# PSI - Issue 55

Afif Rahma et al. / Procedia Structural Integrity 55 (2024) 206 – 213 Afif Rahma/ Structural Integrity Procedia 00 (2019) 000 – 000

212

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These results allowed to conclude that the concrete batch M(4/5.0) is the best mixing where it assures a wide ductility and significant strength. 4. Contribution of fibre on the compression strength Several studies have been interested in knowing the way in which the fibre acts within the concrete. Cox (1952) introduced his original theory of stress transfer from the paper matrix to the fibre, which could be used in the same way for fibre concrete. Li and Stang (2001), Laranjeira (2010) proposed a probabilistic parameter ( f ) to take into account the random distribution of fibre in concrete batch. They proposed a probabilistic parameter ( η ), its value is defined by integration of the density function of 2 parameters p(z), p(Φ), where (z) is the center of gravity of fibres and (Φ) its orientation in the space , where it takes the form ( η 3D ) and has the value η 3D =1/2. Taking into account this parameter, the total compression load F t is transferred within the concrete body in proportion between plain concrete and fibres: F t = F f + F c (3) Where F t , F f , F c are respectively the applied force on the total section, the portion force on the fibres, and the portion force on the plain concrete. Meanwhile, due to the high flexibility of the fibre, they form in the mixture a kind of space mesh tissue. This leads to looking at the contribution as an integral body in the matrix of the concrete. From this point of view, the contribution of the fibres is calculated by the difference in strength between the two cases plain concrete and fibre concrete, (Figure 13). As shown the fibre of 4 cm length and 5 kg volume ratio has the best performance between the four composition of fibre concrete; that confirm the results given below regarding the ductility and the strength of the fibre dune sand. On the other hand, the number of fibres remains the dominant factor to assure a better homogeneity of concrete mix for fresh and hard concrete. Figure (14) shows that the effect of the number of fibres is not limited for 4cm length as well as for 5 kg weight able to increase strength; contrary to 8 cm length here its effect stagnates. Hence, the addition of fibre to the concrete batch needs a good choice of the physical properties of the fibre as well as the volume ratio to have the better number that composes the space fibre tissue in the matrix of the dune sand concrete.

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Fibre contribution Fibre-concrete

5

(3.65 MPa)

(3.52 MPa)

(3.05 MPa)

4

(2.76 MPa)

(2.74 MPa)

(2.61 MPa)

L 4cm L 8cm 5 kg 2.5 kg

3

(2.14 MPa)

(1.85 MPa)

2

1

Concrete strength (MPa)

0 Fibre portion stress (MPa)

0

2000

4000

6000

8000

M(4/2.5) M(8/2.5) M(4/5.0) M(8/5.0)

Number of fibres per cube

Figure 13. The fibre contribution to the strength of concrete

Figure 14. Effect of number of fibres

5. Conclusion The study proves the feasibility of using polypropylene fibre to improve the mechanical properties of dune sand concrete under compression loads. Generally, polypropylene fibre has the ability and the performance to improve moderately the strength of the sand dune concrete and to significantly increase its ductility and its toughness. However, the length and the weight, consequently the number of fibres, condition the performance of the hardened concrete, where for the same weight ratio of fibre, the experimental results show that for the fibre for 4 cm of length and 5 kg of weight perform the concrete better than fibre for 8 cm of length and 2.5 kg of weight.

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