Karakterisering av bergkross till betong
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Due to increasingly strict environmental regulations regarding extraction of gravel the concrete industry need to reduce the use of gravel and replace it with crushed aggregates in concrete. Gravel is very suitable for concrete because of its round grain shape with a smooth surface and very often also a suitable particle size distribution. Crushed aggregates very often have a more flake grain shape and higher content of fine particles. The characteristic of crushed aggregates depends on parameters such as; type of rock, crushing method and degree of refinement. With a suitable rock type and by choosing the right crushing setup it is possible to produce crushed aggregates for concrete. The use of VSI crushers may improve the grain shape but is not always necessary. In case of very high content of fines an air classifier can be used to reduce the filler content (or by washing). Concrete consists of cement, water, aggregates and very often also additional materials and admixtures. Replacing gravel with crushed aggregate as a direct 1:1 substitute might be difficult because of the grain shape of crushed aggregates and its higher fine content. Very often mix-design adjustments are required to achieve the same concrete properties as with gravel and to ensure the fresh concrete workability it might be needed to increase the cement paste. For environmental and concrete technical reasons, it is desirable to substitute gravel with crushed aggregates without increasing the cement paste and to succeed, it requires some kind of refinement of the hard rock. When choosing crush methods to improve the properties of the crushed aggregates decisions always include economic considerations and it is necessary to understand how varying degrees of processing effect the concrete properties. This include a need for test methods that makes it possible to determine if a crushed material is good enough for concrete. This master thesis aims to investigate if it is possible to determine if a crushed aggregate is suitable for concrete by using some practical and simple aggregate test methods. Aggregates with different degree of refinement has been used in the study; conventional crushed and materials processed with a VSI and an air classifier.Fine aggregates 0/4 mm and also the properties of the fines, particles smaller than 0,25 mm, have a major impact on the concrete workability so focus in this investigation is crushed aggregates smaller than 4 mm.The results from this work show that there are correlations between the outcomes from aggregate tests and from concrete tests and that it is possible to assess if a crushed material is suitable for concrete without carry out a large scale concrete tests. It is difficult to assess a material with only one single aggregate test method but a combination of two tests methods describes well how the material will behave in a concrete. Important when producing crushed aggregates for concrete is the particle shape and the particle size distribution. These two parameters are important for how the material affects the concrete properties and aggregate test methods that can describe these parameters are desirable.
Place, publisher, year, edition, pages
2016. , 91 p.
Teknik, Betong, bergkross, Skanska, flödestid, byggmaterial, hållbarhet, naturgrus
IdentifiersURN: urn:nbn:se:ltu:diva-45559Local ID: 33e7dbba-6d9e-431a-bf51-6fa53a9dbbb4OAI: oai:DiVA.org:ltu-45559DiVA: diva2:1018853
Subject / course
Student thesis, at least 30 credits
Civil Engineering, master's level
Validerat; 20160408 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved