Papers by Author: Jun Chang

Abstract: The testing method for detecting cement paste agglomeration is investigated. Furthermore, the procedure and feasibility are also discussed. Paste agglomeration is an abnormal phenomenon of part hydration along with many granules forming. Base on measurement of cement setting time, needle-penetration method is used to check the degree of agglomeration by vicat apparatus. Through researching the influence of cement fineness, content of gypsum and hydrating time on amount of agglomeration, the dependability, reproducibility and enantiotropy of this method are analyzed. The results show that the variation laws of paste agglomeration could be reflected by needle-penetration method effectively, and this method is easy to be carried out. There are better reproducibility and enantiotropy, and this method be used to study the mechanism of agglomeration.

Abstract: The effects of carbonation on structure and properties of steel slag specimens are evaluated by some different testing technologys in this paper. The experimental results of strength and soundness show that the compressive strength of samples is improved 6-8 times due to carbonation, and carbonated specimens have qualified autoclave soundness. Also the carbonation reactions of steel slag and the reason that why strength and soundness improved are analyzed by chemical titration, XRD, TG, SEM and MIP etc. Experimental results indicate that in steel slag specimens, f-CaO, f-MgO, partial C2S and C3S minerals could be carbonated, and 105～110 gram CO2 gas could be sequestrated after carbonating per kilogram of steel slag specimens.

Abstract: Accelerated carbonation is a new technology of materials preparation, which may have potential for the treatment of industrial solid residues and the sequestration of CO2, an important greenhouse gas. In this study, accelerated carbonation was used to recycle steelmaking slag and sequestrate CO2 to manufacture building materials. The experimental results show that the strength of specimens increases along with the increase of carbonation degree. Moisture content, carbonation temperature and curing time have significant effects on the degree of carbonation, and carbonated specimens have larger weight increase and compressive strength increases under the condition of moisture content 12.6%，reaction time 117 min and reaction temperature 361 K. The SEM and XRD analyses indicate that dogtooth like CaCO3 crystals appear on the surface of carbonated aggregate specimens. Strength and soundness test shows that steelmaking slag building materials have higher strength and eligible soundness after accelerated carbonation.

Abstract: In coastal areas, corrosion has been found in bridge piers made of Portland cement concrete. In an trail to protect the piers from further damages, Ba bearing sulphoaluminate cement concrete was tested as the repairing layers. It is showed that the Ba bearing sulphoaluminate cement concrete has a lower porosity and a more compact structure than Portland cement concrete under the same conditions, and consequently, better performances, such as high strength and corrosive resistance both in lab and real corrosive environments. Stimulating experiments indicate that Ba bearing sulphoaluminate cement is more suitable for repairing bridges in coastal area.

Abstract: The phase composition of (1-x)BaO·xSrO·0.7TiO2·0.3Nb2O5 (BSTN) composite ceramics was analyzed by XRD, and the effect of Sr/Ba ratio on the dielectric properties of BSTN was investigated by impedance analyzer. The results showed that any sample with different x value contained two phases-the perovskite phase and the tungsten bronze phase. The dielectric constants of BSTN basically decreased while the tanδ increased with the increase in x value. Both dielectric constant and tanδ decreased with the applied frequency increased for the same x value. There were two Curie points for BSTN composite ceramics. The first one belonging to the perovskite phase decreased with the increase in x value, but the second one belonging to the tungsten bronze phase kept almost constant at about 300°C.