\documentclass{article}
\usepackage{expl3}
\ExplSyntaxOn
\cs_new:Npn \astsInner #1 {\prg_replicate:nn {#1} {*}}
\ExplSyntaxOff
\newcommand\astsExpliii[1]{\edef\asts{\astsInner{#1}}}
\begin{document}
  \astsExpliii{10000}
\end{document}