Browsing by Author "Lopez, Mauricio"

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    (33, 33) Navarrete, Ivan; Vargas, Felipe; Martinez, Patricia; Paul Quiroz, Álvaro Rafael; Lopez, Mauricio; 33
    The reduction in fly ash production in coal-fired power plants has created an opportunity to explore alternative types of fly ashes previously deemed unfit for use in concrete. In plants using flue gas desulfurization (FGD) processes, fly ash could contain high amounts of sulfur oxides, making its use in concrete inadvisable. However, the type of sulfur compound present in a fly ash strongly impacts its performance in concrete. In this study, two types of fly ash were used to evaluate the effect of sulfur oxides on mortar mixtures incorporating fly ash as supplementary cementitious material (SCM); one from an FGD unit, with high sulfur oxide content (in the form of hannebachite), and the other generated in a system without FGD, with negligible sulfur oxide. Calorimetry results show that hannebachite can effectively control C3A hydration similar to gypsum; however, its presence in FGD fly ash does not induce deleterious expansion associated with internal sulfate attack in mortars. TGA and XRD analyses suggest that hannebachite has lower reactivity than sulfate. Hannebachite not only maintains the pozzolanic reactivity of the fly ash, but its fineness may promote OPC hydration, increasing compressive strength. The results of this study indicate that FGD fly ash can be used as an SCM, allowing more sustainable concrete production.
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    (33, 33) Paul, Alvaro; Murgadas, Sofía; Delpiano, José; Moreno-Casas, Patricio A.; Walczak, Magdalena; Lopez, Mauricio; 33
    Internal curing (IC) of concrete by pre-wetted lightweight aggregate (LWA) is an established technology to assist cement hydration and reduce shrinkage and cracking in concrete. However, the current understanding in what makes a certain LWA effective for IC gives opportunities to improve the technique. The aim of this article is to identify the moisture transport mechanisms within an LWA that govern IC performance. Results on LWA of different internal structures (natural, manufactured), and different size distributions (fine, coarse), pre-soaked with either pure water or water containing shrinkage reducing admixtures (SRA), indicate that there are different mechanisms involved in water uptake and release: one controlled by capillary action, and one controlled by air diffusion into the pore water. It is concluded that it is the internal structure, geometry, and particle size distribution of the LWA that determine the effect of SRA and the overall LWA impact on the IC performance. By using 3D micro-CT images LWAs are studied in order to determine which characteristics (pore size, pore connectivity, pore distribution) are better suited for improving IC. This contribution to understanding water transport in LWAs may help to engineer the characteristics of LWA optimized for IC applications.