Structural performance of reinforced concrete beams repairing from spalling

The effectiveness of a repair work for the restoration of spalled reinforced concrete (r.c.) structures depends to a great extent, on their ability to restore the structural integrity of the r.c. element, to restore its serviceability and to protect the reinforcements from further deterioration. This paper presents results of a study concocted to investigate the structural performance of eight spalled r.c. beams repaired using two advanced repair materials in various zones for comparison purposes, namely a free flowing self compacting mortar (FFSCM) and a polymer Modified cementitious mortar (PMCM). The repair technique adopted was that for the repair of spalled concrete in which the bond between the concrete and steel was completely lost due to reinforcement corrosion or the effect of fire or impact. The beams used for the experiment were first cast, then hacked at various zones before they were repaired except for the control beam. The beam specimens were then loaded to failure under four point loadings. The structural response of each beam was evaluated in terms of first crack load, cracking behavior, crack pattern, deflection, variation of strains in the concrete and steel, collapse load and the modes of failure. The results of the test showed that, the repair materials applied on the various zones of the beams were able to restore more than 100 of the beams' capacity and that FFSCM gave a better overall performance

Investigating the deterioration of an industrial heritage structure

Conservation and rehabilitation of heritage structures has turned into a prime concern in historically enriched countries, especially in developed societies. Modern technologically advanced societies often wish to keep and maintain the remains of architectural heritage sites and pass the essence of these tangible and intangible cultural values to future generations. The present study introduces a historical industrial structure in Guimarães, Portugal which was once renowned as part of the leather industry but has now been dilapidated for many years. As part of the city authority’s plan to regenerate the whole town, this industrial heritage structure needs to be rehabilitated. This study presents an intensive structural survey with conventional non-destructive tests (NDT). Visual survey was used to attempt to identify problems in the structure and their possible decay mechanisms. Damages to the building include the decay of timber and stones, dampness problems and incompatible structural assemblage. The lack of long-term maintenance is one of the potential causes which has aggravated decay. NDTs were utilised to characterise the basic mechanical properties of the deteriorated timber elements. The findings allowed the safety of this industrial heritage structure to be appraised which could be beneficial for the conservation management plan of this city

A review of the corrosion behavior of metallic heritage structures and artifacts

Awareness about restoring and preserving historically important structures and artifacts is gradually growing in many parts of the world. These artifacts and structures represent the culture, tradition and past of a nation. They are often also a source of national income through tourist activities. Besides masonry and wood work, metallic forms and relics are a vital part of the heritage which needs to be conserved. Certain metals have been used significantly throughout history in the creation of objects and structures. However, metals are prone to decay over time, particularly decay through corrosion. The basic mechanisms of metal corrosion, the various types of corrosion and existing remedial solutions are reviewed in this paper. The most significant factor affecting metal corrosion was found to be the surrounding environment, especially in marine areas. Different remedial measures can be implemented on corroded metals according to their specific properties. Recommendations for further study are offered at the end of the paper

Probiotics [LGG-BB12 or RC14-GR1] versus placebo as prophylaxis for urinary tract infection in persons with spinal cord injury [ProSCIUTTU]: a randomised controlled trial

© 2019, The Author(s). Study design: Randomised double-blind factorial-design placebo-controlled trial. Objective: Urinary tract infections (UTIs) are common in people with spinal cord injury (SCI). UTIs are increasingly difficult to treat due to emergence of multi-resistant organisms. Probiotics are efficacious in preventing UTIs in post-menopausal women. We aimed to determine whether probiotic therapy with Lactobacillus reuteri RC-14+Lactobacillus GR-1 (RC14-GR1) and/or Lactobacillus rhamnosus GG+Bifidobacterium BB-12 (LGG-BB12) are effective in preventing UTI in people with SCI. Setting: Spinal units in New South Wales, Australia with their rural affiliations. Methods: We recruited 207 eligible participants with SCI and stable neurogenic bladder management. They were randomised to one of four arms: RC14-GR1+LGG-BB12, RC14-GR1+placebo, LGG-BB12+ placebo or double placebos for 6 months. Randomisation was stratified by bladder management type and inpatient or outpatient status. The primary outcome was time to occurrence of symptomatic UTI. Results: Analysis was based on intention to treat. Participants randomised to RC14-GR1 had a similar risk of UTI as those not on RC14-GR1 (HR 0.67; 95% CI: 0.39–1.18; P = 0.17) after allowing for pre-specified covariates. Participants randomised to LGG-BB12 also had a similar risk of UTI as those not on LGG-BB12 (HR 1.29; 95% CI: 0.74–2.25; P = 0.37). Multivariable post hoc survival analysis for RC14-GR1 only vs. the other three groups showed a potential protective effect (HR 0.46; 95% CI: 0.21–0.99; P = 0.03), but this result would need to be confirmed before clinical application. Conclusion: In this RCT, there was no effect of RC14-GR1 or LGG-BB12 in preventing UTI in people with SCI

Structural performance of reinforced concrete beams\ud repairing from spalling

The effectiveness of a repair work for the restoration of spalled reinforced concrete\ud (r.c.) structures depends to a great extent, on their ability to restore the structural integrity\ud of the r.c. element, to restore its serviceability and to protect the reinforcements from\ud further deterioration. This paper presents results of a study concocted to investigate the\ud structural performance of eight spalled r.c. beams repaired using two advanced repair\ud materials in various zones for comparison purposes, namely a free flowing self compacting\ud mortar (FFSCM) and a polymer Modified cementitious mortar (PMCM). The repair\ud technique adopted was that for the repair of spalled concrete in which the bond between the\ud concrete and steel was completely lost due to reinforcement corrosion or the effect of fire\ud or impact. The beams used for the experiment were first cast, then hacked at various zones\ud before they were repaired except for the control beam. The beam specimens were then\ud loaded to failure under four point loadings. The structural response of each beam was\ud evaluated in terms of first crack load, cracking behavior, crack pattern, deflection, variation\ud of strains in the concrete and steel, collapse load and the modes of failure. The results of\ud the test showed that, the repair materials applied on the various zones of the beams were\ud able to restore more than 100% of the beams’ capacity and that FFSCM gave a better\ud overall performance

Strengthening of RC Beams Using Externally Bonded Reinforcement Combined with Near-Surface Mounted Technique

This study investigates the flexural behaviour of reinforced concrete (RC) beams strengthened through the combined externally bonded and near-surface mounted (CEBNSM) technique. The externally bonded reinforcement (EBR) and near-surface mounted (NSM) techniques are popular strengthening solutions, although these methods often demonstrate premature debonding failure. The proposed CEBNSM technique increases the bond area of the concrete–carbon fibre reinforced polymer (CFRP) interface, which can delay the debonding failure. This technique is appropriate when any structure has a narrow cross-sectional width or is in need of additional flexural capacity that an individual technique or material cannot attain. An experimental test matrix was designed with one control and five strengthened RC beams to verify the performance of the proposed technique. The strengthening materials were CFRP bar as NSM reinforcement combined with CFRP fabric as EBR material. The test variables were the diameter of the NSM bars (8 and 10 mm), the thickness of the CFRP fabrics (one and two layers) and the U-wrap anchorage. The strengthened beams showed enhancement of ultimate load capacity, stiffness, cracking behaviour, and strain compatibility. The ultimate capacity of the CEBNSM-strengthened beams increased from 71% to 105% compared to that of the control beam. A simulation method based on the moment-rotation approach was also presented to predict the behaviour of CEBNSM-strengthened RC beams

Prestressing of NSM steel strands to enhance the structural performance of prestressed concrete beams

Prestressing of strengthening materials can enhance the performance of strengthened structures as the materials become more efficient as a greater portion of their tensile capacity is employed. Prestressed concrete beams are widely used in the construction field, however, there is a lack of studies on the strengthening of these structural elements. This paper presents an experimental study on strengthening prestressed beams using near surface mounted (NSM) prestressed steel strands. A total of seven prestressed beams were constructed for static testing, with one unstrengthened control beam, one beam strengthened with a non-prestressed NSM steel strand, and five beams strengthened with NSM steel strands prestressed to varying levels of their nominal tensile strength. The structural behavior and failure modes of these specimens were investigated and the differences in performance due to the effect of the prestressing force in the NSM strands were analyzed. Based on the results, applying prestress force provides an increase in load carrying capacity with corresponding higher concrete cracking and steel yielding initiations when compared to beams strengthened with no added prestress force. The influence of various prestress levels on the deflection of the tested beams was also assessed, and the relevant results were presented and discussed. The test results showed that the strengthened prestressed beam with a 70% prestressed steel strand performed better compared to the other strengthened beams. The first crack load, yield load and ultimate load of the prestressed beam strengthened with a 70% prestressed steel strand increased by 40%, 57% and 40%, respectively, compared to the control beam

Combining EBR CFRP sheet with prestressed NSM steel strands to enhance the structural behavior of prestressed concrete beams

In this study, a combined strengthening technique is used to improve the flexural performance of prestressed concrete beams using CFRP sheets as EBR and prestressed steel strands as NSM. Seven prestressed beams were tested under four-point loading with one control specimen, one EBR CFRP sheet strengthened specimen, one NSM steel strand without prestress strengthened specimen and four specimens strengthened with a combination of EBR CFRP sheet and NSM steel strands prestressed from 0% to 70% of their tensile strength. The flexural responses and failure modes of the specimens were investigated and the variations due to the level of prestressing force in the PNSM steel strands were also assessed. A finite element model (FEM) was developed using ABAQUS to verify the flexural responses of the strengthened specimens. The test results revealed that the combined strengthening technique remarkably enhanced the flexural performance of the specimens. The serviceability, first crack, yield, and ultimate load capacities improved up to 44%, 49%, 55% and 70%, respectively when compared with the control specimen. The combined technique also ensured the flexural failure of the specimens with significant enhancement in stiffness and energy absorption. The results of the FEM model exhibited excellent agreement with the experimental results

A review of the corrosion behavior of metallic heritage structures and artifacts

Awareness about restoring and preserving historically important structures and artifacts is gradually growing in many parts of the world. These artifacts and structures represent the culture, tradition and past of a nation. They are often also a source of national income through tourist activities. Besides masonry and wood work, metallic forms and relics are a vital part of the heritage which needs to be conserved. Certain metals have been used significantly throughout history in the creation of objects and structures. However, metals are prone to decay over time, particularly decay through corrosion. The basic mechanisms of metal corrosion, the various types of corrosion and existing remedial solutions are reviewed in this paper. The most significant factor affecting metal corrosion was found to be the surrounding environment, especially in marine areas. Different remedial measures can be implemented on corroded metals according to their specific properties. Recommendations for further study are offered at the end of the paper