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The density of concrete varies, but is around 2,400 kilograms per cubic metre (150 lb/cu ft). [1] Reinforced concrete is the most common form of concrete. The reinforcement is often steel rebar (mesh, spiral, bars and other forms). Structural fibers of various materials are available.
The addition of 1 kg/m 3 of polypropylene fibers to concrete has been shown to reduce spalling during a simulated fire. [44] (The improvement is thought to be due to the formation of pathways out of the bulk of the concrete, allowing steam pressure to dissipate. [44]) Another problem is the effectiveness of shear reinforcement.
The applied reinforcement yield stress is = 500 N/mm². The mass density of the reinforcing bars is 7800 kg/m 3. In the table is the computed brittle material stress. is the optimised amount of reinforcement.
Modern tests show that opus caementicium had as much compressive strength as modern Portland-cement concrete (c. 200 kg/cm 2 [20 MPa; 2,800 psi]). [23] However, due to the absence of reinforcement, its tensile strength was far lower than modern reinforced concrete, and its mode of application also differed: [24]
Rebar (short for reinforcement bar or reinforcing bar), known when massed as reinforcing steel or steel reinforcement, [1] is a tension device added to concrete to form reinforced concrete and reinforced masonry structures to strengthen and aid the concrete under tension.
The parts are in terms of weight – not volume. For example, 1-cubic-foot (0.028 m 3) of concrete would be made using 22 lb (10.0 kg) cement, 10 lb (4.5 kg) water, 41 lb (19 kg) dry sand, 70 lb (32 kg) dry stone (1/2" to 3/4" stone). This would make 1-cubic-foot (0.028 m 3) of concrete and would weigh about 143 lb (65 kg). The sand should be ...
Where K c is an experimentally derived constant between 0 and 1. This range of values for K c reflects that particle reinforced composites are not characterized by the isostrain condition. Similarly, the tensile strength can be modeled in an equation of similar construction where K s is a similarly bounded constant not necessarily of the same ...
The High Speed 1 tunnel linings incorporated concrete containing 1 kg/m 3 or more of polypropylene fibers, of diameter 18 & 32 μm, giving the benefits noted below. [16] Adding fine diameter polypropylene fibers, not only provides reinforcement in tunnel lining, but also prevents "spalling" and damage of lining in case of fire due to accident. [17]