•Fly ash is modified by NaOH using fluidized bed reactor–vapor deposition (FBR-VD).•NaOH crystals are coated onto the surface of the fly ash particles.•FBR-VD improves the strength of paste and mortar without affecting the workability.•FBR-VD prompts the hydration around the FA, and FA is fixed to the paste by Ca(OH)2.Fly ash (FA) can improve the workability and durability of concrete. However, the utilization of FA is usually limited due to its low pozzolanic activity. In this study, a fluidized bed reactor was designed to modify FA by the fluidized bed reactor–vapor deposition (FBR-VD), using NaOH solution as the activation material. We investigated the pozzolanicity of FBR-VD modified FA (MFA), and the workability of cement paste. The results were compared against traditional chemical activation method, using Ca(OH)2, NaOH, Na2SO4, or NaCl. The microstructures and hydration products were analyzed by scanning electron microscopy (SEM), and thermogravimetric–differential scanning calorimetry (TG-DSC). The experimental results show that FBR-VD accelerates the early-age pozzolanic reaction of FA, without affecting the workability of the paste. The 7-day and 28-day activity indices of the paste and mortar with MFA were higher than those with raw FA, while the 60-day activity index of the paste became even close to that without FA. The SEM results indicate that FBR-VD can make the activation material coat onto the surfaces of the FA particles, breaking down part of the Si–O and Al–O bonds in the FA. The remaining NaOH crystals on the FA surface also promote the growth of Ca(OH)2 crystals during the hydration process, so the FA particles are fixed tightly to the hardened cement paste, resulting in a higher compressive strength. TG-DSC shows that the MFA has a stronger effect on consuming the Ca(OH)2 in the paste than traditional activation materials and methods, indicating an enhanced pozzolanic activity of the FA.

The mechanical property of a novel expanded polystyrene cement-based material (EPS-C), which was prepared by compressing semi-dry materials molding, was investigated. The compressive behavior was analyzed by compression tests to gain the energy absorbed during failure. Performance for impact resistance was tested by a self-made device. The results figures out that the EPS-C has good toughness and can reach strain of 0.7 without failure. The stress-strain curve is quite different from that of normal EPS concrete. It can be divided into three stages and in the third stage the compressing exhibits the highest energy absorption. With the rising of cement ratio, the impact force absorption (IFA) decreases first and then increases. The impact energy absorption (IEA) increases first and then decreases. The lowest IFA and the highest IEA appear at the cement dosage from 233 g/L to 267 g/L and from 233 g/L to 300 g/L, respectively.

This study aimed to introduce fluidized bed reactor-vapor deposition (FBR-VD) into the modification of fly ash (FA) using the activators of NaOH, Na2SO4, and NaCl. The compressive strength, non-evaporable water and the hydration degree fly ash (HDFA) were investigated. The scanning electron microscopy (SEM), and the X-ray powder diffraction (XRD) Rietveld analysis were also conducted. The results demonstrate that FBR-VD can benefit the compressive strength when the dosage rates of NaOH, Na2SO4 and NaCl are 0.1%, 0.5%, and 0.5%, respectively. The non-evaporable water and HDFA also increased at certain activator dosage rates. A modification layer consisting of nanometer-scale crystals forms on the surface of the FA beads, with NaOH or Na2SO4 applied. NaOH can react with FA and promote its pozzolanic activity. Na2SO4 and NaCl can benefit the HDFA by remaining undissolved, to increase their concentration around FA. The enhanced HDFA is also proved by the consumption of Ca(OH)2.