Concrete structures are responsible for a substantial share of the total global CO2 emissions. This has led to the establishment of the Betonakkoord in the Netherlands, which aims to significantly reduce the emissions from concrete structures.

Reinforcement bars made from Basalt Fibre Reinforced Polymer (BFRP) offer a potential solution for making concrete structures more sustainable. Firstly, the Environmental Cost Indicator (ECI) of BFRP rebar is 43% lower than that of steel rebar. Additionally, BFRP does not corrode, which eliminates the requirement for a thick concrete cover to meet environmental class standards. Consequently, the use of BFRP reinforcement instead of steel could potentially reduce the amount of concrete needed, further enhancing the sustainability of concrete structures.

This study investigates the feasibility of enhancing the sustainability of a bridge deck in an inverted T-girder bridge by using BFRP rebars. BFRP differs from steel in several material properties. Although its strength, at approximately 1200 N/mm², is significantly higher than that of B500B steel, the much lower E-modulus of BFRP presents challenges. Additionally, BFRP behaves in a fully linearly elastic manner until failure in the absence of a yield plateau. The lower stiffness results in higher deformations and crack widths. The hypothesis is that this could potentially be problematic for shear capacity, as the concrete compression zone is reduced, aggregate interlock decreases, and dowel action is less effective due to the low transverse strength of the rebar.

In this study, various design variants for a bridge deck in an inverted T-girder bridge were modeled to assess the impact of different design parameters. A reference design variant with steel reinforcement was used as a baseline and compared with several variants incorporating BFRP rebars. The BFRP design variants differed in terms of reinforcement quantity, concrete cover, and effective depth.

A quasi-linear model of an inverted T-girder bridge was developed using the numerical software SCIA Engineer. The bridge deck design alternatives were modeled as an orthotropic plate with centroidal ribs. The numerical model clearly demonstrated that, due to the less stiff nature of the BFRP-reinforced bridge decks, there is less distribution of traffic loads compared to relatively stiff steel-reinforced bridge deck. Ultimately, the model showed that shear force is indeed the critical failure mechanism for BFRP-reinforced bridge decks. Reducing the effective depth of the BFRP reinforced bridge deck variants, decreases the shear force distribution in transverse direction by 5% and further decreases the shear capacity by 23% to 30%, depending on the adjusted parameters for each design variant.
The application of BFRP rebar in a bridge deck and the reduction of concrete cover to 25 mm, instead of the usual 50 mm used with steel reinforcement, is shown to be feasible in this study. An optimization was conducted to develop a bridge deck design, that meets the structural performance criteria of shear force while minimizing concrete usage. This resulted in an optimized design with a bridge deck height of 215 mm, compared to the conventional 250 mm.

A sustainability study based on the LCA cradle-to-gate life cycle phases (A1-A3) has demonstrated that BFRP reinforcement can significantly enhance the sustainability of a bridge deck. For the optimized design variant that meets all the structural requirements, the ECI reductions range from 27% to as much as 32%, depending on the cement type used in the concrete mixture. This study has shown that the application of BFRP rebars in a concrete bridge deck is certainly feasible and results in significant sustainability improvements.

This report describes the effect of microfibre reinforcement on the printability and strain hardening properties of Strain-Hardening Cement-based Composites (SHCC). To determine this effect, a study was conducted with three different fibre types and two different concrete matrices. In total, this has led to 6 different concrete mixtures. The three different fibre types are PVA(Poly-Vinyl-Alcohol) 6mm length, PVA 8mm length and HDPE(High Density Poly Ethylene) 6mm length. The difference between the two matrices is mainly in the water-cement ratio, which leads to a stronger and weaker matrix. The strong matrix is the C mix and the weaker one is the D mix.
The printability of the different mixtures is determined by means of a slump flow test. Printability can be divided into buildability and pumpability. Buildability describes how well the printed concrete layers hold together and do not collapse. Pumpability of the mixture says how well it is able to be pumped. If the slump flow test shows that a mixture behaves stiff, than it will have a higher buildability and lower pumpability. If the mixture behaves very fluidly in the slump flow test, it will have a lower buildability and higher pumpability.
The strain hardening properties of the SHCC are determined by doing compressive tests, four-point bending tests and tensile tests. These tests determine the compressive strength, flexural strength and tensile strength of each mixture. It was also found out to what extent each mixture is able to stretch, bend and then exhibits strain hardening. After the tests, the samples were also visually examined to see how the bending and cracking took place.
The weak D mix seems to show the most strain hardening. The fibres in this matrix can transfer the tensile stresses better, because in this matrix they are more able to stretch.
The research has shown that the mixtures with PVA 6 mm in the fresh state are very stiff and are therefore the least suitable for 3D printing. In addition, the mixtures with the PVA 6 mm microfibre reinforcement show the least strain hardening. In the four-point bending tests it was already noticeable that the samples failed at very low deflection and there was little cracking. It was therefore decided not to include these mixtures in the tensile tests in order to save time.
HDPE microfibre has shown to have good printability and significantly outperforms PVA 8 mm in strain hardening. The HDPE fibres provide a very flexible and stretchable material. Compared to PVA, HDPE shows a much finer cracking pattern, which has a positive effect on the durability of the concrete. All in all, it can be concluded that HDPE performs best and would be the best choice for application in 3D printing.