Sintered Fly Ash Aggregate Research Articles

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English

Physical characteristics of sintered fly ash aggregate containing clay binders

A comprehensive research has been conducted to explore the influence of sintering on the properties of fly ash aggregate containing clay binders (bentonite and kaolinite). Fly ash aggregate containing clay binders, have been subjected to various sintering temperatures at different durations of 700–1400 °C and 15–120 min, respectively. The variation in aggregate properties, viz strength, water absorption, density and shrinkage during sintering, have been determined and discussed. In addition to these, the uniformity of sintering and rate of water absorption of sintered aggregate were also determined. No significant changes in aggregate properties were observed for aggregate sintered up to 900 °C, due to the insufficient sintering temperature range. However, the aggregate properties substantially enhanced for temperature above 1000 °C, which is attributed to the activation of liquid phase sintering. For temperatures between 1000 and 1300 °C, the aggregate with bentonite shows significant increase in shrinkage (30 %), density (density ratio 0.70), higher ten percent fines value (TPFV) (6.13 tonne), reduction in porosity (35 %), and water absorption of 4 %. However, at 1400 °C, the aggregate properties degraded due to the decomposition of mineral phases in bentonite. For aggregates with kaolinite, highest TPFV of 8.5 tonne with lowest water absorption of 2 % have been observed at 1400 °C. The presence of a higher amount of interconnected pores for aggregates sintered between 700 and 1000 °C leads to a higher rate of water absorption and then reduces to 30 % for temperatures between 1200 and 1300 and 1200 to 1400 °C for bentonite and kaolinite aggregates, respectively. This reduction is due to the reduced interconnected pores. Duration of sintering has no impact on the aggregate properties for temperatures up to 800 and 1000 °C for aggregates with bentonite and kaolinite, respectively. However, between 1000 and 1400 °C, there has been considerable improvement in the aggregate properties for increasing duration up to 60 min. In comparison, during sintering, aggregates with bentonite possessed better properties for temperature less than 1000 °C, whereas aggregates with kaolinite exhibited superior properties between 1100 and 1400 °C.

MODIFICATION OF PROPERTIES OF STRUCTURAL LIGHTWEIGHT CONCRETE WITH STEEL FIBRES / LENGVOJO BETONO SAVYBIŲ MODIFIKAVIMAS PLIENINĖMIS FIBROMIS

Structural lightweight aggregate concrete (SLWAC) is an alternative building material to normal-weight one, due to its ability to reach a relatively high compressive strength at still significantly lower density. Nevertheless, the application of lightweight aggregate instead of normal-weight one to concrete must result in deterioration of some characteristics of the composite. One of the methods of improving SLWAC properties is incorporation of fibers into concrete. This paper focuses on the influence of steel fibres on modification of properties of structural lightweight concrete with sintered fly ash aggregate. Two different concrete mixtures, producing various levels of matured composite density and compressive strength, were modified with three dosages of fibers: 30, 45 and 60 kg/m3. The applied amounts did not result in significant deterioration of the rheological parameters of concrete mixtures. Despite relatively low volume content of fibres, a considerable increase of flexural and tensile splitting strength was observed. Fibres also improved concrete shrinkage as well as post-peak deformability in uni-axial compression. The effect of steel addition on compressive strength proved to be dependent on specimen type. Nevertheless, it was not as crucial as in the case of the above characteristics. However, the modulus of elasticity of SLWAC was not affected by fibre addition. Santrauka Konstrukcinis su lengvaisiais užpildais betonas (SLWAC) yra normalaus svorio statybinių medžiagų alternatyva, turinti mažesnį tankį ir gebėjimą pasiekti gana didelį gniuždomąjį stiprį. Nepaisant to, lengvieji užpildai, naudojami vietoj normalaus svorio užpildų, realiai gali pabloginti kai kurias kompozito savybes. Vienas iš lengvojo betono SLWAC savybių tobulinimo būdų yra plieninių fibrų įterpimas į betono sudėtį. Šiame darbe aptariamas plieninių fibrų poveikis konstrukcinio lengvojo betono su lakiaisiais pelenais savybėms. Tikslui pasiekti buvo parinktos pagal tankį ir gniuždomąjį stiprį dvi skirtingos betono sudėtys su skirtingais (30, 45 ir 60 kg/m3) plieninių fibrų tankiais. Paruošti bandiniai buvo naudoti gniuždomajam stipriui ir kitoms savybėms nustatyti. Tyrimų rezultatai parodė, kad plieninių fibrų priedas nepablogino reologinių betono mišinio rodiklių. Nepaisant palyginti mažo fibrų kiekio, labai padidėjo bandinių lenkiamasis ir tempiamasis stipris. Fibros taip pat pagerino deformacines betono savybes. Gauto kompozito gniuždomasis stipris iš dalies priklausė nuo naudojamų plieninių fibrų charakteristikų. Tačiau plieninių fibrų priedas nepakeitė SLWAC tamprumo modulio.

Durability of lightweight concretes with lightweight fly ash aggregates

This paper presents the effects of aggregate properties such as strength, porosity, water absorption, bulk density and specific gravity on the strength and durability of lightweight fly ash aggregate concrete (LWAC). The influence of properties of four aggregates (sintered lightweight fly ash aggregates, cold-bonded lightweight fly ash aggregate and normalweight aggregate) on mechanical and durability properties of concrete is discussed. Experimental results revealed that durable high-strength air-entrained lightweight concretes could be produced using sintered or cold-bonded lightweight fly ash aggregates, having comparable performance with the normalweight concretes. The use of lightweight aggregates (LWA) instead of normalweight aggregates in concrete production decreased the strength and stiffness due to the higher porosity and lower strength of the aggregate included in the concrete. However, permeability of sintered fly ash aggregate lightweight concretes was comparable and slightly lower than normalweight concrete whereas permeability of cold-bonded fly ash lightweight concrete was greater than the others. All concretes had a durability factor greater than 85, which met the requirements by showing quite perfect resistance to freeze–thaw.

Influence of binders on properties of sintered fly ash aggregate

Sustained research and development work on the utilization of fly ash for various productive uses have been carried out in the past. In the construction industry, major attention has been devoted to the use of fly ash in concrete as a cement replacement. The production of artificial lightweight coarse aggregate using fly ash has potential for its large-scale utilization in the construction industry and this is an area that merits attention in many parts of the world, bearing in mind the rapid dwindling of sources of natural aggregates. As only limited details on manufacture and parameters influencing properties of sintered fly ash aggregates have been reported in the literature, a systematic study was undertaken. In this paper, the relative performance of three binders, viz., cement, lime and bentonite, on the properties of sintered fly ash aggregate is reported. The salient observations are (i) the characterization studies on sintered fly ash aggregates show that the properties of aggregates depend on the type of binder and its dosage, (ii) the significant improvement in strength and reduction in water absorption of sintered fly ash aggregate is observed when bentonite is added with fly ash, (iii) the binders used did not alter the chemical composition, while they influence the microstructure of the aggregate, which results in enhancement in the properties of aggregates.

Chloride induced reinforcement corrosion in lightweight aggregate high-strength fly ash concrete

Reinforced lightweight aggregate high-strength concrete slabs that incorporated fly ash were exposed to 2% chloride solution for over 15 months. Chloride ion ingress, corrosion potentials, corrosion current density and electrical resistivity were determined. These slabs were compared with slabs from normal weight concrete of medium and high-strength. The results indicated that lightweight high-strength concrete slabs with fly ash in the concrete mixture showed the least amount of chloride concentration. Values of corrosion current density were very low and values of electrical resistivity were very high and indicative of extremely low corrosion current. The dense matrix of the lightweight high-strength concrete is believed to restrict continuous pores that may carry chloride ions. The effect of fly ash in lowering the chloride diffusivity further contributed to reduce harmful chloride ions. In addition, the porous sintered fly ash aggregates are believed to have acted as buffer reservoirs for the chloride laden solution and thus prevented the chloride ions from reaching the steel surface.

Some characteristics of high strength fiber reinforced lightweight aggregate concrete

The effect of polypropylene and steel fibers on high strength lightweight aggregate concrete is investigated. Sintered fly ash aggregates were used in the lightweight concrete; the fines were partially replaced by fly ash. The effects on compressive strength, indirect tensile strength, modulus of rupture, modulus of elasticity, stress–strain relationship and compression toughness are reported. Compared to plain sintered fly ash lightweight aggregate concrete, polypropylene fiber addition at 0.56% by volume of the concrete, caused a 90% increase in the indirect tensile strength and a 20% increase in the modulus of rupture. Polypropylene fiber addition did not significantly affect the other mechanical properties that were investigated. Steel fibers at 1.7% by volume of the concrete caused an increase in the indirect tensile strength by about 118% and an increase in the modulus of rupture by about 80%. Steel fiber reinforcement also caused a small decrease in the modulus of elasticity and changed the shape of the stress–strain relationship to become more curvilinear. A large increase in the compression toughness was recorded. This indicated a significant gain in ductility when steel fiber reinforcement is used.

Techno-commercial perspective study for sintered fly ash light-weight aggregates in India

Enhanced construction activities, shortage of conventional building materials and abundantly available industrial wastes have promoted the development of new building materials. Annual production of approx. 50 million tonnes of fly ash in India has still limited applications, the large bulk quantity of which remains abandoned as waste. Production of sintered fly ash aggregates has the unique possibility for bulk utilization of fly ash. A techno-commercial feasibility study was undertaken on the production of the light-weight aggregates from fly ash. This paper describes the production method, pilot plant investigations, process engineering of a demonstrative unit, major plant and equipment specifications, cost-economics, etc. The prospects for setting up a commercial unit in the state of West Bengal in the proximity of thermal power plants have been observed to be significantly potential.

Water absorption by aggregates a simple approach to assessment of pore characteristics

Although the fundamental importance of pore structure of aggregates is recognised it is noted in the paper that successful linking of this with properties of concrete has not yet been possible. The authors accept that absorption of water by aggregates is important per se; it also allows indirect assessment of pore structure by characterising the pores, not in terms of sizes (based on assumptions about their shapes) but in terms of accessibility to water under simple immersion, low pressure (0.2 N/mm 2) and partial vacuum (630 mm Hg). Results are given for immersion periods from 20 seconds up to 2 years, for the first, and up to 90 days for the other two methods. The simple BS 812 technique used with normal weight aggregates is shown to be acceptable with the crushed limestone and with the five lightweight aggregates used. It is shown that the disturbance during mixing of ‘saturated’ high-porosity aggregates can lead to emission of significant volumes of water. The difference in behaviour between the sintered fly ash aggregate and the others is thought to be related to its more uniform and accessible pore structure arising from the fly ash particles and their sintering. It is concluded that useful information on aggregate pore characteristics is available from studies of simple water absorption tests.

1041 人工軽量骨材とそのコンクリートの試験結果(材料・施工,第1回 日本建築祭 研究発表会 学術講演要旨集)

1041 人工軽量骨材とそのコンクリートの試験結果(材料・施工,第1回 日本建築祭 研究発表会 学術講演要旨集)