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-Performance and Multifunctional Cement-Based Composite Material

Concrete is a continuously evolving material, and even the definition of high-performance concrete has changed over time. In this paper, high-performance characteristics of concrete material are considered to be those that support the desirable durability, resilience, and sustainability of civil infrastructure that directly impact our quality of life. It is proposed that high-performance material characteristics include tensile ductility, autogenous crack-width control, and material “greenness.” Furthermore, smart functionalities should be aimed at enhancing infrastructure durability, resilience, and sustainability by responding to changes in the surrounding environment of the structure in order to perform desirable functions, thus causing the material to behave in a manner more akin to certain biological materials. Based on recent advances in engineered cementitious composites (ECCs), this paper suggests that concrete embodying such high-performance characteristics and smart multifunctionalities can be designed, and holds the potential to fulfill the expected civil infrastructure needs of the 21st century. Highlights of relevant properties of ECCs are provided, and directions for necessary future research are indicated.

Form and Mechanism of Sulfate Attack on Cement-based Material Made of Limestone Powder at Low Water-binder Ratio under Low Temperature Conditions

The development of strength and the form of attack of cement-based material made of limestone powder at low water-binder ratio under low-temperature sulfate environment were studied. The results indicate that when water-binder ratio is lower than 0.40, the cement-based material with limestone powder has insignificant change in appearance after being soaked in 10% magnesium sulfate solution at low temperature for 120 d, and has significant change in appearance after being soaked at the age of 200 d. Expansion damage and exfoliation occur on the surface of concrete test cube at different levels. When limestone powder accounts for about 28 percent of cementitious material, with the decrease of water-binder ratio, the compressive strength loss has gradually decreased after the material is soaked in the magnesium sulfate solution at low temperature at the age of 200 d. After the specimen with the water-binder ratio of less than 0.4 and the limestone powder volume of greater than 20% is soaked in 10% magnesium sulfate solution at low temperature at the age of 200 d, gypsum attack-led destruction is caused to the concrete test cube, without thaumasite sulfate attack.

Usability of Waste Steel Grits in Concrete Pavement

The usability of waste steel grits and limestone sand in the construction of concrete pavement was investigated.Four different types of pavement concretes were produced,including coarse limestone concrete not containing waste steel grit,coarse limestone concrete containing waste steel grit,limestone sand concrete not containing waste steel grit,and limestone sand concrete containing waste steel grit.In this study,water/binder ratio in concrete production was taken as 0.44.In the production of limestone sand concrete containing waste steel grit,limestone sand with a grain diameter of 0.1-1.0 mm was used as aggregate.Waste steel grits with a grain diameter of 0.2-0.7 mm were added to the concrete mixture.Standard water curing and combined curing were applied to concrete samples.After standard water curing and combined curing,compression and bending tests of the same types of cube and beam concrete samples were carried out.As a result of the study,the maximum compressive and bending strengths were found to be 50.21 MPa and 5.07 MPa for limestone sand concrete containing waste steel grit.The study results show that waste steel grits increase the compressive and bending strength of concrete pavement.

Experimental study on mechanical properties of a novel micro-steel fiber reinforced magnesium phosphate cement-based concrete

Magnesium phosphate cement(MPC)received increased attention in recent years,but MPC-based concrete is rarely reported.The micro-steel fibers(MSF)were added to MPC-based concrete to enhance its ductility due to the high brittleness in tensile and flexural strength properties of MPC.This paper investigates the effect of MSF volume fraction on the mechanical properties of a new pattern of MPC-based concrete.The temperature development curve,fluidity,cubic compressive strength,modulus of elastic,axial compressive strength,and four-point flexural strength were experimentally studied with 192 specimens,and a scanning electron microscopy(SEM)test was carried out after the specimens were failed.Based on the test results,the correlations between the cubic compressive strength and curing age,the axial and cubic compressive strength of MPC-based concrete were proposed.The results showed that with the increase of MSF volume fraction,the fluidity of fresh MPC-based concrete decreased gradually.MSF had no apparent influence on the compressive strength,while it enhanced the four-point flexural strength of MPC-based concrete.The four-point flexural strength of specimens with MSF volume fraction from 0.25%to 0.75%were 12.3%,21.1%,24.6%higher than that of the specimens without MSF,respectively.

半浸泡硫铝酸盐水泥混凝土蒸发区孔结构变化

硫铝酸盐水泥水化需水量大、水化速度快,凝结硬化后留下的大量未水化水泥在后期继续水化生成钙矾石,影响混凝土的孔结构变化和力学性能发展。用半浸泡方式模拟半掩埋混凝土实际工况,运用背散射电镜和核磁共振等微观测试手段,研究了水灰比为0.35、0.45和0.55的硫铝酸盐水泥混凝土半浸泡35 d、70 d和130 d后蒸发区孔结构和混凝土抗压强度变化规律,结果表明:水灰比为0.35和0.45的混凝土孔隙率呈现先增大后降低再增大的变化特点;水灰比为0.55的混凝土孔隙率呈现先降低后增大的变化特点。研究表明:硫铝酸盐水泥凝结硬化后水化生成的钙矾石会产生结晶膨胀和填充密实两种效应,共同影响硫铝酸盐水泥混凝土孔结构变化。

吸波泡沫混凝土的物理力学性能研究

通过X射线衍射与热重分析对比研究了纳米炭黑和硅灰的加入对硫铝酸盐水泥水化进程及水化产物的影响,并结合孔结构分析了泡沫混凝土的抗压强度。结果表明:纳米炭黑易结合其他颗粒成为水化“成核中心”,促进氢氧化钙、钙矾石以及C-S-H的生成;随着泡沫混凝土密度的增加,炭黑对力学强度和孔结构稳定性的提升逐步显现;复掺硅灰弥补了前期水化进程缓慢的缺陷,提高了小孔径占比率,且对于3 d强度的提升较为明显。

硫铝酸盐高性能水泥混凝土的制备及性能研究

以P.O 42.5硫铝酸盐水泥为基体材料,通过将不同掺杂量的S105矿渣添加到混凝土中制备了硫铝酸盐高性能水泥混凝土。研究了S105矿渣的掺杂量对混凝土晶格结构、微观形貌、力学性能、抗冻性能和氯离子扩散性能的影响。结果表明,适量S105矿渣的添加加速了混凝土的水化反应,增大了水化凝胶的均匀性和致密度,减少了孔洞和裂纹的出现。随着S105矿渣掺杂量的增大,混凝土的抗压强度、抗折强度和劈裂抗拉强度均表现出先增大后降低的趋势,养护28 d时,S105矿渣掺杂量30%(质量分数)的混凝土的抗压强度、抗折强度和劈裂抗拉强度均达到最大值,分别为47.4,10.4和2.59 MPa。S105矿渣的添加减小了混凝土的氯离子扩散系数,养护28 d时,S105矿渣掺杂量60%(质量分数)的混凝土的氯离子扩散系数最小为1.35×10^(-8)cm^(2)/s。S105矿渣的添加提高了混凝土的抗冻性能,经过冻融循环90次后,S105矿渣掺杂量30%(质量分数)的混凝土的抗压强度最大为35.1 MPa,抗压强度衰减最少为25.95%。

NaCl干湿交替作用对复配水泥活性粉末混凝土性能的影响

本工作研究了硫铝酸盐水泥(SAC)和聚丙烯纤维(PPFs)掺量对活性粉末混凝土(RPC)养护1、3、7、14和28 d抗压、抗弯强度的影响。此外,本工作研究了NaCl干湿交替作用对复配水泥(SAC占水泥总质量的50%)RPC抗压强度、抗折强度、粘结强度以及氯离子渗透系数的影响。结果表明,早龄期(养护龄期低于7 d)RPC中SAC掺量增加有助于RPC抗压和抗折强度的提升。当养护龄期大于7 d时,RPC抗压和抗折强度会随着SAC的加入而下降。对于掺入量为50%SAC的RPC试件,其强度会随着PPFs体积率的增加而整体上升,当纤维体积率从2.5%增加至3.0%时,RPC的强度趋于稳定。NaCl干湿交替作用会引起RPC强度降低,并增加RPC的氯离子渗透性。PPFs的掺入会延缓RPC强度的降低并减小氯离子的渗透性。

含钡硫铝酸盐水泥混凝土界面结构与性能研究

实验通过对含钡硫铝酸盐水泥混凝土试块宏观断裂面的形貌观察和微观界面结构及界面产物的研究,发现断裂面从集料内部断开,说明含钡硫铅酸盐水泥混凝土的界面结合力大于集料内部自身的结合力;并利用扫描电子显微镜、能谱分析和差热分析仪对混凝土试块的微观界面区的形貌及水化产物进行分析观察,研究界面结构以及界面的水化产物对混凝土性能的影响。

硫铝酸盐水泥混凝土抗氯离子侵蚀机理分析

采用欧洲BUILD492《非稳态氯离子迁移试验法》测定普通硅酸盐水泥与硫铝酸盐水泥混凝土的氯离子非稳态扩散系数,应用X射线衍射分析(XRD)、扫描电镜分析(SEM)以及孔结构分析分别对这种水泥水化产物和水泥石内部结构进行研究,并对其抗氯离子侵蚀性能及其抵抗机理进行了研究分析.结果表明:硫铝酸盐水泥是提高混凝土抗氯盐侵蚀性能的一种理想胶凝材料.随着水灰比的降低,硫铝酸盐水泥的抗氯离子侵蚀能力逐渐增强.

早强微膨胀泵送C50钢管混凝土的研制

将硼酸、葡萄糖酸钠和聚羧酸盐减水剂按一定比例复合,研制出一种用于硫铝酸盐水泥的新型缓凝减水剂M,实验表明,该外加剂对硫铝酸盐水泥具有较强的缓凝及减水作用。采用该外加剂和42.5级快硬硫铝酸盐水泥,配制出具有良好工作性的C50早强微膨胀钢管混凝土:初始坍落度为24 cm,3 h后仍达18 cm以上,不离析、不泌水,满足泵送施工要求;其3 d抗压强度达50 MPa以上6、0 d自由膨胀率3.41×10-4,能有效解决钢管混凝土中普遍存在的脱粘问题。

钢纤维快硬硫铝酸盐水泥混凝土性能研究及在桥梁伸缩缝改造工程中的应用

本文介绍了以预拌方式应用快硬硫铝水泥配制钢纤维特快硬混凝土的研究和应用。指出配制该快硬混凝土的关键是要解决新拌混凝土的凝结时间和可工作时间之间的矛盾,在试配中要考虑快硬硫铝酸盐水泥专用外加剂的组成和掺量以及混凝土中粉煤灰与专用外加剂的适应性问题;在拌制、运输、浇筑和养护等一系列环节,要严格遵循有关注意事项方能确保混凝土工程质量。

含钡硫铝酸盐水泥混凝土的抗渗透性能研究

通过对含钡硫铝酸盐水泥混凝土的抗压强度、抗渗性能及氯离子扩散系数的测定,同时借助SEM,压汞仪等测试手段,研究和分析了含钡硫铝酸盐水泥混凝土的水化过程及抗渗透性机理.结果表明,与硅酸盐水泥混凝土相比,含钡硫铝酸盐水泥混凝土具有较低的孔隙率和更合理的孔径分布,致密度高,抗压强度高,抗渗透性能优良.

硫铝酸盐水泥早强微膨胀钢管混凝土的制备

通过正交实验设计,分析和研究了硫铝酸盐水泥混凝土的早强和微膨胀特性,进行了钢管混凝土短柱的承载力测试,并与C50,C60强度等级的普通钢管混凝土短柱试件进行了对比.结果表明:控制硫铝酸盐水泥中Al2O3与SO3质量比为1.2时,可制备出符合泵送施工工艺要求的早强、微膨胀钢管高强混凝土,用其制作的钢管混凝土短柱试件也比相同强度等级的普通钢管混凝土短柱的承载能力高.

水化环境和膨胀剂对混凝土膨胀性能的影响

以工程实测温升曲线分别建立绝湿温升、100%RH温升模拟水化环境,将硫铝酸钙-氧化钙类膨胀剂、硫铝酸钙类膨胀剂(CSA、AEA)配制的补偿收缩混凝土,置于标准养护及上述模拟水化环境中,研究水化环境和膨胀剂类别对补偿收缩混凝土膨胀性能的影响。结果表明,标准养护、100%RH温升模拟水化环境下,三种补偿收缩混凝土均有膨胀性,且硫铝酸钙-氧化钙类膨胀剂、硫铝酸钙类膨胀剂补偿收缩混凝土的膨胀性能优于CSA和AEA。绝湿温升水化环境中,只有硫铝酸钙-氧化钙类膨胀剂、硫铝酸钙类膨胀剂补偿收缩混凝土发生膨胀,CSA和AEA膨胀率几乎为零。因此,无法进行湿养护的工程部位,补偿收缩混凝土应以硫铝酸钙-氧化钙类混凝土膨胀剂为主。

沥青-水泥复合防水材料的制备及性能研究

在特殊环境深井巷道开挖和修复过程中,由于巷道围岩极其破碎,围岩松动破碎范围大,直接影响井下安全和高效生产,需要灌浆加固。将快硬硫铝酸盐水泥进行改性,通过一定的复合工艺将它与改性的沥青进行复合。在聚合物乳液和硫铝酸盐水泥组成与其流变性能、力学性能及凝结时间关系研究的基础上,系统研究沥青乳液的掺入对其力学性能的影响,制备出沥青-水泥复合灌浆材料。此材料具有低水灰比、高流动性、柔韧性好、适当变形、界面粘结力强度高,早强、高强、凝结时间短以及环保、生产成本低等优良性能。应用于某些对流动性和凝结时间有较高要求的工程上,可扩大工程选材的范围,并实现裂缝修补灌浆材料绿色环保高性能化。

高性能贝利特-硫铝酸盐水泥的研究及进展(续)

通过第一次的工业试验，总结了熟料的烧成和矿物形成的各种要素，对影响熟料烧成的工艺技术参数进行了进一步优化，在山西阳泉天隆特种材料有限公司完成了第二次工业试验，煅烧出了3d抗压强度30—58MPa，28d抗压强度57—65MPa的高性能贝利特-硫铝酸盐水泥熟料，工业化生产试验取得突破性进展。利用工业化煅烧的新型水泥熟料，对高性能贝利特-硫铝酸盐水泥混凝土的基本性能进行了详细研究，发现利用新型水泥制备的混凝土，工作性良好，强度高．与减水剂有较好的相容性。

掺合料对硫铝酸盐水泥基混凝土耐久性影响的研究

研究了掺合料复掺(矿渣∶粉煤灰=2∶1)、单掺矿渣、单掺粉煤灰对硫铝酸盐水泥基混凝土强度、抗渗性、抗冻性的影响,并与相同水灰比下掺合料复掺对普通硅酸盐水泥基混凝土对应性能的影响进行对比。结果表明:在硫铝酸盐水泥基混凝土中,掺合料的加入使混凝土的早期和后期强度都明显降低,抗渗性稍微降低,抗冻性明显降低,且掺量越高,其强度、抗渗性、抗冻性降低越明显;但复掺时的效果比单掺时的效果好,粉煤灰的效果最差;而在普通硅酸盐水泥基混凝土中,掺合料的加入使混凝土的早期强度降低,但后期强度超过空白样的强度,抗渗性、抗冻性明显提高,但是,在无掺合料时其抗渗性、抗冻性大大低于相同水灰比下硫铝酸盐水泥基混凝土的抗渗性、抗冻性。

新型硫铝酸盐水泥泡沫混凝土的制备与研究

以硫铝酸盐水泥为胶凝材料,复掺一定比例的粉煤灰和硅灰,以氯化铝和碳酸氢钠为发泡剂,采用化学发泡的方式制备新型硫铝酸盐水泥泡沫混凝土,并对泡沫混凝土的性能进行了研究。结果表明,该泡沫混凝土与已报道的硫铝酸盐水泥泡沫混凝土相比具有更高强度和更低的导热系数。