09 A Manual for Precast Systems
Volume II - Localized Ferrocrete System for Slabs, Lintels and Steps
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Ritwik Behuria UA5617
Ritwik Behuria | UA5617
Introduction A Modern Precast Flooring System, known as The Barrett System, was introduced in the year 1930 as an experimentational method for ease of supervision due to a lack of skilled workers available on site. Traditional in-situ construction techniques had certain limitations due to workmanship errors and supervision inefficiencies. As a result, the Barrett modern flooring system strived to minimise these errors, while being more economical in its production due to reduced cross sections. Incidentally, the system used 46% less construction materials as compared to conventional RCC slab construction methods. The precast system comprises of precast reinforced concrete units with semi-circular arched cross sections at the bottom and flat surfaces on top. Each unit was prepared in a nearby depot, saving up on transportation costs. The arches allowed the units to be lightweight and provided thermal insulation and helped improve the spatial acoustics to an extent. The lengths of the units were made according to the desired spans, with bearing on opposite walls. The series of arches act as beams for spanning, whilst acting in compression in the transverse direction. Additionally, the system resists compression without the need for using reinforcements in that direction. Over the years, the concept of the flooring system has evolved and has become widely popular. Innovations in the making of these units have also allowed newer systems to come about. The Barrett system, being an experimentational system, was not documented to a good extent and its relevance in the presentday context cannot be validated. Consequently, The precast flooring systems this study focuses on are the hollow core precast flooring system and the ferrocrete precast flooring system, with the latter being extensively illustrated in the scope of this manual. Both of these systems are used in urban and rural contexts in the current scenario, and their extent of usage depends on parameters like regional demand and structural system used in the building. The intent of the manual is to illustrate the steps of Precast systems for local masons in a language anyone can comprehend, i.e., visuals. A kit of parts and sequence of assembly have been laid out in a way that skilled or unskilled masons can execute the system on the basis of the instructions illustrated.
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Volume I The Hollow Core Precast Flooring System For Urban and Industrial Context (Not included in this manual)
The Hollow Core flooring system involves precast and prestressed concrete modules, manufactured using steel casting molds. This system helps in contributing towards passive thermal comfort of the building. The flooring system is durable, and its applications are viable for all scales of infrastructures. Furthermore, this flooring system also facilitates large unsupported spans; thereby reducing the need for intermediate horizontal or vertical members. This system is fairly ubiquitous and standardized, allowing for the production process to happen away from the site, reducing noise emissions and waste production.
Volume II Precast Ferrocrete Slab and Lintel System For Rural/Remote Context The Precast Ferrocrete system involves significantly lesser usage of materials than a conventional slab system. This system can be implemented in very remote areas, as there are nominal transportation costs and a simple kit of parts involved. The system only requires four easy-to-carry shutter types which can be used to create GI reinforced U-shaped panels. These panels need 60% lesser cement and 70% lesser steel reinforcements than a conventional slab. Additionally, the U-panels can be inverted and have reinforcements to be further used as lintels for openings, or be used as seating with bearings on opposite walls. The same can also be cast as steps for a staircase shaft. The panels are cast close to the site based on requirement, implying lesser wastage. Furthermore, the preparation of these can be executed by basic skilled labourers, which also reduces dependency on multiple agencies. The flooring system can provide unsupported spans up to eighteen feet, which can further be enhanced through more GI reinforcements in their making. The production process can also be implemented away from the building site, but requires a higher level of supervision than a conventional precast slab as it is more labour intensive and requires supervision to a
Figure 1. Hollow Core Precast System A commonly used system for modern-day precast flooring, widely used with frame structures
Figure 2. Ferrocrete Panels as Lintels, Chajjas The U-panels can be inverted and be poured with RCC to be used as lintels for openings
Figure 3. Ferrocrete Panel being cured Due to their U-shape, they can be cured for days with the same poured water, reducing wastage
Figure 4. Ferrocrete Panels as Roofing With a bearing of six inches, these panels can be continuously placed along the shorter span of spaces
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Sequence of assembly Preparation of shutter - Transportation of the MS Shutters to site - Rod bending of the U-shaped GI reinforcement grids for each shutter - Cleaning and greasing of the shutters Preparation of the panels - Composition of concrete mix for pouring into the shutter - Vibrating and checking for honeycombing - Placement of MS Hooks onto freshly cast panels - Curing for 2-3 days Placement of panels - Crane-lifting of panels onto roof level, followed by manual adjustment on site - Running a reinforcement grid over the adjoined panels - Pouring mortar+Flooring as specification
Composition + Parts - Four Aluminium Shutters : - ( 9’-0” x 1’-0” ) - ( 9’-0” x 1’-6” ) - ( 4’-0” x 1’-0” ) - ( 4’-0” x 1’-6” ) - Tools/Machines : - Rod bending setup - Fine-tip Vibrator - JCB/Crane/Tractor - RMC Mixer - Cement mix : - Lime - Sand - Waterproof Cement - 6mm, 8mm, 12mm fine and course aggregates - Ancillary Components : - Steel bent hooks - Leveler (preferably Aluminium) - Grout/sealant - Grease
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Kit of Parts Fig. 5. Aluminium Custom Clamps
9’-0” X 1’-6”
Fig. 6. MS Turnlocks
4’-0” X 1’-6”
9’-0” X 1’-0”
Fig. 7. MS Reinforcement Hooks
4’-0” X 1’-0” Fig. 9. Aluminium Shutters (Sets of 3)
Fig. 8. Wooden Beading Pattis
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Placement of Shutters Fig. 10. Placement Sets of Aluminium shutters are brought to site and assembled based on the panel schedule specified in the drawings. This is followed by inserting wooden pattis on the inner edge of the shutters
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Greasing of Shutters Fig. 11. Greasing Once the shutters are put in place, a layer of grease is applied to the inner surfaces of these shutters for easier removal post casting of the panel.
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Placement of Shutter Lock Fig. 12. Shutter Lock A custom-made MS Shutter lock is fixed at a marked point on the shutter to demarcate the end of the panel. Shutters of 9’ and 4’ lengths allow for panel sizes of various lengths to be cast with the help of this shutter lock.
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Reinforcement Bar Bending Fig. 13. Bar Bending As the shutters are prepared, the process of bar bending for the reinforcement grid is done simultaneously before the pouring is done.
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Positioning the Rebar Grid Fig. 14. The Reinforcement Grid When the shutter is ready and the reinforcement grid is made according to measurements, the grid is placed into the inner side of formwork, using either cover blocks or aggregates as spacers.
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Locking + Clamping shutters Fig. 15. Locking the Shutters The MS shutter lock is re-adjusted after the reinforcement grid is in place, and then it is locked in place with the turnscrews.
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Making the Concrete Mix Fig. 16. Preparation of Concrete Mix Post the placement of the reinforcement grid, an M20 concrete mix is prepared, mostly manually in remote regions, or using an RMC on the basis of budget and availability.
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Pouring & Smoothening Fig. 17. Pouring and Smoothening The mixed cement is poured into the shutters that are ready. This is checked for honeycombing using a fine tip vibrator and then smoothed using an aluminium patti.
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Placement of Hooks Fig. 18. Placement of Hooks On the freshly poured concrete, MS hooks are inserted on the center of the panel. These hooks later act as anchors for the flooring to be laid out above. Hence, this process is only required when the panels are used as a slab and not as a lintel.
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Shutter Rotation & Removal Fig. 19. Shutter Removal After a few days, the shutters are removed. The entire setup is first rotated upside down with the help of ropes, followed by the removal of turnscrews and the shutters.
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Curing the Panel for 2-3 days Fig. 20. Curing the Panels Using local site paraphernalia like bricks, the ends of panels are shut and water is filled in for a few days for curing, this allows for constant curing without supervision, along with minimal wastage of water.
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Erecting FC Panels on Site Fig. 21. Erection of Panels A Crane is involved when all the roof panels are cast. Lintels are manually put up using scaffolding, but roof panels require machinery for being erected on-site.
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Passing a Grid through Hooks Fig. 22. Grid for Flooring Post the erection of all roof panels, an MS reinforcement grid is laid out through the hooks. This acts as a base for the flooring above. As a result, the time and labour required for tying GI wires and laying cover blocks is reduced.
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Finished Flooring on Panels Fig. 23. Finished Flooring Once the entire grid is set up, the scaffolding used for the masonry is used to send batches of cement onto roof level. This is then used to lay out mortar and flooring according to specifications.
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Fig. 24. Other Applications
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Reference List
List of Figures
1. Indian Concrete Journal (Ed.). (1930, August). The Barrett System of Precast Units. Modern Flooring, 229-232.
Fig. 1., Hollow Core Precast System, British Precast Flooring Federation, 2019 Fig. 2., Ferrocrete Panels as Lintels, Ritwik Behuria, 2020 Fig. 3., Ferrocrete Panel being cured, Ritwik Behuria, 2020 Fig. 4., Ferrocrete Panels as Roofing, Ritwik Behuria, 2021 Fig. 5., Aluminium Custom Clamps, Ritwik Behuria, 2022 Fig. 6., MS Turnblocks, Ritwik Behuria, 2022 Fig. 7., MS Reinforcement Hooks, Ritwik Behuria, 2022 Fig. 8., Wooden Beading Pattis, Ritwik Behuria, 2022 Fig. 9., Aluminium Shutters (Sets of 3), Ritwik Behuria, 2022 Fig. 10., Placement, Ritwik Behuria, 2022 Fig.11., Greasing, Ritwik Behuria, 2022 Fig. 12., Shutter Lock, Ritwik Behuria, 2022 Fig. 13., Bar Bending, Ritwik Behuria, 2022 Fig. 14., The Reinforcement Grid, Ritwik Behuria, 2022 Fig. 15., Locking the Shutters, Ritwik Behuria, 2022 Fig. 16., Preparation of Concrete Mix, Ritwik Behuria, 2022 Fig. 17., Pouring and Smoothening, Ritwik Behuria, 2022 Fig. 18., Placement of Hooks, Ritwik Behuria, 2022 Fig. 19., Shutter Removal, Ritwik Behuria, 2022 Fig. 20., Curing the Panels, Ritwik Behuria, 2022 Fig. 21., Erection of Panels, Ritwik Behuria, 2022 Fig. 22., Grid for Flooring, Ritwik Behuria, 2022 Fig. 23, Finished Flooring, Ritwik Behuria, 2022 Fig. 24., Other Applications, Ritwik Behuria, 2022
2. British Precast Flooring Federation. (2019, August). Hollowcore Floor Systems. www. precastfloors.info. https://www.precastfloors. info/Precast/media/BPMediaLibrary/ Publications/Hollowcore-Floor-Systems_1. pdf?ext=.pdf