International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 04 Issue: 07 | July -2017
p-ISSN: 2395-0072
www.irjet.net
Effect of Controlled Permeable Formwork on Concrete Syed Afzal Basha1, K Mallikarjuna Reddy2, C G Mohan Babu3, K Anand4 Associate Professor, G Pullaiah College of Engineering & Technology, Kurnool Assistant Professor, G Pullaiah College of Engineering & Technology, Kurnool ---------------------------------------------------------------------***--------------------------------------------------------------------1
2, 3, 4
Abstract - In recent years the number of reinforced concrete structures experiencing premature deterioration has grown considerably. It is worth noting that in many cases the structures in question were constructed less than 20 years ago. However, most were designed with an anticipated design life of approximately 100 years. This has forced governments to make provisions in routine maintenance budgets for structural rehabilitation, a process that is both expensive and also disruptive to the travelling public. This paper shall compare concrete cast against conventional Impermeable Formwork (IMF) and demonstrate how a Controlled Permeability Formwork (CPF) liner can reduce initial construction costs, whilst at the same time achieving durability, through the natural enhancement of the near surface cover. The quality of the surface zone of concrete is a crucial factor for durable concrete structures, as it is the first line of resistance to penetration of aggressive agencies. Use of controlled permeable formwork (CPF) liner is one of the techniques employed to improve the quality of the surface zone of concrete. CPF line drains mix water and entrapped air from the near surface of concrete while retaining cement and other fine particles. This helps to reduce water-cement ratio, increase cement content and decrease surface pores in the surface zone of concrete. It is postulated that CPF drains air and water, which migrate towards the formwork due to vibration caused while compacting concrete and hydrostatic pressure. Key Words: Concrete, Controlled permeable formwork, Structure, Properties
1. INTRODUCTION Permeable formwork is a special class of lined formwork intended to produce improvements in the strength and durability of the surface of concrete. The bracing and the liner in the formwork are engineered to resist the pressure of plastic (or fresh) concrete, but to allow trapped air and excess water to pass through and be removed during concrete placement and consolidation. The objective in using permeable formwork is to eliminate voids (bug holes) on the surface of the concrete and to increase the strength and durability of the concrete surface immediately behind the formwork. The quality of the surface zone of concrete is important for reinforced concrete elements, as all the aggressive agents penetrate through the surface zone of concrete to initiate damage. Durability of concrete structure Š 2017, IRJET
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Impact Factor value: 5.181
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is primarily dependent on the characteristics of surface zone of concrete. To facilitate the process of placing and compaction of fresh concrete, it is necessary to increase the volume of free water slightly above that actually required for complete hydration of cement. It had been postulated that the mix water and the entrapped air would migrate towards the formed surface due to compaction and hydrostatic pressure of concrete. As the formed surface is impermeable the water and air are retained at the interface. This causes an increase in water-cement (w/c) ratio at the surface level of concrete and visually the most obvious sign of presence of blowholes, pinholes and surface blemishes following removal of the formwork. The net result of this process would modify the surface zone of concrete with higher w/c ratio and lower cement content than that had originally been contemplated. In other words, the surface zone of concrete would be of poorer quality compared to the bulk concrete. On the contrary, a well compacted dense concrete surface zone is invariably preferred to enhance the durability of RC structures.
2. LITERATURE REVIEW Philip G. Malone [1] Absorptive or permeable formwork behaves as a filter that allows air and water to escape from the concrete that is directly behind the formwork. The concrete is retained by the filter medium (often a woven or nonwoven fabric); however, air, water, and materials dissolved in the water and very fine suspended solids can escape from the concrete adjacent to the formwork. The water draining through the liner contains a variety of dissolved and fine suspended materials. The liquid extracted from cement paste typically is a saturated calcium hydroxide solution with a pH in the range of 12.5 to 13.5. The fine suspended material can include cement particles, with an average size of 10 Îźm, and fine mineral admixtures, such as silica fume with an average size 0.1 Îźm. Cuicui Chena [2] The concrete surfaces resulting from CPF were blow-hole free with no blemishes but the control one, corresponding to the inner sides of the conventional steel mould walls, presented many blow-holes. Strength from rebound method of concrete from CPF was improved more than 10% than control one. Water sorption and chloride ion penetration of concrete could be restrained if the concrete was casted using CPF due to the denser surface. Pore structure of concrete surface from CPF was modified remarkably, compared with the control one. The porosity of 0-3mm slice was reduced from 10.48% of the Control sample ISO 9001:2008 Certified Journal
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