Journal of Materials in Civil Engineering

This paper presents a series of experiments carried out to determine the characteristics of a pultruded fiber-reinforced polymer (FRP) sheet pile profile for waterfront retaining wall applications. The profile’s flexural and shear stiffness were determined through a multiple-span test method, and the moment resistance was obtained by simulating the earth pressures using a uniformly distributed load. It was found that the load-carrying capacity was dominated by the buckling of the compressive flange and web. Water absorption tests were performed to assess the maximum percent absorption and the corresponding mechanical property change; a saturated pultruded FRP was shown to decrease tensile strength substantially, but this did not cause significant change in the longitudinal modulus of elasticity. Pultruded FRP exhibited excellent resistance to freeze–thaw cycling. The results of the creep tests predict that, over $30\text{years}$ , the deflection creep of the sheet pile profile will exceed 70% of its static deflection.

The paper presents the results of an experimental investigation conducted on clay bricks and different types of restoration products commonly available on the European market, specifically a tixotropic mix for production of mortars and structural plasters, two cement-free binders for dehumidifying mortars, a cement-free grout to be used as filler for voids and cavities in masonry structures, a cement-free dehumidifying mortar for the restoration of damp stone, brick and tuff masonry, and a one-component mortar for plaster repair. Prism-shaped specimens were produced using single materials and coupled materials. They were subjected to static compressive tests for the determination of their mechanical properties and cyclic compressive tests for the analysis of their fatigue behavior; the final aim is to develop an experimental procedure for assessing the effectiveness of strengthening materials. A parameter, $\alpha$ , was defined based on the results of the static compressive tests. It was used for the characterization of the long-term interaction between parent material and restoration mortar. Finally, a simple procedure for selecting an appropriate repair mortar is suggested based on such a parameter.

This paper examines the effectiveness of a high and an ultrahigh modulus carbon-fiber-reinforced polymer (CFRP) composite prepreg, both of which have been specifically developed for the civil engineering industry. A film adhesive, compatible with the matrix material of the CFRP composite, has been introduced. The bonding characteristics of this film adhesive have been compared with those of a standard two-part adhesive—widely used in the construction industry—with those of a two-part adhesive—frequently used for high-grade bonding applications in the aerospace industry. The results have shown that when bonding carbon fiber composites to steel, the film adhesive has more favorable characteristics compared to those of the standard civil engineering adhesive, though the high-grade, and higher-cost, aerospace adhesive has superior bonding qualities. It has also been demonstrated that a good understanding of the full load-deformation response of relevant joints, including load-strain and load-extension characteristics, as well as failure mode characterization, is essential.

This work is part of a wide study related to the structural behavior of concretes prepared by substituting natural aggregates with recycled aggregates from building demolition. In this work, recycled aggregates coming from an industrial crushing plant in which rubble are suitably treated were employed in substitution of ordinary aggregates. In order to evaluate the real-scale behavior of reinforced recycled-aggregate concrete, several beam-column joints were manufactured, then cured in open air at a temperature of approximately $20°\mathrm{C}$ in order to simulate the real conditions of the building site. Subsequently, they were submitted to low-cycle loading, characterized by a load history containing few cycles but having a large range of bond reversal stresses in order to simulate real structures subjected to earthquake or high winds. In this way, the ductility of joints, made of either ordinary or recycled-aggregate reinforced concrete, could be investigated and compared. The results gave experimental evidence of the suitability of recycled-aggregate concrete for structural use, although some measures in the structural design of the joint should be taken.

This paper presents and discusses the results of an experimental investigation on the use of composite materials for controlling the type of plastic collapse mechanism of existing reinforced concrete structures. The research has been carried out on a full-scale structure obtained starting from an existing building, which was designed and constructed at the end of 1970s. Competent authority has destined demolition of this building, which is now the subject/object of a wider experimental investigation, also briefly described in the paper. The structure has been first tested “as-is,” thus providing the control response of the original behavior. Then, it has been repaired and strengthened by means of carbon-fiber-reinforced polymers (CFRP), externally bonded in such a way to change the plastic collapse mechanism from a column-sway to a beam-sway type. Finally, the structure has been tested again in order to assess the effectiveness of the designed seismic upgrading system.

In order to improve the load bearing behavior of concrete structures which are subject to bending and tensile stresses, a steel reinforcement is, in general, applied. For reasons of corrosion protection, the steel reinforcement requires a concrete cover with a thickness of several centimeters. The demand for corrosion-resistant thin-walled parts is a motivation for the application of alternative reinforcement materials. Within the scope of the Collaborative Research Centre “SFB 532” the application of textiles made of polymer, carbon, and alkali-resistant (AR) glass filaments in a fine concrete matrix are examined. The long term aim is to reach the filament strength of the immersed textiles as thoroughly as possible. As a consequence of textile manufacturing processes and of bad bond properties, the utilization of AR glass textiles is approximately 30% compared to the material strength. In this paper the possibility of improving the load bearing behavior of textile-reinforced concrete structures through the saturation of textiles and the modification of concrete with liquid polymers is discussed. The increase of the internal bond between the filaments doubled the maximum component load-carrying capacity.

The writers are investigating the use of steel fibers, recovered from used tires (RSF), as concrete reinforcement, aiming at the development of design recommendations. This paper presents part of this research and examines initially an existing design guideline, developed by RILEM for steel fiber-reinforced concrete (SFRC), in order to assess the suitability of the guideline for the flexural design of concrete reinforced with RSF (RSFRC). This examination indicates that, although the RILEM guideline is in general suitable for the flexural design of RSFRC, there are some fundamental issues related to the evaluation of the tensile stress–strain behavior of SFRC that affect the accuracy of the guideline. Thus, based on this conclusion, a new approach is outlined for the evaluation of the tensile stress–strain behavior of SFRC and models are derived for different types of RSF and industrially produced fibers. These models are applied to the flexural design of concrete reinforced with RSF (RSFRC) and results are compared with those obtained by using the RILEM tensile stress–strain models. It is concluded that the model proposed in this study is more conservative and accurate than the RILEM models. Recommendations are also made on values of tensile strain to be used as the ultimate limit state, when predicting the resistance capacity of SFRC and RSFRC.

The objective of the research was the evaluation of moisture effect on deformability of vinylester binder carbon-fiber- reinforced plastic (CFRP) rebars. Moisture sorption was investigated at different humid conditions. Maximal moisture content of the binder was about 1.86% by weight and for rebars 0.5%. For the CFRP rebars it was estimated that the degree of anisotropy of diffusion coefficient tensor is approximately 40. The elastic moduli of the materials were determined in stress–strain tests and compared with dynamic elastic and shear moduli. The moduli dropped about 10% for maximally moistened materials. The long-term deformability of the composite rebars and binder were examined in tensile creep tests. The principle of moisture–time equivalence was used for creep description of moistened specimen. Creep strain for the wet resin is approximately 5 times larger then for the dry one. Creep forecast was made for a period about $40\text{years}$ .

Brick was proved to be one of the main building materials in the region of today’s Serbia, especially in the time of late antiquity and in the following medieval time. Hence, the idea was born to make a comparison between the main characteristics of late antique and medieval bricks and brickworks from this region that could confirm the continuity and variety of its use. A question of evolution of the use of bricks was partly based on comparison of their estimated properties and also on comparison of applied building techniques and known characteristics of brick production. It has been confirmed that although it is possible to discuss and confirm the continuity in the use of bricks and adequate building techniques, up-to-date research based on quantitative analysis of historical bricks do not offer enough comparable data regarding their quality. Therefore a new field of possible qualitative research is needed in the future.

This paper presents work to characterize the Unistrut steel connection method for M10 blind fixings using pultruded fiber- reinforced polymer (PFRP) profiles of channel section. Both the standard nut and a smooth nut (standard without the serrations), have been used in the series of tests to determine the degree of shear connection via load-slip behavior, under various applied bolt torques, and pure shear loading. It is shown that the standard nut provides adequate connection shear strength and stiffness, but with severe PFRP material damage that might be detrimental to the connection’s structural performance over $30\text{years}$ or more. The smooth connection is shown to significantly reduce PFRP damage. However, this advantage is linked to a 35% reduction in the connection’s shear resistance, making it less suitable for the development of an economic connection. Preliminary hot/wet aging and creep tests are used to estimate the reduction in strength and stiffness with time. The test results are used to establish four Unistrut connection design parameters that are required for the development of lightweight modular systems of PFRP.

Until recently, it was not possible to make structural concrete using expanded glass aggregate. This was because of the relatively low strength of the expanded glass aggregate, and also because the lightweight aggregates had a high water absorption that can make concrete placing difficult. Expanded glass aggregate with relatively high crushing resistance and low water absorption is now available from a manufacturing plant in Hungary. The new aggregate is similar to conventional lightweight aggregates, but the ratio of density of concrete to compressive strength is much more favorable to making structural concrete. This paper summarizes the results of experiments on the mechanical properties of concrete made of this new expanded glass aggregate.

Fiber-reinforced composites based on epoxy resins are used in the restoration of historical buildings, for example, in the restoration of the Basilica di S. Francesco (Assisi, Italy). In this study, the epoxy resin that served as a matrix in the composite was analyzed, focusing attention on the factors that could affect its durability in service. The curing process of the epoxy resin was monitored. Thermal, chemical, and mechanical properties were measured on samples exposed, after curing, to levels of humidity, temperature, and water above the ordinary values. The properties of the cured resin were calculated before and after the treatments. The thermal treatments led to an increase in glass-transition $\left(T_g\right)$ temperature and a strengthening of the system; the exposition to moisture or water yields a reduction in $T_g$ , while it does not affect considerably the mechanical properties of the resin; the effects of thermohygrometric treatments are more complex.

Fiber reinforced polymer (FRP) sheets have been increasingly used as externally bonded reinforcements in the rehabilitation of concrete structures. The efficacy of the FRP bonding technology highly depends on the bond integrity between the FRP sheets and the concrete. The bond performance may directly influence the cracking of the concrete, whereas the presence of concrete cracks would impair the bond between the FRP sheets and the concrete. This paper aims to clarify the effect of interface bond properties on the performance of FRP-strengthened reinforced concrete (RC) beams in terms of concrete cracking, interface stress transfer, and failure mechanisms using nonlinear fracture mechanics based finite element analyses. To represent the typical crack patterns and capture the local interaction between FRP debonding and concrete cracking, a specially designed structural model with uniformly distributed cracking is used within the frame of the discrete crack approach. A detailed parametric study is performed to investigate the effects of interface bond properties in terms of stiffness, strength, fracture energy (or toughness), and bond curve shape. It is concluded that bond fracture energy (or toughness) is the main parameter influencing the structural strength and ductility. This study may serve as a valuable reference for optimization of the FRP-concrete bond interface in practical applications.

There is a pressing need for development and implementation of advanced materials and methods for rehabilitation of infrastructure worldwide. To this end, externally bonded fiber-reinforced polymer or plastic (FRP) composites to concrete for repair and strengthening has been proven to be an effective technology, but uncertainty remains with durability and long-term performance of the interface bond, requiring developments for effective testing and analysis methods. This paper describes the favorable attributes and implementation of a new experimental fracture approach known as the single contoured cantilever beam (SCCB) specimen to evaluate fracture energy of the FRP–concrete interface. This study describes the design and fabrication of the SCCB specimen; calibration tests to obtain constant compliance rate change and avoid measurements of crack lengths; and application to fracture tests under Mode-I loading to obtain interface fracture energies for glass fibers bonded to both normal and high-performance concretes. A total of eight specimens for each concrete type were initially tested at time zero, followed by a total of 18 specimens, nine for each concrete type, after being conditioned at $28°\mathrm{C}$ and 50% relative humidity for 25, 50, and $75\text{days}$ , respectively. The results showed increase in fracture energy with time for the conditioned specimens relative to those tested at time zero, due mainly to continued strength gains of both concrete and bonding resin. The significance of this study is the potential practical application of the SCCB specimen for durability investigations of FRP–concrete interfaces, as will be reported in the future, using changes in fracture toughness as a measure of degradation and leading to development of design guidelines.