Junzhe Liu

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.

Study on the properties of sea sand concrete

Sea sand concrete is a kind of concrete in which mixed sea sand as fine aggregate, which is large-scale application in the coastal areas in recent years, especially in Ningbo area. The sea sand solves the problem of river sand shortage, coupled with cheaper price, most of the ready-mixed concrete companies are willing to use desalted sea sand instead of river sand. Many companies even are using sea sand without any treatments. The history of using sea sand in our country is very short, so the durability of the sea sand concrete need to be tested by many projects in the future, along with the development of science and technology and the invention of precision instruments, the durability of sea sand concrete will be adequate assurance. Ningbo area has a wide range usage of sea sand concrete. By measuring the strength of sea sand concrete with fly ash, finding out the law of strength for the sea sand concrete by the presence of fly ash. At the same time, we used electron scanner to analysis the sea sand concrete internal microstructure, researched the influence of chlorine salts on sea sand concrete micro-structural features.

Study on the strength of sea sand concrete introduced by chloride ions

In sea sand by the determination of free chlorine ions to study the chloride ion to the strength of sand concrete. Experimental data show that between 0% to 0.1% chloride ion content of sea sand concrete strength comparison between the value of a group that is found in 20% of fly ash were mixed with 3 days flexural strength is increased with the concentration of chloride ion Rise, the other group had no obvious rule, dilute the sand and did not play down the comparison that does not dilute the sand sea sand either 3 days or 28 days strength values are higher than the desalination of sea sand, the presence of chloride ions in sea sand Early strength has a positive role in promoting.

Study on Performance of Concrete Made from Sewage Sludge Ceramsite

In this paper, using sewage sludge carried out to manufacture high performance ceramsite. At the same time, the performance of concrete made from sewage sludge ceramsite was analyzed. The results show that the ceramist is mainly composed of cristobalite and mullet, and has dense enamel structure on surface and honeycomb closed fine porous structure in internal. Too large ceramsite size can cause concrete strength decrease, poor stability and workability; mineral admixtures make strength and workability of ceramsite concrete improve, but excessive addition could reduce concrete strength particularly in the early stage, so there is a reasonable dosage; ceramsite concrete strength is increased with the decrease of water-cement ratio, the increase of strength is not obvious when water-cement ratio reduced to a certain extent; increasing sand-ratio can improve concrete strength, but have adverse impact on the workability of fresh concrete.

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.

Using sludge ceramic to prepare LC40 lightweight aggregate concrete

Researched the mix proportion of using self-made high-performance sludge ceramic to prepare LC40 LWAC. Studied the effect of ceramic-size, supplementary cementitious materials, water-cement ratio and sand-ratio on the LWAC performance. The study shows, size of ceramic too large can cause strength decrease, poor stability and workability; supplementary cementations materials make strength and workability of LWAC improve, but excessive addition could reduce concrete strength particularly in the early stage, so there is a reasonable dosage; LWAC strength is increased with the decrease of water-cement ratio, but for the limit of strength of LWA, the increase of strength is not obvious when water-cement ratio reduced to a certain extent; increasing sand-ratio can improve concrete strength, but have adverse impact on the workability of fresh concrete. Using the study results, optimized the concrete mix proportion and prepared LC40 LWAC with density level 1700, slump degree over 18cm, extended degree over 50cm.