Catherine G. Papanicolaou

Concrete Confinement with Textile-Reinforced Mortar Jackets

The application of textile-reinforced mortars (TRMs) as a means of increasing the axial capacity of concrete through confinement is investigated experimentally in this study. TRM may be thought of as an alternative to fiber-reinforced polymers (FRPs), addressing many of the problems associated with application of the latter without compromising performance by a significant degree. Based on the response of confined cylinders and short rectangular columns, it is concluded that textile-mortar jacketing provides a substantial gain in compressive strength and deformability; this gain is higher as the number of confining layers increases and depends on the tensile strength of the mortar. Compared with their resin-impregnated counterparts, mortar-impregnated textiles may result in reduced effectiveness. This reduction was more pronounced in cylindrical specimens but rather insignificant in rectangular ones. Favorable confinement characteristics on rectangular columns were also obtained by using helically applied unbonded strips with end anchorages-an interesting concept that deserves further investigation. Modeling of concrete confined with jackets other than resin-impregnated ones is presented by the authors as a rather straightforward procedure through the proper introduction of experimentally derived jacket effectiveness coefficients. From the results obtained in this study, it is believed that TRM jacketing is an extremely promising solution for the confinement of reinforced concrete.

Textile-Reinforced Mortar versus Fiber-Reinforced Polymer Confinement in Reinforced Concrete Columns

Poorly detailed reinforced concrete (RC) columns have limited deformation capacity under seismic loads due to buckling of the longitudinal bars. This study experimentally investigates the effectiveness of textile-reinforced mortar (TRM) jackets as a means of confining these columns. The effectiveness of TRM is evaluated by comparing TRM jackets with fiber-reinforced polymer (FRP) jackets of equal stiffness and strength. Tests were carried out both on short prisms under concentric compression and on nearly full-scale, nonseismically detailed, RC columns subjected to cyclic uniaxial flexure under constant axial load. The compression tests on 15 RC prisms show that TRM jackets provide a substantial gain in compressive strength and deformation capacity by delaying buckling of the longitudinal bars. This gain increases with the volumetric ratio of the jacket. Compared with their FRP counterparts, TRM jackets used in this study are slightly less effective in terms of increasing strength and deformation capacity by approximately 10%. Tests on nearly full-scale columns under cyclic uniaxial flexure show that TRM jacketing is very effective (and equal to the FRP jacketing) as a means of increasing the cyclic deformation capacity and the energy dissipation of RC columns with poor detailing by delaying bar buckling.

Innovative Applications of Textile-Based Composites in Strengthening and Seismic Retrofitting as Well as in the Prefabrication of New Structures

The authors review investigations which have provided fundamental knowledge on the use of a new generation of composite materials, namely textile-reinforced mortar (TRM) and textile-reinforced concrete (TRC), as strengthening and seismic retrofitting materials of existing concrete and masonry structures, as well as in the prefabrication of new reinforced concrete (RC) structural elements. In the first part of the paper, TRM are investigated as a means to provide confinement in concrete, to increase the deformation capacity of old-type RC columns subjected to simulated seismic loading, to increase the shear and flexural resistance of RC members and to increase the out-of-plane or in-plane strength of unreinforced masonry walls. In all cases, the effectiveness of TRM systems is quantified through comparison with equivalent fiber-reinforced polymer (FRP) ones. It is concluded that TRM jacketing is an extremely promising new technique, which is expected to enjoy the attention of the research community and to be employed in numerous applications in the near future. In the second part, the paper gives a brief overview of the application of TRC in the field of advanced prefabricated systems, with a focus on stay-in-place (or permanent) formwork elements in hybrid construction projects. Along these lines, the paper provides experimental results on the behavior of TRC/RC composite beams and one-way slabs under flexure. The results indicate that the use of prefabricated TRC stay-in-place formwork elements is a promising solution for achieving reduction of the construction time, minimization of labor cost and defect-free finishing of external surfaces.

Effect of High Temperatures on the TRM-to-Masonry Bond

This work is devoted to the experimental assessment of the Textile Reinforced Mortar (TRM)-to-masonry residual bond characteristics as a function of temperature. For this purpose, shear bond tests on single-lap/single-prism specimens were conducted after their exposure at different temperature levels, namely at 100°C, 200°C and 300°C. Specimens consisted of a strip of cementitious mortar reinforced with an uncoated alkali-resistant (AR) glass fiber textile unilaterally bonded on a fired clay brick masonry wallette (prism). For each heating event, a sharp temperature rise rate was opted for the achievement of the target temperature at which the specimens remained for one hour. Reference specimens were also tested at ambient conditions (20°C). Tests were carried out by varying both bond lengths and exposing temperatures. Two specimens were tested for each combination of bond length and exposing temperature. Material characterization tests were also carried out at each temperature level including ambient. The experimental results provide valuable insight on the degradation of the TRM-to-masonry bond capacity following a heating event and on the related failure modes.

Comparison of Double-Lap/Double-Prism and Single-Lap/Single-Prism Shear Tests for the TRM-to-Masonry Bond Assessment

Τhe efficient use of Textile Reinforced Mortar (TRM) overlays as a strengthening means of structurally deficient built facilities depends on the bond between the externally bonded grids and the existing substrate. Different types of experimental set ups have been used for the investigation of the bond mechanism of TRM strips externally bonded on masonry (and other) substrates including double-lap/double-prism, single-lap/single-prism and double-lap/single-prism configurations. This paper presents the results of an experimental program aiming to assess the bond characteristics of interfaces comprising glass fiber textile reinforced cementitious mortars applied as overlays on solid clay brick unreinforced masonry wall prisms. For this purpose, both double-lap/double-prism and single-lap/single-prism shear tests were employed, providing the basis of a comparison between the two test set ups. Double-lap/double-prism specimens are heavier, more labor-intensive and of higher handling care demand than single-lap/single-prism ones but are thought to better simulate actual shear bond phenomena. For the specific interfaces dealt with herein, a common failure mode (textile slippage) was observed for both test set-ups. The results obtained demonstrate that maximum load values derived from both test set-ups are comparable. Nevertheless, this does not apply to relative displacement values which bear a strong dependence on the different load introduction means and (where applicable) on the assumptions made for their computation.