自密实混凝土早期自收缩及微观孔结构研究

采用混凝土早期自收缩测量系统研究了粉煤灰掺量及水胶比对自密实混凝土早期自收缩的影响,并通过硬化混凝土孔隙结构测定仪和压汞仪研究了自密实混凝土的微观孔结构.结果表明:粉煤灰的掺入能降低自密实混凝土早期的自收缩,且随粉煤灰掺量的增加,减缩效果更为显著;随着水胶比的降低,自密实混凝土的自收缩逐渐增大;自密实混凝土早期自收缩与其微观孔结构关系密切,自密实混凝土自收缩主要是因孔径为0~50 nm的孔隙量的增加而造成的.     

再生细骨料自密实混凝土收缩性能研究

再生细骨料的高吸水特性可有效提高再生细骨料自密实混凝土内部相对湿度,降低收缩。研究了再生细骨料掺量(0,25%,50%,75%)和干湿状态(干燥、饱和面干)对再生细骨料自密实混凝土内部相对湿度及干燥收缩的影响规律,建立了内部相对湿度及干燥收缩之间的关系。试验结果表明,封闭及单面干燥条件下,再生细骨料延缓了混凝土内部相对湿度的下降过程,提高不同龄期混凝土的内部相对湿度。封闭条件下饱和再生细骨料自密实混凝土的内部相对湿度高于干燥再生细骨料自密实混凝土。再生细骨料可以明显降低混凝土的干燥收缩,且随再生细骨料掺量的增加,降低程度提高。再生细骨料自密实混凝土干燥收缩与相对湿度降低值以及再生细骨料引入水量呈现线性关系。     

HCSA膨胀剂对自密实混凝土早期收缩的影响

采用非接触混凝土收缩变形测试方法,研究了掺HCSA膨胀剂自密实混凝土的早期收缩性能。结果表明,随着强度等级的提高,自密实混凝土的早期收缩率有增大的趋势;对于典型的强度等级为C40的普通自密实混凝土,3d收缩率约为1350×10-6;当掺加8%的HCSA膨胀剂时,其早期收缩可减少80%~92%;在充分保湿养护的条件下,掺HCSA膨胀剂的自密实混凝土可处于零收缩状态。     

配合比参数对自密实混凝土早期收缩及开裂性能的影响研究

研究了配合比参数（水胶比和砂率）对自密实混凝土早期收缩及开裂性能的影响,结果表明,自密实混凝土的水分蒸发速率随水胶比增加而增加,随砂率的提高而减小;而配合比参数对开裂及早期收缩的影响较为复杂,水胶比小于0.45时,随着水胶比增加自密实混凝土开裂面积提高,而混凝土3d收缩应变与之相反,当水胶比超过0.45后,开裂面积随之减小而混凝土3d收缩应变随之增加;随着砂率由48％增至55％时,砂率在51％时,自密实混凝土开裂裂缝面积达到最大值;随着砂率增加,混凝土3d应变收缩逐渐增大.     

自密实混凝土自由收缩试验

进行了自密实混凝土的自由收缩试验,以粉煤灰掺量和混凝土龄期作为影响因素,研究其收缩的发展规律;基于试验数据,通过双曲线方程拟合了自密实混凝土自由收缩的计算式。研究结果表明:自密实混凝土自由收缩随混凝土龄期的增加而增大,后期自由收缩应变增长较缓慢;当粉煤灰质量掺量在40%时,各阶段的自由收缩应变都最小;拟合的自密实混凝土自由收缩计算式可以为自密实混凝土结构相关设计提供参考。     

自密实混凝土收缩变形及改善措施研究

与普通混凝土相比,自密实混凝土的胶凝材料含量大,势必导致混凝土收缩变形增大。本文主要介绍自密实混凝土的收缩特点,并给出其收缩补偿的改进方法和途径,包括掺入膨胀剂UEA及减缩剂JM-Ⅲ。     

高强自密实混凝土徐变特性的研究

以徐变度和干燥收缩应变为评价指标,对高强自密实混凝土与普通泵送混凝土进行徐变和收缩特性研究,并分析其与混凝土配合比之间的联系。研究表明:混凝土的徐变度随其强度等级的提高而降低,同样强度等级的自密实混凝土比普通泵送混凝土的徐变度大。研究表明:开始加载龄期延长可降低混凝土的徐变度,高强混凝土的干燥收缩规律与其徐变类似,凡是使徐变增大的因素也会使混凝土的干燥收缩增大;掺加高吸水性树脂的高强自密实混凝土的早期徐变度增长快,但是后期徐变发展速度明显降低,表明其可改善高强混凝土结构的长期变形性能。     

低强度自密实混凝土收缩补偿研究

与同强度等级的普通混凝土对比,通过试验研究了低强度自密实混凝土收缩特点以及膨胀剂对自密实混凝土的收缩和抗压强度的影响.研究结果表明:低强度自密实混凝土收缩值高于同强度等级的普通混凝土;随着膨胀剂掺量的增加,自密实混凝土收缩值在降低,而其抗压强度先增加后降低,存在峰值.并对其机理进行了初步探讨.     

SAP对火山灰混凝土收缩性能的改善作用

研究了高吸水树脂(SAP)对C40和C60火山灰混凝土自收缩、干燥收缩及水分损失率的影响,并探讨了SAP对火山灰混凝土收缩性能的作用机理.结果表明:SAP内养护可以显著降低C40和C60火山灰混凝土的自收缩,提高火山灰混凝土的抗裂性,且内养护减缩率与内养护水胶比呈正比关系;SAP内养护增大了火山灰混凝土的干燥收缩和水分损失率,且增大幅度随着内养护引入水量的增加而增大;根据干燥环境中火山灰混凝土的水分损失率与干燥收缩的拟合关系得出了火山灰混凝土产生干燥收缩时的临界水分损失率;虽然SAP内养护增大了火山灰混凝土的干燥收缩,但其总收缩较基准混凝土显著降低.     

膨胀剂对自密实钢管核心混凝土变形的影响

为满足工程中钢管混凝土施工技术和经济效益的需要,将绿色高性能的自密实混凝土取代普通混凝土应用到钢管混凝土中。钢管中核心混凝土的收缩关系到整体的受力性能,为研究钢管混凝土中核心混凝土的收缩特性,制作了8个圆钢管自密实混凝土试件来进行收缩试验,探讨分析了膨胀剂掺量对试件收缩的影响。研究结果表明:钢管自密实混凝土中核心混凝土的收缩变形要远小于普通混凝土的收缩变形;掺入膨胀剂可以减小钢管混凝土的早期纵横向变形;适量掺入膨胀剂可以减小核心混凝土的收缩变形和钢管壁的环向变形,但过量掺入膨胀剂会增大钢管壁的环向膨胀率;对于钢管自密实混凝土,膨胀剂的最佳掺量在5%~10%之间,而膨胀剂的掺入量与收缩之间的关系十分敏感,建议实际应用中最佳掺量尽量精确到1%。     

Strength and drying shrinkage properties of self-compacting concretes incorporating multi-system blended mineral admixtures

Drying shrinkage can be a major reason for the deterioration of concrete structures. The contraction of the material is normally hindered by either internal or external restraints so that tensile stresses are induced. These stresses may exceed the tensile strength and cause concrete to crack. The present study investigated compressive strength and particularly drying shrinkage properties of self-compacting concretes containing binary, ternary, and quaternary blends of Portland cement, fly ash (FA), ground granulated blast furnace slag (GGBFS), silica fume (SF), and metakaolin (MK). For this purpose, a total of 65 self-compacting concrete (SCC) mixtures were prepared at two different water to binder ratios. It was observed that drying shrinkage lessened with the use of FA, GGBFS, and MK while incorporation of SF increased the drying shrinkage.     

乌鲁木齐地区C30自密实混凝土配合比的正交试验研究

采用乌鲁木齐地区原材料配制C30自密实混凝土,运用正交试验方法进行9组试验,分析矿物掺合料掺量、水胶比、砂率、外加剂掺量等因素对自密实混凝土工作性能及强度的影响。在此基础上优化调整,得出适合乌鲁木齐地区的C30自密实混凝土配合比。     

Predicting the core compressive strength of self-compacting concrete (SCC) mixtures with mineral additives using artificial neural network

In this study, an artificial neural networks study was carried out to predict the core compressive strength of self-compacting concrete (SCC) mixtures with mineral additives. This study is based on the determination of the variation of core compressive strength, water absorption and unit weight in curtain wall elements. One conventional concrete (vibrated concrete) and six different self-compacting concrete (SCC) mixtures with mineral additives were prepared. SCC mixtures were produced as control concrete (without mineral additives), moreover fly ash and limestone powder were used with two different replacement ratios (15% and 30%) of cement and marble powder was used with 15% replacement ratio of cement. SCC mixtures were compared to conventional concrete according to the variation of compressive strength, water absorption and unit weight. It can be seen from this study, self-compacting concretes consolidated by its own weight homogeneously in the narrow reinforcement construction elements. Experimental results were also obtained by building models according to artificial neural network (ANN) to predict the core compressive strength. ANN model is constructed, trained and tested using these data. The results showed that ANN can be an alternative approach for the predicting the core compressive strength of self-compacting concrete (SCC) mixtures with mineral additives.     

低碳低水泥用量自密实混凝土的研究

以较低水泥用量180kg/m3,大掺量矿渣粉、粉煤灰研制出C50高强高性能自密实混凝土,混凝土排碳量仅为88.136kg/m3,是普通自密实混凝土的49.52%。试验表明该混凝土和易性好、流动性保持性好,性能与采用高水泥用量配制出的自密实混凝土相当。该文研究的自密实混凝土大大降低了水泥用量,降低混凝土的排碳量,同时大大降低混凝土成本。     

大掺量粉煤灰自密实高性能混凝土的实践

自密实混凝土作为一种高性能混凝土应用的工程已经越来越普遍,本文就威海市环翠楼公园钢结构改造工程实践了通过大掺量Ⅱ级粉煤灰的方式提高自密实混凝土的保水性、流动性及强度。同时节约了大量的水泥,中低强度等级自密实混凝土的实现也为绿色无噪音施工带来了可行性,也为钢管柱的施工带来了方便。     

影响自密实混凝土坍落度损失因素的试验研究

自密实混凝土拌合物坍落度损失问题是自密实混凝土研究的热点和难点之一.从延缓水泥早期水化速度出发,分别针对原材料中水泥品种、粉煤灰、高效减水剂种类及缓凝剂等4个因素,对坍落度损失的影响进行了试验研究,并就其机理进行了初步探讨.     

Splitting tensile strength and modulus of elasticity of self-compacting concrete

In this experimental work, the splitting tensile strength and the modulus of elasticity are studied for self-compacting concretes of different ages. At the same time, its porous structure is analysed, since this aspect is directly related with mechanical properties of the material. Eight different concretes were used, four self-compacting and four normally-vibrated, with different water/cement ratios and different types of cement. The results obtained show that in self-compacting concretes made with limestone filler the splitting tensile strength is on average 15% less than that of normally-vibrated concretes. It is therefore suggested that the standard expressions that are normally used for normally-vibrated concretes should be modified for these concretes. In addition, it is seen that the cementitious paste’s modulus of elasticity is greater in the self-compacting concretes because the addition of limestone fines creates lower porosity and a finer microstructure. Despite this, the concrete’s modulus of elasticity tends to be around 2% less in the self-compacting concretes as a result of the greater amount of cement paste in the self-compacting concretes.     

不发火自密实混凝土研究

以不发火粗、细骨料、复合掺合料、普通硅酸盐水泥以及氨基磺酸盐高效减水剂、降低离析的羟丙基甲基纤维素为主要原料制备了不发火自密实混凝土,讨论和分析了不发火自密实混凝土的工作性和强度性能.试验结果表明,不发火自密实混凝土满足工程中的性能要求和消防要求.     

Self-compacting concrete with different levels of pulverized fuel ash

This research investigated self-compacting concrete (SCC) with levels of up to 80% cement replacement by fly ash in mixes adjusted to give constant fresh concrete properties. The hardened concrete and the relationships between hardened properties were then studied.The results show that SCC with up 80% cement replaced by fly ash is possible. To keep the filling ability constant, replacement of cement with fly ash would require an increase in water/powder (W/P) ratio and a reduction in superplasticiser dosage. They also show fly ash have negative effects on passing ability, consistence retention and hardened concrete properties such as strength. The comparison between SCC and normally vibrated concrete (NVC) shows that their material properties of are similar. The successful completion of this project can lead to the use of higher volume fly ash in SCC.     

缩缝宽度对路面板荷载应力的影响分析

水泥混凝土路面缩缝宽度的变化将导致路面板块之间荷载传递状况的改变,进而影响路面板的荷载应力状态。利用三维有限元计算程序EverFE分析缩缝宽度与路面板荷载应力的关系,指出减少缩缝宽度变化的影响,对延长水泥混凝土路面的使用年限具有重要作用。