E. Zornoza

Corrosion Behavior of Steel Reinforcement in Concrete with Recycled Aggregates, Fly Ash and Spent Cracking Catalyst

The main strategy to reduce the environmental impact of the concrete industry is to reuse the waste materials. This research has considered the combination of cement replacement by industrial by-products, and natural coarse aggregate substitution by recycled aggregate. The aim is to evaluate the behavior of concretes with a reduced impact on the environment by replacing a 50% of cement by industrial by-products (15% of spent fluid catalytic cracking catalyst and 35% of fly ash) and a 100% of natural coarse aggregate by recycled aggregate. The concretes prepared according to these considerations have been tested in terms of mechanical strengths and the protection offered against steel reinforcement corrosion under carbonation attack and chloride-contaminated environments. The proposed concrete combinations reduced the mechanical performance of concretes in terms of elastic modulus, compressive strength, and flexural strength. In addition, an increase in open porosity due to the presence of recycled aggregate was observed, which is coherent with the changes observed in mechanical tests. Regarding corrosion tests, no significant differences were observed in the case of the resistance of these types of concretes under a natural chloride attack. In the case of carbonation attack, although all concretes did not stand the highly aggressive conditions, those concretes with cement replacement behaved worse than Portland cement concretes.

Electronic and Electrolytic Conduction of Cement Pastes with Additions of Carbonaceous Materials

Additions to concrete may change some of its basic properties in several ways depending on the nature of these additions. The addition of fibers, in particular, has enabled new concrete characteristics, making standard concrete a very modern composite material. If the fibers are electrical conductors, the properties that change in addition to the mechanical ones, are the thermal and electrical conductivities. The results indicate that the arrangement of the electrodes and the electrode-material interface are relevant, because the use of sponges between electrode and concrete prevents the contact between the metallic electrode and the carbon material which ends in different values of electrical resistance with and without sponges. Moisture conditions, that critically influence the electrical resistance of concrete without additions, resulted, also very relevant when conductive substances are present in the matrix. If the proportion of the carbonaceous addition, that lowers significantly the resistivity, is to be quantified, the best procedure seems to measure in dry concrete (0 % relative humidity) with sponges or, alternatively, wet concrete (100 % relative humidity) with silver painted electrodes (without sponges).