Shuguang Hu

An in-situ synthesis of Ag/AgCl/TiO2/hierarchical porous magnesian material and its photocatalytic performance.

The absorption ability and photocatalytic activity of photocatalytic materials play important roles in improving the pollutants removal effects. Herein, we reported a new kind of photocatalytic material, which was synthesized by simultaneously designing hierarchical porous magnesian (PM) substrate and TiO2 catalyst modification. Particularly, PM substrate could be facilely prepared by controlling its crystal phase (Phase 5, Mg3Cl(OH)5·4H2O), while Ag/AgCl particles modification of TiO2 could be achieved by in situ ion exchange between Ag+ and above crystal Phase. Physiochemical analysis shows that Ag/AgCl/TiO2/PM material has higher visible and ultraviolet light absorption response, and excellent gas absorption performance compared to other controls. These suggested that Ag/AgCl/TiO2/PM material could produce more efficient photocatalytic effects. Its photocatalytic reaction rate was 5.21 and 30.57 times higher than that of TiO2/PM and TiO2/imporous magnesian substrate, respectively. Thus, this material and its intergration synthesis method could provide a novel strategy for high-efficiency application and modification of TiO2 photocatalyst in engineering filed.

Research on optimizing components of microfine high-performance composite cementitious materials

The relationship between material components and mechanical properties was studied in terms of composite material principles and orthogonal experimental design. Moreover, the microstructure of microfine high-performance composite cementitious material (MHPCC) paste was investigated by means of scanning electron microscopy (SEM) methods. The results showed that the composite material consisting of blast furnace slag (BFS), gypsum (G{sub 2}) and expansive agent (EA) could obviously improve the strength of the cementitious material containing 40% fly ash (FA). Although microfine cement (MC) was merely 45% percent of the MHPCC, the compressive strength of MHPCC paste was higher than that of neat MC paste. BFS played an important role in MHPCC. The optimum-added quantity of BFS was 15%. The needle-shaped ettringite obtained from the EA reacting with Ca(OH){sub 2} forms a three-dimensional network structure, which not only improved the early strength of MHPCC paste but also increased its late strength. The reason was that the network structure, which was similar to a fiber-reinforced composite, was formed in the late period of hydration with the progress of hydration and the deposition of hydration products into the network structure.

TiO 2 @Ag修饰的粉煤灰微集料增强水泥基材料光催化性能

Abstract A TiO 2 photocatalyst is coated on the surface of a zeolite fly ash bead (ZFAB) to improve its dispersability and exposure degree in a cement system. The application of Ag particles in TiO 2 /ZFAB modified cementitious materials is to further enhance the photocatalytic performance. Various Ag@TiO 2 /ZFAB modified cementitious specimens with different Ag dosages are prepared and the characteristics and photocatalytic performance of the prepared samples are investigated. It is observed that the multi-level pore structure of ZFAB can improve the exposure degree of TiO 2 in a cement system and is also useful to enhance the photocatalytic efficiency. With an increment of the amounts of Ag particles in the TiO 2 /ZFAB modified cementitious samples, the photocatalytic activities increased first and then decreased. The optimal Ag@TiO 2 /ZFAB modified cementitious sample reveals the maximum reaction rate constant for degrading benzene (9.91 × 10 −3 min −1 ), which is approximately 3 and 10 times higher than those of TiO 2 /ZFAB and TiO 2 modified samples, respectively. This suggests that suitable Ag particles coupled with a ZFAB carrier could effectively enhance the photocatalytic effects and use of TiO 2 in a cement system. Thus, ZFAB as a carrier could provide a potential method for a high efficiency engineering application of TiO 2 in the construction field.

Hydration mechanism of silica fume-sulphoaluminate cement

Setting time and strength of sulphoaluminate rapid hardening cement (SAC) incorporated in the presence and absence of silica fume (SF) were determined. Combined with the techniques of isothermal calorimeter, XRD and FSEM, the hydration kinetics of the two systems and the effect mechanism of SF on SAC were investigated. The experimental results showed that SF was proved to be beneficial for SAC system, in terms of setting time and late strength gain. Evidence of accelerator effect of silica fume was found during the first 8 hours of hydration. The formation of AFt was accelerated and the microstructure of the hydration products grew denser with incorporation of SF. SF was proved to play the role of dispersion and setting control at early age and had a greater contribution to later strength due to the increment of crystal nucleation point and the pozzolanic activity. Therefore, SF can be used to not only control the hydration kinetics of SAC, but also develop the late strength and improve the microstructure.

Effect of curing regime on degree of Al3+ substituting for Si4+ in C-S-H gels of hardened Portland cement pastes

The effect of curing regime on degree of Al3+ substituting for Si4+ (Al/Si ratio) in C-S-H gels of hardened Portland cement pastes was investigated by 29Si magic angel spinning (MAS) nuclear magnetic resonance (NMR) with deconvolution technique. The curing regimes included the constant temperature (20, 40, 60 and 80 °C) and variable temperature (simulated internal temperature of mass concrete with 60 °C peak). The results indicate that constant temperature of 20 °C is beneficial to substitution of Al3+ for Si4+, and Al/Si ratio changes to be steady after 180 d. The increase of Al/Si ratio at 40 °C is less than that at 20 °C for 28 d. The other three regimes of high temperature increase Al/Si ratio only before 3 d, on the contrary to that from 3 to 28 d. However, the 20 °C curing stage from 28 to 180 d at variable temperature regime, is beneficial to the increase of Al/Si ratio which is still lower than that at constant temperature regime of 20 °C for the same age. A nonlinear relation exists between the Al/Si ratio and temperature variation or mean chain length (MCL) of C-S-H gels, furthermore, the amount of Al3+ which can occupy the bridging tetrahedra sites in C-S-H structure is insufficient in hardened Portland cement pastes.

Design and test of new cement based microwave absorbing materials

Combined with space electromagnetic wave propagation principle, a design idea of space wave impedance matching to advantage absorption and matching for new cement based microwave absorbing materials (CBMAM) is given to aim at the current existing problems for CBMAM in this paper. To test and verify this idea, continuous basalt fiber, spherical expansion perlite with closed pore and graphite are used as components. A new CBMAM characterized with better microwave absorbing properties (the minimum reflectivity is -11.8 dB), wide frequency bandwidth (reflectivity less than -10 dB reaches 4GHz of bandwidth), better mechanical properties (28 d compressive strength is 16.9Mpa, bending strength is 2.27 Mpa), is prepared by using 20 mm sample between 8 to 18 GHz. The results provide a basis to the design and preparation of CBMAM.

Hydration products of cement-silica fume-quartz powder mixture under different curing regimes

Composition, morphology, and structure of hydration products in hardened pastes of three kinds of blended cement (cement-silica fume, cement-quartz powder and cement-silica fume-quartz powder) hydrated under different curing regimes (standard curing, 90 °C steam curing, 200 °C and 250 °C autoclave curing) were investigated by X-ray diffraction and field emission scanning electron microscope equipped with EDAX system. Results showed that the main hydration products in three kinds of hardened pastes under standard curing condition are all C-S-H gels, CH, and AFt. Under 90 °C steam curing condition, the main hydration products of cement-silica fume and cement-silica fume-quartz powder are C-S-H gels, whereas those of cement- quartz powder are C-S-H and CH. Under 200 or 250 °C autoclave curing condition, no obvious crystallized CH phase is found in hardened pastes of three kinds of blended cement, and C-S-H gels are transformed into one or more crystalline phases such as tobermorite, jennite, and xonotlite. The chemical composition and morphology of these crystalline phases depend on the composition of mixture and autoclave temperature.

Preparation and Design of Function Aggregate in Concrete

In order to essentially improve interfacial transition zone between cement paste and aggregate, the concept and ideal model of function aggregate are developed. Function aggregate is composed of a porous matrix with high strength and low water absorption, and a coating layer which can hydrate in cement paste. It can improve ITZ between aggregate and cement paste and control curing range of cement paste. Based on optimization of raw materials and processing techniques, high strength aggregate with low absorption and minor C2S and C4AF phase in coating layer is acquired. Results indicate that cordierite is formed in aggregate when MgO content reaches 2%, and it shows that the presence of cordierite minimizes the potential for micro-crack formation, thus decreases water absorption.

Improvement of the FRP sheet bonded to concrete substrate by silane coupling agent

We experimentally studied the fine lightweight aggregate with the particle size range of 3.15-4.75 mm used as functional bridge between FRP sheet and concrete substrate. However, problems would appear and how to deal with the interfacial transition zone (ITZ) and make it stronger is the key point for this concept. Considering that silane coupling agent (SCA) can provide a better bond on a silicon-containing material surface, it was introduced as a modifying material to further improve the bond quality of the ITZ between lightweight aggregate and cement paste. Results indicated that the water absorptivity of lightweight aggregate can be controlled by SCA solutions, and the pull-off bond strength, mechanical strength, and microhardness were increased, which was attributed to the optimized microstructure under the condition of an appropriate concentration of SCA.

Dehydration Characteristics of C-S-H with Ca/Si Ratio 1.0 Prepared Via Precipitation

Calcium silicate hydrate (C-S-H) with Ca/Si ratio 1.0 was prepared via precipitation in solution and heated at various temperatures to investigate its dehydration behavior. The dehydration, structural collapse and recrystallization characteristics of C-S-H and its microstructural change during heating process were investigated by XRD, SEM, Raman and TG-DSC techniques. C-S-H gradually lost non-evaporable water upon heating, about 50% and 80% non-evaporable water was removed below 200 and 400 °C, respectively, and the rest was removed up to about 1 000 °C. At 400 °C, dehydrated C-S-H exhibited the increasing disordering of calcium/silicon environment and the decreasing symmetrical bending vibration of Si-O-Si of Q2 silicate chains. At 650 °C non-bridging oxygen atoms (Onon) attached to silicon were almost removed, and significant structural change occurred, and at 815 °C C-S-H dehydrated to wollastonite.