Development of sustainable prestressed concrete sleepers using mineral admixtures: An experimental and numerical investigation Bhukya Vamsi Naik, Srinivas Jeela, Nutakki Sobha Saranya, Turaka Suresh, Yugal Kishor, Sharan Kumar Goudar

The railway track structures rely on sleepers to fulfil an important role of bearing the loads exerted on the rails, subsequently dispersing these loads to the ballast bed. In doing so, they uphold the integrity of the track’s geometry. Prestressed concrete sleepers are at risk of getting damaged when a train derails. In these situations, the sleepers experience strong impacts. To decrease the chances of derailments, we can make the concrete sleepers absorb more energy and handle heavier loads. One way to achieve this is by making the concrete stronger, which can be done by increasing its compressive strength. However, this traditional method uses a lot of cement and other resources that are not eco-friendly. A better and more sustainable approach is to utilize industrial by-products like fly ash (FA) and ground granulated blast furnace slag (GGBS) in the production of these sleepers. This study examines the performance of normal prestressed concrete sleeper and prestressed concrete sleeper produced with fly ash and GGBS when subjected to impact loading and static bending tests. The results clearly demonstrate that the sleeper made with fly ash and GGBS performs slightly better when compared to standard prestressed concrete sleeper made with ordinary Portland cement (OPC). The accuracy of the numerical findings is confirmed through comparison with experimental results.

Implication of high-volume mineral admixture on mechanical properties and microstructure at steel-concrete interface Sharan Kumar Goudar, E. P. Sumukh, B. B. Das

The existence of a non- homogeneous unique zone in concrete along the periphery of steel surface is being referred as steelconcrete interface (SCI). The interface between steel and concrete exhibits a porous zone, with a thickness measuring several micrometers. This porous zone thickness around SCI plays a crucial role in influencing bond strength, durability, and is a significant parameter used in service life prediction models for reinforced concrete structures. The value of porous zone thickness around SCI is being assumed and adopted without any practical studies in service life prediction models as well as in reinforced concrete mesoscale structure modelling. In the present study, porous zone thickness was experimentally measured through obtaining backscattered electron images around SCI. Gray scale-based thresholding technique was employed to ascertain the porous zone thickness (PZT) around SCI. Furthermore, the influence of incorporating ground granulated blast furnace slag (GGBS) in high-volume on the interfacial transition zone (ITZ) between steel reinforcement bars and the surrounding concrete was investigated. It was observed that porous zone thickness around SCI varies in every other point along the periphery of reinforcement bar. The pozzolanic reaction in high volume GGBS concrete resulted in a substantial decrease of porous zone thickness (PZT) and reduced the accumulation of Portlandite around SCI with the progress in curing age. The factors contributing to the enhanced ultimate bond strength of high volume GGBS concrete compared to control concrete are the decrease in the Porous Zone Thickness (PZT) along with the reduced Ca/Si ratio around the SCI.

Efficacy of fly ash and slag in controlling the heat of hydration, strength, and durability of mass concrete Manish Prabhakar Mokal, Romio Mandal, Sanket Nayak, Sarat Kumar Panda

In this paper, the effectiveness of fly ash (FA) and ground granulated blast-furnace slag (GGBS) in controlling the heat of hydration, strength, and durability of mass concrete is presented. For this purpose, five concrete blocks having dimensions of 0.9 × 0.9 × 0.9 m were cast with varying proportions of cement, FA, and GGBFS. The rise in temperature with the increase in hydration time was measured by Type-k thermocouples. The compressive strength and rapid chloride permeability test (RCPT) were measured by extracting the cores of size 103 mm diameter with two different heights (200 mm height for compressive strength test and 50 mm height for RCPT test) from the centre of the blocks. Analysing the results, it is noted that the use of 20 and 35 % FA lowered the peak core temperature by 7.7 and 15.4 %, respectively, and enhanced the strength of cores by 29.7 and 36.1 %, respectively, at 56 days of curing than the 100 % ordinary Portland cement-based sample. Similarly, the use of 50 and 70 % GGBS lowered the peak core temperature by 11.5 and 17.3 %, respectively, and enhanced the core strength by 31.1 and 29.1 %, respectively. This is attributed to the lower amount of evolution of heat at the early age and the increase in homogeneity of hydrated products and refinement of pores of the FA and GGBS-based samples during secondary hydration reaction at higher curing temperatures. The utilization of FA and GGBFS will not only reduce the peak core temperature and enhance the strength, but also improve the durability of mass concrete.

Study on behavior of tension zone concrete in beams using shredded rubber Manoj Kumar H. R., Shivaprasad K. N.

In reinforced simply supported concrete beam neutral axis separates two zones namely the tension zone and compression zone. Concrete is a material which is good at taking compressive load and steel is capable of carrying tensile load. The main focus of this paper is to use sustainable concrete in the tension zone with shredded rubber below the neutral axis in a view that tensile load is carried mainly by steel and the role of concrete in taking tension is minimum. In the present study, the compression zone of the reinforced concrete beam is prepared with regular M30 grade concrete and tension zone is prepared by partially replacing sand with shredded rubber. From the experimental results, it is observed that with an increase in the shredded rubber quantity in the mixes, the strength of the reinforced concrete beam gets reduced. Here it is observed that fine aggregates in concrete when replaced with more than 160 kg per m3 of shredded rubber, mechanical properties are not achieved. Similarly, the performance of the reinforced concrete beam gets reduced when compared to the control beam.

Structural response to blast loads with varying stand-off distances Vikram S. Singh, Keshav K. Sangle, Partap Singh

The present study aims to assess the impact of a blast on a five-story reinforced concrete (RC) frame structure through computational analysis. The study examines the effect of different standoff distances, which is the distance between the source of the explosion and the structure, on the structural behavior. The standoff distances being studied are 5, 10, and 15 meters, and a charge weight of 25 kilograms is used in each scenario. Blast loads can cause severe damage to the exterior frames of a building, resulting in the collapse of walls and internal structural elements. Older buildings not designed for blast loads are particularly vulnerable and can be completely destroyed or damaged in the event of an explosion. Direct impact, structural collapse, fire, debris, and smoke from an explosion can threaten the occupants, leading to injury or death. The study’s results help identify the best practices for designing structures to withstand the impact of an explosion and protect occupants from harm. The results will provide valuable information for architects, engineers, and building designers, as well as for disaster response and preparedness organizations. The study will contribute to understanding the structural response to blast loads and the influence of the blast on the structure.

Methods for characterization of aggregate pore structure for concrete durability Bharath Melugiri Shankaramurthy, Kejin Wang, Franciszek Hasiuk

Pore structure of concrete aggregate has always been overlooked in the context of concrete durability, especially for concrete transport properties. Aggregate pore structure is relevant in the modern-day infrastructure as there is more demand for durable high-performance concretes (HPC). When the different phases of a HPC (specifically, the paste and interfacial transition zone) are being carefully engineered for their best performance, ignoring the aggregate phase could be riskier for the in-service performance of HPC. As detailed research related to aggregate pore structure characterization is extremely limited to date, the current study explores various simple techniques to bridge this identified gap and extract quantitative information from aggregate pores. Few selected methods are later used to evaluate key pore features (connected and disconnected pore volumes, tortuosity, resistivity) in aggregates. The results indicate a considerable impact of aggregate pores on concrete durability. A summary of potential techniques for aggregate pore structure characterization is also provided to serve as a quick reference guide for selecting a suitable technique to obtain valuable information from aggregate pore network.

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