INFLUENCE OF AIRCRAFT DEICER ON FREEZE-THAW DURABILITY OF HIGH PERFORMANCE CONCRETE

The influence of glycol,the main composition of the most frequently used aircraft dicer,on the freeze-thaw durability of high performance concrete（HPC）is investigated.Freeze-thaw durability of HPC is tested by accelerated freeze-thaw test.Four kinds of the solution,i.e.,tap water,3.5% NaCl solution,glycol solutions,and a LBR-A type commercial aircraft deicer are employed.Results show that freeze-thaw durability of HPC exposed to glycol solutions is closely related to the solution concentrations.The failure of HPC exposed to 3.5% glycol solution is similar to that of those exposed to 3.5% NaCl solution,i.e.,serious surface scaling.While the damage of HPC exposed to 12.5%—25% glycol solutions is postponed.Compared with glycol solution,the commercial aircraft deicer has much more negative effects on HPC freeze-thaw durability compared with 3.5% NaCl solution.In the presence of commercial aircraft deicer for HPC subjected to freeze-thaw cycles,the deterioration is mainly due to scaling and spalling.

The Frost-resisting Durability of High Strength Self-Compacting Pervious Concrete in Deicing Salt Environment

A high strength self-compacting pervious concrete(SCPC) with top-bottom interconnected pores was prepared in this paper. The frost-resisting durability of such SCPC in different deicing salt concentrations(0%, 3%, 5%, 10%, and 20%) was investigated. The mass-loss rate, relative dynamic modulus of elasticity, compressive strength, flexural strength and hydraulic conductivity of SCPC after 300 freeze-thaw cycles were measured to evaluate the frost-resisting durability. In addition, the microstructures of SCPC near the top-bottom interconnected pores after 300 freeze-thaw cycles were observed by SEM. The results show that the high strength SCPC possesses much better frost-resisting durability than traditional pervious concrete(TPC) after 300 freeze-thaw cycles, which can be used in heavy loading roads. The most serious freeze-thaw damage emerges in the SCPC immersed in the 3% of Na Cl solution, while there is no obvious damage in 20% of Na Cl solution. Furthermore, it can be deduced that the high strength SCPC can be used for 100 years in a cold environment.

A Simple Mix Proportion Design Method Based on Frost Durability for Recycled High Performance Concrete Using Fully Coarse Recycled Aggregate

Durability design of recycled high performance concrete（RHPC） is fundamental for improving the use rate and level of concrete waste as coarse recycled aggregate（CRA）. We discussed a frostdurability-based mix proportion design method for RHPC using 100 % CRA and natural sand. Five groups of RHPC mixes with five strength grades（40, 50, 60, 70 and 80 MPa） were produced using CRA with four quality classes, and their workability, 28 d compressive strengths and frost resistances（measured by the compressive strength loss ratio and the relative dynamic modulus of elasticity） were tested. Relationships between the 28 d compressive strength, the frost resistance and the CRA quality characteristic parameter, water absorption, were then developed. The criterion of a CRA maximum water absorption limit value for RHPC was suggested, independent of its source and quality class. The results show that all RHPC mixes achieve the expected target workability, strength, and frost durability. The research results demonstrate that the application of the proposed method does not require trial testing prior to use.

Development of Optimal Structural System for Hybrid Cable-Stayed Bridges Using Ultra High Performance Concrete

This study developed an optimal structural system for the hybrid cable-stayed bridge expected to have a durable lifetime of 200 years and of which major structural members are made of ultra high performance concrete (UHPC) with 200 MPa-class compressive strength. This innovative cable-stayed bridge system makes it possible to reduce each of the construction and maintenance costs by 20% compared to the conventional concrete cable-stayed bridge by improving significantly the weight and durability of the bridge. Therefore, detail design is carried out considering a real 800 m cable-stayed bridge and the optimal structure of the hybrid cable-stayed bridge is proposed and verified.

Durability of Concrete Subjected to the Combined Actions of Flexural Stress,Freeze-thaw Cycles and Bittern Solutions

Freeze-thaw durabilities of three types of concretesnormal portland cement concrete （OPC）, high strength concrete （HSC） and steel fiber reinforced high strength concrete （SFRHSC） were systemically investigated under the attacks of chemical solution, and combination of external flexural stress and chemical solution. Four kinds of bitterns from salt lakes in Sinkiang, Qinghai, Inner Mongolia and Tibet provinces of China were used as chemical attack solutions. The relative dynamic modulus （RDM） was used as an index for evaluating the damage degree during the course of chemical attack and stress corrosion. The experimental results show that the freeze-thaw durability of concrete is visibly reduced in the present of the flexural stress, i e, stress accelerates the damage process. In order to quantify the stress accelerated effect, a stress accelerating coefficient was proposed. The stress accelerating coefficient is closely related with the types of bitterns and the numbers of freeze-thaw cycles is. The more numbers of freeze-thaw cycles is, the greater the stress accelerating coefficient for various concretes will be. In addition, there also exists a critical ratio of external stress to the maximum flexural stress. If the stress ratio exceeds the critical one, the freeze-thaw durability of various concretes will be greatly decreased compared to the responding concretes without applied stress. The critical stress ratio of OPC, HSC and SFRHSC is 0.30, 0.40 and 0.40, respectively, indicating that HSC and SFRHSC have advantages over OPC and are suitable to use in the bittern erosion regions.

Durability and Micro-structure of Reactive Powder Concrete

Durability of traditional reactive powder concrete （RPC） with rich cement and high volume of fly-ash reactive powder concrete （FRPC） were studied. The X-diffraction and scanning electron microscope （SEM） measurement was imployed to analyze the microstructure. The results show that both types of RPC have higher compressive strength, less volume shrinkage ratio and better carbonation-, chloride-, freezing-resistances than the conventional concrete. The results of X-diffraction indicate that they basically have C-S-H as the main composition without Ca（OH）2 crystal and ettringite. SEM results show that hydration products of FRPC is mainly Ⅲ-C-S-H which is piled up closely like densely arranged stone body and it has very compacted structure, in addition, Ca/Si ratio of C-S-H gel is lower than 1.5.

Assessment on Chloride Contaminated Resistance of Concrete with Non-steady-state Migration Method

A preparation technology of chloride contaminated resistant concrete was presented. The newly developed non-steady-state migration test method was employed for the evaluation of chloride ions diffusion coefficient of the concrete. The experimental results show that this method has a good correlation with the traditional NT Build 443 method, and it provides an effective and quick approach to assess the resistant capacity of concrete against chloride ions.

Properties and Microstructure of Marine Concrete with Composite Mineral Admixture

The influences of compositing mineral admixtures on the regularity of mechanical property, workability, durability and microstructure of C50 marine concrete were investigated. The results show that the incorporation of mineral admixtures can improve the mechanical properties and workability of C50 marine concrete, 3 min-doped mineral admixture had excellent resistance to chloride ion permeability. The microscopic structure mixing mineral admixtures system was well-distributed and compact, little macroporeare can be found.

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.

海砂超高性能混凝土试验

采用未淡化的海砂制备超高性能混凝土(UHPC)和普通混凝土,研究了不同氯离子含量的海砂对UHPC抗压强度、孔结构、快速氯离子渗透性以及内置钢筋耐久性的影响,并与普通混凝土进行分析比较。结果表明,海砂中的氯离子含量对UHPC抗压强度并不会产生较大的消极影响;海砂UHPC的临界孔半径约为2 nm,与海砂普通混凝土不同,孔隙率随海砂中氯含量的增加而增加;即使海砂氯离子含量高达0.636%,海砂UHPC的氯离子渗透性仍可忽略不计;海砂UHPC中钢筋在28 d后处于钝化状态并趋于稳定。

高韧性纤维混凝土材料及应用性能研究

为了降低混凝土材料成本并优化材料性能,本实验制备了含聚丙烯(PP)纤维的高韧性纤维混凝土(UHTCC),并通过材料参数优化实验、SEM分析以及耐久性实验探究了UHTCC材料性能。实验结果表明,含聚丙烯(PP)纤维的高韧性纤维混凝土(UHTCC)材料的最佳PP纤维直径为30μm,最佳PP纤维长度为8mm,最佳PP纤维掺量为2%,最佳砂胶比为0.5%左右,最佳粉煤灰掺量应小于65%,此时,高韧性纤维混凝土材料水泥砂浆的流动性能较好、材料抗压强度以及抗折强度较高,韧性和耐久性能良好。实验制备的含PP纤维的UHTCC材料不仅成本低,且综合性能良好。

考虑混凝土耐久性-地震随机性的高桩码头时变可靠度研究

为了研究高桩码头长期使用情况下,其结构性能出现的退化现象,利用时间相关的钢筋混凝土性能退化模型,综合考虑混凝土耐久性与地震随机性之间的相关性,结合直接概率积分(DPIM)方法对高桩码头进行随机动力分析和时变可靠度分析,获得不同运行年限下高桩码头在地震激励下的响应概率信息以及时变可靠度曲线。结果显示:随着运行年限的增加,码头上部结构的水平位移概率密度曲线(PDF)、累积分布曲线(CDF)峰值有所下降,动力可靠度随使用年限大幅下降,反映结构体系的性能退化逐渐加快,体现出钢筋混凝土退化对高桩码头地震安全性的显著影响。

双掺陶粒轻质高强混凝土的力学及耐久性能试验研究

通过在混凝土中掺入黏土陶粒和页岩陶粒,使其具备较高强度的同时具有较低的干表观密度和较好的耐久性能,旨在探索制备28 d干表观密度不大于1950 kg/m3、28 d强度不小于50 MPa的轻质高强混凝土(Lightweight High-Strength Concrete,缩写:LWHSC)的方法。同时研究了黏土陶粒和页岩陶粒双掺对轻质高强混凝土抗压强度、干表观密度和耐久性的影响。结果表明,所制备的LWHSC的抗压强度试件破坏形态无异于普通混凝土,但使用黏土陶粒部分替代页岩陶粒可有效降低LWHSC干表观密度;适当增加胶凝材料用量并辅以优化陶粒的双掺比例,对除抗冻性以外的其它耐久性能具有一定的改善作用。研究成果可为认识、优化和开发页岩陶粒和黏土陶粒双掺LWHSC及其在工程中的应用提供参考。

采用纳米氧化铝制备高弹性模量超高性能混凝土的可行性研究

纳米材料具有粒径小、比表面积大、化学活性高等独特性能,能够提升水泥基材料的力学性能和在恶劣环境下的耐久性,在水泥基材料领域具有广阔的应用前景。弹性模量是超高性能混凝土(UHPC)的重要力学参数之一。虽然目前UHPC的抗压强度得到了大幅提升,但是其弹性模量并未随抗压强度同幅度增长。为了探究采用纳米氧化铝(NA)制备高弹性模量UHPC的可行性,本工作利用MAA (Modified Andreasen and Andersen)模型设计UHPC初始配合比,研究不同掺量的NA对UHPC工作性能、力学性能和耐久性能的影响。此外,本工作还探究了NA对UHPC微观孔结构和微观力学性能的影响。研究表明:(1)NA能使UHPC的28 d抗折强度、抗压强度、弹性模量分别提高8.23%~16.31%、8.04%~26.39%、9.44%~16.55%;(2)NA能使UHPC的干缩、氯离子迁移系数分别降低2.54%~13.01%、8.21%~17.28%;(3)NA能够优化UHPC的孔结构,提高其浆体弹性模量;(4)综合考虑NA对UHPC工作性能、力学性能和耐久性能的影响,NA在UHPC中的优选掺量为1.0%。本工作的研究结果对利用NA制备高弹性模量的UHPC具有指导意义。

钢渣粉对高强混凝土力学性能和耐久性的影响

超细矿渣是制备高强混凝土的优质矿物掺合料,但是超细矿渣水化放热量较大、凝结较快,不利于高强混凝土的强度和耐久性发展。而钢渣粉具有延缓水泥水化、降低水化放热的作用,可以充当“缓凝剂”。通过在高强混凝土中复掺钢渣粉和超细矿渣,研究了钢渣粉对高强混凝土性能的影响。结果表明复掺15%钢渣粉时初凝时间和终凝时间分别比纯水泥组延长53.0%和35.9%。同时早期强度降低,但与超细矿渣复掺后28 d和90 d强度分别为77.3 MPa和84.6 MPa,比对照组高4.3%和8.6%。此外,钢渣粉有效降低了高强混凝土的绝热温升和自收缩率。单掺15%超细矿渣时7 d自收缩率为1189.63×10^(-6),约为纯水泥组的2.5倍;复掺15%钢渣粉时自收缩率为211.62×10^(-6),比纯水泥组降低了52%。复掺钢渣粉的高强混凝土与纯水泥制备的混凝土的抗氯离子渗透性等级均为“低”。

高海拔寒冷地区混凝土抗冻耐久性研究综述

高海拔寒冷地区具有海拔高、气温低、昼夜温差大等特点,严重威胁混凝土结构安全和正常使用年限。因此,提高混凝土结构的抗冻耐久性、保证结构安全和可靠性是研究高海拔寒冷地区混凝土抗冻耐久性能、施工技术以及评价方法的关键。综合分析了水胶比、外加剂、掺合料对高海拔寒冷地区混凝土宏观力学的影响,混凝土内部微观结构测试方法取得的成就和存在的不足,混凝土微观结构与宏观力学之间的关系,以及高海拔寒冷地区混凝土冻融损伤模型以及数值模拟的研究进展。通过上述分析和总结,以期进一步完善高海拔寒冷地区混凝土抗冻耐久性的理论体系、试验和评估方法,为高海拔寒冷地区混凝土的理论研究和工程应用提供理论基础。

高钛矿渣在水泥混凝土中的研究应用进展

区别于普通高炉矿渣,高钛矿渣中TiO_(2)含量较高、矿物组成差异大、利用率低。高钛矿渣大量堆存会造成资源浪费,且给生态环境带来严重负担,因此亟需实现其固废资源化利用。近年来,基于高钛矿渣的矿物成分和结构稳定、微火山灰活性、多孔、集料性能优良等特点,研究人员逐渐将其作为矿物掺合料、粗细骨料等应用于水泥混凝土中,实现高钛矿渣的高效利用以及提高其使用附加值,促进高钛矿渣在混凝土中的工程应用。本文系统梳理了高钛矿渣在水泥混凝土中的研究应用进展,对高钛矿渣的来源、物理化学性质、在混凝土中的利用方式,介绍了其对混凝土工作性能、力学性能、耐久性能等方面影响的研究进展,此外深入论述了高钛矿渣作为矿物掺合料以及再生骨料对混凝土性能的影响及作用机理。最后,针对现阶段研究中的不足提出相应建议,旨在为高钛矿渣在水泥混凝土中的研究和工程应用提供参考。

玄武岩机制砂高性能混凝土组分相容性及耐久性研究

研究了玄武岩机制砂对不同种类水泥-粉煤灰胶凝体系与不同种类减水剂间的相容性及工作性的影响,基于最优配比配制出C25和C30强度等级玄武岩机制砂高性能混凝土,系统研究了其工作性、力学性能与耐久性。结果表明,不同减水剂与不同水泥的相容性不同,玄武岩机制砂及其石粉含量对水泥浆体的工作性影响较大。玄武岩石粉含量在5%以内或同时增加减水剂掺量均可最有效提高净浆流动度,而采用干筛法生产的机制砂对砂浆流动度的提升效果较佳。14 d膨胀率试验显示,玄武岩机制砂具有一定潜在的碱活性,在使用中应进一步试验研究。

预制UHPC雨污水检查井的设计与仿真分析

为了解决传统混凝土雨污水检查井易出现病害(如井体开裂)的问题,提出了一种预制超高性能混凝土(UHPC)雨污水检查井。通过结构设计和仿真分析对预制UHPC雨污水检查井的性能进行了评估研究,并对其制作和运输方式进行了介绍。结果表明:UHPC雨污水检查井的性能指标满足相关规范要求,受力性能较好,制作和运输方便,可为后续预制UHPC雨污水检查井的设计与应用提供参考。

石粉含量对机制砂高强混凝土性能影响的研究现状

在机制砂的生产过程中,石粉是不可避免的附加产物,而且不同的石粉含量会给混凝土的性能带来不同的变化。机制砂高强混凝土具有高强度、高工作性和高耐久性的特点,石粉对其性能的影响已然成为研究热点之一。主要论述了不同的石粉含量对机制砂高强混凝土的工作性能、力学性能和耐久性能的影响,并对其影响的作用机理进行阐述。