Question

The ‘Slab’ is an important element of building structure. In Palestine we have traditional slabs known as ‘Hollow Block Ribbed Slabs’, and ‘Solid Slabs’. In these slabs, traditional formwork and traditional materials such as ‘Hollow block’ were being used.

In recent days; other types of slabs using different techniques and materials were used in few projects in Palestine. These types were considered as ‘contemporary issues’, relating to special techniques in slab construction.

Discuss what these types of slab are; showing its features and you can make photos for these slabs if possible.

Answer 1

Hollow core slab :

It is a type of precast slab through which cores are run. Not only do these cores decline slab self-weight and increase structural efficiency but also act as service ducts. It is suitable for cases where fast constructions are desired.There is no restriction on the span of the hollow core slab units, and their standard width is 120mm and depth ranges from 110mm to 400mm.The slab units are commonly installed between beams using cranes and the gaps between units are filled with screeds. It has been observed that, hollow core slab can support 2.5 kN/m2 over a 16m span. It is suitable for offices, retail or car park developments.

Features: Hollow core slabs have minimal deformation even with high slenderness ratios due to the transversal load distribution and even when the elements do not have any concrete topping. The produced elements have high load resistances thanks to a low water/cement ratio of concrete from 0.32 to 0.38.

Hardy Slab :

It is constructed using hardy bricks which significantly decline the amount of concrete and eventually the slab’s self-weight. The thickness of hardy slab is commonly greater than conventional slab and around 270mm.The construction of hardy slab involves formwork installation, hardy block placement, placement of reinforcement into gaps between blocks, placement of steel mesh on the blocks, and finally pouring of concrete.

Features :

It is economical for spans of length up to 5m, and it reduces the quantity of concrete below neutral axis, and moderate live loads shall be imposed. It is constructed at locations where the temperatures are very high. The application of this type of slab can be seen in Dubai and China.

Bubble Deck Slab

It is constructed by placing plastic bubbles which are prefabricated and the reinforcement is then placed between and over plastic bubbles and finally, fresh concrete is poured. The plastic bubbles replace the ineffective concrete at the center of the slab.

Features :

Bubble Deck slabs reduce weight, increase strength, larger spans can be provided, fewer columns needed, no beams or ribs under the ceiling are required. Consequently, not only does it decline the total cost of construction but it is also environmentally friendly since it reduces the amount of concrete.

Precast Slab :

Precast concrete slabs are cast and cured in manufacturing plants, and then delivered to the construction site to be erected. The most outstanding advantage of the preparation of slabs in manufacturing plants is the increase in efficiency and higher quality control which may not be achieved on site.The most commonly used precast slabs are the channel and double-T types. They can be used for spans up to 15m. The double-T slabs vary in sizes and spans up to 15m have been used.The tongue-and-groove panel could vary in size based on the design requirement. When they are placed, the tongue of one panel is placed inside the groove of adjacent panel.With regard to the cost of precast slabs, it is reported that precast concrete slabs are cheaper than cast in situ concrete slab by approximately 24%.

Features :

Precast concrete structures provide superior resistance to fires, natural disasters, insects and mold. Like no other building material, its resistance to rain, wind damage, earthquakes, termites and decay provides lower maintenance and insurance costs.

Solid Slabs

Solid slabs are prestressed concrete elements that have a constant cross section. They are manufactured using high tensile strength prestressed strands or single wire which are embedded within the element.the production of these elements is achieved using our Slipformer or Wet Casting machines that cast an element continuously on a long production bed without the need of any formworks.

Solid slabs are used as floor elements in residential, social and commercial construction which require a slab with a high level of loading, high fire resistance and good acoustic and thermal insulation.To ensure adequate fire resistance the slab can be manufactured with a different configuration of the lower part to give a greater concrete covering of the steel mesh.

Advantages of Solid Slab Bridges: Such type of decks has the following advantages over other type of superstructures: i) Formwork is simpler and less costly. ii) Smaller thickness of deck thereby reducing the height of fill and consequently the cost of the approaches.

These are the slabs used in new type of constitutions.

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