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The production of fiber reinforced polymer (FRP) composite materials is a major source of non-degradable waste. The use of FRP bars for reinforcing concrete is increasing in construction. This study investigates the impact of replacing coarse natural aggregate (NA) in concrete with cut FRP bar waste (FRP-RA) on the compressive and tensile strength of both high strength and normal strength concretes. Concrete cylinders without any FRP-RA, with 40% of NA (the large-grade particles) replaced with FRP-RA, and with 100% of NA replaced with equivalently graded FRP-RA were tested. The results show that the effect of the FRP-RA on the mentioned mechanical properties depends on the concrete strength, replacement ratio and the gradation-size of the NAs replaced. High-strength concrete performed better than low strength concrete and replacement of larger sized NA with FRP-RA resulted in better performance compared to full replacement. The test results show that existing empirical models can sometimes overestimate the tensile strength of lower-strength FRP-RA concretes. The findings show that although the use of FRP waste in concrete reduces the strength, concrete with structural grade mechanical properties can be produced with FRP-RA. The potential durability issues of FRP-RA concrete are discussed and future studies on this topic is proposed.

Shear failure of reinforced concrete members is brittle and catastrophic, and should be avoided. This work presents a comparative study of concrete beams with natural crushed stone and those incorporating recycled concrete aggregate (RCA). The study indicates that the equation presented in ACI 318-14 Code requirements for predicting the shear strength of concrete is less conservative for RCA concrete beams. The presented experimental investigations show that strengthening with fiber reinforced polymer (FRP) fabrics can be designed so that the shear capacity of the beams with weaker (RCA) concrete is higher than that of the control beams with natural aggregate concrete. The design of the FRP strengthening system and the reasons for the effectiveness of the design are explained.

This paper describes an experimental program designed and executed to investigate the failure mode and ultimate capacity of web-reinforced pultruded FRP beams subjected to concentrated loads in the plane of the web. Six 203.2 mm × 101.6 mm × 12.7 mm beams and five 203.2 mm × 203.2 mm × 9.5 mm beams manufactured with vinylester resin were strengthened with one of three systems and subjected to concentrated loads applied directly to the top flange. The three systems were (a) full-depth web bearing stiffeners, (b) “doubler” plates attached to the web, or (c) stiffening elements applied to the upper (loaded) web-flange junction of the specimen. Experimental results showed that the junction stiffeners (58.7%), bearing stiffeners (52.8%), and “doubler” plates (31.7%) all increased the ultimate capacity of the beams when compared to unstrengthened control beams. Beams prepared with bearing stiffeners and “doubler” plates failed in the same manner as the control beams (shear “wedge” failure at loaded web-flange junction), while failure in the beams with reinforced loaded web-flange junctions occurred in the bottom flange near the simple supports. Digital image correlation software was used to capture out of plane displacement of the web and confirms the modes of failure.

The objective of the research reported in this paper was to investigate the use of short arc-length segments and semi-circular segments of paperboard (also known as cardboard) tubes as formwork in bridge deck applications for either long-span [20–50 m (60–160 ft)] steel or prestressed concrete bridges or short-span [6–20 m (20–60 ft)] “Beam-in-Slab” bridges. In both these types of structures conventional plywood and light framing lumber formwork can be expensive and time consuming to install. For over 30 years, paperboard tubes have been used throughout the world to form round, reinforced concrete columns or occasionally voided slabs. These tubes (also know as Sonotubes) are produced throughout the world, and are preferred to conventional steel, plywood, or even fiber reinforced plastic (FRP) formwork because they are economical, disposable and recyclable. Due to their tubular shapes they have not been considered for use in “flat” elements such as slabs and walls. This paper presents results of a series of laboratory tests conducted at the University of Wisconsin – Madison that demonstrate that paperboard tube segments can be used as formwork for certain types of slabs, particularly for bridge decks and a variety of other types of construction where a flat surface is not essential. The testing, which was intended to simulated construction site loading conditions, included ultimate and service load tests, as well as impact loading. Tests were also conducted to investigate how moisture content affects the structural performance of the tubes. Results showed that commercially produced large diameter paperboard tubes may well be viable economical and recyclable materials for forming concrete elements, particularly those used in bridge decks when wide-flange prestressed girders are used.

Sustainable recyclable paper and composite materials can be ideal choices for the construction of temporary structures for both exhibition spaces or for rapid-recovery shelters in emergency operations. The unique engineering and sustainable features of these structures need to be considered as an integral part of the design process from the conceptual phase. Engineering studies to analyze these structures should be as important as the overall artistic and architectural vision. This paper examines the use of environmentally creep-formed paper tubes for the design, construction, and exhibition of, “Portals to an Architecture”, a large temporary outdoor sculpture.

Studies on two novel uses of hybrid structural members consisting of commercially produced glass reinforced pultruded ribbed fiber reinforced polymer (FRP) planks and concrete are discussed in this paper. Pultruded planks are produced by all the major pultruders in the world and are utilized primarily as decking for platforms. These highly optimized panels have the potential to be used in many other infrastructure applications, but their flexural stiffnesses have generally been too low to be used in highway and pedestrian bridges due to current span requirements. However, when used “compositely” with concrete or cementitious materials in a hybrid form they have the potential to be much more widely used. Two research studies conducted on two possible hybrid systems of different structural depths are discussed in this paper. The first study describes the use of pultruded planks as permanent formwork in highway bridge decks where the plank is used with concrete to produce a solid slab of 200 mm depth that is typical of slabs seen in highway bridge decks. The second study describes the use of pultruded planks in pedestrian bridge decks where the pultruded plank is used with a cement-board or a cast-in-place concrete panel to produce a hollow slab of 75 mm depth that is typical of timber decking used in FRP pedestrian bridges. Tests were conducted on beam-type specimens of the hybrid slabs to investigate the load transfer mechanisms between the pultruded plank and the cementitious “overlays” for both the 75 mm and 200 mm depths. From analysis of the load-carrying capacity and failure mechanisms of the hybrid slabs it was concluded that such hybrid slabs are viable systems for both highway and pedestrian bridge decks. A bridge deck using the 200 mm deep hybrid slab system was recently constructed on a highway in Wisconsin, USA.

This paper discusses the development of a model design and construction specification for thin [less than 38 mm (1.5 in.)] non-participating permanent formwork panels (also known as, stay-in-place forms and lost forms) made of FRP or FRC materials with or without non-metallic reinforcements for use in the construction of concrete slabs, in particular, highway bridge decks. The use of such forms is motivated by the narrow gaps [less than 1 m (39.4 in.)] that are often found between the flanges of wide flange ‘‘bulb-T” prestressed girders that are becoming commonplace in the US highway construction industry. Bridge contractors have expressed an interest in using non-participating permanent forms to reduce the time and cost required in forming and stripping the plywood forms for such narrow gaps. A model specification that was developed to enable engineers to design and specify such forms is provided in the appendix to this paper. To develop the specification, different permanent formwork panels were fabricated and tested. These included (1) flat cementitious panels reinforced with short glass or polypropylene fibers, (2) flat cementitious panels reinforced with bi-directional FRP thin grids, (3) flat cementitious panels reinforced with unidirectional FRP reinforcing bars, and (4) off-the-shelf, commercially manufactured pultruded FRP thin-walled, ribbed planks. The specification provides guidance for the width of gaps permissible for each Class of system and details of prescriptive and performance tests that must be performed to qualify the products for use in construction.

The investigation of a structural fiber-reinforced-polymer (FRP) stay-in-place (SIP) form used to construct and reinforce a deck for a prototype military bridge system is discussed in this paper. For this application the deck is subjected to combined bending and compressive longitudinal axial load because it also serves as the top chord of the truss for the bridge system. In an experimental program, deck specimens were tested in several configurations. The results are compared to ACI 440 design guide equations, and capacity prediction techniques are proposed for limit states associated with flexural and flexural-shear under the combined loading. It was found that the ACI 440 equations accurately predicted the flexural and flexural-shear capacities under combined loads provided that eccentricity due to the combined loading was accounted for in the calculations.

This paper describes the use of FRP materials as reinforcements and formwork for a concrete highway bridge deck. It describes the construction process and provides a cost analysis of the project. A continuing research program at the University of Wisconsin–Madison is developing concepts for bridge decks reinforced with fiber reinforced polymers (FRP). This project involved the implementation of one of these concepts in a major highway bridge. Three forms of FRP reinforcing were combined to reinforce the concrete deck: FRP stay-in-place (SIP) forms, deformed FRP reinforcing bars (rebars), and a special prefabricated pultruded FRP reinforcing grid. The research project, supported by the Innovative Bridge Research and Construction Program (IBRC) in the United States, resulted in the construction of a two-span highway overpass on US Highway 151 in Wisconsin. Based on the analysis of the short-term material and labor costs it appears that given the savings in construction time and their potential long-term durability and maintenance benefits, FRP reinforcements for bridge decks may be cost-effective, notwithstanding their currently high initial costs. Optimization of FRP stay-in-place formwork is recommended to decrease the cost of the FRP reinforcing system in the future.

A proposed model specification for FRP composite materials for use in civil engineering structural systems is described in this article. The model specification provides a classification systems for FRP materials, describes admissible constituent materials and limits on selected constituent volumes, describes tests for specified mechanical and physical properties, specifies limiting values of selected properties in the as-received condition and in a saturated state, and provides a protocol for predicting long-term property values subjected to accelerated aging based on the Arrhenius model. The model specification is included as an appendix to the article.

Local buckling of pultruded fibre-reinforced plastic beams is discussed. The paper focuses on three issues related to the prediction of buckling loads both from experimental data and from analytical and numerical approaches, viz . nonlinearity, anisotropy and inhomogeneity. Experimental data obtained from full-scale buckling tests are reviewed and a method proposed for estimating the buckling stress in pultruded beams. Analytical studies based on classical orthotropic plate buckling theory are used to determine the edge restraint coefficient for pultruded beams and also to show the influence of the in-plane material properties on the buckling loads. Numerical studies using the finite element method in which inhomogeneous material properties in the beam cross-section are considered are used to give predictions of buckling loads of the beams. Although the paper focuses on local buckling of pultruded beams, it raises issues which are relevant to the analysis of pultruded material structures of all types.