120 / 2022-04-26 23:54:15

Quantification Assessment on Chemicals and Pore Structures of Limestone Calcined Clay Cement under Carbonation

LC3,Caronation Performance,Chemicals Quantification,Pore Structure

Limestone Calcined Clay Cement (LC3) has been utilized in civil engineering industry in some coastal regions and nations not only because it is a category of low-carbon cement, but also due to its brilliant capacity of blocking and binding Cl^-. On the other aspect, carbonation of cementitious materials has been a well-known issue for several decades due to problems like alkalinity neutralization, hydrates decomposition and swelling products formation (CaCO₃, CC), damaging durability performance severely. In this paper, the carbonation performance of LC3 cement was investigated, especially regarding its quantification and distribution of essential chemicals like gel products, Al-Fe-mono phases (AFm), Ca (OH)₂ (CH) and CC; and its development of pore structure, which is significantly crucial for service life. It was found that LC3 cement demonstrated much higher phenolphthalein carbonation depth compared to Portland Cement (PC), with a carbonation rate k = 3.04, shown in Fig.1, indicating that LC3 cement is possibly carbonated more easily than PC. The XRD results revealed that in case of slight carbonation (sample from deep position), there was higher amount of AFm phases (X = OH^-, CO₃^2-, etc.) but obvious lower content of CH in LC3 paste, compared to PC, Fig.2.

 

Under intensive carbonation, it was quantitively disclosed that CH was nearly depleted (Fig.3) and enormous of gel products and AFm phases were decomposed to yield CC (Fig.2 & 4), compared to PC sample. As can be seen in Fig.5, the contribution of CH and other hydrates (gel products and AFm, etc.) on CC yield in PC and LC3 is completely different. Around 70% of CC in PC sample was mainly yielded from CH reaction while in LC3, around 60-70% of CC was formed by hydrates reaction with CO₂.  Based on the phase quantification, the fully carbonated, partially carbonated and non-carbonated areas were defined. LC3 demonstrated evidently wider carbonation area (X_f) than PC, with apparent fully carbonated width (X_b).

 

With respect to the changes of pore structure, as is shown in Fig.6, the pores diameter became larger (from 0.01 to 0.1 microns) when LC3 was severely carbonated. On the contrary, in PC, the pore structure became rather denser after carbonation.