Flexural behavior of structure of laminated cementitious composites with different types of mesh reinforcements

Abstract

In this study, 17 plates of cementitious ferrocement composite structure reinforced with two types of fabrics (jute and polypropylene) derived from biaxially oriented jute and polypropylene canvas with three reference unreinforced plates are experimentally investigated. The aim was to increase the flexural load carrying capacity and ductility of unreinforced laminated composite. The matrix was prepared using a ratio of 1:2:0.3 (Portland cement: sand: fly ash) by weight and water-to-cementitious material ratios (w/cm) of 0.4, 0.5, and 0.6. In accordance with ASTM C1609 procedure, the structural behavior of studied laminated composites with a size of 450 × 100 × 25 mm under a four-point load configuration, including first crack, maximum post cracking strength or modulus of rupture (MOR), deflection, toughness, crack pattern, and failure modes, are investigated with the effectiveness of type of fiber and the number of fabric layer reinforcements. The results indicate that types of fiber and number of layers of fiber have a significant effect on enhancement of resistance, strength, and ductility of the cementitious material mortars. The results showed that the first cracking strength generally decreased as the number of fibric layers increased. In comparison to the reference plates, the first cracking strength decreased by 92.8, 83.0, and 34.3% for plates reinforced with polypropylene fiber at 0.4 w/cm, as layer number increased from zero to six, eight, and ten, respectively. The post-flexural strength of the jute fiber-reinforced plates increased as layer number increased relative to the reference plate, whereas this was completely the opposite for polypropylene fiber-reinforced plates. The maximum flexural strength was 10.82 MPa for plates reinforced with jute fabrics whereas polypropylene fibers had a maximum flexural strength of 5.21 MPa. The post flexural strength of plates reinforced with jute fiber increased for w/cm ratio of 0.6 by 2.1, 68.0, and 78.4%, whereas it dropped for plates reinforced with polypropylene fiber by 6.7, 9.0, and 53.6% as layer number increased from zero to six, eight, and ten, respectively. Polypropylene fiber reinforced plates have a wider crack width than jute fiber reinforced plates and the effect of increasing layer number was not clear, but it did generally reduce crack spacing. A comparison of the maximum post-cracking strength against the first cracking strength indicated that jute fiber plates exhibited deflection hardening behavior, while the behavior was completely reversed for plates reinforced with PP fiber, whose curve behavior was softening deflection. The maximum deflection recorded 18.5 mm, and the energy absorption and deflection capabilities of jute fabric reinforced composites have both improved with layer number increased. Conversely, for polypropylene fabric reinforced composites, where the maximum deflection was 21 mm and the deflection and energy absorption capacity decreased as layer number increased. However, laminates made of polypropylene fabrics displayed significantly weaker bonds than jute fabric laminates, resulting in the appearance of horizontal cracks that separated the Polypropylene laminate layers and spread towards both supports emphasized by SEM test. As a result, the indices described in ASTM C1608 specifications cannot be generalized to the behavior of such materials for such a curve because, based on the experimental data, the calculated residual strength ratio exceeded 100% in only three plates. The toughness values in the composites suggest that this eco-friendly, ductile composite has a promising future in the construction industry.