Glimmer i bergmaterial för vägbyggnation: en kunskapsöversikt

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Mica is a common mineral in the Swedish bedrock and in some places the levels are high. Two important factors when it comes to road damages caused by high amounts of mica have been identified: moisture and frost damage. The Swedish Transport Administration requirements on the mica content needs to be reviewed, since they do not take into account a number of factors such as rock type, type of mica, used grain curve and climate factors. The purpose of this report is to compile the current state of knowledge on mica in unbound layers. Information about mica in asphalt is included because it contains information that may be relevant also for the unbound layers. The goal with this report is to identify knowledge gaps and define areas where greater understanding is needed about why and how mica minerals can be harmful in unbound layers in road construction. Damages associated with mica and other ballast-related properties can be difficult to understand because there are often multiple factors that interact and cause damage. Two important factors when it comes to road damages caused by high amounts of mica have been identified from literature and experience: 1. Moisture - high mica in combination with moisture produces higher risk of damages related to low bearing capacity and fast rutting development. 2. Frost damage - high mica decrease frost resistance and increase the risk of road damages. It can clearly be identified that more research is needed, including both laboratory experiments and monitoring of road sections, in order to find more relevant requirement demands on mica content in unbound aggregates for road construction.

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