Issue 64

D. Derdour et alii, Frattura ed Integrità Strutturale, 64 (2023) 31-50; DOI: 10.3221/IGF-ESIS.64.03

higher than that of date palm fibers. Thus, with a greater number of fibers, the probability of trapping air bubbles is greater, also increasing the volume of occluded air and therefore decreasing the density of PPSCC compared to DPSCC.

(a) (c) Figure 15: L-Box test of concretes: (a) RSCC, (b) PPSCC12 and (c) DPSCC12. (b)

0 0,5 1 1,5 2 2,5 3 3,5

2400

RSCC PPSCC DPSCC

RSCC PPSCC PDSCC

2300 Apparent density (kg/m 3 ) 2320 2340 2360 2380

Air content (%)

2280

0

600

900

1 200

0

600

900

1 200

Rate fiber (g/m 3 )

Rate fiber (g/m 3 )

(a) (b) Figure 16: Effect of fiber rate on: (a) air content of SCC and (b) density of SCC.

Influence of natural and synthetic fibers on mechanical behavior of SCC in the hardened state Influence on compressive and flexural strengths

According to Figs. 17 and 18, it is found that the dosage of 600 g/m 3 recommended by the manufacturer of the polypropylene fiber guarantees optimal resistance at any age. It can be noted that the compressive strength of RSCC reached 58 MPA at 90 days. Reinforcement of the SCC by the fibers leads to a noticeable improvement in the resistance to bending compared to the RSCC as demonstrated by different researches. Date palm fibers guarantee the best results compared to polypropylene fibers, this can be explained by the influence of the surface condition of the rough date palm fiber (Fig. 8) which ensures better adhesion with the cementitious matrix [7,36,61] in relation to the surface state of the polypropylene fiber which is smooth. The compressive strength of the studied concrete is more or less altered; this is related to the increase in the porosity of the concrete (entrained air). It is assumed that it is not the fibers directly that reduce the resistance but rather the occluded air entrained by them. The incorporation of fibers into the concrete leads to a reduction in the compressive strength (Fig. 17).

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