Partially Precast RC Joist and Brick Panel roofs/slabs

 

A.    INTRODUCTION TO PRECAST RC JOIST & BRICK PANEL SLAB/ROOF

In India, the technology to be adopted for housing components should be such that the production and erection technology be adjusted to suite the level of skills and handling facilities available under metropolitan, urban and rural conditions.

The reinforced brick panel is such an option for your roof/floor construction. This technology uses brick panels with reinforcement bars as fillers between the partially precast joists and deck concrete over it. The roofing panels can be easily prefabricated at the site. This technique of roofing has been utilised in the construction of thousands of affordable and energy efficient (wrt. conventional system) houses all over India. Not only itself it is a cost effective technology for roofing but saves on the cost and time of form erection and rebar requirement may also reduce for the deck slab.

The construction of the slab is similar to other beam and composite panel systems comprising of deck concrete laid over distribution reinforcement. Brick being lighter than concrete it makes the structure light and the slab exhibits similar live load carrying capacity as of in-situ slab. The precast brick panel of size 1150 x 530 x 75 mm weighs 75 kg and the partly precast joist about 15 kg/m.

Prefabricated brick panels are made by a combination of concrete, bricks and rebars. These prefab brick panels are placed on partially precast RC joists supported on walls/beams. Here the RC joist acts as a T-beam.

The system consists of

  1. Prefab brick panels.
  2. Partially precast RC joists.
  3. Topping/screed concrete.
B.    MATERIAL SELECTION

Prefab brick panels

  • Bricks confirming to IS: 2180 and having compressive strength >40 N/mm2 to be used.
  • Length: Maximum panel length to be 1.2 m. For further economising your structure, panel length to be decreased to 0.9 m.
  • Width: to be 530 mm for conventional burnt clay bricks (230x110x75) and 450 mm for panel of modular bricks (190x110x75)
  • Longitudinal joints: thickness to be 40 mm to accommodate 6 dia rebar with adequate cover.
  • Transverse joints: thickness to be 15-30 mm depending on the brick size.

 

Partially precast RC joist

  • The joist shall be designed as a composite T-beam with 35 mm thick flange concrete.
  • The width of the joist shall support two successive spans of brick panels.
  • Width: minimum 130 mm, which can be increased as per required for structural strength.
  • Depth: minimum 100 mm for a joist span upto 4200 mm.

 

Reinforcement bars

  •  Precast Brick panel: Reinforcement conforming to IS: 432 to be used for designing the panel. Conventionally for brick panels, 2 bars of 6 mm embedded in the longitudinal joints.
  • Precast RC joist: Reinforcement conforming to IS: 14142 to be used for designing the joist.
  • Cover: minimum 15 mm for the brick panel and 25 mm for joist rebars to be maintained.

 

Moulds for precast elements

  •  Mould to be made on site of seasoned good quality timber for small applications.
  • For mass housing projects, it is recommended to have steel/FRP which are non absorbents and non-corrodible materials. These also saves the fabrication time and construction time is shortened.

 

C.    CONSTRUCTION PROCEDURE 

 

Fig 1: Construction procedure: RC joist and brick panel slabs

 

 

D.     ADVANTAGES

  • By adopting this method of roof construction, you can save on approx. 20-25% of your total slab concrete cost. Also the centering and the shuttering cost is also eliminated giving a total saving of approx. 25-35% on the overall slab cost.
  • Time is saved by the use of precast elements which are casted off-site during the course of foundations being laid. The finishes and services can be done below the slab immediately. While in the conventional in-situ RCC slabs, due to props and shuttering, the work cannot be done, till they are removed. Thus, saving of time attributes to saving of money.
  • In conventional methods, the shuttering gets damaged due to its repetitive use because of frequent cutting, nailing etc. On the other hand, the mould for the precast components can be used for large number of repetitions thereby reducing the cost of the mould per unit.
  • In the panel and joist system, similar types of components are produced repeatedly, resulting in increased productivity and economy in cost too. It results in faster execution, more productivity and economy.
  • In panel and joist system, the work at site is reduced to minimum, thereby, enhancing the quality of work, reliability and cleanliness.
  • Efficient utilization of natural resources/raw materials which are energy intensive and thus adding an attribute in the list of Green and sustainable building technologies.
  • Service’s installations should be planned during the construction if not exposed.
  • Decrease in high energy consuming materials also helps to reduce the Embodied Energy of virgin materials and save the production of Green House Gases (GHG’s) into the atmosphere.

 

 

E.    IMAGE GALLERY: RAT TRAP BOND COURSES

 

Image 1 : Partially precast RC joists (picture taken from BMTPC website)

 

 

Image 2: Prefab brick panels. (picture taken from BMTPC website)

Image 3: Laying of panels over the joists. (picture taken from BMTPC website)

Image 4: Ceiling view of RC joist and prefab brick panel slab. (picture taken from BMTPC website)

 

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