This Week's Featured Presentation
The Role of Cracking on Corrosion of Reinforced Concrete (ACI Spring 2018 Convention, Salt Lake City, UT) The Role of Cracking on Corrosion of Reinforced Concrete (ACI Spring 2018 Convention, Salt Lake City, UT) Many factors-such as concrete slump, compressive strength, and evaporation rate affect the tendency of concrete to crack. While good construction practices can minimize cracking, the vast majority of flat reinforced concrete structures, such as bridge decks, will develop some degree of cracking, which can lead to early corrosion initiation, durability issues, and rapid deterioration. The majority of these cracks are small-less than 0.01 in. (0.25 mm) in width, and there is some debate about the impact cracks of this size have on the service life of structures, particularly with respect to initiation of corrosion on the reinforcing steel in concrete. Laboratory specimens evaluating corrosion in cracked specimens do exist; however, the cracks in these specimens are usually artificially created (typically with stainless steel shims extending to the level of reinforcing steel) and are wider than 0.01 in. (0.25 mm), sometimes significantly so. This presentation will describe the creation of a settlement cracking test capable of inducing cracks as small as 0.001 in. (0.025 mm) in width over the surface of a reinforcing bar. Initial corrosion initiation tests show early corrosion initiation in specimens with maximum crack widths as small as 0.002 in. (0.05 mm), suggesting that even narrow cracks are potentially detrimental to service life.
October 21 – 27
Performance of Cracked High-Performance Concrete in a Harsh Marine Environment
by Edward G. Moffatt, University of New Brunswick; Andrew Fahim, University of New Brunswick; and Herwing Lopez-Calvo, University of New Brunswick
The Role of Cracking on Corrosion of Reinforced Concrete (ACI Spring 2018 Convention, Salt Lake City, UT) This paper presents the long-term durability performance of cracked concrete containing silica fume and various levels of fly ash, and corrosion inhibiting admixtures exposed to a harsh marine environment for 9 years. Eighteen reinforced concrete prisms (100 x 150 x 1200 mm [3.9 x 5.9 x 47.2 in.]) were placed at the high-tide level at Treat Island, Maine in order to study their resistance to corrosion. The specimens included mixtures with various fly ash contents (0, 20 and 40%) incorporating two commercially available corrosion-inhibiting admixtures (disodium tetrapropenyl succinate and calcium nitrite at 5 and 12.5 L/m3, respectively). All concrete mixtures were cast using a CSA Type GUb-8 (ASTM Type I) cement with 8% silica fume. A water-to-cementitious ratio between 0.37 and 0.42 was used. A crack of approximately 0.25 mm (1/100 in.) was achieved in the tensile region of each beam using a stainless-steel loading frame, as shown in Figure 1. Testing included the determination of compressive strength, bulk electrical resistivity, chloride penetration and electrochemical corrosion monitoring. Chloride penetration results in accordance with ASTM C1556 showed a marked reduction in diffusion coefficient in concrete containing fly ash with respect to the control (0% fly ash). A similar trend was observed in concrete containing disodium tetrapropenyl succinate. The performance of such systems is also highlighted by electrical resistivity and electrochemical measurements. Electrochemical corrosion monitoring showed an improved performance on the corrosion propagation in concrete containing fly ash and corrosion inhibiting admixtures.