Effects of Epoxy-Coating on the Bond of Reinforcing Steel to Concrete

The effects of deformation pattern! bar size, concrete cover, casting position, concrete slump 1 consolidation, transverse reinforcement, and concrete strength on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests include beam-end and splice specimens containing No. 5, No. 6, No. 8, and No. 11 bars. A preliminary investigation of the behavior of epoxy-coated hooks is also described. Epoxy coatings reduce bond strength. In general, this reduction increases with bar size and changes with deformation pattern: bars with a relatively large rib-bearing area are affected less by the coating than bars with a smaller bearing area. The bond strength of both uncoated and coated bars increases as concrete cover increases. The bottom to top-cast bar strength ratio, B/T, increases for uncoated bars and decreases for coated bars as concrete slump increases. Transverse steel increases bond strength; coated confined bars had virtually the same bond strength as uncoated unconfined bars. Design recommendations are made. Analytical studies are conducted on a statical model, consisting of two rigid bodies (steel and concrete) in contact, and a finite element model, representing onehalf of a beam-end specimen. Statical model analyses indicate that 0.35 and 0.10 can be adopted as representative coefficient~ of friction for uncoated and coated bars, respectively. Finite element analyses indicate an increase in bond force will occur with an increase in cover, lead length, or bar size

Bond of Epoxy-Coated Reinforcement Concrete: Cover, Casting Position, Slump, and Consolidation

The effects of concrete cover, casting position, concrete slump, and degree of consolidation on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests include beam-end specimens containing No. 5, No. 6, No. 8, and No. 11 bars. Bottom-cast and top-cast bars with 1, 2, or 3 bar diameters of cover are evaluated. Concrete slump ranges from 21/4 to 8 in. Some specimens containing high slump concrete are not vibrated. The results of the study are used to develop improved development length modification factors for epoxy-coated bars. Epoxy coatings significantly reduce bond strength. However, the extent of the reduction is less than used to select the development length modification factors in the 1989 ACI Building Code and the 1989 AASHTO Bridge Specifications for bars with cover < 3 bar diameters or a clear spacing < 6 bar diameters. The development length modification factor can be reduced from 1.5 to 1.35 for these bars. The relative bond strength of epoxy-coated reinforcement increases as cover increases. In most cases, the bond strength of coated bars exceeds the bond strength of uncoated bars that have one bar diameter less cover. As a result, the current provisions of ACI 318-89 are realistic as they are applied to epoxy-coated bars with a cover :2: 3 bar diameters and a clear spacing :2: 6 bar diameters. However, the provisions of the 1989 AASHTO Bridge Specifications are somewhat unconservative for these bars and should be modified. The ratio of bond strength of bottom-cast bars to the bond strength of top-cast bars, B/T, is about the same for coated and uncoated bars cast in low slump concrete. The ratio increases significantly for uncoated bars and decreases slightly for coated bars as slump increases. The results indicate that the upper limit on the product of the epoxy-coating factor and the top-bar factor can be reduced from 1.7 to 1.5. A lack of vibration has a negative effect on the bond strength of both coated and uncoated reinforcement in high slump concrete. This is the fifth in a series of reports describing research at the University of Kansas on epoxy-coated reinforcement The research is aimed at gaining a better understanding of the bond of epoxy-coated reinforcement to concrete and developing design procedures that accurately reflect the changes in bond strength caused by epoxy coating

Bond of Epoxy-Coated Reinforcement: Bar Parameters

The effects of coating thickness, deformation pattern, and bar size on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests include beam-end and splice specimens containing No.5, 6, 8, and 11 bars with average coating thicknesses ranging from 3 to 17 mils (0.08 to 0.43 mm). Three deformation patterns are evaluated. All bars are bottom~cast. Beam-end specimens have covers of two bar diameters, while splice specimens have covers that depend on bar size and are less than 2 bar diameters. The results are compared with the splice tests that were used to establish the epoxy-coated bar provisions in the 1989 A CI Building Code and 1989 AASHTO Bridge Specifications. Epoxy coatings are found to reduce bond strength significantly, but the extent of the reduction is less than that used to select the development length modification factors in the ACI Building Code and AASHTO Bridge Specifications. Coating thickness has little effect on the amount of bond strength reduction for No. 6 bars and larger. However, the thicker the coating, the greater the reduction in bond strength for No. 5 bars. In general, the reduction in bond strength caused by an epoxy coating increases with bar size. The magnitude of the reduction depends on the deformation pattern; bars with relatively larger ribbearing areas with respect to the bar cross section are affected less by the coating than bars with smaller bearing areas. This is the first in a series of papers concerning bond of epoxy-coated reinforcement. Subsequent papers will address the effects of concrete cover, bar position, concrete strength, and transverse reinforcement

Bond of Epoxy-Coated Reinforcement to Concrete: Bar Parameters

The effects of coating thickness, deformation pattern, and bar size on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests include beam-end and splice specimens containing No. 5, No. 6, No. 8, and No. 11 bars with average coating thicknesses ranging from 3 to 17 mils. Three deformation patterns are evaluated. All bars are bottom-cast. Beam-end specimens have covers of 2 bar diameters, while splice specimens have covers that depend on bar size and are less than 2 bar diameters. The results are compared with the splice tests that were used to establish the epoxy-coated bar provisions in the 1989 ACI Building Code and 1989 AASHTO Bridge Specifications. Epoxy coatings are found to significantly reduce bond strength, but the extent of the reduction is less than used to select the development length modification factors in the ACI Building Code and AASHTO Bridge Specifications. Coating thickness has little effect on the amount of bond strength reduction for No. 6 bars and larger. However, the thicker the coating, the greater the reduction in bond strength for No. 5 bars and smaller. In general, the reduction in bond strength caused by an epoxy coating increases with bar size. The magnitude of the reduction depends on the deformation pattern: bars with relatively larger ribbearing areas are affected less by the coating than bars with smaller bearing areas. This is the first in a series of reports. Subsequent reports will address the effects of concrete cover, bar position, concrete strength, and transverse reinforcement

Bond of Epoxy-Coated Reinforcement: Cover, Casting Position, Slump, and Consolidation

The effects of concrete cover, casting position, concrete slump, and degree of consolidation on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests include beam-end specimens containing No. 5, No. 6, No. 8 and No. 11 (16, 19, 25, and 46 mm) bars. Bottom-cast and top-cast bars with 1, 2, or 3 bar diameters of cover are evaluated. Concrete slump ranges from 2 1/4 to 8 in. (55 to 205 mm). some specimens containing high slump concrete are not vibrated. The results of the study are used to develop improved development length modification facts for epoxy-coated bars. Epoxy coatings significantly reduce bond strength. However, the extent of the reduction is less than used to select the development length modification factors in the 1989 ACI Building Code and the 1989 AASHTO Bridge Specifications for bars with cover 3 db and a clear space > 5 db (ACI) or a center-to-center spacing > 6 in. (AASHTO). However, the modification factor of 1.15 in the 1989 AASHTO Bridge Specifications is slightly unconservative for these bars and should be modified. The ratio of the bond strength of bottom-cast bars to the bond strength of top-cast bars, B/T, is about the same for coated and uncoated bars and decreases slightly for coated bars as slump increases. As a result, the upper limit on the product of the epoxy-coating factor and the top-bar factor can be reduced from 1.7 to 1.5. A lack of vibration has a negative effect on the bond strength of both coated and uncoated reinforcement in high slump concrete. This is the third in a series of papers describing research at the University of Kansas on epoxy-coated reinforcement. The research is aimed at gaining a better understanding of the bond of epoxy-coated reinforcement to concrete and developing design procedures that accurately reflect the changes in bond strength caused by epoxy coating