Strength and Degradation Characteristics of Concrete Pavements Containing Coir Fibers

This study fundamentally investigates three key aspects of coir-fiber-reinforced concrete pavements: the primary parameters of coir influencing the paving concrete strength, the mechanisms contributing to strength reduction, and the degradation processes of coir within the concrete matrix. In this study, several coir parameters were considered, including fiber maturity (mature and immature), aspect ratio (40 and 200), dosage (0.1%–0.7% by volume), treatment (alkaline treatment with NaOH), and concrete grades (M30 and M40). Methods such as simulated pore solution exposure, accelerated weathering, thermal and chemical analysis, and image analysis were employed to examine coir degradation. The results indicated that inclusions of coir, irrespective of its type and length, up to ≤0.4% by volume will not significantly affect the quality of concrete. However, beyond this proportion, the compressive and flexural strengths for short and long fibers were found to be reduced by 54%, 40%, 36%, and 18%, respectively. Although it was found that the coir did not alter the cement hydration kinetics, it swelled initially in the presence of moisture and ultimately shrank by ∼6%. This shrinkage followed by swelling led to the complete detachment of coir from the surrounding cement matrix by 0.02–0.10 mm resulting in the development of a poor interfacial transition zone. The results of the degradation tests indicated that coir fibers will eventually degrade due to the coupling effect of alkali hydrolysis and mineralization; however, this phenomenon would occur only after the concrete-hardening stage and thus would not affect the performance of concrete significantly. Based on this investigation, the use of coir fibers in less proportions (≤0.4%) is recommended for paving concrete mixes.