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The durability of alkali-activated slag grouting materials (AASGMs) has attracted significant research attention. This paper investigated the mechanical properties and microstructure of AASGMs mortars and pastes immersed in a flowing 5% NaHCO3 solution. Compared with the strengths of AASGMs immersed for 3 days, the flexural and compressive strengths of AASGMS immersed for 56 days increased by 11.1% and 37.8%, respectively. The leaching depth of AASGMS immersed for 56 days was 0.627 mm. The AASGMs had good antiflowing NaHCO3 solution deterioration performance. The leaching process of AASGMS in flowing NaHCO3 solution was divided into three stages: (1) neutralization of residual alkali in gel pores; (2) decalcification of calcium aluminate silicate hydrate (C-A-S-H) gels in the surface and intermediate layers to form calcium carbonate and silica gels; and (3) leaching of calcium and silicon in surface layers from calcium carbonate and silica gels. [ABSTRACT FROM AUTHOR]

In this paper, the effects of different aluminum to silicon ratios in silicate chains of calcium silicate hydrates (C-S-H) are evaluated on the diffusion coefficient of chloride ions by molecular dynamics method. Tobermorite is a crystalline phase that is used for studying C-S-H properties in nano scale, because of its analogous chemical composition to C-S-H. Aluminum incorporation in C-S-H and the formation of calcium aluminosilicate hydrates (C-A-S-H) is due to both of hydration of tricalcium aluminate (C3A) in portland cement and aluminum oxides in pozzolans. There exist different Al/Si ratios in the tetrahedral chains of C-A-S-H depending on available aluminum oxides in cementitious raw materials. In order to compare the simulation results with previously-published experimental researches on cement pastes, a novel method is introduced here to calculate Al/Si ratio in tetrahedral chains of C-A-S-H using pozzolan replacement ratio in cementitious paste. MK (metakaolin) and FC3R (Fluid Catalytic Cracking Catalyst Residue) are the pozzolans that are used to validate the obtained results in this paper. Results showed that diffusion coefficients of chloride ions in C-A-S-H decrease by Al/Si ratio increasing in the tetrahedral chains as it was observed experimentally in previous researches.

C-A-S-H (CaO-Al2O3-SiO2-H2O) and N-A-S-H (Na2O-Al2O3-SiO2-H2O) have a wide range of chemical compositions and structures and are difficult to separate from alkali-activated materials. Therefore, it is difficult to analyze their microscopic properties directly. This paper reports research on the synthesis of C-A-S-H and N-A-S-H particles with an average particle size smaller than 300 nm by applying the hydrothermal method. The composition and microstructure of the products with different CaO(Na2O)/SiO2 ratios and curing conditions were characterized using XRD, the RIR method, FTIR, SEM, TEM, and laser particle size analysis. The results showed that the C-A-S-H system products with a low CaO/SiO2 ratio were mainly amorphous C-A-S-H gels. With an increase in the CaO/SiO2 ratio, an excess of Ca(OH)2 was observed at room temperature, while in a high-temperature reaction system, katoite, C4AcH11, and other crystallized products were observed. The katoite content was related to the curing temperature and the content of Ca(OH)2 and it tended to form at a high-temperature and high-calcium environment, and an increase in the temperature renders the C-A-S-H gels more compact. The main products of the N-A-S-H system at room temperature were amorphous N-A-S-H gels and a small amount of sodalite. An increase in the curing temperature promoted the formation of the crystalline products faujasite and zeolite-P. The crystallization products consisted of only zeolite-P in the high-temperature N-A-S-H system and its content were stable above 70%. An increase in the Na2O/SiO2 ratio resulted in more non-bridging oxygen and the TO4 was more isolated in the N-A-S-H structure. The composition and microstructure of the C-A-S-H and N-A-S-H system products synthesized by the hydrothermal method were closely related to the ratio of the raw materials and the curing conditions. The results of this study increase our understanding of the hydration products of alkali-activated materials. [ABSTRACT FROM AUTHOR]

In recent years, stabilization and dispersion of catalysts and adsorbents have been widely studied in the field of air and water pollution treatment. In this paper, a novel functional carrier, ceramsite sand (CS) with honeycomb-like C-A-S-H (CSHC) was synthesized by spontaneous self-assembly of C-A-S-H. The self-assembly conditions, mechanisms and physicochemical properties of honeycomb-like C-A-S-H were studied in detail. The results show that C-A-S-H on the surface of CS has a honeycomb-like structure comprising numerous nanoscale cells in the range of 50–300 nm, which results in an increase of the specific surface area by more than 46 times. In addition, Ag/AgBr loaded ceramsite sand with honeycomb-like C-A-S-H (ACSHC) was prepared for further application. The Ag/AgBr nanoparticles were homogenously embedded into the honeycomb-like structure of C-A-S-H with a close and robust contact. Therefore, the photocatalytic efficiency of ACSHC is improved significantly and remains nearly 100% after 5 months. The results suggest that the novel self-assembly C-A-S-H with a honeycomb-like structure could provide a high specific surface area, good pore structure and more active sites. It is a promising functional carrier for catalysts or adsorbents in the field of air and water pollution treatment. [ABSTRACT FROM AUTHOR]

This paper discusses the design of hybrid alkali-activated binders at ambient temperature, specifically the development of mixes based on ground granulated blast-furnace slag (GGBFS) with calcium aluminate cement (CAC) as an additive, aiming to obtain high early strength binders with optimised Al incorporation, increased crosslinking and degree of polymerisation. The effects of 10 wt% CAC replacement of GGBFS, activated with sodium silicate with varying modulus (SiO2/Na2O molar ratio) or with sodium hydroxide, on fresh and hardened properties are investigated. The inclusion of CAC in GGBFS mixtures activated using sodium silicate results in an unexpected retardation of the polycondensation reactions required to form the main calcium aluminosilicate hydrate gel phase. This is due to incomplete dissolution of the GGBFS precursor, inhibited by the rapid formation of additional reaction products (especially cubic aluminate hydrates, C3AH6) resulting in lowered reaction kinetics, and thus delayed setting and hardening times. For sodium silicate activators, this retarding effect appears to be only slightly dependent on the activator solution modulus. When activating with 4 M NaOH, the retarding effect is reduced, along with the incorporation of CAC in the C-A-S-H gel, increasing the amount of reactive aluminium present in the binder to form a more compact gel product. Increasing the molarity of NaOH solutions results in a similar delay in reaction kinetics. The results suggest the existence of only a limited pH range in which the addition of CAC can promote the formation of a binding gel with enhanced mechanical properties, whilst other factors including the effect of sodium silicate inclusion in CAC systems are still unclear. The typical hydration products of CAC were not detected in this study.

We review our recent paper which resolves the long-standing dilemma of the location and nature of the six-fold coordinated aluminum in calcium aluminate silicate hydrate (C-A-S-H) samples. First principles calculations predict that at high Ca:Si and H2O ratios, aluminum is incorporated into the bridging sites of the linear silicate chains and that the stable coordination number is six. We confirm this hypothesis experimentally by one- and two-dimensional dynamic nuclear polarization enhanced 27 Al and 29 Si solid-state NMR experiments in which we correlate the distinctive six-fold coordinated aluminum NMR signal at 5 ppm to 29 Si NMR signals from silicates in C-A-S-H.

Geopolymer setting is seen to be substantially accelerated by addition of calcium and the objective of this study was to determine the mechanism for this effect by examining metakaolin geopolymers with and without calcium. Solid-state 27Al NMR tests were used to examine the dissolution extent both qualitatively and quantitatively. Solid-state 29Si NMR tests were conducted to determine the amount and structure of each phase. Prior to the quantitative tests, chemical extractions were used to facilitate assignment of peaks in each spectrum. On addition of calcium, it was found that both the rate and the extent of metakaolin dissolution were enhanced. Accelerating dissolution increases the Al concentration in solution, thus reducing Si/Al available for geopolymer gel formation and further accelerating the gel formation to cause faster setting. Although C-A-S-H was observed in the calcium mix, no evidence indicated that it is directly involved in setting. [ABSTRACT FROM AUTHOR]

C-A-S-H (CaO-Al2O3-SiO2-H2O) and N-A-S-H (Na2O-Al2O3-SiO2-H2O) have a wide range of chemical compositions and structures and are difficult to separate from alkali-activated materials. Therefore, it is difficult to analyze their microscopic properties directly. This paper reports research on the synthesis of C-A-S-H and N-A-S-H particles with an average particle size smaller than 300 nm by applying the hydrothermal method. The composition and microstructure of the products with different CaO(Na2O)/SiO2 ratios and curing conditions were characterized using XRD, the RIR method, FTIR, SEM, TEM, and laser particle size analysis. The results showed that the C-A-S-H system products with a low CaO/SiO2 ratio were mainly amorphous C-A-S-H gels. With an increase in the CaO/SiO2 ratio, an excess of Ca(OH)2 was observed at room temperature, while in a high-temperature reaction system, katoite, C4AcH11, and other crystallized products were observed. The katoite content was related to the curing temperature and the content of Ca(OH)2 and it tended to form at a high-temperature and high-calcium environment, and an increase in the temperature renders the C-A-S-H gels more compact. The main products of the N-A-S-H system at room temperature were amorphous N-A-S-H gels and a small amount of sodalite. An increase in the curing temperature promoted the formation of the crystalline products faujasite and zeolite-P. The crystallization products consisted of only zeolite-P in the high-temperature N-A-S-H system and its content were stable above 70%. An increase in the Na2O/SiO2 ratio resulted in more non-bridging oxygen and the TO4 was more isolated in the N-A-S-H structure. The composition and microstructure of the C-A-S-H and N-A-S-H system products synthesized by the hydrothermal method were closely related to the ratio of the raw materials and the curing conditions. The results of this study increase our understanding of the hydration products of alkali-activated materials.

"Roman concrete" was used as building material during Roman Imperial times for a great number of famous constructions with different functions. Well-known examples are aqueducts, for example the Pont du Gard in France and the Aqua Alexandrina in Rome, and numerous monuments such as the famous Coliseum and Pantheon in Rome. While visually less apparent today, ancient harbors also were an important part of constructions supporting the power of the Roman imperial system and were invaluable to control the Mediterranean Sea trade. The article "Unlocking the secrets of Altobermorite in Roman seawater concrete" by Jackson et al. (2013) describes the investigation of several extremely interesting samples drilled from 2000-yearold Roman maritime concretes in 11 harbors along the Mediterranean coast [the ROMACONS project 2002-2009 (Oleson et al. 2004)]. [ABSTRACT FROM AUTHOR]