Chloride Diffusion in Blended Cement Concrete Made with Quartzite Recycled Aggregate
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Chloride Diffusion in Blended Cement Concrete Made with Quartzite Recycled Aggregate Claudio J. Zega1,2, Yury A. Villagrán-Zaccardi1,2, Ángel A. Di Maio1,2 1 LEMIT, 52 e/121 y 122, (1900) La Plata, Argentina 2 CONICET, Argentina ABSTRACT Using waste materials as aggregate for new concrete production is a growing tendency, because of several environmental problems. Recycled coarse aggregate (RCA) obtained from crushing waste concrete has lower density and greater absorption than natural aggregate, because of the higher porosity of the mortar attached to the RCA particles. Compressive strength level achieved in recycled concrete may be similar to that of conventional concrete. On the other hand, durable performance of recycled concrete is variable, and diverse evidence can be found in literature for different durability issues. In this paper, chloride ingress in conventional and recycled concrete, made with quartzite aggregate and blended Portland cement is evaluated when immersed in NaCl solution. Two strength levels (21 and 35 MPa) and two contents of RCA (25 and 75%), as substitute of natural quartzite aggregate, were considered. The chloride diffusion coefficient and the relationship between water-soluble chloride and bound chloride are analyzed.
INTRODUCTION Using waste materials as aggregate for the production of concrete has gained importance because of the shortage of natural resources and environmental problems caused by storing waste from building demolition. Recycled coarse aggregate (RCA), obtained from crushing waste concrete, has different characteristics than those of natural coarse aggregate (NCA), such as greater absorption and lower density. These differences are attributed to the mortar from original concrete attached in RCA particles, which is more porous than the natural rock. The use of RCA for new concrete production in replacement of NCA can modify some properties of concrete, especially those associated with durability. However, a compressive strength level similar to those of conventional concrete may be obtained, even with a percentage of RCA as high as 75% [1]. Regarding chloride penetration in particular, recycled concrete (100% RCA) having similar or slightly higher chloride penetration rate than that of equivalent conventional concrete (100% NCA) has been reported [2, 3], but differences between recycled and conventional concrete decreasing with increasing strength level have also been informed [4]. A fraction of the total chloride content that penetrates into concrete is bound by cement hydration products, and only some of it remains in the pore liquid (free chloride). This last fraction of chloride content is responsible for the depassivation of reinforcement. Blended Portland cement (BPC) has lower clinker content than ordinary Portland cement. Limestone filler and slag may be included in BPC up to 35%. Limestone filler does not offer pozzolanic activity, but it increases early hydration rate. Slag is a pozzolanic latent hydraulic admixture additive that offers nucleation sites for e
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