Investigating the Effects of Polypropylene Fibers on the Mechanical Strength, Permeability, and Erosion Resistance of Freshwater and Seawater Mixed Concretes

Abstract

Seawater mixed (SW) concrete lessens the freshwater (FW) demand and eases the stress on the already depleting FW resources. The use of SW concrete is a sustainable solution that mitigates the environmental impact of concrete production, especially in coastal regions and islands vulnerable to FW scarcity. This study investigated the influence of polypropylene (PP) fiber incorporation on high-performance-SW concrete’s long-term mechanical and durability performance. The findings indicate that the incorporation of seawater in the production of concrete containing ground granulated blast furnace slag (GGBFS) has a beneficial effect on its early strength. This is due to the fact that SW accelerates the hardening process. SW concrete mixes showed an improvement in strength with aging. The difference between the strength of SW and FW concretes reduced with aging. The PP fiber showed phenomenal improvements in the tensile properties of SW and FW concretes. At the addition of 0.3% PP fiber, SW yielded 56% and 48% higher splitting tensile and flexural strength than plain FW concrete at 28 days, respectively. The use of 0.15% of PP fiber caused notable reductions of around 20% in the water absorption (WA) capacity and a 12–20% reduction in chloride ion permeability (CIP) of SW concrete. The incorporation of PP fiber increases the number of drying–wetting cycles to initiate the erosion of SW and FW concretes in a simulated environment. The use of 0.15% PP fiber is beneficial, as compared to 0.3% PP fiber to control the tidal erosion of SW and FW concretes. After exposure to 126 drying–wetting cycles (stimulated tidal erosion), the mass loss of SW concrete was reduced from 0.56% to 0.22%.

Influence of Polymer Fibers on the Structure and Properties of Modified Variatropic Vibrocentrifuged Concrete

“…At the same time, zones inside the composite body with a large and dense concentration of PF will have low strength, which negatively affects the overall final strength of the entire composite [ 72 , 78 ]. The positive effect of fiber on the properties of heavy concrete is also confirmed by the following studies [ 32 , 79 , 80 , 81 ]. For example, in [ 79 ], the introduction of PF improves the structure of the samples and improves the strength characteristics; however, when the structure of the composite is oversaturated with polypropylene fibers, a negative effect is observed.…”

“…As for individual factors, as mentioned earlier, the VCC modified with polypropylene fiber showed the least improvement in performance. And first of all, this is due to the fact that polypropylene fiber itself has lower strength and deformation characteristics than concrete itself, and cannot properly perceive the stresses arising in concrete and redistribute them [ 8 , 31 , 32 ]. Modification of VCC with basalt fiber is more effective, since basalt fiber has a higher elastic modulus, tensile strength, and when stresses occur in the composite structure, it prevents microcrack formation [ 11 , 12 , 13 , 14 , 69 ].…”

“…Polypropylene and basalt fibers are the most popular and most often used in the technology of normal-density concrete, and the effectiveness of their use has been confirmed by many scientific studies [ 8 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. Basalt fiber is of inorganic origin, obtained by melting basalt rock in smelting furnaces and drawing continuous threads from this melt through special dies, which are subsequently dried and chopped into fibers.…”

“…Polypropylene fiber is produced by extrusion. Special raw materials are brought to high temperatures and passed through holes with an individual profile and cross-section, and then the resulting fibers are cut to the required length [ 8 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ].…”

“…During multiple freeze–thaw cycles in an aggressive environment, polypropylene fibers effectively suppress the propagation of microcracks and prevent concrete destruction. In a study [ 32 ], the authors were able to achieve a significant improvement in compressive and splitting strength, a decrease in water absorption and chloride ion permeability by introducing 0.3% polypropylene fiber. Polypropylene fiber in the composition of cement composites has a positive effect on their strength characteristics, namely on bending and splitting strength to a greater extent and to a lesser extent on compressive strength, also increases impact resistance and reduces permeability [ 33 , 34 , 35 , 36 , 37 , 38 ].…”