# Novel one-part ferro-phosphate geopolymer cement

Aleksandar Nikolov

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Aleksandar Nikolov. Novel one-part ferro-phosphate geopolymer cement. Review of the Bulgarian Geological Society, 2020, 81 (3), pp.43-45. hal-04494184

HAL Id: hal-04494184

https://hal.science/hal-04494184v1

Submitted on 7 Mar 2024

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<figure><img src="image_1.png" /></figure>
<table><caption>Table 1. Composition design, compressive strength, density and water absorption of the prepared geopolymer sample</caption><thead><tr><th rowspan="2">Series</th><th rowspan="2">SP, g</th><th colspan="2">Molar ratio</th><th rowspan="2">Compressive strength, MPa</th><th rowspan="2">ρ<sub>0</sub>, g/cm<sup>3</sup></th><th rowspan="2">Water absorption, %</th></tr><tr><th>Fe<sub>2</sub>O<sub>3</sub>/P<sub>2</sub>O<sub>5</sub></th><th>H<sub>2</sub>O/P<sub>2</sub>O</th></tr></thead><tbody><tr><td>GFP200</td><td>200</td><td>4.08</td><td>13.01</td><td>11.6 ± 0.6</td><td>2.24</td><td>14.62</td></tr><tr><td>GFP250</td><td>250</td><td>3.27</td><td>10.84</td><td>17.1 ± 0.8</td><td>2.19</td><td>14.83</td></tr><tr><td>GFP300</td><td>300</td><td>2.72</td><td>9.40</td><td>21.0 ± 1.5</td><td>2.14</td><td>14.98</td></tr><tr><td>GFP350</td><td>350</td><td>2.34</td><td>8.36</td><td>24.77 ± 1.25</td><td>2.09</td><td>15.40</td></tr></tbody></table>

solid ratio (w/w) for all series was constant – 0.15. The fresh geopolymer pastes were stirred 2 min with mechanical mixer. The use of retarder agent allowed the increase of setting time to about 15–20 min. The composition design is presented at Table 1 per 1000 g of fayalite slag. The molar ratios were calculated of each geopolymer composition.

*Physical and mechanical properties.* The compressive strength tests were performed at 14th day and result with standard deviation is presented in Table 1. The compressive strength steady grows with the increase of the calcium tripolyphosphate to reach 25 MPa for series GFP350. The increase from GFP200 to GFP250 was the most significant – 47%. Contrary to the usual correlation, the compressive strength increases while the density decreases. This could be explained by the difference in the specific

density of the raw materials. The fayalite was characterized by 3.85 g/cm³ specific density, while the super phosphate – 2.85 g/cm³. Thus, when relatively more SP was used the density decreases despite of the strength increases. In such manner, the water absorption increases with the increase of SP.

*SEM.* The images of the precursor and prepared geopolymer are presented in Figure 1. The raw fayalite consists of different in size particles of fayalite and magnetite including also submicron grains (Fig. 1a). Figure 1b shows the morphology of the particles of the prepared geopolymer cement. The co-grinding of fayalite slag and SP ensure homogenization. Based on morphology we can assume that particle 1 in Figure 1b is probably phosphate, while particle 2 – fayalite. On Figure 1c we can observe hardened geopolymer, which

<figure><img src="image_2.png" /><figcaption>Fig. 1. SEM images of: a, raw fayalite; b, geopolymer cement (Fayalite + SP); c–d, geopolymer GFP250</figcaption></figure>
characterize with presence of spherical pores with
diameter up to 100 µm resulted from entrained
air during mixing. The structure appears porous
which could explain the high water absorption of
the samples. The higher magnification (Fig. 1d)
shows that surface morphology of the prepared
geopolymer was characterized by globular micro-
structure.

**Conclusion**

The present study demonstrates a potential usage of
commercial super phosphate (calcium tripolyphos-
phate) as dry activator for geopolymers based on
fayalite slag. Co-grinding ensure proper homoge-
neity and one-part geopolymer was designed and
prepared. By “just-add water” fast setting mixture
was obtained. The hardened geopolymer was char-
acterized by compressive strength up to 25 MPa on
14th day. Further more detailed studies and optimi-
zations are required to design material with more
practical significance.

***Acknowledgments:*** The study was financed by the
National program “Post-doctoral students” funded

by the MES under contract PMC #577. The publica-
tion was financed by K2-2020 of IMC-BAS.

**References**

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