Übergreifungsstöße von Betonstahl in selbstverdichtendem Beton

Load Carrying Capacity of Lap Splices in Self Consolidating Concrete This paper presents the results of experimental investigations on the load carrying capacity of lap splices under compression and tensile forces in self consolidating concrete (SCC). The test program consisted of four full scale beam tests and three column tests. It was concentrated on two common types of SCC, a powdertype concrete with limestone powder and a combination‐type concrete with fly ash. Depending on the specific lap length l_s/d_s the transmission mechanisms as well as the distribution of the bond‐, steel‐ and concrete stresses within the joint area were examined. The research project was sponsored by the German Association of Structural Concrete (DAfStb – V429).     

Frischbetondruck bei Verwendung von Selbstverdichtendem Beton

Formwork Pressure Asserted by Self‐Compacting‐Concrete On the basis of tests on the friction and deformation behaviour of Self‐Compacting Concrete (SCC) in the fresh state, analytical models to calculate the formwork pressure on vertical formwork were developed. One model, which is based on silo theory and takes into account time dependent material parameters of fresh concrete, as well as a simplified model makes it possible to estimate the fresh concrete pressure during setting. A proposal for the design of formwork, based on semi‐probabilistic safety concept was developed. It was noted that even for SCC, in the design of formwork and scaffolding the load is often less than hydrostatic concrete pressure. The pressure can be best controlled on site by limiting the casting rate.     

Rissmonitoring von Betonoberflächen unter Verwendung digitaler Bildanalyseverfahren

Concrete‐crack monitoring using digital image processing techniques. Cracks in concrete and plaster were analyzed until now by use of a crack width rulers or a measurement lens. The major problems of these methods are subjectivity, low accuracy, less traceability and major difficulties in documentation. The application of digital image processing techniques for in‐situ measurements are promising, especially for gaining higher accuracy and objective documentation. This paper presents a method for the digital assessment of a concrete surface. Already sufficient results were reached even by using a usual digital camera and a standard software.Therefore it is easy to apply in practice. In this paper the general application of crack measurment is shown. For the used mathematical algorithms it is relegated to according references.     

Experimental behaviour of thin-walled hollow structural steel (HSS) columns filled with self-consolidating concrete (SCC)

In modern building construction, thin-walled hollow structural steel (HSS) sections are often filled with concrete to form a composite column. In recent years, the use of self-consolidating concrete (SCC), or self-compacting concrete, in such kinds of columns has been of interest to many structural engineers. Due to its rheological properties, the disadvantage of vibration can be eliminated while still obtaining good consolidation. Apart from reliability and constructability, advantages such as elimination of noise in processing plants, and the reduction of construction time and labor cost can be achieved. It is expected that SCC will be used in concrete-filled HSS columns in the future because of its good performance. However, the composite members are susceptible to the influence of concrete compaction. The lack of information on the behavior of HSS columns filled with SCC indicates a need for further research in this area.The present study is an attempt to study the possibility of using thin-walled HSS columns filled with SCC. New test data on 38 HSS columns filled with SCC to investigate the influence of concrete compaction methods on the member capacities of the composite columns are reported. The specimen tests allowed for the different conditions likely to arise in the manufacture of concrete: cured, well compacted with a poker vibrator, well compacted by hand, and self-consolidating without any vibration. The main parameters varied in the tests are: (1) column section type, circular and square; (2) tube diameter (or depth) to thickness ratio, from 33 to 67; and (3) load eccentricity ratio (e/r), from 0 to 0.3 mm. Comparisons are made with predicted column strengths using the existing codes such as AISC-LRFD-1999, AIJ-1997, BS5400-1979, EC4-1994, DL5085/T-1999 and GJB4142-2000.     

Bond strength of deformed bars in large reinforced concrete members cast with industrial self-consolidating concrete mixture

The bond strength of reinforcing bars embedded in full-scale heavily reinforced concrete sections made with industrial self-consolidating concrete (SCC) was investigated and compared with that of normal concrete (NC). The flowability of SCC mix through the dense reinforcement was visually monitored from a transparent formwork. The bond stress was tested for bars located at three different heights (150 mm, 510 mm, and 870 mm from the bottom of the pullout specimens) and at different tested ages (1, 3, 7, 14, and 28 days). The bond stress-free end slip relationship, the top bar effect and the effect of age on bond stress was investigated in both SCC and NC pullout specimens. Bond stresses predicted based on some major codes were compared with those obtained from experiments. The results indicated that casting SCC was much faster and easier and could be done with less labor effort and no concrete blockage among the heavy reinforcements compared to NC. The results also indicated that the bond stress was slightly higher in the SCC pullout specimen compared to the NC pullout specimen. The difference was more pronounced in the top bars and at 28 days of testing.     

自密实钢管混凝土的研究与应用

采用自密实混凝土作为钢管核心混凝土．针对钢管混凝土的受力特点和施工工艺．进行自密实混凝土材料的选择和配合比优化。为了确保自密实钢管混凝土的顺利施工和硬化后良好的力学、变形性能，进行了自密实钢管混凝土与普通泵速铜管混凝土拱的现场模拟施工对比试验，以及钢管混凝土短柱的轴心受压对比试验。试验结果表明．自密实混凝土作为钢管核心混凝土，其施工性能明显优于普通泵送混凝土。在施工过程中不泌水、不离析。硬化的混凝土能在各截面上均匀分布；自密实钢管混凝土短柱的组合弹性模量、极限承载力和延性以及后期承载能力方面均与普通泵送混凝土短柱相似。在此基础上．成功地将自密实混凝土应用于莆田市一钢管混凝土拱桥工程，应用结果表明，采用自密实混凝土技术，钢管混凝土拱桥施工顺利、快捷。且更好地保证了工程质量，同时混凝土材料造价与普通泵送混凝土基本持平。     

Effect of Grade of Concrete on the Performance of Self-Compacting Concrete Beams Subjected to Elevated Temperatures

Self-compacting concrete (SCC) is a new generation concrete that consolidates without any external effort. Due to its advantages over the conventional concrete, the usage of SCC increases day by day. Understanding the behaviour of SCC is important in the design of structures subjected to elevated temperature. A study was carried out to understand the behaviour of SCC beams of various grades exposed to elevated temperatures under flexural loading. The beams were exposed to a temperature of 900°C. The heated specimens were cooled either by air or water. The research work was carried out for different grades of concrete. It is found from the results that the loss of strength of SCC beams of higher grades was more than that of the lower grade SCC beams. It was also found that the reduction in compressive, tensile and flexural strength of the specimens depends on type of heating and cooling conditions.     

Bond and cracking properties of self-consolidating concrete

The experimental program is aimed at investigating the possible differences between bond and cracking properties of self-consolidating concrete (SCC) and vibrated concrete (VC). Four different mechanical tests were performed: splitting test, direct axial tension test, tension member test and beam test in flexure. Moreover specific additional tests were carried out in order to study the effect of the concrete skin (i.e. the surface layer of concrete which do not have the same mechanical and physical properties as bulk concrete mostly due to the wall effect and the evaporation of water) on cracking.Tension member tests did not show any significant difference between SCC and VC in terms of transfer length irrespective of the compressive strength of the concrete. Then, bond properties of both types of concrete are similar. No significant difference between SCC and VC tensile strength was observed by using the splitting test, the direct axial tension test and the beam test. Results obtained on not sawn tension members have shown that SCC cracking load can be significantly lower (up to 40%) than VC one. This reduction in cracking load can be attributed to a lower quality of the SCC skin. If the concrete skin is removed by sawing the specimens or if the concrete skin proportion in the tension cross-section is low (as in beam tests), the cracking loads and then the tensile strength deduced are similar for SCC or VC. The structural performance of the beams cast with SCC or VC can be considered similar under service loading (deflection) or at ultimate state.     

Messung und Auswertung von Verbundträgerverformungen

Measurement and interpretation of the deflection behaviour of composite beams. Steel concrete composite beams are an economical alternative for wide spanned slender structures in parking lots, office and industrial buildings. To ensure an unrestricted usage of the building the expected deformations, vibrations and cracks are calculated during the analysis of the serviceability stage. In reality major differences between the calculations and the real deflections of beams in particular are observed. Therefore in [1] the deflection behaviour of composite beams was analysed and recommendations were developed to improve the calculation of the deformations. The deflection history was measured continuously during construction in four parking lots built with steel concrete composite beams. One result was that the fabrication of the beams at the manufacturing plant has an influence on the subsequent deflection behaviour of the beam.     

Analytical prediction of transfer length in prestressed self-consolidating concrete girders using pull-out test results

While self-consolidating concrete (SCC) is comparable to conventional concrete (CC) in terms of strength, the comparability of SCC’s bond to steel is less well-defined. A keen understanding of SCC’s bond strength is essential to advance SCC within the prestressed concrete industry. This study presents an analytical method for predicting the transfer length of steel strands in prestressed girders using pull-out test results. The experimental data from a series of 56 pull-out tests is utilized to derive bond stress–slip relationships for 12.7 mm steel strands embedded in SCC and CC. Modification factors are used to correlate pullout bond stresses to transfer bond stresses in prestressed members, and the modified relationships are integrated in three-dimensional finite element models to predict transfer lengths in prestressed SCC girders. The analytical predictions correlate well with experimental results and transfer length requirements of current US design codes.     

Predicting the core compressive strength of self-compacting concrete (SCC) mixtures with mineral additives using artificial neural network

In this study, an artificial neural networks study was carried out to predict the core compressive strength of self-compacting concrete (SCC) mixtures with mineral additives. This study is based on the determination of the variation of core compressive strength, water absorption and unit weight in curtain wall elements. One conventional concrete (vibrated concrete) and six different self-compacting concrete (SCC) mixtures with mineral additives were prepared. SCC mixtures were produced as control concrete (without mineral additives), moreover fly ash and limestone powder were used with two different replacement ratios (15% and 30%) of cement and marble powder was used with 15% replacement ratio of cement. SCC mixtures were compared to conventional concrete according to the variation of compressive strength, water absorption and unit weight. It can be seen from this study, self-compacting concretes consolidated by its own weight homogeneously in the narrow reinforcement construction elements. Experimental results were also obtained by building models according to artificial neural network (ANN) to predict the core compressive strength. ANN model is constructed, trained and tested using these data. The results showed that ANN can be an alternative approach for the predicting the core compressive strength of self-compacting concrete (SCC) mixtures with mineral additives.     

Die Dywidag‐Versuchsschale in Wiesbaden‐Biebrich von 1931

The Dywidag Test Shell in Wiesbaden‐Biebrich from 1931 – A Contribution to the Early History of Reinforced Concrete Shell Construction in Germany In 1931, a photo was taken in Wiesbaden that made history in the field of engineering: A group of employees of the construction company Dyckerhoff & Widmann posed on a reinforced concrete test shell being just a few centimeters thick. To date, this experimental construction is presented as a symbol of the beginnings in concrete shell construction in numerous publications in Germany as well as in other countries. The paper deals with the lesser‐known circumstances of the erection of the test shell as well with its colorful history. The building does not only document the early history of shell construction. It also shows the challenges that may occur when protecting a monument of construction and industrial history that is not usable or economically exploitable.     

自密实混凝土徐变性能试验研究

对28个开放和28个经密封处理的自密实混凝土和普通混凝土试件进行加载徐变试验及同条件对比收缩试验,比较分析自密实混凝土基本徐变和干燥徐变构成特点,并与普通混凝土进行对比。试验结果表明,自密实混凝土干燥徐变所占比例较大;随着水胶比的减小,自密实混凝土徐变度减小;自密实混凝土总徐变度较普通混凝土早期增长较快,且随着龄期增长逐渐减小低于普通混凝土。根据试验结果,建议采用双曲线幂函数形式计算徐变时变曲线,以供自密实混凝土实际工程应用参考。     

Kugelfallrheometer zur Prüfung von Selbstverdichtendem Beton

Falling-Ball Rheometer to prove Self-Compacting Concrete Self-compacting concrete (SCC) is a high-performance concrete whose performance is predicated by the flow characteristics of the fresh concrete mix. In a fresh state, SCC may be viewed as a two-phase suspension containing coarse disperse aggregates as well as a viscous mortar that, when compared to conventional concrete, achieves its specific flow characteristics through a relatively high mortar content. The selection of appropriate raw materials – particularly for manufacture of plastic mortars – are essential factors in determining the rheological properties and thus performance of the concrete. By adding organic or inorganic admixtures, or a combination thereof, one may influence the flow characteristics of the mortar. Mix design for SCC is largely dictated by the rheological properties of the fresh concrete, such that the volumetric design approach, as used for conventional concrete with a given design compressive strength, is no longer applicable. This paper reviews the possibility to optimize the viscosity of mortar by replacing cement by rock powders with the objective to design SCC with normal strength. A research investigation has been conducted, investigating the effect of rock powders on flow characteristics of mortar matrices. Self-compacting concrete requires a careful control of its flow behaviour. Fresh concrete acts as a non-Newtonian fluid. It is insufficient to describe the rheological behaviour of non-Newtonian fluids with a conventional one-point workability test. Rheological measurements are essential, to determine the flow behaviour dependent on the shear rate and to modify the mixture with the aim to achieve self-compacting properties. In order to measure the flow behaviour of SCC, the authors developed a rheometer which can be used simply.     

浅谈自密实高性能混凝土配合比的计算方法

与普通混凝土相比,自密实混凝土配合比计算涉及的因素多,除了要满足强度要求外,对工作性更有很高的要求,因此,自密实混凝土配合比与普通混凝主配合比有很大差别。自密实混凝土至今没有形成统一的设计计算方法。本文对常用的自密实高性能混凝土配合比计算方法作了简单介绍,在对自密实高性能混凝土配合比计算参数如水胶比、浆集比、粗细骨料体积等方面作了一些探讨的基础上,结合固定砂石体积计算法,对全计算法进行了改进。改进后的计算方法更能符合自密实高性能混凝土的特点并且计算简单,使用方便,该方法对自密实混凝土的配制知应用推广有一定的意义。     

A preliminary concrete mix design for SCC with marble powders

The marble has been commonly used as a building material since ancient times. Disposal of the waste materials of the marble industry, consisting of very fine powders, is one of the environmental problems worldwide today. However, these waste materials can be successfully and economically utilized to improve some properties of fresh and hardened self-compacting concrete (SCC).The aim of this study is to find some relationship between properties of the fresh SCC and the hardened SCC containing marble powder. For this purpose, the mix design approach based on monogram developed by Monteiro and co-workers for normal vibrated concrete was adapted to SCC mixes. In order to obtain this monogram, a series of SCC mixes with different water/cement ratios and water/powder ratios were prepared. Several tests such as slump-flow, T₅₀₀ time, L-box, V-funnel and sieve segregation resistance were applied for fresh concrete and tests such as compressive strength and split-tension strength at 7, 28 and 90 days were performed for hardened concrete. In conclusion, the mix design method based on monogram can be suggested for preliminary design in SCC.     

自密实混凝土梁长期变形性能研究

对13根自密实混凝土梁在长期荷载作用下的变形性能进行了试验研究,探讨了早龄期加载时混凝土的固化程度、预加应力以及结构超静定次数对梁的长期变形性能的影响。试验研究和理论分析表明:(1)同组梁实测结果的离散性很小,自密实混凝土品质优良。(2)早龄期加载时混凝土的固化程度、预加应力以及结构超静定次数对梁的长期变形性能有较大的影响。(3)自密实混凝土梁的挠度徐变系数在1.0～1.8之间,在工程中采用自密实混凝土时一般不需要对自密实混凝土的徐变加以特殊考虑。(4)采用修正的MC90徐变和收缩模型及龄期调整有效模量法结合截面分析能较准确地计算自密实混凝土梁的徐变挠度。同时为自密实混凝土工程设计和结构分析提供可靠的试验依据。     

Utilization of Rice Husk Ash as viscosity modifying agent in Self Compacting Concrete

Self Compacting Concrete (SCC) is defined by two primary properties: Deformability and Segregation resistance. Deformability or flowability is the ability of SCC to flow or deform under its own weight (with or without obstructions). Segregation resistance or stability is the ability to remain homogeneous while doing so. High range water reducing admixtures are utilized to develop sufficient deformability. At the same time, segregation resistance is ensured, which is accomplished either by introducing a chemical viscosity modifying admixture (VMA) or by increasing the amount of fines in the concrete. These viscosity modifying admixtures are very expensive and the main cause of increase in the cost of SCC. Therefore, for producing low cost SCC, it is prudent to look at the alternates to help reducing the SSC cost. This research is aimed at evaluating the usage of Rice Husk Ash (RHA) as viscosity modifying agent in SCC, and to study the relative costs of the materials used in SCC.In this research, the main variables are the proportion of RHA, dosage of superplasticizer for flowability and water/binder ratio. The parameters kept constant are the amount of cement, water, fine and coarse aggregate contents.Test results substantiate the feasibility to develop low cost SCC using RHA. In the fresh state of concrete, the different mixes of concrete have slump flow in the range of 595–795 mm, L-box ratio ranging from 0 (stucked) to 1 and flow time ranging from 2.2 to 29.3 s. Out of nine mixes, four mixes were found to satisfy the requirements suggested by European federation of national trade associations representing producers and applicators of specialist building products (EFNARC) guide for making SCC. The compressive strengths developed by the SCC mixes with RHA were comparable to the control concrete. Cost analysis showed that the cost of ingredients of specific SCC mix is 42.47% less than that of control concrete.     

Prediction of compressive strength of SCC and HPC with high volume fly ash using ANN

An artificial neural network (ANN) is presented to predict a 28-day compressive strength of a normal and high strength self compacting concrete (SCC) and high performance concrete (HPC) with high volume fly ash. The ANN is trained by the data available in literature on normal volume fly ash because data on SCC with high volume fly ash is not available in sufficient quantity. Further, while predicting the strength of HPC the same data meant for SCC has been used to train in order to economise on computational effort. The compressive strengths of SCC and HPC as well as slump flow of SCC estimated by the proposed neural network are validated by experimental results.     

自密实混凝土无腹筋梁抗剪性能

为研究自密实混凝土无腹筋梁的抗剪性能和裂缝开展形态,进行了集中荷载作用下12根无腹筋钢筋混凝土简支梁(8根自密实混凝土和4根普通混凝土)的剪切破坏试验,变量为混凝土强度和剪跨比。探讨了《混凝土结构设计规范》(GB 50010―2010)、Zsutty拟合公式、美国规范(ACI318-11)抗剪承载力计算公式对自密实混凝土无腹筋梁抗剪承载力计算的适用性和准确性。收集了在集中荷载作用下的130根自密实混凝土和798根普通混凝土矩形截面无腹筋梁剪切破坏试验数据,将自密实混凝土和普通混凝土无腹筋梁抗剪承载力进行了对比。结果表明:自密实混凝土梁和普通混凝土梁的裂缝发展、破坏形态大致相同,自密实混凝土梁斜裂缝断面更为光滑;Zsutty拟合式计算结果与本文试验结果最接近;GB 50010—2010计算结果与本文试验结果也比较吻合,但偏于不安全;美国规范ACI 318-11计算公式偏差较大;自密实混凝土梁受剪承载力略低于普通混凝土梁。