Elaborex, Quality in Construction S.L. has the personnel and technical means necessary for the execution of the tests of complementary information of the concrete defined in the article 86.8 of the EHE instruction, these being the following:
- The manufacture and breaking of specimens in a way analogous to the statistical control process, but with specimens preserved in the same conditions as the concrete of the work.
- Breaking of control specimens extracted from the concrete.
- The use of reliable non-destructive methods, as a complement to the tests described above and duly correlated.
In the comments of the instruction they are accepted as non-destructive methods reliable testing of determination of the bounce rate and the determination of the velocity of ultrasound propagation, according to UNE standards 12504-2 y ONE 12505-4 respectively, but the standard is blunt regarding the use of these methods for estimating the strength of concrete, not allowing its use exclusively, should be correlated with the methods a) o b)
In this sense, Elaborex, Quality in Construction S.L. also offers its clients the possibility of carrying out the estimation of the compressive strength "in situ" of a region from the correlation of direct tests and non-destructive methods.
In this regard, In today's post we are going to briefly show the method used to estimate the compression resistance "in situ" of a region of concrete columns using the correlation between the resistance values obtained by direct methods. (concrete cores) and those obtained by non-destructive methods (ultrasonic pulse rate).
The UNE norm 13791, in its section 8.3, allows establishing a relationship between the results obtained by the direct method (breaking strength of control specimens – Fis), and non-destructive or indirect methods (in our case determination of the speed of ultrasonic pulses- Fv), and calculate the increment of the basic curve that establishes the relationship between the two test methods with which to determine the value of compressive strength "in situ" of the region under investigation..
Following this method, for the study commissioned by our client we carried out the following works:
- Extraction and breaking of 9 witness specimens of the concrete of the pillars (minimum number indicated in the standard)
- A sampling of 35 determinations of the velocity of ultrasonic pulses on pillars, within which measurements were included in the pillars in which the extraction of control specimens had been carried out. – Fv
This way, for our study we had 9 pairs of results from both direct methods (Fis), as indirect (Fv)
Basic curve to estimate the value of Fv from the speed of ultrasonic pulses
The correlation between the nine pairs of values obtained is achieved through the procedure indicated in section 8.3.3 of the rule, using the following steps:
- The values of the resistance to compression of the controls are represented in the graph shown above against the results of determining the speed of the ultrasonic pulses..
- For each test site, the difference in resistance "in situ" between the value measured on the control and the value obtained from the basic curve is determined..
- The mean of the results and the standard deviation of the sample are calculated.
- The value that the basic curve should move is calculated "∆f”From a formula indicated in the standard.
- The basic curve is shifted by the calculated value "∆f"To obtain the relationship between the values of the speed of propagation of sonic impulses obtained in the campaign carried out, and the in situ compressive strength of the concrete in the analyzed region.
In this way, the correlation between a direct and indirect test method for the estimation of the compressive strength "in situ" in a given region is established..
From Elaborex, Calidad en la Construcción, S.L. We remain at the disposal of our clients for any questions they may have about the control of materials in concrete structures.