The Effect of Gel-Type Contributions in Lime-Sand Bricks, Alkali-Activated Slags and CEMI/CEMIII Pastes: Implications for Next Generation Concretes

Abstract

Lime-sand bricks of different ages were investigated using IR-spectroscopy, thermogravimetry, and X-ray diffraction/scattering. After subtraction of the dominant quartz contribution (80%), the IR spectra show the absorption peaks of the hydrothermally formed binder phases. The spectra also show the alteration of the binder during ageing under atmospheric conditions by the influence of CO2 forming carbonate and a condensed SiO2-gel (secondary gel). The alteration could also be proven in X-ray pattern, obtaining a separation between crystalline CSH and amorphous contributions in the freshly produced lime-sand brick, too. Here, the formation of CSHamorph could be understood as a precursor state (primary gel) to the crystallization of CSH phases. X-ray patterns of aged bodies of alkali-silicate solution activated slags (AAS), CEM-I/CEM-III pastes, and CEM-I concrete indicate that in all cases a similar amorphous CSH-type phase (CSHamorph) was formed, which is responsible for the hardening properties as the glue. The main X-ray peak of CSHamorph obtained using CuKα-radiation with a usual diffractometer is observed between 24° and 35° 2 Theta with maximum at about 29° 2 Theta, whereas it appears much more broadly distributed between 15° and 35° 2 Theta with maximum between 26° and 28° 2 Theta for a geopolymer body prepared using the reaction of alkali-silicate solution and metakaolin (AAMK). This is due to the network formed by siloxo and sialate units in the case of AAMK, given that any crystallization can be ruled out. The origin of increasing mechanical strength during the ageing of AAS mortars must be due to further crosslinking of the preformed siloxo chains. Thermal treatment up to 800 °C leads to a complete loss of any mechanical strength of the CEM pastes due to the destruction of crystalline CSH-phases, whereas geopolymer bodies maintain their strength. Implications for next generation concrete include that cement clinker could be completely replaced by using a using alkali silcate solution technology for gel formation.

Investigation of clay brick waste for the removal of copper, nickel and iron from aqueous solution: batch and fixed – bed column studies

“…However the comparison of spectral bands allows for easier establishment of identity of specific compounds formed during adsorption. A comparison can be made between the spectral band of MGBW and other materials used by (Jozanikohan and Nosrati, 2022), (Rüscher et al, 2022) where clay and Alkali-Activated Slags and CEMI/CEMIII Pastes were respectively used.…”

The Investigation of Compacting Cement Systems for Studying the Fundamental Process of Cement Gel Formation

“…The study of the microstructure of calcium silicate hydrate (CSH) gels from theoretical and computational points of view, as well as the fractality of CSH and the evaluation of the mechanical properties and durability of CSH—with particular reference to carbonization and chloride/sulfate exposure—are also important in influencing the mechanical properties and durability of cement-based materials [ 30 , 31 ]. The most recent works of authors who studied the formation of the structure of cement pastes from the point of view of the mechanisms of gel formation and hardening are primarily aimed at the microstructural component of these processes and mechanisms [ 32 , 33 , 34 , 35 , 36 ]. Today, a large role is given to the study of the microstructure of cement pastes, in particular, microcracking [ 32 ], the characteristics of the pore structure [ 33 ], the effect of nanoadditives [ 34 ], and the mechanisms of carbonization and hydration, along with their products: calcium carbonate, aluminosilicate gel, and CSH phase [ 35 ].…”

“…Today, a large role is given to the study of the microstructure of cement pastes, in particular, microcracking [ 32 ], the characteristics of the pore structure [ 33 ], the effect of nanoadditives [ 34 ], and the mechanisms of carbonization and hydration, along with their products: calcium carbonate, aluminosilicate gel, and CSH phase [ 35 ]. The study of these processes and mechanisms at the micro level contributes greatly to developing an understanding of the gel-type contributions to various materials that form next-generation concretes [ 36 ].…”