KEYWORDS:

SHORT DESCRIPTION:

• These prefabrication techniques for ceilings were designed to achieve strong and durable constructions of qualities approaching those of reinforced concrete, but with considerably less cement.

• Ceilings and roofs can be constructed without or with considerably less timber formwork, than is required for standard reinforced concrete constructions. Saving on timber not only reduces costs, but also helps to conserve the rapidly diminishing forests.

• The materials and constructions are capable of withstanding all kinds of destructive agents in the same way as reinforced concrete.

• However, the main precondition for the implementation of these techniques is the availability of good quality bricks and tiles, a requirement that may not always be fulfilled by local brick production in rural areas.

Further information: Bibl. 00.12, 00.41, 21.03, 21.07, 21.09, 23.12.

Reinforced Brick / Tile Panels

FIGURE

• The brick / tile panels described here were developed in India.

• In principle, the panels are made by assembling bricks or tiles on an appropriate surface, laying reinforcing rods in the longitudinal joints and bonding the components with mortar. Reinforced concrete joists of relatively small cross-section are precast in lengths corresponding to the roof span. These are placed manually on top of the walls at distances slightly greater than the length of the panels. The joists are propped and the panels arranged in parallel across them. Reinforcing rods are laid along and at right angles to the joints. A 1: 3 (cement: sand) mortar is filled in the joints and concrete spread about 30 mm thick over the panels, thus forming a T-beam structure, with the deck concrete acting as the flange.

• The flat panels, developed by the Central Building Research Institute in Roorkee, are made of standard burnt bricks, forming 75 mm thick panels of 560 mm width and lengths of 1040 or 1200 mm.

• Similar panels have been developed at ASTRA, Indian Institute of Science in Bangalore. Extruded hollow tiles are used instead of solid bricks, thus reducing the dead load. The tile height of 50 mm also reduces the panel thickness while the tile dimensions of 250 x 125 mm result in panel sizes of 400 x 800 mm and 400 x 1050 mm with 9 and 12 tiles respectively.

• Arched panels can also be produced and used for ceilings. They are capable of carrying greater loads than the flat panels, but need more deck concrete to even out the curvature for the floor above.

Structural Clay Joist and Filler Elements

FIGURE

• An extruded structural clay unit, which by virtue of its shape is used both as Joist and filler elements, has been developed at CBRI, Roorkee. The dimensions of the unit are 16.5 x 15.0 x 19.0 cm. It has three rectangular cavities, and the outer faces have grooves for better bonding of mortar and concrete.

• The prefabrication of a joist is done by laying the fired clay units end to end on a flat surface, in a row of desired length, with the wider base below, and joined with a 1: 3 (cement: sand) mortar. Two wooden planks, cleaned and oiled are placed on either side and held together with clamps. The gaps between the clay units and planks are filled with concrete, in which reinforcing rods are embedded. The planks can be removed after 45 to 90 minutes, depending on the weather conditions; the joists are water-cured for 7 days and air-cured for 21 days, before use.

• When constructing the ceiling or roof, the joists, which weigh about 80 - 90 kg, are inverted and laid manually in parallel lines, at distances of 30 cm (centre to centre). For rigidity and levelling, they are placed on levelling pads of cement-sand mortar, and temporarily propped where necessary. The structural clay units, with their wider base below, are laid between the joists as filler units, ensuring that the joints in the joist member and filler units are broken (by using half length units at the ends). The joints and gaps are filled with mortar, reinforcement and concrete, as in the prefabrication of the joists, and the completed slab kept wet for 14 days, before finishing the floor surface.

Reinforced Concrete - Brick Composite Beams

FIGURE

• In order to reduce the need for timber formwork, which is becoming increasingly expensive and environmentally unacceptable, in view of the rapidly depleting forests, a substitute for reinforced concrete beams was developed at Chulalongkorn University in Bangkok.

• U-section clay tiles are laid in a row of required length and bonded together with cement-sand mortar, thus forming a channel. Longitudinal steel bars and stirrups are placed in the channel, which is subsequently filled with concrete. One or more layers of structural clay bricks (wetted from all sides) are laid in between the stirrups, forming the centre portion of the beam. The joints are filled with cement-sand mortar. The top compression zone can comprise another row of U-section tiles filled with concrete.

• Alternatively, this top layer (and even the centre portion) can be completed after installing the beam, which is lighter and can be placed manually. The top layer can also be integrated in a cast-in-place floor slab, producing a T-beam structure.

• In addition to the simplicity of construction, the composite beams have been found to cost 11 - 35 % less than reinforced concrete beams of the same dimensions and reinforcement.

(Source: Bibl. 21.09)