Probabilistic Estimation of Corrosion Propagation Period for Prestressed Concrete Structures Exposed to Chlorides

The overall service life of concrete structures can be divided into corrosion initiation and corrosion propagation phases. The durations of these two phases depend on the chloride threshold (Clth) and corrosion rate (icorr), respectively, of the embedded steel reinforcement. Quantitative information on Clth and icorr of conventional steel reinforcement are available in literature. Now‑a‑days, the use of prestressed concrete elements are rapidly increasing and there is a dire need for estimating their service life. Quantitative information on the Clth and icorr of prestressing steel are required for this estimation. However, very limited quantitative information is available on these parameters. As such, the current practice is to assume that both conventional and prestressing steels have similar Clth and icorr – which might result in unrealistic estimations. This paper provides data on icorr obtained from a 9-month long experimental program. The icorr data was obtained using linear polarization resistance (LPR) tests on prestressing wire embedded in mortar. 10 specimens (made using the center king-wires obtained from 7-wire strands) were cast, cured, and subjected to a cyclic wet-dry exposure using 3.5 % sodium chloride solution. It is observed that the average value of icorr of prestressing steel exposed to chloride‑contaminated mortar is around 5.8 mA/cm2. The paper also provides the probabilistic estimations on corrosion propagation period, tp (defined as the time to crack after corrosion initiation) by substituting the measured icorr data into two models from literature [i.e., Morinaga (1990) and Wang and Zhao (1993)]. It is found that the estimated average tp for prestressed concrete systems are 5.4 and 9.7 years with large scatter. This paper also provides probabilistic estimations on tp for the prestressed concrete systems with 50, 65, and 80 mm cover depths

Residual Service Life Estimation and its Importance for Pretensioned Concrete (PTC) Bridges in Coastal Cities

Many pre-tensioned concrete (PTC) bridges are experiencing premature chloride-induced corrosion. Hence, it is crucial to estimate their residual service life and update it with newer data on a periodic basis - to plan for corrosionpreventionorcontrolmeasuresandensuresafetyofexistingbridges.Criticalchloridethreshold(Cl th) is one of the parameters necessary to estimate the corrosion initiation period. However, quantitative estimates on Clth for prestressing (PS) steel are not well-reported in literature. This paper presents experimental data on the Clth of PS steel, the chloride diffusion coefficient (Dcl), and surface chloride concentration (Cs) of concrete samples obtained from a PTC bridge girder in a coastal city in India. For estimation of Clth, 5 specimens were cast with PS steel wires embedded in ordinary Portland cement (OPC) mortar containing 30% of Class F fly ash (similar composition as that of the bridge girder). They were cured for 28 days and then subjected to cyclic wet-dry exposure using simulated concrete pore solution containing 3.5%sodiumchloride.(Linear polarization resistance (LPR) tests were performed at the end of each exposure cycle, corrosion initiation was detected using statistical methods, and Clth was determined). Using the determined Clth and Dcl, and other relevant parameters, the cumulative distribution functions of time to corrosion initiation was developed. It was found that the average time to corrosion initiation was about 40 years, whereas the structure was designed for 120 years. Also, it was estimated that the corrosion products will accumulate within the interstitial space between the 7 wires in a strand and will not flow through the concrete cover and reach the concrete surface (showing rust stains) until about 5% of strand is corroded (about 10 years). This indicates a dire need for regular data collection, updating the residual life estimates, which will help in developing corrosion prevention strategies for PTC structures

Service Life and Life-Cycle Assessment of Reinforced Concrete with Fly ash and Limestone Calcined Clay Cement

Environmental impact due to the emission of carbon dioxide during concrete production can be taken care by reducing the clinker content in the cement. The clinker content can be reduced by replacing it with fly ash and limestone calcined clay. Such systems can have a potential to exhibit enhanced durability/service life when exposed to chloride and carbon dioxide. However, estimating probabilistic service life of concretes with such alternative binder systems is difficult due to the lack of quantitative estimates of the input parameters such as chloride diffusion coefficient (DCl), ageing coefficient (m), carbonation coefficient (KCO2), and chloride threshold (Clth). This paper presents the experimentally observed estimates of these parameters for the following systems: (i) 100% OPC, (ii) 70% OPC + 30% fly ash, and (iii) limestone calcined clay cement (LC3) – known as OPC, PFA, and LC3 concretes, respectively, herein. A total of three concrete mixes were designed. Also, based on these input parameters, the probabilistic service life estimates of a bridge pier and a girder made of these three concretes and exposed to chlorides and carbon dioxide are presented. For chloride ingress study, Fick’s 2nd Law of diffusion and Clth have been used. For carbonation study, a recently developed model for estimating carbonation depth (using mixture proportion) have been used. Then, the life‑cycle assessment (LCA) of these three concrete systems in terms of the CO2 emissions per unit of concrete per year of estimated service life is presented - for both chloride and carbonation induced corrosion. In chloride laden environments, the service life of the bridge pier and girder systems could be enhanced by about 10 times by using fly ash or LC3 concretes – for similar strength grade concretes. Also, the average annual CO2 emissions (during the expected service life) of PFA and LC3 concretes could be about 3 and 7 times, respectively, lower than that of OPC concretes of similar strength grade. In case of carbonation-induced corrosion, the limited experimental data indicate that the PFA and LC3 concretes could exhibit a lower service life and higher average annual CO2 emissions (during the expected service life) than OPC concretes

MTar: a computational microRNA target prediction architecture for human transcriptome

<p>Abstract</p> <p>Background</p> <p>MicroRNAs (miRNAs) play an essential task in gene regulatory networks by inhibiting the expression of target mRNAs. As their mRNA targets are genes involved in important cell functions, there is a growing interest in identifying the relationship between miRNAs and their target mRNAs. So, there is now a imperative need to develop a computational method by which we can identify the target mRNAs of existing miRNAs. Here, we proposed an efficient machine learning model to unravel the relationship between miRNAs and their target mRNAs.</p> <p>Results</p> <p>We present a novel computational architecture MTar for miRNA target prediction which reports 94.5% sensitivity and 90.5% specificity. We identified 16 positional, thermodynamic and structural parameters from the wet lab proven miRNA:mRNA pairs and MTar makes use of these parameters for miRNA target identification. It incorporates an Artificial Neural Network (ANN) verifier which is trained by wet lab proven microRNA targets. A number of hitherto unknown targets of many miRNA families were located using MTar. The method identifies all three potential miRNA targets (5' seed-only, 5' dominant, and 3' canonical) whereas the existing solutions focus on 5' complementarities alone.</p> <p>Conclusion</p> <p>MTar, an ANN based architecture for identifying functional regulatory miRNA-mRNA interaction using predicted miRNA targets. The area of target prediction has received a new momentum with the function of a thermodynamic model incorporating target accessibility. This model incorporates sixteen structural, thermodynamic and positional features of residues in miRNA: mRNA pairs were employed to select target candidates. So our novel machine learning architecture, MTar is found to be more comprehensive than the existing methods in predicting miRNA targets, especially human transcritome.</p

Report from a symposium on catalyzing primary and secondary prevention of cancer in India

PurposeOral, breast, and cervical cancers are amenable to early detection and account for a third of India’s cancer burden. We convened a symposium of diverse stakeholders to identify gaps in evidence, policy, and advocacy for the primary and secondary prevention of these cancers and recommendations to accelerate these efforts. MethodsIndian and global experts from government, academia, private sector (health care, media), donor organizations, and civil society (including cancer survivors and patient advocates) presented and discussed challenges and solutions related to strategic communication and implementation of prevention, early detection, and treatment linkages.ResultsInnovative approaches to implementing and scaling up primary and secondary prevention were discussed using examples from India and elsewhere in the world. Participants also reflected on existing global guidelines and national cancer prevention policies and experiences.ConclusionsSymposium participants proposed implementation-focused research, advocacy, and policy/program priorities to strengthen primary and secondary prevention efforts in India to address the burden of oral, breast, and cervical cancers and improve survival

Galvanic corrosion and cathodic protection of re-grouted, post-tensioned (PTd) concrete systems

Grouted post-tensioned (PTd) concrete systems are widely used in long-span segmental bridges with a target service life of 100+ years. However, the usage of inadequate grout materials and grouting practices have resulted in the formation of unwanted air voids in the duct, which in turn led to premature corrosion (say, within about 20 years) of strands and failure of tendons. Also, the re-grouting/repairing of void regions have led to localized corrosion of strands at the interface between the dissimilar base-grout (usually carbonated) and repair-grout. This study aims (i) to quantify the galvanic corrosion at the void region in a PTd system re-grouted with a dissimilar grout and (ii) to develop cathodic protection system to protect PTd anchorage regions. Specimens simulating the re-grouted strand-grout-air (SGA) interface were prepared with prestressing steel wires and cementitious grout. The macro-cell current (galvanic current) between the prestressing steels embedded in carbonated base-grout and repair-grout indicated that galvanic corrosion can be possible at the SGA interface – reducing the long-term structural reliability of re-grouted PTd bridges. In addition, the feasibility of galvanic anode cathodic protection system to protect PTd anchorage regions was assessed. For this, a proof-of-concept study was conducted to validate that a thin layer of grout around the strand will be sufficient for a galvanic anode (connected to the end of the strand at outside the tendon anchorage) to protect the strand portions inside the duct/anchorage

Effect of the degree of corrosion on bond performance of Cement Polymer Composite (CPC) Coated steel rebars

Currently, large infrastructures (bridges, highways, etc.) are designed for more than 100 years. To achieve long service life, coated rebars (mostly, cement polymer composite (CPC) coated rebars) are being used to enhance the corrosion resistance. However, inadequately coated rebars can lead to premature corrosion. This can also affect the bond between the rebar and the concrete. To assess the effect of CPC coating on bond strength, pull-out specimens of (150×150×100) mm with 12 mm diameter rebar with 100 mm embedded length were cast and tested. For this, three replica specimens with two types of reinforcement namely, i) Uncoated steel ii) CPC coated steel were cast. To induce corrosion, additional five specimens with CPC coated steel rebars were cast with premixed chloride and cured for 28 days. During the curing period, continuous monitoring of corrosion potential and rate was done and degree of corrosion was assessed. The effect of degree of corrosion on bond of steel-concrete-coating interface was quantified. The CPC coated rebars without corrosion exhibited 10% bond reduction. CPC coated rebars with corrosion exhibited 30-70% reduction in bond strength. Also, the corrosion is found to adversely influence the stiffness of the bond

Microstructure encryption and decryption techniques in optical variable and invariable devices in printed documents for security and forensic applications

Today, document counterfeiting is a global menace because of the advanced technologies available at ever decreasing prices. Instead of eschew the paper documents; applying efficient cost effective security methodologies are the feasible solutions. This paper reports a novel cost effective and simple optical technique using micro text encrypted optical variable device (OVD) threads, ultra-violet (UV) based optical invariable device (OID) patterns and artistic fonts for secure preparation of the documents and its forensic application. Applying any one of the above technique or together can effectively enhance the level of security of the most valuable document. The genuineness of the documents can be verified using simple decryption techniques

Side Population Cells as Prototype of Chemoresistant, Tumor-Initiating Cells

Classically, isolation of CSCs from tumors exploits the detection of cell surface markers associated with normal stem cells. Invariable expression of these cell surface markers in almost all proliferating tumor cells that albeit impart specific functionality, the universality, and clinical credibility of CSC phenotype based on markers is still dubious. Side Population (SP) cells, as defined by Hoechst dye exclusion in flow cytometry, have been identified in many solid tumors and cell lines and the SP phenotype can be considered as an enriched source of stem cells as well as an alternative source for the isolation of cancer stem cells especially when molecular markers for stem cells are unknown. SP cells may be responsible for the maintenance and propagation of tumors and the proportion of SP cells may be a predictor of patient outcome. Several of these markers used in cell sorting have emerged as prognostic markers of disease progression though it is seen that the development of new CSC-targeted strategies is often hindered by poor understanding of their regulatory networks and functions. This review intends to appraise the experimental progress towards enhanced isolation and drug screening based on property of acquired chemoresistance of cancer stem cells

Mutant p53 protein, Bcl-2/Bax ratios and apoptosis in paediatric acute lymphoblastic leukaemia

Purpose: The Bcl-2 family of proteins regulates a late step in the apoptosis pathway. Bcl-2 protein is believed to be involved in imparting resistance to or apoptosis induced by chemotherapeutic agents and radiation. The anti-apoptotic function of the Bcl-2 protein appears to be modulated by its ability to heterodimerize with other members of the gene family, predominantly Bax, a protein favouring induction of apoptosis. Susceptibility to undergoing apoptosis may, therefore, be dependent on the ratio between Bcl-2 and Bax. Both Bax and Bcl-2 are regulated by the tumour-suppressor protein p53. The present study therefore aims to study the significance of the Bcl-2:Bax ratio, p53 expression and apoptosis in paediatric acute lymphoblastic leukaemia (ALL). Methods: Expression of Bax, Bcl-2 and p53 was determined by immunocytochemistry, and apoptosis was evaluated by an enzymatic end-labelling technique using biotin-dUTP and further confirmed by annexin binding. The presence of mutant p53 was determined using a mutant-p53-specific enzyme-linked immunosorbent assay (ELISA). Results: A total of 32 cases and 20 controls were evaluated. Bcl-2 was found to be expressed in 22/32 of the ALL cases. Pretreatment (spontaneous) apoptosis was observed in 23/32 cases. The mean pretreatment apoptotic index was 11.34-2.04% with a median value of 7.5%. Conclusions: There was a positive correlation between apoptosis and Bax expression (r=0.5044; P=0.0038). There was good correlation between the immunoreactivity of p53 and detection of mutant p53 by ELISA (r=0.4605; P=0.0079). The apoptosis index showed a negative borderline correlation to the expression of Bcl-2 protein (r=-0.3181; P=0.076). There was an inverse correlation between extent of apoptosis and the presence of mutant p53 protein (r=-0.4732; P=0.006). p53 protein expression also showed a correlation with both Bcl-2 (r=0.4647; P=0.007) and Bax (r=0.4128; P=0.018). The Bcl-2/Bax ratio, however, showed no significant correlation with apoptosis (r=-0.3131; P=0.08) or with p53 expression. No significant association was evident between clinical and laboratory parameters with the Bcl-2/Bax protein expression except lymphadenopathy (r=0.5774; P=0.03). However, Bax expression showed a borderline correlation with the immediate tumour response to chemotherapy (r=-0.338; P=0.0628). These patients are being followed-up to look for any association between clinical outcome, Bcl-2/Bax ratio and apoptosis