Influence of Recycled Concrete Fine Powder on Durability of Cement Mortar

In this paper,the durability of cement mortar prepared with a recycled-concrete fine powder(RFP)was examined;including the analysis of a variety of aspects,such as the carbonization,sulfate attack and chloride ion erosion resistance.The results indicate that the influence of RFP on these three aspects is different.The carbonization depth after 30 days and the chloride diffusion coefficient of mortar containing 10%RFP decreased by 13.3%and 28.19%.With a further increase in the RFP content,interconnected pores formed between the RFP particles,leading to an acceleration of the penetration rate of CO_(2)and Cl^(−).When the RFP content was less than 50%,the corrosion resistance coefficient of the compressive strength of the mortar was 0.84-1.05 after 90 days of sulfate attack.But the expansion and cracking of the mortar was effectively alleviated due to decrease of the gypsum production.Scanning electron microscope(SEM)analysis has confirmed that 10%RFP contributes to the formation of a dense microstructure in the cement mortar.

Durability of Lining Concrete of Subsea Tunnel under Combined Action of Freeze-thaw Cycle and Carbonation

Through the fast freeze-thaw cycle test,accelerated carbonation test,and natural carbonation test,the durability performance of lining concrete under combined action of freeze-thaw cycle and carbonation were studied.The experimental results indicate that freeze-thaw cycle apparently accelerates the process of concrete carbonation and carbonation deteriorates the freeze resistance of concrete.Under the combined action of freeze-thaw cycle and carbonation,the durability of lining concrete decreases.The carbonation depth of lining concrete at tunnel openings under freeze-thaw cycles and tunnel condition was predicted.For the high performance concrete with proposed mix ratio,the lining concrete tends to be unsafe because predicted carbonation depth exceeds the thickness of reinforced concrete protective coating.Adopting other measurements simultaneously to improve the durability of lining concrete at the tunnel openings is essential.

Service Life Prediction of Lining Concrete of Subsea Tunnel under Combined Compressive Load and Carbonation

Qingdao Jiaozhou Bay subsea tunnel is the second self-built tunnel in China with the designed service life over 100 years.The durability of lining concrete are one of an important factors to determinate the service life of tunnel.Considering the main environmental loads and mechanical loads of subsea tunnel,the durability properties of lining concrete under combined action of compressive load and carbonation has been studied through the critical compressive load test,accelerated carbonation test,natural carbonation test and capillary suction test.The tests results show that critical compressive load apparently accelerates the carbonation and deteriorates the anti-permeability of concrete.Under the combined action of critical compressive load and carbonation,the durability of lining concrete decreases.Based on the carbonization life criteria and research results,for the high-performance concrete with proposed mix ratio,the predicted service life of lining concrete for Jiaozhou bay subsea tunnel is about 80 years which fails to reach the required service life.It is necessary to adopt other measurements simultaneously to improve the durability of lining concrete.

Durability Analysis and Carbonation Life Prediction of Shajiang River Bridge

The shajiang river bridge on the appearance test, concrete rebound detection, concrete cover depth detection, concrete carbonation depth detection, concrete chlorine ion content detection, and the detection results in statistics and analysis. Based on the bridge of the service the atmospheric environment parameters and testing data, the paper calculates and analyzes the main stress components the carbonation bridge reliability index and remaining life of carbide, assessing the bridge for the service life and reinforcement maintenance and offer the scientific basis.

Comparison study of durability design for concrete bridges:Chinese-code and Eurocode

Differences and similarities of durability design for concrete bridges in Chinese-code and Eurocode are identified and discussed. Exposure environment classes and regulations of the minimum concrete cover and strength of the two codes are compared and analyzed. Numerical calculations for predicting the durable life of bridges related to carbonization and chlorides corrosion （marine and de-icing） are conducted. The results show that provisions in the two codes can satisfy the durability requirements under carbonization whereas they cannot guarantee the durability for bridges in spray and splash zones. Enhancing the waterproof capacity and reducing the frequent use of de-icing agents are vital to improving the bridge durability. Some recommendations for upgrading the durability are also included.

Probabilistic durability assessment approach of deteriorating RC bridges

A stochastic finite element computational methodology for probabilistic durability assessment of deteriorating reinforced concrete（RC） bridges by considering the time-and space-dependent variabilities is presented.First,finite element analysis with a smeared cracking approach is implemented.The time-dependent bond-slip relationship between steel and concrete,and the stress-strain relationship of corroded steel bars are considered.Secondly,a stochastic finite element-based computational framework for reliability assessment of deteriorating RC bridges is proposed.The spatial and temporal variability of several parameters affecting the reliability of RC bridges is considered.Based on the data reported by several researchers and from field investigations,the Monte Carlo simulation is used to account for the uncertainties in various parameters,including local and general corrosion in rebars,concrete cover depth,surface chloride concentration,chloride diffusion coefficient,and corrosion rate.Finally,the proposed probabilistic durability assessment approach and framework are applied to evaluate the time-dependent reliability of a girder of a RC bridge located on the Tianjin Binhai New Area in China.

Durability of concrete beams reinforced with CFRP sheet under wet-dry cycles and loading

The test results of eight concrete beams reinforced with carbon fiber reinforced polymer （CFRP） sheets subjected to an aggressive environment under a sustained load are presented. The beams are 1 700 mm long with a rectangular cross-section of 120- mm width and 200-mm depth. The beams are precracked with a four-point flexural load, bonded CFRP sheets, and placed into wet-dry saline water（ NaCl） either in an unstressed state or loaded to about 30% or 60% of the initial ultimate load. The individual and coupled effects of wet-dry saline water and sustained bending stresses on the long term behaviour of concrete beams reinforced with the CFRP are investigated. The test results show that the coupled action of wet-dry saline water and sustained bending stresses appears to significantly affect the load capacity and the failure mode of beam strengthened with CFRP, mainly due to the degradation of the bond between CFRP and concrete. However, the stiffness is not affected by the coupled action of wet-dry cycles and a sustained load.

Durability of Lightweight Concrete Using Oil Palm Shell as Aggregates

Oil Palm Shell (OPS) concrete can be used in different fields of construction. To determine more accurately the fields of application, it is important to know and understand the behaviour of OPS concrete over the long term and when it is in aggressive environments. This paper presents the results of studies conducted on the durability of OPS concrete. Water absorption capacity, electrical resistivity and apparent diffusion of chloride ions have been measured on different concrete samples. In addition, the behaviour of OPS concretes to carbonation was studied in an environment rich in carbon dioxide. Results show that OPS concrete has an absorptivity of 0.97 kg/m2·h1/2, an electrical resistivity of 64.37 Ω·m and an apparent diffusion coefficient of chloride ions of 3.84 × 10-12 m2/s after 90 days. All these results of OPS concrete are very close to those of concrete with normal aggregate and other lightweight concrete, which mean OPS concretes have globally good properties with regard to durability.

矿冶固废制备混凝土配合比优化及耐久性研究

目的:为解决工业固废大量堆存、占用土地造成的环境污染问题,提高工业固废综合利用效率。方法:以钢渣、矿渣、脱硫石膏等工业固废为原材料制备的固废基胶凝材料,与水泥、粉煤灰按照不同比例混合,再以铁尾矿砂、铁尾矿碎石为骨料,制备C30强度等级的低碳混凝土,试验研究了水泥取代率、粉煤灰掺量对低碳混凝土抗压强度的影响,分析了全固废低碳混凝土的耐久性能,并通过XRD、TG-DSC、SEM的手段探究了固废基胶凝材料的水化产物及过程。结果:结果表明:在粉煤灰掺量80 kg/m^(3)的条件下,固废基胶凝材料对水泥的取代率可达50%~70%,固废基胶凝材料完全取代水泥时宜作为单一胶凝材料使用;全固废低碳混凝土具有良好的耐久性能,其抗氯离子渗透性能、抗冻性能均优于普通混凝土。结论:固废基胶凝材料的早期水化进程较慢,其强度发展依赖于AFt和C-S-H凝胶的大量生成,二者相互交织、穿插提高了胶凝体系的密实度和强度。意义与创新性:本文论证了工业固废制备低碳混凝土的可行性,对混凝土绿色低碳发展具有实际指导意义。

生蚝壳应用于混凝土中的研究进展

分析了生蚝壳(OS)的主要化学成分及其作为胶凝材料或骨料的制备方法,综述了OS粉等质量部分替代水泥或OS砂等质量部分替代天然细骨料对混凝土工作性、力学性能和耐久性能的影响,评价了OS应用到混凝土中的环境效益,可为OS的资源化利用提供参考,同时降低混凝土的生产成本,减少碳排放。

复杂环境下纤维混凝土改性及耐久性试验研究

为解决在盐蚀等复杂环境下混凝土性能下降的问题,试验利用网状聚丙烯纤维、玄武岩纤维及碳酸钙晶须对混凝土进行改性,制备一种改性纤维混凝土并研究不同晶须掺量下混凝土的性能。结果表明,在纤维混凝土中掺入碳酸钙晶须,混凝土的坍落度下降,工作性能提高,并且抗压、抗折强度提升;试验制备的碳酸钙晶须改性纤维混凝土综合性能较好,可以应用于高浓度盐碱等复杂环境。

基于原位测试的现役铁路混凝土桥梁耐久性评估

碳化是导致混凝土结构内部钢筋锈蚀及承载力下降的主要原因,进行现役铁路桥梁耐久性评估及剩余寿命预测,对其后续的维护和加固具有重要意义。对铁路特大桥中若干预应力混凝土梁的耐久性进行评估,测试其混凝土强度、碳化深度以及保护层厚度等指标;并结合实测数据与耐久性模型,对该桥梁的剩余耐久性寿命进行预测。结果表明,服役时间32年的预应力混凝土强度均值38.5 MPa,碳化深度均值约10 mm。相较于翼缘和腹板,梁底实际保护层厚度较小,此处内部钢筋发生锈蚀的概率较大。基于原位测试的碳化深度修正的耐久性模型表明,在服役29.5年时预应力梁底部开始发生钢筋锈蚀;最后基于7%临界钢筋锈蚀率耐久性准则,对该预应力桥梁不同部位的使用寿命进行预测。

煤矸石混凝土性能与资源化应用研究评述

煤矸石是一种煤炭共伴生矿物生产的副产品,属于大宗固废弃物,煤矸石混凝土是其资源化应用的重要实践。碳中和碳达峰要求各行业为绿色生态的可持续发展做出相应规划,在建筑材料资源化利用方面,将煤矸石用作集料研制高性能混凝土开始了建筑与土木工程行业的新兴材料革新,同时将其作为不可或缺的低碳化资源处理的中坚力量能够为碳中和进程加速。国内外学者对煤矸石混凝土的力学性能与工程应用等方面进行了很多理论和实验研究,在改善煤矸石混凝土性能、工程实际应用及生产技术革新等方面取得重大进展,构建了较为完整的研究体系。基于不同地区煤矸石化学矿物特性和物理性质的差异性,阐述了煤矸石作为不同集料制备的煤矸石混凝土的力学性能与耐久性能,分析了煤矸石在土木工程领域应用的可行性和目前研究局限性,展望了煤矸石作为集料制备新型混凝土在道路工程和建筑结构中的资源化应用前景,为煤矸石大宗化再生利用和煤矸石混凝土进一步研究提供新的视角和参考。

大掺量矿物掺合料混凝土耐久性研究

对9种不同掺量矿物掺合料条件下的不同配合比混凝土的耐久性能进行了研究。研究发现:随着矿物掺合料的掺入比例不断增加,由于混凝土内部孔结构和级配得到较为有效改善,混凝土的氯离子扩散系数不断减小,混凝土抵抗氯离子渗透能力逐渐增强,抗碳化能力不断降低,在混凝土的水胶比较大时效果明显。当水胶比为0.26,粉煤灰掺量为50%时,C70混凝土的氯离子扩散系数最小,达到0.403/(10-8 cm 2/s);粉煤灰掺量为40%时,C70混凝土的抗碳化性能最强,达到1.0 mm。

多壁碳纳米管对钢渣混凝土力学及耐久性能的影响

多壁碳纳米管(MWCNTs)作为新兴纳米材料,能够改善混凝土材料的宏观性能及微观结构。本文研究MWCNTs对钢渣混凝土的力学性能及耐久性能的影响,并利用扫描电镜(SEM)分析其增强机理。研究结果表明:MWCNTs掺量为0.08%时,钢渣混凝土的力学性能及耐久性能显著提高,28 d标准养护条件下,钢渣掺量为15%时,与未掺加MWCNTs的钢渣混凝土相比,抗压强度和抗折强度分别提高了13.2%和14.6%;28 d氯离子扩散深度和氯离子扩散系数分别降低了29.8%和27.4%;200次冻融循环过程中,掺入MWCNTs的钢渣混凝土质量损失率及相对动弹性模量变化率偏低,材料抗冻性能增强。MWCNTs通过桥联和拔出效应,可抑制微裂缝的产生和扩展,有效改善骨料界面过渡区,从而提高混凝土材料的力学性能及抗冻、抗氯离子侵蚀性能。

热带岛礁珊瑚骨料混凝土的耐久性及提升方法

为探究热带岛礁环境下珊瑚骨料混凝土的耐久性研究现状,提升其耐久性能。本文采用试验与理论分析相结合的方法,研究了珊瑚骨料混凝土的抗氯离子扩散性能、抗渗透性能以及抗碳化性能指标。结果表明:珊瑚骨料混凝土的表面自由氯离子含量以及表观氯离子扩散系数等耐久性指标远高于普通骨料混凝土以及再生骨料混凝土;相同水压作用下,珊瑚骨料混凝土的渗水高度比再生骨料混凝土、普通骨料混凝土以及轻骨料混凝土高5倍以上,表明珊瑚骨料混凝土的抗渗透性能明显劣于再生骨料混凝土、普通骨料混凝土和轻骨料混凝土;相同暴露时间下,珊瑚骨料混凝土的抗碳化性能优于普通骨料混凝土、轻骨料混凝土。为确保长期服役条件下珊瑚骨料混凝土具有较好的抗碳化性能,建议采用改善珊瑚骨料密实度、添加外加剂、降低水灰比以及掺入矿物掺合料等方法。

再生骨料混凝土研究的知识基础及热点主题——基于CiteSpace和VOSviewer的知识图谱可视化分析

为全面了解再生骨料混凝土研究领域近年来的研究情况,基于WoS核心数据库和中国知网(CNKI)数据库,通过CiteSpace和VOSviewer软件对2000—2022年的再生骨料混凝土研究文献进行了计量分析,分析其年发文情况、主要作者、研究国家、研究机构、关键词和期刊共被引,并探讨了其知识基础及热点主题。结果表明:再生骨料混凝土领域的发文量变化经历了初始阶段、缓慢增长期、快速增长期三个阶段;De Brito Jorge是英文文献发文量最多的作者,肖建庄是国内外发文量最多的中国作者;中国、美国、澳大利亚、西班牙和印度是该领域研究成果最多的5个国家,同济大学是再生骨料混凝土领域发文最多的机构;未来再生骨料混凝土的研究将围绕改性研究、碳化、相关预测模型研究、工艺优化和应用推广等方向继续发展。

一种高机械耐久性油水分离网的制备及性能

为提高超疏油/超亲水涂层的机械耐久性,首次提出以碳纳米管、正硅酸乙酯和丙烯酸树脂为原料,加入全氟辛酸和壳聚糖季铵盐进行改性,喷涂制备出一种具有高机械耐久性的油水分离网。利用接触角测试、砂纸磨损实验和油水分离实验,评价分离网的润湿性、机械耐久性和油水分离能力,并通过光学显微镜和扫描电子显微镜对涂层磨损前后的形貌变化进行分析。结果表明,当碳纳米管掺杂量为1.5%时,制备的涂层油接触角为155.5°,水接触角为0°,具有良好的超润湿性;经过160次砂纸磨损实验,仍保持超疏油/超亲水状态,表现出优异的机械耐久性;在油和水(碱性、酸性、中性、冷、热)的混合溶液中均有96%以上的分离效率和1.6×104L/(m^(2)·h)以上的渗透通量,经过20次分离后分离效率为96.33%,具有良好的油水分离能力。

表面磨损与碳化作用下船闸混凝土耐久性研究

船闸混凝土在涨水期受船体摩擦碰撞及船行波冲蚀磨损,落水期受空气中CO_(2)的侵蚀。采用水下钢球法模拟涨水期船闸混凝土的物理磨损,结合快速碳化试验模拟落水期的CO_(2)侵蚀,研究船闸混凝土的性能退化规律。根据船闸设计服役指标和通航量确定表面磨损和碳化时长,以及二者的交替循环机制,宏观上通过碳化深度和抗冲磨强度反映船闸混凝土的工程性能退化规律,微观上基于热重法和压汞法表征船闸混凝土的成分和孔结构演化。结果表明,表面磨损作用会加速碳化反应,表面磨损和碳化循环作用机制符合内河船闸混凝土实际破坏情况。

炭灰/硅烷化SiO_(2)复合涂层的制备及其性能研究

针对混凝土结构表面多孔隙易吸水,冻融环境差的缺点,对其进行了炭灰/硅烷化SiO_(2)表面处理,并对两种单一处理后的涂层混凝土表面性质进行了对比研究。展现了可控层的炭灰涂层和硅烷化SiO_(2)涂层的物理性质和耐磨性的变化,以及两种单一处理时最优涂层的微观结构。结果表明:硅烷化SiO_(2)溶液处理向基底引入了甲基,Si-CH 3基团增加,粒子间作用力增强,耐磨性提高,最大接触角达到156°;炭灰溶液处理促进了混凝土表面羟基的交联,最大接触角达到142°,耐磨性虽得到了较大提高,但稍弱于硅烷化SiO_(2)涂层的耐磨性;当炭灰涂层为4层,硅烷化SiO_(2)涂层为3层时,整个衬底被完全覆盖,疏水效果为最优。