Journal Apr 2024

Characteristic strength and behavior of steel plate reinforced concrete beam with and without crank bar Prakash Mondal, Amiya Kumar Samantam Dilip Kumar Singha Roy

Investigations have indicated that the inclusion of a prefabricated cage significantly enhances the flexural strength, ductility, and deformation characteristics of prefabricated cage ceinforced composite (PCRC) Beams. The confinement offered by the prefabricated cage demonstrates notable improvements in the aforementioned structural properties of the composite beams based on experimental studies. This study explores the impact of substituting internal embedded tension bars with an external steel plate welded to the prefabricated cage on crack patterns, ultimate strength, and load-deflection behavior of plate-reinforced concrete beams, both with and without crank bars. The experimental investigation involves flexural testing of 1600 × 100 × 150 mm concrete beam specimens. A series of four experiments, each comprising three concrete beams, aims to discern the most cost-effective structural approach concerning ultimate strength. Results indicate that beams reinforced with external steel plates exhibit behavior akin to composite sections until reaching ultimate loads, with failure predominantly occurring through the yielding of the external plate rather than plate separation. Utilizing this method for reinforcement showcased a remarkable 8-10% increase in ultimate load compared to the control beam.

Surface quality of concrete enhanced through controlled permeable formwork - a review S. Kandasamy, P. Gowdhamramkarthik, G. Arun Kumar, J. Vijayaraghavan, J. Thivya

Controlled permeability formwork liner (CPF) is a novel approach for improving the concrete cover zone’s quality. This method is used to keep tiny cement and sand particles in place while removing excess water and trapped air from the surface of freshly laid concrete. The concrete’s surface zone consequently has a higher cement content, a lower surface porosity, and a lower water to cement ratio. CPF action produces a smooth and even surface and also free of pinholes, blow holes and other flaws. The quality of surface concrete can be increased by utilisation of CPF and destructive agencies won’t be able to find an easy way into the concrete to damage it. Even though this technology marginally raises the initial construction costs, the increased durability achieved through the use of a CPF system may result in lower structural life cycle costs. However, by use of CPF liner the service life of concrete is enhanced by 2.3-2.5 times compared with conventional concrete. This paper presents a review on the use of CPF to enhance the quality of the surface of concrete, principle of its function, types and cost implication.

Flexural characteristic and cost analysis of ferro-cement composite beams Supran Chakravarty, Mrinal Kanti Sen, Girija T. R.

The construction industry has a pressing need to identify a dependable and cost-effective element as an alternative to conventional reinforced concrete. As a result, ferro-cement has emerged as a promising solution. Its exceptional qualities as a construction material have been thoroughly validated through numerous theoretical and experimental investigations that have taken place across the globe over the course of many years. The endeavour to locate a dependable and more economical alternative in the construction sector instigated the adoption of ferro-cement. This study endeavours to investigate the flexural behavior of both reinforced cement concrete and ferro-cement beams utilizing M30 grade concrete, with the primary objective of conducting a thorough examination of the subject matter. Additionally, the investigation delves into crucial aspects such as ultimate load capacity, deflection characteristics, and the analysis of crack patterns. Moreover, a comprehensive comparison is drawn regarding the total costs incurred for each of the specified types of beams. It is noteworthy that the doublelayer Ferro-cement variant, due to its enhanced resilience and potential to serve as a cost-efficient substitute for traditional concrete beams, emerges with discernibly superior flexural strength. This study serves as a testament to the continuous evolution of construction materials and techniques, showcasing the ever-persistent drive to enhance structural performance while optimizing costs.

Formwork removal time for concrete members using nominal mixes at different temperatures Siddharth Shankar, Kumar Neeraj Jha, Amarjit Singh

A critical factor in the construction of reinforced cement concrete (RCC) structures is the timing of the safe removal of formwork. This time can be forecast using the maturity of concrete techniques and principles. Numerous academic publications suggest that formwork should be removed from the flexural members of RCC structures when concrete achieves at least 70 % of design strength. Early formwork removal might result in significant deformations or even failure. Nevertheless, delaying removal can cause construction delays that impact the profitability of the construction company and the use of the facility by the owner. Various countries’ codes, guidelines, and standards suggest stripping-time periods of different elements of RCC structures from twelve hours to thirty days. However, according to experiments conducted by authors, formwork for vertical concrete members must be stripped between 6 hours and 5.5 days, depending on the types of cement used and temperature ranges of 0°C to 45°C. Depending on the grade of the cement used and if the surrounding temperature is 45°C or 0°C, the time required to remove horizontal formwork ranges from 2.6 days to 124.4 days. Care must be taken when removing the formwork to prevent overstressing and damaging the concrete, especially when the ambient temperature is below 15°C. This is because many standard codes of practice are silent on the stripping time when the temperature is below 15°C. According to laboratory results conducted in this study at IIT Delhi, nominal mix cement concrete must have a compressive strength greater than 3.50 MPa to remove the vertical formwork in concrete made with ordinary Portland cement (OPC) and 3.25 MPa for Portland Pozzolana Cement (PPC).

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