Mohammed Abdulrahman Qadir Technique (MAQT)
It’s known that amount of compressive strength is the most important property for the concrete and cannot be ignored during evaluation of concrete structures, and this can be got by laboratory (destructive and non-destructive) tests, since the destructive test cannot be done everywhere and the test by the ultrasonic pulses & Schmidt hammer is the most used, although their result reliabilities are not enough because they are depending on two parameters (pulse velocity & mean of Hammer readings), but in this research the standard deviation is increased as a third parameter so the reliability increased to more than (%90) and reaches (%95) for most cases, this is beside getting new information in concrete technology.
Research idea?
To get results that differ from previous researches founder has installed a number of foundations developed during (40) years of laboratory works and these foundations are summarized by the following:
- Concrete samples are made up of mortar (cement + sand) and gravel and there is a prefect bond between these two components during the test until it exposes to a pressure more than the resisting strength for one of these two components because the test manner is unconfined, where the test samples are cubes or cylinders.
- Any increase in the amount of cement increases the resisting strength of (cement + sand) mortar only and has no effect on gravel resisting strength.
- Its not possible to make a mix design for concrete which its resisting strength increases the used gravel resisting strength.
- Resisting strength of concrete is the resisting strength of the used gravel or its (cement +sand) mortar whichever is lower.
- The pulse velocity through the concrete during testing is the average of the pulse velocity in the gravel particles on its way and the pulse velocity in the (cement+ sand) mortar between those gravel particles (according to their existing ratio).
- Since in our concrete tests resisting strengths mostly are not much more than (50mpa) for cylinder samples and the used gravel sources are mostly rivers or bolders and the number of crushed gravel particles due to the test are very few at most, this is meaning that the (cement+ sand) mortar resisting strength represents concrete resisting strength *(proved below) , whenever the influence of the coarse aggregates on the pulse velocity in the concrete is reduced as much as possible it approaches to the pulse velocity in the mortar. So the relation between this approximate pulse velocity in the mortar and the compressive strength of the concrete should have a high reliability.
- The amount of Hammer readings during concrete test depends on the extent solidity of the strike site and this indicates that the largest part of the amount of standard deviation of a set of Hammer readings resulting from coincidence of the blow to the gravel blocks and this means that the standard deviation of a set of Hammer readings during concrete test is a function of gravel presents in the concrete.
*Proving of mortar resisting strength represents concrete resisting strength:
Nature of the research required knowing the correctness of the representation of the mortar resisting strength to the concrete resisting strength, this was required making a number of concrete samples with a mortar and gravel and making same number of samples from mortar only having the same strength of their alternative samples which was made from mortar and gravel in another words for a concrete sample which made from gravel and mortar having a strength(X) there is a sample with the same strength(X) made from mortar only.
This intended target obtained by fixing (w/c) water cement ratio and sand cement ratio (s/c) in both cases and for more illustration, information about these samples prepared by these two cases and their test results are recorded in the below table (table no.1).
Table No 1: Test results of concrete (Cement + Sand + Coarse.Agg) cylinders & mortar (cement + sand) cylinders.
|
Sample No |
Max Agg.size |
Coarse Agg. (Kg/m3) SSD* |
Sand (Kg/m3) SSD* |
Cement (Kg/m3) |
Water/ cement (W/C) |
Sand/ cement (S/C) |
Compressive strength (28 days) (Mpa) |
|
1 |
10mm |
665 |
1183 |
295 |
0.78 |
4.01 |
21.2 |
|
2 |
10mm |
665 |
1183 |
295 |
0.78 |
4.01 |
21.3 |
|
3 |
10mm |
665 |
1183 |
295 |
0.78 |
4.01 |
20.7 |
|
4 |
10mm |
665 |
1183 |
295 |
0.78 |
4.01 |
20.9 |
|
5 |
4.75mm |
0.0 |
1647 |
410.6 |
0.78 |
4.01 |
19.3 |
|
6 |
4.75mm |
0.0 |
1647 |
410.6 |
0.78 |
4.01 |
18.4 |
|
7 |
4.75mm |
0.0 |
1647 |
410.6 |
0.78 |
4.01 |
21.3 |
|
8 |
4.75mm |
0.0 |
1647 |
410.6 |
0.78 |
4.01 |
20.1 |
|
9 |
20mm |
969 |
792 |
429 |
0.49 |
1.846 |
35.1 |
|
10 |
20mm |
969 |
792 |
429 |
0.49 |
1.846 |
34.4 |
|
11 |
20mm |
969 |
792 |
429 |
0.49 |
1.846 |
33.9 |
|
12 |
4.75mm |
0 |
1318 |
713.97 |
0.49 |
1.846 |
34.1 |
|
13 |
4.75mm |
0 |
1318 |
713.97 |
0.49 |
1.846 |
36.1 |
|
14 |
4.75mm |
0 |
1318 |
713.97 |
0.49 |
1.846 |
33.8 |
*Weights are based on (SSD) saturated surface dry conditions.
Type of used materials:
- Cement: O.P.C
- Sand: uncrushed- zone No.2
- Coarse.Agg: crushed (crushed river bolders).
- Water: drinking water.
