Leaching behavior of carbonate bearing backfill material – An experimental and modelling approach

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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 pHstat 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 (RCa_cc; normalized on exposed carbonate surfaces) were found to reflect mineralogy, carbonate content, flow rates and thus saturation state conditions. RCa_dol values for dolomite are significantly lower (10−12 < RCa_dol < 10−13 mol cm−2 s−1) compared to calcite (10−9 < RCa_cc < 10−12 mol cm−2 s−1). The experimentally obtained RCa 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.

Original languageEnglish
Pages (from-to)254-264
Number of pages11
JournalConstruction and Building Materials
Volume223
DOIs
Publication statusPublished - 30 Oct 2019

Keywords

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

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Building and Construction
  • Materials Science(all)

Fields of Expertise

  • Advanced Materials Science
  • Sustainable Systems

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