The Role of Pozzolanic Activity of Siliceous Fly Ash in the Formation of the Structure of Sustainable Cementitious Composites

Abstract

The following article introduces, in a thorough manner, how the chemical pozzolanic reaction takes place in cement composites containing the fly ash (FA) additive. In the research part, however, the development of phases in the structure of the cement paste in the initial period of its curing and after 28 days from its preparation was traced. For this purpose, a Scanning Electron Microscope (SEM) was used. In order to accurately highlight all the characteristic stages of the formation of the structure of the composite containing FA, an analysis of the cement matrix was carried out between 0.5 and 28 days of their curing. Microstructural studies were complemented by tests of pozzolanic activity of FAs used. In order to conduct a full analysis of this feature, experiments were carried out using two types of research methods, i.e., chemical and physical. On the basis on the conducted studies it was found that: in cement composites with the addition of FA, in the period until the third day of curing, the development of the material structure is mainly the result of the hydration reaction, and between the seventh and fourteenth day after sample preparation, the first signs of the pozzolanic reaction on FA grains are visible; however, in the period between 14 and 28 days, there is a clear homogenization of the structure of the cement composite with the addition of FA, resulting from the change of disordered phases into compact and homogeneous forms and filling in the composite of porous places with pozzolanic reaction products. The use of cement composites based on materials whose application makes it possible to reduce GHG emissions to the atmosphere, reduce energy consumption, and reduce industrial waste landfills leads towards the development of ecological and sustainable building engineering.

The influence of selected grain size fractions of coal fly ash on properties of clay-cement mortars used for the flood levees construction

“…Figure 8 shows the in uence of particle size on the microstructure formations. For both ashes, there is a noticeable intensi cation of strain gain at later stages, which is consistent with the theory of delayed reactions in y ashes [16,23,57].…”

Examination of water absorption of low volume fly ash concrete (LVFAC) under water immersion conditions

“…The implementation of the FA additive into the binder composition caused that in addition to products related to the hydration reaction, additional phases in the cement matrix structure resulting from the pozzolanic reaction also began to appear. As shown by the detailed results of the FA pozzolanic activity studies, in the case of substitution of 25% OPC with this waste, a significant positive effect of strengthening the matrix based on a binary binder is observed [146]. In the presented studies, the OPC substitution was used at the level of 20 and 30%.…”

“…Moreover, this amount is also too small to change the size and structure of the pores of the concrete composite. In previous studies it has been observed that the highest activity had OPC-FA mixtures with a FA content of 25% [146].…”

“…The compressive strength of concrete-f cm was tested in accordance with the European Standard EN 12390-3:2011+AC:2012 [146] on 150 mm cubes with the use of Walter +bai ag hydraulic servo testing machine. Six specimens were tested for each concrete type.…”

Effects of extended mixing processes on fresh, hardened and durable properties of cement systems incorporating fly ash

“…It is common knowledge that adding fly ash to cement systems can result in a denser microstructure and reduced porosity at later ages. This is because pozzolanic reactions (reaction between CaO and S to form C-S-H products) progress at later ages 47,48 . Golewski 47 mentioned that the homogenous and uniform structure of the portland cement system containing FA was seen after 14-day curing period, which resulted from the transformation of disordered phases into compact and homogenous forms and the filling of porous voids of C-S-H phase.…”