A review on alkaline activation: new analytical perspectives

Abstract

For many years now the idea of including alkalis in a Portland cement matrix has been regarded as a daft or inexcusably erroneous proposition: despite its absurdity, that opinion has been widely accepted as a basic premise by the scientific and technical community working in the area of the chemistry of cement. In 1957 Glukhovsky proposed a working hypothesis in which he established a close relationship between alkalis and cementitious materials. That hypothesis has become consolidated and has served as a basis for developing a new type of binders, initially called "alkaline cements". The present paper reviews the most significant theoretical interpretations of the role played by alkalis in the formation of the "stony" structure of cement. It ends with a broad overview of the versatility of this type of materials for industrial applications and a discussion of the possibility of building on the existing legislation to meet the need for the future regulation of alkaline cement and concrete manufacture. RESUMEN: Activación alcalina: Revisión y nuevas perspectivas de análisis.Hace algunos años, la sola idea de la presencia de álcalis en una matriz de cemento Portland se consideraba casi como una aberración, o como un error imperdonable; convirtiéndose en un postulado básico (absurdo) ampliamente aceptado por la comunidad científica y técnica vinculada a la química de los cementos. En 1957 Glukhovsky propuso una hipótesis en la que se establecía una estrecha relación entre los álcalis y los materiales cementantes. Hoy día nadie duda de que dicha hipótesis ha servido de base para el desarrollo de una nueva clase de materiales cementantes: "cementos alcalinos". En el presente trabajo se hace una revisión sobre los aspectos teóricos más relevantes del papel de los álcalis en la formación de estos conglomerantes. También se da una visión genérica de su versatilidad, desarrollo industrial y estado de la normativa actual para regular en el futuro la fabricación de cementos y hormigones alcalinos.

Natural pozzolan-and granulated blast furnace slag-based binary geopolymers

“…As one can see, the compressive strength increased proportionally to the quantity of GBFS, reaching a strength of up to 48.11 MPa after 28 days of curing at ambient temperature (25 °C) when the SiO 2 /Al 2 O 3 ratio and GBFS % were 6.5 and 30%, respectively. If this value is compared with that reported for the simple system (NP) after 28 days of curing (12.96 MPa), the increase is 73%, which confirms that the reaction kinetics are positively affected by the addition of GBFS to the system and agrees with the results reported by other researchers (6,13,16,21).…”

“…This type of material could be advantageous as an alternative cementing agent to replace portland cement in certain applications and contribute positively to reducing the environmental impact of its production (1)(2)(3)(4)(5)(6). It is worth noting that approximately 0.84% of soils from tropical regions of the world are composed of volcanic ashes, and in Colombia they occupy approximately 11.6% of the national territory.…”

“…However, other researchers have noted the need for thermal curing treatments or the addition of secondary CaO and Al 2 O 3 sources such as granulated blast furnace slag (GBFS) and metakaolin (MK) to achieve good mechanical performance in a short amount of time due to the semi-crystalline nature and the deficiencies in the reactivity of CaO and Al 2 O 3 in these materials (10,(12)(13)(14). According to Rodríguez et al (15) and Li et al (16), the addition of GBFS as a source of Ca 2+ cations allows the curing and hardening of alkaline activation blends at ambient temperature, which contributes to the formation of calcium silicate hydrate gels (C-S-H) and hydrated calcium silicoaluminates (C-A-S-H) (6,17).…”

Contributions to the study of porosity in fly ash-based geopolymers. Relationship between degree of reaction, porosity and compressive strength

“…Examining the results of Figure 2a and 2b, it seems that the vitreous phase is the parameter that controls the degree of reaction in the activation of fly ashes, but the reactivity and particle size distribution must also be taken into account in reactions with slags. In any case, the presence of slag results in a high interconnected gel-like network with precipitates of calcium silicate hydrate gel, which can embrace a small percentage of aluminium in its structure, forming calcium aluminium silicate hydrate gel (43), which acts as nucleation sites (44,45). Contributions to the study of porosity in fly ash-based geopolymers • 7 Regarding the curing temperature, in all the cases the highest degrees of reaction are obtained when geopolymers are cured at 60 ºC.…”

A comparative study on the influence of metakaolin and kaolin additives on properties and structure of the alkali­activated slag cement and concrete

“…The AACs vary in proportions of basic oxides in the system N(K) 2 O-CaO-Al 2 O 3 -SiO 2 -H 2 O and, according to this, can be divided into three types: high, low and medium-calcium alkali-activated cements [5]. This predetermines a phase composition of the hydration products, hence, properties of the cements and concretes on their basis [6].…”