Analysis of Concrete Crack Treatment Technologies in Buildings

With the continuous development of civil engineering,concrete crack treatment technology has become an important research field.This paper proposes treatment techniques for different types of cracks,including the prevention and repair of surface cracks,the reinforcement and grouting of structural cracks,and the design and construction of controlled cracks through the analysis of the causes and classification of concrete cracks.The methods and suggestions proposed in this paper are practical and can improve the quality and safety of buildings.

Investigation on Cracking of Concrete Shear Wall under Exceeded Temperature Differences Rate

In situ, the changes of temperature, deformation, and stressing of steel bar of C40 reinforced concrete shear wall were measured, respectively. The results are obvious that the temperature change of climate is one of the most effective factors which could lead the concrete shear wall to cracking at earlier age. The temperature differences between inside and outside concrete shear wall are so large that the concrete will gain larger shrinkage. This larger shrinkage which is caused by the temperature reducing ratio will gain the strained action of head, end and reinforced steel bar of concrete shear wall. This action can lead to tensile stress on the surface and inside concrete shear wall. If the tensile stress would exceed the pull strength of concrete, the concrete shear wall would crack and cause deterioration. Thus, the enhancing curing of concrete shear wall in suit at earlier age, and controlling temperature reducing ratio and deform caused by shrinkage, will be available treatments which control occurring and developing of cracking on concrete shear wall.

Causes and Management of Concrete Cracks in Construction Engineering

In today’s comprehensive development of the domestic economy,China’s construction industry has reaped remarkable achievements.As a very important composition in the field of construction in China,the characteristics of concrete engineering itself determines that it is prone to encounter a variety of problems,the most frequent of which is various cracks.Cracks not only affect the aesthetics of the building,but also affect the durability and safety of the project.Considering these potential hazards,the causes of concrete cracks must be carefully analyzed to control and improve them in an effective way to ensure the safety and stability of concrete buildings.

Simulation of the Cracking and Ablation Behavior of Ferrosiliceous and Siliceous Nuclear Sacrificial Concretes

We investigated the simulation of the cracking and ablation behavior of ferro-siliceous and siliceous nuclear sacrificial concretes. To this end, four type of sacrificial concretes were fabricated, i e, the ferro-siliceous(F) and siliceous(S) plain concretes, and the polypropylene fiber reinforced concretes of the above two(FF, SF). The cracking and ablation behaviors of the sacrificial concretes were investigated by simulation tests, and the simulated elevated temperature was obtained by means of thermite powder. The number and the width of the cracks were compared and the pore size distribution of sacrificial concretes was measured. In addition, the interface and chemical composition of melt at different positions were analyzed, and the ablation depth of the sacrificial concrete crucibles was also measured. It was found that the siliceous concrete shows to be more prone to cracking than the ferro-siliceous concrete due to the higher content of fly ash and lower water to binder ratio; though the ablation depth of siliceous concrete is found to be slightly larger, no clear difference can be detected for the basemat ablation rate.

Spatial Thermal Crack Control in Mass Concrete

The finite element software,MIDAS is used to predict the distribution of temperatures and,analyzes the cracking control methods within a hydrating mass concrete.The temperature control of mass concrete has great significance in assuring the project quality.Adiabatic or semi adiabatic temperature measurement is mostly used for measuring and controlling the temperature fluctuation during construction.The temperature distribution produced by the finite element thermal analysis of the model is used to quantify the maximum allowable internal temperature difference before crack initiation on concrete.This study analyzes the data from one high-rise structure project in Shanghai are used to verify the finite element model developed.Results suggest that reliance on a limiting maximum temperature differential to control cracking in massive concrete applications should be supplemented with a requirement for analysis showing the calculated spatial temperature and stress response to the predicted temperature distribution within the concrete,to ensure that the induced tensile stresses will not exceed the tensile strength of the concrete and so minimize the risk of having thermal cracks at early age.

Analysis on Construction Technology of Concrete Structure in Civil Engineering

The rapid development of science and technology puts forward higher requirements for new building construction,especially in civil engineering construction.The construction quality of construction engineering is the core management and the testing link.The Concrete structure is an important safety and quality guarantee in the project and is the top priority in the civil engineering.In civil engineering,the concrete structure has an important social impact on the continuous research and development,and application of construction technology.This paper,discuss the advantage and disadvantage of using concrete in building construction.

Experimental Study on Chloride Ion Penetration Resistance of Coal Gangue Concrete under Multi-Factor Comprehensive Action

In order to investigate the chloride ion penetration resistance of coal gangue concrete under multi-factor comprehensive action, the non-steady-state accelerated chloride ion migration test was used to test the chloride diffusion law of coal gangue concrete specimens by crack width, curing temperature and water-cement ratio. Three groups of crack width (0 mm, 0.05 - 0.12 mm, 0.12 - 0.2 mm), three curing temperatures (high temperature 45, medium temperature 25, low temperature 10), three water cement ratios (0.3, 0.4, 0.5) were set in the experiment. The results show that when the curing temperature and water cement ratio are constant, the crack width less than 0.12 mm has little effect on the chloride content and chloride diffusion coefficient. When the crack width is larger than 0.12 mm, the chloride penetration depth increases with the crack width. The resistance to chloride ion penetration of gangue concrete is greatly influenced by the water cement ratio. The influ-ence degree of three factors on chloride ion migration coefficient of gangue concrete is as follows: water cement ratio > crack width > curing temperature.

Multi-powder dam concrete with high performance and low adiabatic temperature rise

Based on the fluidity, strength, heat of hydration and loop crack resistance experiment of multi-powder paste, the components and proportion of multi-powder were optimized and the concrete properties were studied. The multi-powder consists of limestone powder, slag, fly ash and moderate heat Portland cement (PMH cement). The results show that the compressive strength of the multi-powder paste and mortar is close to those of PMH cement, fly ash paste and mortar currently used in dam concrete, yet the flexural strength is relatively higher. The multi-powder paste is featured by larger fluidity, lower heat of hydration and delayed cracking time. In comparison, less unit water consumption and cement is used in multi-powder concrete, and under premise of equal mechanical performance, deformation, thermal performance and durability, the adiabatic temperature rise at 28 d is reduced by 2 ℃. In this way, the crack resistance is improved and it is feasible both technically and economically to produce HPC for dam concrete.

斜拉桥施工阶段π型混凝土梁翼缘板裂缝成因分析与防裂措施研究

为了解斜拉桥施工阶段π型混凝土梁翼缘板斜向裂缝成因并制定合理的防裂措施,以某主跨120 m的π型预应力混凝土梁斜拉桥为背景,针对其悬臂施工阶段主梁翼缘板下表面出现斜向裂缝的现象进行分析。采用ANSYS软件建立该桥施工阶段杆系模型与混凝土梁实体模型,分析梁体自重、斜拉索张拉、预应力张拉、混凝土收缩、混凝土水化热作用下主梁翼缘板下表面应力情况。结果表明:梁体自重及斜拉索张拉作用下,翼缘板下表面未出现拉应力;横向及纵向预应力张拉作用下,翼缘板下表面产生一定的拉应力,但未超过混凝土抗拉强度标准值;混凝土收缩作用下,翼缘板下表面产生极小的拉应力,不会引起裂缝;混凝土养护过程中水化热作用下,翼缘板下表面混凝土与周边混凝土存在一定温差,部分测点第一主应力超过混凝土抗拉强度标准值,是开裂的主要原因。针对混凝土水化热作用影响,提出主肋布置冷却水管与翼缘板下方火炉加热并用的防裂措施,建立热流耦合模型分析防裂效果。结果表明:所采用的措施能够改善主梁养护过程中水化热温度场分布,各测点第一主应力均未超过混凝土抗拉强度标准值。

简支变结构连续小箱梁桥负弯矩区UHPC-NC组合桥面板抗裂性研究

针对当前简支变结构连续小箱梁桥负弯矩区钢束易堵孔、运营中桥面开裂病害等问题,提出一种无负弯矩钢束的UHPC-NC组合桥面板结构。以一座3×30 m简支变结构连续小箱梁桥为研究对象,以正常使用极限状态梁体不开裂为控制准则确定UHPC合理构造尺寸,对所提出的负弯矩组合桥面板结构进行1∶2的缩尺模型试验。试验显示:裂缝首先出现于UHPC-NC交界面处的普通混凝土部分,随后逐渐向UHPC层沿伸,且C50混凝土开裂、梁体破坏对应的截面弯矩分别为3 520,9 152 kN·m(考虑1∶8弯矩缩尺比),大于正常使用极限状态、承载能力极限状态梁体截面弯矩3 300,5 838 kN·m,即该组合桥面板结构满足小箱梁的抗裂与承载能力要求。基于试验结果建立精细化有限元模型,采用参数分析法研究UHPC厚度对梁体开裂荷载、极限承载力等方面的影响。结果表明:梁体开裂弯矩主要由UHPC上覆层厚度决定,相较于普通钢筋混凝土梁,5 cm厚的UHPC上覆层可将梁体开裂弯矩提高28.9%,7.5 cm厚的UHPC上覆层可将梁体开裂弯矩提高41.6%;在配筋率不变的情况下,增大UHPC层厚度对梁体承载力无显著提升。综合考虑梁体受力性能以及施工便利性,建议背景工程UHPC厚度取10 cm。

低温季节泵送混凝土结构施工期温控防裂研究

低温季节施工时针对泵闸等结构泵送混凝土防冻与防裂的技术难题,以SYG工程为例,结合工程实际施工过程及现场温控监测成果进行大体积泵送混凝土温控防裂反馈分析;对比分析了不通水工况与实际通水工况下的应力曲线与混凝土容许拉应力曲线,并结合现场温控过程中存在的主要问题探讨了低温季节下泵闸工程的温控防裂技术.结果表明,在-8℃的较低温度下,采取充分的水管冷却和严格的表面保温措施可有效控制结构内部最高温度、内外温差以及最大拉应力水平,减小水闸结构开裂风险.本工程温控实践经验可为类似条件下的泵闸工程提供参考.

高压岔管衬砌混凝土施工期温控防裂研究

高压岔管承受高压水和高速水流冲刷,为了满足这一结构和工作特点,混凝土常采用泵送混凝土,利用其强度高的优点,但其温升高、弹性模量大,且一般是早强混凝土,容易产生温度裂缝。针对这一问题,以阳江抽水蓄能电站高压岔管为例,结合结构和材料特点,借助三维有限单元法,对高压岔管施工期的温度应力进行研究,筛选温控防裂措施。计算结果表明,高压岔管分缝长度对防裂影响显著,同时降低入仓温度,采用内部通水降温,可起到更好的温控防裂效果。高压岔管混凝土在有通水冷却措施条件下,浇筑温度控制在26℃以内,最小安全系数可达1.50以上,可作为工程现场浇筑施工方案。

直线加速器机房超厚大体积混凝土温度裂缝控制技术

直线加速器机房的主屏蔽墙厚度达3.2m,顶板厚度达1.8m,超厚混凝土结构防辐射性能要求高,为控制直线加速器机房大体积混凝土温度裂缝,提出了原材料选取、配合比优化、混凝土浇筑和振捣等混凝土硬化前控制措施,浇筑前在超厚墙体和楼板结构内预先安装了温度监测系统和冷却水循环降温管网,冷却水循环降温管网的水循环阀门与温度监测系统的报警模块通过基站网络进行连接,智能控制循环管网内冷却水流动和冷却水温度。基于实时温度监测结果,采用冷却水智能循环管网系统对硬化后混凝土进行智能化控温,解决了混凝土中心部位温度和内外温差过大问题,有效保证了超厚大体积混凝土防辐射性能要求。

建筑工程大体积混凝土浇筑施工与防裂技术研究

针对大体积混凝土浇筑时间较长,使混凝土出现温变反应,形成混凝土裂缝的问题,研究了建筑工程大体积混凝土浇筑施工与防裂技术这一课题。绑扎建筑工程混凝土结构受力筋,使用钢筋绑扎的形式连接钢筋,并根据建筑工程要求布置钢筋位置、间距、数量,确保混凝土结构的耐久性与安全性。在建筑工程中,大体积混凝土箱梁的分层浇筑通过连续浇筑的方式对角分割箱梁的整个截面来确保混凝土浇筑的质量。养护大体积混凝土浇筑平台结构,用木抹子将混凝土表面抹平,用铁抹子压实打磨,避免混凝土水分迅速流失,出现收缩裂缝。采用实例分析,验证了该技术的防裂效果更佳,能够应用于实际生活中。

地铁车站大体积混凝土裂缝产生原因及解决措施分析

地铁建设近年来流行于各大中城市,地铁车站建设工程大体积混凝土施工比较普遍,在混凝土凝固过程中由于其体积收缩以及各种压力的作用,会造成大量的墙体裂缝;大面积的裂缝会导致建筑渗漏,给地铁车站带来了很大威胁。本文从荷载、位移、温度三个方面分析了地铁车站大体积混凝土结构的开裂成因;根据裂缝的大小、深度、成因等几个角度对裂缝进行了划分;从设计、材料、施工三个角度,对如何防止混凝土开裂进行了探讨。本文研究成果对保障地铁车站大体积混凝土施工质量有一定的参考意义。

隧道钢筋混凝土防开裂施工技术

由于现有的防开裂施工技术混凝土限制膨胀率高、强度低、裂缝现象严重,为此,开展隧道钢筋混凝土防开裂施工技术研究。在隧道开挖前,搭建复拱钢架支护,运用喷射混凝土填塞缝隙。固结注浆初支围岩,形成环向保护壳。隧道开挖后,洞内反向填充,防止坍塌部位变形破坏,并喷射混凝土修复施工面。运用逐榀环形掏槽预留核心土开挖,将填充材料填入裂缝中,提升混凝土衬砌承载能力。在施工过程中,用防水砂浆整平裂缝表面,定期养护。隧道竣工后,对裂缝衬砌断面进行安全性分析和等级判定。测试结果表明,在隧道施工28 d时,混凝土强度为45 MPa,限制膨胀率为0.045%,符合预期施工效果,裂缝现象得到较好缓解。

东南亚地区某碾压混凝土坝裂缝成因及防治措施研究

混凝土裂缝是影响水工结构强度和耐久性的主要因素之一,东南亚地区全年高温多雨,月均最大温差较小(8.6℃),年均温差大(20.2℃),混凝土温度容易控制,但裂缝问题时有发生。依托东南亚地区某碾压混凝土坝,采用有限元研究施工期温度应力的变化规律,分析混凝土开裂的敏感因素,并就其温控防裂措施开展详细研究。结果表明,浇筑长间歇及寒潮侵袭显著影响混凝土温度应力的变化,老混凝土的强约束作用及新老混凝土的温差影响叠加寒潮应力,导致混凝土应力超标出现温度裂缝。在上述研究的基础上,进一步探讨了降低新浇混凝土温度应力的温控措施,为东南亚地区大体积混凝土工程的建设提供一定的参考。

建筑工程中筏板基础大体积混凝土温度裂缝计算及施工技术

该文以某高层建筑为例,探究筏板基础大体积混凝土温度裂缝的计算方法及混凝土施工技术。分别计算各龄期混凝土的收缩变形值、弹性模量、温度应力等参数,然后求解抗裂安全系数。计算结果显示,大体积混凝土各龄期的抗裂安全系数均大于1.0,满足抗裂要求。在大体积混凝土施工中,重点加强物料质量检验与配合比设计,以及混凝土浇筑、养护等环节的施工管理,把握施工技术要点,才能提高筏板基础的施工质量。在混凝土养护结束后进行温度测控,结果表明大体积混凝土内外温差较小,不存在温度裂缝的风险。