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BVFF nummer:
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2018:2-18
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Projekttitel
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Optimization of particle size distribution for unbound granular materials
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Projektledare/Kontaktperson
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Shafiqur Rahman
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Telefon
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+4613204109
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Utförarorganisation
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VTI
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Medutförare
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VTI
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Bakgrund
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Mechanical strength of unbound granular materials (UGMs), used in the base and subbase layers of pavements, greatly relies on the aggregate interlocking which is a function of the particle size distribution (PSD). In various studies, it has been shown that only a certain range of particle sizes function as the load bearing structure in an aggregate assembly whereas the rest of the sizes either float or act as fillers. The French Olard method used for the mix design of asphalt concrete attempts to maximize the aggregate to aggregate contact in order to maximize the strength by systematically proportioning the different fractions of the PSD curve. This method can be equally applicable for UGMs albeit seldom practised. Another study at VTI, assigned by NCC (Per Muren), showed that open graded materials (2/32) may perform as good as well graded (0/32) materials in triaxial tests. In high moisture content, the open graded materials performed even better than the well graded material (Rahman et al 2017). The possible reason is that the moisture sensitivity was low because of lack of fines and the fines did not contribute to the strength. Thus, it appears that if the PSD curve can be optimized by applying Olard’s method and if the proportion of fines can be reduced, this will improve the mechanical strength of the UGMs and simultaneously improve drainage properties, moisture and frost susceptibility. The range of PSD curves required by Trafikverket is mainly based on empiric experience (and Fuller curve theory). Hence it is important to conduct studies to validate previous findings, to develop optimized PSD curves and to compare performance with the standard PSDs. This should aid the industry in obtaining better performing materials and alleviating issues such as poor drainage, moisture and frost susceptibility.
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Sammanfattning
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PSDs and interlocking of aggregates are probably the most significant factors associated with the mechanical performance of UGMs. This project will investigate to optimize the PSDs of UGMs applying Olard’s method and will compare the performance with UGMs having standard PSDs. Furthermore, the performance of open graded UGMs with different PSDs will be investigated to obtain material with better drainage properties and reduced moisture and frost susceptibility.
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Förväntat resultat
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• Optimized PSDs for different materials will be developed
• Better insight on the effect of different PSDs on performance will be developed
• PSDs for certain UGMs to get the best mechanical performance will be found
• Drainable UGMs with better mechanical strength will be developed
• UGMs with better moisture and frost resistance will be developed
• The Olard method gives better control of properties that may influence the stability of UGMs e.g. grain shape, mica content, density differences and other properties. These properties are hard to control with conventional testing methods.
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Plan för resultatspridning och implementering
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• Publishing journal/conference articles
• Participating in seminars and workshops
• Preparation of regulatory framework
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Tidsramar
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Startdatum: 2018-09-01
Slutdatum:2020-12-30
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