*2.4. Testing and Analysis Methods*

The setting time of AAFA paste through underwater placement was measured using the Vicat test [33]. The test was conducted at room temperature using the Vicat apparatus, where the mould was placed beneath the water level. The initial setting and final setting time of the AAFA paste were recorded.

The specimen's compressive strength was determined based on ASTM C109 [34] using Instron 5582 Mechanical Tester (Instron, Massachusetts, United States America). A minimum of three specimens was tested for each mix design, and the average results recorded. Total of all 108 specimens were produced for this testing. The AAFA were tested on 3rd days, 7th days, and 28th days for both the control specimens and specimens cast underwater.

The chemical composition of the AAFA paste after going through underwater placement and dry condition is determined using X-ray fluorescence (XRF). XRF was conducted using the PA Nanalytic PW 4030, MiniPAL 4 (Malvern Panalytical, Malvern, United Kingdom) X-ray fluorescence spectrometer. After 28 days placement in various water types, the specimens were crushed to a powder form for analyses.

A JSM-7001F (JEOL, Tokyo, Japan) model of Field Emission Scanning Electron equipped with energy dispersive spectroscopy (EDS) was used to image the AAFA's morphology and determine its elemental composition after underwater placement. The specimens were cut into small pieces and coated with carbon using Auto Fine Coater (JEOL, Tokyo, Japan). The images were observed with accelerating voltage of 15 kV for all specimens.

#### **3. Results and Discussion**

#### *3.1. pH Value and Temperature of Water*

The water's pH value and temperature before and after underwater placement of the AAFA are illustrated in Figures 2 and 3. The seawater's original pH is 7.5, while the river water and lake water pH value are 7.4. All types of water recorded an increment in value when the AAFA paste was placed into the tanks. The seawater's pH value recorded the lowest increment of 0.6, while the highest increment was 1.8 from the lake water. From the underwater placement of AAFA paste, there is washout effect with the increment in the surrounding water's pH value. However, visible changes in the pH are evident, probably due to the smaller tank (275 mm length × 160 mm width × 160 mm depth) used during underwater placement of the AAFA specimens.

**Figure 2.** Effect on pH value for different type of water due to placement of the AAFA paste.

**Figure 3.** Effect on temperature when casting the AAFA in water.

The temperature for all types of water increased when the AAFA paste was placed into the tanks, proving that the AAFA reaction is exothermic, as heat is released during the hardening process, which increased the temperature of the water. Temperature increment in the seawater and river water was 2.5 ◦C, while lake water had a temperature increment of 2.6 ◦C. Previous researchers reported that the reaction between the source materials and alkaline activator is an exothermic reaction when the AAFA is cured at high

temperature [33–37]. However, it was observed in this study that even though the AAFA paste was placed in water, heat release can still be detected.
