3.4.1 Fresh state tests
A- Slump
Table 15below summarizes the results obtained on the different formulations studied:
Table 15
Slump tests for different formulations
Formulations
|
Slump-test (mm)
|
Qualification
|
F1
|
55
|
Plastic
|
F2
|
60
|
Plastic
|
F3
|
55
|
Plastic
|
F4
|
50
|
Plastic
|
F5
|
60
|
Plastic
|
F6
|
30
|
Closed
|
F7
|
20
|
Closed
|
F8
|
55
|
Plastic
|
F9
|
60
|
Plastic
|
B- Segregation, Entrapped Air and Density
Table 16below summarizes the results obtained:
Table 16
Segregation index, percentage of entrained air and concrete density
Formulations
|
Slump-test (mm)
|
Segregation
|
Density
(t/m3)
|
F1
|
1.9
|
0.7
|
2.425
|
F2
|
0.2
|
0.6
|
2.448
|
F3
|
1.9
|
0.7
|
2.463
|
F4
|
0.3
|
0.5
|
2.425
|
F5
|
0.2
|
0.8
|
2.394
|
F6
|
4.8
|
0.9
|
2.432
|
F7
|
0.5
|
1.1
|
2.425
|
F8
|
1.5
|
1.2
|
2.432
|
F9
|
1.4
|
1.6
|
2.394
|
According to these results:
- The concretes produced do not risk segregation ;
- The content of entrained air remains acceptable in all formulations ;
- The densities of the concretes obtained are similar to those of ordinary concretes (2100 to 2400 kg/m3).
3.4.2 Tests in the hardned state
For campaign No. 1, It is carried out at a constant slump-test (60 mm) with a cement dosage of 350 kg/m3:
In Fig. 15, by trying to maintain a constant slump-test around 60 mm (by adjusting the water dosage). It can be seen that this was obtained with a gradual decrease in the water dosage as a function of the increase in the fineness modulus.
Dredging sands gave lower results than sand of Mf = 2.6 (variation of 37%), The compressive strength increases according to the modulus of fineness, but at the same time, we must not forget aspect of the concrete becomes rough for large enough fineness moduli (Mf = 3) and the concrete flows badly, because it lacks homogeneity.
For the companion N°2 :
⇨ Serie N°1 : This series was carried out to study the influence of an increase in cement dosage on concretes based on dredged sand compared to the results obtained in the first campaign.
Figure 16 shows that a 7.0% increase in cement dosage resulted in a marked increase in strength, between 13% and 40% compared to normal concrete based on dredged sand (cement dosage of 350 Kg/m3), the resistances obtained are similar to those obtained with a sand-based concrete with a fineness modulus Mf = 2.6, with a reduction in the water dosage, this was obtained at the cost of workability which fell, the concrete seems obviously dry, it is visible that adding water or admixture will solve the problem. But, the concrete, although not very plastic, nevertheless retains a good homogeneity.
⇨ Serie N° 2 : This series aims to study the influence of adding an admixture on the characteristics of concretes based on dredged sand compared to the results obtained in the first campaign.
In Fig. 17, the addition of an admixture allowed us to adopt the same water dosage of the sand-based concrete of Mf = 2.6, this made it possible to obtain higher resistances than those obtained with a normal concrete based on sand of dredging without admixture, Azemmour dredged sand-based concrete gave similar strength to sand-based concrete of Mf = 2.6 (30 MPa). As for the workability, the slump-test is greater than 55 mm, which satisfies the conditions for normal implementation.
According to Fig. 18, with an addition of admixture or cement, concretes based on dredged sand give satisfactory results in terms of resistance compared to concrete based on sand with a fineness modulus Mf = 2.6, the implementation of these concretes is conditioned by the water or additive dosage, in the case of cement overdose, the concretes based on dredged sand appear less workable by giving satisfactory resistances, it will then suffice to increase the water dosage or add an admixture with a quantity allowing good workability without the resistance falling above the desired value.