Simulation of Corrosion-Induced Cracking of Reinforced Concrete Based on Fracture Phase Field Method

Accurate simulation of the cracking process caused by rust expansion of reinforced concrete(RC)structures plays an intuitive role in revealing the corrosion-induced failure mechanism.Considering the quasi-brittle fracture of concrete,the fracture phase field driven by the compressive-shear term is constructed and added to the traditional brittle fracture phase field model.The rationality of the proposed model is verified by a mixed fracture example under a shear displacement load.Then,the extended fracture phase model is applied to simulate the corrosion-induced cracking process of RC.The cracking patterns caused by non-uniform corrosion expansion are discussed for RC specimens with homogeneous macroscopically or heterogeneous with different polygonal aggregate distributions at the mesoscopic scale.Then,the effects of the protective layer on the crack propagation trajectory and cracking resistance are investigated,illustrating that the cracking angle and cracking resistance increase with the increase of the protective layer thickness,consistent with the experimental observation.Finally,the corrosion-induced cracking process of concrete specimens with large and small spacing rebars is simulated,and the interaction of multiple corrosion cracking is easily influenced by the reinforcement spacing,which increases with the decrease of the steel bar interval.These conclusions play an important role in the design of engineering anti-corrosion measures.The fracture phase field model can provide strong support for the life assessment of RC structures.

Conductive Mortar as Anode Material for Cathodic Protection of Steel in Concrete

The behavior of a new type of secondary anode material made of carbon fiber reinforced cement used for cathodic protection of steel in concrete was studied. The mechanical, electrical and electrochemical properties of this conductive mortar were investigated. Results indicate that the addition of carbon fiber enhances the strength and ductility of the mortar, as well as the electrical property. The anodic polarization behavior was tested on specimens immersed in aqueous solutions of saturated Ca（OH）2 in the presence or absence of 3% NaCl. Based on impedance measurements the electrochemical parameters of conductive mortar were calculated. It is shown that the investigated conductive mortar can be used in cathodic protection of reinforced concrete. The study also shows that the optimum fiber content in mortar should be in the range from 0.5 vol% to 0.7 vol%.

Preparation of Eco-environmental Protection Bricks from Lake Sludge

Eco-environmental protection hollow bricks manufactured from lake sludge collected from North Lake in Wuhan of China were investigated. At first, the recipes of round sam- pies（diameter in 5 cm and thickness in 1 cm） prepared by pressing molding under a pressure of 8 MPa and firing system were optimized, and properties such as bending strength, compressive strength, total shrinkage rate, water adsorption rate, apparent porosity and bulk density of the fired samples were tested. The experimental results showed that water adsorption rate and apparent porosity decreased, while bulk density increased with firing temperature increasing. Addition of additive can result in the improvement of strength of fired samples. At the same time, fly ash and additive may also broaden the firing temperature range and reduce firing temperature. Toxic characteristic leaching procedure （TLCP） tests of samples also show that the metal leaching level is low. The conditions for manufacturing good quality sample include 80% sludge with 10% additive and 10% flyash fired at 1000 ℃ for 60 min. Bending strength and compressive strength of samples prepared under the conditions are 24.64 MPa, 131.95 MPa, respectively,which are far beyond the requirements of clay solid bricks of CNS. Finally, according to the optimized recipe,the eco-environmental protection hollow bricks with the sizes of 40 mm × 38 mm ×25 mm were made and tested by extrusion molding. Compared with the Chinese National Standards （CNS： GB 13545-2003）, compressive strength, water adsorption and bulk denstiy of the hollow bricks are 11.55 MPa ,14.5% and 986 kg/m^3 when they were fired at 1040 ℃, which are far beyond the require of of CNS. Especially, its water adsorption arrives to standard of high-class products（16.0%） and compressive strength is above the hightest class（MU 10.0）.

Research on market-based policy instruments for eco-environmental protection

The selection of policy instruments involves policy efficiency and policy effect.Effective settlement of eco-environment problems in the process of industrialization and implementation of active eco-environment protection depend on the innovation of policy instruments.In this paper,based on a descriptive analysis of the policy instruments for ecoenvironmental protection of our country,combined with the theoretical analysis and the empirical research on current marketization of eco-environmental protection,the authors indicate that eco-environmental problems originate fi'om the damage of eco-environment and the extemalities of eco-service,and that the market-based policy instruments which are helpful to balance the relationship between fight,responsibility and interest in the eco-service are effective measures to eliminate externalities and protect eco-environment.

Fibre Optic Protection System for Concrete Structures

The design concepts, modelling and implementation of various fibre optic sensor protection systems for development in concrete structures were investigated. Design concepts and on-site requirements for surface-mounted and embedded optical fibre sensor in concrete were addressed. Finite element （FE） modelling of selected sensor protection systems in strain-transfer efficiency from the structure to the sensing region was also studied. And experimental validation of specified sensor protection system was reported. Results obtained indicate that the protection system for the sensors performs adequately in concrete environment and there is very good correlation between results obtained by the protected fibre optic sensors and conventional electrical resistance strain gauges.

Water resources optimization and eco-environmental protection in Qaidam Basin

In order to realize sustainable development of the arid area of Northwest China, rational water resources exploitation and optimization are primary prerequisites. Based on the essential principle of sustainable development, this paper puts forward a general idea on water resources optimization and eco-environmental protection in Qaidam Basin, and identifies the competitive multiple targets of water resources optimization. By some qualitative methods such as Input-output Model & AHP Model and some quantitative methods such as System Dynamics Model & Produce Function Model, some standard plans of water resources optimization come into being. According to the Multiple Targets Decision by the Closest Value Model, the best plan of water resources optimization, eco-environmental protection and sustainable development in Qaidam Basin is finally decided.

A Critical Examination of the European Standard EN 1504 ＂Products and Systems for Protection and Repair of Concrete Structures＂

The European Standard EN 1504 ＂Products and systems for protection and repair of concrete structures -- Definitions, requirements, quality control and evaluation of conformity＂ can be considered a real milestone for the companies involved in the rehabilitation of buildings, bridges, piers, pipelines, and other civil or industrial concrete structures. However in some cases the examination and, even more, the practical application of the proposed guidelines are made difficult by a complicated sub-division in principles and methods, and by a confusing and repetitive layout. The paper deals in particular with the principles and methods for the rehabilitation of concrete damage due to reinforcement corrosion, often strictly connected, anyway, to those adopted in order to rehabilitate the concrete itself. Suggestions are given for a possible future update of the Standard, based on the personal experience of the Authors.

Oyster Cementation as Protective Covers for Exposed Marine Concrete

Cored concrete specimens from seawall exposed to marine environment for 22 years were evaluated by carbonation depth test,rapid chloride permeability test,absorption of water test and microstructure examination.The results show that concrete exposed to marine environment has smaller carbonation depth and carbonation depth of concrete exposed to tidal zone is less than that in splash zone.There are similar water absorption rate and chloride permeability for concrete exposed to splash zone compared with concrete exposed to splash zone removed 3mm surface layer.However,concrete exposed to tidal zone with bio-films has lower chloride permeability and water absorption rate than those of concrete exposed to tidal zone removed 3mm surface layer.In addition,Results of FE-SEM and EDAX indicate that concrete exposed to splash zone has loose structure,exposed finer aggregate and concrete exposed to tidal zone covers by dense structure of oyster cementation and shell.Microstructures analysis further verified that concrete covered with oysters and their cementation has beneficial effects to durability of concrete.

Research Progress of Eco-Friendly Portland Cement Porous Concrete:A Review

With the great impetus of energy conservation and emission reduction policies in various countries,the proposal of concepts such as“Sponge City”and“Eco-City”,and the emphasis on restoration and governance of ecological environment day by day,portland cement porous concrete(PCPC),as a novel building material,has attracted more and more attention from scientific researchers and engineers.PCPC possesses the peculiar pore structure,which owns numerous functions like river embankment protection,vegetation greening as well as air-cleaning,and has been of wide application in different engineering fields.This paper reviews the salient properties of PCPC,detailedly expounds the research progress of domestic and foreign literature about this subject in the past ten years(2010–2020),conducts the statistical analysis of the distribution rule of its major properties around the world,combines with the engineering application to summarize the excellent properties of PCPC,and makes a forecast of future research direction.

Research Review on Construction and Protection of Tibet Eco-environment

Tibet is not only famous ＂ the roof of the world＂ but also is recognized as the ＂ third pole of the earth＂ by the whole world, with very im-portant significance in construction and protection of plateau eco-environment. In Qinghai - Tibet Plateau, there are abundant wild animal and plant resources and a lot of high-mountain mineral resources, and water resources, light resources and characteristic agriculture and animal husbandry resources have broad development and utilization space. When Tibet economy and society improve and develop, eco-environment construction and protection work is also mentioned in the schedule. In this paper, the history, status quo and prospect of Tibet eco-environment protection and development are explored, which could promote the understanding on Tibet eco-environment construction and protection in academic world.

Effectiveness of Surface Coatings Against Intensified Sewage Corrosion of Concrete

Three different kinds of coatings were coated on the concrete surface, and the changes in appearance, surface roughness, microstructure and components of coatings in artificial sewage were investigated. In addition, the strength, micrograph, mineral compositions and pore structure of concrete specimens after removing coatings were also studied. The results show that epoxy coal tar pitch coating(ECTPC) has the best effect of protecting concrete from the sewage corrosion. After being immersed in sewage for 90 days, the compressive strength of concrete coated with ECTPC is still as high as that of specimen immersed in water, and the cement paste has a high CH content and dense structure with low porosity, which mainly accounts for its excellent barrier property and certain antibacterial function. Cement-based bactericidal coating(CBC) also has good effectiveness to sewage corrosion of concrete. The strength and microstructure of concrete coated with CBC in sewage are still significantly superior to those of uncoated concrete. Although cement-based capillary crystalline waterproofing coating(CCCWC) is a good waterproof material, it is not suitable for the corrosion resistance of concrete in sewage. After 2 months corrosion, almost all of the CH crystals in coating reacted with the metabolic acid substance by microbes. Therefore, the strength and pore structure of concrete coated with CCCWC are only slightly superior to those of uncoated concrete. Overall, the protective effect of cement-based inorganic coatings is relatively poor.

A Method of Assessing Parameters of Air-Void Structure in Air-Entrained Concretes

The air-void size distribution and number of air voids are crucial characteristics of air-entrainment. The standard spacing factor L is based on the Powers model, in which considerable simplifications are assumed. A better solution is provided by the Philleo factor, which determines the percentage content of protected paste located at a distance S from the edge of the nearest air void. Developing the concept put forward by Philleo, a method of determining the volume of protected paste on the basis of images generated from the numerical model of concrete grain structure including layout of aggregate-paste-air, is proposed. It is the ratio of the volume of the paste protected by air voids to the total paste volume. The PPV （protected paste volume） index accounts not only for sizes and number of air voids, but also for the role of aggregate particles in the placement of these pores, which is often disregarded in analyses. The PPV results obtained from image analysis were compared with standard spacing factor L and with the parameter developed by Philleo. The analyses conducted by the authors shows that accounting for aggregate grains in calculations substantially affects the assessment of the quality of the air-pore structure.

钢壳沉管隧道耐火极限标准与防火保护技术研究——以深中通道沉管隧道为例

为提高我国超大断面钢壳沉管隧道火灾防控水平,以深中通道海底沉管隧道为例,采用热力耦合模拟和材性试验等方法开展钢壳沉管隧道耐火极限标准研究,考虑到龙骨、拼缝等防火构造薄弱环节,进行管节结构和管节接头耐火试验,并提出相应的防火保护技术方案。主要结论如下:1)管节结构的耐火极限标准为火灾时,应将结构内侧钢壳最高温度控制在300℃以内;2)OMEGA橡胶管节接头的耐火极限标准为OMEGA橡胶超过70℃的时间小于2 h,超过100℃的时间小于1 h,且最高温度不得超过150℃;3)GINA橡胶管节接头的耐火极限标准为GINA橡胶超过100℃的时间小于1 h,且最高温度不得超过150℃;4)管节结构可采用35 mm单层防火板L型拼缝,对接面涂热膨胀胶;5)管节接头可采用35 mm防火板+50 mm陶瓷纤维毯双层防火保护体系,龙骨自由端取500 mm,拼缝处采用防火胶封堵。

马鞍山长江公铁大桥主航道桥中塔下横梁施工关键技术

马鞍山长江公铁大桥主航道桥Z4号中塔采用空间四肢A形钢-混组合塔,横向两塔肢间设下横梁,下横梁间设3道系梁,纵向两塔肢间不设置横梁。下横梁采用支架法分层浇筑施工。下横梁施工支架采用落地式钢管支架配套模板体系,受力性能满足要求;通过有限元计算比选下横梁混凝土分层浇筑方案并进行优化,采取(5.5+2.5)m分层方案,上、下层混凝土分别分为2块、3块分层分块浇筑;通过低温升、易泵送、高抗裂的C60混凝土研制、下横梁与塔柱倒弧结合面抗裂措施优化、分块间接缝构造形式及施工工艺优化、下横梁与系梁混凝土浇筑施工组织优化、混凝土温度智能化监控、预应力束张拉时机控制等混凝土防裂措施,有效解决了下横梁大体积混凝土易开裂的难题。

基于数值模拟的蜂窝钢管约束混凝土靶抗侵彻机理

多孔蜂窝钢管约束混凝土靶具有良好的抗侵彻性能和拓展性能。基于ANSYS/LS-DYNA软件,采用FEM/CSCM-SPH/HJC耦合法,模拟了多孔蜂窝钢管约束混凝土靶抗硬芯枪弹侵彻过程,研究了蜂窝钢管约束混凝土靶的抗侵彻机理。结果表明:与单孔正六边形钢管约束混凝土靶和无约束混凝土靶相对比,蜂窝钢管约束混凝土优异的抗侵彻性能主要体现在隧道侵彻阶段,表现为限制弹丸头部附近混凝土的径向膨胀,增大侵彻阻力;对比单孔正六边形钢管约束混凝土靶,蜂窝钢管约束混凝土靶周边单元为钢管提供了支撑,限制了钢管壁的面外弯曲变形,强化了钢管的约束效应,即形成周边单元的附加约束作用;对比无约束混凝土靶,钢管的存在限制了蜂窝钢管约束混凝土靶被打击单元的径向膨胀,强化了被打击单元混凝土的围压效应,提高了混凝土的强度和变形性能,增大了弹丸的侵彻阻力,从而使其抗侵彻能力提高。因此,蜂窝钢管约束混凝土靶由于蜂窝钢管的侧向约束和周边单元的附加约束双重约束效应而体现出良好的抗侵彻性能。

发泡水泥板的应用背景、现状及前景概述

为深层次、全面了解发泡水泥板诞生背景、应用现状和发展前景,本文对发泡水泥板应用背景、市场需求、技术标准沿变、整体性能、综合成本、应用现状、发展前景进行全方位、多角度、深层次剖析。综合认为:尽管发泡水泥板具有隔热、防火(A1级)、环保、抗老化、强度高等优点,但其研发技术壁垒低,加上劣质产品挡道、厂家恶性竞争等恶劣现象,致使其市场容纳空间已非常狭小。本文将为建筑从业人员全面了解发泡水泥板的“来龙去脉”和实时动态提供最新现实科学依据,为科研工作者研发新型建筑保温材料提供更多理论科学依据。

混凝土微生物腐蚀的防护方法研究进展

混凝土是国家基础建设的重要工程材料,然而由于服役环境的复杂性,混凝土面临微生物腐蚀造成的劣化问题,给各行业发展和设施安全运行带来了安全隐患和经济损失,因此对混凝土的防护尤为重要。简要介绍了混凝土材料的应用现状和微生物腐蚀混凝土材料的机理,针对微生物腐蚀混凝土的方式,详细综述了目前保护混凝土免受微生物腐蚀的4种主要方法。重点讨论了微生物灭活、混凝土改性、涂层和生物矿化阻止微生物腐蚀的原理和研究进展,列举了不同方法抵抗微生物腐蚀的案例,总结了4种方法存在的优缺点;并且通过综述已有的混凝土防护方法,展望了未来微生物腐蚀混凝土的防护方法研究方向。

带有防火保护的圆钢管约束钢筋混凝土柱抗火性能分析与设计

抗火性能是圆钢管约束钢筋混凝土柱设计时的关键问题之一,尽管目前相关研究已逐渐完善,但带有防火保护条件下该类构件的抗火性能研究与设计仍不充分,已有的行业标准中构件高温稳定承载力公式未与常温公式相连续,且其中的防火保护层设计公式不具有明确的物理意义。基于ABAQUS软件,该文开展了带有防火保护圆钢管约束钢筋混凝土柱在ISO 834标准火灾作用下温度场和耐火极限的有限元分析,研究了荷载比、截面尺寸、长细比、防火保护层厚度等关键参数对构件耐火极限的影响规律,并提出了钢管温度、钢筋温度以及混凝土等效温度的简化计算公式。结果表明:随着防火保护层厚度的增大,构件的耐火极限近似线性增大。基于系统性参数分析,提出了带有防火保护圆钢管约束钢筋混凝土柱高温下截面承载力和稳定承载力设计公式,以用于确定构件达到不同耐火极限所需的防火保护层厚度,该方法保持了与现行标准中常温承载力计算公式的连续性。

水下自护混凝土与钢筋握裹力试验研究

随着水下自护混凝土技术的推广和应用,其关键工艺参数水下保护剂浓度对水下自护钢筋混凝土结构性能的影响成为关注的热点。基于水下自护技术,在常用工作浓度范围内,对水下自护混凝土的素混凝土力学性能、混凝土与钢筋握裹力、微观孔隙结构开展了试验研究。试验结果表明:在不同水下保护剂浓度下,水下自护素混凝土抗压强度水陆强度比均超过80%;混凝土与钢筋握裹力水陆强度比约在40%~65%,水下保护剂浓度越高,混凝土与钢筋握裹力水陆强度比越低;混凝土基质区域孔隙率和混凝土与钢筋握裹力存在负相关关系;水下保护剂能够有效提升水下自护混凝土的力学性能,但水下保护剂浓度的提升会对混凝土与钢筋握裹力强度造成不利影响。因此,合理选择水下保护剂浓度并增加钢筋用量是提升水下自护钢筋混凝土工程的可靠性的重要举措。