The Swedish Fortifications Agency

’s (FORTV) property stock consists of numerous concrete structures built both above and below rock. Some of these structures have experienced cracking overtime which, in turn, can lead to subsequent problems such as reinforcement corrosion and deterioration of structural performance. Due to the fact that in many cases there are building requirements related to protection against forced entry and weapon attacks, it is of great importance for FORTV to gain an understanding of how cracks are developed, the significance of the crack development, how do cracks affect the performance, as well as how cracks can be remediated. A similar project, with a focus on so-called access protection, has earlier been managed by FORTV. During the project, it was ascertained that there is inadequate knowledge pertaining to crack repair.

The goals of this project were the following:

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• Suggest a method or a tool to evaluate the extent of cracking in concrete structures which are included in protective facilities.
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• Describe which parameters can initiate cracking.
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• Describe repair methods to reinstate the functionality of concrete structures.

Cracking naturally takes place during the normal use of a concrete structure without influencing

the structure’s functionality given that it is designed correctly. However, there are other mechanisms which can initialize cracking in concrete structures. These mechanisms take place during various time periods (hardening, after hardening and

during the service life). Three crack groups have been identified accordingly: a) cracks due to poor workmanship, b) cracks due to chemical deterioration mechanisms and c) loading cracks.

Damage identification and a condition assessment can be conducted in different stages to determine the extent of cracking. It is firstly recommended to review the existing documentation coupled to the structure, followed by a preliminary inspection (visual), additional non-destructive testing and lastly destructive testing. Repairs are selected according to the source of the damage, it is to say concrete defects or corroded reinforcement. In addition, the functionality requirements for the structure shall be evaluated and the selected methods shall be assessed according to e.g. lifespan and cost.

Pull-out mechanisms for different common steel fibers were investigatedusing adapted pull-out tests performed in-situ in an x-ray micro tomograph(µXRT). High-resolution volume images from the µXRT scans enable clearvisualization of aggregates, pores, the fiber and the fiber-matrix interface.Furthermore, the natural density speckle pattern from aggregate distributionand pores was found suitable for Digital Volume Correlation (DVC) analysis.From the DVC results it was possible to visualize and quantify the straindistribution in the matrix around the fiber at the different load levels up tofinal failure, being marked by either pull-out or fiber rupture. This studydemonstrates that strain measurements within the concrete matrix can beobtained successfully using µXRT imaging and DVC analysis, which leads to anincreased understanding of the interaction mechanisms in fibre reinforcedconcrete under mechanical loading.

Prefabricated and non-load bearing sandwich façade elements were developed using Textile Reinforced Reactive Powder Concrete (TRRPC) along with low density Foamed Concrete (FC) and Glass Fiber Reinforced Polymer (GFRP) continuous connecting devices. Four-point bending tests were performed on large-scale TRRPC sandwich element beams to characterize the structural performance, which included the flexural capacity, level of composite action, resulting deformation, crack propagation and failure mechanisms. Optical measurements based on Digital Image Correlation (DIC) were taken simultaneously to enable a detailed analysis of the underlying composite action. The structural behavior of the developed elements was found to be highly dependent on the stiffness and strength of the connectors to ensure composite action between the two TRRPC panels.

Within the EC funded project smart elements for sustainable building envelopes, carbon textile reinforcement was incorporated into reactive powder concrete, namely textile reinforced reactive powder concrete (TRRPC), to additionally improve the post-cracking behaviour of the cementitious matrix. This high-performance composite material was included as outer and inner façade panels in prefabricated and non-load bearing sandwich elements along with low density foamed concrete (FC) and glass fibre reinforced polymer continuous connecting devices. Experiments and finite element analysis (FEA) were applied to characterize the structural performance of the developed sandwich elements. The mechanical behaviour of the individual materials, components and large-scale elements were quantified. Four-point bending tests were performed on large-scale TRRPC-FC sandwich element beams to quantify the flexural capacity, level of composite action, resulting deformation, crack propagation and failure mechanisms. Optical measurements based on digital image correlation were taken simultaneously to enable a detailed analysis of the underlying composite action. The structural behaviour of the developed elements was found to be highly dependent on the stiffness and strength of the connectors to ensure composite action between the two TRRPC panels. As for the FEA, the applied modelling approach was found to accurately describe the stiffness of the sandwich elements at lower load levels, while describing the stiffness in a conservative manner after the occurrence of connector failure mechanisms. © 2018, The Author(s).

This report provides an overview about recent research activities and current practice concerning inspection and monitoring of the structural performance of bridges and the related decision-making process. A brief review of common methods of collecting information on structural performance of bridges is presented, followed by a description of the use of the information collected in structural analysis and maintenance planning. An overview about the state of the art is given including recent scientific developments. Finally, the current Swedish practice for bridge management is presented.

In fibre reinforced concrete (FRC), understanding the underlying interaction mechanisms between discrete fibres and the surrounding concrete matrix can lead to the optimization of the fibre-matrix combination. This paper presents the initial development of a method enabling the analysis of this given interaction on ameso-mechanical level. The method is such that volume images are initially captured using X-ray Computed Tomography (XCT) on small-scale FRC specimens under loading which are thereafter analysed to measure full 3D strainand deformation via Digital Volume Correlation (DVC). It is anticipated that the method developed in this project can be a useful tool for the developmentof new innovative and high performance FRC.

The mechanical properties of textile reinforced high-performance concrete (TRHPC) applied in innovative lightweight sandwich elements has been investigated in the framework of EC supported FP7 project, H-House (Healthier Life with Eco-innovative Components for Housing Constructions). TRHPC offers new possibilities for architects and engineers to create thinner and more durable concrete façade elements. Textile reinforcement grids are typically woven from non-metallic rovings usually consisting of continuous glass, rock or carbon fibres. The most promising performing textile reinforcement alternative in terms of mechanical and durability performance consists of carbon fibres. Carbon fibres do however have an inherent smooth surface which is unfavourable concerning its bond to the cement paste, which is often improved by polymer-based coatings. The bond behaviour, being a critical design parameter, should be investigated for TRHPC in order to understand limitations regarding required anchorage lengths for use in applications such as façade elements. The aim of this study was to quantify and verify the required anchorage length for a selected epoxy impregnated carbon textile reinforced TRHPC combination. To achieve this aim, the bond behaviour, leading to a suitable anchorage length (or overlap), was firstly studied by means of pull-out tests. Thereafter, the ultimate strength of the composite material was measured via uniaxial tensile testing with and without an overlap splice according to the findings from the pull-out tests. Optical measurements during the pull-out tests were performed using a video extensometer technique and by Digital Image Correlation (DIC) for the uniaxial tensile tests. Results indicated that the required anchorage length to yield rupture of the textile reinforcement in pull-out was deemed appropriate as an overlapping length when tested in tension. The combination of these two experimental methods on the composite level was useful for determining the overlapping length required for the TRHPC which could be applied in larger scale applications.

A novel sandwich element design consisting of two facings made of carbon reinforced Textile Reinforced Concrete (TRC), a low density foamed concrete (FC) core and glass fibre reinforced polymer (GFRP) connecting devices was experimentally investigated according to quasi-static and cyclic quasi-static fourpoint bending. Optical measurements based on Digital Image Correlation (DIC) were taken during testing to enable a detailed analysis of the bending behaviour and level of composite action. A model, verified by the experiments, was developed based on non-linear finite element analysis (NLFEA) to gain further insight on the failure mechanisms. Under both loading conditions, the bending behaviour of the TRCFC composite elements was characterized by favourable load bearing capacity, partial composite action, superior ductility and multiple fine cracking. The connecting devices were found to be the critical elements causing the initial failure mechanism in the form of localized pull-out within an element.

The EC funded project SESBE (Smart Elements for Sustainable Building Envelopes) focused on utilizing new types of cementitious materials for reducing the mass and thickness of façade elements while increasing their thermal performance. A method enabling the quantification and verification of the required anchorage length for a given textile reinforced reactive powder concrete (TRRPC) is presented. At the material level, tensile tests were conducted to determine the tensile properties of the reinforcement. Pull-out tests were applied to quantify the required anchorage length, while uniaxial tensile tests were performed to quantify the ultimate strength and verify the suitability of the anchorage length at the composite level. The combination of these methods was deemed useful to determine the overlapping length required for larger scale façade applications.

Textile reinforced concrete (TRC) is an innovative high performance composite material which has revealed many promising attributes in various applications but test methods and reliable numerical models need to be established to reduce uncertainty and the need for extensive experimental studies. The aim of this paper was to evaluate the flexural behaviour of carbon textile reinforced TRC slabs both experimentally and numerically along with the characterization of the material and interaction level properties. The experimental results characterizing the bond behaviour were linked to the experimental behaviour of a rectangular TRC slab in bending through numerical analyses. A 2D macro-scale FE-model of the tested TRC slab was developed based on the related experimental input. Comparison of the numerical results to the experiments revealed that the flexural failure was governed by bond, and reasonable agreement was obtained in terms of crack development, deflections, maximum load, and failure mode. Accordingly, the experiments further indicated that the flexural behaviour of TRC slabs is greatly influenced by the bond quality.