CONCRETE AS A FIRE-RESISTANT.
The report of the committee on reinforced concrete formed under the auspices of the Royal Institute of British Architects deals with concrete in respect of its constitution, its treatment, and its uses in building construction. As a fire-resistant it is the subject of the following notes: (a) Floors, walls, and other construction in steel and concrete formed of incombustible materials prevent the spread of fire in varying degrees, according to the composition of the concrete, the thickness of the parts, and the amount of cover given to the metal, (b) Experiment and actual experience of fires show that concrete in which limestone is used for the aggregate is disintegrated, crumbles and loses coherence when subjected to very fierce fires, and that concretes of gravel or sandstone also suffer, but in a rather less degree. The metal reinforcement in such cases generally retains the mass in position, but the strength of the part is so much diminished that it must be renewed. Concrete in which coke-breeze, cinders or slag form the aggregate is only suoerficially injured, does not lose its strength, and in general may be repaired. Concrete of broken brick suffers more than cinder concrete and less than gravel or stone concrete, (c) The material to be used in any given case should be governed by the amount of fire resistance required as well as by the cheapness of, or the facility of procuring, the aggregate, (d) Rigidly attached web-members, loose stirrups, bent-up rods, or similar means of connecting the metal in the lower or tension sides of beams or floor-slabs (which sides suffer most injury in case of fire) with the upper or compression sides of beams or slabs not usually injured, are very desirable, (e) For main beams covering of i’ Tin. to 2-in. of concrete’over the metal reinforcement appears from experience in actual fires to afford ample protection to the structural parts. In floor-slabs the cover required may be reduced to i in. All angles should be rounded or splayed to prevent spalling off under heat. (f) More perfect protection to the structure is required under very high temperature, and, in the most severe conditions, it is desirable to cover the concrete structure with fife-resisting plastering which may be easily renewed. Columns may be covered with cokebreeze concrete, terra-cotta, or other fire-resisting facing.