Corrosion resistance and chloride diffusivity of volcanic ash blended cement mortar K.M.A. Hossain * , M. Lachemi Department of Civil Engineering, Ryerson University, 350 Victoria Street, Toronto, ON, Canada M5B 2K3 Received 17 December 2002; accepted 27 October 2003 Abstract This article reports the results of an investigation on the chloride diffusivity and corrosion resistance of volcanic ash (VA) blended cement mortars with varying curing times of up to 1 year. The mortars had 20% and 40% VA as cement replacement and water/binder ratio of 0.55. The accelerated chloride ion diffusion (ACID) test was used to calculate the chloride ion (Cl  ) diffusion coefficient (D i ) of the mortars using the Nernst– Plank equation for steady state condition. In addition, electrical resistivity, mercury intrusion porosimetry and differential scanning calorimetry (DSC) tests were conducted. Electrochemical measurement such as linear polarization resistance was used to monitor the corrosive behavior of the embedded steel bars. The chloride ingress into the mortars was also studied. Good correlations were found among D i , total pore volume (TPV) and electrical resistivity of the mortars. It was also found that blending cement with VA significantly reduced the long-term D i and hence increased the long-term corrosion resistance of mortars. This fact was also supported by the presence of lower quantity of Ca(OH) 2 and higher quantity of Friedel’s salt in the VA blended mortars as observed from the DSC tests. Mortars with 40% VA showed better performance in terms of Cl  diffusivity, chloride ingress and passivation period of embedded steel compared with the control mortar with 0% VA. D 2004 Elsevier Ltd. All rights reserved. Keywords: Volcanic ash; Chloride ion diffusion; Pore volume; Electrical resistivity; Differential scanning calorimetry; Steel corrosion; Blended cement mortar 1. Introduction The search for alternative binders or cement replacement materials had been continued for the last decades. Research had been carried out [1–8] on the use of volcanic ash (VA), volcanic pumice (VP), fly ash (FA), pulverized-fuel ash (PFA), blast furnace slag, rice husk ash, silica fume, etc., as cement replacement material. The VA, VP, PFA and FA are pozzolanic materials because of their reaction with lime (Ca(OH) 2 ) liberated during the hydration of cement. Amor- phous silica present in the pozzolanic materials combines with lime and forms cementitious materials. These materials can also improve the durability of concrete and rate of gain in strength and reduce the rate of liberation of heat, which is beneficial for mass concrete. The reactivity of FA has been found to depend on the mineral substitution in the glassy silica structure. FAs containing high amounts of calcium oxide have both cementing and pozzolanic activities while those containing mainly aluminum oxide and iron oxide as the major minerals substituted in the structure of the silica glass only have pozzolanic activity. Studies had been published concerning the effect of FA on concrete porosity and resistivity [9], pore solution chemistry [10], oxygen and chloride ion (Cl  ) diffusivity [9–13], carbonation rates [14], passivation [15] and corrosion resistance [16], espe- cially chloride-induced corrosion. Comprehensive research had been conducted over the last few years [1,17 – 19] on the use of VA and VP in cement and concrete production. The meaningful use of such volcanic debris can transform them into natural resources and not only can provide low-cost cement and concrete but also can help to decrease environmental hazard in volcanic areas of the world. Research results suggest that the man- ufacture [1] of blended Portland VA cement (PVAC) and Portland VP cement (PVPC) similar to Type C Portland cement and Type FC Portland FA cement (PFAC) is possible with maximum replacement of up to 20%. 0008-8846/$ – see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconres.2003.10.021 * Corresponding author. Tel.: +1-416-979-5000x7867; fax: +1-416- 979-5122. E-mail address: ahossain@ryerson.ca (K.M.A. Hossain). Cement and Concrete Research 34 (2004) 695 – 702