Search Results (4)

This research elucidates the idea of eco-friendly concrete and highlights the benefits attainable from its effective practice towards sustainable construction materials. The design mix employed a water/cement ratio of 0.5, a concrete mix ratio of 1:2:4, varying percentages of 2.5 mm seashells, 4.75 mm river sand as fine aggregates, and granite 20 mm as coarse aggregates. Laboratory tests showed that the true slump was achieved for all mixes as a decrease in workability was observed with seashell additions. Compressive strength declined with increasing percentages of seashells at all curing ages (7, 14, and 28 days). No seashell-modified mix achieved the target strength for concrete grade 25. Nevertheless, the 10 and 20% seashell blends obtained strength requirements for concrete grade 20. The splitting tensile strength results indicated that 10–50% seashell-concrete blends yield acceptable splitting tensile strength after 28 days of curing. Correlation and regression analysis showed that compressive strength has a high negative correlation with seashell percentage and a significant correlation with splitting tensile strength. However, no significant correlation was seen between seashell percentage and splitting tensile strength. Models were further developed for predicting workability, splitting tensile strength, and compressive strength, with seashell percentage data. Green concrete production, which reutilizes waste seashells should be promoted, bearing in mind its environmental sustainability and economic prospects. Full article

Vehicle emissions have become one of the most prevailing air contamination sources, including nitrogen oxides, volatile organic compounds, carbon monoxide and particulate matter (PM). Among other air pollutants, PM limits visible sight distance and poses health risks upon inhalation into the human body. This study focused on assessing PM_2.5 concentrations in air at different periods of the day at the highly trafficked grade-separated intersection of Sango-Ota, Ogun State, Nigeria. PM_2.5 readings were taken at three at-grade points around the intersection’s roundabout between 10:00 a.m. and 5:00 p.m. for four (4) days using the BR-SMART-126 Portable 4-in-1 air quality monitor. The highest level of PM_2.5 obtained on Day 1 (Monday) and Day 4 (Thursday) was about 45.1% and 38.6%, respectively, lower than that of Day 3 (Wednesday). The highest concentrations of PM_2.5 were recorded between 11:00 and 13:00 and between 16:00 and 18:00 (up to 217 µg/m³) whereas the lowest levels were recorded between 14:00 and 15:00 (as low as 86 µg/m³). The concentration of PM_2.5 at the Sango-Ota intersection is adjudged “very poor” with average hourly concentrations between 97 and 370 µg/m³. Outcomes obtained indicate the need for improved measures to control air quality along major road corridors and at intersections in Ogun State and Nigeria at large. Full article

Across the world, ballasted railway tracks are utilised extensively due to their cost efficiency, ease of drainage, and capacity to withstand cyclic imposed loadings from heavy trains. In spite of these benefits, the ballast is often considered as a flexible medium; as such, its continuous deterioration is largely disregarded. Geotechnical challenges such as ballast contamination in the form of particle fragmentation, deposition of weathered materials, upward pumping of clay and fines from underlayers, and coal intrusion have led to differential settlements and reduced drainability of tracks, thereby exacerbating track maintenance costs. This study reviews existing works of literature to expound on the mechanisms for ballast contamination and to highlight the fundamental parameters that guide the characterisation and performance evaluation of railway ballasts. The study shows that ballast fragmentation accounts for about 76% of commonly recorded contaminations, while it is also observed as the most critical to track stability. As such, a variety of indices and specifications for ballast gradation have been established worldwide to guide practice in ballast characterisation and performance evaluation. However, the mechanisms of ballast fragmentation and deterioration require further research to guide the improvement of contemporary guidelines, and mitigate the risk of abrupt track failures, especially in developing countries. Full article

Fire outbreaks in buildings have been a major concern in the world today. The integrity of concrete is usually questioned due to the fact that after these fire outbreaks the strength of the concrete is reduced considerably. Various methods have been adopted to improve the fire resistance property of concrete. This study focused on the use of coconut fibre to achieve this feat. In this study, varying percentages of treated and untreated coconut fibres were incorporated into concrete and the compressive strength was tested for both before heating and after heating. The percentages of replacement were 0.25, 0.5, 0.75 and 1% fibre content by weight of cement. Concrete cubes that had 0% fibre served as control specimens. After subjecting these concrete cubes to 250 °C and 150 °C for a period of 2 h, the compressive strength increased when compared to the control. The compressive strength increased up to 0.5% replacement by 3.88%. Beyond 0.5% fibre, the compressive strength reduced. Concrete having coconut fibre that had been treated with water also exhibited the highest compressive strength of 28.71 N/mm². It is concluded that coconut fibres are a great material in improving the strength of concrete, even after it was exposed to a certain degree of elevated temperature. Full article