A comparative study of the mechanical properties,fracture behavior,creep, and shrinkage of chemically based self-consolidating concrete

This study presents the results of an experimental investigation that compares the mechanical properties, fracture behavior, creep, and shrinkage of a chemically-based self-consolidating concrete (SCC) mix with that of a corresponding conventional concrete (CC) mix. The CC and SCC mix designs followed conventional proportioning in terms of aggregate type and content, cement content, air content, water-cementitiuos materials (w/cm) ratio, and workability. Then, using only chemical admixtures, the authors converted the CC mix to an SCC mix with all of the necessary passing, filling, flowability, and stability requirements typically found in SCC. The high fluidity was achieved with a polycarboxylate-based high-range water-reducing admixture, while the enhanced stability was accomplished with an organic, polymer-based viscosity-modifying admixture. The comparison indicated that the SCC and CC mixes had virtually identical tensile splitting strengths, flexural strengths, creep, and shrinkage. However, the SCC mix showed higher compressive strengths and fracture energies than the corresponding CC mix.     

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.     

Evaluation of strand bond equations for prestressed members cast with self-consolidating concrete

A total of 26 rectangular concrete beams were constructed, instrumented, and tested over the course of several research projects which all focused on examining the bond of prestressed strand with self-consolidating concrete (SCC). The same concrete cross-section was used for all specimens, but SCC using Type I and Type III cements and a conventional high strength concrete mixture were tested using a 0.6 in. (15.2 mm) prestressed strand and a lightweight SCC was used along with a 0.5 in. (12.7 mm) prestressed strand. Transfer length was measured using concrete surface strains and development length was determined using iterative flexural tests. The results of these tests were then compared to the transfer and development length equations proposed from nine different research projects conducted using several different sets of variables. Since the concrete types used in this research were different from those utilized to develop the current code equations, it was desired to examine whether other proposed equations were more applicable. While the different variants of SCC examined using these specimens were also very different from those used to develop all of the examined transfer and development length equations, several of these equations were found to be adequate for use with SCC.     

有机硅烷与透水衬里模板对提高混凝土表层渗透性试验研究

有机硅烷与透水衬里模板(CPF)都是通过降低混凝土表层渗透性而提高混凝土耐久性的技术,通过空气渗透性试验与表层水吸附试验(ISAT)分别研究了有机硅烷、透水衬里模板单独使用时,以及有机硅烷与透水衬里模板共同使用时对混凝土表面渗透性的影响,试验表明有机硅烷能有效降低普通混凝土表层水吸附作用但对空气渗透性没有明显影响,透水衬里模板对普通混凝土表层的空气渗透性与水吸附作用都有明显降低作用,有机硅烷和透水衬里模板同时使用能进一步提高混凝土表层上的抗渗透性.     

透水模板改善混凝土性能试验

对比分析了2种透水模板(CPF)的主要物理性能;结合宏观、微观试验,探讨了透水模板改善混凝土性能的机理与效果.结果表明:透水模板能有效降低混凝土浇注时的表面水灰比,提高混凝土的表面密实度,改善混凝土的孔隙分布和表观质量,提高混凝土抗渗性和耐久性.     

Evaluation of concrete mixes and mineral additions when used with controlled permeable formwork (CPF)

The influence of concrete mixes and commonly used mineral additions and their effects on the near surface performance of vertically cast concrete against controlled permeable formwork (CPF) are the focus of this study. Three grades of concrete (C25, C30 and C45) and mineral additives including GGBS and PFA have been tested for surface performance in situ with CPF. The various loadings were chosen to represent the minimum and maximum levels seen in standard industry practice. The range of tests used to characterise the near surface performance include subjective assessment of surface quality, surface hardness and surface tensile strength. Permeability studies of the liners after casting indicate that no excessive embedding of fine particles occurred irrespective of constituents used. Surface quality was dramatically improved in each case and changes to surface colour through densification were quantified. Near surface performance studies indicated a significant improvement for all systems studied.     

基于现场条件下混凝土空气渗透性检测CLAM test法和Sch(o)nlin法的应用研究

透水衬里模板(CPF)通过其滤层排除新拌混凝土表层水分和因振捣而富集于混凝土表层的气体来提高混凝土表层强度和抗渗透性。通过混凝土表层水吸附试验(ISAT)评价了透水衬里模板对混凝土抗渗透性的提高作用,并利用文献提供的混凝土表层水吸附试验(ISAT)与压汞法(MIP)之间的关系式分析了采用透水衬里模板后混凝土表层孔结构参数的变化。在对比分析用压力试验机获得的混凝土整体抗压强度与回弹法得到的表层抗压强度后,可以发现透水衬里模板可以提高混凝土的表层抗压强度而不是混凝土的整体抗压强度。     

透水模板布对海工混凝土性能影响研究

研究了国产透水模板布与进口透水模板布在重复使用过程中对海工混凝土外观质量、表面强度、抗压强度和抗渗透性能的影响.研究表明:透水模板布随使用次数的增多,混凝土的外观质量、表面强度、抗压强度和抗渗透性能会有不同程度的降低.国产QS透水模板布在前两次使用时性能与两种进口透水模板布相当,部分性能优于进口产品,但第3次使用时效果不如丹麦透水模板布.     

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.     

Self compactability of high volume hybrid fiber reinforced concrete

Self compacting concrete (SCC) offers several economical and technical benefits; the use of fibers extends its possibilities. SCC is a relatively new type of concrete with high flowability and cohesiveness when compared to conventional concrete. In this article carbon and steel fibers were used in combination, and the effects of fiber inclusion on the compactability of hybrid fiber reinforced concrete are studied. The effects of fibers are quantified based on the fiber volume and type of the fibers. It was concluded that in addition to the above-mentioned quantifiable properties, other properties of fibers such as strain sensing, shape, and surface roughness are also found to be important but they cannot be quantified at this stage.     

Oberflächenbearbeitung von Industriebetonböden bei Verwendung von SVB mit und ohne Fasern

Surface processing of industrial Concrete Floors made of SCC with and without Fibres. Self‐compacting concrete (SCC) is one the most important innovations in materials technology. However, from the point of producers and processors problems can be identified for certain application cases, e.g. for industrial concrete floors. In particular for surface processing and evenness requirements difficulties may occur. The following report summarises practical tests related to this topic and shows that SCC is indeed an alternative compared to conventional construction methods.     

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。     

An Investigation into the critical factors affecting the performance of composite controlled permeable formwork liners: Part I – Drainage medium

The critical elements associated with a CPF drainage medium and their associated effects on the near surface performance of vertically cast concrete slabs are the focus of this study. A range of board absorption levels, textured features and texture depth are investigated using a Taguchi orthogonal array approach. A permeable polypropylene filter layer was used in conjunction with the various drainage mediums. Statistical software was utilised to determine significant variables as a function of the near surface performance. The range of tests used to characterise the surface performance of the various drainage mediums include surface roughness, surface hardness, surface tensile strength and water absorption. Results are compared to a control sample which was cast against impermeable plywood formwork. All drainage medium permutations showed similar evidence of water/cement ratio reduction at the near surface region of the concrete slab. Surface quality was analysed using quantitative methods and showed significant improvements for all systems over the control. The results for the systems studied indicate that the features of a drainage medium are not critical to the functionality of a CPF liner to reduce the near surface w/c ratio. In fact, it is indicated that the absence of a drainage medium has the same enhancement in near surface concrete slab properties as that of a complex structure when compared to the control sample.     

聚羧酸系高效减水剂的近期研究进展

聚羧酸系高效减水剂(PC)越来越广泛的应用于混凝土中,特别是自密实混凝土(SCC)。与木质素磺酸盐、密胺或者萘系减水剂相比,尽管聚羧酸系高效减水剂在一些方面有显著优点,比如,高减水率、水泥颗粒分散性好、掺量低、对水泥成分的敏感性小、保坍好而不延长混凝土的凝结硬化时间等。但传统的聚羧酸系高效减水剂在许多情况下还是难以满足要求,特别是对于自密实混凝土。而通过改变聚羧酸分子中主链、枝链和羧基的化学结构,可以实现保坍、凝结控制、减缩等多种功能。满足高性能自密实混凝-土的设计和施工的需要。本文综述了近期发展的一些新型聚羧酸系高效减水剂。     

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.     

Production of low cost self compacting concrete using bagasse ash

Self compacting concrete (SCC) is a development of conventional concrete, in which the use of vibrator for compaction is no more required. This property of self compacting concrete has made its use more attractive all over the world. But its initial higher supply cost over conventional concrete, has hindered its application to general construction. 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 bagasse ash 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 bagasse ash, dosage of superplasticizer for flowability and water/binder ratio. The parameters kept constant are the amount of cement and water content.Test results substantiate the feasibility to develop low cost self compacting concrete using bagasse ash. In the fresh state of concrete, the different mixes of concrete have slump flow in the range of 333 mm to 815 mm, L-box ratio ranging from 0 to 1 and flow time ranging from 1.8 s to no flow (stucked). Out of twenty five different mixes, five 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 self compacting concrete. The compressive strengths developed by the self compacting concrete mixes with bagasse ash at 28 days were comparable to the control concrete. Cost analysis showed that the cost of ingredients of specific self compacting concrete mix is 35.63% less than that of control concrete, both having compressive strength above 34 MPa.     

Influence of limestone filler and viscosity-modifying admixture on the porous structure of self-compacting concrete

The objective of this experimental work is to study porosity in self-compacting concrete (SCC) made without adding limestone filler, comparing the results with other SCC and with normally-vibrated concrete (NVC). Several types of concrete were made, keeping the w/c ratio constant. The results show that the air content in SCC depends on the flowability and viscosity of the material, putting a forward an expression to estimate the air content in accordance with these two parameters. SCC shows a finer and more tortuous porous structure than NVC, leading to lower permeability to water under pressure. Nevertheless, in the absence of pressure, when water penetrates by capillary action, the results obtained from the different types of concrete were very similar, with differences below 3.5%. This is due to the fact that the content of pores over 0.5 μm is practically the same in SCC and NVC, but for smaller pore sizes, which are therefore only accessed when water under pressure is applied, the differences in porosity between the different samples is more pronounced. On the other hand, it was observed that the use of more fluid mixtures permitted more impermeable concrete to be obtained. The use of viscosity-modifying admixture on SCC as a replacement for limestone filler does not affect the total volume of pores, but generates a slightly more coarse porous microstructure, thereby leading to concretes in which water penetration depth under pressure is a little higher (around 4 mm).     

电渗结合透水模板成型混凝土表观质量试验

基于电渗均匀快速的排水特性,建立了电渗滤水试验模型,阐述电压加载初始时点、电压值、电渗历时及电极间距对混凝土成型效果的影响,并研究了结合透水模板垫层来改善电渗混凝土成型外观的方法.结果表明:电渗结合透水模板工艺排水可形成致密无孔洞混凝土表面,显著降低混凝土渗水透气性能,且可提高混凝土表面强度.     

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.