Fill an array using a foreach loop

I'm trying to fill an array with my foreach loop, but I don't get it to work. What am I doing wrong?

$a = array();

$activities = Project::getProjectnames($_DB, $projectnaam);
if(!empty($activities)) {
    foreach($activities as $k => $v) {
          $a .= array_fill($v['name']);
    }
}

All I get back is the string Array...