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Compressive Strength of Hardened Concrete

Autor:   •  November 16, 2017  •  1,387 Words (6 Pages)  •  766 Views

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From the Compression machine (destructive method):

Cube 1

Density (kg/m3)

2342

Cross section area (mm2)

10180

Compression Failure Load (kN)

496

Compressive strength (MPa)

48.7

[pic 22]

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Discussion of Results

Non-destructive experiment

Using the Schmidt hammer, we recorded 10 different rebound numbers, which included: 47.5, 33.5, 33.0, 33.0, 38.5, 32.5, 40.5, 36.0, 33.5 & 31.5. We then divide it by the number of readings, 10, which will give as an average rebound number of 36.0. Then, using the calibration chart, we managed to find to corresponding value on the y-axis of the curve in which the Schmidt hammer is perpendicular to the surface, the corresponding value in the y-axis gave us the estimated compressive strength of 41.0MPa which classifies the concrete as moderate-strength concrete.

The non-destructive testing method does not consume a lot of time, can test the same structure repeatedly without harming the structure and it enables us to continuously monitor the structure. In contrast, the disadvantage of this method is that, since the strength properties are not measured directly, calibration is needed to determine the value of the compressive strength as well as the lack of precision of the readings.

Destructive experiment

To initiate, we measured the width and the depth of the concrete cube twice using an electron Vernier caliper in which we obtained the readings 100.8 mm and 100.2mm for the width, and the readings 101.2 mm and 101.3 mm for the depth. The average calculated was 100.5 mm and 101.3 mm respectively. Using the average width and depth, we calculated the cross sectional area using the formula: A = W × D; the cross sectional area was 10180mm2. Then, after measuring the height, which was 98.60 mm, we were able to calculate the volume using the formula: V = W × D × L; the volume was 1004000mm3. The mass of the concrete cube obtained from the digital balance was 2.351 kg. We also obtained the value of the density using the formula: Density = Mass / Volume; the density of the concrete cube was 2342 kg/m3. Lastly, we placed the concrete cube in the compression machine to measure the compression failure load which was 496 kN which enabled us to calculate the compressive strength by using the formula: Compressive strength = F / A; the value of the compressive strength was 48.7 MPa.

The destructive testing method consumes a lot of time, it costs a lot to constantly crush the concrete to be tested and the concrete does not represent an actual structure. In contrast, this method is capable of testing and attaining the compressive strength of a wide-range of diverse mix designs in an accurate and precise manner.

Conclusion

The purpose of this lab experiment is to obtain and determine the compressive strength of concrete through non-destructive and destructive methods. The destructive method is much more expensive and time consuming relative to the non-destructive method. In contrast, the result obtained by the destructive method more accurate and precise compared to the destructive method as the concrete cube is compressed to destruction rather than just recording the number of rebounds in the non-destructive method. However, the Schmidt Hammer (non-destructive) can continuously monitor the surface’s compressive strength without damaging it. All the objectives of the experiment was met as we understood both methods to test for compressive strength.

Recommendations

Abrasive grinding stone should be rubbed against the surface to be tested before using the Schmidt hammer against it for a smoother surface that will lead to more accurate results.

The compression machine should be covered properly before usage.

For the sake of accuracy and precision, different samples of the same concrete material should be tested in the compression machine for better results.

The purity of the materials of the concrete cube must be ensured in order to obtain more accurate results.

References

[1] CVE Lab handout of Dr. Arshi Faridi, 2015.

[2] CVE Presentation- Compressive Strength of Hardened Concrete of Dr. Arshi Faridi, 2015.

[3] Jim Lucas. 2014, “What Is Civil Engineering?”, Retrieved from:

http://www.livescience.com/47612-civil-engineering.html

[4] ABOUT CEMENT AND CONCRETE (n.d.) retrieved from:

http://www.nanocem.org/index.php?id=24

[4] Concrete: A Material for the new Stone Age, Materials Science and Technology 1995

http://matse1.matse.illinois.edu/concrete/concrete.html

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