锂渣对水泥浆体强度和收缩性能的试验研究

研究了不同掺量锂渣的水泥浆体强度、自收缩和干燥收缩,并采用压汞法和扫描电镜分析了水泥浆体的微观结构。结果表明:锂渣的掺入明显降低了水泥浆体的早期抗压强度、自收缩和干燥收缩,但后期抗压强度下降幅度降低,当锂渣掺量不超过15%时,锂渣可以提高水泥浆体的后期抗压强度。掺15%锂渣的水泥浆体120 d的孔隙率小于纯水泥浆体,且锂渣颗粒表面有大量水化产物生成。同时,锂渣的掺入明显降低水泥浆体10～50 nm的孔隙率,从而降低了水泥浆体的自收缩和干燥收缩。     

表面改性粉煤灰对水泥浆体强度和自收缩的影响

在生石灰激发下,采用水热-煅烧处理对粉煤灰进行表面改性,利用X射线衍射、扫描电镜和能谱分析等测试方法时表面改性粉煤灰的物相结构和化学组成进行了表征,并采用背散射扫描电镜和压汞仪研究了掺表面改性粉煤灰水泥浆体的微观结构.试验测定了掺表面改性粉煤灰的硅酸盐水泥浆体的抗压强度、自收缩和孔隙率.结果表明,表面改性粉煤灰颗粒表面生成了具有水化活性的β-C2S,其水化产生凝胶,明显改善了复合水泥浆体中粉煤灰颗粒与水泥基体的界面,降低了复合水泥浆体的孔隙率和自收缩,提高了掺表面改性粉煤灰复合水泥浆体的早期强度.     

矿粉、高钙灰及脱硫石膏对水泥收缩性能的影响

研究了50.0%(质量分数,下同)矿粉和高钙粉煤灰等量替代水泥对水泥净浆早期自收缩性能的影响及水泥砂浆的长期干燥收缩性能和初始开裂敏感性.结果表明,在水泥-矿物材料体系中,自收缩与矿物材料的水化活性成正相关性,用50.0%的矿粉和高钙粉煤灰替代水泥后,水泥浆体的自收缩率随着矿物材料活性的降低而降低;硫酸盐激发材料既具有增加水化程度和提高化学收缩的作用,又具有增加AFt量和产生膨胀的作用,因而对水泥浆体的自收缩影响不大;掺50.0%矿粉及1.0%元明粉可显著提高干燥收缩;脱硫石膏和煅烧脱硫石膏按照一定比例复合能显著降低干燥收缩;初始开裂时间、自收缩与矿物材料水化活性的相关性较大,自收缩越高则其开裂敏感性越大,早强措施增加开裂风险;采用矿物材料尤其是采用低活性矿物材料替代水泥可使水泥水化减缓,自收缩和干燥收缩减少,开裂敏感性降低.     

3℃下不同矿粉掺量对水泥水化影响的试验研究

试验采用直接法和近似矩形法研究了3℃环境下不同矿粉掺量的水泥浆体在一定龄期内的水化热以及水化程度。通过试验计算水泥水化放热量得出添加不同矿粉掺量的水泥浆体在3℃下的水化程度;比较不同配合比水泥浆体水化放热以及添加矿粉掺量的水泥水化程度得出其水化规律;同时提出水泥浆体在低温下水化热测定的改进办法。试验结果表明:10%、30%、50%的矿粉替代量在1、3、7、14、28 d龄期下水化放出的热量比不加矿粉掺合料的水泥浆体放热量低1%~8%,同时得出在一定龄期下,水泥的取代率越高水泥水化程度越低。     

-3℃下不同矿粉掺量对水泥水化影响的试验研究

通过试验研究在-3℃环境下不同矿粉掺量的水泥浆体在一定龄期内的水化热以及水化程度,利用试验数据采用近似矩形法和直接法计算出水泥水化放热量,分析出不同矿粉掺量的水泥浆体在-3℃的水化程度,比较不同矿粉掺量水泥浆体水化放热量得出其水化规律,比较不同入模温度对水泥水化的影响程度,同时提出水泥浆体处于负温下水化热测定的方法。试验结果表明:-3℃下10%、20%、30%的矿粉替代量在1、3、7、14、28 d龄期下水化放出的热量比不加矿粉掺合料的水泥浆体放热量低1%~6%。通过试验得出入模温度以及水化温度对水泥水化过程影响至关重要,同时在一定龄期下,矿粉对水泥的水化有抑制作用,矿粉取代水泥的量越高水泥水化放热量越低。     

偏高岭土对水泥浆体强度和收缩的影响

测定了不同偏高岭土掺量下水泥浆体的强度、自收缩和干燥收缩,并采用压汞法研究了水泥浆体的孔结构,探讨了偏高岭土对水泥浆体强度和收缩的作用机理。结果表明:偏高岭土可明显的提高水泥浆体的强度,降低其干燥收缩,且掺量越大,强度越高,干燥收缩越小。但偏高岭土的掺入会增加水泥浆体的自收缩,且随着掺量的增加而增加。偏高岭土具有高的火山灰活性,可明显的降低水泥浆体的总孔隙率,细化孔结构,从而改善了水泥浆体的性能。     

粉煤灰和矿粉对水泥胶砂自收缩的影响

试验研究了粉煤灰和矿粉对水泥胶砂自收缩的影响.结果表明:当胶砂比(质量比)为1:0.5,水胶比(质量比)为0.3时,随水化龄期延长,水泥胶砂自收缩增大,早期自收缩发展急剧.粉煤灰降低了水泥胶砂的自收缩,随着粉煤灰掺量(质量分数)增大,水泥胶砂自收缩减小;掺10%和20%粉煤灰水泥胶砂的21 d自收缩较纯水泥胶砂分别下降了21.1%和29.5%.水化早期(5d前),矿粉掺量(质量分数)在10%～20%时,随着矿粉掺量增大,水泥胶砂自收缩降低;掺10%和20%矿粉水泥胶砂的21 d自收缩较纯水泥胶砂分别增加了11.1%和6.6%.     

复合矿粉细度对高性能混凝土工作性影响

采用了五种细度层次的粉煤灰与一定细度的沸石粉按一定比例复合(称之为复合矿粉)，以不同掺量取代水泥，通过试验分析了复合矿粉的细度对高性混凝土工作性的影响。     

煤矸石细度和掺量对水泥性能的影响

研究了热活化煤矸石的细度和掺量对水泥浆体流动度、凝结时问,水泥硬化浆体抗压强度、化学结合水量和微观结构的影响．结果表明：提高热活化煤矸石的细度和掺量,水泥浆体的流动度降低,凝结时间延长;水泥浆体的抗压强度和化学结合水量随热活化煤矸石细度的提高而增大,随掺量的增加而减少．热活化煤矸石的细度和掺量对水泥硬化浆体的孔结构分布和形貌也有较明显的影响．     

粉煤灰对水泥浆体自收缩和抗压强度的影响

设计组装了水泥浆体自收缩测量装置,进行了不同粉煤灰掺量和水胶比的水泥浆体自收缩和抗压强度测试,采用压汞测孔仪(MIP)、扫描电镜(SEM)等测试技术研究了粉煤灰对水泥浆体孔结构、产物形貌等微观结构的影响,并对其影响机理进行了分析.结果表明:粉煤灰能够有效抑制水泥浆体的早期自收缩,在7d前,其自收缩随着粉煤灰掺量的增加而...     

Influence of organic coatings on the stability of macrodefect-free cements exposed to water

It is known that macrodefect-free (MDF) cements show instability in water, with swelling and reduction in strength. The weight and dimensional changes of three MDF cements, formulated from different aluminous cements, during immersion in quiescent tap water, were evaluated. The results show that the cement with the highest Al₂O₃ percentage had the lowest degradation after prolonged immersion. Hence, this material was selected for further analysis. As the time taken for water to diffuse into the body of MDF composites is considered a key factor in the collapse of their mechanical properties, the effect of organic coatings with different barrier properties on the composite behaviour, when exposed to water, was studied. The water permeability of seven surface coatings was evaluated by electrochemical impedance spectroscopy (EIS). Three of them were chosen for application to the selected MDF cement. The data presented show that the application of organic coatings, not necessarily characterised by extremely low water permeabilities, improves the stability of the composite when subjected to different conditions of exposure to water.     

膨胀水泥石的孔结构探讨

本文探讨了膨胀水泥和掺加膨胀剂的硅酸盐水泥的孔结构试验结果。分析表明,膨胀水泥石的孔结构特征不仅与水泥品种相关,而且与限制状态有很大关系。不同的膨胀水泥水化产生膨胀性晶体和填充性凝胶相不同,是造成不同水泥石孔结构特征差异的内在原因。影响膨胀水泥石孔结构特征的外在原因是限制条件,限制会明显改善膨胀水泥石的孔结构特征。     

环境协调型复合掺合料低水泥用量混凝土研究

为使水泥和混凝土可持续发展,大幅度降低水泥在混凝土中的含量,是减少环境负荷的关键。在不影响混凝土的各项性能的前提下,利用复合掺合料降低每立方米混凝土中的水泥用量,降低了工业渣体的排放对环境的影响,在使其资源化的同时,可制备出低水泥用量的各种环境协调型混凝土。     

锰渣和沸石作为水泥混合材的研究

通过高细粉磨和添加硫酸钠作为激发剂,激发锰渣与沸石的火山灰活性作为水泥混合材使用,利用SEM和压汞等测试方法对复合水泥水化后的微观形貌和孔结构进行了研究。研究结果表明:经激发的锰渣和沸石表现出很高的活性,并且可以明显改善水泥浆体的孔径分布;利用锰渣、粉煤灰和沸石配制P.C 32.5级水泥,混合材总量可以达到50%。     

复合胶凝材料胶砂强度性能研究

本文通过对不同比例的水泥、矿渣微粉和粉煤灰组成的复合胶凝材料的胶砂强度的测定,分析了水泥品种、不同比例的复合胶凝材料组成对复合胶凝材料胶砂强度的影响.通过试验,证明了水泥基复合胶凝材料的胶砂强度并不是简单的与几种掺合料活性指数线性相关,由于存在“诱导激活”等效应其作用明显优于单一的掺合料,反应了效应叠加的优点,存在着优化的掺量搭配.     

Zemente mit mehreren Hauptbestandteilen im Betonbau

Cements with Several Main Constituents in Concrete Construction – Sustainable Solutions for Building with Concrete In view of the reduction of climate‐related CO₂ emissions in the cement industry the manufacture of cements with several main constituents is of particular significance. One reason is the production process, which is more energy‐efficient and more ecological compared to “traditional” CEM I‐cements (Portland cements). But also the durability and performance in their use in concrete constructions are reasons why Portland‐composite cements (CEM II) and blastfurnace cements (CEM III) have meanwhile reached a market share of about 65% in Germany. For a few years now, approximately only 30% Portland cements have been used throughout Europe – with a continuous downward trend. The application‐specific properties, the possible areas of use as well as the ecologic advantages of the cements with several main constituents used in Germany so far are described in the following and illustrated by two practical examples. An outlook into possible further developments is given by examples of the performance of new cements in concrete.     

Exploring the potential of functionally graded materials concept for the development of fiber cement

In this study we establish the concept of functionally graded fiber cement. We discuss the use of statistical mixture designs to choose formulations and present ideas for the production of functionally graded fiber cement components for Hatschek machines. The feasibility of producing functionally graded fiber cement by grading PVA fiber content has been experimentally evaluated. Thermogravimetric analysis (TG) was employed to assess fiber distribution profiles and four-point bending tests were applied to evaluate the mechanical performance of both conventional and graded composites. The results show that grading PVA fiber content is an effective way to produce functionally graded fiber cement, which allows for a reduction of the total fiber volume without a significant reduction on modulus of rupture of composite. TG tests were found adequate to assess the fiber content at different points in functionally graded fiber cements.     

颗粒级配对矿渣水泥的性能影响研究

通过调整粉磨时间获得不同细度矿渣水泥,并将不同细度水泥按一定比例混合获得颗粒级配不同的矿渣水泥。试验研究了细度对水泥标准稠度用水量、凝结时间、强度发展和砂浆收缩变形的影响,结果表明:不同细度的矿渣水泥混合后改善了水泥的颗粒级配,对水泥性能有积极作用;不同细度的矿渣水泥混合后配制的砂浆抗压和抗折强度略有增加,收缩明显减小。     

三种聚羧酸系外加剂与水泥的相容性对比试验

研究了新疆市场上三种聚羧酸系外加剂与乌鲁木齐地区的三大品牌的普通硅酸盐42．5水泥的相容性。得出结论：三种水泥与聚羧酸系外加剂的相容性情况为屯河水泥较好,天山水泥其次,青松水泥较差。相容性较好的水泥与每一种聚羧酸系外加剂相容性均相对较好,相容性较差的水泥则与每一种外加剂的相容性均相对较差。粉煤灰矿物掺和料对聚羧酸系外加剂与水泥的相容性有较好的调节作用。     

Effect of environmental conditions on the properties of concretes with different cement types

The paper reports on the changes in properties of concretes with different cement types associated with environmental conditions. Three strength classes with three different cement types (ordinary portland cement PC 42.5 (CEM I 42.5), portland composite cements PKC-A 42.5 (CEM II/A-M 42.5) and PKC-B 32.5R (CEM II/B-M 32.5R)) were used in the study. Also, a mixture was prepared with PC 42.5 and silica fume (SF). The effects of variable ambient conditions on plastic shrinkage of fresh concrete and cement paste, compressive strength, modulus of elasticity, capillary absorption and drying shrinkage of hardened concrete were investigated. In contrast to PC 42.5 cement paste, plastic shrinkage cracks were observed in PKC-B 32.5 and PKC-A 42.5 pastes. Water absorption coefficients of all concretes stored in natural environment were higher at all ages as compared to coefficients of concretes kept in laboratory. Drying shrinkage values of concrete with SF, except the first week, were significantly lower than those of others. Although different behaviors for different cement types were observed, water–cement ratio was one of the dominating factors determining the behavior of concrete. This ratio should be lowered to improve the durability of concrete.