•The suitable synthesis condition for tobermorite was 5 h in autoclave at 180 °C.•Addition of aluminum resulted in an increased interlayer spacing.•The tobermorite with the incorporated of aluminum had a longer mean chain length.•The microstructure of tobermorite with aluminum had larger and more ordered foils.Tobermorite is an important mineral analog of calcium silicate hydrate (C-S-H), the main phase formed by hydration of Portland cement, due to the structural similarity. As part of a broader study on the effect of aluminum substitution C-S-H, the synthesis and characterization of tobermorite with and without aluminum were conducted. The X-ray diffraction pattern indicated that a suitable synthesis time for tobermorite with or without aluminum was 5 h in an autoclave at 180 °C and saturated steam pressure around 1 MPa. In both samples the mineral is 11 Å-tobermorite. X-ray fluorescence showed that the sample with aluminum had a higher molar ratio of Ca/(Si + Al). Thermogravimetry-differential scanning calorimetry showed the same general changes, loss of free water at 55 °C, loss of interlayer water at 187 °C, dehydroxylation at 664 °C, and conversion to wollastonite at 841 °C. With the incorporation of aluminum, 29Si and 27Al magic angle spinning-nuclear magnetic resonance spectra showed aluminum addition increases the mean chain length, Al mainly occupies Q2 bridging and Q3 branching sites. Scanning electron micrographs indicated that tobermorite crystals are larger than those of sample without alumina. This work is beneficial for understanding the implication of the use of admixtures containing aluminum in concrete on its micro- and atomic-scale properties.

•Different dosages and chemical valences of chromium obviously affect geopolymers.•Chromium affects compressive strength, reaction products and pore structures of geopolymers.•Chemical bonding and physical encapsulation coexisting in chromium containing geopolymers.•DTCR has a good detoxification performance in chromium containing geopolymers.Geopolymers are new cementitious materials that with 3 dimensional networks, which can effectively solidify/stabilize heavy metals. Utilization of fly ash as precursor to prepare geopolymers, and influences of dosages and chemical valences of chromium reagents on geopolymers, as well as detoxification effectiveness of chemical agents for geopolymers were studied. The results showed that compressive strength of geopolymers could be improved when dosage of Cr(NO3)3 is small. Reinhardbraunsite (Ca5(SiO4)2(OH)2) was generated in geopolymers with Cr(NO3)3 or CrO3 due to ‘ions exchange’. Respectively dosing Cr2O3, Cr and CrO3 could make total pore volume of geopolymers smaller and make geopolymers more compact. Chemical bonding and physical encapsulation both existed in geopolymers. Chemical bonding played main role in geopolymers with Cr(NO3)3, and physical encapsulation played main role in geopolymers with Cr2O3, Cr and CrO3, respectively. Chemical agent DTCR could effectively improve compressive strength and capture Cr3+ of geopolymers, enhancing their abilities of anti-erosion.

•Effects of nano-SiO2 and nano-γ-Al2O3 on geopolymers from MSWIFA and CFA.•The optimum contents of nano-SiO2 and nano-γ-Al2O3 are 1.5% and 2.0%.•Nanomaterials improve structure, and immovability of heavy metals of geopolymer.Nano-modified composite geopolymers were successfully prepared from municipal solid waste incineration fly ash (MSWIFA) and class C fly ash (CFA). The results indicate that both nano-SiO2 and nano-γ-Al2O3 have a good modification effect on geopolymer, of which nano-SiO2 has a better performance than nano-γ-Al2O3. The optimum content of nano-SiO2 and nano-γ-Al2O3 are 1.5% and 2.0%, respectively. XRD shows that there is no new phase emerging after adding a small amount of nanomaterials. By FT-IR and SEM, it means that nanomaterials facilitate the reaction of geopolymer, making the modified geopolymer more compact. BET shows nano-SiO2 especially modifies the pore distribution and pore structure of geopolymers. Additionally, nanomaterials have an improvement to the solidification/stabilization (S/S) of heavy metals.

•1H NMR is applied to monitor the geopolymerization process at an early age.•Two water phases existed in the initial geopolymer paste.•1H NMR is an ideal experimental tool for following the geopolymerization process.Proton nuclear magnetic resonance (1H NMR) was used to characterize the geopolymerization process of a metakaolin-based geopolymer. In the spin-lattice relaxation time (T1) distribution curve obtained for the first 15-min time point, two relaxation peaks were observed, which were assigned to two different water phases in the initial paste. Based on the evolution curve of the average mean value of T1, the geopolymerization process in the early age can be divided into four successive stages: the induction period, acceleration period, deceleration period and stabilization period. This work reveals that 1H NMR is a noninvasive and non-destructive method for the analysis of structural evolution during the geopolymerization process.

The decontamination and disposal of municipal solid waste incineration (MSWI) fly ash has great significance in the world. In this work, MSWI fly ash was successfully used as a raw material in sintering and preparing calcium sulphoaluminate (CSA) cement in the laboratory. Compressive strength, durability and microstructure of the prepared CSA cement-based materials were studied. The results show that compressive strength of the CSA cement has a developing trend similar to that of the Control Cement I which develops strength quickly at an early curing age, but after 7 d, strength increases more slowly. The prepared CSA cement-based materials perform well with respect to resistance to drying shrinkage, carbonation, and water permeation. The CSA cement mortar immersed in sulfate solution has a more compact microstructure and has the potential to be used in engineering constructions which require high resistance to sulfate corrosion. Parts of the chloride ion from the MSWI fly ash could be sintered within the cement clinker and subsequently stabilized in hydration products. The leaching values of heavy metals from these systems are all within the current threshold limits.

Modification of steel slag powder by mineral admixture and chemical activators to utilize in cement-based materials was studied in this work. The results showed that for cement pastes with steel slag alone, the normal consistency water requirement and compressive strength were decreased significantly. Both of the initial setting time and final setting time were also retarded than that of the control sample. When a compound admixture of ground granulated blast furnace slag (GGBFS) -steel slag powder added the compressive strength was evidently improved. Modification of steel slag powder by “Gypsum-type” and “Sodium-type” chemical activators were further studied. Cement paste with the modified compound admixture by 1.5 % calcium sulfate hemihydrate or sodium sulfate, its 28 days compressive strengths could reach to 75.4 and 76.2 MPa, respectively. X-ray diffraction (XRD) patterns showed that the main hydration products mainly included Ca(OH)2 and ettringite. It indicated that proper mineral admixture and chemical activators had a positive effect regarding early hydration of steel slag powder, and enhanced forming calcium silicate hydrate(C–S–H) gel and ettringite. This work contributes to understanding of how to sustainably manage wastes and byproduct materials and has the potential to provide several important environmental and economic benefits.

In order to study the influence of waste brick powder (WBP) and nano-modification on class C fly ash (CFA) based geopolymer, pore properties (i.e. bulk density, apparent porosity, and true porosity, and closed porosity) were tested according to the related Chinese National Standard, and the pore structure was also explored by mercury intrusion porosimetry (MIP); Water leaching procedure were performed to study the inner chemical environment; X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) were measured to the microstructure and modification mechanism. The results show that WBP as additive results in a denser structure of geopolymer; nano-modification improves the pore structure, ameliorates the anti-leaching ability of geopolymer by constraining the soluble ions in gels, makes the geopolymerization more complete, and results in a denser paste structure by filling gaps between the particles with amounts of reaction products.