Showing papers by "Ángel Palomo published in 2004"
TL;DR: In this paper, reaction products formed during alkaline activation, with 8M NaOH solutions, of fly ashes have been characterized with 29Si and 27Al magic-angle spinning nuclear magnetic resonance (MASNMR) spectroscopy.
Abstract: Reaction products formed during alkaline activation, with 8M NaOH solutions, of fly ashes have been characterized with 29Si and 27Al magic-angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. In particular, the influence of curing conditions (time and temperature of reaction) has been analyzed. NMR results show the formation of amorphous tecto-silicates in which the amount of aluminum decreases in the two consecutive formed phases. The Si/Al ratio of zeolite precursor obtained at 85°C changes from 0.95 to 1.86 when curing time is increased from 5 h to 1 week. The evolution of the mechanical properties of prepared cements has also been discussed in terms of the phases formed and texture and morphology of samples.
407 citations
TL;DR: In this article, metakaolin (MK) and (MK + Ca(OH) 2 ) mixes were activated with 5M and 12M NaOH solutions and cured at 45°C.
Abstract: The alkali activation of metakaolin (MK) leads to the production of high-mechanical-performance network-structure materials. Adding calcium hydroxide (Ca(OH) 2 ) to the raw MK produces a somewhat different reaction: a network structure and C-S-H gel form. In the present study, MK and (MK + Ca(OH) 2 ) mixes were activated with 5M and 12M NaOH solutions and cured at 45°C. A 5M concentration, in the absence of Ca(OH) 2 , did not produce MK activation within the test time. An activator concentration of 12M resulted in complete activation and the formation of a network structure. When Ca(OH) 2 was present in the raw mix, a small amount of C-S-H gel formed.
283 citations
TL;DR: In this paper, the effect of certain working variables on the microstructural evolution of oven-dried, alkali-activated fly ash was described and the main reaction product in the activation process was an amorphous aluminosilicate gel with a three-dimensional structure.
Abstract: The present paper describes the effect of certain working variables on the microstructural evolution of oven-dried, alkali-activated fly ash. The results show that the main reaction product in the activation process (in all the systems studied) is an amorphous aluminosilicate gel with a three-dimensional structure. Nonetheless, the type and concentration of the activator used as well as the natural ageing of the materials and origin of the prime materials were also found to have a substantial impact on microstructural development in the "geopolymers " synthesised, particularly from the morphological standpoint.
55 citations
TL;DR: In this article, a combination of scanning and transmission electron microscopy along with energy-dispersive X-ray analysis of argon-milled sections were used to study fly ash matrices containing arsenic and found that little arsenic was incorporated in the matrix of hydration product but it was associated with iron derived from the hydration of the fly ash.
Abstract: A variety of natural and industrial waste product materials rich in SiO2 and Al2O3 may be activated with alkalis to produce cementitious systems which when cured under mild temperature conditions, set and harden to give a very compact paste. When fly ash is the activated material, fast setting and rapid strength development have been reported. In addition to their application in construction, they may have a role in the immobilisation of toxic waste. Alkali-activated fly ash matrices containing arsenic were studied by a combination of scanning and transmission electron microscopy along with energy-dispersive X-ray analysis of argon-milled sections. Little arsenic was incorporated in the matrix of hydration product but it was apparently associated with iron derived from the hydration of the fly ash. There was no association of As with added Fe2O3.
52 citations