Investigation of the sustainability potential of BFRP reinforcement compared with reinforcing steel and CFRP reinforcementReinforced concrete construction causes significant greenhouse gas emissions due to the production of cement and reinforcement. Non-metallic reinforcements such as carbon- (CFRP) and basalt fiber-reinforced polymers (BFRP) offer a corrosion-resistant alternative. This paper investigates the sustainability potential of BFRP compared with reinforcing steel and CFRP using an analytical case study of non-prestressed and prestressed parking decks. The comparison is based on the global warming potential (GWP) of the production stage A1-A3. With the support and loading conditions held constant, the reinforcement demand is determined for two representative spans by varying the reinforcement material. At a span of 4.5 m, the cross-section remains uncracked and the ultimate limit state governs. BFRP reinforcement exhibits the lowest and CFRP reinforcement the highest GWP. At a span of 6.5 m, the cross-section is cracked, so the deflection limit in serviceability limit state becomes decisive. The lower Young's modulus of BFRP reinforcement results in a larger required reinforcement area and therefore a higher reinforcement demand, which can be mitigated by prestressing. Prestressed BFRP-reinforced components enable slender and material-efficient cross-sections. Further potential arises from reduction in concrete cover, lower-binder concrete mixes, and longer service life of components.
Self-prestressed carbon-reinforced concrete - Current researchCarbon reinforced concrete, a composite material, is characterized by its very slender structural design and high durability, making it particularly suitable for the construction of shell-type structures. However, concrete elements reinforced with textile carbon grids tend to exhibit large crack widths. This is attributed to the high shrinkage tendency of high-strength concrete in combination with the low compressive stiffness of the carbon grid. This limits the full exploitation of the potential of carbon reinforced concrete. A promising solution to this problem is the use of expansive concrete, which can not only compensate for shrinkage but also induce prestress when appropriately designed. This activates the carbon textile reinforcement and significantly improves the structural performance. As part of CRC/TRR 280, numerous experimental investigations on the production of self-prestressed carbon reinforced concrete slabs were carried out at the Institute of Concrete Structures at Dresden University of Technology. These studies included the development of a high-performance expansive concrete, the analysis of the bond behavior between expansive concrete and carbon textile reinforcement, and tests on the structural performance of slabs. The results show that expansive concrete with a deliberately adjusted expansion behavior and full bond to the carbon reinforcement can be produced. The induced prestress leads to a significant improvement in structural performance, including increased stiffness, reduced deflections, and reduced crack widths compared to non-prestressed carbon concrete. This article provides an overview of the methodology for self-prestressed carbon reinforced concrete.
3D concrete printing can be used not only on construction sites but also in precast plants for the resource-efficient and automated prefabrication of modular concrete structures. A key challenge in this context is designing high-performance dry joints between the individual modules. This paper first provides an overview of existing modular 3D-printed structural systems and then examines various dry joint geometries, as well as their subtractive manufacturing using CNC milling and cutting. Additionally, it discusses the geometric specification of joint surfaces and evaluates the results of experimental investigations under pure compression and combined shear-compression loading. These tests included specimens produced using shotcrete, extrusion and particle-bed 3D printing. The results demonstrate that curved joint profiles offer the highest load-bearing capacity. However, these profiles must be manufactured by milling, which takes a long time. Triangular joints have only slightly lower load-bearing capacities, but they can be manufactured by cutting, which is significantly less machining-intensive. They therefore represent an advantageous compromise between mechanical performance and manufacturability when transmitting compressive and shear forces. Flat joints, on the other hand, are primarily suitable for transmitting pure compressive stresses.
Particle-bed 3D printing of concrete components - Process and potential of Selective Cement ActivationThis article focuses on Selective Cement Activation, a particle-bed 3D printing process for cementitious building materials. It aims to provide an overview of the research findings on this printing process that have emerged within the framework of the DFG Collaborative Research Centre TRR 277 'Additive Manufacturing in Construction'. First, the selective cement activation process is described, and the manufacturing steps for a reinforced component are compared with those of conventional production. The fundamental relationships between material properties and process parameters are then explained. Various methods for increasing the mechanical strength and dimensional accuracy of printed components are discussed. Additionally, design requirements for components produced via Selective Cement Activation are outlined, along with three concepts for integrating reinforcement. Finally, potential application areas, showcased by two demonstrators developed within the TRR 277, are presented, and current challenges are emphasised.
Ultra-high performance concrete (UHPC) exhibits pronounced autogenous shrinkage due to its high binder content. When shrinkage is restrained, restraint stresses develop already at early age. This affects reinforced UHPC members in general, since shrinkage is restrained by the embedded reinforcing steel, as well as composite sections such as UHPC overlays used for the rehabilitation and strengthening of existing bridge decks. An equivalent-load model is presented that allows the strain and self-equilibrated stress state resulting from restrained shrinkage to be determined directly by crosssectional analysis. The model is based on linear elasticity. The reduced stiffness of young UHPC, its creep behaviour, and the loss of stiffness associated with micro-crack formation are accounted for by employing an effective modulus of elasticity. For calibration, reinforcement strains were measured over 40 days in UHPC specimens with different section depths, reinforcement ratios and fibre contents. From these measurements, a free shrinkage strain of approximately-1000 mu m/m and the effective modulus of elasticity were identified inversely for the investigated fine-grained UHPC. The effective modulus amounts to only about 11-12 % of the 28-day modulus of elasticity. The equivalent-load model can be applied to UHPC composite sections without changing its underlying mechanical principle.
