3of 11 Considering the simplification of the alkali-activated cementitious material production and the convenience of storage and transportation, sodium silicate powder was used to prepare activators. The composition of sodium silicate powder was 46.07% of SiO 2 and 51.35% of Na 2 O. The AE of the activators was 10%, the silicate modulus (Ms) of the activators was 0.93, and the water-binder ratio (W/B) was 0.5. The experimental procedures included the preparation of the activator or material mixture, preparation of slurry, casting of specimens, and testing. Firstly, the alkali activator solution was prepared by mixing sodium silicate powder and water, then sealed and cooled to room temperature. Meanwhile, the raw materials were weighed in the required quantity and thoroughly mixed for 1 min. Subsequently, the mixture of dry materials was added to an alkali activator and mixed for another 10 min to finish the slurry. According to ASTM C109, the specimens for compressive strength tests were cast in 50 mm × 50mm × 50mm molds with two layers of mortar, followed by compaction and vibration to eliminate air bubbles. After the initial setting, specimens were sealed with plastic films to prevent moisture loss. In this study, samples were de-molded after 24 h of casting and stored in a control box at 20 ◦ C and 95% relative humidity. Considering the experimental design and the number of samples, three of each experimental series were separately tested on the compressive strengths at 3, 7, and 28 days; the stress-time curves at day 28 were recorded. The specific steps and test parameters are shown in Figure 2 and the experiment’s process records in the laboratory are shown in Figure 3. The experimental procedures included the preparation of the activator or material mixture, preparation of slurry, casting of specimens, and testing. Firstly, the alkali activa- tor solution was prepared by mixing sodium silicate powder and water, then sealed and cooled to room temperature. Meanwhile, the raw materials were weighed in the required quantity and thoroughly mixed for 1 min. Subsequently, the mixture of dry materials was added to an alkali activator and mixed for another 10 min to finish the slurry. According to ASTM C109, the specimens for compressive strength tests were cast in 50 mm × 50 mm × 50 mm molds with two layers of mortar, followed by compaction and vibration to elim- inate air bubbles. After the initial setting, specimens were sealed with plastic films to pre- vent moisture loss. In this study, samples were de-molded after 24 h of casting and stored in a control box at 20 °C and 95% relative humidity. Considering the experimental design and the number of samples, three of each experimental series were separately tested on the compressive strengths at 3, 7, and 28 days; the stress-time curves at day 28 were rec- orded. The specific steps and test parameters are shown in Figure 2 and the experiment’s process records in the laboratory are shown in Figure 3. Table 1. Chemical composition of paper industrial wastes and BFS. Item SiO 2 ( wt. % ) CaO ( wt. % ) Al 2 O 3 ( wt. % ) SO 3 ( wt. % ) Fe 2 O 3 ( wt. % ) L.O.I ( wt. % ) Other ( wt. % ) BFS 28.1 53.7 71.6 18.2 16.7 13.2 -- 0.5 3.4 0.5 7.9 -- 4.5 1.5 2.1 lime mud -- -- -- -- 16.2 3.2 paper sludge bottom ash 3.7 5.2 74.2 18.2 33.5 4.4 Legend: SiO 2 —Silicon dioxide; CaO—Calcium oxide; Al 2 O 3 —Aluminum oxide; SO 3 —Sulphur tri- oxide; Fe 2 O 3 —Ferric oxide; L.O.I—Loss on ignition; wt.%—weight percentage. 14.1
Sustainability 2022 , 14 , 13536
Figure 2. Experimental steps and test item. Figure2. Experimental steps and test item.
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