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Bergkrossmaterial som ballast
RISE, SP – Sveriges Tekniska Forskningsinstitut, CBI Betonginstitutet AB.
2008 (Swedish)Report (Refereed)
Abstract [sv]

Concrete is a product that in the fresh state shall be able to flow and fill a form without segregating. This gives demands on flow properties and workability of the fresh concrete. Between 60 and 70 volume % of concrete consists of aggregate and thus its properties are fundamental for flowability. Presently in Sweden concrete is made from natural glaciofluvial aggregates in sizes less than 8 mm and with stones from local crushed rocks._x000D_ _x000D_ Locally in Sweden there is a lack of good natural aggregates. Moreover, for environmental reasons the government wants to preserve remaining gravel pits especially those in eskers. As a consequence one must find an alternative aggregate. Concrete is a bulk commodity and a cheap building material. Thus it is only crushed rocks that locally and in sufficient amounts can replace natural aggregates. The rock quarries in Sweden are mainly destined to give good coarse aggregate. In this process one also gets fine aggregates but this product is not optimized for concrete production._x000D_ _x000D_ The main problem is thus to replace the natural fine aggregate in a cost effective way with crushed rocks. Fine aggregates from crushed rocks develop other properties than natural aggregates. This is especially the case in Sweden with predominant granitic rocks. As a consequence concrete with crushed fine aggregates must be proportionated differently. The aim of this project has been to find quality criteria for fine aggregates from crushed rocks to be used in concrete and to measure how to improve the properties. Another important aspect is to find systems for quality insurance for continuous concrete production. The tools used are mainly classification of the aggregates to correlate this with rheological properties. Most effort has been put on understanding the influence of different fine material from granitoid rocks falling through the 2-mm sieve. The reason is that it is this material that causes most problems. The results have, however, been correlated against the properties of (0-16 mm) concrete. Material from 16 different rock quarries have been analysed in great detail and some additional ones in less detail. They have been compared with natural glaciofluvial aggregates. All of the material has been studied by petrographic and image analysis, laser sieve, sand equivalent test and methylen blue test._x000D_ _x000D_ The results show that there is a large variation in properties of fine aggregates from the crushed granites. The reason is that granite is regarded as the mineral composition of a family with varying amounts of different minerals and the different granites have different textures. This is reflected especially in the fine material. The finest fractions contain pure minerals and the geometry of these mineral particles is given by the crystallographic form. One mineral that especially hinders the flow is free mica due to its flaky mineral form. Larger particles are normally composed of rock fragments, i.e. several minerals. In which fraction free mineral grains starts to appear depends on the texture of the granitoids. The amount of free mica grains in the fractions below the 0,5 mm sieve varies from almost none to almost 50 %. There may, however, also be problems related to extreme amounts of filler, variation in grading curve, weathering, clay formation and hydrothermal alteration._x000D_ _x000D_ The main method to analyse flow and workability has been different rheometers where one can split between yield stress and plastic viscosity. The yield stress gives the force to set the particle slurry in motion while the plastic viscosity measures the force needed to keep it in motion. Rheological tests on the different material have been conducted on micro mortar (<0.25 mm) mortar (< 2 mm) and concrete (<16 mm). One finds that the properties of the micro mortar strongly influence that of the mortar, which in turn influences that of the concrete. To a certain degree by careful proportioning it is possible to reduce the influence of the fine material but it is not possible to eliminate it. Some of the fine materials from crushed rocks can almost directly replace natural sand while other fine aggregates are very difficult to use in concrete production._x000D_ _x000D_ This work gives a basic understanding of how to characterise fine aggregate (0-2 mm) in such a way that it gives information on how it will affect the rheological properties of concrete. Moreover, it gives information about how to improve the properties and methods for quality control. A major problem is, however, that there is no single test to be used. This work indicates that one must first do a general characterisation and based on this work develop a method or methods for quality assurance that considers the specific properties of the material from the individual stone quarry. _x000D_

Place, publisher, year, edition, pages
CBI Betonginstitutet , 2008. , p. 121
Series
CBI rapport, ISSN 0346-8240 ; 2008:1
Keyword [sv]
ballast, bergtäkt, reologi, materialanalys, mineralogi, petrologi, betong, bruk, packning, arbetabrhet, tunnslip, XRD, specifik yta, metylenblå, sandekvivalent
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:ri:diva-2962OAI: oai:DiVA.org:ri-2962DiVA, id: diva2:960567
Note
645 Går att beställa: kontakta eva.lundgren@cbi.se "Crushed rock as aggregate in concrete" (500kr) 978-91-976070-1-8Available from: 2016-09-07 Created: 2016-09-07Bibliographically approved

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