Transport von drückendem Wasser in Betonbauteilen

Effect of Water Pressure on Moisture Transport in Concrete Structural Components The effect of water pressure on moisture transport in concrete has been investigated. The uptake of water under pressure at an end surface of concrete cylinders and the release of moisture at the opposite dry surface were measured over a period of 500 days. In addition, ¹H NMR was used to observe directly the penetration of water into mortar prisms. The results show that penetration depth and amount of absorbed water are both limited by the self‐sealing effect in concrete. It is concluded that moisture transport through water‐tight concrete thicker than 200 mm is negligible for water pressures up to 5 bar. Self‐sealing also reduces liquid penetration when concrete is exposed to NaCl solutions under pressure. The penetration of salt solutions is slower than water, less liquid being taken up.     

Feuchtetransport in Bauteilen aus wasserundurchlässigem Beton: Grundlagen und Praxisbetrachtungen

Moisture Transport in Components made of Water‐Tight Concrete Basics and Practical Considerations In water‐tight constructions, the concrete takes charge of a sealing function beside a load bearing function. A skin‐sealing on the surface is not necessary. The property of water‐tightness can be seen herewith as additional serviceability‐property. A very often occurring question is, whether despite the in soil appearing ground‐humidity or the upcoming water and the in concrete existing building moisture, dry interior rooms are achievable. To give answer to the questions, examinations by the help of a building physical calculation programme were carried out. Essential input parameters were calibrated in laboratory tests. A comparison of the inherent material moisture to the removable humidity by ventilation and to the humidity caused by using is given.     

Beschichtungen auf direkt befahrenen Tiefgaragenbodenflächen von Weißen Wannen. Physikalische Beanspruchungen – Planungsgrundlagen – alternative Beschichtungsvarianten

Coatings on directly vehicle‐carrying floor slabs of watertight concrete constructions in underground carparks physical stresses – design codes – alternative coating systems According to DIN 1045‐1 directly vehicle‐carrying park decks have to be realized with additional measures (crack‐bridging coating systems). At least surface protection system 11 (SPS 11) according to the Guidelines for the Protection and Repair of Concrete Components of the German Committee on Reinforced Concrete (DAfStb) are among others a possibility to meet this requirement. On the market available crack‐bridging coating systems with a general technical approval are not usefull on concrete surfaces with high water contents (water saturation values of 90 %) as they may occur in floor slabs of watertight concrete constructions. Experiences with practical damage cases show, that with approved SPS 11‐systems osmotic induced bubbles may occur preferably on backside saturated floor slabs of watertight concrete constructions. In consequence the physical stresses of a coating (osmotic processes, capillarity reactions, hydraulic pressures as well as gas pressures) will be quantitatively estimated and compared with the capability of market systems. Alternative coating systems are presented and practical recommendations in order to avoid damages are given.     

Practical evaluation of relationship between concrete resistivity,water penetration,rapid chloride penetration and compressive strength

There are several factors and test methods for evaluating the durability of concrete. In recent years a great deal of attention has been paid to research and development of relationships of these parameters for production of sustainable concretes: water penetration and Rapid Chloride Penetration Test (RCPT) methods which are most commonly used to evaluate the permeability of concrete are two of the most famous methods specified by BS EN-12390-8:2000 and ASTM C1202 respectively. Concrete surface resistivity (SR) test is also a suitable indicator for concrete penetration and chloride ion permeability. It is a non-destructive, simple, rapid and economical method that can also be used on site.The present study is an exploratory research concerned with the relationship of these methods. Based on the correlation of concrete resistivity with water penetration and Rapid Chloride Penetration Test (RCPT) results, two new models for relating these parameters are presented.     

Ursachen der Blasenbildung bei Reaktionsharzbeschichtungen auf Beton – Welche Rolle spielt die Osmose?

Causes of Blistering of Reaction Resin Coatings on Concrete – Is Osmosis Relevant? Polymeric coatings are nowadays used for many applications. They ensure either the durability of the reinforced concrete construction by protection against migration of aggressive substances e.g. chlorides or they are essential for the use of the building e.g. in the production of semi‐conductors in clean rooms. The phenomenon of blistering of these coatings has been reported for the first time about 35 years ago: Some weeks or months after application usually liquid filled blisters occur within or under the coating. In recent research projects the mechanisms of blistering were mainly described as osmotic transport processes in the contact zone between concrete and base coat. In an ongoing research project at the Institute of Building Materials Research of Aachen University, ibac, funded by the German Research foundation DFG it could be shown that osmotic processes seem not to be involved in the effect of blistering. In fact interactions between the epoxy base coat and the capillary system of the concrete, depending on the composition of the epoxy resin and the capillarity of the concrete, may lead to flaws in the base coat and variances of crosslinking of the epoxy resin. Change of pressure in the partially water filled pore system of the concrete depending on humidity and temperature variation may lead to blistering in the area of these flaws and destruction of the coating.     

Self-curing concrete: Water retention,hydration and moisture transport

Water retention of concrete containing self-curing agents is investigated. Concrete weight loss, and internal relative humidity measurements with time were carried out, in order to evaluate the water retention of self-curing concrete. Non-evaporable water at different ages was measured to evaluate the hydration. Water transport through concrete is evaluated by measuring absorption%, permeable voids%, water sorptivity, and water permeability. The water transport through self-curing concrete is evaluated with age. The effect of the concrete mix proportions on the performance of self-curing concrete were investigated, such as, cement content and w/c ratio.     

Feuchtetransport in 15 cm dicken,liegend hergestellten wasserundurchlässigen Fertigteilen aus Stahlbeton bei drückendem Wasser

Moisture Transport in 15 cm Thick, Horizontally Lying Manufactured, Waterproof Pre‐Cast Reinforced Concrete Construction at Pressuring Water The working model of the “Deutscher Ausschuss für Stahlbeton” (German Commission for Reinforced Concrete) for humidity conditions in a concrete component under a one‐sided loading with pressuring water on pre‐cast reinforced concrete walls, which were manufactured in a lying position, could be broadened in tests. For wall thicknesses of 15 cm, in spite of varying loading with pressuring water over a period of one year, no significantly varying moisture transfer (neither qualitative nor quantitative) could be determined. The low water‐cement ratio of the precasted segments, as well as the manufacturing in lying position, and the densification lead to the assumption that in the tests, a moisture emission was determined only as a result of the diffusion of the initially present excess water.     

预制缝隙式线性排水沟透水水泥混凝土地面施工技术研究

透水水泥混凝土是一种新型多孔轻质混凝土,孔隙率大,透气、透水效果好。预制缝隙式线性排水沟透水水泥混凝土地面渗排水速度快,可避免洪涝灾害发生,符合国家"海绵城市"建设政策,能够改善城市水循环,调节空间温度和湿度,在促进节能减排、建设人与自然和谐发展过程中具有重要作用。     

海底隧道非饱和混凝土中水分渗透研究

引入相对渗透率(饱和程度)kr描述非饱和与饱和状态的区别。基于Darcy定律考虑压力作用的方程,建立混凝土内各位置处压力及渗透深度随时间变化的理论模型。同时自制压力控制装置,研究压力水头下水分在非饱和混凝土中的迁移特性。对各种试验条件下的水分渗透深度进行理论分析,并同时与试验值进行比较。理论值与试验值能很好地吻合。得到渗透深度随时间的增加总是变大,且在后期的增加幅度小于前期。压力对水分渗透深度有促进作用,强度等级与水分渗透深度呈反比,而水灰比则与渗透深度呈正比。各种因素的讨论过程中,理论值与试验值都能很好的吻合。     

Dichten von Rissen in wasserundurchlässigen Bauwerken aus Beton

Sealing Cracks in Water impermeable Concrete Structures Cracks prejudice the serviceability of a water proofed concrete structure. The paper gives an overview of post‐measures of waterproofing in consideration of the current national codes. The filling of cracks under pressure and the applicability of the different injection products are discussed in detail. Consequences for the practice are deducible from this.     

基于湿陷性黄土场地的地下旋流池结构防水性分析

对处于湿陷性黄土场地的地下旋流池结构进行分析,重点分析了结构的防水性能,提出旋流池结构除应满足沉井结构设计要求外,应着重分析旋流池结构的抗渗性、抗裂性和耐久性。由于混凝土结构裂缝的不可避免性,单纯采用抗渗混凝土进行结构自防水,难以阻止压力水的渗透和旋流池的渗漏。通过对旋流池结构的分析,提出旋流池井壁选择大直径钢筋及增加池壁混凝土保护层厚度;采用结构自防水与附加防水层防水相结合的方法进行结构防水。     

XYPEX(赛柏斯)的应用

介绍了XYPEX(赛柏斯)渗透结晶型防水材料的作用机理、性能特点、施工工艺及其在地下、桥梁等工程中的应用。     

高强混凝土的抗渗性试验研究

通过对水灰比分别为0.25、0.30、0.50的混凝土标准养护28d抗压强度和抗渗等级研究,并根据低渗透性混凝土的特点,测量了压力水渗透的深度,利用公式初步估计了混凝土的渗透系数。采用硅灰与高效减水剂双掺的方法,可以制备抗渗透性能极为优异的混凝土。     

Auf Kapillardruckmessung basierende Nachbehandlung von Betonflächen im plastischen Materialzustand

Early Age Concrete Curing Based on Capillary Pressure Measurement Due to evaporation of water at fresh concrete surfaces, a capillary pressure is built up in the pore system of the material leading to shrinkage deformations. At a certain material dependent pressure, air penetrates into the pore system. This air entry appears to be a local event and results in an inhomogeneous strain field and possibly in cracks. By controlling the capillary pressure build‐up the risk of cracking in the early age, i.e. within the first about 6 hours after casting, may be reduced significantly. A method of controlled concrete curing is proposed. It is based on in situ measurements of the capillary pressure. If the latter reaches a previously defined threshold value the concrete surface is rewetted. Thereby, the capillary pressure decreases temporarily, but is not completely relieved. Consequently, the rewetting does not create a continuous water film on the concrete surface which might degrade the near‐surface material properties due to an increased water‐cement ratio.     

水压法评价混凝土渗透性的适用性研究

本文应用透水法政进快速Cl^-渗透法测定了不同强度等级、不同配合比混凝土试件的渗透性。结果表明透水法未考虑实际工程中混凝土所受的约束作用,其适用性对强度等级的依赖性很强。     

非饱和开裂混凝土中水分运移研究

根据双重孔隙介质模型将开裂混凝土视为由完好混凝土和裂缝组成的复合孔隙材料,基于非饱和混凝土的水分运动方程和裂隙渗流的立方定律提出非饱和开裂混凝土中的水分运动方程,同时采用渗水装置对预制裂缝混凝土试块进行渗水试验,研究混凝土初始饱和度、水胶比和裂缝宽度对渗水深度的影响;采用TOUGH 2软件数值分析开裂混凝土中饱和度和水分流速的变化,根据平均流速计算渗水深度并与试验结果比较.研究发现:混凝土初始饱和度越小、裂缝宽度越大,则渗水深度越大,且渗水深度增长先快后慢,反映了混凝土基质势是开裂混凝土中水分运移的驱动因素;裂缝宽度与混凝土渗透性正相关;水分入渗开裂混凝土后流速差和平均流速随时间延长逐渐降低;采用平均流速计算的渗水深度能更好地反映渗水试验中渗水深度的变化趋势.     

Neue Wege der Feuchtemessung und Beurteilung von Estrichen und Betonen

New ways of Measuring and Evaluation of Humidity of Screed and Concrete This article concerns a new method to measure and to value the humidity of screeds/concretes of floor constructions. It is suggested to measure the relative humidity ϕ_ii(x,t) within the pores of the porous material (screed/concrete) instead of the moisture in percentage by weight. In case of steady state conditions both values are connected by the sorption isotherm of the material. A measuring method for ϕ_i(x,t) is available. The valuation shall be done by using boundary values ϕ_zul for the relative humidity within the pores of the material. Some boundary values ϕ_zul are suggested for different constructions.     

Wasser‐ und Salzhaushalt im Gefüge zementgebundener Baustoffe – Modellierung der auftretenden Mechanismen

Water and Salt in the Pore Structure of Cementitious Building Materials – Modelling the mechanisms Moisture and salt penetration can lead to significant damage in reinforced concrete structures. Thus a realistic calculation of moisture and salt distributions in cementitious building materials is essential to estimate the service life of reinforced concrete structures. The main mechanisms and interactions affecting moisture and salt transport in cementitious building materials were observed and described mathematically with the aim of developing a numerical model. As well as the effect of salt on known moisture transport phenomena, the cause of the self‐sealing effect of concrete against penetrating water was investigated using nuclear magnetic resonance tomography (NMR) and gamma ray absorption. Based on the results, a model was developed which describes the capillary transport of moisture and salt in concrete taking the self‐sealing effect into account.     

Elementwände im drückenden Grundwasser. Diskrepanz zwischen Theorie und Praxis?

Double Wall Systems used in Pressing Groundwater Is there a Discrepancy between Theory and Practice? The use of double wall systems in a pressing groundwater requires a special care during design, execution and supervision. It is prerequisite for the functionality of double walls in pressing groundwater that the stringent requirements of the guideline for watertight structures (WU‐Richtlinie – German Committee for Reinforced Concrete) on the planning and execution but also on the production of the double wall panels also are realized in the precast plant. Likewise to water impermeable in‐situ concrete structures, joints and penetrations in water impermeable double wall structures are possible weak points which shall be waterproofed in a professional and durable way. However, a clear discrepancy is frequently to be seen between theory and practice. This article highlights fundamental background information, explains typical faults and gives advice for the avoidance of them.