We have three questions regarding the series of articles on Repair of Fire Damage which appeared in the March, April and May 1972 editions of CONCRETE CONSTRUCTION.
We are an insurance company and we frequently become involved with stave agricultural silos. We usually experience several exposure fires per year as well as fires in which the silo contents burn, usually from spontaneous combustion.
1 . Do the same principles apply to structural strength of nonreinforced concrete such as silo staves
2. What guidelines may be used to determine extent of damage and whether there is need for replacement
3. Is the Portland Cement Association in a position to run tests on damaged staves if a sample is provided?
1. In general the same principles apply for nonreinforced concrete as for reinforced. Strength loss from chemical changes would be about the same for both. Nonreinforced concrete, however, would not be subject to steel restraining forces that can sometimes be damaging.
2. In general, if the surface of the concrete is intact or only peeling superficially, whether blackened with soot or not, the concrete is most likely in satisfactory condition. Fire-exposed staves can be tapped with a hammer and if the sound produced is much like that produced by good staves in a part of the silo not exposed to fire, the staves in question are probably good.Further confirmation might be made by use of an impact hammer. If, however, the concrete appears to be in worse condition than this, some of the further tests described in the April issue (pp 154-159) should be employed.
3. The Portland Cement Association is now able to undertake some kinds of technical service work. Evaluations of whether such work can be undertaken are made by Mr. J. H. Walker, Vice President, Portland Cement Association, Old Orchard Road, Skokie, Illinois 60076.