Effects of Mix Proportions and Polypropylene Fibers Reinforcement on the Mechanical and Long-Term Durability Behavior of Carbonated Concrete

The growing need for sustainable construction material has stimulated the objective and active interest in using recycled polymers and CO 2 cure method in the production of concrete. Traditional cement-based products are a source of intense pollution of global CO 2 and resource consumption. In this regard, the creation of carbonated reinforced concrete with polypropylene fiber can be viewed as a feasible step toward enhancing the mechanical characteristics, as well as reducing the environmental impact. This study offers an in-depth and novel evaluation of the effect of the changes in the water-to-cementitious materials (w/cm) ratio along with the inclusion of recycled polypropylene fibers on the mechanical response and long-term durability of concrete under in situ CO 2 injection using a CarbonCure-like process. Mixtures with lower w/cm ratios (0.25–0.45) exhibited higher compactness but reduced workability, which was further affected by polypropylene fiber additions (0.5–1.0% by cementitious mass), necessitating superplasticizer use. The addition of fibers increased the air content of the mixture from 1.8 to 2.6 at the dosage of 1.0% and reduced the density slightly, as the values of 2405–2410 kg/m 3 reduced to about 2395 kg/m 3 . Both variables had a positive impact on mechanical behavior, compressive strength improved up to 20 percent in lower w/cm ratios, and improvements in splitting tensile and flexural strengths were up to 15 percent with the addition of fiber. Accelerated CO 2 curing durability tests showed that the carbonation penetration depths dropped to 8.0mm to 6.6mm at w/cm of 0.25 and 17.5mm to 14.9mm at w/cm of 0.45 with 1.0 percent fiber contents. The microstructural examination revealed homogeneous dispersion of fibers, good fiber–matrix interfacial bonding, and a reduced number of microcracks in compact mixtures. The outcomes of SEM also showed that there was more calcite production and less content of portlandites especially in fiber-reinforced mixes with less w/cm ratio, which is a testament to successful carbonation.