MICRO REINFORCEMENT
2. LITERATURE REVIEW
Several attempts have been made by researchers to propose cost-effective alternatives to conventional solid RC slabs. The underlying principle in these alternatives is that portion of Concrete below the neutral axis (Tension Zone) is either eliminated, as in the case of voided, ribbed, grid or waffle slabs are replaced by a relatively cheaper filler material. A brief survey of literature about the alternatives to conventional concrete slab has presented below
Abdul Rahman [1] et.al., carried out research on the feasibility of precast prestressed concrete slab incorporating structural hollow clay blocks in floors and roofs. In this study, the precast slab strips have been tried out on a large scale of the roof of a school building at Adyar in Madras. The total area of the roof was 420 m2. The slab strips were precast in the pre-casting yard. All the precast slab strips had uniform width 0.57 m and 3.80 m spans and thickness 0.83 m and a self-weight of 0.58 kN /m. The slab strips were prestressed in a long line pre-tensioning bed by two 5mm diameter high tensile steel wires, one in each of the two outer longitudinal ribs, and two 4 mm diameter high tensile wires in the middle longitudinal rib. The total initial prestressing force imparted through the four wires was about 8.5 tones.
The concrete used in the precast slab strips had a mix proportion slightly richer than 1: 1.5:3 by weight. The maximum size of aggregate used was 10mm. The hourdi blocks used in the work had an overall cross-section size of 230mm x 830mm with a length of 300mm. The longest one precast slab strip weighs only 2.25kN. The stability of the precast slab strips for large–scale application was further checked by field loading test. After testing, the actual
Umesh S.S and Dr.A.V. Pradeepkumar
http://www.iaeme.com/IJCIET/index.asp 1002 [email protected] ultimate load carried by the composite slab strip was 4.32 kN /m which were in addition to the self-weight of 1.127 kN /m.Sharma [2] et.al., carried out a study on design and construction of precast hollow or ribbed slab. In his study, he developed a simple design procedure based on the ultimate strength design concepts of conventional solid slabs for precast hollow and ribbed slabs has been developed. The variation of the flexural stiffness of the precast hollow trough or cross ribbed structural forms due to the creation of voids has been derived and expressed graphically in relation to conventional equivalent solid slab rigidity. By using, developed formula, judicious balancing of the width of the ribs and thickness of the flanges in relation to the spacing of ribs and effective depth respectively, considerable economy and saving of time in construction can be achieved, aside from obtaining an attractive structure.
This design procedure is limited to short intermediate building spans. Desayi, [3] et.al., focused the research on, an experimental and semi–analytical study on the strength of fibrocement roofing elements tested under symmetric two point loading are presented. Nine trapezoidal – shaped fibrocement roofing elements were cast and tested. The variables included were span / depth ratio, amount of longitudinal reinforcement and the type of mesh wire. Methods of computing cracking load, ultimate flexural strength and deflection have been proposed and the predicted results compared with test results. Load factors based on limiting deflection and limiting crack width are also examined. Paramasivam [4] et.al., carried out the research, to assess the flexural behavior of ferrocement slabs made up of cellular mortar matrix was investigated for possible use as a partial or non-load bearing elements in precast building construction. They studied on variables such as the thickness of the slab, the number of layers of wire mesh and density of mortar are considered to study the cracking behaviour of ductility and ultimate strength of slabs. The effect of inclusions of various volume fractions of short steel fibers was also included in the test programme. Singh [5] et.al., carried out the research to assess the salient features of filler block roofing system, developed at the institute which are non – autoclaved; compared to other types of cellular concrete material available in the country. Hence, use of heavy equipment and machinery and high capital investment for autoclaving are avoided. As the blocks need only curing under atmospheric conditions, the considerable amount of energy is saved. Utilization of fly ash in large quantities for the production of blocks is a major advantage. Therefore, there is a saving in cement, steel and overall cost of construction, compared to conventional in-situ RC slabs for floors and roofs Ambalavanan[6] et.al., carried out research on the effective analysis of alternate one – way floor/roof systems. They did a systematic cost-effectiveness analysis of one – way slabs with filler blocks and partial prefabrication system and the results are compared with that of conventional R.C. slab. The study is aimed at assessing the relative structural performance of alternate roof/floor slab systems adopting limit state design concept with a view of evolving design tables to serve as a ready reckoner for designers. A comparison of the relative cost and reduction in self – weight of these systems has been made for establishing their range of applicability. Jaising [7] et.al., carried out research on A R.C filler slab with non – autoclaved cellular concrete blocks for sustainable construction. In this work, explained about construction technique of the floor/roof cast in situ RC filler slab with non – autoclaved cellular concrete filler blocks. The filler blocks are 110mm thick and 260 x 560 mm at the top tapering down to 250 x 550mm at the bottom. The slab is cast with cement concrete of grade M15. Spanning in two perpendicular directions, the slab can be designed as a grid with compression taken by the deck concrete at top and tension taken by the reinforcement at the bottom of the rib portion. The cellular concrete blocks act as non – structural fillers. The technique can be adopted for floor/roof in single and multistoried residential and other types of buildings. Sheela[8] et.al., carried out research on the ductile behaviour of optimized Ferro cement corrugated flexural elements. In this investigation, an attempt was made to obtain an optimum cross section of the polymer modified corrugated
Investigation on Cost Effective Slab System Having Different Types of Micro Reinforcement
http://www.iaeme.com/IJCIET/index.asp 1003 [email protected] Ferro cement element by an efficient optimization technique like genetic Algorithm. The study reveals that the engineering properties such as energy absorption capacity, ductility, and cracking characteristics of corrugated element can be enhanced with the increase of polymer content and volume fraction of reinforcement. In this experimental work, a total of 75 numbers of 3m length corrugated shaped specimens were prepared in the laboratory.
Adequate care was taken while placing the reinforcement cage over the mould to maintain a minimum cover of 3mm on all sides of the specimen. Reinforcement cage consists of layers of 6 x 22 gauges or 4 x 20 gauge wire mesh with 6 mm skeletal steel bars at junctions, where the mesh changes its direction and is tied well together with the wire mesh. Hand plastering was done for preparing the specimen with and without polymer modified cement sand mortar of ratio 1:2. The specimens were removed from the mould after 2 days wet jute curing and were cured for 28 days by ponding water on the specimen. During testing it was observed that after first crack load for each increment of load, a number of smaller cracks were formed on the flexural zone. Out of these only one crack widened to its maximum width and the specimen failed at maximum load. Deflection is less in specimens having 6 x 22 gauge wire meshes than 4 x 20 gauge wire mesh in lower loads and deflection is more at higher loads.
Sheela[9] et.al., carried out research on predicting the ultimate load carrying capacity of polymer modified Ferro cement flexural elements. This paper reports the flexural behaviour and ultimate load carrying capacity of ferro cement flexural elements having a span of 3m.
The investigation was for i) two cross-sectional shapes: channel and trapezoidal ii)mixes with and without styrene butadiene rubber (SBR) iii) woven wire mesh of 4 x 20 gauge and 6 x 22 gauge and iv) the number of Wire mesh layers. The results indicate that the addition of polymer in the mortar matrix and the use of 4 x 20 gauge wire mesh, instead of 6 x 22 gauge wire mesh, significantly increased the load carrying capacity of the elements. A method for predicting the ultimate load carrying capacity of the ferro cement flexural elements is also proposed. YavuzYardim [10] et.al., Investigated on AAC – concrete light weight precast composite floor slab. In this study, the use of autoclaved Aerated Concrete (AAC) as an in fill material for semi precast panel is investigated experimentally. The effectiveness of proposed light weight slab is reached by comparing the behavior of specimens with that of conventional solid precast slab. The comparisons were based on structural performance and total weight reduction. The composite AAC slabs section chosen are one way slabs with a size of 1m x 3m x 0.13m (width x Length x Depth). The specimens vary in the AAC blocks layouts and total weight reduction ratio. The test results showed that the AAC composite precast panel provides reasonable weight reduction without sacrificing the structural capacity. Ganesan[11]
et.al., carried out research on the effect of steel fibre on the flexural behaviour of simply supported one way SCC slabs. A total number of nine specimens were cast and tested with steel fibers of aspect ratio of 50 and Volume fraction of 0 %, 0.5 % and 0.75 %. The load deflection characteristics, first crack load, ultimate load, crack propagation and widening of cracks were investigated. Addition of fibers enhanced the first crack load and post cracking behaviour. A marginal improvement in the ultimate strength was observed. Ductility and toughness characteristics improved significantly due to the fiber addition. GeethaKumari[12]
et.al., Investigated on Flexural Characteristics of SFRSCC and SFRNC one way slabs. In the present study, a total number of 20 slabs of size (1050 x 500 x 65) mm were cast and tested under flexure. Out of 20 slabs, 10 slabs were cast using steel fibre reinforced Normal concrete (1.0 % Vf) and 10 steel slabs (1.0 % Vf). The grade of concrete used was M40 and M70. Five different variations of tensile reinforcement were considered for SFRNC and SFRSCC. An attempt has been done to produce M40 and M70 grade of SFRSCC reinforced slabs. Under flexure, cracking load, ultimate load, mid-span deflections, the width of crack, strain in steel reinforcement using strain gauge were measured during the testing of specimens. Literature
Umesh S.S and Dr.A.V. Pradeepkumar
http://www.iaeme.com/IJCIET/index.asp 1004 [email protected] survey reveals that the information available on micro reinforcement in cost effective slab system is not reported. Therefore it is proposed to study on the micro reinforcement roofing system.