Mingfang Ba

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.

Effects of specimen shape and size on water loss and drying shrinkage of cement-based materials

The effects of specimen size and shape on development of water loss and shrinkage of mortar and concrete respectively were investigated. The experimental results showed that the effects of specimen size and shape on water loss ratio were consistent with those on drying shrinkage strain. It is also indicated that drying shrinkage strain has obvious linear correlation with water loss ratios independent of specimen size and shape. The effects of specimen size and shape on the water loss ratio were embodied in established model of averaged relative humidity improved by considering effects of sequential hydration and calculated by finite difference method. Furthermore, the effects of specimen size and shape on drying shrinkage strain of concrete were experimentally deduced and applied to modify criterion EB-FIP1990. The comparison between experimental and calculated results shows that the modified EB-FIP1990 can be adopted to predict drying shrinkage strain of concrete with reasonable accuracy.

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.

Designing Method of Anti-Neutralization for Vehicle Tunnel Lining Concrete

The neutral erosion of lining concrete in vehicle tunnel under the condition of load and composite acid gases is noticeable. The anti-neutral analysis and prediction of an under-river tunnel lining concrete were discussed, and the neutral level was analyzed by a numerical way based on the effect of load level and composite acid gases. It was proposed that the anti-neutral level affected by moisture content exists a high and low range and the neutral depth increase with the increase of capillary porosity. Then the design method for highly anti-neutral lining concrete of vehicle tunnel was put forward based on the corrected carbonation depth. Finally the micro-structural parameters of highly anti-neutral lining concrete, such as moisture content, content of Ca(OH)2 and capillary porosity in concrete, were analyzed. The content of Ca(OH)2 was determined to be greater than or equal to the solubility of Ca(OH)2 under the condition of environmental temperature. The critical maximum connected capillary porosity was 9.15%. The research provides basis for the design and preparation of anti-neutral lining concrete of vehicle tunnel.

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.