*2.1. Materials*

In this study, fly ash was used as source materials for AAM which is supplied by Cement Industries of Malaysia Berhad (CIMA), Perlis, Malaysia. Noted that the major elements in fly ash are silica (SiO2), alumina (Al2O3), ferum (Fe2O3) and calcium (CaO). According to the American Society for Testing Materials (ASTM C618), the ash containing more than 70 wt.% of SiO2, Al2O3, Fe2O3, and low CaO is considered to be Class F; while that with total of SiO2, Al2O3, and Fe2O3 ranging within 50–70 wt.% defined Class C. Due to the relatively high calcium content (22.30%), the fly ash used in this experiment is classified as Class C according to the ASTM C618 [31].

Waterglass or sodium silicate solution was supplied by South Pacific Chemical Industries Sdn. Bhd. (SPCI), Malaysia. The waterglass consists of 30.1% SiO2, 9.4% Na2O and 60.5% H2O (modulus SiO2/Na2O = 3.2). Its specific gravity and viscosity are 1.4 g/cm3 and 0.4 Pas, respectively.

Sodium hydroxide (NaOH) powder brand Formosoda-P from Taipei, Taiwan with 99% purity was used. The desired concentration of NaOH solution was prepared 24 h before experiments by diluting NaOH powder with distilled water. The activator solution was prepared by mixing waterglass and NaOH solution at a ratio of 2.5.

#### *2.2. Collection of Water Samples*

In this study, the seawater, river water, and lake water samples are collected around Perlis, Malaysia. The water collected was left in the laboratory to allow the impurities to precipitate at the container's bottom. Later, the water was transferred to a plastic tank via infiltration and the pH value for each type of water was recorded.

#### *2.3. Specimens Preparation*

The concentration of NaOH solution is fixed at 12 M [32], the ratio of waterglass-to-NaOH and ratio fly ash-to-alkaline activator fixed at 2.0 and 2.5 respectively [22]. The details of mix design are summarized in Table 1. The fly ash and alkaline activator were mixed and stirred for 5 min using a mechanical mixer. Then the fresh AAFA paste poured into the 50 mm × 50 mm × 50 mm [33] moulds that already placed in a container with seawater, river water, and lake water as shown in Figure 1. The AAFA specimens were left in the container for 3, 7, and 28 days, respectively. The pH level and temperature of the water before and after the placement of AAFA paste were recorded. For the control specimens, the AAFA paste was prepared in dry conditions (without underwater placement).

**Table 1.** Mix design for AAFA paste.


**Figure 1.** AAFA paste poured into mould in seawater.
