No abstract

Over the last 20 years, remarkable advances have taken place in the research on reactive powder concrete (RPC). However, because of the high contents of cement and silica fume (SF) usually used in those types of concrete, the cost and environmental impact of RPC is considerably higher than conventional concrete. Hence, the use of supplementary cementitious materials as partial substitution of cement and SF has been an object of great interest by the scientific community. However, the replacement of cement and SF can result in the deterioration of certain properties of RPC, such as the early strength; however, RPC usually needs great amounts of cement and SF. This work presents a study to analyze the effect of metakaolin (MK) as a partial substitute of cement in a previously optimized mixture of RPC using statistical tools such central composite design, main effect plot analysis, and response surface methodology. In addition to MK, supplementary cementitious materials such as SF, limestone powder and recycled glass powder, and fine Type III cement were used. Based on the laboratory experiments results and statistical analysis, it was concluded than MK develops a high activity in the hydration process of RPC, helping it reach high strength at early ages, such as 1 and 7 days, which may be of interest for applications such as the connection of prefabricated elements or accelerated bridge construction. However, the effect of the partial substitution of Type III cement by MK on 28-day compressive strength was nonsignificant. Moreover, the MK inclusion in RPC provides a significant decrease in workability as the amount of MK increases.

The aim of this study is to evaluate the permeation properties of concrete added with a residue of a petrochemical industry located in Colombia, called catalytic cracking catalyst residue (FCC). Concrete samples with 10, 20 and 30 % of FCC incorporated as cement replacement were evaluated. As reference materials, concrete without addition and concrete added with 20 % of metakaolin (MK) were used. MK is a high performance pozzolan of chemical composition similar to the FCC. The properties studied, in addition to the compressive strength, were: water absorption by total immersion, porosity, surface absorption and capillary sorption. The results showed that the concrete added with FCC and MK had similar behavior, and were slightly higher than the control sample. The total absorption and porosity were below 5 % and 10 % respectively for all samples; this means that the incorporation of the addition reduces the permeability of concrete. In this sense, FCC is considered as a good alternative for producing more durable concrete, being the optimum percentage, 10 % cement replacement.Keywords: Fluid catalytic cracking, metakaolin, pozzolanic additions, blended concrete, permeation properties, durability. RESUMENEl objetivo de este estudio es evaluar las propiedades de permeación de concretos adicionados con un residuo de una industria petroquímica localizada en Colombia, llamado residuo de catalizador de craqueo catalítico (o FCC, por sus siglas en inglés). Se evaluaron concretos con 10, 20 y 30 % de FCC incorporado como reemplazo del cemento. Como materiales de referencia se utilizaron concreto sin adición y concreto adicionado con 20 % de metacaolin y una puzolana de alto desempeño que presenta composición química similar al FCC. Además de la resistencia a la compresión, las propiedades estudiadas fueron la absorción de agua por inmersión total, la porosidad, la absorción superficial y la absorción capilar. Los resultados mostraron que los concretos adicionados con FCC y MK tuvieron un comportamiento similar, y fueron ligeramente superiores a la muestra control. La absorción total y la porosidad estuvieron por debajo del 5 % y 10 %, respectivamente para todas las muestras, esto significa que la incorporación de la adición contribuye a una menor permeabilidad. En este sentido, el FCC se considera una buena alternativa para producir concretos durables. A su vez, se recomienda utilizar un porcentaje del 10 % como reemplazo del cemento.Palabras clave: Catalizador de craqueo catalítico, metacaolín, adiciones puzolánicas, concreto adicionado, propiedades de permeación, durabilidad.