Experimental investigation on uniaxial tensile creep behavior of cracked steel fiber reinforced concrete

This paper mainly investigates the uniaxial tensile creep behavior of pre-cracked steel fiber reinforced concrete. Hooked-end fiber RC65/60BN with fiber dosage of 80 kg/m3 was used with normal strength concrete. A suitable tensile creep frame and a pre-cracking test set-up were developed. Cylindrical specimens were pre-cracked at crack opening displacement (COD) of 0.05 and 0.2 mm respectively before the tensile creep test. The pre-cracked specimens were loaded at a load level of 30 % of the maximum pre-cracking load Pmax\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$P_{\max }$$\end{document}. The specimens were unloaded after 3 months and then reloaded to 60 % of Pmax\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$P_{\max}$$\end{document}. Time dependent COD were continuously measured by LVDTs under constant temperature of 20° and relative humidity of 60 %. The measured time dependent COD Wtotal\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$W_{\rm total}$$\end{document} was considered as the summation of three parts, the irreversible part Wirr\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$W_{\rm irr}$$\end{document}, the instantaneous part Winst\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$W_{\rm inst}$$\end{document} and the creep part Wcreep\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$W_{\rm creep}$$\end{document}. It was observed that Wirr\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$W_{\rm irr}$$\end{document} and the loading level have a great impact on the tensile creep behavior. For the specimens with a pre-cracking COD of 0.05 mm, the maximum creep deformation Wcreep\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$W_{\rm creep}$$\end{document} is almost the same as the initial instantaneous deformation Wisnt.\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$W_{isnt.}$$\end{document} after 3 months loading. For the specimens pre-cracked at 0.2 mm, the damage evolution at the fibre/matrix interface in terms of irreversible crack opening and load level is also discussed. It is interesting to be noted that the creep deformation under load level of 30 % will not introduce extra damage even though the Wirr\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$W_{\rm irr}$$\end{document} increases.