 for flexural strength. There are also higher corelation coefficients in calibration relations for compressive strength of cement material, which is substantial in terms of evaluation of cement s strength parameters, because strength class of the cement material is to be determined only on the basis of its values of compressive strength. As for practical use, calibration relations processed separately for each type of cement are considered here as suitable. It is obvious in figures and 12 and in comparison of calibration relations (3) and (4) which are used for determination of cement compressive strength taken from ultrasonic pulse velocity, which is shown in figure 14, so it is obvious that when determining compressive strength of cement taken from ultrasonic pulse velocity or dynamic modulus, there is influence of cement s type - portland cement or portland slag cement. This fact can be explained by different composition of listed types of cement as well as by different increase of strength during the time period in hydratation process. When testing cement by ultrasonic pulse method, it is necessary to keep constant testing conditions. Above all, it is necessary to eliminate those effects which could cause change in moisture state of the tested specimens. Therefore, it is necessary to always use probes of identical frequency. Practical usefulness of ultrasonic pulse method during measuring compressive as well as flexural strength of cement materials has been demonstrated here. These pieces of knowledge extend the range of possible applications of this nondestructive method also to materials other than concrete mass. 322

10 ACKNOWLEDGEMENTS The work was supported by FAST-S--4 project: Dynamic nondestructive method as a tool for cement strength tests rationalization and by the MSM plan: Progressive Building Materials with Utilization of Secondary Raw Materials. REFERENCES [1] Brozovsky, J., Matejka, O. and Martinec, P. Using of non-destructive methods for strength detection on blended cements and paving blocks. International Journal of Microstructure and Materials Properties (IJMMP), 3/4 (1) (06) [2] Brožovský, J., Brožovský, J., Jr. and Zach, J. Tracing of crack depth in concrete structure using ultrasonic pulse method. In International RILEM JCI Seminar on Concrete Durability and Service Life Planning ConceteLife 06, [3] Brozovsky, J., Zach, J. And Brozovsky, J., jr. Gypsum free cements and concretes made with them: strength determination using nondestructive testing methods. In IV Conferencia Panamericana for Non destructive Testing, Buenos Aires, Argentina, 0,