Synergistic effects of ASR and fly ash on the corrosion characteristics of RC systems

Abstract This research investigated the synergistic effects of fly ash and aggregate reactivity on chloride transport and time to corrosion. Specimens containing fly ash replacement levels of 0, 20, and 40% by weight with and without reactive aggregate were exposed to wetting/drying cycles. Expansion, corrosion potential, and macrocell current were measured monthly until corrosion of the embedded reinforcement initiated. The results indicate that inclusion of fly ash in specimens containing non-reactive aggregate results in lower apparent diffusion coefficient values ( D a ) and lower critical chloride threshold values ( C T ) in concrete. The benefits from the lower D a values are more significant than the disbenefits from the reduction in C T when assessing time to corrosion initiation. Specimens containing reactive aggregate and 20% fly ash exhibited longer times to corrosion initiation than specimens containing 40% fly ash. Results indicate that the ASR gel resists the transport of chlorides and the formation of small amounts of ASR gel in the specimens containing 20% fly ash reactive aggregate results in slower transport rates and longer times to corrosion initiation.

[1]  Farshad Rajabipour,et al.  How does fly ash mitigate alkali–silica reaction (ASR) in accelerated mortar bar test (ASTM C1567)? , 2013 .

[2]  D. Hausmann,et al.  STEEL CORROSION IN CONCRETE -- HOW DOES IT OCCUR? , 1967 .

[3]  Raoul François,et al.  Development of chloride-induced corrosion in pre-cracked RC beams under sustained loading: Effect of load-induced cracks, concrete cover, and exposure conditions , 2015 .

[4]  E. Garboczi,et al.  Percolation and pore structure in mortars and concrete , 1994 .

[5]  Michael D. A. Thomas,et al.  Modelling chloride diffusion in concrete: Effect of fly ash and slag , 1999 .

[6]  Ueli Angst,et al.  Critical Chloride Content in Reinforced Concrete: A Review , 2009 .

[7]  Michael D.A. Thomas,et al.  The effect of fly ash composition on the expansion of concrete due to alkali-silica reaction , 2000 .

[8]  Sidney Diamond,et al.  Effects of two Danish flyashes on alkali contents of pore solutions of cement-flyash pastes , 1981 .

[9]  Hans Beushausen,et al.  Corrosion in cracked and uncracked concrete – influence of crack width, concrete quality and crack reopening , 2010 .

[10]  J. Gillott,et al.  Mechanism of alkali-silica reaction and the significance of calcium hydroxide , 1991 .

[11]  Karen L. Scrivener,et al.  Microstructural Gradients in Cement Paste Around Aggregate Particles , 1987 .

[12]  J. Ideker,et al.  Influence of Alkali-Silica Reaction Reactivity on Corrosion in Reinforced Concrete , 2017 .

[13]  Michael D.A. Thomas,et al.  Use of ternary blends containing silica fume and fly ash to suppress expansion due to alkali-silica reaction in concrete , 2002 .

[14]  Xinying Lu,et al.  An experimental study on the properties of resistance to diffusion of chloride ions of fly ash and blast furnace slag concrete , 2000 .

[15]  Kimberly E. Kurtis,et al.  Assessment of binary and ternary blends of metakaolin and Class C fly ash for alkali-silica reaction mitigation in concrete , 2010 .

[16]  M. Pourbaix Atlas of Electrochemical Equilibria in Aqueous Solutions , 1974 .

[17]  J E Gillott,et al.  EFFECT OF CA(OH)2 ON ALKALI-SILICA REACTION , 1991 .

[18]  K. Byfors,et al.  Influence of silica fume and flyash on chloride diffusion and pH values in cement paste , 1987 .

[19]  Jan Olek,et al.  Alkali–silica reaction: Kinetics of chemistry of pore solution and calcium hydroxide content in cementitious system , 2015 .

[20]  Michel Pigeon,et al.  Influence of the interfacial zone on the chloride diffusivity of mortars , 1997 .

[21]  Tamon Ueda,et al.  Simulation of Chloride Diffusivity for Cracked Concrete Based on RBSM and Truss Network Model , 2008 .

[22]  U. H. Jakobsen,et al.  Composition of alkali silica gel and ettringite in concrete railroad ties: SEM-EDX and X-ray diffraction analyses , 1996 .