Carbonation Resistance of Sulphoaluminate Cement-based High Performance Concrete

The influences of water/cement ratio and admixtures on carbonation resistance of sulphoaluminate cement-based high performance concrete （HPC） were investigated. The experimental results show that with the decreasing water/cement ratio, the carbonation depth of sulphoaluminate cement-based HPC is decreased remarkably, and the carbonation resistance capability is also improved with the adding admixtures. The morphologies and structure characteristics of sulphoaluminate cement hydration products before and after carbonation were analyzed using SEM and XRD. The analysis results reveal that the main hydration product of sulphoaluminate cement, that is ettringite （AFt）, decomposes after carbonation.

High Water Content Material Based on Ba-Bearing Sulphoaluminate Cement

A new type of high water content material which is made up of two pastes is prepared, one is refute from lime and gypsum, and another is based on Ba-bearing sulphoaluminate cement. It has excellent properties such as slow single paste solidifing ,fust double pustes solidifing ,fast coagulating and hardening, high early strength, good suspeasion property at high W/C ratio and low cost. Meanwhile, the properties and hydration mechanism of the material were analyzed by using XRD, DTA- TG and SEM. The hydrated products of new type of high water content material are Ba-bearing ettringite, BaSO4 , aluminum gel and C-S-H gel.

Carbonation of Sulphoaluminate Cement with Layered Double Hydroxides

The increasing importance of the ecologically minded production of building materials makes it necessary to develop reasonable alternatives to the CO2-intense production of ordinary Portland cement （OPC）. The development of new or modified concrete is an important part of existing strategies to improve performance and minimize life-cycle costs. Therefore, we investigated carbonation resistance properties of sulphoaluminate cement （SAC） concrete incorporating layered double hydroxides （LDHs）. X-ray diffraction （XRD） and IR-spectroscopy were employed to characterize the component and structural changes of LDHs and cement paste before and after carbonation test. Carbonation resistance of concrete was experimentally evaluated. Finally, carbonation of Portland cement and SAC concrete was compared. The experimental results show that carbonation depth decreases remarkably with the addition of LDHs, especially the calcinated LDHs. Carbonation depth of SAC concrete is smaller than that of PC concrete regardless of curing time.

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

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.

STUDY ON HYDRAULIC REACTIVITIES AND CHEMICAL BONDS OF MINERALS OF SULPHOALUMINATE CEMENTS

Structures and hydraulic reactivities of minerals of sulphoaluminate cements, Ca4Al6SO16 and SrCa3Al6SO16, are studied by SCF-DV-X alpha method. The calculated results of net charges, energy level's of moleclar orbitals and bond orders all give support to the experimental result that the hydraulic reaction of strontium sulphoaluminate takes place more moderately, so its hydrate has better mechanical properties.

Effects of LiAl-Layered Double Hydroxides on Early Hydration of Calcium Sulphoaluminate Cement Paste

As a 3D micro-nano material, layered double hydroxides have been widely used in many fields, especially for reinforced composite materials. In this paper, Li Al-LDHs was obtained by a hydrothermal method. In order to investigate the effects of Li Al-LDHs on the early hydration of calcium sulphoaluminate（CSA） cement paste, compressive strength, setting time and hydration heat were tested while X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FT-IR）, scaning electron microscopy（SEM） and differential scanning calorimetry（DSC） analysis were employed. The results indicated that Li Al-LDHs could significantly improve the early compressive strength and shorten the setting time of calcium sulphoaluminate cement paste with 3 wt% concentration. Besides, the hydration exothermic rate within 5h was accelerated with increasing Li Al-LDHs content. Moreover, the addition of Li Al-LDHs did not result in the formation of a new phase, but increased the quantity of hydration products providing higher compressive strength, shorter setting time and denser microstructure.

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.

Effects of Portland cement addition on the early-age properties of solid-waste-based sulphoaluminate cement

This paper investigated the effects of different proportions of Portland cement addition(0-20%)on the setting time and early-age strength of solid-waste-based sulphoaluminate cement.The mechanism of hydration process was analyzed by X-ray diffraction(XRD)technology.It was found that the incorporation of Portland cement could reduce the early-age strength of the composite cement,and shorten the setting time.When the Portland cement reached 20%,the early-age strength of the composite cement was the lowest and the setting time was the shortest.The XRD analysis demonstrated that the addition of Portland cement could accelerate the hydration process of the composite cement,and the more the Portland cement was added,the faster the hydration process of the composite cement was observed.The main reason is that the addition of Portland cement could increase the alkalinity of the composite cement and promote the hydration of anhydrous calcium sulphoaluminate.This study provides an important reference for the production of solid-waste-based composite cement.

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 250?),and enhances its strength.

Investigation of PAT for Advanced Sulphoaluminate MDF Cement

The method of examining micro-pores in su lp hoaluminate MDF cement by means of the Positron Annihilation Technique (PAT) was discussed.The results show that the intensity I 2 of positrons annihilation wi th moderate life-span (τ 2≈330Ps) increases regularly with the addition of t he numbers of micro-pores (less than 250?). Therefore, the value of I 2 may b e used to opitomize the compactness and integrity of the MDF cement structure. A t the same time, the experiment result of PAT was compared with that of Mercury Intrusion Porosimeter (MIP).

Preparation and Performance Research of Cement-based Grouting Materials with High Early Strength and Expansion

Main performance of the cement grouting materials made up by Portland cement（PC） and sulphoaluminate cement（SAC） was investigated in this program, a kind of expanding agent（EA） which was mainly constituted by metakaolin and alunite was utilized for the compensation of the shrinkage, the hydration products and micro structure of the grouting materials were researched by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The results showed that a high expansion rate of the grouting materials could be reached as the expanding agent mixed in 6% of PC mass; the addition of SAC in the S2（PC：SAC：EA=34：6：2.25） brought a further improvement of the expansion rate of the grouting materials, the analysis of XRD and SEM showed that due to the reaction of expanding agent and SAC in the grouting materials, more ettringite crystal was generated, which resulted in a higher early strength, the addition of SAC played an expansion and strength reinforcement role in the grouting materials.

Experimental on C50 Ultra-high-early Strength Concrete

In this paper,C50 ultra-high-early-strength concrete was prepared with rapid-harden sulphoaluminate cement,alkali carbonate early strength agent,inorganic tribasic acid retarder and polycarboxylate water reducing agent. The properties testing results of C50 ultra-high-early-strength concrete indicated that the compressive strength at 12 h exceeded 37 MPa and at 3 d exceeded 59 MPa. Compared to the C50 ordinary reference concrete,the durability of C50 ultra-high-early strength concrete was investigated. The results indicated that C50 ultra-high-early-strength concrete had the same chloride ion permeability resistance,carbonization resistance and abrasion resistance to the C50 ordinary concrete. As to the sulfate resistance,the ultra-high-early-strength concrete was much better than the ordinary concrete.