International Concrete Abstracts Portal

Geopolymer, an inorganic polymer material, has recently gained attention as an eco-friendly alternative to portland cement. Numerous studies have explored the potential of geopolymer as a primary structural material. This study aimed to examine the efficacy of geopolymer composites as repairing and strengthening materials rather than as structural materials. Data from 782 bond strength tests and 164 structural tests were collected and analyzed, including those on beams, beam-column connections, and walls. The analysis focused on critical factors affecting the bond strength of geopolymer composites with conventional cementitious concrete, and the structural behaviors of reinforced concrete members repaired or strengthened with these composites. The findings highlight the potential of geopolymer composites for enhancing the resilience and toughness of existing damaged or undamaged concrete structures. Additionally, they offer valuable insights into the key considerations for using geopolymer composites as repair or strengthening materials, providing a useful reference for future research in this field.

This paper investigates the efficacy of ultra-high-performance concrete (UHPC) jacketing as an option for seismic retrofit (repair or strengthening) of structural components that have been damaged by reinforcement corrosion. Previous work has illustrated that UHPC cover fully mitigates corrosion in the absence of service cracks and significantly reduces the corrosion rate in the case of preexisting cracks. In the present experimental study, cover replacement by UHPC is used to repair and strengthen corroded columns. Six lap-spliced columns designed based on pre-1970s design standards were constructed and subjected to artificial corrosion. Parameters of the investigation were: a) the aspect ratio of the specimens; b) the bar size (to account for the effect of bar diameter loss on bond); and c) the condition of the specimen (repair or strengthening after damage due to application of simulated seismic load to assess the effectiveness of retrofitting corroded components, even after having endured earthquake damage). The results show that thin UHPC jackets replacing conventional concrete cover suffice to impart a significant increase in strength and ductility of the columns. The jackets also endow the corroded and unconfined lap splices with significant force and deformation development capacity, thus alleviating a source of excessive column flexibility in existing construction.

Most of the studies conducted on the rehabilitation of reinforced concrete (RC) beam-column joints are on pre-1970 structures. Recently, it was reported that seismically designed beam-column joints might also suffer damage under lateral loading. On the other hand, there is an increasing interest among researchers to study the effectiveness of geopolymer as an alternative repair material. To date, no study has been conducted to examine the performance of geopolymer for the rehabilitation of seismically detailed beamcolumn joints following the removal and replacement method under cyclic loading. In the present investigation, two groups of exterior beam-column joints with different flexural strength ratios were rehabilitated with geopolymer mortar. For comparison, another set of beam-column joints (one from each group) were rehabilitated with cement mortar following the same rehabilitation technique and testing. Test results indicated that geopolymer rehabilitated specimens exhibited 20 to 21% higher initial stiffness, 19 to 22% higher displacement ductility, 24 to 37% higher cumulative energy dissipation, 14 to 17% higher initial equivalent viscous damping ratio, 21 to 26% higher ultimate equivalent viscous damping ratio at failure, and 10 to 14% lower damage index compared to specimens rehabilitated with cement mortar. However, irrespective of repair material, removal and replacement technique was only able to partially restore the cyclic performance of rehabilitated specimens.

Reinforced concrete structures possess good fire-resistance properties and rarely experience failure during a fire incident. However, following a fire incident, proper post-fire assessment and repair of the structure may be needed for rehabilitation of the building. This paper presents the application of the X-ray diffraction technique in the analysis of powder samples extracted from concrete members for the estimation of sectional temperatures reached in a real fire incident. Using these sectional temperatures, a simplified evaluation approach was applied for evaluating the residual capacity of structural members in a fire-damaged building. Results of the analysis showed a reduction of 30% and 27% of beam and column capacity after exposure to a fire incident, respectively. Based on the analysis, recommendations were made for rehabilitating the fire-damaged building to meet current design code specifications.

A repair technique for severely damaged precast reinforced concrete (RC) bridge columns with grouted splice sleeve (GSS) connections has been developed that uses a carbon fiber-reinforced polymer (CFRP) shell and epoxy-anchored headed bars to relocate the column plastic hinge. Four original specimens were built using an accelerated bridge construction (ABC) technique with two different GSS systems and were tested to failure using cyclic quasi-static loads. One GSS system was used to connect an RC bridge pier cap to a column and the second GSS system was used to connect an RC footing to a column. Failure of the four original specimens occurred at drift ratios between 5.6 and 8.0% with longitudinal bar fracture or pullout from the GSS connections. The repair method successfully relocated the plastic hinge to the original column section adjacent to the repair and was capable of restoring the diminished load and displacement capacity. The method is a viable and cost-effective technique for rapid seismic repair of severely damaged precast bridge assemblies.