Fibre Reinforced Polymer Composite Deck Elements for Highway Bridges in Developing Countries

Fibre Reinforced Polymer (FRP) composite bridge decks are increasingly being accepted by bridge owners and designers as a suitable alternative to traditional construction materials such as reinforced concrete, steel and masonry. This is because FRP as a material has several advantages such as high strength to weight ratio and high durability due to inherent corrosion resistance properties. Additionally, the material lends itself to a large degree of prefabrication which saves construction time thus minimising traffic disruptions. This paper explores the possible application of FRP to bridge construction in developing countries and its implications on project management and delivery

Review of Concrete Resistance to Abrasion by Waterborne Solids

In the last four decades, numerous investigations have been undertaken on abrasion-erosion of concrete using various test methods. These have suggested existence of different abrasion mechanisms, limitations of existing test methods and inconsistencies on the importance of compressive strength to abrasion resistance of concrete. The objective of this review is to: understand the mechanisms of concrete abrasion-erosion, assess the suitability of existing test methods to simulate field conditions and investigate the relationship between abrasion resistance and compressive strength. It is found that concrete abrasion mechanisms are dependent on both transport modes of abrasive charge and the ratio of coarse aggregate to matrix hardness. The ASTM C1138 (underwater) test method appears to simulate all the critical modes of sediment induced abrasion expected in field conditions and specific energy can be used as a framework to correlate ASTM C1138 test results with field measurements. With the exception of concrete with rubber aggregates, abrasion loss is found to fit a simple power function of its compressive strength, and no significant improvements in abrasion resistance can be gained by using concretes with compressive strengths exceeding 60 MPa (8.70 ksi). Also, the influence of cementitious additives and coarse aggregate properties is only significant at compressive strengths below the optimal value of 60MPa (8.70 ksi)

Influence of Coarse Aggregate Parameters and Mechanical Properties on the Abrasion Resistance of Concrete in Hydraulic Structures

The objective of this experimental investigation is to use the ASTM C1138 (underwater) test method to investigate the influence of the quantity and type of coarse aggregates on the hydrodynamic abrasion resistance of concrete. Thereafter, relationships between the abrasion resistance of concrete with its principal mechanical properties are comparatively examined. It is found that the use of natural coarse aggregates to replace fine aggregates by up to 25% does not significantly affect concrete abrasion performance, but the use of recycled tire rubber aggregates with aspect ratios of 4 to replace 25% of natural coarse aggregates increases the abrasion resistance by up to 64% depending on the test duration. Further, concretes produced with natural rounded coarse aggregates of 10 mm significantly outperformed those with angular 20 mm maximum particle size at all test durations by up to 57%. Finally, for the concrete mixtures tested, results indicate that tensile splitting strength is a superior parameter to compressive strength for predicting the concrete abrasion resistance in the ASTM C1138 test and the relations developed for the concretes tested predicted percentage abrasion loss within the margin of ±0.5%.</p

Subtypes A1 and D, and recombinant HIV-1 natural polymorphisms associated with lenacapavir drug resistance in Uganda

BackgroundLenacapavir, a novel HIV-1 capsid inhibitor, shows promise for treating MDR HIV-1, as well as for pre-exposure prophylaxis (PrEP) in prevention of HIV infection. Its unique mechanism and lack of cross-resistance with other antiretroviral classes make lenacapavir a significant addition to HIV therapy. The clinical trials CALIBRATE and CAPELLA have demonstrated high viral suppression rates in both ART-naive individuals and individuals with MDR HIV-1. Lenacapavir-associated resistance mutations, such as M66I and Q67H, rarely seen as natural polymorphisms in lenacapavir-naive populations, are predominantly studied in subtype B HIV-1.ObjectivesOur study aimed to investigate the prevalence of lenacapavir resistance-associated mutations in HIV-1 subtypes A1 and D in a cohort of individuals living with HIV-1 from southwestern Uganda.MethodsUtilizing plasma samples from ART-naive adults living in Uganda, HIV-1 Gag p24 (capsid) sequences were analysed for lenacapavir resistance mutations.ResultsAmong 546 lenacapavir-naive participants, no major lenacapavir resistance-associated mutations were found. Minor mutations were present in 1.6% of participants, with T107A being the most common. Longitudinal data indicated the persistence of T107A for at least 3 years post-ART initiation in one participant. Phylogenetic analysis indicated individuals carrying T107A were found independently in distinct locations within the tree, suggesting that T107A might have arisen from multiple distinct base substitution events. Shannon entropy analysis showed high variability in certain capsid sites, but none overlapped with known lenacapavir resistance sites.ConclusionsThese findings suggest a low prevalence of naturally occurring lenacapavir resistance mutations in Uganda, supporting lenacapavir's potential efficacy in this region

Effect of using recycled waste glass coarse aggregates on the hydrodynamic abrasion resistance of concrete

This experimental study is aimed at evaluating the hydrodynamic abrasion resistance of concrete produced with recycled waste glass as coarse aggregates. The underwater (ASTM C1138) method is used to test concretes containing 0%, 12.5%, 25%, 50% and 100% glass aggregates as replacement for natural coarse aggregates. To benchmark performance, the abrasion resistance of glass-aggregate concretes is compared with that of a high-strength concrete mixture typically used in coastal defences where abrasion resistance is critical. Further comparison is made with a general application concrete mixture containing crushed limestone coarse aggregates. At 95% confidence, results of the Kruskal-Wallis test show that the use of recycled waste glass as coarse aggregates in concrete at contents of up to 25% does not significantly affect its abrasion resistance. When compared with the typical high-strength mixture with proven field performance, the results of the Kruskal-Wallis test at 95% confidence indicated that abrasion resistance at glass aggregate replacement levels of up to 25% was not significantly different. Concrete produced with 100% recycled waste glass coarse aggregates had comparable abrasion resistance with that produced with 100% crushed limestone coarse aggregates. Additionally, there was a stronger and significant dependence of the abrasion resistance of glass-aggregate concretes on tensile splitting strength in comparison to both compressive strength and modulus of elasticity

Influence of basalt micro-fibres on the abrasion resistance of concrete in hydraulic structures

AbstractIn hydraulic structures, abrasion resistance can be a significant driver in concrete specification. Basalt micro-fibres represent a potentially sustainable construction product and have been shown to provide various benefits in concrete, however the implications for hydrodynamic abrasion resistance are to date unclear. This paper is the first investigation of its kind to examine the abrasion resistance of basalt fibre-reinforced (BFR) concretes using the ASTM C1138 underwater test method. Towards this, concretes incorporating fibre dosages of 0.5, 1, 1.5 and 3 kg/m3 were tested. The relationships between concrete abrasion and its fundamental mechanical properties are evaluated. For the particular concretes examined, it is found that based on the Shapiro-Wilks tests at 95% confidence, abrasion loss in BFR concretes followed a normal distribution; the use of basalt fibre in contents of up to 3 kg/m3 did not have a significant effect on abrasion resistance, compressive and tensile splitting strengths, as well as modulus of elasticity. It can be concluded that basalt micro-fibre can be used for their other attributes such as controlling bleeding, shrinkage and plastic cracking in concrete hydraulic structures without deleterious effects on abrasion resistance. The regression models proposed to predict concrete abrasion loss from its mechanical properties were found to be only significant at 48 h for compressive strength and 24 h for both tensile splitting strength and modulus of elasticity.</jats:p