Information is presented on prestressed concrete. Benefication of aggregate by heavy-media separation, elastic fractionation and hydraulic jugging and benefication of sand through attrition are discussed. Currently a reexamination of the effect of maximum size aggregates is being made, and significant results to date are included. The use of water-reducing, set-retarding admixtures is sometimes advantageous. Their application and use, together with precautions to be considered, are described. Thermosetting plastics, principally epoxy resins, have great versatility.