粗骨料对透水混凝土性能的影响研究

试验研究了粗骨料品种、粗骨料粒径、胶骨比等对透水混凝土力学性能和透水性能的影响,结果表明:采用天然骨料配制的透水混凝土的各项性能均优于采用再生骨料配制的透水混凝土;对于同一来源的粗骨料,骨料粒径越大,配制的透水混凝土透水性能越好,力学性能则略有降低;相同品质和粒径的再生骨料配制的透水混凝土,随胶骨比增加,混凝土透水性能逐渐降低,力学性能却呈增加趋势。     

用于北方满族民居墙体的再生混凝土性能研究

通过试验研究了再生混凝土作为北方满族民居建造材料的可行性。研究重点:再生骨料的物理性质测定、再生混凝土基本力学性能试验,以及粉煤灰、聚丙烯纤维以及附加水对其力学性能的影响。通过试验得到,再生混凝土立方体抗压强度最高应力达37.1 MPa、轴心抗压强度平均应力28.4 MPa、静力受压弹性模量平均应力22 300 MPa、抗折强度平均应力3.8 MPa、劈裂抗拉强度平均应力1.68 MPa。结果表明:在再生混凝土中加入粉煤灰和聚丙烯纤维都对立方体抗压强度有所提高,但附加水的加入对立方体抗压强度产生了降低作用。整体来说,再生混凝土各方面的力学指标都能满足一定的强度要求。因此可以作为北方满族民居的建设材料。     

基于细观尺度的再生混凝土性能研究综述

基于当前国内外学者对再生混凝土性能试验的结果,研究骨料、砂浆、界面过渡区等细观参数对再生混凝土宏观性能影响.在骨料方面,骨料分布的均匀程度高、颗粒级配较好、大中型骨料颗粒数越多的再生混凝土在抗拉、抗压、抗折强度及弹性模量等方面都会有所提高;在砂浆方面,随着新、老砂浆的强度提高,再生混凝土力学性能更好,老砂浆厚度越高,再生混凝土内部氯离子浓度越大;在界面过渡区方面,随着新、老界面过渡区弹性模量的提高,再生混凝土的性能表现地越好,界面过渡区厚度越大,氯离子扩散系数越大.     

Influence of Aluminosilicate for the Prediction of Mechanical Properties of Geopolymer Concrete – Artificial Neural Network

In this paper, details and results of experimental and predictive studies carried out to determine the mechanical properties of Aluminosilicate materials like Ground Granulated Blast furnace Slag (GGBS) and Fly Ash (FA) based geopolymer concrete specimens are presented and discussed. The major parameters considered in the experimental study are the percentages of GGBS and Fly ash and the percentage of manufactured sand (m-sand) used to replace conventional river sand used in the production of geopolymer concrete. Sodium hydroxide and sodium silicate solutions were used as the activator in the production of geopolymer concrete. The mechanical properties of the geopolymer concrete determined were the compressive strength, split-tensile strength and flexural strength. The test results showed that the mechanical properties of geopolymer concrete improved with increase in the percentage use of GGBS. Also, it was observed from the test results that increase in the percentage use of m-sand increased the mechanical properties of the geopolymer concrete up to an optimum dosage beyond which reduction in the mechanical properties was observed. The predicted mechanical properties of the geopolymer concrete using Artificial Neural Network (ANN) was found to be in good agreement with the test results.

     

碳纤维对导电混凝土性能和微结构的影响

导电混凝土较好的导电性能,可用于道路工程除冰,保障交通通行安全.采用碳纤维制备导电混凝土,观察其性能和微结构的变化.研究结果表明:碳纤维的掺用使得混凝土拌合物的工作性变差,但仍然能满足施工要求.随着碳纤维掺量的增加,导电混凝土的抗压强度下降,但劈拉强度增大.导电混凝土的电阻率随碳纤维掺量的增大而降低,持续通电后,呈良好的电热效应和发热效果.掺加碳纤维后,水泥石结构的密实性降低,从而导致其性能发生变化.     

Optimum usage of a natural pozzolan for the maximum compressive strength of concrete

Pozzolans provide an economic production possibility in the concrete industry and improve the properties of concrete, such as durability. Effects of a pozzolan on the properties of concrete vary with the pozzolan type and volume.In this study, effect of a natural pozzolan on the properties of concrete was investigated. Fifteen concrete mixtures were produced in three series with control mixes having 300, 350 and 400 kg cement content. These control mixes were modified to have a combination of 250, 300 and 350 kg cement content and 40, 50, 75 and 100 kg pozzolan addition for 1 m³ concrete. The efficiency of the pozzolan was obtained by using Bolomey and Feret strength equations on 28-day-old concretes. Maximum pozzolan amount with the optimum efficiency was determined. This study shows that the efficiencies obtained from each strength equations are similar and these values decrease with the increase of pozzolan/cement ratio.     

Contribution of hybrid fibers on the properties of the high-strength lightweight concrete having good workability

The contribution of hybrid fibers to the workability, mechanical and shrinkage properties of lightweight concrete (LWC) with high strength and workability was investigated. The results show that adding fiber to the lightweight concrete mixture greatly reduces the sedimentation of aggregates during mixing and improves the uniformity of the mix; however, the slump value is reduced. Compared with single type of fibers, hybrid fibers significantly improve the mechanical properties and brittleness of lightweight concrete, and restrain the long-term shrinkage.     

废石膏泡沫混凝土性能及影响因素

研究了以脱硫石膏-矿渣粉-水泥复合胶凝材料体系为胶凝材料的泡沫混凝土性能及其主要影响因素。结果表明,适当提高水胶比,有助于泡沫混凝士起泡性和稳泡性。掺加硫铝酸盐水泥和水玻璃的泡沫混凝土性能劣化,这丽种材料不适合应用于泡沫混凝土制备中。掺加适量甲基纤维素、减水剂可较好地改善泡沫混凝土的性能。经优化研究可得到容重低于1000kg／m^3,强度大于6MPa的脱硫石膏泡沫混凝土。     

海洋环境下干湿循环对结构混凝土性能影响的研究现状、存在问题及其发展趋势

干湿循环是导致干湿交替区混凝土劣化的主要原因.从海洋环境下干湿循环区结构物易遭受干湿循环-环境因素耦合作用破坏的现状出发,针对干湿循环破坏机理、影响干湿循环下混凝土性能的因素、干湿循环与环境因素耦合下混凝土力学性能、耐久性能演变规律等几个方面,对干湿循环影响海洋环境下结构物性能的研究现状进行了归纳与总结.分析了此研究领域存在的问题,提出了加强干湿循环条件、干湿循环-碱骨料反应共同作用对混凝土长期性能演化规律的研究,引入能更加准确反映干湿循环下混凝土材料力学性能损伤程度的指标,深入研究三轴应力状态下混凝土性能损伤变化规律等新的研究思路.     

短切纤维增强改性磷酸盐水泥抗折性能研究

分别采用短切碳纤维和短切玻璃纤维对磷酸盐水泥进行了增强改性研究.采用羧甲基纤维素溶液做分散剂使短切纤维在水泥基体中得到了很好的分散;通过凝结时间及抗折强度测试,研究了纤维种类与掺量对磷酸盐水泥性能的影响.结果表明,短切纤维的加入对磷酸盐水泥的凝结时间影响不明显;两种短切纤维的加入都使磷酸盐水泥的抗折强度显著提高,磷酸盐...     

Influence of metakaolin on the properties of mortar and concrete: A review

Supplementary cementing materials (SCM) have become an integral part of high strength and high performance concrete mix design. These may be naturally occurring materials, industrial wastes, or byproducts or the ones requiring less energy to manufacture. Some of the commonly used supplementary cementing materials are fly ash, silica fume (SF), granulated blast furnace slag (GGBS), rice husk ash (RHA) and metakaolin (MK), etc. Metakaolin is obtained by the calcination of kaolinite. It is being used very commonly as pozzolanic material in mortar and concrete, and has exhibited considerable influence in enhancing the mechanical and durability properties of mortar and concrete. This paper presents an overview of the work carried out on the use of MK as partial replacement of cement in mortar and concrete. Properties reported in this paper are the fresh mortar/concrete properties, mechanical and durability properties.     

A study on the effect of fine mineral powders with distinct vitreous contents on the fluidity and rheological properties of concrete

This paper presents an investigation on the effects of fine mineral powders on the fluidity and rheological properties of concrete. It was observed that the fluidity of concrete increased noticeably, and the plastic viscosity decreased, when vitreous powders were substituted partially for cement. It was found that vitreous powders have a strong dispersion effect on the fluidity and rheological properties of concrete, and this effect can be correlated with the vitreous content of the powders incorporated.     

Properties of fresh and hardened concrete

The present paper reviews the literature related to the properties of fresh and hardened concrete published after the previous (12th) International Congress on the Chemistry of Cement held in Montreal in 2007.Workability and fundamental rheological properties, reversible and non-reversible evolution, thixotropy, slump loss, setting time, bleeding, segregation and practical issues related to formwork filling and pressure, are addressed among the properties of fresh concrete.Among hardened concrete properties compressive strength and other mechanical and physical properties of hardened concrete, such as tensile strength, elastic properties, shrinkage, creep, cracking resistance, electrical, thermal, transport and other properties are covered. Testing, interpretation, modeling and prediction of properties are addressed, as well as correlation with properties of fresh concrete and durability, effects of special binders, recycled and natural aggregates, fiber reinforcement, mineral and chemical admixtures. Special attention is given to the properties of hardened lightweight and self-compacting concrete.     

层布式钢纤维混凝土力学行为及破坏特性研究

通过力学性能试验,研究了钢纤维体积掺量和长径比对层布式钢纤维混凝土力学性能影响,对比了层布式钢纤维混凝土与素混凝土和钢纤维混凝土的力学性能,结果表明层布式钢纤维混凝土改善了混凝土的力学性能,提高了混凝土的延性和弯曲韧性。     

不同品质粉煤灰对混凝土性能的影响及其作用的评价

研究了不同品质粉煤灰对普通混凝土性能的影响 ,综合评价了它们在混凝土中的作用     

Effect of the use of mineral filler on the properties of concrete

Engineers of the concrete technology are increasingly concerned with the material passing through a sieve of the size under 0.149 mm. Materials called very fine aggregate or mineral filler may affect the performance of concrete in an either positive or a negative way. Discussions on aggregate containing very fine material are vitally important. Washing the aggregate residue has been the sole way to solve this matter to date. This is mainly based on the debatable opinion that materials of this kind are regarded as clay material. The goal of the study was to determine how the content of mineral filler might affect properties of concrete. Two types of aggregates with different amounts of cement and mineral filler were used. Basically, mineral filler replaced sand. The effect of applying different amounts of mineral filler on concrete was then determined. The addition of 7-10% of mineral filler to fine aggregate (0-2 mm) was found to considerably improve the properties of concrete.     

新拌混凝土的匀质性对其性能的影响

良好的匀质性是制备高性能混凝土的基础,本文通过调整外加剂的种类和掺量,设计了一系列匀质性不同的混凝土,通过对混凝土的流变性、力学性能、氯离子渗透性、界面结构等进行了测试分析,研究了匀质性对普通混凝土和高强混凝土的影响.结果表明,改善混凝土复合体系的匀质性可以提高混凝土的整体性能.     

不同因素对混凝土抗碳化性能的影响实验

混凝土碳化是空气中CO2气体渗透到混凝土内,与其碱性物质发生化学反应后生成碳酸盐和水,这个过程会降低混凝土的pH值,又称为中性化过程,碳化使混凝土碱度降低,强度下降,易引起钢筋锈蚀,使钢筋混凝土的使用寿命减短。本文主要从粉煤灰、矿渣粉掺量、水胶比、胶材总量等方面对混凝土抗碳化性进行了分析研究。     

A method for assessment of the freeze-thaw resistance of preformed foam cellular concrete

The growing use of cellular concrete for building materials and geotechnical fills brings forth the question of suitable durability and performance standards. Of particular importance is the performance of cellular concrete in freezing and thawing environments. Since the macrostructure of cellular concrete or cellular control low-strength material is not like that of normal-weight concrete, a modified procedure is needed to specify the required characteristics of cellular concrete that lead to freeze-thaw durability. This research investigated the freeze-thaw durability of cellular concrete and developed a modified freeze-thaw test procedure, based on ASTM C666. Physical properties related to freeze-thaw durability were measured for each mixture and compared to the initial properties. As a result of these comparisons, recommendations are made regarding the production of freeze-thaw-resistant preformed foam cellular concrete exposed to freeze-thaw environments. The results of the study show that depth of absorption was a key predictor in developing freeze-thaw-resistant concrete. Compressive strength, depth of initial penetration, absorption and absorption rate are the important variables in producing cellular concrete that is resistant to cycles of freezing and thawing. Density and permeability were shown not to be significant variables.     

姚家坪水利水电枢纽面板混凝土力学性能研究

结合姚家坪水利水电枢纽大坝面板混凝土实验研究,通过对混凝土的抗压强度性能、劈拉强度、轴拉强度、极限拉伸和抗压弹性模量进行了分析.重点研究了水胶比、粉煤灰、水泥品种等对混凝土力学性能的影响.