混合石膏作水泥调凝增强剂的研究

以天然硬石膏和天然二水石膏为主要成分的复合调凝剂,不仅可以调节硅酸盐系列水泥的凝结时间。而且其各龄期强度也有一定增长,与高温煅烧石膏作水泥调凝剂具有相似的效果。     

天然硬石膏的活性激发和膨胀控制

使用煅烧明矾、矿渣、水泥3种典型激发剂对天然硬石膏进行活性激发,研究了激发后天然硬石膏的凝结时间、强度、吸水率、软化系数、膨胀率等性能,并通过激发剂复掺控制了硬石膏的体积过度膨胀.     

石膏种类及掺量对硫铝酸盐水泥性能的影响研究

以二水磷石膏、半水磷石膏、无水磷石膏和天然硬石膏分别配置硫铝酸盐水泥,研究石膏种类及掺量对硫铝酸盐水泥性能的影响。结果表明:二水磷石膏配置的硫铝酸盐水泥早期抗折强度较高,但后期增长缓慢,而无水磷石膏配置的硫铝酸盐水泥抗折、抗压强度优于无水磷石膏和二水磷石膏,甚至略高于天然硬石膏,完全可以取代天然石膏配置硫铝酸盐水泥。     

改性盐石膏制备墙体砌块的研究

利用矿粉、硅酸盐水泥、促凝剂和碱性激发剂对盐石膏进行改性,配制的盐石膏基胶凝材料28d抗折强度6.0MPa,抗压强度33.4MPa,软化系数0.87。其主要水化产物为C-S-H凝胶和少量的钙矾石（AFt）、硬硅钙石[Ca6Si6O17(OH)2],盐石膏中的硬石膏经促凝剂的激发,其活性增强,水化生成二水石膏,与盐石膏中的二水石膏形成饱和溶液,并析出新的二水石膏晶体,形成结构骨架。外掺膨胀珍珠岩,制备了不同密度等级的墙体砌块,研究了不同掺量下砌块的各项性能,在降低密度的同时,获得了优良的热工性能和抗风化性能。     

石膏基复合材料性能影响因素的研究

从材料组分、缓凝剂掺量和水灰比,采用正交实验方法研究各因素对石膏基复合材料性能影响的规律。结果表明,石膏基复合材料的强度和软化系数均明显高于纯石膏;硅酸盐水泥对复合材料具有明显的促凝作用,当掺量在10%～15%时,水泥能提高石膏基复合材料的强度和软化系数,掺量过大,则会导致材料强度和软化系数下降;磷酸盐缓凝剂改变了二水石膏晶体生长习性和材料内的孔径分布,使得晶体粗化,孔结构劣化,最终导致强度下降。     

石膏组份对水泥强度的影响

本文考察不同组份石膏对水泥强度的影响，发现用硬石膏取代二水石膏可提高水泥的强度。石膏组成中硬石膏含量越高，水泥的强度增长越快。硬石膏组份中混有少量碳酸钙，将对提高水泥的早期强度有利     

石膏组份对水泥强度的影响

本文考察不同组份石膏对水泥强度的影响，发现用硬石膏取代二水石膏可提高水泥的强度，石膏组成中硬石膏含量越高，水泥绵强度增长越快，硬石膏组份中混有少量碳酸钙，将对提高水泥的早期强度有利。     

石膏晶型对水泥性能的影响机理研究

通过设计硬石膏替代不同比例的二水石膏系列实验,借助X射线粉末衍射仪(XRD)与电子扫描显微镜(SEM),研究了石膏晶型对水泥性能的影响,并对其影响机理进行了探究.结果表明:石膏的晶体差异导致了水泥强度的不同,掺入硬石膏的水泥强度较二水石膏的好;掺入硬石膏的水泥石形成的针状的钙矾石不仅对强度无影响而且可以填补水泥石的裂缝,从而增加了水泥石的密实度,而掺入二水石膏的水泥水化生成的柱状钙矾石晶体过大而且密,使水泥石产生较大的毛细裂缝,进而导致掺入二水石膏的水泥强度比较低.     

用硅酸盐水泥改性石膏的性能研究

本试验涉及到用不同掺量硅酸水泥改性的建筑石膏硬化体在水同养护制度条件上的强度，耐水性及尺寸稳定性。根据软化系数、溶蚀率、尺寸稳定性及早期强度等指标，提出了硅酸盐水泥在建筑石膏中的参考掺量及养护制度。并从凝结时间、水化热ＣａＯ浓度、酸碱度、电导率五个角度研究了建筑石膏与不同掺量硅酸盐水泥混合后的水化动力学特征。     

使用熟石膏提高水泥的强度

几年来,在生产矿渣硅酸盐水泥和火山灰质硅酸盐水泥时,我们曾一度使用陶瓷厂的废坯模——熟石膏代替天然二水石膏作缓凝剂,结果不仅缓凝效果显著,并且相应的水泥强度也有了不同程度的提高。废坯模是天然二水石膏粉磨至0.080毫米方孔筛筛余10％后,经过了1300℃左右的温度烘炒,其成分接近于半水石膏,再加水成型,其硬化后的成分接近于二水石膏。化学分析结果(％)如下:SiO_2 10.28,Al_2O_3 2.60,     

磷石膏制备复相磷石膏煅烧工艺研究

对磷石膏制备的复相石膏煅烧工艺进行了研究。结果表明:保温时间和升温速率对两种石膏的烧成比例影响较大。获得不同半水-无水比例的复相磷石膏体系可以通过控制升温速率和保温时间来实现。复相磷石膏与单相石膏比较,具有较好的早期强度和后期强度。     

Analysis of drying and saturating natural gypsum samples for mechanical testing

The stability of underground abandoned gypsum mines is dependent on the gypsum pillar's strength,and most abandoned mines are in a fully saturated condition. Moisture affects the strength of gypsum and is therefore commonly measured when testing rock strength. For most rocks, this is a simple task of weighing the rock's mass before and after oven-heating at a specified temperature and duration. For natural gypsum, however, this is not a straightforward process. Heating natural gypsum can result in dehydration and transformation of gypsum to hemihydrate and anhydrite, thus changing the physical characteristics of the gypsum such as its particle density which in turn affects the moisture content and strength measurements. To prevent transformation when determining the moisture content of gypsum,the American Society for Testing Materials(ASTM) recommends lowering the drying temperature from 110℃ to 60℃ . To investigate the temperature at which gypsum transforms to hemihydrate, we used a helium pycnometer to measure the particle densities of gypsum, hemihydrate and anhydrite. In this research, we suggest that a higher drying temperature of 80℃ can be used for drying gypsum without transforming gypsum to hemihydrate. Further, preparing saturated samples for mechanical testing,which is required in stability analyses of abandoned mines, is challenging due to the dissolution of gypsum when placed in water. To address this problem, we investigated the following methods to saturate gypsum cores taking into account the solubility of gypsum:(1) water immersion,(2) vacuum saturation, and(3) improved vacuum saturation. The research indicates that all the three methods are acceptable but they should be conducted using a saturated gypsum-water solution to minimize dissolution. Further, the research found that the improved vacuum saturation method saturated the test samples within 24 h, while duration of 30 h was required for the other two methods.     

Development of calcium sulfate–ggbs–Portland cement binders

Binders manufactured using a blend of gypsum, ground granulated blast furnace slag and Portland cements are technically viable and possess considerable environmental and economic advantages when compared to binders manufactured using Portland cement alone. As such, the evaluation of binders made from these materials offers a promising research focus in the quest to produce technically sound, environmental and economical binders for specialist uses as an alternative to traditional concrete binders of higher carbon footprint. The aim of the test programme was to investigate the viability of a series of binders designed to fulfil particular user needs while having significantly decreased carbon footprints.Two distinct series of binders were designed; the dominant ingredient in the first was calcium sulfate while in the second it was ggbs. Potential applications for both series of binders were considered and the strength development of each binder was analysed. In addition, the effect of water on the gypsum-based binders was analysed, as was the sulfate resistance of the ggbs-based binder.The results of the laboratory tests carried out were varied. For the calcium sulfate-based binders, those manufactured using anhydrite II as the dominant ingredient were found to achieve highest strengths. However these binders were found to be particularly susceptible to moisture-induced deterioration. For the ggbs-based binders, it was found that the early strength development was improved by the addition of small quantities of anhydrite II and gypsum. The strengths and sulfate resistance at later ages remained unaffected. These binders may have significant potential in situations where early strength development is a requirement.     

The influence of gypsum ratio on the mechanical performance of slag cement accelerated by calcium sulfoaluminate cement

This paper investigates the use of calcium sulfoaluminate cement to improve the strength of high-grade slag cement composed of granulated blast-furnace slag and anhydrite. Two quaternary binders, composed of granulated blast-furnace slag, Portland cement, calcium sulfoaluminate clinker and calcium sulphate are compared with the reference. The only parameter studied is the gypsum ratio in the calcium sulfoaluminate cement. The results of compressive strength testing on standard mortar (in accordance with the European standard NF EN 196-1) indicate that the early and medium-term mechanical performances increase as the amount of gypsum increases. To explain this, pore size distribution in the mortar was studied and XRD, DTA–TGA and SEM techniques were applied to pure paste. The investigation showed that the hydration reactions of the individual constituents are dependent on the gypsum ratio and that its variation can lead to the formation of different hydrates.     

Calcium sulfate hemihydrate activated low heat sulfate resistant cement

Investigations were undertaken to produce low heat sulfate resistant cement by activation of granulated slag obtained from the blast furnace process of iron making and phosphate industries with the calcium sulfate hemihydrate. Experimental data showed that cement gives fast setting characteristics in addition to high strength development. The setting time of cement was regulated with a small addition of set retarder without adversely affecting the strength development of cement. It is noted that beta hemihydrate plaster gives better strength results than the anhydrite activated cement. The results also confirm that granulated blast furnace slag can be replaced with phosphatic slag up to 10% by mass without loosing strength. DTA and X-ray diffraction analysis have been used to identify the hydration products formed in the hydrated cement. The heat of hydration data of cement is reported in the paper.     

无水石膏外墙板18年后的相组成和显微结构

用ＸＲＤ和ＳＥＭＥＤＡＸ研究了无水石膏外墙板使用１８年后的相组成和显微结构．结果表明：水泥水化产物的形成及其对二水石膏晶体的保护作用,和未水化ＣａＳＯ４的长期稳定性是无水石膏外墙板具有较好耐候性的关键．     

石膏掺量对硅酸盐和硫铝酸盐水泥复合体系性能的影响

硅酸盐水泥与硫铝酸盐水泥复合后水泥的矿物组成变得多而复杂,这种复合体系水泥的水化硬化过程是一个多元复杂体系的多种矿物的水化硬化过程。将硫铝酸盐水泥熟料、硅酸盐水泥、无水石膏以合适的比例混合,通过试验和分析,制得早期强度相近、28d强度接近或超过纯硫铝酸盐水泥的复合胶凝体系,得出石膏的最佳掺量。     

钛石膏作水泥缓凝剂研究

介绍了钛石膏中的杂质组成与形态,以及用钛石膏作水泥缓凝剂时,杂质对水泥性能的影响。研究结果表明,钛石膏中杂质主要为Fe(OH)3、FeSO4和Al(OH)3。杂质对水泥性能影响不大,不经预处理作水泥缓凝剂,其性能与采用天然石膏的水泥相当。     

Long-term evolution of delayed ettringite and gypsum in Portland cement mortars under sulfate erosion

The magnitude evolution of ettringite and gypsum in hydrated Portland cement mortars due to sulfate attack was detected by X-ray powder diffraction. The influences of sulfate concentration and water-to-cement ratio on the evolution of ettringite and gypsum were investigated. Experimental results show that the magnitude of ettringite formation in sodium sulfate solution follows a three-stage process, namely, the ‘penetration period’, ‘enhance period of strength’, and ‘macro-crack period’. The cracking of concrete materials is mainly attributed to the effect of ettringite. The gypsum formations occurred in two stages, the ‘latent period’ and the ‘accelerated period’. The gypsum formation including ettringite formation was relative to the linear expansion of mortars to some extend. Both water-to-cement ratio and sulfate concentration play important roles in the evolution of ettringite and gypsum.