PSI - Issue 64

Hamzeh Shdeifat et al. / Procedia Structural Integrity 64 (2024) 1360–1368 Shdeifat et al. / Structural Integrity Procedia 00 (2019) 000–000

1363

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Table 1. Chemical composition (100%) SiO 2 Al 2 O 3

Fe 2 O 3

CaO 3.47

TiO 2 1.34

K 2 O 1.81

MgO

LOI*

FA

64.6

22.1

4.61

1.23

0.13

*LOI = Loss on ignition

2.2. Synthesis of FA geopolymer Potassium-based FA geopolymer mixes have been proportioned based on 3 intrinsic ratios: alkali activator’s oxides content to binder ratio (AA/B), activator oxides molar ratio (SiO2/K2O) and water to binder ratio (W/B). Ground slag was incorporated in all mixes as it’s reported to increase the mechanical strength at room temperature (Park et al., 2016, Hager et al., 2021). It’s critical to note that the binder is considered to consist of FA and slag powders only. Geopolymer mixes and their proportioning are depicted in Table 2. The first letter of the mix ID stands for the type of activator, C and R stands for the activator total oxide content and molar ratio of oxides (SiO2/K2O), respectively.

Table 2. Mix proportions of geopolymer pastes

Tot. Water (g)

MOH solids (g) 78.40 54.88 131.53

M 2 Sio 3 oxides (g) 294.18 205.92 212.36

FA (g)

Slag (g)

W/B

AA/B

SiO 2 /K 2 O*

Mix I.D

KC20R1.2 KC14R1.2 KC14R.6

1710 1710 1710

90 90 90

450 450 450

25% 25% 25%

0.20 0.14 0.14

1.20 1.20 0.60

*SiO 2 /K 2 O = molar ratio of oxides from the alkali activator only.

2.3. Mixing and preparation of samples Fly ash and slag were dry mixed for 30 seconds using Hobart Mixer N50 at speed of 281 RPM. Alkali activator was added gradually. Mixing was paused at 2.5 minutes to scoop down dry powder that is stuck to the sides of the bowel, then mixing continued at the same speed for another 1.5 minutes. Mixes were casted into cubic moulds with the dimensions of 50x50x50 mm as per ASTM C109 (ASTM, 2016). Cubic moulds are shown in Fig. 3. Curing of geopolymer mixes. The mix was casted into two layers and each layer was vibrated for 30 seconds to allow the entrapped air to escape. Afterwards, a plastic laminate was placed on top of the casted mix to prevent moisture loss. The plastic laminate was chosen instead of polythene rolls to avoid any surface distortion of the geopolymer. Casted mixes were placed in a curing chamber at 25 ° C and humidity of 50% for 28 days.

Fig. 3. Curing of geopolymer mixes