Abstract

Carbon dioxide is known as an important agent in aqueous media to induce chemical attack on building materials. The leaching behavior of pea gravels, which are used as backfill material in continuous tunneling, is not entirely resolved until now. Evaluating the durability and economical advantage of individual backfill materials requires a proper experimental design to survey the dissolution reactions and to develop a useful modelling approach to calculate dissolution for carbonate bearing pea gravels. In this study a combined flow through reactor unit was developed, where conditions for chemical attack on gravel material can be simulated by changing flow rate and/or CO2 partial pressure. The addition of CO2(gas) was adjusted by pH(stat) conditions. Solution chemistry was monitored in-situ and by analyzing samples throughout experimental runs. For 5 natural gravels with different calcite(dolomite)/quartz ratios, the dissolution rates of Ca2+ for carbonates (R-Ca_cc; normalized on exposed carbonate surfaces) were found to reflect mineralogy, carbonate content, flow rates and thus saturation state conditions. R(Ca_dol )values for dolomite are significantly lower (10(-12) < R-Ca_dol < 10(-13) mol CM-2S-1) compared to calcite (10(-9)< R-Ca_cc < 10(-12)MOl CM-2S-1). The experimentally obtained R-Ca values from the pea gravels and literature data were used to develop a model that estimates the durability of pea gravel and Ca2+ transfer to a drainage system for potential carbonate scaling at various environmental conditions. Our contribution highlights that the application of limestone and dolostone as backfill material can only be reliably assessed by considering the local hydrological and hydrochemical conditions. (C) 2019 Elsevier Ltd. All rights reserved.

Keywords

TBM; Pea-gravel; Calcite; Backfilling; Durability; Tunnel-stability

Published in

Construction and Building Materials
2019, Volume: 223, pages: 254-264
Publisher: ELSEVIER SCI LTD

SLU Authors

• Köhler, Stephan

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Building Technologies
Building Technologies


Publication identifier

DOI: https://doi.org/10.1016/j.conbuildmat.2019.06.168

Permanent link to this page (URI)

https://res.slu.se/id/publ/102163