Effect of Fine Steel Slag Powder on the Early Hydration Process of Portland Cement

Hydration heat evolution, non-evaporative water, setting time and SEM tests were peorormed to investigate the effect of fine steel slag powder on the hydration process of Portland cement and its mechanism. The results show that the effect of fine steel slag powder on the hydration process of Portland cement is closely related to its chemical composition, mineral phases, fineness, etc. Fine steel slag powder retards the hydration of portland cement at early age. The major reason for this phenomenon is the relative high content of MgO , MnO2, P2O5 in steel slag, and MgO solid solved in C3 S contained in steel slag.

Effect of Phosphorus and Fluorine on Hydration Process of Tricalcium Silicate and Tricalcium Aluminate

By means of hydration heat, XRD and SEM, effect of phosphorus and fluorine （P205 and F-） in phosphorous slag on hydration process of tricalcium silicate （C3S） and tricalcium aluminate （C3A） was explored. The results indicated that the early hydration exothermic rate of C3S and C3A was obviously lowered by P205 and F- in phosphorous slag, the second peak occurring time of C3A was delayed by 0.9 h, the exothermal output of C3S was reduced by 25.04% and the time of accelerating stage was postponed by 0.86 h. The early hydration degree of C3S and C3A was also decreased. Due to the influence of P205 and F, more pores and thinner crystals can be observed in the microstructure of hardened paste and the chance of cracks was reduced.

Hydration Process of Cement-Based Materials by AC Impedance Method

AC impedance is a new method to study the changes of pore structure and the hydration degree during the hydration and hardening process of cement paste by the change of the electrochemical parameters. Employing AC impedance method, we studied the hydration and hardening process of cement paste with fly ash and slag, and analyzed the influence of different hydration age, water-binder ratio and mineral admixture on the impedance parameters. Moreover, we compared the results with those by the conventional porosity testing method and X-ray diffraction method. The results showed that AC impedance could be taken as a new technology in cement and concrete research.

Effect of Nano-TiO_2 Addition on the Hydration and Hardening Process of Sulphoaluminate Cement

The influences of nano-TiO2 on the setting time, hydration process, hydration products and morphology of sulphoaluminate cement were studied by Vicar apparatus, isothermal calorimetry, X-ray diffraction （XRD）, thermal analysis and scanning electron microscopy （SEM）. The experimental results show that the incorporation of nano-TiO2 can obviously promote the setting and hardening process of sulphoaluminate cement, and shorten the interval between the initial and final setting time, the hydration induction period of sulphoaluminate cement is significantly shortened and the acceleration period begins immediately, but the hydration exothermic rate at hydration stationary phase is not obviously impacted. The nano-TiO2 additives have influence on the formation rate and degree of crystallinity, but do not affect the type of hydration process. The structure of hydration products is compact at middle age, but their content and microstructure do not change

Research on the Low-carbon Cementitious Materials:Effect of Triisopropanolamine on the Hydration of Phosphorous Slag and Steel Slag

Cement,phosphorous slag(PS),and steel slag(SS)were used to prepare low-carbon cementitious materials,and triisopropanolamine(TIPA)was used to improve the mechanical properties by controlling the hydration process.The experimental results show that,by using 0.06%TIPA,the compressive strength of cement containing 60%PS or 60%SS could be enhanced by 12%or 18%at 28 d.The presence of TIPA significantly affected the hydration process of PS and SS in cement.In the early stage,TIPA accelerated the dissolution of Al in PS,and the formation of carboaluminate hydrate was facilitated,which could induce the hydration;TIPA promoted the dissolution of Fe in SS,and the formation of Fe-monocarbonate,which was precipitated on the surface of SS,resulting in the postponement of hydration,especially for the high SS content.In the later stage,under the continuous solubilization effect of TIPA,the hydration of PS and SS could refine the pore structure.It was noted that compared with portland cement,the carbon emissions of cement-PS-TIPA and cement-SS-TIPA was reduced by 52%and 49%,respectively.

Evaluation on the natural gas hydrate formation process

Gas hydrates have endowed with great potential in gas storage,and rapid formation of gas hydrates is critical to use this novel technology.This work evaluated the natural gas hydrate formation process,which was compared from six parameters,including conversion of water to hydrate,storage capacity,the rate of hydrate formation,space velocity(SV)of hydrate reaction,energy consumption and hydrate removal.The literature was selected by analyzing and comparing these six parameters mentioned above,meanwhile placing emphasis on the three parameters of storage capacity,the rate of hydrate formation and space velocity of hydrate reaction.Through analysis and comparison,four conclusions could be obtained as follows.Firstly,the overall performance of the stirring process and the spraying process were better than other processes after analyzing the six parameters.Secondly,the additive types,the reactor structure and the reactor size had influence on the natural gas hydrate formation process.Thirdly,the energy consumption via reciprocating impact in the hydrate formation process was higher than that via stirring,spraying and static higee.Finally,it was one key for hydrate removal to realize the hydrate industrial production.

Effect of M/P and Borax on the Hydration Properties of Magnesium Potassium Phosphate Cement Blended with Large Volume of Fly Ash

The effect of the borax content and magnesia to phosphate ratio（M/P） on the hydration properties of the magnesium potassium phosphate cement（MKPC） with large volume of fly ash was investigated, and a five-hydration-stage for MKPCs was proposed. The results show that MKPC sets rapidly with less than 8% of borax, which is unfavorable to the application of MKPC on construction. Adding more than 8%（including 8%） of borax results in a secondary hydration peak for MKPC, in which the process of hydration can be divided into five stages, namely, pre-induction period, induction period, acceleration period, deceleration period and stable period. M/P ratios could not change the multi-step reactive stages but higher M/P ratios could accelerate the hydration. Borax tends to impact the formation of Mg-containing hydrated products.

VISUAL OBSERBATION OF HCFC141b GAS HYDRATE FORMATION/DECOMPOSITION PROCESS OUTSIDE OF A TUBE

In order to design a kind of heat exchanger suitable to the indirect-touched gas hydrate cool storage vessel, a visual observation of HCFC141b gas hydrate formation/decomposition process was presented through a self-designed small-scale visualization apparatus of gas hydrate cool storage. Based on the shooted photos and recorded temperatures, the formation/decomposition process of HCFC141b are described, some characteristics are concluded, and some suggestions of designing heat exchanger are indicated according to the specific characteristics of HCFC141b gas hydrate formation/decomposition process.

Simulation of the Accumulation Process of Biogenic Gas Hydrates in the Shenhu Area of Northern South China Sea

Previous work has largely discussed the relations between sediment structures and accumulation of gas hydrates in the Shenhu area of South China Sea, but has not documented why the gas hydrates occurred at the seafloor topographic highs. Many gas hydrate exploration examples abroad also indicate that the saturation of gas hydrates was higher at seafloor topographic highs. This work aims to understand why gas hydrates accumulated at topographic highs and why their saturation is higher.

Influence of Nano-SiO2 Addition on Properties of Sulphoaluminate Cement Based Material

The influences of different nano-SiO2（NS） contents on the mechanical properties and rheological behavior of sulfoaluminate cement（SAC） based composite materials were studied.Results show that with increasing content of NS,the apparent viscosity,and shearing strength of fresh paste gradually increase but the fluidity decreases.With a dosage of 3.0%NS,the tensile and flexural strengths of mortars at 56 days were increased by 87.0%and 84.6%,respectively,compared with that in the absence of NS,indicating that the toughness of hardened mortars is significantly improved.Besides,the exothermic peaks of hydration are obviously increased and will earlier occur,and the second and the third peaks appear 2.61 hours and 2.56 hours earlier,respectively than that in the absence of NS,and the hydration of SAC before 8 hours is accelerated.The forming mechanism of strengths was revealed by scanning electron microscopy（SEM）,hydration heat,X-ray diffraction（XRD） and derivative thermogravimetry（DTG）.The micro-aggregate filling effect and nucleation effect at early age and weak pozzolanic effect at late age of NS make the microstructure more compact,which obviously enhances the strength of SAC mortars.

Preparation of Micro-Iron Ore Tailings by Wet-Grinding and Its Application in Sulphoaluminate Cement

Herein,micro iron ore tailings(micro-IOTs)were prepared by wet-grinding and applied to improve sulphoaluminate cement(SAC)performance.The physicochemical properties of micro-IOTs were investigated by particle size analysis,XRD,and XPS.The hydrates trait and the hydration mechanism of micro-IOTs-SAC composite were studied by XRD,TGA,MIP,and SEM.The results demonstrated that micro-IOTs with an average grain diameter of 517 nm could be obtained by wet-grinding.The setting time of SAC gradually decreased with increasing micro-IOTs content.By adding 2%micro-IOTs,the compressive strengths of SAC pastes were enhanced about 22%and 10%at 4 h and 28 d,respectively.Moreover,the addition of micro-IOTs accelerated ettringite precipitation and changed its morphology,resulting in early strength improvement of the binary system.And increased later strength by micro-IOTs was closely related to the high content of AH_(3),fine pore structure,and high hydration degree of SAC.The findings suggested one new approach to utilize iron ore tailings in cementbased materials.

Enhanced debromination of 4-bromophenol by the UV/sulfite process：Efficiency and mechanism

Halogenated aromatic compounds have attracted increasing concerns due to their toxicity and persistency in the environment, and dehalogenation is one of the promising treatment and detoxification methods. Herein, we systematically studied the debromination efficiency and mechanism of para-bromophenol（4-BP） by a recently developed UV/sulfite process. 4-BP underwent rapid degradation with the kinetics accelerated with the increasing sulfite concentration, pH（6.1–10） and temperature, whereas inhibited by dissolved oxygen and organic solvents. The apparent activation energy was estimated to be 27.8 kJ/mol. The degradation mechanism and pathways of 4-BP were explored by employing N2O and nitrate as the electron scavengers and liquid chromatography/mass spectrometry to identify the intermediates. 4-BP degradation proceeded via at least two pathways including direct photolysis and hydrated electron-induced debromination. The contributions of both pathways were distinguished by quantifying the quantum yields of 4-BP via direct photolysis and hydrated electron production in the system. 4-BP could be readily completely debrominated with all the substituted Br released as Br-, and the degradation pathways were also proposed. This study would shed new light on the efficient dehalogenation of brominated aromatics by using the UV/sulfite process.