Fracture toughness determination of adhesive and co-cured joints in natural fibre composites

Adhesive bonding has become more efficient in the last few decades due to the adhesives developments, granting higher strength and ductility. On the other hand, natural fibre composites have recently gained interest due to the low cost and density. It is therefore essential to predict the fracture behavior of joints between these materials, to assess the feasibility of joining or repairing with adhesives. In this work, the tensile fracture toughness (Gc n) of adhesive joints between natural fibre composites is studied, by bonding with a ductile adhesive and co-curing. Conventional methods to obtain Gc n are used for the co-cured specimens, while for the adhesive within the bonded joint, the J-integral is considered. For the J-integral calculation, an optical measurement method is developed for the evaluation of the crack tip opening and adherends rotation at the crack tip during the test, supported by a Matlab sub-routine for the automated extraction of these quantities. As output of this work, an optical method that allows an easier and quicker extraction of the parameters to obtain Gc n than the available methods is proposed (by the J-integral technique), and the fracture behaviour in tension of bonded and co-cured joints in jute-reinforced natural fibre composites is also provided for the subsequent strength prediction. Additionally, for the adhesively- bonded joints, the tensile cohesive law of the adhesive is derived by the direct method.

Influence of the use of recycled concrete aggregates from different sources on structural concrete

This paper intends to evaluate the capacity of producing concrete with a pre-established performance (in terms of mechanical strength) incorporating recycled concrete aggregates (RCA) from different sources. To this purpose, rejected products from the precasting industry and concrete produced in laboratory were used. The appraisal of the self-replication capacity was made for three strength ranges: 15-25 MPa, 35-45 MPa and 65-75 MPa. The mixes produced tried to replicate the strength of the source concrete (SC) of the RA. Only total, (100%) replacement of coarse natural aggregates (CNA) by coarse recycled concrete aggregates (CRCA) was tested. The results show that, both in mechanical and durability terms, there were no significant differences between aggregates from controlled sources and those from precast rejects for the highest levels of the target strength. Furthermore, the performance losses resulting from the RA's incorporation are substantially reduced when used medium or high strength SC's. (C) 2014 Elsevier Ltd. All rights reserved.

Reusability assessment of thermoset polymeric composite wastes as reinforcement and filler replacement for polymer concrete materials

The development and applications of thermoset polymeric composites, namely fiber reinforced polymers (FRP), have shifted in the last decades more and more into the mass market [1]. Production and consume have increased tremendously mainly for the construction, transportation and automobile sectors [2, 3]. Although the many successful uses of thermoset composite materials, recycling process of byproducts and end of lifecycle products constitutes a more difficult issue. The perceived lack of recyclability of composite materials is now increasingly important and seen as a key barrier to the development or even continued used of these materials in some markets.

A reliability-based measure of robustness for concrete structures subjected to corrosion

This work is a contribution to the definition and assessment of structural robustness. Special emphasis is given to reliability of reinforced concrete structures under corrosion of longitudinal reinforcement. On this communication several authors’ proposals in order to define and measure structural robustness are analyzed and discussed. The probabilistic based robustness index is defined, considering the reliability index decreasing for all possible damage levels. Damage is considered as the corrosion level of the longitudinal reinforcement in terms of rebar weight loss. Damage produces changes in both cross sectional area of rebar and bond strength. The proposed methodology is illustrated by means of an application example. In order to consider the impact of reinforcement corrosion on failure probability growth, an advanced methodology based on the strong discontinuities approach and an isotropic continuum damage model for concrete is adopted. The methodology consist on a two-step analysis: on the first step an analysis of the cross section is performed in order to capture phenomena such as expansion of the reinforcement due to the corrosion products accumulation and damage and cracking in the reinforcement surrounding concrete; on the second step a 2D deteriorated structural model is built with the results obtained on the first step of the analysis. The referred methodology combined with a Monte Carlo simulation is then used to compute the failure probability and the reliability index of the structure for different corrosion levels. Finally, structural robustness is assessed using the proposed probabilistic index.

Lean production in the precast concrete components’ industry

Proceedings IGLC-19, July 2011, Lima, Perú

Numerical simulation of blast effects on fibre grout RC panels

The main purpose of the present dissertation is the simulation of the response of fibre grout strengthened RC panels when subjected to blast effects using the Applied Element Method, in order to validate and verify its applicability. Therefore, four experimental models, three of which were strengthened with a cement-based grout, each reinforced by one type of steel reinforcement, were tested against blast effects. After the calibration of the experimental set-up, it was possible to obtain and compare the response to the blast effects of the model without strengthening (reference model), and a fibre grout strengthened RC panel (strengthened model). Afterwards, a numerical model of the reference model was created in the commercial software Extreme Loading for Structures, which is based on the Applied Element Method, and calibrated to the obtained experimental results, namely to the residual displacement obtained by the experimental monitoring system. With the calibration verified, it is possible to assume that the numerical model correctly predicts the response of fibre grout RC panels when subjected to blast effects. In order to verify this assumption, the strengthened model was modelled and subjected to the blast effects of the corresponding experimental set-up. The comparison between the residual and maximum displacements and the bottom surface’s cracking obtained in the experimental and the numerical tests yields a difference of 4 % for the maximum displacements of the reference model, and a difference of 4 and 10 % for the residual and maximum displacements of the strengthened model, respectively. Additionally, the cracking on the bottom surface of the models was similar in both methods. Therefore, one can conclude that the Applied ElementMethod can correctly predict and simulate the response of fibre grout strengthened RC panels when subjected to blast effects.

The encore project: sustainable solutions for cementitious materials

Since concrete is the most widely utilized construction material, several solutions are currently being developed and investigated for enhancing the sustainability of cementitious materials. One of these solutions is based on producing Recycled Concrete Aggregates (RCA) from existing concrete members resulting by either industrial processes or demolitions of existing structures as a whole. Moreover, waste resulting from industrial processes other than the building construction (i.e., tire recycling, production of steel, powders resulting from other depuration processes) are also being considered as possible low-impact constituents for producing structural concrete and Fiber-Reinforced Cementitious Composites (FRCC). Furthermore, the use of natural fibers is another option for producing environmentally-friendly and cost-effective materials, depending on the local availability of raw materials. To promote the use of concretes partially composed of recycled constituents, their influence on the mechanical and durability performance of these concretes have to be deeply investigated and correlated. This was the main goal of the EnCoRe Project (www.encore-fp7.unisa.it), a EU-funded initiative, whose activities and main findings are summarized in this paper.

A model to simulate the moment-rotation and crack width of FRC members reinforced with longitudinal bars

The present work describes a model for the determination of the moment–rotation relationship of a cross section of fiber reinforced concrete (FRC) elements that also include longitudinal bars for the flexural reinforcement (R/FRC). Since a stress–crack width relationship (σ–w)(σ–w) is used to model the post-cracking behavior of a FRC, the σ–w directly obtained from tensile tests, or derived from inverse analysis applied to the results obtained in three-point notched beam bending tests, can be adopted in this approach. For a more realistic assessment of the crack opening, a bond stress versus slip relationship is assumed to simulate the bond between longitudinal bars and surrounding FRC. To simulate the compression behavior of the FRC, a shear friction model is adopted based on the physical interpretation of the post-peak compression softening behavior registered in experimental tests. By allowing the formation of a compressive FRC wedge delimited by shear band zones, the concept of concrete crushing failure mode in beams failing in bending is reinterpreted. By using the moment–rotation relationship, an algorithm was developed to determine the force–deflection response of statically determinate R/FRC elements. The model is described in detail and its good predictive performance is demonstrated by using available experimental data. Parametric studies were executed to evidence the influence of relevant parameters of the model on the serviceability and ultimate design conditions of R/FRC elements failing in bending.

Mechanical performance of natural fiber-reinforced composites for the strengthening of masonry

The growing concerns regarding the environmental impact generated by the use of inorganic materials in different fields of application increased the interest towards products based on materials with low environmental impact. In recent years, researchers have turned their attention towards the development of materials obtained from renewable sources, easily recoverable or biodegradable at the end of use. In the field of civil structures, a few attempts have been done to replace the most common composites (e.g. carbon and glass fibers) by materials less harmful to the environment, as natural fibers. This work presents a comprehensive experimental research on the mechanical performance of natural fibers for the strengthening of masonry constructions. Flax, hemp, jute, sisal and coir fibers have been investigated both from physical and mechanical points of view. The fibers with better performance were tested together with three different matrices (two of organic nature) in order to produce composites. These experimental results represent a useful database for understanding the potentialities of natural fibers as strengthening systems.

Resilience of concrete structures in the marine environment through microstructural innovation

Dissertação de mestrado integrado em Engenharia Civil

Estudo da ligação entre componentes estruturais de GFRP (glass fiber reinforced polymer) e componentes estruturais em betão

Dissertação de mestrado integrado em Engenharia Civil

Higher education as formation of the self and citizenship: an ethnography of the University Students from Amman, Jordan

My interest in higher education and citizenship in the Middle East at large and in Jordan in particular is fostered by some of the reflections Eickelman proposed (1992). Being a quite recent phenomenon, intimately linked with the more general topic of state formation it seemed to me more suitable to study it in a little country with a recent history (a field study left almost unexplored until now as far as Jordan is concerned, to the best of my knowledge, since Antoun 1994 focuses on the migration as a quest for higher education). The process of state formation in Jordan is quite studied. I thus intended to study the higher education policies as an attempt both to create a national citizenry and more recently as a way of controlling the more problematic part of the population (youth, which constitutes more than the double of the population. See UNDP and Ministry of Planning 2000). How do the young students enter the university system, and in which way does this system work? How is this system designed, in order to retain social control of the students (since they are usually perceived to be a factor of social and political instability, as in Iran or in Egypt)? Is there any significant difference between different faculties? And if so, why? My conclusions at this stage are that the university system is an integral part of the survival of the regime. The system works quite well, and Jordan has one of the best educational position in the region. Yet there are important distinctions to be made: the access to the better faculties is socially selective while the less valued faculties are left to the poorer and less wealthy youth. This results in a different treatment of the students and of the courses that I analysed. In the better faculties the teaching standards are quite high, and the relationship between professors and students is almost on a same-level base, while in the less privileged faculties the opposite is true. Thus we can observe a concrete politics of divide et impera intended to split the youth in two. For the more privileged there are some freedoms, both within and outside classes, designed I guess at forging them as autonomous individuals. On the opposite the less privileged are kept under tight control, even if also these students are a privileged category among youth at large.

Steel Diaphragms in Prestressed Concrete Girder Bridges, September 2004

Over the years, bridge engineers have been concerned about the response of prestressed concrete (PC) girder bridges that had been hit by over-height vehicles or vehicle loads. When a bridge is struck by an over-height vehicle or vehicle load, usually the outside and in some instances one of the interior girders are damaged in a bridge. The effect of intermediate diaphragms in providing damage protection to the PC girders of a bridge is not clearly defined. This analytical study focused on the role of intermediate diaphragms in reducing the occurrence of damage in the girders of a PC-girder bridge that has been struck by an over-height vehicle or vehicle load. The study also investigated whether a steel, intermediate diaphragm would essentially provide the same degree of impact protection for PC girders as that provided by a reinforced-concrete diaphragm. This investigation includes the following: a literature search and a survey questionnaire to determine the state-of-the-art in the use and design of intermediate diaphragms in PC-girder bridges. Comparisons were made between the strain and displacement results that were experimentally measured for a large-scale, laboratory, model bridge during previously documented work and those results that were obtained from analyses of the finite-element models that were developed during this research for that bridge. These comparisons were conducted to calibrate the finite element models used in the analyses for this research on intermediate diaphragms. Finite-element models were developed for non-skewed and skewed PC-girder bridges. Each model was analyzed with either a reinforced concrete or two types of steel, intermediate diaphragms that were located at mid-span of an interior span for a PC-girder bridge. The bridge models were analyzed for lateral-impact loads that were applied to the bottom flange of the exterior girders at the diaphragms location and away from the diaphragms location. A comparison was conducted between the strains and displacements induced in the girders for each intermediate-diaphragm type. These results showed that intermediate diaphragms have an effect in reducing impact damage to the PC girders. When the lateral impact-load was applied at the diaphragm location, the reinforced-concrete diaphragms provided more protection for the girders than that provided by the two types of steel diaphragms. The three types of diaphragms provided essentially the same degree of protection to the impacted, PC girder when the lateral-impact load was applied away from the diaphragm location.

Effective Structural Concrete Repair, Volume 1 of 3, Repair of Impact Damaged Prestressed Concrete Beams with CFRP, March 2004

Structural concrete is one of the most commonly used construction materials in the United States. However, due to changes in design specifications, aging, vehicle impact, etc. – there is a need for new procedures for repairing concrete (reinforced or pretressed) superstructures and substructures. Thus, the overall objective of this investigation was to develop innovative cost effective repair methods for various concrete elements. In consultation with the project advisory committee, it was decided to evaluate the following three repair methods: • Carbon fiber reinforced polymers (CFRPs) for use in repairing damaged prestressed concrete bridges • Fiber reinforced polymers (FRPs) for preventing chloride penetration of bridge columns • Various patch materials The initial results of these evaluations are presented in this three volume final report. Each evaluation is briefly described in the following paragraphs. A more detailed abstract of each evaluation accompanies the volume on that particular investigation.

Effective Structural Concrete Repair, Volume 2 of 3, Use of FRP to Prevent Chloride Penetration in Bridge Columns, March 2004

Structural concrete is one of the most commonly used construction materials in the United States. However, due to changes in design specifications, aging, vehicle impact, etc. – there is a need for new procedures for repairing concrete (reinforced or pretressed) superstructures and substructures. Thus, the overall objective of this investigation was to develop innovative cost effective repair methods for various concrete elements. In consultation with the project advisory committee, it was decided to evaluate the following three repair methods: • Carbon fiber reinforced polymers (CFRPs) for use in repairing damaged prestressed concrete bridges • Fiber reinforced polymers (FRPs) for preventing chloride penetration of bridge columns • Various patch materials The initial results of these evaluations are presented in this three volume final report. Each evaluation is briefly described in the following paragraphs. A more detailed abstract of each evaluation accompanies the volume on that particular investigation.