Long Shizong

Investigation of the effect of minor ions on the stability of β-C2S and the mechanism of stabilization

Abstract In this paper the effect of minor ions on the stability of β-C 2 S has been studied. It is discovered that the effect of minor ions on the stability of β-C 2 S is closely related to the polarization ability of the ions. According to this the authors propose a new judgement, the ion polarization ability judgement, by which we can determine if minor ions have the stabilizing affect on β-C 2 S. The judgement is that those ions, either having smaller polarization ability than that of calcium ion or greater than that of silicon ion, all have the ability to effect the stability of β-C 2 S. This judgement is more practical than those made by other authors. In this paper a new mechanism about the stabilization has been described on the basis of applying the principles of thermodynamics and dynamics of the transformation of solid phases in accordance with the above judgement.

The pore structure and hydration performance of sulphoaluminate MDF cement

The hydration and pore structure of sulphoaluminate MDF cement were studied by X-ray diffractometer (XRD), scanning electron microscope (SEM) and mercury intrusion porosimeter (MIP) etc. The experimental results indicate that hydration products of the materials are entringites (AFt), aluminium hydroxide and CSH (I) gel etc. Due to its very low water-cement ratio, hydration function is only confined to the surfaces of cement grains, and there is a lot of sulphoaluminate cement in the hardenite which is unhydrated yet. Hydration reaction was rapidly carried under the condition of the heat-pressing. Therefore cement hydrates AFt, CSH (I) and aluminium hydroxide gel fill in pores. The expansibility of AFt makes the porosity of MDF cement lower (less than 1 percent) and the size of pore smaller (80 percent pore was less than 250Å), and enhances its strength.

Investigation on the formation of ettringite in the presence of BaO

Two mechanisms of forming ettringite have been proposed: one, through solution reaction; the other, through topochemical reaction. Using XRD and SEM, ettringite were investigated, which formed form very low SO42− concentration [SO42−] ≈ 10−10ML. That low SO42− concentration was caused by adding soluble BaO. The results show that ettringite can still form when mixing CaSO4 · 2H2O with C3A, CA, C12A7 or C4A3S∗ respectively. Since the SO42− concentration is far below that normally needed to crystallize ettringite ([SO42−] > 10−5ML), it is difficult to explain the formation of these ettringite by the above mentioned two mechanisms. The authors believe that solid-phase reaction mechanism should be the answer.

Investigation of PAT for advanced sulphoaluminate MDF cement

The method of examining micro-pores in sulphoaluminate MDF cement by means of the Positron Annihilation Technique (PAT) was discussed. The results show that the intensity I2 of positrons annihilation with moderate life-span (τ2≈330Ps) increases regularly with the addition of the numbers of micro-pores (less than 250Å). Therefore, the value of I2 may be used to opitomize the compactness and integrity of the MDF cement structure. At the same time, the experiment result of PAT was compared with that of Mercury Intrusion Porosimeter (MIP).

Research of positron annihilation and hydration of doped β-C2S

Abstract The lifetime spectrum of positron in β-C2S of added Na2O or P2O5 is studied with positron annihilation technique. According to the theory of the capture of positron, we discuss the relationship between lifetime spectrum parameters obtained through experiment and the microstructure of β-C2S. The results show that the long living component τ2 (about 470 ps) represents the capture of positron in the defects of Ca2+ vacancies and that the intensity of I2 of τ2 decreases with the increasing of Na+ and increases with the increasing of P5+. The results also verify that Na+ replaces Ca2+ and creates anion vacancies; while P5+ replaces Si4+ and creates cation vacancies. Vacancy concetration increases Na+ and P5+. Our work shows that the positron annihilation technique is a useful tool for studying the change of microstructure defects in doped β-C2S. The relationship between heat treatment and hydration activity of doped β-C2S and its impurities are also studied and discussed.

Effect of microwave processing on aluminate cement clinkering

When raw materials were preheated to 1000–1300°C by electricity and microwave was inputted for 1 min 5 s-4 mins, then alunminate clinkers were obtained. The f-CaO contents, XRD patterns and lithofacies analysis show that the microwave processing accelerates the clinkering reaction, and Fe2O3 is contributed to the aluminate cement clinkering. The appearance of liquid phase in process of microwave heating increases the microwave absorbability of materials greatly.

Investigation of β-C2S twins

Abstract Crystal microstructures, pure and doped with K 2 O or Na 2 O β-C 2 S, were studied by HREM. The results show that the twin was not observed in pure β-C 2 S. After doping, many (100) twins were produced and evidence of the existence of (001) twins was observed.

Effect of minor elements on silicate cement clinker

The effect of rare-earth and HX addition agent on the burn-ability of silicate cement clinker was investigated by orthogonal experiment. The result shows, compared with blank sample, f-CaO of the samples added with rare-earth and HX agent drops by 84.95%, its 3d and 28d comprssive strength enhances by 24.40% and 16.90%, respectively. It was discovered by means of X-ray diffraction and high temperature microscope analysis that sintering temperature of the sample added with rare-earth and HX addition agent is about 1320°C. At the same time, the burning temperature of tricalcium silicate desends and its crystal growth forming-rate increases. Tricalcium silicate content in burning clinker is higher and its crystal is larger.