Journal of Composites for Construction

Although fiber-reinforced polymer (FRP) materials are considered noncorrosive, the FRP bar surface resin has been shown to deteriorate when exposed to aggressive environments and this can result in a significant loss of bond strength with the surrounding concrete. To study the durability of the FRP bar-to-concrete bond, numerous investigations utilizing the FRP bar pull-out test arrangement have been conducted. These studies have, however, largely been considered in isolation without any systematic attempt to critically analyze the ever increasing pool of results based on variable exposure regimes and differing geometric and mechanical properties. To address this limitation, and to quantify the durability of the FRP bar-to-concrete bond, this paper presents an experimental database comprising 1,244 individual test results from 35 unique studies which were critically analyzed in terms of bond performance. The analysis highlighted the large scatter that exists for experimental results between studies and attempted to explain this scatter through discussion of the impact of exposure to material properties and the importance of sound experimental design.

A comprehensive study on the fatigue behavior of stirrup free reactive powder concrete (RPC) beams prestressed with carbon fiber-reinforced polymer (CFRP) tendons is presented in this paper. A total of six specimens were tested, and the effects of the shear span/depth ratio, load amplitude, and steel fiber content on the fatigue behavior of the beams were analyzed. The test results showed that the fatigue damage evolution of the RPC beams exhibiting flexural failure experienced two stages: a rapid development stage and a stable stage. In contrast, the fatigue damage of the RPC beams exhibiting shear failure developed rapidly, and the fatigue life notably decreased. It was recommended based on the test results that shear reinforcement should not be omitted from RPC beams, especially for those with a thin web where diagonal tension shear failure might occur under fatigue loading. Based on the experimental results, a method for predicting the fatigue deflection of RPC beams prestressed with CFRP tendons was proposed, and then a cumulative damage model was developed to evaluate the fatigue damage of RPC beams prestressed with CFRP tendons.

This paper presents an experimental study about the transverse tensile fracture properties of several off-the-shelf pultruded glass fiber-reinforced polymer (GFRP) materials, with different fiber layups and geometries and significant variations of elastic and strength properties. Determining these fracture properties should enable more-accurate advanced numerical simulation of the failure behavior of pultruded GFRP materials and members used in civil engineering applications, namely in the analysis of structural connections or members subjected to concentrated loads (web-crippling phenomenon). For the different GFRP materials, based on compact tension (CT) and wide compact tension (WCT) tests, both the critical energy release rate (G_c) and the cohesive law were determined at the laminate level, applying the following four data reduction methods: standardized analytical expressions, J-integral, Compliance Calibration (CC), and Modified Compliance Calibration (MCC). The CT tests were unsuccessful in reaching a stable propagation stage and provided overestimations of G_c. Conversely, the WCT tests were able to achieve a stable propagation stage and thus provided more-consistent estimates of G_c and cohesive laws. Among the various data reduction methods, a good agreement was found between visually based methods. On the contrary, the MCC method was found to provide significantly lower estimates of G_c when compared with the remainder. Different reasons for this variation are identified and discussed. The sample of GFRP materials presented a significant variation of G_c, which was found to be highly dependent on the fiber architecture: (i) for the material with weaker transverse reinforcement layers, consisting only of continuous filament mats, G_c ranged between 6.6 and 10.7 N/mm; (ii) materials presenting cross-ply layers presented intermediate G_c values, ranging from 13.1 and 21.3 N/mm; and (iii) materials comprising quasi-isotropic layups presented the highest overall G_c estimates, ranging from 19.3 N/mm (similar to cross-ply materials) to above 150 N/mm.

Glass fiber-reinforced polymer (GFRP) bent bars were used as shear reinforcement for precast/prestressed concrete box beams in Ontario, Canada. Differential scanning calorimetry (DSC) tests performed on the bent GFRP bars revealed a curing ratio varying from 88% to 94% and a glass transition temperature ranging from 63°C to 71°C (lower than the limits of 95% and 100°C, respectively, specified in the CSA S807 FRP-material specifications). This study investigated the consequence of implementing partially cured GFRP bars in constructing steam-cured precast-prestressed concrete bridge box beams. The physical and mechanical properties of the partially cured GFRP bars were evaluated and compared with the properties of GFRP bars postheated at 80°C for 4 h. The durability performance was also assessed by immersing the GFRP bars in alkaline solution at 70°C for 2,200 and 4,300 h. Moreover, scanning electron microscopy (SEM) observations were performed to assess the microstructure of the GFRP bars. The results show that the glass transition temperature, T_g, and interlaminar shear strength were the criteria most affected by the degree of curing. Exposing the bars to steam treatment (as is the case for precast concrete box beams) increased the cure ratio and, consequently, the T_g and interlaminar shear strength of the bars. This was verified by simulating the concrete mix design used in the precast concrete process [including the same water-to-cement ratio (w/c) and aggregate type] and exposing the concrete to the same steam-treatment conditions. The steam treatment promoted the postpolymerization of the GFRP bars, leading to a cure ratio of 98%, which exceeds the limit specified in CSA S807 and enhanced bar properties. The results of this study have been instrumental in developing the new edition of CSA S807 standard incorporating evaluation of the physical, durability, and mechanical properties of bent FRP bars. Moreover, the reported study constitutes a valuable contribution to the state-of-the-practice.

The external bonding of fiber-reinforced polymer (FRP) composite plates and sheets to the tensile surface of reinforced concrete structural elements is a viable retrofitting technique. The performance of such strengthened members is strongly influenced by the capacity of the FRP-to-concrete bonded interface. However, over time, harsh environmental conditions can compromise the integrity of the interface. This paper reports an experimental investigation on 135 single lap shear tests that sought to quantify the change in bond strength and local bond stress–slip properties due to thermal cycling loading, as well as wet–dry cycling in both potable water and saltwater conditions. Two types of FRP strengthening materials are tested, namely carbon FRP (CFRP) plates formed by pultrusion and wet lay-up, in addition to three types of epoxy adhesives with varying degrees of viscosity. The results show that the failure modes of specimens under all the considered environmental conditions transitioned from cohesive failure to interfacial failure, regardless of the conditioning regime. For cyclic thermal conditioning, the transition from cohesive to interfacial failure is due to the reduction of the adhesive bonding strength, whereas for cyclic wet–dry conditioning the change in failure mode is likely due to the combination of lowered adhesive bonding strength and enhanced concrete strength arising from post-curing in the presence of moisture. Finally, a bond stress versus slip model that incorporates degradation is used to analyze the changes in the key bond parameters that define the trilinear relationship adopted in a partial-interaction modelling approach.

Knee-joints are a common element in concrete structures, which may be problematic when reinforced with glass fiber-reinforced polymer (GFRP) bars. GFRP bends are significantly weaker than the straight portions due to transverse loading on fibers as well as nonstandardized manufacturing processes. The behavior of GFRP-reinforced knee-joints has not been previously studied. In the presented research, eight full-scale GFRP-reinforced concrete corner joint specimens were constructed and tested under monotonic closing loads. The specimens consist of a beam and column, which are connected and terminate at the joint. The experimental program was designed to study the effect of reinforcement ratio, confinement reinforcement, and corner geometry on the behavior of the joint. Increasing reinforcement ratio of bent bars through the joint altered the failure mode from bar rupture to diagonal strut failure; however, this had minimal effect on ultimate strength efficiency. The addition of confinement reinforcement in the joint resulted in a significant increase in ultimate strength efficiency and maximum deflection. Joints with altered geometry by including an interior chamfer performed better than the regular joint type; failure mode was altered to a nonbrittle failure and a marginal increase in strength efficiency was observed.

This study investigated the monotonic and cyclic axial compressive properties of predamaged concrete retrofitted using externally bonded basalt fiber-reinforced polymer (BFRP) sheets. Plain concrete cylindrical specimens were manufactured and predamaged under three axial compressive loading levels corresponding to peak strength, 10%, and 20% strength degradation after the peak strength of the plain concrete. Specimens for undamaged series were retrofitted with 2-, 4-, and 6-layer BFRP sheets, while the predamaged specimens were retrofitted with 2- and 4-layer BFRP and all the specimens for the cyclic loading series were retrofitted with 4-layer BFRP. Then these BFRP-retrofitted predamaged cylinders were retested under monotonic and cyclic compressive loadings to assess their compressive behavior. For BFRP-retrofitted specimens under monotonic compressive loading, the compressive strength and deformation capacities of the predamaged concrete cylinders were improved remarkably after the retrofitting. However, the initial elastic modulus and compressive strength of the BFRP-retrofitted predamaged cylinders decreased by 38%–55% and 7%–15%, respectively, compared to the retrofitted undamaged cylinders. Under cyclic compressive loading, the energy dissipation capacity of the BFRP-retrofitted concrete decreased gradually with an increase of the predamage level. Based on the test results and existing experimental data collected from the literature, peak strength, ultimate strain, and monotonic stress–strain relationship were newly defined for BFRP-retrofitted predamaged concrete considering the influence of the predamage level. Furthermore, based on the existing cyclic stress–strain model of FRP-retrofitted concrete, an equation for residual strain was introduced, and a modified cyclic compressive stress–strain model was established for BFRP-retrofitted damaged concrete.

This paper presents the results of an experimental work aimed at determining the effect of the width of a steel fiber-reinforced polymer (FRP) composite on the load-carrying capacity of a composite–concrete interface. Single-lap shear tests were performed in which the main parameter was the width of the composite strip. Steel FRP strips were applied to three different faces of each concrete prism and it was observed that the load-carrying capacity is strongly related to the face to which the composite is applied. In addition, a few tests were carried out at a displacement rate, used to control the test, equal to ten times the rate employed for the majority of the specimens. A great influence of the rate on the load-carrying capacity was observed, although the number of tests was limited. The authors argue that most of the width effect formulas available in the literature use data from different sources without taking into account the face of application and the rate. A new width effect formula is proposed, which takes into account the most recent articles on this subject.

Flange local buckling (FLB) of pultruded glass fiber-reinforced polymer (pGFRP) I-sections subject to flexure is investigated in this study. An experimental program, consisting of 62 four-point bending tests that had various constant moment region and shear span lengths, was conducted. It was shown that critical FLB moment capacities increased as the flange slenderness ratios decreased and FLB was the dominant buckling mode for sections that had large flange slenderness ratios. Using classic plate theory and the energy method, an analytical study was carried out and an explicit equation for predicting the critical FLB moments of pGFRP I-sections was proposed. The elastic rotational restraint at the flange–web junction was studied and a modified spring constant, k, was proposed. In addition, the buckling stiffening effect of the test geometry was described through a numerical study. The proposed predictive FLB equation was validated using experimental results from this study and others and was compared with two commonly accepted design guides, Kollár's numeric solution, and finite strip method (FSM) solutions. A good agreement was found between the proposed equation and experimental results and FSM. The proposed equation showed improved predictive accuracy over existing design guides and numeric solutions.

The effect of seawater used as mixing water in concrete on the long-term properties of glass fiber–reinforced polymer (GFRP) bars is the focus of this work. The durability of GFRP bars embedded in seawater-mixed concrete was studied in terms of residual mechanical properties (i.e., tensile strength, horizontal and transverse shear strength, and GFRP–concrete bond strength) after immersion in seawater at 60°C for a period of 24 months. Benchmark specimens were also cast using conventional concrete. Results showed comparable performance in tensile and shear properties between the two sets of bars with some degradation of the mechanical properties in both cases. However, bond strength showed some differences between the two sets of bars. SEM was used to identify degradation mechanisms. Areas with large concentrations of voids near the bar edge, formed during manufacturing, may provide a pathway for moisture and alkalis, which could lead to the fiber disintegration and debonding between fibers and the resin. Over time, a greater number of fibers are affected, which leads to the formation of significant cracking near the edge. Results were qualitatively similar for embedded bars in seawater-mixed and conventional concrete, explaining a similar reduction in tensile properties, horizontal shear strength, and transverse shear strength seen in both sets of bars. However, the bond strength does not significantly decrease in these specimens over time for unclear reasons.

Fiber-reinforced polymer (FRP) materials have been increasingly used for external strengthening of reinforced concrete (RC) infrastructure. However, the focus has been almost exclusively on epoxy-based composites, and other potential options such as polyurethane (PU) have not been fully investigated. This paper characterizes the flexural behavior of concrete strengthened with PU matrix–adhesive laminates using small-scale single lap shear specimens, unreinforced flexural specimens, and large-scale RC girders. Experimental results demonstrate that although the normal and shear strengths of PU-based adhesives are low, PU-strengthened beams show increased strength and deformability, owing to the load redistribution ability within the bond line. It is found that a linear brittle bond–slip model adequately predicts the interfacial shear behavior of the PU adhesive, exhibiting a lower stiffness and comparable cohesive energy to epoxy. Finite element (FE) analysis was performed to validate the effect of the bond–slip model relative to the experimental results.

Using grid-type stirrups as transverse reinforcements in reinforced concrete (RC) columns can not only provide higher confinement of the concrete core but also lead to an improved concrete cover and better protection to longitudinal reinforcements when compared with conventional stirrups. Fiber-reinforced polymer (FRP) grids, which combine the advantages of grid-type stirrups and FRP composites, are viable for use as transverse reinforcement in square-section RC columns in corrosive environments. However, there were few researches addressing RC columns reinforced with FRP grids. To investigate the axial compressive behavior of RC columns transversely reinforced with FRP grids, experimental investigations were conducted on 17 short square-section columns in small scale (180 × 180 × 600 mm³). Columns were transversely reinforced by CFRP/BFRP grids, weld reinforcement grids (WRG), and steel hoops. The results indicate that although FRP grids could provide less confining pressure than WRG, their performance is better than that of conventional hoops. Finally, an analytical model for predicting the stress–strain behavior of concrete core reinforced with grid-type stirrups is proposed considering the arching action of the confined concrete core. The proposed model shows a good agreement with the present test results as well as those from the existing literature.

Short columns undergo larger drift ratios during earthquakes compared to ordinary ones, making them vulnerable structural elements if they are unable to withstand the demanded drift ratio and shear force without significant deterioration. In order to ensure proper structural performance, deficient reinforced concrete (RC) short columns should be effectively retrofitted. Carbon-fiber-reinforced polymer (CFRP) composites can be utilized effectively to provide adequate shear capacity and confinement for RC short columns to have a desirable performance during an earthquake event. In this study, six RC short columns were subjected to constant axial and reversed cyclic lateral loads to compare the three different confinement techniques of full-wrapping (FW), corner strip-batten (CSB), and corner strip-wrap (CSW) in terms of their efficiency. Moreover, the effect of a novel configuration of fiber anchors was investigated in improving the behavior of such short columns. Results indicated that the performance of a typical RC short column improved significantly with the use of the CSB technique, because its ductility and dissipated energy increased by 125% and 800%, respectively. Furthermore, the application of fiber anchors was observed to further improve the overall performance of short columns confined through either the CSB or the FW techniques.

Strengthening of reinforced concrete (RC) columns through lateral confinement with a fiber-reinforced polymer (FRP) jacket has become an increasingly popular technique over the last two decades. To enable the safe and reliable design of such FRP jackets, extensive research has been conducted on the behavior of FRP-confined concrete columns. Most of the existing research, however, has been focused on FRP-confined concrete columns under concentric axial compression, so the current understanding of the behavior of FRP-confined RC columns under eccentric loading is inadequate. This paper presents the results of an experimental study involving 10 FRP-confined circular RC columns with a diameter of 300 mm under eccentric compression. The variables included the FRP jacket thickness, the initial load eccentricity, and the column slenderness. The test results show that FRP confinement is effective in enhancing both the ultimate load and the ductility of circular RC columns under eccentric loading, and the load eccentricity and the column slenderness have important effects on the column behavior. Finally, the design equations in the Chinese national standard and the UK Concrete Society design guidance for the ultimate axial load of eccentrically loaded slender FRP-confined RC columns are evaluated by comparing their predictions with the test results. It is found that the design equations in both the Chinese national standard and the UK design guidance predict the test results well, with the latter providing slightly more conservative predictions.

For conventional reinforced concrete (RC) beams, it is well established that the so-called size effect tends to decrease the shear strength attributed to concrete at failure when the size is increased. This contrasts with strengthened RC beams using externally bonded (EB) fiber-reinforced polymer (FRP) sheets or laminates, where very few studies have been devoted to the size effect. The main objective of this study is to examine the size effect of RC T-beams strengthened in shear with EB carbon FRP (CFRP) L-shaped laminates. The experimental investigation involved six RC T-beam laboratory tests performed on geometrically similar beams of two different sizes. Three series of beams were considered, each consisting of medium- and large-sized beams with a total depth of 406 and 605 mm, respectively, as follows: one series of control (unstrengthened) beams with transverse steel stirrups, and two series strengthened in shear using EB-CFEP L-shaped laminates in U-wrap schemes, with and without an anchorage system. The anchorage system considered in this investigation consists of embedding the laminates into the compression zone (flange). The results clearly revealed the effectiveness of specimens with embedded laminates, which achieved a substantially greater shear resistance gain compared to those with no anchorage. Results also confirmed the presence of a size effect in all series. In addition, they revealed an additional size effect related to the CFRP strengthening system in both strengthened series, particularly in anchored specimens despite the higher shear resistance gain they achieved. For instance, the losses in shear strength at failure in large specimens with respect to medium ones were 24% and 16% in strengthened specimens with and without an anchorage system, respectively. Therefore, the anchorage system amplified the decrease in shear strength at failure as the effective depth (d) of the beams increased.

Reinforced concrete deep beams are common structural elements in bridges and high-rise buildings because of their ability to support higher concentrated loads compared with slender beams. In this study, three simply supported deep beams and three continuous deep beams reinforced with glass fiber-reinforced polymer (GFRP) bars were constructed and tested to failure. The test variable was the shear span-to-depth ratio, which varied between 1.0 and 2.0. Test results are presented in terms of cracking, deflection, strains in concrete and reinforcement, load capacity, and mode of failure. The cracking pattern and measured strains indicated the development of the arch action mechanism in all specimens. Test results indicated that increasing the shear span-to-depth ratio led to a significant decrease in the load-carrying capacity of the beams. Moreover, continuous beams exhibited higher load capacity than did their simply supported counterparts. In addition, a comparison between the experimental and code-predicted load capacity of beams is presented.

Externally bonded reinforcement fiber-reinforced polymer (EBR FRP) laminates have been used around the world for the shear strengthening of reinforced concrete (RC) beams with corroded stirrups. The shear span-to-depth ratio (a_v/d) can significantly influence the behavior of an RC beam shear strengthened with EBR FRP composites and can even determine the shear failure mode of RC beams. Therefore, 18 RC beams were constructed and tested in this study to analyze the effect of the a_v/d ratio on the performance of RC beams with corroded stirrups strengthened in shear with U-wrapped carbon fiber-reinforced polymer (CFRP) strips. The investigated parameters included three stirrup corrosion levels (0%, 5%, and 15%) and different shear span-to-depth ratios (a_v/d = 1.0, 2.0, and 3.0). The test results indicated that the high corrosion level of the stirrups significantly decreased the shear capacity of both the strengthened and unstrengthened beams. The experimental results were compared with those of established models provided in the literature. The design formulation was conservative for both the unstrengthened and strengthened beams with different stirrup corrosion levels.

This paper presents the results of an experimental study into the behavior of rubberized concrete-filled fiber-reinforced polymer tube (CFFT) columns, where the fiber-reinforced polymer (FRP) confining layer is prestressed by using an expansive agent (EA). The study focuses on utilizing the incompressibility property of rubber in improving the strength properties of crumb rubber concrete (CRC). A total of 27 CFFT columns were tested under axial compression and the effect of rubber content, prestress level, confinement amount and curing condition was studied. Different EAs with cement replacement ratios of 0%, 7.5%, and 15% were used to examine the influence of different levels of hoop prestress on the axial compressive behavior. The influence of amount of confinement was examined with specimens prepared with either one or two layers of CFRP. The influence of the curing condition was also examined by preparing half of the one-layer specimens with steel plates confining the specimens in the axial direction during curing. Finally, both flexible and stiff molds were used to examine the influence of mold stiffness on prestress development during curing. The lateral prestress provided by the expansive agent and FRP confinement was used to mitigate the typical strength reduction associated with CRC. The positive effect of this technique is two-fold. First, the pressure produced by the expansive agent compresses the cement paste and rubber particles together, reducing porosity and increasing interaction and interface friction between the rubber particles and cement paste. Second, rubber is generally considered nearly incompressible, with a Poisson's ratio of approximately 0.5, hence as the rubber is compressed in one direction, it expands significantly in the other directions. Using rubber in unconfined and non-prestressed concrete results in strength reduction; however, the combined effects of FRP-confinement and lateral prestress on CRC can lead to significant increases in the columns' axial stiffness and strength. The stresses and strains developed during curing for the expansive mixes were found to be considerably higher in CRC compared with conventional concrete (CC), indicating that an EA is more effective in developing prestress in rubberized concrete. Moreover, the mold stiffness was found to have a noticeable influence on the compressive strength of concrete. Using stiff molds resulted in unrealistic and unsafe strength evaluation and, hence, should be avoided if expansive concrete is used, or the results should be modified to account for the effect of confinement provided by the stiff molds. It was also observed that the confinement effect in CRC was higher compared with that of CC, which is due to the incompressibility of rubber. Finally, applying confinement plates to the ends of the concrete during curing had insignificant impact on the compressive behavior.

Many regions are experiencing freshwater shortages, which is projected to worsen in the coming years. The concrete industry is one of the largest consumers of water worldwide, limiting water available for agriculture and human consumption. Many affected areas have access to ample supplies of seawater, presenting an attractive alternative for concrete if certain issues can be addressed. The use of fiber-reinforced polymer (FRP) reinforcement rather than steel eliminates corrosion concerns associated with the high chloride content of seawater. Six beam anchorage specimens reinforced with spiral glass FRP (GFRP) bars were tested with embedment lengths ranging from 300 to 500 mm and cast using either potable water or artificial seawater. The bond stress, normal stress, and slip distributions along the bars are examined in detail, and a method for calibrating analytical bond–slip formulations is proposed. The results suggest that the short-term structural performance of seawater concrete is similar to that of concrete made with potable water, and that a relatively high friction stress can delay bond failure of spiral GFRP bars after the formation of longitudinal splitting cracks.

While glass fiber-reinforced polymer (GFRP) tubes have emerged as a corrosion-resistant alternative to buried steel pipelines, they are not as well understood or widely used. This study examines the response of ±55° angle-ply filament-wound GFRP pipes to ground deformations in the form of vertical fault offset. Full-scale tests were conducted on 5.65-m-long buried pipes of 141-mm diameter (D) and 4.1-mm wall thickness (t), with internal pressures of 300 and 1,000 kPa, and results were compared with an identical unpressurized pipe from a separate study. A special 7.3 × 1.8 × 1.8-m split-box apparatus able to simulate a vertical fault plane at the midlength of the pipe with up to 120-mm offset was employed. Strain gauges and optical fibers were used to construct lengthwise and circumferential strain profiles. The GFRP pipes withstood a fault offset of 110 mm (0.8D) before failing in the form of pressure loss due to pipe weeping after GFRP matrix cracking. The total length of the pipe subjected to curvature and bending was only 2.85 m (20D) in the vicinity of the fault, a length apparently independent of fault offset and internal pressure. The maximum curvature occurred on the stationary side, about 1.4D–2D from the fault line. This curvature was 43%–70% higher than the peak curvature on the moving side. The internal pressure of 1,000 kPa resulted in 25% and 35% reductions in peak curvatures at the stationary and moving sides, respectively. Upon excavation, tension failure was apparent at the crown (the point at the top of the circular pipe cross section) on the stationary side of the pipe, and compression failure, also at the crown, was observed on the moving side. These locations correspond to the estimated locations of peak curvature.

Design guides for fibre-reinforced polymer-reinforced concrete (FRP-RC) require that the design tensile strength of FRP bars be determined by multiplying the guaranteed tensile strength by an environmental reduction factor (C_E), to account for the long-term effects of environmental exposure. The recommended C_E values in the American Concrete Institute (ACI) design guide are based on a consensus of the opinion of ACI 440 Committee members and believed to be conservative. The ACI design guide notes the expectation that, with continued research, C_E values will become more reflective of observed environmental performance. In this study, C_E values were estimated for a compiled database of glass FRP (GFRP) bars based on short-term results from accelerated aging tests. The C_E values were calculated with a prediction model considering the effects of seasonal temperature fluctuations, service year, and relative humidity (RH) of exposure. The analysis shows that the calculated values of C_E depend to a certain extent on the mean annual temperatures and RH. In all cases, however, the calculated values were higher than those recommended in the ACI design guide. The authors recommend a C_E value of 0.85 for an assumed service life of 75–100 years to be applied to the guaranteed tensile strength as the basis for determining the design tensile strength. This value is recommended for GFRP bars complying with ASTM Standards, whether exposed or unexposed to earth and weather in cold temperatures and climates encountered in most regions of the world.