Effects of CNT and MgO-Type Expansive Agent on the Cracking Resistance of Face-Slab Concrete of CFRD

Zhifang Zhao*, Hougui Zhou, Kejin Wang, Xu Wu, Surendra P. Shah

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Concrete face rockfill dam (CFRD) is a commonly used and cost-effective type of dams. However, random cracks are often seen in the face slab concrete (FSC) of a CFRD during construction, largely due to the shrinkage caused by concrete temperature gradients, drying, and cementitious hydration. This study aims to improve the cracking resistance of FSC by using shrinkage compensating and cracking control materials. In this study, 5.0% by weight MgO-type expansive agent (MEA) or 0.1% by weight carbon nanotube (CNT) was added to a reference FSC (FSC-REF) selected from a CFRD. Fresh and hardened state properties of the developed concrete were tested. Different properties such as hydration heat, capillary pressure, mechanical properties at various ages, drying and autogenous shrinkage, thermal expansion coefficient (CTE), pore structure, and cracking resistance at early age of the FSC mixes (FSC-REF, FSC-MgO, and FSC-CNT) were determined. The results showed that the CNT addition lowered the capillary pressure and reduced the risk of plastic shrinkage cracking, while it also reduced drying and autogenous shrinkage of FSC. The addition of both CNT and MgO had little influence on the heat of hydration of FSC, but these slightly improved the axial tensile properties of FSC. CNT reduced the thermal expansion coefficient of FSC, whereas MgO increased it. Both CNT and MgO decreased the total porosity of the FSC, and the CNT addition significantly reduced the number of mesopores. The temperature-stress test results showed that MgO/CNT improved the cracking resistance of the FSC at early age under both temperature matching curing mode and constant temperature curing mode. Based on measured properties, CNT can be considered a promising additive for cracking control of FSC.

Original languageEnglish (US)
Article number04022331-1
JournalJournal of Materials in Civil Engineering
Volume34
Issue number12
DOIs
StatePublished - Dec 1 2022

Funding

This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 51879235 and 51479178). Authors Zhifang Zhao and Kejin Wang contributed equally to the work.

Keywords

  • Carbon nanotube (CNT)
  • Concrete face rockfill dam (CFRD)
  • Cracking resistance
  • Face slab concrete (FSC)
  • MgO-type expansive agent (MEA)
  • Pore structure

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Building and Construction
  • General Materials Science
  • Mechanics of Materials

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