Invalid argument supplied for foreach ()

 class Menu 
  {
    private $array_menu;

    public function __construc($arr)
    {
        $this->array_menu= $arr;
    }
    public function construirMenu()
   {
     $ret_menu=" <nav><ul> ";
    foreach ($this->array_menu As $opcion) {
        $ret_menu .="<li>" .$opcion. "</li>";
     }
     $ret_menu .= "</ul></nav>";
     return $ret_menu;
    }

   }

class Welcome extends CI_Controller {

        function __construc()
        {
            parent::__construc();
        }
        public function index()

       {

        $this->load->library('menu',array('Inicio','Acerca de','Contacto'));
        $data['mi_menu'] = $this-> menu ->construirMenu();

        $this->load->view('nuevo',$data);

       }