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- Thermal performance of concrete with reactive magnesium oxide as an alternative binderPublication . Forero Valencia, Javier Andres; Bravo, Miguel; Pacheco, João; Brito, Jorge de; Evangelista, LuisThis study evaluates the thermal conductivity of concrete produced with reactive magnesium oxide (MgO) as a partial replacement for cement. MgO is a viable option for the concrete industry, mainly due to its benefits in sustainability and reducing CO2 emissions compared to cement emissions. Four different MgO's produced in Australia, Canada, and Spain were used in concrete mixes as a partial replacement of cement at 5%, 10%, and 20% by mass. The experimental results showed that the thermal conductivity is higher when MgO increases in mixes after 28 days of curing. With the incorporation of MgO, the thermal conductivity increased between 3.2% and 10.2%, and the mechanical properties declined: compressive strength between 12.7% to 26.2%, splitting tensile strength between 9.7% to 34.0%, and modulus of elasticity between -4.1% to 7.8%. Finally, it is important to highlight that the addition of different contents of MgO in the concrete mixes modified the microstructure of the cement matrix. As a result, there was an increase in porosity, which negatively influenced the mechanical properties and thermal conductivity. Therefore, the relationships between these properties were also analyzed.
- Use of bottom ash additions in the production of concrete with recycled aggregatesPublication . Raposeiro Da Silva, Pedro; Silva, Rui V.; Brito, Jorge deThis paper provides a literature review on the use of bottom ashes in the production of concrete with recycled aggregates. Three types of bottom ash were studied, namely: biomass bottom ashes, coal bottom ashes and sewage sludge bottom ash. The characterization of these ashes focused on the analysis of their physical, chemical, and mineralogical properties. The effect of these ashes was subsequently studied on the fresh, mechanical, and durability-related performances of concrete. Bottom ashes generally present lower pozzolanicity than that typically observed, for example, in coal fly ashes. Their use as partial cement replacement normally leads to some loss in performance of the resulting cementitious composites. Also, using them as aggregates or in combination with recycled aggregates of other sources similarly causes an overall loss in performance. Nevertheless, such decline is still acceptable and often within manageable limits for the production of concrete under specific conditions including some structural applications. The use of these by-products including recycled aggregates may assist in solving a two-fold problem. Firstly, it reduces the consumption of cement and, consequently, the extraction of natural resources, also including the decrease of the consumption of natural aggregates to produce concrete. Furthermore, it solves the problem of the final destination for the significant quantities of bottom ashes produced by different industrial processes. In general, it is possible to conclude that, in moderate contents and when adequately processed, bottom ashes can be considered as viable substitutes of cement with manageable losses in terms of mechanical and durability-related performances. The use of coal bottom ashes was also found to significantly reduce the drying shrinkage strain of concrete.