Yushun Li

Preparation and microstructure of green ceramsite made from sewage sludge

A pilot study was conducted to produce high performance green ceramsite by using sewage sludge, fly ash and silt. According to the theory of Riley, the proportions of raw materials were chosen to perform the sintering experiments. Thereby, the optimum proportion of sludge, fly ash and silt and sintering parameters were determined. The microstructure of the optimized mixture and the leaching of heavy metal elements were also analyzed. The lab testing results show that sintering parameters have significant impact on the performance of ceramsite. For solid waste ceramsite with high loss of ignition, inadequate pre-burning process lowers the strength and increases the water absorption. Low water absorption can be achieved by the enameled surface and closed pore structure. The high performance green ceramsite has the density grade of 700, water absorption of 6% and compressive strength of 6.6 MPa. The ceramsite is mainly composed of cristobalite and mullite. The leaching of heavy metal elements from the solid waste ceramsite are lower than the limits required by the national standard. This study shows that the utilization of solid waste ceramsite as the light weight aggregate is feasible and safe.

Failure behavior of adhesive bonded interface between steel and bamboo plywood

Abstract Bamboo–steel composite structure is constructed with bamboo plywood and cold-formed thin-walled steel, which are bonded by structural adhesive. To investigate the failure behavior of the adhesive bonded interface between bamboo plywood and steel, both experimental and numerical analyses were performed. An adhesive bonded member was designed to observe the failure behavior through the variation of stress distribution on steel sheet under tension. Further analysis of failure behavior was carried out by the numerical model through the stress analysis at the adhesive bonded interfaces. The experimental and numerical analyses revealed the failure mainly occurred at the adhesive bonding interface, caused by the stress concentration at the end of the overlap. The influences of modulus of elasticity of bamboo plywood in the parallel to grain direction and the thickness of steel sheet on the stress distribution at the adhesive bonding interface were investigated, which indicated the stress distribution had a major effect on the load-carrying capacity of the composite structural member. It also suggests enlarging the geometry properly and choosing the bamboo plywood with large modulus of elasticity in the parallel to grain direction are effective to increase the load-carrying capacity.

Progressive failure of bamboo-steel adhesive bonding interface subjected low-energy impact and tension in sequence

Abstract Bamboo–steel composite structure is a newly developed structure, composed of bamboo plywood and cold-formed thin-walled steel bonded by structural adhesive. This paper configured a three-dimensional (3D) numerical model to characterize the progressive failure of bamboo–steel adhesive bonding interface subjected low-energy impact and tension in sequence. A 3D cohesive zone model (CZM) with reloading trapezoid softening law was adopted to characterize the debonding behavior of the bamboo–steel interface. Investigations on the debonding damage propagation of the bamboo–steel interface subjected low-energy impact and tension after impact were completed, and the influence factors of the residual tensile strength were studied.

Low energy impact on the interface of bamboo-steel composites

ABSTRACT The bamboo-steel composite structure is a newly developed structure, combining Phyllostachys Pubescens (also called Moso bamboo) plywood and cold-formed thin-walled steel with structural adhesive. The aim of this study is to investigate the debonding propagation mechanism in detail at the bamboo-steel adhesive bonding interface (bamboo-steel interface) under low-energy impact using a progressive failure model. A three-dimensional cohesive zone model with reloading traction-separation law was adapted to simulate and characterize the progressive adhesive debonding at the bamboo-steel interface. Results show that the model can predict the failure behavior of the bamboo-steel interface under low-energy impact. The stress distribution and debonding propagation of the bamboo-steel interface were analyzed. The results reveal that the debonding is mostly due to the shear stress and the tensile peeling stress at the impact loading stage and the unloading stage, respectively. Furthermore, analyses of the impact failure show that the shear stress at the impact loading stage is generated by the tangential sliding between the steel sheet and bamboo plywood due to different flexural stiffness, while the tensile peeling stress at the unloading stage is due to the normal separation owing to different rebounding of the two different materials.

Effect of Chloride Ion on Free Nitrite Ion in Cement

This was an experiment in which chloride was externally permeated into cement paste. The influence of on the content and distribution of free-form in the cement paste was researched using the chemical quantitative analysis method. The action mechanism was investigated by the micro-means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the physical competitive adsorption of with on C-S-H and the chemical substitution of to NO2-AFm caused more free-form in the cement paste. In the cement paste with chloride salt erosion, the concentration in the erosion surface was the lowest, and the concentration reached the highest value at 10mm from the erosion surface. The concentration decreased gradually with the depth from the erosion surface.

Chemical Composition of Corrosion Products of Rebar Caused by Carbonation and Chloride

The microstructures of steel bars were studied by X-ray photoelectron spectroscopy (XPS), and the mechanism of corrosion of steel bars under the corrosion factors was elucidated. The results show that the passivation film and corrosive surface of the steel surface in the solution of the chloride-containing salt were coarser and the surface state was denser. The main corrosion products are FeOOH and FeO. The surface of the steel immersed in the simulated carbonized solution had loose pores. The main components are FeOOH, Fe3O4, and Fe2O3. The surface of the steel bar has a large amount of yellowish brown corrosion products in the simulated carbonization and chloride salt. The surface of the corrosion products was stripped and the main components are FeOOH, Fe3O4, and FeCl3, where the content of FeOOH is as high as 60%. The peak value of iron is gradually increased from the simulated chloride salt solution to the carbonized solution to the combined effect of carbonation and chloride salt; the iron oxide content is increased and corrosion of steel is obviously serious.

Effects of carbonation on micro structures of hardened cement paste

In order to investigate the effects of carbonation on the microstructure of cement concrete, the carbonation depth and microstructure of cement paste with 0.3, 0.4 and 0.5 water/cement ratio after 7, 14, 21 and 28 d accelerated carbonation were studied respectively. The results showed that with the increase of waterto- cement ratio and carbonation age, the carbonation depth was deepened with faster early carbonation speed and slower later carbonation rate. Carbonation densified the structure of hardened cement stone with refinement of pore structure and reduced porosity. Then, during the carbonation process from the surface to the inside of carbonation area, it was prone to form micro-cracks extending to the interior specimen, resulting in cement paste carbonation depth uneven. It is further illustrated that the color reaction method using phenolphthalein solution combined with X-CT and X-ray diffraction analysis is much more reasonable to evaluate the cement concrete carbonation degree. Moreover, during carbonation process sulfur element in cement paste migrated to the area un-carbonated and the concentrated shape of sulfur element is consistent with the coloring region in carbonation interface. Finally it was identified that carbonation not only reduced the pH value in cement concrete but also made prone to crack in carbonation zone, which increased the probability of reinforcement corrosion.