Textile-reinforced mortars (TRM) have recently received significant attention for the externally bonded reinforcement (EBR) of masonry and reinforced concrete structures. The fiber-to-mortar bond, the TRM-to-substrate bond, and the mechanical properties of the TRM constituents have a fundamental role in the performance of this strengthening technique and therefore require special attention. Despite this importance, only few investigations are devoted to characterization of the single fiber-to-mortar bond response in these systems. This paper, as an step towards addressing the fiber-to-mortar bond, presents a combined experimental and analytical investigation on the effect of test setup on the pull-out response and bond-slip laws in TRM composites. Three different pull-out test setups, consisting of one pull-pull and two pull-push configurations, are developed and investigated for characterization of the single fiber-to-mortar bond behavior. The experimental and analytical results are critically discussed and presented and bond-slip laws are extracted for each test setup.@en

This study presents a comprehensive experimental investigation on the fracture properties of hardened alkali-activated slag/fly ash (AASF) pastes in relation to the microstructure formation and reaction product composition. The main reaction product in AASF is C-(N-)A-S-H gel along with minor hydrotalcite phase, with the polymerization of C-(N-)A-S-H gel substantially governed by its Ca/Si ratio. Strong positive correlations are identified between the Ca/Si ratios of C-(N-)A-S-H gel and the fracture properties KIc (Jtip), whereas, the compressive strength of AASF pastes is primarily determined by its capillary porosity (>0.01 μm). The disagreements between the Ca/Si ratios and corresponding intrinsic mechanical properties of C-(N-)A-S-H gel as proof by contradiction indicate that the fracture properties KIc (Jtip) of AASF pastes could be dominated by a cohesion/adhesion-based mechanism. These findings provide promising guidance for fine-tuning the fracture properties of AASF and also advise on the tailoring strategies for high-performance composite such as strain-hardening geopolymer composite.@en

Near Surface Mounted (NSM) reinforcement is an interesting technique for seismic strengthening of masonry and historical structures. Despite having several advantages compared to conventional techniques, little attention has been given to understanding the involved mechanisms (such as bond behavior) in the performance of masonry components strengthened with this reinforcement technique. This study presents an experimental and analytical investigation on the bond performance of NSM-strengthened masonry bricks aiming at filling the existing gaps in the available experimental results in the literature. The main focus is on the effect of test setup and bond length, but attention has also been given to the groove size and loading regime effect on the bond performance. The accuracy of the existing bond strength prediction models is also assessed and the required modifications are proposed.@en

The effect of curing conditions (sealed and unsealed) on the pore solution composition and carbonation resistance of different binary alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) pastes is investigated in this study. The studied mixtures were with FA/GBFS ratios of 100:0, 70:30; 50:50, 30:70, 0:100. Ordinary Portland cement (OPC) and Cement III/B (70 wt% of GBFS and 30 wt% OPC) pastes with the same precursor content were also studied to provide a baseline for comparison. Accelerated carbonation conditions (1% (v/v) CO2, 60% RH for 500 days) were considered for evaluating the carbonation resistance of the pastes. The results show a substantial lower [Na+] in the pore solution of the unsealed cured samples compared to the sealed cured samples. It is also found that unsealed curing of the samples leads to a faster carbonation rate. Additionally, it is observed that the carbonation rate decreases with increasing GBFS content independent of the curing conditions. The potential risks with respect to carbonation of the pore solution are also identified and discussed.@en

The sustainability of infrastructure projects is becoming increasingly important issue in engineering practice. This means that in the future the construction materials will be selected on the basis of the contribution they can make to reach sustainability requirements. Geopolymers are materials based on by-products from industries. By using geopolymer concrete technology it is possible to reduce our waste and to produce concrete in the environmental-friendly way. An 80% or greater reduction of greenhouse gases compared with Ordinary Portland Cement (OPC) can be achieved through geopolymer technology. However, there are limited practical applications and experience. For a broad and large scale industrial application of geopolymer concrete, challenges still exist in the technological and engineering aspects. The main goal of GeoCon Bridge project was to develop a geopolymer concrete mixture and to upscale it to structural application. The outputs of projects provide input for development of recommendations for structural design of geopolymer based reinforced concrete elements. Through a combination of laboratory experiments on material and structural elements, structural design and finite element simulations, and based on previous experience with OPC concrete, knowledge generated in this project provides an important step towards a “cement free” construction. The project was performed jointly by three team members: Microlab and Group of Concrete Structures from Technical University of Delft and Technical University of Eindhoven.@en

This article presents a micromodeling computational framework for simulating the tensile response and tension-stiffening behavior of fiber reinforced polymer–strengthened reinforced concrete elements. The total response of strengthened elements is computed based on the local stress transfer mechanisms at the crack plane including concrete bridging stress, reinforcing bars stress, FRP stress, and the bond stresses at the bars-to-concrete and fiber reinforced polymer-to-concrete interfaces. The developed model provides the possibility of calculating the average response of fiber reinforced polymer, reinforcing bars, and concrete as well as the crack spacing and crack widths. The model, after validation with experimental results, is used for a systematic parameter study and development of micromechanics-based relations for calculating the crack spacing, fiber reinforced polymer critical ratio, debonding strength, and effective bond length. Constitutive models are also proposed for concrete tension stiffening and average response of steel reinforcing bars in fiber reinforced polymer–strengthened members as the main inputs of smeared crack modeling approaches.@en

Alkali-activation technology as an environmental friendly approach to produce construction materials can lead to a great CO2 emission reduction and provide high potential for waste reutilization. Alkali activated materials (AAMs) generally exhibit better durability and comparable or superior mechanical performance in comparison to traditional cementitious materials. However, like cementitious binders, AAMs are inherently brittle (quasi brittle). When it comes to engineering practices, the size effect also contributes to a more severe brittleness, which limits the applications in large scale structures. Fiber reinforcement is one of the solutions, which can be used to control the brittleness of AAMs. This paper presents a comparative study on the deflection-hardening behavior of ductile alkali-activated slag/fly ash (DAASF) composites reinforced with three types of synthetic fibers. All the developed DAASFs exhibited a deflection hardening with multiple cracking behavior under four-point bending tests. The influence of different fiber types, different slag/fly ash ratio as well as liquid/solid (L/S) ratio were investigated. The obtained results are a first step contribution to understanding the feasibility of using different fiber types in AAMs and development of mixture design of DAASF composites.@en

The paper deals with the analysis of FRCM (Fiber Reinforced Cementitious Matrix) reinforced masonry panels in simple bending by means of a two-step homogenization approach. In the first step, homogenization is performed on unreinforced masonry through a straightforward procedure already validated for in-plane loaded FRCM reinforced panels, where the elementary cell is discretized by means of 24 CST elastic elements (bricks) and joints are reduced to interfaces with holonomic softening behavior. Out-of-plane homogenized quantities (moment-curvature relationships) are then obtained by simple on-thickness integration. At a structural level (step two), masonry is modeled with rigid elements and homogenized torsional and bending springs, whereas FRCM by two noded trusses with equivalent mechanical properties evaluated on the base of experimental data available. The implementation is handled within the commercial FE software Abaqus. As a matter of fact, the Concrete Damage Plasticity Model (CDP) already implemented into the code allows taking into account the progressive change of stiffness of brittle supports when subjected to alternate cracking-crushing mechanisms, as well as to properly deal with the cyclic behavior. The validation of the procedure is conducted against a series of full scale masonry walls tested by Nanni and co-workers at the University of Miami. A tri-dimensional heterogeneous micro-modeling technique is also used for both unreinforced and FRCM strengthened panels to further validate the homogenization model proposed. The discretization adopted is adjusted in order to allow the presence of two eight-noded FEs along the mortar joint thickness. FRCM is modeled by means of truss elements whose mechanical properties are calibrated to reproduce the behavior of the textile net embedded into the cementitious matrix. The elastic and inelastic mechanical parameters of all the materials involved into the numerical analyses have been calibrated in agreement with laboratory tests, when available. Pros and cons of the two numerical strategies are discussed mostly with respect to the accuracy of the outcomes in terms of global behavior of the panels and damage mechanisms, as well as with respect to the computational effort required by the two approaches to complete the analyses.@en

Textile Reinforced Mortars (TRMs) have found extensive attention for externally bonded reinforcement of masonry and historical structures. However, only few information is available regarding their mechanical properties and effectiveness in improving the seismic performance of strengthened structures. This paper presents an extensive numerical investigation on the effect of TRM composites on the nonlinear response and failure modes of masonry walls. The effect of boundary conditions and the TRM type on the performance of strengthened walls are critically discussed and presented. It is shown that the performance and failure mode of the walls can significantly change after strengthening, an important issue that should be considered at the design stage. Finally, the effect of TRM application on the nonlinear response of a large historical masonry façade in Macau is investigated and presented.@en