Predicting Chloride Profiles in Concrete

Abstract

concentration in the vicinity of steel reinforcing reaches a critical value, corrosion commences. The corrosion rate increases as Clconcentration increases. A concentration of 0.6 kg/m 3 to 0.9 kg/m 3 (1 Ib/yd 3 to 1.5 Ib/yd 3 ) is sufficient to initiate corrosion. Major damage can be expected when the concentration reaches 6 kg/m 3 (10 Ib/yd 3 ). 1-3 Use of a high-quality mix (low water-to-cement [W/C] ratio and high cement factor) and provision of adequate concrete cover over reinforcing steel are the first approaches to increase longevity of concrete. [4][5][6] Clingress into concrete can be modeled by a diffusion process. 1,7-20 Furthermore, the diffusion coefficient (D eff ) can be calculated from the rapid Clpermeability 20 measured according to ASTM C 1202 21 (the ASTM equivalent of AASHTO T277). 22 The AASHTO method essentially determines the electric conductivity of the pore solution. Because conductivity of the pore solution depends on mobility of the ions in the solution, the conductivity is related directly to D eff . 17 Consequently, this noninvasive electrochemical procedure can be used to estimate D eff . This eliminates the need for time-consuming determinations of local Clconcentrations in concrete samples.One problem with this procedure is that the presence of certain admixtures that contain ionic salts increases rapid Clpermeability values, although no change occurs in concrete permeability. Calcium nitrite (Ca[NO 2 ] 2 ), a widely used corrosion inhibitor, is one of these ionic admixtures.Two equations relating rapid Clpermeability to D eff were presented, one for concrete with and the other for concrete without admixed Ca(NO 2 ) 2 . ABSTRACTLaboratory studies were undertaken to compare chloride (Cl -) profile data to predictions obtained using ASTM C 1202 of Cldiffusion into concrete. The effective diffusion coefficients (D eff ) derived can be used to determine long-term Clprofiles of concrete structures. Equations relating D eff with resistivity and permeability of concrete were developed. One-and twodimensional models were used to determine Clprofiles of Clions entering concrete in structures such as square piles and decks.

Environmental Degradation of Reinforced Concrete

“…Chemical admixtures are usually added to improve handling of the fresh concrete or enhance performance of the hardened concrete. A similar reduction is noted in the apparent diffusion coefficient for chloride as shown for mortars 4,5 and for concrete, 6,7 Note that fly ash and silica fume additions result in an even lower apparent diffusion coefficient than just adding additional cement. These materials are typically added to enhance hardened properties of the concrete.…”

“…23,24 Additional means of reducing the ingress of chloride into concrete involves the addition of pozzolans or ground blast furnace slag. 6 When chloride ingress is modeled as a function of w/c 1 p and pozzolan contents for various geometries and environmental exposures, times to corrosion in excess of 25 years are difficult to achieve for low permeability concretes. Several conference proceedings document the positive benefits of these materials.…”

Anion capture and exchange by functional coatings: New routes to mitigate steel corrosion in concrete infrastructure

“…However, even at 5 mol Cl − /L, representative of exposure to concentrated seawater [89,90], the 30 % CN CAC layer delays corrosion by 6.7 times relative to OPC concrete. In this case, NO 3 − release due to ACE is revealed to be the critical parameter in delaying corrosion.…”

Effect of Chlorides on Reinforcing Steel Exposed to Simulated Concrete Solutions

“…Fick's second law of diffusion in one direction has been used frequently to evaluate diffusion of chlorides through concrete. [24][25] It has been proposed that the chloride levels required to initiate corrosion in concrete are between 0.61 kg/m 3 and 0.89 kg/m 3 . 26 This would be ≈ 333 ppm to 500 ppm of chloride.…”