# Effect of Curing Conditions on Microstructure and Pore-Structure of Brown Coal Fly Ash Geopolymers
## 3 Experimental Procedure
### Specimen Preparation and Curing  
In the brown coal fly ash geopolymer mortar preparation, fly ash and sand were mixed using a 5-L Hobart mixer for 4 min. The alkaline activator solution, consisting of sodium hydroxide and sodium silicate solutions as well as additional water, was prepared manually 15 min prior to mixing. The mortar mixture was produced by the addition of pre-prepared alkaline solution to the dry mix of fly ash and sand, and mixing for 4 min at a speed of 140 rpm followed by an additional mixing for 2 min at 285 rpm in a Hobart mixer. After mixing, the geopolymer mortar was poured into the 50 mm cubic Teflon moulds and vibrated using a vibration table at a speed of 225 rpm for 30 s. In the geopolymer concrete preparation, the fly ash, coarse aggregate and sand were mixed using a 60-L concrete mixer (speed of 290 rpm) for 4 min, the pre-mixed alkali activator solution together with the extra water were added and mixed for further 8 min. The geopolymer concrete mix was placed into 50 mm, 100 mm, 200 mm and 300 mm cubic timber moulds, and vibrated using a vibration table at a speed of 225 rpm for 1-2 min to remove air bubbles.  
The temperature probes were placed at fixed depths in the specimens in order to monitor the temperature profile of the mortar and concrete when exposed to heat curing as experienced under normal oven conditions, Figure 1. The temperature probes were monitored through a data logger attached to a computer. In mortar specimens, a single thermocouple was positioned in the center. In the 100 mm cube, the concrete sample probes were positioned along the centerline at the 25, 50, and 75 mm distance from the side and from the top surface. In the 200 and 300 mm cubes, the probes were positioned at 25 mm intervals from the side along the centerline and the depth increased by 25 mm from the top surface respectively.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{3}{*}{\begin{tabular}{c} **Loy Yang** \\ **Geopolymer** \\ \end{tabular} } & \multirow{3}{*}{**Fly Ash (kg)**} & \multicolumn{3}{c}{**Aggregates (kg)**} & \multicolumn{3}{c}{**Activator (kg)**} \\ \cline{3-6}  & & & **Sand** & **7 mm** & **10 mm** & \begin{tabular}{c} **Na\({}_{2}\)SiO\({}_{3}\)** \\ **(Liquid)** \\ \end{tabular} & \
\begin{tabular}{c} **NaOH** \\ **(15 M)** \\ \end{tabular} \\ \hline
\begin{tabular}{c} Mortar \\ Concrete \\ \end{tabular} & 279 & 1677 & \multirow{3}{*}{319} & \multirow{3}{*}{637} & \multirow{3}{*}{263} & \multirow{3}{*}{261} \\ \cline{3-6}  & 279 & 721 & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: The optimum mix design (kg/m\({}^{3}\)).  
Both mortar and concrete specimens were covered to prevent moisture loss and left for 24 h under laboratory conditions (24 \({}^{\circ}\)C and 70% relative humidity) before heat curing. A curing temperature of 120 \({}^{\circ}\)C was employed with a range of curing times between 4 and 14 h at 2-h time intervals for the mortar and concrete specimens with a further concrete specimen monitored for 24 h. This curing temperature was obtained in the mix optimization process of 100% brown coal fly ash geopolymer mortar, based on 28-day compressive strength [15]. The geopolymer specimens were evenly placed at the center of the dry oven to ensure uniform heating of all specimens. The specimens (either mortar or concrete) were removed from the oven after the specified curing time. Following heat curing, all specimens were taken out from the oven, then demoulded and stored in laboratory conditions.