Predicting the Behaviour of Large-Scale BFRP-Reinforced Concrete Structures

Abstract

The quest for sustainable and durable infrastructure in marine environments has driven innovations in material science and structural engineering. Basalt Fibre Reinforced Polymer (BFRP) has emerged as a promising alternative to conventional steel reinforcement due to its non-corrosive nature, reduced CO₂ footprint, and more lenient crack width requirements. Although BFRP has been extensively studied at small scale, large-scale BFRP-reinforced concrete structures remain largely absent. This is also reflected in current codes and guidelines, where the effects of BFRP on large-scale concrete structures are insufficiently documented, preventing full validation.

The Port of Rotterdam aims to reduce CO₂ emissions from new infrastructure by 49% by 2030. BFRP reinforcement could contribute to reducing the environmental footprint of future infrastructure. This thesis investigates the impact of BFRP on large-scale concrete structures and applies these findings to an existing quay wall model using both theoretical and numerical approaches.

Basalt is an abundant volcanic rock which, when processed into BFRP bars, provides high tensile strength and lower density than steel, but also lower stiffness and brittle failure behavior. A review of European and North American codes and guidelines shows that conventional steel design rules cannot be directly applied to BFRP-reinforced structures, mainly due to the absence of yielding. As a result, excessive deflections, wider cracks, and different failure modes are commonly observed.

The Modified Compression Field Theory (MCFT), a strain-based method for predicting shear strength in reinforced concrete structures, was evaluated for BFRP applications. However, its constitutive laws limit direct application to brittle reinforcement. Adjustments including brittle failure incorporation, reduced aggregate interlock contribution, tensile strength reduction, and shear span ratio were explored, but no satisfactory modification was achieved.

Building on this finding, numerical investigations using Nonlinear Finite Element Analyses (NLFEA) were conducted. After calibration and validation against medium-scale experiments, NLFEA reproduced experimental and theoretical trends in BFRP-reinforced concrete with reasonable accuracy. The linear-elastic behavior and reduced stiffness of BFRP bars led primarily to concrete compression failure and stirrup rupture. Sensitivity analyses highlighted the importance of bond-slip behavior, reinforcement modeling approach, and mesh size, all of which significantly influenced predicted failure loads and crack development.

Large-scale simulations indicated that reinforcement modeling is particularly important in NLFEA, as increased structural size also affects shear transfer mechanisms such as dowel action. When applied to the quay wall case study, the BFRP-reinforced configuration showed higher tensile strains and deflections compared to conventional steel-reinforced designs, with stirrup rupture occurring under increasing terrain loads. Increasing reinforcement stiffness improved performance slightly but did not replicate the ductility observed in steel-reinforced quay walls.

From an environmental perspective, Life Cycle Assessment showed that replacing steel reinforcement with BFRP can reduce shadow costs and CO₂-equivalent emissions. Reducing concrete cover was also investigated, but the maximum achievable reduction was only 1.75%, limiting its practical impact on construction methods and emission reduction. The overall environmental benefit is therefore constrained primarily by the properties of BFRP reinforcement rather than the concrete itself.

Overall, this thesis concludes that BFRP reinforcement is a technically viable alternative for small- and medium-scale concrete structures, provided serviceability requirements and brittle failure behavior are carefully addressed. However, the absence of full-scale validation and the sensitivity of analytical and numerical predictions highlight the need for dedicated experimental research on large-scale BFRP-reinforced structures. Future work should focus on improving shear modelling approaches.