The Impermeability Mechanism of Self-compacting Water Proof Concrete

The impermeability mechanism of water-proof self-compacting concrete (WPSCC )w as studied. The mechanism and influential factors, such as water-cement ratio(w /c), dosage of powder, superplasticizer, sand content, aggregate conte nt, fly ash, UEA, PP fiber, on compactibility and crack resistance of WPSCC were analyzed. A type of WPSCC successfully applied in tunnel liner with its validit ies, conveniences and economies by mockup test was developed and optimized. Expe rimental results show that the WPSCC has good workability, mechanical properties and impermeability when reasonable requirements are fulfilled.

Investigation on the Free and Restrained Shrinkage of Self-compacting Concrete

A novel ellipsis-ring cracking apparatus with an automatic monitoring system was used to measure the restrained shrinkage and initial cracking time of self-compacting concrete (SCC). The free shrinkage, restrained shrinkage and strength were integrated to evaluate the effect of the mineral admixtures and content of cementitious materials on shrinkage of SCC. The experimental results show that the initial cracking time of SCC incorporating fly ash was delayed, the shrinkage value and rate was reduced. The hydration achievement of silica fume increased free shrinkage and reduced initial cracking time of FA-SCC comparing to control sample, but silica fume improved the mechanical properties of FA-SCC in early age. As same strength, with the reducing the content of cementitious materials, the initial cracking time of SCC delayed and cracking sensitivity decreased markedly, especially when the content of cementitious materials achieve 450 kg/m3.

Comparison of Shrinkage, Creep and Elastic Shortening of VMA and Powder Type Self-Compacting Concrete and Normal Vibrated Concrete

Self-compacting concrete (SCC) is flowing in nature and hence viscosity modified agent (VMA) or higher amount of binder is used for stability of mix. The mix proportion of SCC is also different from normal vibrated concrete (NC). This modifies the properties of concrete at fresh as well as at hardened state. Three mixes, one VMA type SCC, one powder type SCC and one NC, are considered with identical water to binder ratio. Properties at fresh state such as workability and segregation resistance and at hardened stage such as compressive strength, elastic modulus, shrinkage, creep and elastic shortening are determined and compared. Powder type SCC shows superior properties at fresh stage. Also compressive strength of powder type SCC is found better than that of VMA SCC and NC. Observations show more shrinkage, elastic shortening and creep for powder type SCC as compared with VMA SCC and NC.

Design and Preparation of High Elastic Modulus Self-compacting Concrete for Pre-stressed Mass Concrete Structures

Requirements of self-compacting concrete （SCC） applied in pre-stressed mass concrete structures include high fluidity, high elastic modulus, low adiabatic temperature rise and low drying shrinkage, which cannot be satisfied by ordinary SCC. In this study, in order to solve the problem, a few principles of SCC design were proposed and the effects of binder amount, fly ash （FA） substitution, aggregate content and gradation on the workability, temperature rise, drying shrinkage and elastic modulus of SCC were investigated. The results and analysis indicate that the primary factor influencing the fluidity was paste content, and the main methods improving the elastic modulusof SCC were a lower sand ratio and an optimized coarse aggregate gradation. Lower adiabatic temperature rise and drying shrinkage were beneficial for decreasing the cement content. Further, based on the optimization of mixture, a C50 grade SCC （with binder amount of only 480 kg/ m3, fly ash substitution of 40%, sand ratio of 51% and proper coarse aggregate gradation （Vs.~0 mm： V10-16 ram： V16.20 mm= 30%： 30%：40%）） with superior workability was successfully prepared. The temperature rise and drying shrinkage of the prepared SCC were significantly reduced, and the elastic modulus reached 37.6 GPa at 28 d.

不同掺量矿粉对混凝土性能的影响试验研究

文中对不同掺量矿粉下C30、C50混凝土的收缩性能、抗氯离子收缩性能、抗渗性能及抗压强度性能差异开展试验。结果表明,掺入矿粉后,混凝土早期强度相较普通混凝土有所降低,但养护龄期达一定天数后,抗压强度进一步增长;混凝土抗压强度随矿粉掺量增加而降低,但其耐久性能有一定提升,建议在工程实践中,结合实际需求调整矿粉用量,充分改良混凝土性能。

矿物掺合料复掺对超高性能湿接缝混凝土性能的影响

采用石灰石粉和粉煤灰微珠作为调节超高性能湿接缝混凝土性能的矿物掺合料,通过设置石灰石粉和粉煤灰微珠的不同复掺比例,研究了两种矿物掺合料对超高性能湿接缝混凝土流变性能、力学性能、收缩性能和抗渗性能的影响,并采用水化热分析了超高性能湿接缝混凝土的水化特性。结果表明:当石灰石粉掺量高于30%(质量分数)时,随着石灰石粉掺量的增加,超高性能湿接缝混凝土的塑性黏度先增大后减小,复掺50%石灰石粉和50%(质量分数)粉煤灰微珠时,混凝土塑性黏度可降低38.0%;掺入石灰石粉可以促进水泥的早期水化,提高超高性能湿接缝混凝土的早期抗压强度,3 d抗压强度最大涨幅为11.6%;复掺石灰石粉和粉煤灰微珠可以降低超高性能湿接缝混凝土的自收缩;当复掺30%石灰石粉时,超高性能湿接缝混凝土的抗渗性能最优,28 d氯离子扩散系数为0.15×10^(-12)m^(2)/s。

Relationship Between Coarse/Fine Aggregate Space Coefficient and Properties of Self-compacting Concrete

For the sake of expounding the relationship between coarse/fine aggregate volume content and properties of self-compacting concrete(SCC),a parameter of aggregate space coefficient is proposed to study systematically the effects of fine/ coarse aggregates on workability,strength and volume stability of SCC by experiments. The optimized coarse/fine aggregates volume content of SCC was discussed with regard to specified properties. Results indicate there is a close relationship between aggregate space coefficient and properties of SCC not only in fresh state but also in hardened state. With the increasing coarse/fine aggregate space coefficients,workability of fresh SCC will be improved,the compressive strength decreases slightly and shrinkage of SCC however increases. When coarse aggregate space coefficient ranges from 1.2 to 1.7 and the fine aggregate space coefficients is from 0.6 to 1.0,SCC can meet self-compactability requirements in fresh state and have a good volume stability and appropriate strength in hardened state. The results will benefits for developing a new mixing design method for SCC.

混杂合成粗纤维及钢纤维对盾构管片混凝土性能的影响

为提升盾构管片质量,优选合成粗纤维,将4种性能的高强合成粗纤维分别与钢纤维混杂制备盾构管片混凝土,研究其强度、抗渗性和收缩变形,并通过孔结构和电镜观测分析微观结构。结果表明,对比钢纤维混凝土,钢⁃合成粗纤维混凝土的56d劈裂抗拉强度提升32.7%,氯离子抗渗性提高37.3%,达到标准规定的良好水平。混杂合成粗纤维增强了混凝土限制收缩的能力,早龄期的收缩变形降低约23%。毛细水吸附系数有所增大,总孔隙率增大4.9%,且主要增加了孔径>30nm的大孔,无论钢纤维还是合成粗纤维,纤维混凝土过渡区均较致密,纤维与水泥黏结良好。

石灰石粉对主塔大体积混凝土性能的影响

以水泥、粉煤灰和石灰石粉为胶凝材料,制备了一种低温升主塔大体积混凝土,研究了石灰石粉掺量(5%、10%、15%)对砂浆流变性能和混凝土绝热温升、干燥收缩性能、力学性能、抗渗性能的影响,采用SEM观察了水化产物的微观形貌,并与水泥-粉煤灰-矿渣粉胶凝体系(对照组)进行了对比。结果表明:与对照组相比,掺入石灰石粉可以降低砂浆的塑性黏度和屈服应力,延缓胶凝材料的水化进程,降低混凝土的绝热温升;石灰石粉的掺量越大,抑制混凝土干燥收缩的作用越显著;随着石灰石粉掺量的增加,混凝土的抗压强度下降,但掺5%石灰石粉混凝土的抗压强度较对照组高;与对照组相比,掺石灰石粉混凝土的抗渗性能较好,且掺量为5%时性能最好。

Basf早强剂对混凝土耐久性能的影响及作用机理分析

以新型早强剂Basf为研究对象,采用泵送C30、振捣C60混凝土为基础配合比,对添加Basf的混凝土进行碳化、冻融、抗渗和收缩试验。结果表明,C60混凝土的抗碳化能力远好于C30混凝土,Basf对C60混凝土碳化性能影响较小,但使得C30混凝土碳化深度增加;添加Basf后,C60和C30混凝土试件的抗渗性和抗冻性能得到显著提高,但混凝土的收缩值变大。

轻质高强陶粒混凝土制备与路用性能试验研究

为了分析轻质高强陶粒混凝土的路用性能,选取碎石型陶粒制备了不同掺合料添加的轻质高强陶粒混凝土试件,掺合料中硅灰与矿渣的质量比为1∶2。开展了混凝土的抗压、抗折、抗渗、干燥收缩、抗冻等性能测试,研究了轻质高强陶粒混凝土路用性能随掺合料质量比的变化规律。研究结果表明:当掺合料替换水泥量为15%~20%时,轻质高强陶粒混凝土的抗压性能和抗折性能最佳;当掺合料替换水泥量为15%以上时,轻质高强陶粒混凝土的抗渗性能最优;掺合料添加对轻质高强陶粒混凝土的干燥收缩率的影响较小;掺合料替换水泥量为20%左右条件下轻质高强陶粒混凝土的抗冻性能最好。

再生砖混骨料混凝土的干燥收缩及抗渗性研究

大规模拆迁改造过程产生了大量的建筑固废,其中大部分均含有黏土砖成分。与传统天然骨料相比,再生砖混骨料具有孔隙率大、吸水率高等特点,对用其制备的再生混凝土性能具有较大的影响。采用再生砖混骨料制备混凝土,测试其干燥收缩及抗渗性。结果表明,再生砖混骨料混凝土早期干燥收缩较明显,随龄期延长,干燥收缩率不断增大,但干燥收缩速率逐渐减小,而且在超过34 d后干燥收缩仍在持续,没有出现平缓的趋势;干燥收缩同时受水灰比及再生砖混骨料用量的综合影响;各强度等级再生混凝土的抗渗等级均能达到P10以上,再生砖混骨料的掺入不会对再生骨料混凝土的抗水渗透性能有明显的负面影响。

养护措施和湿养护时间对掺与未掺矿渣混凝土性能的影响(英文)

研究了采用湿棉絮覆盖、喷养护剂、塑料薄膜密封3种养护措施对混凝土强度、收缩、中心温升、氯离子渗透性的影响,并通过不同龄期强度、氯离子渗透深度(5% NaCl溶液介质,质量分数)、钢筋腐蚀电位、加速腐蚀保护层开裂时间研究湿养护时间(1,7,14d和28d)对未掺和掺矿渣(等量取代水泥40%,质量分数)混凝土强度、抗渗性、护筋性的影响。结果表明:合适的养护措施能有效提高混凝土强度和抗渗性,降低水化温升和早期收缩。对未掺与掺矿渣的混凝土,更长的湿养护有助发展更高强度、耐久性和护筋性;而不充分养护导致混凝土较差的抗渗性和护筋性,该影响对掺矿渣混凝土尤为明显。7d湿养护对掺矿渣混凝土发展更高的潜在抗渗性是不够的。

C40自密实混凝土抗渗性研究

以干缩及变形“落差”指标并结合抗渗性试验方法,评价自密实混凝土的抗渗性能,系统研究了膨胀剂用量、水胶比、引气剂及养护制度对C40自密实混凝土干缩和抗渗性的影响规律。试验结果表明,收缩及抗渗性能受到水胶比及体系的自密实能力的共同影响,引气剂可以有效减少收缩,提高抗渗性,膨胀剂最佳掺量为30kgm3。

补偿收缩混凝土抗渗性研究

为探究补偿收缩混凝土中膨胀剂掺量对混凝土抗渗性能的影响,以掺膨胀剂后混凝土的抗渗性研究为重点,对不同水灰比和不同掺量膨胀剂的补偿收缩混凝土试件进行了抗渗试验,主要探讨了水灰比、膨胀剂掺量两者耦合对混凝土抗渗性能的影响,并对最优值进行了探讨。试验结果表明：水灰比、膨胀剂掺量均能影响混凝土的抗渗性能,两者的组合形式不同,对混凝土的抗渗性能影响也不同;水灰比为0.45时,掺入膨胀剂反而会降低混凝土的抗渗性能;水灰比为0.55和0.65时,混凝土中掺入一定量膨胀剂可以提高其抗渗性能,最佳掺量分别为6%~8%和11%~12%。

城市生活垃圾焚烧底灰混凝土耐久性研究

将30%质量的城市固体废物焚烧(MSWI)底灰掺入混凝土中替代水泥,通过对底灰混凝土的收缩率,抗碳化性、抗渗性、抗冻性等进行试验,并与普通混凝土进行对比,研究了底灰作为水泥替代物的可行性。研究结果表明,测试的垃圾焚烧底灰具有一定的火山灰活性,一定范围内掺加底灰的混凝土具有较小的收缩率,抗碳化性、抗渗性、抗冻性能优异,底灰的引入可以改善混凝土的耐久性。

清水混凝土耐久性试验研究

针对清水混凝土作为饰面直接暴露于自然环境中的特点,对混凝土的耐久性能提出了更高的要求,通过对比试验,经过对数据的收集、整理和分析,找出了清水混凝土在不同配合比下其耐久性的差异,对施工中原材料的选取及技术措施的选择具有一定的指导意义。

磨细矿粉对轻骨料混凝土耐久性能影响的研究

通过磨细矿粉对轻骨料混凝土耐久性能影响的试验研究,重点探讨了磨细矿粉对轻骨料混凝土的抗冻性能、抗渗性能、抗碳化性能、干缩性能的影响。研究结果表明:轻骨料混凝土中掺加磨细矿粉可大幅度提高其抗渗透性能,增强混凝土的抗冻融能力,改善其抗碳化性能,但混凝土的收缩率提高。

硅粉对轻骨料混凝土耐久性能影响的研究

通过硅粉对轻骨料混凝土耐久性能影响的试验研究,重点探讨硅粉对轻骨料混凝土抗冻性能、干缩性能、抗渗透性能的影响。研究结果表明,轻骨料混凝土中掺加硅粉,可大幅度提高其抗渗透性能,增强混凝土的抗冻融能力,但随着硅粉掺量增大,混凝土的收缩率提高。

混凝土增效剂对碎屑混凝土性能的影响

混凝土增效剂能减少胶凝材料用量,保持混凝土各项性能不降低甚至有所提高。通过调整配比,研究了混凝土增效剂对碎屑混凝土性能和微观形貌的影响。结果表明,掺加增效剂后,在减少水泥用量的同时,能有效改善混凝土的工作性能;混凝土的早期强度与基准相当,后期有所提高;早期收缩略大,后期收缩趋缓;电通量下降,抗渗性能有所提高。混凝土增效剂能够优化混凝土的微观形貌,增加混凝土密实度,混凝土增效剂在碎屑混凝土中应用完全可行,能够提高混凝土原材料的使用效率。