amine curing agents for epoxies is required for this invention the first type comprises triethylene glycol diamines and tetraethylene glycol diamines these materials are sold as jeffamine u00ae edr 148 triethyleneglycoldiamine and jeffamine u00ae edr 192 tetraethyleneglycoldiamine by texaco chemical company the second type of amine curing agent comprises polyoxypropylenediamines and may be represented by the general formula str2 wherein x ranges from about 2 to about 33 specifically the following commercial products are available from texaco chemical company individual multiple products from both types of amine curing agents may be combined for purposes of this invention any accelerator known to those skilled in the art may be useful in this invention if it does not detract from the properties or the system a particularly preferred accelerator is designated accelerator 399 accelerator 399 is a mixture of piperazine and 5 10 n aminoethylpiperazine in triethanolamine it is described in u s pat no 4 189 564 to h g waddill because of the relative cost it is desirable to minimize the amount of binder in any composition to achieve this end while maintaining a product of acceptable quality the aggregate combination must be chosen to yield the smallest void volume the aggregate formulation used in the example is based on the results of the publication optimization of polymer concrete for flame spread specimens by troy madeley technical memorandum no 2 university of texas austin.