Abstract
The aim of this article is to analyse the changes of apparent activation energy (Ea) of alkali-activated materials (AAM) at temperatures up to 100°C. Apparent activation energy (Ea) refers to the minimum amount of energy is required for the occurrence of reaction. The existing AAM research is based on assumptions about Portland cement (OPC). A number of studies have been conducted on the development of concrete strength depending on, inter alia, the duration of seasoning and the liquid to solid ratio (L/S). Based on the apparent activation energy and taking into account the effect of time and temperature at the same time, the physical and mechanical properties of OPC can also be predicted. The influence of the activator on the solidification process should also be taken into account for alkali-activated materials. This article shows the effect of changes in the concentration of the alkaline solution used in the AAM process on activation energy. The synthesized AAM material uses a solution based on water glass, sodium hydroxide, sand and volatile ash from the ‘Skawina’ coal-fired power plant (located in Skawina, Lesser Poland). The chemical composition of the material used is classified as class F ash. The concentration of the alkaline solution was 8M, 10M, 12M and 14M. The described research method was based on the use of thermistors with a negative temperature factor. It enabled prediction of the physical and mechanical properties of the materials tested. The results clearly indicate that this method can be used to determine the activation energy of the AAM. However, when determining apparent activation energy (Ea), the time and activation temperature of the binding processes of these types of materials should be taken into consideration.
Highlights
Carbon fly ash (CFA) is an unavoidable by-product of thermal energy production from coal combustion [1,2,3,4,5]
Of the total amount of ash produced, CFA constitutes 85-95% wt. and consists of fine particles of fly ash retained from the flue gas [6]
In the chemical reaction rate model, it is believed that the apparent activation energy (Ea) is a key parameter with the cure temperature in the hydration reaction [18,19,20]
Summary
Carbon fly ash (CFA) is an unavoidable by-product of thermal energy production from coal combustion [1,2,3,4,5]. What is considered industrial waste or by-products can be used to produce cement materials without the high-temperature calcination process used in cement production. This reduces CO2 emissions and the extraction of natural resources. AAFA composites have relatively low compressive strength, especially at an early age, due to the incomplete dissolution of fly ash at room temperature [12]. It is widely used to assess concrete compressive strength assuming a linear relationship with temperature or a non-linear relationship with the chemical reaction rate of cement. Due to the range of curing temperatures and the accuracy of the forecast result, an equivalent age model is widely used to interpret strength development, which takes into account the cement chemical reaction rate. This paper describes the possibility of using NTC thermistors to determine thermal phenomena occurring during binding in alkali-activated materials
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