Clinkering Reactions During Firing of Recyclable Concrete

Abstract

Thermal transformations occurring during firing of recyclable concrete and hydrated Portland cement paste were monitored quantitatively by in situ and ex situ X‐ray diffraction, thermal analysis, and clinker microscopy. Reactions below 1150°C were dominated by either the decarbonation of calcium carbonates of the limestone aggregate fraction in the recyclable concrete or the low temperature decomposition of cement hydrates of the cement paste. Continued heating of the cement paste showed a rapid and extensive reaction of the free lime to form intermediate calcium silicate and aluminate phases such as belite, gehlenite, mayenite, and ye'elimite. The combination of free lime was less rapid in the dominantly limestone‐rich recyclable concrete. Similarly, subsequent melt and clinker phase formation (1250°C and higher) occurred more rapidly in the hydrated cement paste, indicating a positive contribution of cement hydrates to raw meal burnability. Reactions below typical cement clinkering temperatures were enhanced (1) by the intimate mixing of lime, silicate, and aluminate components in the hydrated cement and (2) by the elevated sulfate content that acted as flux and belite mineralizer. Lime formed in the thermal decomposition of portlandite (±450°C) was partially carbonated to calcite at temperatures below the onset of calcite decarbonation (±650°C).

The hydration of cement regenerated from Completely Recyclable Concrete

“…Preliminary studies have shown that the properties of the eventually regenerated clinker and cement were comparable to reference cements of similar composition [32,35]. The clinkering reactions during firing of Completely Recyclable Concrete were studied in detail earlier [36].…”

Ladle metallurgy stainless steel slag as a raw material in Ordinary Portland Cement production: a possibility for industrial symbiosis

“…A slight difference occurred between TG/DSC data and XRD analysis, but this relates mostly to the different heating/cooling processes followed and not the analytical techniques; as reported also elsewhere (Snellings et al, 2012), it may be that the crystallisation was improved by soaking time, whereas the carbonation was promoted by air cooling.…”

“…For both samples three measurements were done and the average was considered. In order to better understand the phenomena which occurred between 900 C and 1350 C the procedure proposed elsewhere (Snellings et al, 2012) was followed. Pellets of OPC and OPC14 were heated at 900 C, 1050 C, 1200 C, 1350 C and 1450 C in a static air furnace (bottom loading furnace).…”

EFFECT OF FERRITE PHASE ON THE FORMATION AND COEXISTENCE OF 3CaO.3Al₂O₃.CaSO₄ AND 3CaO.SiO₂ MINERALS

“…The diffraction peak of C 4 A 3 $ is generally weakened and the characteristic peak of C 3 S are almost not observed with the increasing burning temperatures. It is probably related to the decomposition of C 4 A 3 $ at temperature higher than 1350°C [27,28] which provides an unfavorable condition for the formation of C 3 S. In general, the intensity of diffractive peak is related to the content and crystallinity of phase [29]. Therefore, this suggests that excessive the A/F molar ratio not facilitates the formation of C 3 S and the coexistence of C 4 A 3 $ and C 3 S. Thus, it can be drawn that the composition and content of liquid phase have the significantly effect on the formation of clinker mineral.…”