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.

Two important properties of calcium nitrite are that it is an accelerator and a corrosion inhibitor when used as an admixture in concrete. With its performance as an accelerator enhanced, calcium nitrite can be used as an effective non-corrosive, non-chloride accelerator in normal and fly ash concrete. The calcium nitrite-based accelerator provides good accelera-tion in initial setting times at 50°F (10°C) and 72°F (22°C) produces a significant improvement in compressive strengths at early ages. Electrochemical solution tests can be used to conduct a quick screening test to determine the potential corrosivity of a non-chloride accelerator. Potential and linear polarization resistance measurement tests provide a quick indication regarding the potential corrosivity of a non-chloride accelerator.

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

The availability of separately ground granulated iron blast-furnace (GGBF) slag, as a separate cementitious material or supplement, has prompted new research on its effects on concrete properties. One area in which GGBF slag has particular promise in concrete is its ability to alter the permeability characteristics of concrete to the extent that its resistance to chloride intrusion is significantly improved. This paper discusses the ability of GGBF slag-cement mixtures to reduce the potential detrimental effects of chloride intrusion into concrete. Three test methods for chloride penetration were used and the results of each are discussed. The following conclusions were developed. 1. Significant reductions in permeability are achieved as the replacement level of the slag increases from 40 to 65% of total cementitious material by mass. 2. The permeability of concrete containing GGBF slag is less affected by increases in water-cement ratio than concrete containing regular portland cement alone. 3. The detrimental effects of accelerated curing on the permeability of concrete are virtually eliminated with cement blends containing GGBF slag greater than 50%. 4. Concrete containing GGBF slag may require less depth of cover to protect the reinforcing steel than those concretes using portland cement alone.

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.