EVALUATION OF CALCULATION CORRELATION EFFICIENCY AS MENTIONED IN en 13791 IN ORDER TO DETERMINATION CONCRETE COMPRESSION STRENGTH BY NONDESTRUCTIVE TESTING
The paper presents evaluation of correlations for calculation of concrete compression strength using nondestructive testing parameters for both impact and ultrasonic pulse methods, as listed in EN 13791:2007. This standard indicates procedures relating to compression strength determination in construction and building elements. These procedures relate to compression strength evaluation based either on test specimens (drill cores) or combination of NDT and drill core testing. These nondestructive methods are not covered by procedures taking into account only nondestructive testing parameter pursuant to common calibration correlation. Correlation based on Schmidt impact hammer rebound does not respect various positions of this instrument although positioning of the same is essential for rebound value. No specific type of impact hammer is given for particular calculation correlation. In addition, another challenge is preparation of test surface along with evaluation of impact hammer measurement according to EN 12504-2 as compared with EN 13791. Dispersion of significant values varies between 15 % and 50 % depending upon specific values of impact hammer rebound. Calculation correlation based on ultrasonic pulse velocity implies that – at 4 km/s – concrete compression strength is equal to zero which is absurd conclusion, indeed. We indicate confrontation with calibration correlation as stated by technical bibliography and technical standards as well.
Experimental Studies on the Homogeneity and Compressive Strength Prediction of Recycled Aggregate Concrete (RAC) Using Ultrasonic Pulse Velocity (UPV)
The reuse of material from collapsed building debris as a natural aggregate substituent has been an alternative to solve concrete waste in Indonesia. However, its use in larger structures needs further research. The objectives of this research are to study the concrete homogeneity at a certain sample height and to find the strength prediction of Recycled Aggregate Concrete (RAC). In the previous laboratory study, the obtained concrete compressive strength with 20% RAC substitution (from the concrete ruins with fc’ = 30 MPa) was 27-30 MPa. Since, RAC contains natural aggregates and mixed cement paste, it is important to research the distribution, homogeneity and strength prediction of the concrete. The measurement was done using a nondestructive instrument called Ultrasonic Pulse Velocity (UPV). This paper presents a series of experiments investigating homogeneity and predicting compressive strength using both Destructive and Non-Destructive Tests (NDT). To do so, three steps in the experimental works were done. Firstly, UPV propagation measurements at four different levels through vertical prismatic beam specimens was performed. Two transducers were used in the direct mode of transmission with a 15 cm distance of measurement. Secondly, identical concrete samples cast in cubic form were measured using UPV and tested under compression. Thirdly, the core-drilled samples were taken from the vertical prismatic beam specimens for further investigation. The wave propagation velocity through RAC and the concrete compressive strength relationship demonstrate similar pattern as concrete with GFC (Gypsum-free-cement) performed by Brozovsky. This pulse velocity-concrete strength relationship can be used to predict the strength of RAC. Both the prediction curve and the homogeneity properties can be useful when casting a larger element of structures using RAC.
Geomagnetic Polarity Epochs: Sierra Nevada Data, 3
Available paleomagnetic and radiometric results for about 60 igneous rocks 3.6 m.y. old or less are consistent with the following geomagnetic polarity epoch time scale: Brunhes normal polarity epoch, 0.0 to 0.85±0.15 million years; Matuyama reversed polarity epoch, 0.85±0.15 to 2.4±0.1 million years; Gauss normal polarity epoch, 2.4±0.1 to 3.35±0.1 million years; Gilbert reversed polarity epoch, 3.35±0.1 million years to (?). A brief interval of normal polarity (the Olduvai event) occurs within the Matuyama reversed epoch at about 1.9 m.y., and a brief interval of reversed polarity (the Mammoth event) occurs within the Gauss normal epoch at about 3.06 m.y. Data for twelve units from eastern California and Nevada, reported here for the first time, are particularly useful in defining the Gauss-Gilbert boundary and for recognizing the Mammoth event.