Acid resistance of calcium aluminate cement–fly ash F blends

Abstract

The short-term resistance to sulfuric acid at 90°C of four calcium aluminate cement (CAC)-fly ash class F (FAF) blends activated with sodium metasilicate (thermal shock resistant cements (TSRCs)), cured at 300°C, was compared to that of a calcium phosphate cement (CPC) (CAC-FAF blend activated with sodium hexametaphosphate) and a Portland cement class G/silica blend. The mechanical properties and compositions of the acid-exposed samples were evaluated by measuring their compressive strength and by means of x-ray diffraction, μEDX (energy-dispersive x-ray spectrometry), thermogravimetric and Fourier transform infrared analyses. All calcium-containing hydrates were sensitive to the conditions of acid exposure. In the TSRC blends, these hydrates included hydrogrossular, feldspar family minerals and zeolites; in CPC, feldspar minerals and phosphate phases; and in the class G/silica blend, portlandite and tobermorite.Crystalline calcium sulfates formed in the acid-exposed surfaces with the exception of the most aluminium-rich TSRC samples where only potassium(sodium) aluminium sulfate, alunite, was detected. This sample underwent the least changes in weight, compressive strength and had the lowest sulfur permeation into the sample core. Calcium sulfates precipitated on sample surfaces limited sulfur penetration into the core of calcium-rich TSRC, CPC and G/silica blends.

Effect of slag content and activator dosage on the resistance of fly ash geopolymer binders to sulfuric acid attack

“…Sulfuric acid can also be present in groundwater or produced from the oxidation of sulphur bearing compounds in backfill, such as pyrite, causing degradation to concrete substructures [13]. The dissolution of hydrogen sulphide can also form sulfuric acid with a low pH on the concrete walls of geothermal wells [14]. Therefore, sulfuric acid is a major cause of degradation of concrete structures.…”

Role of Tartaric Acid in Chemical, Mechanical and Self-Healing Behaviors of a Calcium-Aluminate Cement Blend with Fly Ash F under Steam and Alkali Carbonate Environments at 270 °C

“…The spectral features closely resembled each other containing the same frequency nine representative frequency bands with the following contributors. The C-O (V as C-O ) stretching vibration in carbonate CO 3 2− emerged in the region of 1510 to 1400 cm −1 [63,64,65], the Si-O-Si linkage-associated V as Si-O vibration in silica gel at 1243 cm −1 [66,67,68], the Al-OH bending (δ as Al-OH ) and (δ s Al-OH ) vibrations, and AlO 4 tetrahedral (V Al-O ) stretching in bohmite (γ-AlOOH), were respectively, at 1148, 1068, and 777 cm −1 , reflecting the presence of typical bohmite-related doublet peaks of O-H group at 3307 (V as O-H ) and 3086 (V s O-H ) cm −1 bands (not shown) [69,70,71,72], the M-O (M: Si or Al) (V as M-O ) in amorphous and crystalline Na 2 O-Al 2 O 3 -SiO 2 -H 2 O (N-A-S-H), CaO-Al 2 O 3 -SiO 2 -H 2 O (C-A-S-H), and CaO,Na 2 O-Al 2 O 3 -SiO 2 -H 2 O (C,N-A-S-H) hydrates appeared at 990 and 902 cm −1 [73,74,48], and the Si-O stretching (V s Si-O ) and Si-O bending (δ O-Si-O ) modes in quartz at 738 and 675 cm −1 , respectively with a possible quartz contribution to the band at 1068 cm −1 (V s Si-O ) [62]. The N-A-S-H, C-A-S-H, and C,N-A-S-H phases were assembled by the interactions between Na + and Ca 2+ released by SMS activator and CAC, and the aluminosilicate anhydrous compounds in FAF [75].…”

“…High temperature hydration of TSRC results in calcium-aluminum silicates, zeolite-family crystalline products and (C,N)-A-S-H amorphous phase [ 43 , 73 ]. The crystalline calcium-aluminum-silicate hydrates include hydrogrossular phases at earlier hydration times (katoite, grossular, and hibschite) and feldspar (dmisteinbergite and anorthite) or feldspathoid (cancrinite in carbonate-rich environment) type minerals after longer curing at temperature above about 250 °C.…”

Cements for High-Temperature Geothermal Wells

“…CaP also forms carbonated apatite. In the case of sulfuric acid attack calcium reacts with sulfates forming anhydrate in both cements and the remaining alkali aluminum-silicates provides structural stability of the acid-treated matrix [22].…”

“…Studies on alkali-activated cement composite of calcium aluminate cement and fly ash F (thermal shock resistant cement, (TSRC)) demonstrated excellent performance under various stresses of simulated geothermal environments [21,22], and outstanding CS bond durability [23]. Further work showed that TSRC has self-healing properties, which is ability to recover its compressive strength and seal the cracks at temperatures up to 300°C [24].…”