Influence of selected activating methods on hydration processes of mixtures containing high and very high amount of fly ash

Abstract

Binders containing fly ash as cement substitute have been used for many years. Typical amount of fly ash in cement composite does not exceed 35% of mass of binder. Replacement of substantial amount of cement mass by fly ash results in retardation of hydration of binder and deterioration of some concrete properties, e.g. delay in setting time and reduction in early compressive strength. These inconveniences may be reduced using proper method of activation. In this paper, possibilities to activate binding mixtures containing high and very high amount of fly ash and low amount of Portland cement were discussed basing on the literature reports as well as on our own research results. Several activating methods were described, such as mechanical activation, exchanging of part of components of binder (cement, fly ash or both of them) by more reactive fine-grained material, chemical activation by the use of alkaline activators as well as combined methods. Possibilities of using these methods were discussed in relation to amount of fly ash introduced as replacement of cement and kind of fly ash used. Usefulness of calorimetry and thermal analysis methods was also presented.

Comparative investigation of reactivity of different kinds of fly ash in alkaline media

“…Fly ash has been utilized as supplementary cementitious material for decades. Different amounts of this by-product in cement composite can be considered: up to 35 mass% (typical amount), about 50% (high volume fly ash concretes (HVFAC) [1][2][3][4][5]) or even 70-80% (very HVFAC [6][7][8][9][10]). Moreover, there is also possibility of using fly ash as binding material performed without cement (alkali activated fly ash, geopolymers) [11][12][13][14][15][16][17][18].…”

“…This binding material is composed of high amount of fly ash (at least 70 mass%) and Portland cement. Moreover, it is activated with alkaline media; thus, it can be considered as hybrid cement [7,8,10,[35][36][37][38][39][40]. It is important that in the case of hybrid cements, alkalinity may increase in situ as a result of chemical reaction, e.g., using Na 2 SO 4 as an activator [5,7,38,39].…”

Holistic Analysis of Waste Copper Slag Based Concrete by Means of EIPI Method

“…Therefore, obtaining hardened material with the required properties requires investigation and analysis of the physicochemical processes occurring over time in the system. In some cases, the starting material may require an additional treatment and modification procedure (e.g., chemical or physical activation) [4][5][6][7], and the composition of the mix should be optimized. It is also important that the final material does not adversely affect its user, so it is necessary to study, e.g., its natural radioactivity.…”

Cellular concrete waste as an economical alternative to traditional supplementary cementitious materials

“…Many researches on concrete are aiming to create more advantageous concrete from strength and durability standpoint with the application of innovative admixtures and supplementary cementitious materials (SCMs) [1]. SCMs are highly advantageous, because besides their positive effects on strength and durability, they have environmental benefits, like the reduction in carbon dioxide emission and decreasing the porosity of normal-strength concrete [2][3][4][5][6]. The strict European air pollution regulations have produced many industrial by-products that can be used as supplementary cementitious materials, like metakaolin (MK) or silica fume.…”