Showing papers by "Ángel Palomo published in 2019"

Hydration mechanisms of hybrid cements as a function of the way of addition of chemicals

Abstract: This research was funded by the Spanish Ministry of the Economy and Competitiveness and FEDER under research projects BIA2016‐76466‐R and RTC2016‐4872‐S.

Mechanical-chemical activation of coal fly ashes: An effective way for recycling and make cementitious materials

Abstract: This paper is wholly committed to resource efficiency through the valorisation of waste from other industries, and more specifically fly ash as a raw material to produce concrete-like geopolymers. In particular, this study aimed to determine the effect of the physical and chemical characteristics of recycled coal fly ash used to manufacture alkaline cement on reaction kinetics and product microstructure and performance. The ash was mixed with 8 M NaOH and cured for 20 h at 85oC and RH of 90 % to form a compact paste, after which mechanical strength was determined and the reaction rate was calculated using isothermal conduction calorimetry. The findings showed that vitreous content, (SiO2/Al2O3)reactive and (especially) particle size distribution play a very important role in both the development of cement mechanical strength and the composition and structure of the reaction products formed.

Alkali activated composites – An innovative concept using iron and steel slag as both precursor and aggregate

Abstract: The present paper addresses the feasibility of using an iron and steel slag aggregate (ISS), resulting from electric arc furnace, as a recycled raw material in the production of a new concept of mortar composite, based on alkaline activation, designated as ‘alkali activated composite’ (AACO). The original ISS aggregate was used both as a precursor and an aggregate, either as received (aggregate fraction) or after mechanical activation (precursor fraction). In the first stage, to determine its potential as a precursor, it was mixed with fly ash (FA), using weight ratios of 100/00, 75/25, 50/50, 25/75 and 00/100. The most effective results were obtained with the blend 50/50, which was subsequently used to study the performance of the aggregate fraction. The second stage was comprised of tests on the mortar composites, combining some of the previously tested pastes with the ISS or with a normalised sand (for reference). A 8 M sodium hydroxide solution was used as the activator for all pastes and mortars tested. The curing developed throughout 2 or 28 days, at 22 °C, after an initial 20 h period at 85 °C. The reaction products were characterised using X-Ray Diffraction and microscopy (scanning electron microscopy, for the pastes, and back-scattering electron microscopy, for the mortars). Results show that, indeed, the ISS can be applied as a precursor and/or as an aggregate in the production of alkaline composites.

Studies About the Hydration of Hybrid “Alkaline-Belite” Cement

Abstract: The mechanical performance of a hybrid cement containing 48 % fly ash, 48 % mineralised belite clinker, 1.5 % gypsum and 2.5 % Na2SO4 was analysed and the hydration products were identified. The findings showed that the newly designed cement met European standard EN 197-1 compositional, mechanical and setting time requirements (cement type IVB). The hydration products forming in this blended ‘alkaline-belite’ cement (as it was determined through XRD, 29Si and 27Al MAS NMR and electron microscopy) consisted in a mix of cementitious gels: C-(A)-S-H and N-(C)-A-S-H, which interacted and over time evolved toward the latter with no detriment to the mechanical strength developed by the cement.

New alkaline-belitic hybrid binders

Abstract: Trabajo presentado al 15th International Congress on the Chemistry of Cement (ICCC), celebrado en Praga (Republica Checa) del 16 al 20 de septiembre de 2019.

Effect of curing temperature in the hydration of a belite cement with high level of fly ash

Abstract: Trabajo presentado al 15th International Congress on the Chemistry of Cement (ICCC), celebrado en Praga (Republica Checa) del 16 al 20 de septiembre de 2019.