Showing papers by "Francisca Puertas published in 2019"

Influence of the alkaline solution and temperature on the rheology and reactivity of alkali-activated fly ash pastes

Abstract: The aim of the present research is to ascertain the effect of the nature and concentration of the alkaline activator and temperature on the rheological behaviour of alkali-activated fly ash (AAFA) pastes. Furthermore, the reaction process of fly ash has been investigated from rheological measurements. Results have shown that the increase of the activator concentration and the temperature leads to an increase of yield stress and apparent viscosity, mainly at temperatures above 65 °C when dissolution of fly ash and precipitation of hydration products is raised. In general, similar activation energies were determined for alkali-activated fly ash pastes, regardless of the concentration and silica modulus of the activator, concluding that the underlying reaction mechanism is the same independently on the nature of the activating solution.

Olive biomass ash as an alternative activator in geopolymer formation: A study of strength, radiology and leaching behaviour

Abstract: Chemical, physical, mineralogical and radiological characterization of olive biomass fly ash (OBFA) and bottom ash (OBBA) was main objective to determine their potential use as alkaline activators in the preparation of alkali-activated materials or geopolymers. Water solubility tests showed that they released K and Na ions, affording a high pH and alkaline content. Pastes made with 70 wt% vitreous blast furnace slag (SL) and 30 wt% of OBFA or OBBA yielded alkali-activated materials with 28 days mechanical strength of 33 to 18 MPa. In pastes prepared with 30 wt% OBFA, strength values were comparable to those developed by slag pastes activated with a commercial KOH. However, the pastes made with 70 wt% coal fly ash and 30 wt% OBFA or OBBA proved to be inviable because the pH reached was not high enough to activate the precursor. The radiological calculations of OBFA- and OBBA-SL bearing pastes would conform to European legislation on protection against exposure to ionising radiation, for the activity concentration index (ACI) found in the final product was less than 1 in all cases. The pastes leached primarily K. The presence of elements such as 210Po and 210 Pb at the end of the decay chain in the eluates would not limit the use of biomass ash and slag blends. These findings have confirmed the feasibility of using olive oil biomass ashes as an alternative alkaline activator in blast furnace slag systems to produce alkali-activated materials or geopolymers, with properties that make them apt for use as building materials.

RILEM TC 247-DTA round robin test: mix design and reproducibility of compressive strength of alkali-activated concretes

Abstract: The aim of RILEM TC 247-DTA ‘Durability Testing of Alkali-Activated Materials’ is to identify and validate methodologies for testing the durability of alkali-activated concretes. To underpin the durability testing work of this committee, five alkali-activated concrete mixes were developed based on blast furnace slag, fly ash, and flash-calcined metakaolin. The concretes were designed with different intended performance levels, aiming to assess the capability of test methods to discriminate between concretes on this basis. A total of fifteen laboratories worldwide participated in this round robin test programme, where all concretes were produced with the same mix designs, from single-source aluminosilicate precursors and locally available aggregates. This paper reports the mix designs tested, and the compressive strength results obtained, including critical insight into reasons for the observed variability in strength within and between laboratories.

Alkali-activated binary concrete based on a natural pozzolan: physical, mechanical and microstructural characterization

Abstract: This article presents the physical, mechanical and microstructural characterization of an alkali-activated binary concrete (AABC) based on a natural pozzolan (NP) of volcanic origin (70%) and granulated blast furnace slag (GBFS) (30%) cured at room temperature (25°C). A solution based on the combination of NaOH and waterglass (Na2SiO3·5H2O) was employed as an alkaline activator. The concrete design was obtained using a modified version of the “absolute volume” method (ACI 211.1). The performance of the AABC was similar and even superior to that of the reference concrete (OPC); e.g., it exhibited a compressive strength of up to 43.4 MPa at 360 days. These results demonstrate that the NP has potential for use in the industrial-scale production of these types of materials in the foreseeable future.

Natural radioactivity of Portland cement mortars made with granite sand

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