Calcium nitrites

Table 5.3 The effect of calcium nitrite on strength development ...

Admixture formulations containing two or more compounds (multicomponent) in which each component plays a specific role or compliments the corrosion resistance capacities of the other are also used. For example, a mixture of calcium nitrite and calcium formate is used to both accelerate strength of the concrete and inhibit corrosion of the steel during steam curing. 

The most widely used anodic inhibitors are calcium and sodium nitrite, sodium benzoate and sodium chromate. With the exception of calcium nitrite, no other chemical is available in North America as a proprietary product. Nitrites have been used in the USA for more than 14 years and for nearly 40 years in Europe. Calcium nitrite is marketed as a non-chloride accelerator, as well as a corrosion inhibitor. For 25-30% solids in solution, dosage rates range from 2 to 4% by weight of cement depending on the application [50]. Calcium nitrite has been used in bridges, parking and roof decks, marine and other prestressed concrete structures that are exposed to chloride attack. 

Fig. 6.9 Weighted total corrosion of concrete with 2% calcium nitrite (NACE International, reprinted with permission).

Table 6.8 Dosage requirements for calcium nitrite at different chloride levels (Berke and Weil)...

Two types of calcium nitrite-based corrosion inhibitors are currently marketed, viz. a set- and strength-accelerating type and a normal-setting type. The former increases the early strength development in concrete. This effect increases with the dosage. Both admixtures are compatible with all types of Portland cements and... 

Although molybdate compounds have been advocated for corrosion inhibition purposes they have not been used as inhibitors in concrete practice. Experiments to ascertain the synergistic effect of a calcium-nitrite- sodium-molybdate combination (4.5 parts to 1 part) on corrosion of steel in concrete [64] showed that at the inhibitor-chloride ratio of 1 11 the combined admixture protected steel from corrosion and that it was more effective than when calcium nitrite was used alone. 

Sodium benzoate has been used singly in concrete structures exposed to severe corrosion attack and also in combination with sodium nitrite in cement slurries to paint on steel reinforcement before embedment in concrete [65, 66]. Work done by Lewis et al. showed that concrete to which 2% benzoate was added produced setting times that were similar to control concretes, but the compressive strengths decreased by about 40% [66, 67]. Lewis et al. [66] however have concluded that sodium benzoate has a more persistent inhibitory effect than calcium nitrite. 

Chin, D. (1987). A Calcium Nitrite-Based Non-Corrosive, Non-Chloride Accelerator, ACI SP-102, 49-77. 

Gaidis, J.M., Rosenberg, A.M. and Saleh, I. (1980). Improved Methods for Determining Corrosion Inhibitors by Calcium Nitrite in Concrete, ASTM, STP 713, 64-74. 

Virmani, Y.P., Clear, K.C. and Pasko, T.J. (1983). Time to Corrosion of Reinforced Steel in Concrete Slabs, Vol. 5, Calcium Nitrite Admixtures or Epoxy Coated Reinforced Bars as Corrosion Protective Systems, FHWA-RD-83-012, FHWA, US Department of Transportation, 71. 

Corrosion inhibitors, like calcium nitrite, are accelerators and depending on their dosage may cause rapid slump loss and shorten the setting time when added at the batch plant. 

CORROSION MITIGATION IN REPAIR CONCRETE MIXES (ACCELERATED SETTING IN CONCRETES CONTAINING CALCIUM NITRITE AND... 

Calcium nitrite (IHiO) [13780-06-8] M 150.1. Crystd from hot water (1.4ml/g) by adding ethanol and cooling. 

Fig. 82.—Solubility Fig. 83.—Solu- Fig. 84.—Solubility of Calcium Nitrite. bility of Stron- of Barium Nitrite, tium Nitrite.

P. 0. Ray and N. R. Dhar also measured the electrical conductivities of soln. of the three nitrites and P. C. Ray and 8. C. Mukherjee observed that the degrees of ionization of soln. of calcium nitrite at dilutions t =28-0 and 19-4 litres are respectively 0-84 and 0-82 for strontium nitrite at dilutions v—22-0 and 21-0 litres, 0-84 in both cases and for barium nitrite for c=21-0 and 31-4 litres, respectively 0-84 and 0-86. 

BaAg2(N02)4.H20, from a soln. of the component salts. The formula is here due to M. Oswald, who examined the three nitrites of the alkaline earths, and found only barium forms a double salt. The conditions of stability are represented by AB, Fig. 85. The corresponding diagrams for strontium and calcium nitrites do not show any evidence of the formation of silver strontium nitrite, or of a silver calcium nitrite nor is any strontium barium nitrite formed, for the two salts give a series of mixed crystals, (Ba,Sr)(N02)2.H20. 

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