Now showing 1 - 10 of 174
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    Self-centering of shape memory alloy fiber reinforced cement mortar members subjected to strong cyclic loading
    (01-04-2013)
    Shajil, N.
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    Srinivasan, S. M.
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    In addition to ductility of the reinforced concrete, it is desirable to have large recoverable deformations (self-centering ability) under strong cyclic loading conditions. Since steel reinforcement cannot regain its shape beyond yielding, the performance deteriorates enormously when subjected to a strong cyclic load. An alternative reinforcement material such as shape memory alloy (SMA) could offer scope for self-centering, thus improving performance especially after a severe loading has occurred. In this study, the load-deformation characteristics of SMA fiber reinforced cement mortar beams under cyclic loading were investigated to assess the self-centering mechanism. The study involves experiments on a beam structure and related analysis for the prediction of self-centering. Apart from the energy dissipation through its ductility, it is shown in this study that shape memory alloy reinforced cement mortar has very good self-centering properties that may be crucial in bringing back the functionality of a structure and prevention of permanent secondary deformations that may lead to catastrophic failure in some structures. © 2012 RILEM.
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    Performance evaluation of sugarcane bagasse ash blended cement in concrete
    (01-05-2015)
    Bahurudeen, A.
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    Kanraj, Deepak
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    Gokul Dev, V.
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    By-products from a number of industrial processes are used as alternative supplementary cementitious materials in concrete. Sugarcane bagasse ash is mainly composed of amorphous silica and can be used as a pozzolanic material in concrete. Production of sugarcane bagasse ash (SCBA) based blended cements with different replacement levels of SCBA, and the performance of concrete with these cements in terms of compressive strength, heat of hydration, drying shrinkage and durability are discussed in this paper. Durability performance was investigated by five different methods in this study, namely oxygen permeability test, rapid chloride penetration test, chloride conductivity test, water sorptivity test, DIN water permeability test and Torrent air permeability test. The results from this study show that use of sugarcane bagasse ash in concrete prominently enhances its performance. Low heat of hydration, additional strength gain due to pozzolanic reaction, significant reduction in permeability because of pore refinement and similar drying shrinkage behavior were observed for bagasse ash blended concrete compared to control concrete.
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    Editorial
    (01-10-2015)
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    Limestone-Calcined Clay (LC2) as a supplementary cementitious material for concrete
    (04-07-2023)
    Basavaraj, Anusha S.
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    Muni, Hareesh
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    Dhandapani, Yuvaraj
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    In this work, limestone‐calcined clay (LC2) is studied as an alternative supplementary cementitious material (SCM), combining two widely available resources – calcinated kaolinitic clay and limestone, to partially substitute portland clinker. The primary goal is to assess the potential of LC2 to produce moderate to high strength concretes with design compressive strengths of 20 to 50 MPa. For this purpose, 27 mixes with LC2 were prepared with a range of binder contents and water‐binder ratios, and the performance was benchmarked against those of mixes having fly ash (PFA). In addition to the quantification of strength and concrete resistivity, life cycle assessment was performed for the concretes considering a typical situation in India. The efficiency of concretes made with LC2, PFA and ordinary portland cement (OPC) was analyzed using the energy intensity index (eics) and apathy index (A-index) as sustainability indicators. This framework establishes the sustainability potential of the LC2 with insights on the influence of strength on the indicators. It is concluded that the LC2 concretes with 45% replacement level, w/b≤0.45 and binder content lower than 400 kg/m3 possess the highest sustainability potential, among the concretes studied here.
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    Durability characteristics of high early strength concrete
    (01-01-2017)
    Chokkalingam, Ramesh Babu
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    High early strength concrete (HESC) is a type of high performance concrete, which attains its specified strength earlier than normal concrete. This type of concrete is normally used in precast and prestressed concrete industries. Many studies have been performed on the production of high early strength concrete, but information on performance of high early strength concrete in durability tests is limited. This article deals with evaluation of durability index characteristics of high early strength concrete mixtures made with two different cements. Durability index tests such as oxygen permeability, sorptivity, rapid chloride permeability and water absorption tests were performed on three HESC mixtures made with two different cements and compared with a reference concrete. Our results reveal that high early strength concrete using steam curing is better than concrete produced using accelerator. The microstructural studies also revealed that steam-cured concrete is better than accelerator-cured concrete supporting the durability index properties of concretes tested.
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    A STUDY ON PERFORMANCE OF CLAY BASED GEOPOLYMERS AT ELEVATED TEMPERATURES
    (01-05-2022)
    Manohar, Swathy
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    Haneefa, K. Mohammed
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    Rathnarajan, Sundar
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    This study investigates performance of clay based geopolymers at elevated temperatures and compares with the conventional geopolymer systems. Class F fly ash, calcined clay, metakaolin, and combination of fly ash-calcined clay are used as binders in various geopolymer mixes. The geopolymer specimens are exposed at 300, 600, and 900°C to evaluate the changes in physical, mechanical and microstructural characteristics which can be corroborated to their performance. Visual observations and mass loss variations showed that metakaolin specimens possessed the most intensive and branched cracking, even at 300°C exposure. Results of compressive strength test and thermogravimetric analysis (TGA) showed that fly ash and fly ash-calcined clay (FACC) mixes perform better than the other two mixes in long temperature range, especially when temperatures cross 120°C. Also, broader humps in the X-ray diffractograms of the FACC samples indicates a high degree of geopolymerisation. Thus, the paper supports the usage of the largely available clays in India after calcination and advocates the suitability of calcined clay for producing geopolymers to be used at elevated temperatures.
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    Performance evaluation of sodium resistant mortars as sacrificial layer in fast breeder reactors
    (01-01-2012)
    Haneefa, K. Mohammed
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    In fast breeder nuclear reactors, sodium is used as a coolant. Accidental spillage of sodium at 550°C and above can cause damage to the structural concrete. For this reason, a sacrificial layer of limestone aggregate concrete is provided over the conventional siliceous aggregate concrete. In spite of extensive understanding of the chemistry of interactions, limited information is available on the microstructural description of deterioration, including creation of mineralogical polymorphs and growth of microcracks. To study and improve the performance of the sacrificial layer in the presence of hot liquid sodium, a research project is taken up at llT Madras. This paper presents overview of the state of the art, research needs and motivations supplemented by results and analysis of first phase of work performed at IIT Madras, which includes thermal performance evaluation of limestone mortars. This study will be followed by an evaluation of sodium attacked mortars.
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    Influence of different processing methods on the pozzolanic performance of sugarcane bagasse ash
    (01-01-2015)
    Bahurudeen, A.
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    Sugarcane bagasse ash is obtained as a by-product from cogeneration combustion boilers in sugar industries. Previous studies have reported that the use of sugarcane bagasse ash as supplementary cementitious material in the concrete can improve its properties. The utilization of bagasse ash has been constrained because of inadequate understanding of the material and lack of suitable processing methodology for use in a large scale. Processing methods significantly influence the pozzolanic activity of any supplementary cementitious material. Proper assessment of pozzolanic activity and processing methodology of bagasse ash were not investigated in earlier research studies. This paper describes a study that involves pozzolanic performance evaluation and microstructural characterization of sugarcane bagasse ash for use as pozzolanic material in concrete. A comprehensive evaluation of pozzolanic activity of sugarcane bagasse ash based on different processing methods including burning, grinding, complete removal of coarse fibrous particles by sieving and combinations of these methods were examined in this study. Suitable processing methodology to attain maximum pozzolanic activity of sugarcane bagasse ash with minimum level of processing is described in this paper.
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    A study of deterioration of cement paste due to acid attack using X-ray computed micro-tomography
    (01-03-2018)
    Ramaswamy, Koodalloor P.
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    Cementitious materials are highly vulnerable to rapid and serious deterioration in aggressive acidic environments. The aim of this paper is to understand the microstructure deterioration of cement paste due to acid attack using the non-destructive technique called X-ray computed micro-tomography (micro-CT). To investigate this deterioration, an accelerated static immersion based leaching test with periodic abrasive action was performed on cement paste specimens of size 10 × 10 × 60 mm, prepared using ordinary Portland cement with a water-to-cement ratio of 0·40. After 28 d of initial curing in saturated lime water, specimens were exposed to 1% sulfuric, 1% hydrochloric, 0·5 M acetic and 0·5 M citric acid solutions for a maximum period of 6 weeks. X-ray micro-CT was used for imaging the deteriorated specimens to investigate the changes in microstructure. Various parameters related to degradation were also deduced based on the image analysis performed on the CT images in order to evaluate the performance of the cement paste in various acid solutions. Parameters such as altered depth/area could be considered as primary indicators of attack, which can be best captured and analysed using X-ray CT.
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    Investigation of sulphate attack on limestone-calcined clay cement mortars
    (01-01-2015)
    Suma, Fathima
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    Calcined clay, especially in combination with limestone powder, is emerging as an excellent supplementary cementitious material. While a number of studies have reported on the pozzolanic performance of calcined clay blended cements, a detailed investigation on the durability characteristics is not available in the existing literature. In this context, the resistance of calcined clay blended cements against sulphate attack needs to be comprehensively studied to understand its potential for use in sulphate rich environments. This paper reports an experimental investigation on cementitious mortars that are subjected to (i) continuous immersion and (ii) alternate wetting and drying, in highly concentrated sodium sulphate solutions, with a methodology based loosely on ASTM C1012. The length change and flexural strengths are monitored periodically to get an assessment of the degree of damage. The cementitious systems considered in the study are: (i) OPC, (ii) OPC with 30% fly ash, and (iii) Limestone calcined clay cement (LC3). The alterations in microstructure are studied using X-ray diffraction and thermal analysis. The work reported in this paper is part of a larger project that investigates the potential for limestone—calcined clay based cementitious binders in concrete.