Investigation of Portland cement composites containing high amounts of different kinds of fly ashes

Abstract

Utilization of fluidized fly ash in cement composite is problematic, e.g. because of its changeable chemical composition and increased water demand of the mixture. However, this kind of by-product shows some self-cementing properties, which may be beneficial for low-cement mixtures. The article compares the impact of various kinds of fly ashes, i.e. fluidized fly ash and conventional one, and their mixtures on hydration of fly ash–cement compositions in relation to properties of final material. The amount of fly ash in the binder was 50 wt%. Calorimetry, thermal analysis (TG/DTG) and infrared spectroscopy were used. Compressive strength and water absorption of hardened composites were also registered. It was found that both fly ashes exhibit delay effect in fly ash-cement pastes which causes extension of initial setting time and lower heat released compared to the reference without fly ash. At later hydration days, fluidized fly ash develops higher pozzolanic activity than conventional one. Compositions with fluidized fly ash show better compressive strength compared to those containing conventional one. Mixing of different materials of high and low activity (fluidized and conventional fly ash in this case) seems to be a good way for creation of new cement replacement material.

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

“…Tables 1 and 2 summarizes the previous studies on wa of composites with the addition of siliceous FA with the provision of important parameters for these experiments, wchich were tested both in fully (table 1) and shallow immersion conditions (table 2). On the other hand, characterizes selected data on the implementation of wa experiments in concrete with the addition of other types of FA can be found, for example, in the works [120][121][122][123][124][125].…”

The Effect of the Addition of Coal Fly Ash (CFA) on the Control of Water Movement within the Structure of the Concrete

“…Therefore, Table 1 summarizes the previous studies on composites with the addition of CFA with the provision of important parameters for these experiments. However, selected data on the implementation of water absorption experiments in concrete with the addition of other types of FA can be found, for example, in the works [82][83][84][85][86][87][88]. At this point, it should also be noted that a beneficial effect on the level of water absorption of the modified concretes, CFA and GGBFS, has been observed in the case of composites exposed to high temperatures [88,89,96,97].…”

“…According to [64], the level of water absorption decreases in the case of cement binder substitution by CFA in a range of up to 35%. However, studies [83][84][85] prove that the addition of CFA from 30 to 90% causes a decrease in water absorption in these materials. However, the low water absorption in these studies was observed in concrete with 30% CFA.…”