Testing of Hardened Concrete

Topics: Concrete, Tensile strength, Compressive strength Pages: 13 (3907 words) Published: April 18, 2013
Part B: Testing of hardened concrete
1. Objectives:
The objective of the hardened concrete test was to determine the compressive and indirect tensile strength. On the other hand, this experiment was also used to examine the effect of curing condition on strength of concrete, the influence of specimen shape on compressive strength, the effect of compaction on compressive strength and this experiment was also to examine the effect of increasing water to cement ratio on compressive and in direct tensile strengths of concrete. 2. Procedure (Refer AS1012 for full details)

2.1 Compressive Strength
* In this test, standard cylinders and cubes will be subjected to uniaxial compressive loading and the load will be applied gradually at a standard stress rate of 15MPa/min., up to failure. The maximum applied load is recorded for the determination of the compressive strength. * When testing a cylinder, a hard- rubber cap is needed to achieve uniform loading. * When testing a cube the load is applied to cast surface and no capping is needed. * Compressive strength of concrete [fc] (MPa)

= Maximum Load [P] (N) / Load bearing area [A] (mm2) Load bearing area for cylinder = π x (r^2), where r is the radius of the cylinder Load bearing area for cube = d x d, where d is the cube size 2.2 In-direct tensile strength (AS 1012:10)

In this test, a standard cylinder is subjected to a compressive loading along its length and the cylinder splits in indirect-tension along the diagonal, due to the induced tension (Poisson's effect). It is necessary to use bearing strips between the concrete and the testing machine platens to avoid local crushing. In-direct tensile strength [fst] (MPa) is calculated using the following expression: (MPa) = 2000 x Maximum load P (kN) / π x l (mm) x d (mm)

Where d and l are the diameter and length of the cylinder in mm. Testing procedure
* Fix the compressometer centrally around the 100mm diameter cylinder. Carefully center the specimen in the testing machine. * Three times gradually load the specimen (15+2 MPa/minutes) to the test load level (40% of the cylinder strength) and unload it. Records need not to be kept during first loading Record the following:

1. Applied load when the deformation is such that the specimen is subjected to a longitudinal strain of 50 microstrain 2. Deformation attained at test load.
3. From these results the following are to be determined: 4. 1 = applied stress at the strain of 50 microstrain
5. 2 = applied stress corresponds to the test load
6. 3 = strain at test load
3. Test Result
3.1 Compressive Strength - Cylinders (Water cured for 28 days) Specimen No.| Diameter| Height| Weight| Max. Load| cylinder strength (Mpa)| average cylinder strength (Mpa)|  | (mm)| (mm)| (g)| (kN)|  |  |

A1.1| 100.1| 200| 4138| 569| 72.3| 71.6|
A1.2| 100.1| 200| 4109| 555| 70.5| |
A1.3| 100.0| 200| 4125| 566| 72.1| |
B1.1| 100.3| 202| 4050| 490| 62.0| 60.5|
B1.2| 100.2| 200| 4025| 463| 58.7| |
B1.3| 100.1| 200| 4018| 478| 60.7| |
C1.1| 100.4| 203| 3995| 345| 43.6| 45.5|
C1.2| 99.7| 204| 3981| 366| 46.9| |
C1.3| 100.4| 202| 3978| 365| 46.1| |
D1.1| 100.2| 198| 3842| 286| 36.3| 36.5|
D1.2| 100.3| 202| 3833| 277| 35.1| |
D1.3| 99.9| 201| 3865| 299| 38.1| |
Table1. Compressive Strength - Cylinders (Water cured for 28 days) Observation:

3.2 Compressive Strength - Cylinders (Air stored for 28 days) Specimen No.| Diameter| Height| Weight| Max. Load| cylinder strength (Mpa)| average cylinder strength (Mpa)| | (mm)| (mm)| (g)| (kN)| | |

A1.4| 100.2| 201| 3946| 373| 47.3| 48.9|
A1.5| 100.2| 200| 3947| 397| 50.3| |
A1.6| 99.7| 201| 3954| 383| 49.1| |
B1.4| 99.8| 200| 3863| 319| 40.8| 41.3|
B1.5| 100.3| 201| 3890| 334| 42.3| |
B1.6| 100.2| 200| 3883| 323...
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