This study determines the mechanical properties of normal and lightweight concrete strengthened with ramie fiber-reinforced polymer (RFRP) as an eco-friendly external confinement material. This research examines the tensile strength and modulus of RFRP, as well as the compressive strength, flexural strength, failure modes, stress-strain and force-displacement behaviors of both unstrengthened and strengthened cylindrical and beam samples. Cylinder and beam samples of normal and lightweight concrete were produced and strengthened using RFRP in different configurations (center strip and full jacketing for cylinders and bottom lamination for beams). The RFRP composites with 33.28 ± 4.11 MPa of tensile strength and 1064 ± 91.85 MPa of Young’s modulus were used as a strengthened material. The results showed that, compared with unconfined samples, full RFRP jacketing improved the compressive strength by up to 47.9% in normal concrete and 30.2% in lightweight concrete. The flexural strength increased by 8.6% in normal concrete and 25.3% in lightweight concrete. The failure mode shifted from brittle cracking to more ductile and controlled failure in the strengthened samples. The study revealed that fiber confinement improved strain capacity with minimal impact on density, however, the enhancement effect may plateau depending on fiber configuration and concrete type. These findings demonstrate that RFRP is a promising, sustainable solution for enhancing structural performance, particularly in lightweight concrete applications where the strength-to-weight ratio is essential.
