Effect of Silica Fume on Metakaolin Geopolymers’ Sulfuric Acid Resistance

Abstract

To demonstrate the importance of the Si/Al ratio in terms of geopolymer mix designs for acid resistance, a metakaolin-based geopolymer was modified by replacing the aforementioned precursor with different percentages of silica fume. Durability tests were performed by exposing geopolymers with varying amounts of silica fume (up to 9%) to sulfuric acid solution (pH 1) over a period of 84 days. Geopolymer samples were analyzed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) before and after 7, 14, 28, 56 and 84 days of exposure. To show the time-dependent change of the elemental composition in the corroded layer after sulfuric acid attack, SEM-EDX elemental mappings were conducted and divided into 100 µm segments to generate element-specific depth profiles. The results show that above a critical silica fume content, the erosion of the sample surface by complete dissolution can be prevented and higher amounts of silica fume lead to a significant densification of large (protective) areas of the corroded layer, which delays the progress of corrosion.

Acid resistance of alkali-activated materials: recent advances and research needs

“…The addition of microsilica to metakaolin-based AAMs at a substitution rate of ≥7.5 % was found to increase their resistance against sulfuric acid attack, presumably due to an increased Si/Al ratio of the resulting K-A-S-H gel, and because the presence of additional SiO 2 led (by some not yet understood reaction mechanism) to a densified silica gel in the corroded layer [23]. Possibly related to this observation is the finding that silica/sodium aluminate-based AAMs performed better in sulfuric acid corrosion testing when they were designed with excess silica (rice husk ash or microsilica) [16].…”

“…As mentioned in the previous Section, the corroded layer of AAMs is generally found to be depleted in Al, usually determined by spatially resolved chemical analysis [scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), electron probe microanalysis (EPMA) etc.]. In addition, several studies found that the X-ray diffraction (XRD) patterns of the corroded layer of low-Ca AAMs exhibits a broad hump centred at d ≈ 4.0 Å (2θ ≈ 22° for Cu Kα radiation), while the XRD patterns of the intact materials generally contain a broad hump centred at d ≈ 3.1 Å (2θ ≈ 29° for Cu Kα radiation) [16,18,22,23] (Fig. 2).…”

Geopolymer Based Electrodes as New Class of Material for Electrochemical CO2 Reduction

“…In this study, we introduce a new class of electrode materials for the eCO2RR by electrocatalytically functionalizing a geopolymer (GP) material with Sn. GP is an inorganic amorphous aluminosilicate polymer made from e. g. metakaolin and alkali silicate precursors and is currently being in research focus as an alternative building material in construction industry [17–23] . GP can be used as a binder to substitute e. g., the established Portland cement (PC) in concrete and thereby inter alia drastically reduce CO 2 emissions of the CO 2 intensive construction sector, [24] while still maintaining the material‘s strength, durability, performance and cost.…”

“…GP is an inorganic amorphous aluminosilicate polymer made from e. g. metakaolin and alkali silicate precursors and is currently being in research focus as an alternative building material in construction industry. [17][18][19][20][21][22][23] GP can be used as a binder to substitute e. g., the established Portland cement (PC) in concrete and thereby inter alia drastically reduce CO 2 emissions of the CO 2 intensive construction sector, [24] while still maintaining the material's strength, durability, performance and cost. To produce GPbased concrete, metakaolin is mixed with other functional additives and can be poured as a fresh mortar with similar properties to self-compacting concrete.…”

Influence of the Integration of Geopolymer Wastes on the Characteristics of Binding Matrices Subjected to the Action of Temperature and Acid Environments

“…Another important property that characterizes these materials is their good resistance to acidic media. Several works have focused on the study of this phenomenon [ 11 , 49 , 50 , 51 , 52 , 53 , 54 ]. Although the experimental conditions varied from one study to another, in terms of the concentration of the etching solution used, the nature of the acids (HCl, H 2 SO 4 or acetic acid), the results showed that geopolymers are generally chemically stable with relatively low short-term mechanical strength losses.…”