古建筑修缮中粉化石灰的占比对灰浆性能的影响

古建筑修缮现场,块状生石灰原材料粉化变质不可避免,实际施工中也难免掺入粉化石灰。为了探究粉化变质石灰的占比对灰浆性能的影响,首先利用X射线衍射(XRD)、X射线荧光光谱(XRF)和热重分析(TG)对块状生石灰及粉化石灰的纯度及变质程度进行了定性及定量分析,然后以相同水灰比、不同粉化石灰占比制样,进行性能对比及机理研究。结果表明:石灰原材料纯度高,块状生石灰未变质,为纯CaO,粉化石灰部分变质,其中CaCO_(3)含量为17.93%。粉化石灰占比增加降低了试样的表面硬度,对养护28 d的试样力学强度影响小,对养护60 d的灰浆试样力学强度有增大趋势,粉化石灰占比达到50%时降低了灰浆的耐水性、抗冻性。干燥表观密度、显气孔率、吸水率、碳化深度及扫描电镜(SEM)结果分析得出性能差异主要是由于粉化石灰胶结性降低,以及制样时粉灰所需水少,相同水灰比条件下剩余游离水多,使得粉灰试样致密度低、孔隙率及吸水率大,从而加快了碳化。工程实际使用中可将粉化石灰占比控制在40%以内。

Enhanced photocatalytic performance of cementitious material with TiO_2@Ag modified fly ash micro-aggregates

A TiO2 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 TiO2/ZFAB modified cementitious materials is to further enhance the photocatalytic performance.Various Ag@TiO2/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 TiO2 in a cement system and is also useful to enhance the photocatalytic efficiency.With an increment of the amounts of Ag particles in the TiO2/ZFAB modified cementitious samples,the photocatalytic activities increased first and then decreased.The optimal Ag@TiO2/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 TiO2/ZFAB and TiO2 modified samples,respectively.This suggests that suitable Ag particles coupled with a ZFAB carrier could effectively enhance the photocatalytic effects and use of TiO2 in a cement system.Thus,ZFAB as a carrier could provide a potential method for a high efficiency engineering application of TiO2 in the construction field.

Fabrication of β-Sialon/ZrN/ZrON composites using fly ash and zircon

β-Sialon/ZrN/ZrON composites were successfully fabricated by an in-situ carbothermal reduction？nitridation process with fly ash, zircon and active carbon as raw materials. The effects of raw materials composition and holding time on synthesis process were investigated, and the formation process of the composites was also discussed. The phase composition and microstructure of the composites were characterized by means of XRD and SEM. It was found that increasing carbon content in a sample and holding time could promote the formation of β-Sialon, ZrN and ZrON. The proper processing parameters to synthesize β-Sialon/ZrN/ZrON composites were mass ratio of zircon to fly ash to active carbon of 49：100：100, synthesis temperature of 1550 °C and holding time of 15 h. The average grain size ofβ-Sialon and ZrN（ZrON） synthesized at 1550 °C for 15 h reached about 2 and 1μm, respectively. The fabrication process ofβ-Sialon/ZrN/ZrON composites included the formation ofβ-Sialon and ZrO2 as well as the conversion of ZrO2 to ZrN and ZrON.

Preparation and sintering properties of zirconia-mullite-corundum composites using fly ash and zircon

Zirconia-mullite-corundum composites were successfully prepared from fly ash,zircon and alumina powder by a reaction sintering process.The phase and microstructure evolutions of the composite synthesized at desired temperatures of 1 400,1 500 and 1 600°C for 4 h were characterized by X-ray diffractometry and scanning electronic microscopy,respectively.The influences of sintering temperature on shrinkage ratio,apparent porosity and bulk density of the synthesized composite were investigated.The formation process of the composites was discussed in detail.The results show that the zirconia-mullite-corundum composites with good sintering properties can be prepared at 1 600°C for 4 h.Zirconia particles can be homogeneously distributed in mullite matrix,and the zirconia particles are around 5μm.The formation process of zirconia-mullite-corundum composites consists of decomposition of zircon and mullitization process.

Silica-alumina molar ratio and some factors effect on the synthesis of zeolites from fly ash

In order to improve the activity and eliminate some impurities, pretreatment was used before hydrothermal synthesis. The fly ash was mixed with an aqueous NaOH solution, the alkali melted fly ash was also adopted, which is hydrothermally treated at about 104 ℃, and the liquid/solid ratio was controlled at 6：1. In order to control Si/Al molar ratio, SiO2 or Al2O3 powers were added to the fly ash. The results of XRD and SEM show that the alkali melted can activate fly ash and eliminate its quartz and mullite, along with the improvement of Si/Al molar ratio and alkalinity. In addition, zeolite Na-A changes into sodalite gradually, and nepheline is the synthesized intermediate product. Those results were discussed on the basis of a formation mechanism of zeolite from fly ash.

铁水预处理低成本生产实践

为了降低铁水预处理成本,对铁水预处理过程参数进行优化,包括喷粉速率、喷枪插入深度等参数,并且在不影响脱硫效率的前提下,采用低CaO含量的钝化石灰粉替代高CaO含量的钝化石灰粉进行喷吹脱硫尝试。结果表明,钝化石灰粉消耗减少0.963 kg/t铁,镁粉脱硫效率提高6.9%,低CaO含量的钝化石灰粉不影响脱硫率。

Effects of Nano Silica, Micro Silica, Fly Ash and Bottom Ash on Compressive Strength of Concrete

In this study, SCM （supplementary cementitious materials）, such as nano silica, micro silica, fly ash and bottom ash, have been evaluated for optimal level of replacement as blending material in cement and concrete. The physical and chemical properties of the above materials were first analyzed. This study focused on compressive strength of concrete with different mixes at different ages. In many cases, products made with fly ash, micro silica, nano silica and bottom ash perform better than products made without them. Test results obtained in this study indicate that up to 5% nano silica, 10% micro silica, 20-30% fly ash and 10% bottom ash could be advantageously blended with cement without adversely affecting the strength. However, optimum levels of these materials are 1-3% nano silica, 3-8% micro silica, 10% fly ash and 5% of bottom ash when we consider the strength of concrete. All percentages are defined by weight unless otherwise mentioned.