Abstract
Limestone powder can cause the thaumasite form of sulfate attack (TSA) of cement-based materials, but the relationship between the content of limestone powder and the degree of TSA is unclear. Hence, six different contents of limestone powder (0%, 5%, 10%, 15%, 30%, and 45%) were used to study the effect of the limestone powder content on the TSA of cement-based materials according to appearance and Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and chemical analyses. The test results indicated that limestone powder could promote sulfate attack. The formation of ettringite and gypsum was accelerated when the content of the limestone powder was not more than 10%. The degradation degree of the TSA was the most severe when the content of limestone powder was 30%. A new product, hydrated calcium carboaluminate, was found when the content of the limestone powder was 45%, and the degradation of the TSA was also delayed.
Highlights
Carbonate is a necessary ingredient of thaumasite. aumasite is generated and thaumasite form of sulfate attack (TSA) is present when carbonate or bicarbonate is available, as well as when there is adequate moisture and a low temperature. e sources of carbonate are generally divided into internal and external sources, which generally come from cement itself, concrete aggregates, and additives, while external sources come from groundwater and CO2 in the atmosphere [10]
3.2.1. e Fourier transform infrared spectroscopy (FTIR) and Raman Spectroscopy. e author’s previous experiments [19,20,21] showed that TSA mainly occurs in the cathode region of the specimen; the identification of thaumasite focuses on the cathode of samples. e microstructure specimens were obtained from the cathode surface of 6 groups and were tested by FTIR and Raman spectroscopy to identify the type of degradation products, as shown in Figure 5. e vibrational spectra and band assignment of thaumasite are shown in Table 4 [21]
E diffraction peak of thaumasite was the most significant when the content of limestone powder was 30%, followed by the 45% content of limestone powder. ere was no obvious diffraction peak of thaumasite when the content of limestone powder was less than 15%. e degradation mechanism is analyzed by X-ray diffraction (XRD) and chemical analyses
Summary
Thaumasite is a rare six-sided crystalline mineral that mainly exists in metamorphic rocks and limestone [1, 2]. aumasite consists of silicate, carbonate, sulfate, and water. e thaumasite formation (TF) was first reported by Erlin and Stark in 1965 and was found in sewers, cement grouting layers, and road holes [3]. e formation of thaumasite is a complex process in multifactorial environments that includes temperature, humidity, the type of sulfate, the concentration of sulfate, the pH of the environment, the type of cementitious material, and the type of aggregates. e typical degradation caused by the formation of large amounts of thaumasite leads to the transformation of cement-based materials into grey pulp that loses its cementitious properties, known as the thaumasite form of sulfate attack (TSA) [4,5,6]. e TSA was found in a 30-year highway bridge in Gloucestershire, England, in the 1990s [7]; thaumasite expert groups were established by the UK government [8]. A high content of limestone powder can greatly increase the risk of concrete corrosion from TSA [11,12,13,14,15,16], and carbonate and ettringite can obviously promote TSA [17]. The electrical field acceleration method can be utilized to study the effects of the limestone content on the TSA mechanism and process of cement-based materials within a short duration. The influence of six kinds of limestone powder content (0%, 5%, 10%, 15%, 30%, and 45%) on TSA of cement-based materials was studied by means of electric field acceleration method, and the influence degree and mechanism of limestone powder content on TSA were explored
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