Published on 18 Apr 2022. Written by Koustubh Prem
Retard-bonded prestressed concrete has been in use since twenty year and is a new and distinctive prestressed system. Mechanical and service property
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of retard-bonded prestressed concrete members are studied. For the research, retard-bonded prestressed strands are made mechanically.
Experimental research and theoretical analysis of three retard-bonded partially prestressed concrete T-beams have to be carried out under static loadings. The law of crack development and distribution both with the relationship between load and maximum crack width have to be studied.
Project Description:
According to concrete construction technologies, post prestressed concrete is divided into two prestressed systems, including un-bonded prestressed concrete and bonded prestressed concrete. Retard-bonded post prestressed concrete absorbs the strong points of both un-bonded and bonded in traditional post prestressed concrete while overcoming the weak points. Un-bonded prestressed system when retard-bonded prestressed concrete is constructed, and after construction, retarding material that is wrapped in tendons starts to coagulate and harden slowly, reaching the same effect with bonded prestressed system.
The controlling crack width plays an important role in the design of the prestressed concrete members which is usually used under service load with multiple-crack. Because if the cracks width are greater than the allowable values in the specifications, it will bring serious security problems to partially prestressed concrete members, especially in the readily corrosive and hostile environment.
Project Implementation:
The implementation of this project starts with following simple steps:
Three retard-bonded partially prestressed concrete T-beams and two traditional partially prestressed concrete T-beams should be made. All having the same cross-section and concrete mix ratio.
Specific Length, span and span-depth ratio must be fixed.
The prestressed tendons in test are steel strand with characteristic value of tensile strength of 1860.
Spacing between the bars must be fixed appropriately. for ex- stirrup spacing of 200mm and 100mm for bending interval. Cover being 15mm.
Analytical process of fracture distribution is done by application of loads at various points
Experiment must be carried taking 1/3rd of the span at regular interval for the whole span.
Then crack width must be measured with 50 times optical microscope.
One can observe that the crack closing moments were related to development of crack width, the bending moment at which the pre-compressive stress vanishes at extreme fiber of the critical section, exposure effect of fracture face and the load-keeping time. The greater development of crack width was, the bigger compressive resistance of concrete produced by exposure effect of fracture face.
Project Analysis:
The first application of external loads occurs in the analysis with the application of the cracking load. It is assumed that the member first cracks at the maximum moment section when the tensile capacity of concrete is exceeded. When the load is increased, the first cracks generally occurs in the pure bending interval of experimental specimens. But the crack width will be small.
Cracking moments of these beam specimens are related to effective prestress, that is larger effective prestress, the larger cracking moments, otherwise, the smaller cracking moments. The crack closing moments are generally related to development of crack width, the bending moment at which the pre-compressive stress vanishes at extreme fiber of the critical section, exposure effect of fracture face and the load-keeping time.
Kit required to develop Crack Width of Retard:
