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.

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.

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.

Durability of Alite-calcium Barium Sulphoaluminate Cement

The durability of the cement was mainly studied. Under 1.0 MPa of hydraulic pressure for 8 hours, water could penetrate completely through the sample made by portland cement, but could not penetrate through that by alite-barium sulphoaluminate cement. Under the condition of freezing and thawing cycle, the loss ratio of compressive strength of the cement was only about 17.3% at curing 28 d ages, but the loss of portland cement was as high as 29.5%. Alite-calcium barium sulphoaluminate cement also has an excellent resistance to sulfate attack. The coefficients of resistance to sulfate attack of the cement exceeded 1.0. Meanwhile, the composition and microstructure of the hardened paste of alite-calcium barium sulphoaluminate cement were analyzed by XRD and SEM.

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

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.

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.

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).

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.

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.

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.

Effects of Technological Parameters on the Mechanical Performances of SAC-cementitious Materials

A new type of SAC-cementitious material was manufactured by taking sulphoaluminate cement(SAC) as the basic material, polyvinyl alcohol(PVA) as the organic polymer and adding coupling agent(KH). Its flexural strength can reach 165 MPa, the compressive strength can be larger than 267 MPa. A set of fitable technological parameters of the material were gained through experiments. In addition, the flexural strength and toughness can be improved greatly by adding KH, whose values can be increased by 49.76% and 14.55%, respectively.

改性硫铝酸盐水泥砂浆力学性能及耐久性能研究

过快的流动度损失和后期不稳定的强度发展限制了硫铝酸盐水泥工程中的进一步应用。因此以葡萄糖酸钠作为缓凝剂,掺入硅灰制备成改性硫铝酸盐水泥砂浆,并对其工作性能、力学性能和抗氯离子渗透性能开展了系统研究。研究结果表明:葡萄糖酸钠掺量0.4%可有效延长硫铝酸盐水泥砂浆凝结时间,提高砂浆流动性和抗氯离子渗透性能;硫铝酸盐砂浆工作性能、力学性能和抗氯离子渗透性能均随硅灰掺量的增加先提高后降低,硅灰最优掺量为20%。

防灭火喷涂材料黏附及封堵性能试验研究

为改善煤矿井下巷道喷涂防灭火材料黏附性差,易开裂、易脱落及封堵效果差等问题,研制了一种以粉煤灰为骨料,普通硅酸盐水泥、硫铝酸盐水泥和石膏为基料,可再分散乳胶粉(VAE)为外加剂的防灭火喷涂材料。通过单轴抗压强度实验、煤岩多相多场真三轴动态渗流实验以及扫描电镜实验等,研究了VAE对喷涂材料的黏附性能、胶结性能、力学性能、封堵性能的影响。结果表明,加入VAE可以促进水化产物中丝状黏结桥的形成,实现黏结桥与水化产物的铆接、桥连,构成一个致密的网络结构。这不仅可以提升喷涂材料的抗开裂能力,同时增强了材料与煤结合后的黏附性能、胶结性能以及封堵性能。加入1%VAE的喷涂材料能够充分包裹住煤体,在煤体表面形成致密的涂层,有效隔绝空气与煤体接触,从而预防煤自燃,研发的材料对防治巷道顶部煤自燃具有一定作用。

硅灰对硫铝酸盐水泥力学和电磁传输性能的影响

研究了硅灰掺量对硫铝酸盐水泥力学性能和电磁传输性能的影响.结果表明:随着硅灰掺量的增加,硫铝酸盐水泥的抗压强度和抗折强度均先增大后降低,硅灰的最优掺量为10%;硫铝酸盐水泥的电磁传输性能随着硅灰掺量的增加而增大,与未掺硅灰的样品相比,硅灰-硫铝酸盐水泥在3.94~5.99 GHz频段范围内电磁传输性能均有所提升,电磁透射率峰值最高提升了23.9%.

搅拌工艺对高掺量丁苯乳液改性硫铝酸盐水泥性能的影响

研究了搅拌速度与搅拌时间对高掺量丁苯乳液改性硫铝酸盐水泥砂浆的匀质性、含气量、流变性能、早期强度等宏观性能的影响,采用TGA、BET等微观手段研究了硬化砂浆的水化程度和孔隙特征。结果表明:延长搅拌时间、提高搅拌速率均可改善砂浆的匀质性和力学强度。但以176 r/min搅拌时,延长搅拌时间会提高新拌砂浆含气量,增大硬化砂浆“凝胶孔”含量,抑制水泥前1 h的水化。以108 r/min搅拌时,延长搅拌时间则促进水泥前1 h的水化。延长搅拌时间和提升搅拌速率阻碍砂浆絮凝,破坏水泥颗粒桥接,显著降低结构构筑速率。延长搅拌时间,砂浆屈服应力和塑性黏度降低。优化搅拌工艺,有助于为充填层修补砂浆的搅拌规范制定提供重要参数。

硫铝酸盐水泥基套筒灌浆料强度性能试验研究

以硫铝酸盐水泥作为套筒灌浆料的胶凝材料,在水胶比一定的情况下,研究掺入5%、10%、15%和20%的粉煤灰及养护温度为-5℃时该灌浆料的流动度和抗压强度。试验结果表明:粉煤灰掺量分别为5%、20%时,30 min后流动度分别为274 mm、293 mm;当粉煤灰掺量分别为5%、20%时,养护时间均为28 d时,灌浆料的抗压强度分别为80 MPa和98 MPa。由试验结果可知,随着粉煤灰掺入量的增加,灌浆料的流动性能逐渐增大,当掺量为20%时,套筒灌浆料的流动度性能最好;灌浆料的抗压强度随时间的推移呈上升趋势,粉煤灰的掺量为20%时,灌浆料的抗压强度最佳。

纤维素醚结构对CSA水泥砂浆拉伸黏结强度的影响

研究了固定水灰比条件下具有不同取代度和取代基团的5种纤维素醚在0.3%和0.6%掺量时对硫铝酸盐(CSA)水泥砂浆拉伸黏结强度的影响,并结合保水率测试及压汞法对砂浆孔结构进行分析,探讨了纤维素醚结构对其拉伸黏结强度的影响机制.结果表明:对于同类纤维素醚,高取代度的引气多,改性砂浆孔隙率大、拉伸黏结强度低;对于不同类纤维素醚,羟乙基甲基纤维素醚改性砂浆的孔隙率较羟丙基甲基纤维素醚改性砂浆的要小,拉伸黏结强度更高.基于测试结果提出了CSA水泥砂浆拉伸黏结强度影响因子模型.

复合缓凝剂改性硫铝酸盐水泥注浆材料性能试验研究

为了改善硫铝酸盐水泥注浆材料(HSAC)的注浆效果,降低硼砂对HSAC强度产生的不利影响,测试和分析了单掺和复掺硼砂与柠檬酸钠的HSAC浆体凝结时间、流动度、强度以及微观结构。结果表明:单掺硼砂的缓凝效果显著,但会对HSAC强度产生不利影响。掺入适量的柠檬酸钠可以有效挽回硼砂导致的HSAC强度损失,且对浆体的流动度与凝结时间无不利影响。其中,硼砂掺量为0.15%时,复掺柠檬酸钠对HSAC强度的提升效果最明显;通过对水泥水化后期结石体中钙矾石(AFt)生成量的测定,发现硼砂掺量一定时,复掺适量的柠檬酸钠能够促进AFt的生成,减少六方板状的Ca(OH)2(CH)生成量,有效减缓HSAC水化速度,从而改善其工作性能。

硫铝酸盐水泥对硅酸盐水泥早期水化和力学性能的影响

装配式建筑推动了建筑行业的快速转型,实现构件的快速脱模是实现装配式行业快速发展的基础。本文研究了硫铝酸盐水泥(CSA)在低取代率(水泥质量的2.5%~7.5%)下对硅酸盐水泥早期水化性能和力学性能的影响规律,通过凝结时间、抗压强度、水化热、XRD、TG、SEM等测试手段揭示其作用机理,为实现装配式构件快速脱模提供解决思路。结果表明,CSA的掺入可以缩短硅酸盐水泥的凝结时间,促进水泥的早期水化,提高早期力学性能。当CSA从2.5%增加到7.5%时,水泥初凝时间分别降低了30%、43%和49%,终凝时间分别降低了24%、40%和46%;5%CSA掺量可使水泥样品12 h抗压强度从5.2 MPa提高到12.8 MPa,提高了169%;此外,CSA的掺入对水泥样品后期力学性能也有一定提升作用。