Publications

At present, most municipal solid waste incineration (MSWI) bottom ash is directly landfilled, raising concerns about environmental issues and loss of resources. Due to its high mineral content, MSWI bottom ash is now being considered as a raw material to prepare alkali-activated materials (AAMs). However, the mineral fraction unavoidably contains metallic aluminium (Al) and zinc (Zn) scraps (<1 wt.%), which easily oxidise and generate H2gas under alkaline conditions. As a result, when using MSWI bottom ash to prepare AAMs, the formation of a porous structure, as well as expansive cracks (both detrimental to strength development) can be observed. In this research, thermal treatment of MSWI bottom ash, at temperatures of 500 and 1000 °C, was performed to deal with the issue caused by metallic Al/Zn. A series of tests, including Quantitative X-ray diffraction (QXRD) analysis, fineness measurements (particle size and surface area), and the dissolution test, were conducted to examine the effects of thermal treatment on as-received bottom ash. The results indicate that it is difficult to oxidise metallic Al/Zn at 500°C, but heating up to 1000 °C can realize the complete oxidation of Al/Zn, which in turn allows the wide utilisation of bottom ash in AAMs.
 Keywords: MSWI bottom ash, thermal treatment, alkali-activated materials.

Abstract In this paper, the atomic structures of sodium aluminosilicate hydrate (N–A–S–H) gels with different Si/Al ratios are studied by molecular dynamics simulation. An N–A–S–H gel model was obtained from the polymerization of Si(OH) 4 and Al(OH) 3 monomers with the use of a reactive force field (ReaxFF). The simulated atomic structural features, such as the bond length, bond angle, and simulated X‐ray diffraction pattern of the gel structure are in good accordance with the experimental results in the literature. Si–O–Al is found to be preferred over Si–O–Si in the N–A–S–H gel structure according to the amount of T–O–T bond angles and distribution of Si 4 (mAl). Pentacoordinate Al is identified in all simulated N–A–S–H models. It provides strong support to current knowledge that pentacoordinate Al in geopolymer does not only come from raw material. Furthermore, the structural analysis results also show that N–A–S–H gel with lower Si/Al ratios has a more cross‐linked and compacted structure.

The effect of aggregate on the chloride diffusivity is mainly due to the presence of interfacial transition zone(ITZ). The experiments were carried out at various volume fractions and aggregate sizes. The effect of aggregate on the chloride binding capacity was analyzed by scanning electron microscopy equipped with energy dispersive X-ray detector. The results show that the addition of aggregate can improve the pore structure of cement-based materials and the chloride diffusion process. When the ITZ content increases with the grain size or the aggregates are sufficiently closely-spaced that the adjacent ITZ overlaps in space, the ITZ effect could be dominant among all the effects of the blocking aggregate and the tortuosity of matrix paste. As a result, the fluid and ions transport would be significantly enhanced. In addition, the binding capacity is greater at a high ITZ content.

Applying blended materials with finer particle size or high reactivity could be an effective and economic way for improving the microsturcture of interfacial transition zone (ITZ). In this study, the porosity characteristics of ITZ in concrete made with OPC and blended binders were determined quantitatively by using backscattered electron microscopy (BSE) image analysis and mercury intrusion porosimetry (MIP) measurements. This paper especially focused on the effects of slag and limestone filler on the thickness and pore structure of the ITZ. Results indicated that the porosity at each distance reduces with increasing limestone filler from 0 to 5%, and a significant increase is observed in the sample with 10% of limestone filler. The addition of 5% of limestone filler is able to densify the pore structure of both ITZ and bulk matrix. The reduction in pore volume in the range coarser than 100 nm contributed to the largest decrease in the total pores. Increasing the incorporation level of limestone filler to 10% resulted in an increase in the total porosity. The influences of slag on the porosity characteristics were highly dependent on the replacement level and the determined pore size regions. The addition of 35% of slag reduces the porosity at all distances and produces a denser microstructure both in the ITZ and bulk cement matrix. However, this improvement disappears when the substitution amount reaches to 70%. The incorporation of slag as a partial substitute for Portland cement tends to refine the pore structure.

Differential shrinkage between repair material and concrete substrate is considered to be the main cause of premature failure of repair systems. The magnitude of induced stresses depends on many factors, for example the degree of restraint, moisture gradients caused by curing and drying conditions, type of repair material, etc. Numerical simulations combined with experimental observations can be of great use when determining the influence of these parameters on the performance of repair systems. In this work, a lattice type model was used to simulate first the moisture transport inside a repair system and then the resulting damage as a function of time. 3D simulations were performed, and damage patterns were qualitatively verified with experimental results and cracking tendencies in different brittle and ductile materials. The influence of substrate surface preparation, bond strength between the two materials, and thickness of the repair material were investigated. Benefits of using a specially tailored fibre reinforced material, namely strain hardening cementitious composite (SHCC), for controlling the damage development due to drying shrinkage in concrete repairs was also examined.