Time-dependent rheological characteristics of self-consolidating concrete containing various mineral admixtures

The study herein was intended to evaluate the influence of elapsing time on rheological properties and thixotropy of self-consolidating concrete (SCC) mixtures containing various mineral admixtures. For this purpose, variation of T50 flow time, torque plastic viscosity, apparent yield stress and thixotropy were investigated as a function of time in a standstill condition. Various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary and quaternary cementitious blends in 17 different SCC mixtures having a constant slump flow value. The results showed that SCC mixtures containing various mineral admixtures were highly stable or moderately stable (VSI between 0 and 1) at 0 min according to ASTM C 1611. However, mixtures containing FAC, FAF and BFS exhibited some bleeding and segregation at 50 min. In a standstill condition, apparent yield stress and thixotropy increased significantly with time while torque plastic viscosity values changed only in a limited range. In addition, with elapsing time, MK and FAC were found to have more influence on torque plastic viscosity and yield stress values in comparison with the other admixtures. However, increase in the yield values were more pronounced in comparison with the torque plastic viscosity values. Increase in thixotropy with time for the SF and MK blended mixtures were higher when compared to the control mixtures and mixtures containing the other mineral admixtures

765 kV Transmission Line Design (Electrical Section)

Nowadays, due to the ever increasing energy consumption and power supply optimization, it is required to construct new power plants, substations and transmission lines. In Iran, also, because of increasing demand for electrical energy, for a significant power loss reduction in power transmission over long distances, and to construct high transmission lines that lead to reduction in the economic costs of transmission lines, the transmission lines must be considered at extra high voltage (EHV) levels. These EHV levels should be compared with the low voltage levels in order to extract the benefits. Therefore, in this paper, a review has been conducted on the types of 765 kV transmission lines used in different countries and a comparison between them and the low voltage levels have been performed. Accordingly, the advantages of EHV transmission lines are summarized. Finally, designing a line of 765 kV single-circuit with 6 conductors per bundle based on existing standards is presented.DOI:http://dx.doi.org/10.11591/ijece.v2i5.159

Mineral katkıların kendiliğinden yerleşen betonun reolojik, tiksotropik ve geçirimlilik özeliklerine etkisi

Mevcut çalışmada odaklanan konu, silis dumanı (SD), uçucu kül (UK), metakaolin (MK) ve granüle yüksek fırın cürufu (GYFC) içeren KYB karışımların reolojik ve geçirimlilik özeliklerininin araştırmasıdır. Çimento ile birlikte bu bağlayıcı malzemelerle elde edilen ikili, üçlü ve dörtlü bağlayıcıların süper akışkanlaştırıcı katkı gereksinimi, taze hal özelikleri, basınç dayanımı ve geçirimlilik özelikleri ile reolojik ve tiksotropik davranışları araştırılmıştır. Üç farklı S/B oranı ve sabit yayılma çapına sahip 57 KYB karışımı tasarlanmıştır. Reolojik parametreler eş eksenli silindir tipli bir reometre ile ölçülmüştür. Sonuçlara göre SD ve GYFC içeren karışımların tork plastik viskozite ve V-hunisi akış süreleri kontrol karışımına göre azalmıştır. Ancak, çimentoyla birlikte MK, C sınıfı UK (CUK) ve F sınıfı UK (FUK) içeren karışımlarda ters bir davranış görülmüştür. Sabit bir yayılma çapında çimento yerine SD, MK ve CUK ikamesiyle elde edilen karışımların süper akışkanlaştırıcı gereksinimleri artmıştır. Bir başka değişle, GYFC içeren karışımlar dışında diğer bağlayıcı malzemelerin KYB karışımında kullanımları, tiksotropi değerlerini kontrol karışımına göre artırmıştır. %8SD %18CUK ve %18GYFC içeren dörtlü bağlayıcılı karışımların, plastik viskozite ve tiksotropi değerleri kontrol karışımına göre azaltmıştır. Buna ilaveten, ikili bağlayıcılı sistemlere GYFC eklenmesiyle oluşan üçlü sistemlerin tork plastik viskozite ve tiksotropi değerleri kayda değer biçimde azalmıştır. S/B oranından bağımsız olarak "yapısal çökme alanı" ve "görünen viskozite düşüşü" yöntemlerinden elde edilen tiksotropi değerlerinin arasında iyi bir ilişki elde edilmiştir. Bunlara ilaveten mineral katkıların KYB'de kullanımı, karışımların basınç dayanımları ve geçirimlilik özeliklerini iyileştirmiştir. Ancak, iyileşme için gereken zaman mineral katkının türüne göre farklılık göstermektedir

Evaluation of three test methods for determining the alkali-silica reactivity of glass aggregate

WOS: 000319086400007Consumption of natural raw materials and pollution have become significant problems due to technological developments and continual increase in demand. Accordingly, great efforts are being made in order to recover wastes including glass. One of the possible applications is utilizing waste glass in concrete; however, alkali-silica reaction (ASR) is of major concern. In this study, tests were conducted by applying three different procedures: ASTM C1293, RILEM AAR-2, and microbar test methods. In microbar testing, glass aggregate was used as coarse aggregate, whereas the other two methods dealt with investigating the reactivity of the finer fraction of the waste glass. The effects of chemical composition, particle size and amount of glass in the mixture were studied. According to the results, flint glass expanded to a greater extent than amber and green glass. Expansions, within the specified time periods dictated by the methods, remained low; however, extended durations resulted in very high length change values of the flint glass-including mixtures, particularly in the MR-2 and microbar tests. (C) 2013 Elsevier Ltd. All rights reserved

Time-dependent rheological characteristics of self-consolidating concrete containing various mineral admixtures

The study herein was intended to evaluate the influence of elapsing time on rheological properties and thixotropy of self-consolidating concrete (SCC) mixtures containing various mineral admixtures. For this purpose, variation of T50 flow time, torque plastic viscosity, apparent yield stress and thixotropy were investigated as a function of time in a standstill condition. Various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary and quaternary cementitious blends in 17 different SCC mixtures having a constant slump flow value. The results showed that SCC mixtures containing various mineral admixtures were highly stable or moderately stable (VSI between 0 and 1) at 0 min according to ASTM C 1611. However, mixtures containing FAC, FAF and BFS exhibited some bleeding and segregation at 50 min. In a standstill condition, apparent yield stress and thixotropy increased significantly with time while torque plastic viscosity values changed only in a limited range. In addition, with elapsing time, MK and FAC were found to have more influence on torque plastic viscosity and yield stress values in comparison with the other admixtures. However, increase in the yield values were more pronounced in comparison with the torque plastic viscosity values. Increase in thixotropy with time for the SF and MK blended mixtures were higher when compared to the control mixtures and mixtures containing the other mineral admixtures. © 2015 Elsevier Ltd

Thixotropy and structural breakdown properties of self consolidating concrete containing various supplementary cementitious materials

WOS: 000353737600004In this study, thixotropy and structural breakdown of 57 self-consolidating concrete (SCC) mixtures containing various supplementary cementitious materials (SCM) were investigated by different approaches. The effects of SCM type and content on high range water reducer demand and plastic viscosity were also studied. For these purposes, various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary, and quaternary cementitious blends in three water/binder (w/b) ratios. Results showed that except BFS, use of SCM in SCC mixtures increased thixotropy values in comparison with the mixtures containing only portland cement (PC). Good correlations were established between structural breakdown area and drop in apparent viscosity values for all w/b ratios. The different methods used to evaluate the thixotropy and structural breakdown got more consistent with each other as w/b decreased. (C) 2015 Elsevier Ltd. All rights reserved.TUBITAK (The Scientific and Technological Research Council of Turkey)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [112M581]This paper is a part of a more extensive study supported by TUBITAK (The Scientific and Technological Research Council of Turkey) under the grant of 112M581. The authors would like to acknowledge this support

Effect of various supplementary cementitious materials on rheological properties of self-consolidating concrete

WOS: 000348255700012In design of self-consolidating concrete (SCC) for a given application, the mixture's rheological parameters should be adjusted to achieve a given profile of yield stress and plastic viscosity. Supplementary cementitious materials (SCM) can be useful for this adjustment in addition to their other advantages. In this study, the rheological properties of 57 SCC mixtures with various SCM were investigated for a constant slump flow value. For this aim, various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary, and quaternary cementitious blends in three water/binder ratios. Results showed that SF and BFS decreased plastic viscosity and V-funnel time values in comparison with mixtures containing only Portland cement (PC). However the opposite tendency was observed when MK, FAC and FAF were incorporated with PC. Substitution of PC with SF, MK and FAC increased high range water reducer (HRWR) demand in the SCC mixtures having constant slump flow. Use of SCM in SCC mixtures increased yield stress values. Good correlations were established between plastic viscosity and V-funnel flow time values for all w/b ratios. (C) 2014 Elsevier Ltd. All rights reserved.TUBITAK (The Scientific and Technological Research Council of Turkey)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [112M581]This paper is a part of a more extensive study supported by TUBITAK (The Scientific and Technological Research Council of Turkey) under the grant of 112M581. The authors would like to acknowledge this support

Permeability properties of self-consolidating concrete containing various supplementary cementitious materials

WOS: 000350927200038In this study, permeability properties of 17 self-consolidating concrete (SCC) mixtures containing various supplementary cementitious materials (SCM) were investigated by different experimental approaches. The effects of SCM type and content on the compressive strength, rapid chloride ion permeability (RCPT), water penetration depth, water absorption and sorptivity were studied. For these purposes, various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary, and quaternary cementitious blends. Results showed that partial replacement of PC by SCM increased the compressive strength of control mixtures at 28 and 90 days (except for FAF at 28 days). Mixtures containing MK presented a better performance compared to other SCM at 7 days. The utilization of SCM reduced the RCPT results of almost all mixtures compared to the control mixtures and the reduction was more significant with an increase in the SCM content. All of the mixtures containing SCM had lower penetration depths when compared to reference mixtures at 28 and 90 days. Good correlations were established between the percentage of permeable voids and water absorption. Moreover, there was an inverse but almost linear relationship between permeable voids content and compressive strength of the mixtures. (C) 2015 Elsevier Ltd. All rights reserved.TUBITAK (The Scientific and Technological Research Council of Turkey)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [112M581]This paper is a part of a more extensive study supported by TUBITAK (The Scientific and Technological Research Council of Turkey) under the Grant of 112M581. The authors would like to acknowledge this support

Influence of thixotropy determined by different test methods on formwork pressure of self-consolidating concrete

In this experimental study, the influence of thixotropy determined by different test methods on the formwork pressure of self-consolidating concrete (SCC) with varying compositions was investigated. In order to determine the effect of water/binder (w/b) ratio, slump flow diameter and coarse aggregate/total aggregate (CA/TA) ratio on thixotropy and formwork pressure of SCC, fifteen concrete mixtures were prepared. Four different test methods i.e., “structural break-down area” (SBDA), “break-down percentage” (BDP), “drop in apparent viscosity” (DAV) and “yield value at rest” (YVR) were performed to determine the thixotropy of the SCC mixtures. Test results showed that the SBDA, DAV and YVR methods were more appropriate to evaluate the thixotropy of SCC than the BDP method. A strong correlation between thixotropy and formwork pressure was found using SBDA, DAV and YVR methods in SCC mixtures having low w/b ratio. There was a strong relationship between thixotropy determined by SBDA, BDP and DAV methods and formwork pressure in low slump flow SCC mixtures, while thixotropy determined by the YVR method showed good correlation with the formwork pressure in SCC mixtures having high slump flow values. Finally, new models were developed to estimate the formwork pressure of all kinds of mixtures as a function of thixotropy and time. The models were found to be successful for each of the thixotropy measurement method.TUBITAK (MAG 109M615