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1. New directions for reinforced concrete coastal structures

   https://doi.org/10.1186/s43065-021-00015-4  

   Nolan, Steven; Rossini, Marco; Knight, Chase; Nanni, Antonio (December 2021, Journal of Infrastructure Preservation and Resilience)

   null (Ed.)

   Abstract Within the last century, coastal structures for infrastructure applications have traditionally been constructed with timber, structural steel, and/or steel-reinforced/prestressed concrete. Given asset owners’ desires for increased service-life; reduced maintenance, repair and rehabilitation; liability; resilience; and sustainability, it has become clear that traditional construction materials cannot reliably meet these challenges without periodic and costly intervention. Fiber-Reinforced Polymer (FRP) composites have been successfully utilized for durable bridge applications for several decades, demonstrating their ability to provide reduced maintenance costs, extend service life, and significantly increase design durability. This paper explores a representative sample of these applications, related specifically to internal reinforcement for concrete structures in both passive (RC) and pre-tensioned (PC) applications, and contrasts them with the time-dependent effect and cost of corrosion in transportation infrastructure. Recent development of authoritative design guidelines within the US and international engineering communities is summarized and a examples of RC/PC verses FRP-RC/PC presented to show the sustainable (economic and environmental) advantage of composite structures in the coastal environment. 

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2. Materials characterization of FRP composite seismic retrofits after long-term service in a subarctic Alaskan environment

   https://doi.org/doi.org/10.1016/j.conbuildmat.2022.127810  

   Milev, Sandra; Goodwin, David G.; Sattar, Siamak; Tatar, Jovan (July 2022, Construction building materials)

   This study assesses physical and chemical properties of fiber reinforced polymer (FRP) composite materials aged in Alaska’s subarctic climate. Carbon FRP (CFRP) and glass FRP (GFRP) samples were collected in 2019 from the exterior and interior of Ted Stevens International Airport (TSIA, retrofitted in 2008) and McKinley Tower (MKT, retrofitted in 2004). Differential scanning calorimetry (DSC) was used to measure glass transition temperature (Tg) and physical aging, FTIR and Raman spectroscopy were used to investigate potential chemical degradation and degree of cure, and scanning electron microscopy (SEM) to evaluate cross-sectional microstructure, respectively. The results indicate that exposure to the subarctic climate had minimal effect on the composites’ and chemical properties. The variability in fiber content at MKT and thermal properties at TSIA suggest there were likely some inconsistencies in the FRP installation that may affect load-carrying capacity. Furthermore, some microcracks were observed in the FRP retrofits which may have resulted from a combination of poor fiber impregnation and thermal cycling. 

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3. Predicting freeze-thaw deterioration in wood-polymer composites

   https://doi.org/10.26168/icbbm2017.79  

   Hess, K. M. (June 2017, Academic journal of civil engireering)

   Natural fiber-reinforced polymers are currently used in a variety of low- to high-performance applications in the automotive, packaging, and construction industries. Previous studies have demonstrated that natural fibers (e.g., flax, hemp) exhibit good tensile mechanical properties and have positive environmental and economic attributes such as low cost, rapid renewability, and worldwide availability. However, natural fibers are inherently susceptible moisture-induced changes in physical and mechanical properties, which can be unfavorable for in-service use. This study illustrates how a micromechanics-based modelling approach can be used to help facilitate durability design and mitigate the deleterious effects of freeze-thaw deterioration in wood-plastic composites (WPCs). The model described in this study predicts the critical fiber volume fraction (V_fcrit) at which damage to the composite will occur under certain environmental conditions for different WPC formulations of hardwood and softwood fiber reinforcement and polymer matrix types. As expected, the results show that V_fcrit increases (a positive result) as anticipated in situ moisture content decreases. In addition, results suggest that fiber packing distribution directly influences V_fcrit and that V_fcrit increases as the mechanical properties of the polymer matrix increase. In sum, the study demonstrates how predictive modeling can be applied during the design phase to ensure the durability of WPCs. 

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4. Shear behavior of reinforced concrete beams with GFRP needles as coarse aggregate partial replacement: Full-scale experiments

   X.F. Nie, B. Fu (September 2019, Advances in Engineering Materials, Structures and Systems: Innovations, Mechanics and Applications)

   Fiber reinforced polymer (FRP) waste is becoming an environmental concern due to the widespread use and non-biodegradable nature of FRP composites. Cutting FRP waste into discrete reinforce-ments (referred to as “needles” hereafter) as coarse aggregate in concrete has been suggested as a possible solution to FRP waste recycling. It has previously been observed in small specimens that FRP needles increase the tensile strength and energy absorption capacity of concrete. This paper presents an experimental investiga-tion into the effect of GFRP needles as coarse aggregate partial replacement in concrete on shear behavior of full-scale reinforced concrete (RC) beams. A total of 10 RC beams without steel stirrups in the critical zone were tested under four-point bending. The volume replacement ratio of the coarse aggregate and the surface type of GFRP needles were chosen as the test parameters. GFRP needles, with either smooth or helically wrapped surfaces, were added to the concrete mix to replace 5% or 10% of coarse aggregate by volume, respectively. All test beams failed in shear in a brittle manner with the ductility being slightly enhanced by the partial replace-ment of coarse aggregate using GFRP needles. An enhancement of 8%-10% in the load carrying capacity was observed in beams with helically wrapped needles, while beams with smooth needles showed a reduction in the load carrying capacity. 

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5. Optimizing Truss Structures Using Composite Materials under Natural Frequency Constraints with a New Hybrid Algorithm Based on Cuckoo Search and Stochastic Paint Optimizer (CSSPO)

   https://doi.org/10.3390/buildings13061551  

   Khodadadi, Nima; Harati, Ehsan; De Caso, Francisco; Nanni, Antonio (June 2023, Buildings)

   This article highlights the absence of published paradigms hybridized by The Cuckoo Search (CS) and Stochastic Paint Optimizer (SPO) for optimizing truss structures using composite materials under natural frequency constraints. The article proposes a novel optimization algorithm called CSSPO for optimizing truss structures made of composite materials, known as fiber-reinforced polymer (FRP) composites, to address this gap. Optimization problems of truss structures under frequency constraints are recognized as challenging due to their non-linear and non-convex search spaces that contain numerous local optima. The proposed methodology produces high-quality optimal solutions with less computational effort than the original methods. The aim of this work is to compare the performance of carbon FRP (CFRP), glass FRP (GFRP), and steel using a novel hybrid algorithm to provide valuable insights and inform decision-making processes in material selection and design. Four benchmark structure trusses with natural frequency constraints were utilized to demonstrate the efficiency and robustness of the CSSPO. The numerical analysis findings indicate that the CSSPO outperforms the classical SPO and exhibits comparable or superior performance when compared to the SPO. The study highlights that implementing CFRP and GFRP composites in truss construction leads to a notable reduction in weight compared to using steel. 

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