Flexural performance of innovative hybrid sandwich panels with special focus on the shear connection behavior

The present study intends to evaluate the flexural performance of hybrid sandwich panels through the execution of four point bending tests. The proposed hybrid sandwich panel uses Deflection Hardening Cementitious Composites (DHCC) on the top layer, a GFRP bottom layer and perforated shear connectors in the GFRP ribs to transfer shear stresses between top and bottom layers. The tested hybrid slabs use two types of shear connectors, which include indented and perforated shapes. The tests were performed to study the behaviour of a novel shear connection between the GFRP ribs and the DHCC layer that is here proposed. A comparison on the obtained experimental results was executed to clarify the influence of the shear connectors’ geometries on the flexural performance of the developed hybrid slabs. The results show that the shear connection mechanical behaviour strongly influences the peak load, the deflection at peak load, the post-peak load carrying capacity and the degree of composite action of the hybrid slabs.The study presented in this paper is a part of the research project "RehabGFRP - Rehabilitation of Building Floors with Lightweight High Performance GFRP Sandwich Panels", with reference number of PTDC/ECM/113041/2009. Furthermore, the authors honestly appreciate the collaboration of the following labs: Civitest for developing DHCC materials (Eng. Delfina Goncalves), PIEP for conducting VARTM process (Eng. Luis Oliveira) and Department of Civil Engineering of Minho University to perform the tests (Mr. Antonio Matos and Eng. Marco Jorge).info:eu-repo/semantics/publishedVersio

Simultaneous flexural and punching strengthening of RC slabs according to a new hybrid technique using U-shape CFRP laminates

One of the main concerns related to flat reinforced-concrete (RC) slabs is the slab’s punching capacity. Punching can occur not only due to a deficient transverse reinforcement, but also when the flexural capacity of the slab needs to be increased. To increase the flexural capacity, carbon-fiber-reinforced-polymer (CFRP) composites have been applied according to near-surface-mounted (NSM) or external-bonded-reinforcement (EBR) techniques, while for the punching strengthening CFRP reinforcements have been applied according to embedded-through-section (ETS) technique. To take advantage of strengthening benefits of the NSM and ETS techniques, in the present paper a new type of CFRP laminate of U-shape is used by adopting a novel hybrid technique for the simultaneous flexural and punching strengthening of existing RC slabs. Besides, this hybrid technique aims to provide a better bond performance for the ETS and NSM CFRPs by improving the anchorage conditions. Moreover, a higher resistance to the susceptibility of occurrence of other premature failure modes, like concrete cover delamination, is offered by using this hybrid technique. A 3D nonlinear finite-element (FE) model is developed to simulate the experimental tests by considering the nonlinear behavior of the constituent materials. The experimental program and numerical model are described, and the relevant results are analyzed.The authors acknowledge the financial support provided by QREN (through the Operational Program COMPETE) in the scope of the CutInov Project (n. 38780) involving the Clever Reinforcement Company and the Structural Composites Research group of ISISE-Minho University.info:eu-repo/semantics/publishedVersio

FACTORS INFLUENCING THE PREPARATION OF TiO2 NANOPOWDERS FROM TITANIA SOL

Titania nanoparticles with high photocatalytic activity were prepared from titanium alkoxide dissolved in alcohol and water under acidic conditions. The effects of the key parameters including (alkoxide/water) ratio, (alkoxide/alcohol) ratio, precursor type, solvent type, type and concentration of stabilizer, calcination temperature, presence of methylcellulose (MC) and hydrothermal treatment were studied. The optimal conditions were obtained through an experimental design technique. This technique is also used to find the main factors influencing the degradation of methylene blue (MB) and mass percent of anatase phase. The powders characteristics were investigated by XRD and Brunauer-Emmett-Teller (BET) methods. The X-ray diffraction studies showed that the product has anatase crystal structure with average particle size below 13 nm. The photocatalytic activities of the TiO2 nanoparticles were assessed by the degradation of MB in aqueous solution. According to the obtained results, the kinetics of photocatalytic reaction followed pseudo-first-order model. The results showed that the main factors influencing the degradation of MB were the type of stabilizer, presence of MC, hydrothermal treatment, solvent type and calcination temperature. Specific surface areas of the nanoparticles were between 76-198 m2/g

Development of innovative hybrid sandwich panel slabs: Experimental results

The authors appreciate the collaboration of the following labs: Civitest for developing DHCC materials, PIEP for conducting VARTM process (Eng. Luis Oliveira) and Department of Civil Engineering of Minho University to perform the tests (Mr. Antonio Matos and Eng. Marco Jorge).In this paper, a new generation of composite sandwich slab is proposed as a solution for the rehabilitation of slabs in old masonry buildings. An innovative solution was developed during this research formed by four components: a Deflection Hardening Cement Composite (DHCC) layer on the top compression skin, a glass fiber reinforced polymer (GFRP) skin at the bottom tension surface, GFRP ribs to transfer shear from top to bottom layers, and foam core for thermal-insolation purposes. The DHCC layer contributes significantly for the load carrying and deflection capacity due to its stiffness, compressive strength and toughness, offers resistance to the occurrence of buckling phenomena in the GFRP ribs, improves the performance of this structural concept against impact and fire, and constitutes an excellent medium for the application of finishing materials, like ceramics or timber. Two different hybrid composite slabs were developed and tested, and their behavior was assessed under flexural loading. The results showed that the developed hybrid sandwich slabs accomplish all design requisites for serviceability and ultimate limit states, and assure a stiffness/dead-weight and load-capacity/dead-weight ratios much higher than conventional structural slab systems.FCT - Fundação para a Ciência e Tecnologi

Clinical Validation of Integrated Nucleic Acid and Protein Detection on an Electrochemical Biosensor Array for Urinary Tract Infection Diagnosis

BACKGROUND: Urinary tract infection (UTI) is a common infection that poses a substantial healthcare burden, yet its definitive diagnosis can be challenging. There is a need for a rapid, sensitive and reliable analytical method that could allow early detection of UTI and reduce unnecessary antibiotics. Pathogen identification along with quantitative detection of lactoferrin, a measure of pyuria, may provide useful information towards the overall diagnosis of UTI. Here, we report an integrated biosensor platform capable of simultaneous pathogen identification and detection of urinary biomarker that could aid the effectiveness of the treatment and clinical management. METHODOLOGY/PRINCIPAL FINDINGS: The integrated pathogen 16S rRNA and host lactoferrin detection using the biosensor array was performed on 113 clinical urine samples collected from patients at risk for complicated UTI. For pathogen detection, the biosensor used sandwich hybridization of capture and detector oligonucleotides to the target analyte, bacterial 16S rRNA. For detection of the protein biomarker, the biosensor used an analogous electrochemical sandwich assay based on capture and detector antibodies. For this assay, a set of oligonucleotide probes optimized for hybridization at 37°C to facilitate integration with the immunoassay was developed. This probe set targeted common uropathogens including E. coli, P. mirabilis, P. aeruginosa and Enterococcus spp. as well as less common uropathogens including Serratia, Providencia, Morganella and Staphylococcus spp. The biosensor assay for pathogen detection had a specificity of 97% and a sensitivity of 89%. A significant correlation was found between LTF concentration measured by the biosensor and WBC and leukocyte esterase (p<0.001 for both). CONCLUSION/SIGNIFICANCE: We successfully demonstrate simultaneous detection of nucleic acid and host immune marker on a single biosensor array in clinical samples. This platform can be used for multiplexed detection of nucleic acid and protein as the next generation of urinary tract infection diagnostics

High strength fiber reinforced one-part alkali activated slag/fly ash binders with ceramic aggregates:microscopic analysis, mechanical properties, drying shrinkage, and freeze-thaw resistance

Abstract One-part alkali-activated binders, also known as the “just-add-water” concept, have received great attention due to their advantages over two-part alkali-activated binders. By avoiding the use of dangerous alkali solutions, these binders are easier to both handle and transport. Ground granulated blast furnace slag is one of the side streams, which can be used in one-part alkali-activated binders to reach high compressive strength at an early age. However, using slag alone has some disadvantages, including a fast setting time and a large drying shrinkage, narrowing the application of these mix compositions and causing crack formation, respectively, thus shortening service life. Fly ash can be used in one-part alkali-activated materials to partially substitute for slag in order to both minimize drying shrinkage and prolong the setting time. Moreover, ceramic waste can be used as a replacement for normal sand, which is great achievement in terms of developing environmentally friendly alkali-activated materials exclusively from side steam. This paper presents new research on the effects on the fresh and hardened-state properties of one-part alkali-activated mortars of replacing up to 80% of slag with fly ash. These properties were characterized by the initial and final setting time, the strength development (compressive and flexural), and the drying shrinkage. Microstructural analyses (SEM/EDS, XRF, TGA/DTG) justified the results. Moreover, different fiber contents and combinations were used to reinforce the developed one-part alkali-activated slag/fly ash mortars to increase the strength, further reduce the drying shrinkage, and improve the freeze/thaw resistance. The results showed that fly ash and fibers can reduce the drying shrinkage and prolong the setting time. The weakened mechanical properties caused by decreasing the amount of slag are still adequate to let the composite slag/fly ash material be considered in construction applications

Valorization of Industrial Wastes on Hybrid Low Embodied Carbon Cement Based Mortars

Waste reuse is crucial in a context of circular economy and zero waste sustainable needs. Some wastes deserve further studies by the scientific community not only because they are generated in high amount but also because they have a low reuse rate. This paper reports results of 32 hybrid cement mortars based on fly ash and waste glass. They allow to explore the influence of mix design on the cost and on the embodied carbon of the hybrid cement mortars. The embodied carbon data for all constituents were taken from the database Ecoinvent. This study led to the development of a mixture with just 70 kg CO2e

Cost and environmental performance of waste based alkali-activated mortars

This paper report experimental results of several mixes regarding the joint effect of replacement percentage of fly ash by waste glass, sodium hydroxide concentration, activator/binder ratio, the use of two commercial superplasticizers and a biopolymer on the cost and global warming footprint performance of alkali-activated mortars. In the mix compositions the significant impact on the cost of mixtures is concerned to the molarity concentration of NaOH solution, while replacing fly ash by milled glass has no great impact on the total price The minimum values for the normalized cost and GWP to compressive strength were measured about 22 Euro/m3.MPa and 17 kgCO2e/m3.MPa in the mixture 80FA_10CH_10MG_4M_0.5A/B

Fiber-reinforced one-part alkali-activated slag/ceramic binders

Abstract In the present experimental/numerical study, a combination of ceramic waste and ground-granulated blast furnace slag were used in the preparation of one-part alkali-activated binders. Moreover, the effect of fiber type and content on hardened-state properties and shrinkage was studied under two different curing conditions. In the first stage of this study water absorption, compressive strength, and flexural strength were assessed. Subsequently, the flexural performance of fiber-reinforced binders was simulated and predicted using finite element models under concentrated and distributed flexural loading, respectively. The experimental results showed that fibers improved mechanical properties, and enhancement was governed by fiber type and curing conditions. Moreover, the numerical results indicated that the developed fiber-reinforced binders offer a flexural load-carrying capacity in the range of 10–40 kN/m² and permissible service loads were well below the ultimate capacity