Assessment of corrosion-induced bond deterioration in reinforced concrete: Towards a splitting crack-based approach

Reinforced concrete structures are subjected to several sources of deterioration that can reduce their load-resisting capacity over time. This has significant consequences for the management of infrastructure, leading to high costs of maintenance, repair, strengthening and premature decommissioning. Assessing the residual capacity of structures is challenging but paramount to manage the infrastructure network effectively. Corrosion of the internal steel reinforcement is among the main causes of deterioration in reinforced concrete bridges. The subsequent reduction in steel-to-concrete bond strength is difficult to evaluate with accuracy. There is no unified theory of general validity. Most existing models adopt measures of the level of corrosion as the key parameter to evaluate the bond reduction. In this paper, a different approach is investigated. Corrosion-induced splitting crack widths are used as the fundamental indicator of bond strength reduction, irrespective of the associated degree of steel corrosion. Available experimental results on deformed steel bars embedded in concrete subjected to either natural or accelerated corrosion, with or without transverse reinforcement, are analysed and compared with a different perspective. The analysis indicates that this new splitting crack-based approach can lead to more accurate predictions. This contributes to a better understanding of the fundamental principles underlying bond of corroded reinforcing bars. Enhanced assessment strategies can lead to a reduction of the safety risks, maintenance costs and environmental footprint of the infrastructure network.EPSRC (EP/M508007/1) EPSRC (EP/N509620/1

Bond degradation and reduced cover in concrete with transverse reinforcement

Corrosion of the internal steel reinforcement is among the main causes of deterioration in concrete bridges. The expansive nature of corrosion products can lead to cracking, delamination or complete spalling of the concrete cover. The subsequent reduction in reinforcement anchorage is difficult to assess accurately. To study the effects of spalling on the steel-to-concrete bond, pull-out tests were carried out on half-joint cantilever specimens. Spalling was simulated with progressively reduced cover. This led to degradation of bond and anchorage of the longitudinal bars. However, the presence of transverse confining reinforcement had beneficial effects, limiting bond degradation and avoiding brittle failures where splitting occurred

Cost-effectiveness analysis of newborn screening for organic acidemias in Hong Kong

published_or_final_versio

Effects of anchorage deterioration on the shear behaviour of reinforced concrete half-joint beams

Reinforced concrete half-joint structures, also called dapped-end beams, are a common type of support configuration in bridges and precast structures. They are characterised by a sudden reduction in depth at the end of a suspended structural element. This detail has advantages for design and construction that justified their widespread use in the past. However, there are numerous problems associated with this type of joint that can translate into significant maintenance costs. A recurrent issue is leakage of water and contaminants that cause corrosion of the internal steel reinforcement. The expansive nature of corrosion products can lead to cracking, delamination or complete spalling of the concrete cover. This is detrimental to the anchorage of the reinforcement. The subsequent reduction in load-transfer capacity is difficult to quantify when assessing damaged structures. It can lead to failure modes that are not taken into account by code provisions for new design. Due to the limited understanding of the behaviour of deteriorated half-joints, experimental evidence is necessary to develop new theories and methodologies to assess existing structures accurately. In this study, an experimental programme was carried out on reinforced concrete beam specimens, investigating the effects of anchorage deterioration in the longitudinal tension bars of the full-depth portion of half-joints. Corrosion-induced spalling and delamination were reproduced by casting the beams without cover and reducing the cover/diameter ratio at critical locations. The results indicate that half-joints are vulnerable to anchorage deterioration in the full-depth section. This is due to the absence of direct confining pressure from the end supports. Bond and anchorage degradation led to a progressive reduction in the overall load-bearing capacity of the beam-ends and combined bending-shear failure modes. Nevertheless, the presence of confining vertical reinforcement allowed for some residual anchorage capacity, even in the case of complete loss of cover.EPSRC (EP/M508007/1) EPSRC (EP/N509620/1

Corrosion-induced cracking and bond strength in reinforced concrete

Corrosion of the steel reinforcement is among the main causes of deterioration in concrete structures. Measures of corrosion levels are typically used to evaluate the subsequent reduction in steel-to-concrete bond, but results lack accuracy. In this study, a new assessment approach based on surface cracks was investigated. Specimens were subjected to accelerated corrosion using an impressed current. With a novel sealing method, mass losses were decoupled from concrete cracking. The results indicate that surface crack widths can be better indicators of bond degradation than corrosion levels. The findings can lead to more accurate assessments and reduced maintenance costs of infrastructure

Correlation between surface crack width and steel corrosion in reinforced concrete

Reinforced concrete structures are subjected to weather conditions, chemical attack and other sources of deterioration that can affect their performance. In particular, corrosion of the internal steel reinforcement is considered to be one of the main causes of structural deterioration. A possible consequence of corrosion is cracking of the surrounding concrete. Visual inspections are often used to inform asset management strategies. Finding a relationship between cracks that are visible on the outer surface of a structure and corrosion of the internal reinforcement can be helpful when making assessment decisions. To this end, unconfined cylindrical concrete specimens with an embedded steel bar have been subjected to accelerated corrosion using an impressed current density of 200µA/cm2, leading to steel mass losses between 5-24%. This paper discusses the measured correlation between corrosion-induced surface crack widths and degree of reinforcement corrosion. The tests highlighted some limitations of a set-up that is commonly adopted for accelerated corrosion and concentric pull-out bond testing. The findings of this study represent a first step towards the standardisation of accelerated corrosion testing procedures using an impressed current.</jats:p

Food security, nutrition and health of food bank attendees in an English city: A cross-sectional study

Food banks in contemporary Britain are feeding record numbers of people. Little is known about attendees’ level of food insecurity, background diet quality or health. We surveyed 112 food bank attendees. Over 50% had experienced food shortage with hunger on a weekly basis or more often. Obesity and mental health problems were prevalent in women. Diet quality was poor, with energy, protein, fibre, iron and calcium intakes inadequate, while saturated fat and sugars intake were disproportionate. Women had poorer diet quality than men. Such patterns may lead to ill health

Comparison of glucose tolerance in renal transplant recipients and hemodialysis patients

BACKGROUND: Impaired glucose tolerance is a risk factor for atherosclerosis in hemodialysis patients and renal transplant recipients. METHODS: To check the relationship of impaired glucose tolerance with the other atherosclerotic risk factors, fasting blood sugar and the standard two hour glucose tolerance test, serum tryglyceride, serum cholesterol, cyclosporine through level (in renal tranpslant recipients) and hemoglobin A1C were measured in 55 stable renal transplant recipients, 55 hemodialysis patients and 55 healthy controls with similar demographic characteristics. Patients with diabetes mellitus and propranolol consumers were excluded. The mean age and female to male ratio were 39 +/- 7 years and 23/22, respectively. RESULTS: Four of the renal transplant recipients and twelve of the hemodialysis patients had impaired glucose tolerance. Significant linear correlation was observed with body mass index and IGT only in hemodialysis patients (r = 0.4, p = 0.05). Glucose tolerance also had a significant correlation with triglyceride levels (217.2 +/- 55 mg/dl in hemodialysis patients vs. 214.3 +/- 13 mg/dl in renal transplant recipients and 100.2 +/- 18 mg/dl in control groups, p = 0.001). The glucose tolerance had significant relationship with higher serum cholesterol levels only in the renal transplant recipients (269.7 +/- 54 in renal transplant recipients vs. 199.2 +/- 36.6 mg/dl in hemodialysis and 190.5 +/- 34 mg/dl in control groups, p = 0.0001). In the renal transplant recipients, a linear correlation was observed with glucose tolerance and both the serum cyclosporine level (r = 0.9, p = 0.001) and the hemoglobin A1C concentration (6.2 +/- 0.9 g/dl). The later correlation was also observed in the hemodialysis patients (6.4 +/- 0.7 g/dl; r = 67, p = 0.001). CONCLUSIONS: We conclude that although fasting blood sugar is normal in non-diabetic renal transplant and hemodialysis patients, impaired glucose tolerance could be associated with the other atherosclerotic risk factors

HIV type 1 that select tRNA(His) or tRNA(Lys1,2) as primers for reverse transcription exhibit different infectivities in peripheral blood mononuclear cells.

The replication in human peripheral blood mononuclear cells (PBMC) of unique HIV-1 that select tRNA(His) or tRNA(Lys1,2) for reverse transcription was compared to the wild-type virus that uses tRNA(Lys,3). HIV-1 with only the primer-binding site (PBS) changed to be complementary to these alternative tRNAs initially replicated more slowly than the wild-type virus in PBMC, although all viruses eventually reached equivalent growth as measured by p24 antigen. Viruses with only a PBS complementary to the 3' terminal 18 nucleotides of tRNA(His) or tRNA(Lys1,2) reverted to use tRNA(Lys3). HIV-1 with mutations in the U5-PBS to allow selection of tRNA(His) and tRNA(Lys1,2) following long-term growth in SupT1 cells were also evaluated for growth and PBS stability following replication in PBMC. Although both viruses initially grew slower than wild type, they maintained a PBS complementary to the starting tRNA and did not revert to the wild-type PBS after long-term culture in PBMC. Analysis of the U5-PBS regions following long-term culture in PBMC also revealed few changes from the starting sequences. The virus that stably used tRNA(His) was less infectious than the wild type. In contrast, the virus that stably used tRNA(Lys1,2) evolved to be as infectious as wild-type virus following extended culture in PBMC. The results of these studies highlight the impact of the host cell on the tRNA primer selection process and subsequent infectivity of HIV-1

Ultrasonic tomographic imaging of defects in industrial materials

Ultrasonic tomography has been fairly widely applied for imaging of inhomogeneities in isotropic materials, particularly in the medical field, however, little success has been made in its application to industrial materials. This is largely due to the complex nature of ultrasonic wave propagation in these anisotropic materials. The three dimensional characteristics of ultrasonic wave propagation in anisotropic materials have been thoroughly studied for single crystals and also studied recently for different composites [1,2,3]. Understanding these characteristics provides the theoretical background for developing appropriate ultrasonic tomographic imaging methods for industrial materials