STR-888: FLEXURAL TESTS OF CONTINUOUS CONCRETE SLABS REINFORCED WITH BASALT FIBER-REINFORCED POLYMER BARS

Continuous steel-reinforced concrete slabs are vulnerable to corrosion damage and cracking. Non-metallic basalt fiber-reinforced polymer (BFRP) bars have a great potential to overcome corrosion problems. In this paper, test results of six continuous concrete slabs internally-reinforced with BFRP bars are reported. The specimens were divided into two groups based on the BFRP reinforcement ratio in the sagging regions (2.5Pfb and 0.8Pfb), where Pfb is the balanced reinforcement ratio of BFRP reinforcement. In each group, the hogging-to-sagging BFRP reinforcement ratio was 0.5, 0.72, or 1. Increasing the hogging-to-sagging BFRP reinforcement ratio increased the ultimate load but had almost no effect on the cracking load. The flexural response of continuous slabs that failed by rupture of BFRP bars was more sensitive to the hogging-to-sagging BFRP reinforcement ratio than that of the slabs that failed by concrete crushing. The moment redistribution ratio in the sagging region at failure of the later specimens was in the range of +40% to +48% compared to +10% to +26% for the former specimens

Hand verification for flexural strength of existing R.C. floors subject to degradation phenomena

Abstract In the present paper, a simplified model for hand verification of the flexural and shear strength of existing corroded T beams cast in place of lightened R.C. orthotropic slabs forming floors is presented and discussed. Diffused and pitting corrosion on steel bars, compressive concrete strength degradation and concrete bond strength degradation are included in the model. The original contribution of the paper is evaluation of the flexural and shear strength considering both the cases of strain compatibility and absence of compatibility and considering the main parameters governing the corrosion process. An arch-resistant model for the calculus of the flexural and shear strength of the beam was adopted in the absence of strain compatibility, while the plane section theory was adopted for the case of strain compatibility. No punching shear is considered. This approach is simple and can be applied on the basis of the experimental information available (carbonation test, chloride content, measurement of the pitting in the bar, gravimetric method for general corrosion) or by utilizing analytical expressions calibrated on the knowledge of the corrosion current intensity determined by linear polarization resistance measurement (LPR). The model was also verified against experimental results recently obtained by the authors

Modelling of corrosion-induced cover cracking in reinforced concrete by an embedded cohesive crack finite element

Corrosion of a reinforcement bar leads to expansive pressure on the surrounding concrete that provokes internal cracking and, eventually, spalling and delamination. Here, an embedded cohesive crack 2D finite element is applied for simulating the cracking process. In addition, four simplified analytical models are introduced for comparative purposes. Under some assumptions about rust properties, corrosion rate, and particularly, the accommodation of oxide products within the open cracks generated in the process, the proposed FE model is able to estimate time to surface cracking quite accurately. Moreover, emerging cracking patterns are in reasonably good agreement with expectations. As a practical case, a prototype application of the model to an actual bridge deck is reported

Application of plastic-damage multidirectional fixed smeared crack model in analysis of RC structures

This paper describes a plasticity-damage multidirectional fixed smeared cracking (PDSC) model to simulate the failure process of concrete and reinforced concrete (RC) structures subjected to different loading paths. The model proposes a unified approach combining a multidirectional fixed smeared crack model to simulate the crack initiation and propagation with a plastic-damage model to account for the inelastic compressive behaviour of concrete between cracks. The smeared crack model considers the possibility of forming several cracks in the same integration point during the cracking process. The plasticity part accounts for the development of irreversible strains and volumetric strain in compression, whereas the strain softening and stiffness degradation of the material under compression are controlled by an isotropic strain base damage model. The theoretical aspects about coupling the fracture, plasticity, and damage components of the model, as well as the model appraisal at both material and structural levels, have been detailed in a former publication. This study briefly summarizes the model formulations, and is mainly dedicated to further explore the potentialities of the proposed constitutive model for the analysis of concrete and RC structures. The model is employed to simulate experimental tests that are governed by nonlinear phenomenon due to simultaneous occurrence of cracking and inelastic deformation in compression. The numerical simulations have predicted with good accuracy the load carrying capacity, ductility, crack pattern, plastic (compressive) zone, and failure modes of all types of structures analysed. The influence of the model parameters that simulate the nonlinear behaviour of concrete under tension and compression is analysed through a parametric study.Portuguese Foundation for Science and Technology in the scope of the SlabSys-HFRC research project, with reference PTDC/ECM/120394/201

Nonlinear analysis of reinforced concrete hollow beam with GFRP bars and stirrups using finite element method under cyclic load

Insufficient knowledge on using fibre-reinforced polymer (FRP) materials in hollow members limits their application. Torsional load results in the less efficient hollow section that plays an important role in hollow members. This load is generated on the members by an external load. The torsional load in hollow members that are reinforced longitudinally with FRP has been discussed for years. However, research on high-strength concrete (HSC) reinforced with glass fibre-reinforced polymer (GFRP) is scarce. Therefore, in this study, the behaviour of hollow beam internally reinforced with GFRP bars under cyclic load is investigated. For this purpose, the HSC-reinforced concrete hollow beam with GFRP bars and hollow beam with normal reinforcement are considered and finite element model is developed and nonlinear dynamic analysis has been conducted by applying cyclic loads to the developed models. In addition, reinforced concrete (RC) solid beam with HSC material is tested experimentally in order to verify and validate the ability of finite element software to predict the result. The analysis results are investigated in terms of the hysteresis loop, stress and strain distribution in the beam and it is indicated that the performance of hollow beam reinforced with GFRP bars and stirrups has improved in comparison with HSC beam with GFRP bars and also HSC beam with normal steel reinforcement. Therefore, based on this research, it is recommended to implement GFRP bars and stirrup for strengthening the concrete members in the high humidity areas where use of normal steel is not feasible due to corrosion threat

Shear strengthening of concrete members with TRM jackets: Effect of shear span-to-depth ratio, material and amount of external reinforcement

An experimental work on reinforced concrete (RC) rectangular beams strengthened in shear with textile reinforced mortar (TRM) jackets is presented in this paper, with focus on the following investigated parameters: (a) the amount of external TRM reinforcement ratio, ρf, by means of using different number of textile layers and different types of textile fibre materials (carbon, glass, basalt); (b) the textile geometry, and (c) the shear span-to-depth ratio, a/d. In total, 22 tests were conducted on simply supported rectangular RC beams under (three-point bending) monotonic loading. The experimental results revealed that: (1) TRM is very effective when the failure is attributed to debonding of the TRM jacket from the concrete substrate; (2) the trend of effective strains for carbon, glass and basalt TRM jackets is descending for increasing values of the TRM reinforcement ratio, ρf, when failure is associated to debonding of the jacket; (3) the effect of textile geometry is significant only for low values of ρf, resulting in variances in the capacity enhancement and the failure modes, and (4) the shear span-to-depth ratio has practically no effect to the failure mode nor to the TRM jacket contribution to the total shear resistance of the RC beams

Outcomes-Based Assessment and Learning: Trialling Change in a Postgraduate Civil Engineering Course

This paper aims to demonstrate how assessment tasks can function within an outcomes-based learning framework to evaluate student attainment of learning outcomes. An outcomes-based learning framework designed to integrate teaching, learning, and assessment activities was developed and implemented in a civil engineering master-level course. The assessment instruments for this course were designed together to form a deliberate, balanced, and practical approach to evaluating student attainment of learning outcomes within the outcomes-based learning initiative. Direct evidence of student learning was derived through analysis of student results in assessment tasks constructively aligned with intended outcomes of learning. Student feedback provided indirect evidence of student attainment of learning outcomes and confirmed the effectiveness of the learning approach implemented in the course under investigation. Results of the direct assessment instruments were, generally, consistent with the student self-perception confirming achievement of learning outcomes. Students tended, however, to overestimate the level of attainment of learning outcomes. Results of the present study are anticipated to assist educators and researchers to efficiently and effectively implement and evaluate outcomes-based learning in higher education thus improving educational quality and student learnin

Microstructure Characteristics of GFRP Reinforcing Bars in Harsh Environment

Fiber reinforced polymer (FRP) composites have been suggested as corrosion-resistant alternatives to traditional steel reinforcement in concrete structures. Within this family of composites, glass fiber reinforced polymers (GFRPs) have been gaining momentum as the primary selection of FRP for construction applications. Despite being advantageous, its wide adoption by the industry has been hindered due to the degradation of its performance in severe environmental conditions. As such, significant studies have been carried out to assess the mechanical properties of GFRP bars subject to different conditioning schemes. However, the inconsistencies and wide variations of results called for more in-depth microstructure evaluation. Accordingly, this paper presents a critical review of existing research on the microstructure of GFRP reinforcing bars exposed to various conditioning regimes. The review analysis revealed that sustained load limits set by codes and standards were satisfactory for nonaggressive environment conditions but should be updated to include different conditioning regimes. It was also found that conditioning in alkaline solutions was more severe than concrete and mortars, where test specimens experienced irreversible chemical degradation, more hydroxyl group formation, and more intense degradation to the microstructure. The progression of hydrolysis was reported correlatively through an increase in hydroxyl groups and a decrease in the glass transition temperature. While moisture uptake was the primary instigator of hydrolysis, restricting it to 1.6% could limit the reduction in tensile strength to 15%. Further, the paper identifies research gaps in the existing knowledge and highlights directions for future research

Properties of Steel Fiber-Reinforced Alkali-Activated Slag Concrete Made with Recycled Concrete Aggregates and Dune Sand

Reutilizing industrial by-products and recycled concrete aggregates (RCA) to replace cement and natural aggregates (NA) in concrete is becoming increasingly important for sustainable development. Yet, experimental evidence is needed prior to the widespread use of this sustainable concrete by the construction industry. This study examines the performance of alkali-activated slag concrete made with RCA and reinforced with steel fibers. Natural coarse aggregates were replaced with RCA. Steel fibers were added to mixes incorporating RCA at different volume fractions. Desert dune sand was used as fine aggregate. The mechanical and durability properties of plain and steel fiber-reinforced concrete made with RCA were experimentally examined. The results showed that the compressive strength did not decrease in plain concrete mixes with 30 and 70% RCA replacement. However, full replacement of NA with RCA resulted in a 20% reduction in the compressive strength of the plain mix. In fact, 100% RCA mixes could only be produced with compressive strength comparable to that of an NA-based control mix in conjunction with 2% steel fiber, by volume. In turn, at least 1% steel fiber, by volume, was required to maintain comparable splitting tensile strength. Furthermore, RCA replacement led to higher water absorption and sorptivity and lower bulk resistivity, ultrasonic pulse velocity, and abrasion resistance. Steel fiber incorporation in RCA-based mixes densified the concrete and improved its resistance to abrasion, water permeation, and transport, thereby enhancing its mechanical properties to exceed that of the NA-based counterpart. The hardened properties were correlated to 28-day cylinder compressive strength through analytical regression models