Effects of two non-chloride accelerating agents -- sodium thiocyanate and calcium nitrate -- in time to achieve initial set of two brands of Type I cement were determined at 70 F (21 C) and 40 F (4 C). Results with these two non-chloride accelerators were compared with results with calcium chloride, the conventional accelerator. Tests show:Low or moderate dosages of the two non-chloride accelerators can reduce time to achieve initial set by l-2 hr.- Any one of the three accelerators may be more effective with one ce-ment than with another cement having similar setting characteristics without accelerators In general, all three of the accel-erators are more effective at 40 F than at 70 F.

Usually concrete is an ideal environment for steel. Reinforcing Steel in most concrete structures is not subject to corrosioin. However, when salts (chlorides or sulfates) penetrate concrete and reach steel rebars, corrosion becomes active. Rust takes up a larger volume than the iron from which it is formed, developing pressure as great as 5000 psi within the concrete. This pressure causes cracking and spalling. Ultimately, failure occurs and major repair or replacement is needed. Once salts (from deicing, bleaching, marine environment, foreign aggregate etc.) contaminate concrete, corrosion progresses rapidly. Penetrants, sealants, surface coatings, and membrane barriers are useless in combatting the effects of salts already in concrete. The use of cathodicprotection to control corrosion on reinforcing steel in concrte is relatively reinforcing steel in concrete is relatively new. Although cathodic protection has been employed on pipelines, offshore cathodic protection has bee employed on pipelines, offshore platforms, ship hulls, buried tanks, etc. for more than 40 years, its use on concrete bridge decks was initiated only in the early 70's. Since the development of conductive coatings (1980-82) the effectiveness of cathodic protection has been enhanced.It has become easier to install and is now applicable to many different types of concrete structures (i .e ., docks; harbor facilities marine terminals; bridge substructures such as piers, pier caps, and beams; bulkheads; parking garages; industrial water and waste treatment plants; tunnels coastal buildings, etc. acceptance ofconductive coating cathodic protection continues to grow , new applications develop. This new form of an established technique holds extraordinary promise for large-scale preservation of concrete structures. (SP-102

A method for evaluation of the corrosion potential of chemical admixtures is presented. The method allows the direct measurement of the macrocell corrosion current between two layers of electrically connected reinforcing bars embedded in concrete. By ponding the specimens with chloride-free water, the potential of the chemical admixture to instigate corrosion can be evaluated. By using a chloride-containing ponding solution, in particular a 15% NaCl solution, it may be possible to assess the potential corrosion inhibiting effects of certain chemical admixtures. The test method was used to compare the corrosion activity in reinforced concrete slabs containing a normal dosage rate of calcium chloride, plain concrete and concrete containing two dosage rates of a multicomponent calcium nitrate based non-chloride accelerator. Only the slabs containing calcium chloride exhibited corrosion when ponded with tap water. When subjected to cyclic ponding with the salt solution, both the plain concrete and the concrete slabs containing the two dosage rates of the non-chloride accelerator exhibited corrosion. However, the slab containing the higher dosage rate of the non-chloride accelerator exhibited only 25% of the corrosion activity of the other two slabs. It is speculated that this reduction may be the result of corrosion-inhibiting effects of the non-chloride accelerator when it is added at sufficient rates.

The wide variety of disciplines involved with the corrosion of steel in concrete has caused difficulties in communication. Each discipline has its own terminology; at times two disciplines use conflicting terms or explanations for the same phenomenon. This paper addresses some areas of such confusion, and presents chemical mechanisms to explain half-cell potentials and causes for chloride-induced corrosion. Examples of such corrosion are presented.

During the past few years, there has been a dramatic change in the atti-tude of specifiers and concrete technologists toward the use of calcium chloride in concrete. Traditionally, admixtures containing chlorides have been banned from use in prestressed concrete, and increasingly it has been recognized that they should not be used in concrete over galvanized metal decks. In 1977, ACI Committee 201 in the Guide to Durable Concrete rec-ommended the limits shown in Table 1 for the water-soluble chloride ion con-tent of concrete, expressed as a percentage of weight of the cement. In 1983, the ACI Building Code 318-83 adopted the similar, but somewhat more liberal, limits in Table 2.