The structure of mayenite, Ca(12)Al(14)O(33), was investigated by neutron powder diffraction up to 1323 K. It has been described previously as a calcium-aluminate framework, in which 32 of the 33 oxygen anions are tightly bound, containing large cages, 1/6 of them being filled randomly by the remaining 'free' oxygen. At ambient temperature excess oxygen was found, corresponding to the composition Ca(12)Al(14)O(33.5) which was attributed to the presence of hydroxide, peroxide and superoxide radicals in the cages. Above 973 K these are lost under vacuum conditions and the composition becomes stoichiometric. From the refined structural parameters it is concluded that the structure is more adequately described as a relatively stable aluminate framework consisting of eightfold rings of AlO(4) tetrahedra with disordered Ca and 'free' O distributed within. At high temperatures the density of the 'free' oxygen is extremely spread out, with the expansion being related to the high ionic conductivity of this material. Since no continuous density distribution between adjacent cages was found and the 'free' O forms bonds with part of the Ca, the diffusion proceeds via a jump-like process involving exchange of the 'free' oxygen with framework oxygen. The results confirm the recent theoretical predictions of Sushko et al.

Structure and oxygen mobility in mayenite (Ca12Al14O33): a high-temperature neutron powder diffraction study Locality: synthetic Sample: T = 1223 K

Multiscale micromechanical analysis of alkali-activated fly ash-slag paste

This review article proposes the identification and basic concepts of materials that might be used for the production of high-performance concrete (HPC) and ultra-high-performance concrete (UHPC). Although other reviews have addressed this topic, the present work differs by presenting relevant aspects on possible materials applied in the production of HPC and UHPC. The main innovation of this review article is to identify the perspectives for new materials that can be considered in the production of novel special concretes. After consulting different bibliographic databases, some information related to ordinary Portland cement (OPC), mineral additions, aggregates, and chemical additives used for the production of HPC and UHPC were highlighted. Relevant information on the application of synthetic and natural fibers is also highlighted in association with a cement matrix of HPC and UHPC, forming composites with properties superior to conventional concrete used in civil construction. The article also presents some relevant characteristics for the application of HPC and UHPC produced with alkali-activated cement, an alternative binder to OPC produced through the reaction between two essential components: precursors and activators. Some information about the main types of precursors, subdivided into materials rich in aluminosilicates and rich in calcium, were also highlighted. Finally, suggestions for future work related to the application of HPC and UHPC are highlighted, guiding future research on this topic.

https://www.mdpi.com/1996-1944/14/15/4304/pdf

Materials for Production of High and Ultra-High Performance Concrete: Review and Perspective of Possible Novel Materials.

Shrinkage mechanisms and shrinkage-mitigating strategies of alkali-activated slag composites: A critical review

Resource utilization of municipal solid waste incineration fly ash in iron ore sintering process: A novel thermal treatment

Hydration of calcium sulfoaluminate cement blended with blast-furnace slag

The present study investigated the carbonation of calcium sulfoaluminate (CSA) cement blended with blast furnace slag. Paste samples were prepared by substituting CSA cement with slag at dosages of 0, 30, 50, and 70 wt%. The samples were carbonated for 28 days at a CO2 concentration of 3% after a sufficient pre-curing period. The test results indicated that slag incorporation did not affect the phase assemblage of the sample regardless of carbonation, while the incorporated slag promoted the formation of monosulfate and stratlingite upon carbonation in which this observation is closely related to the improved reaction degree of Si in the slag by carbonation. Meanwhile, monosulfate and ettringite were the first phases to be carbonated, while the C-A-S-H gel formed due to the carbonation of belite, thereby enhancing the compressive strength by refining the pore size in the gel pore region. On the other hand, the carbonation degree of the samples vastly increased as the slag content increased due to a small amount of ettringite formed along with the low reaction degree of slag which induced the development of macropores.

Carbonation of calcium sulfoaluminate cement blended with blast furnace slag

Characterization of blast furnace slag-blended Portland cement for immobilization of Co

The present study investigated the microstructural evolution and carbonation behavior of lime-slag binary binders. Samples having various lime/slag ratios were fabricated and characterized with the aid of X-ray diffractometry, thermogravimetry analyses, 29Si nuclear magnetic resonance spectroscopy, mercury intrusion porosimetry, autogenous and carbonation shrinkage measurements, carbonation depth measurements, and compressive strength development tests. These test results revealed that the carbonation of lime-slag binary binders yielded stable carbonates and subsequently refinement of the pore size and a corresponding strength modification. In addition, the lime-slag binary binders exhibited much less autogenous shrinkage movement than typical alkali-activated slag made with a combination of sodium hydroxide and water glass due to its low reaction rate and volumetric expansion accompanied by the hydration of lime. On the other hand, the phenomenon of the carbonation shrinkage of lime-slag binary binders resembles that of Portland cement due to the presence of portlandite, which served as a carbonation buffer.

Seonhyeok Kim

Papers

Hydration of calcium sulfoaluminate cement blended with blast-furnace slag

Carbonation of calcium sulfoaluminate cement blended with blast furnace slag

Characterization of blast furnace slag-blended Portland cement for immobilization of Co

Microstructural evolution and carbonation behavior of lime-slag binary binders

Experimental and theoretical studies of hydration of ultra-high performance concrete cured under various curing conditions