如何给已经有数据的DataTable动态增加一列并赋值

Code
DataTable _tbl = new DataTable();

            _tbl.Columns.Add("F_Name", Type.GetType("System.String"));
            _tbl.Columns.Add("F_Age", Type.GetType("System.Int32"));

            _tbl.Rows.Add(new object[] { "aaa", 1 });
            _tbl.Rows.Add(new object[] { "bbb", 2 });

            _tbl.Columns.Add("F_Time", Type.GetType("System.DateTime"));

            for (int i = 0; i < _tbl.Rows.Count; i++)
            {                
                _tbl.Rows[i][_tbl.Columns.Count - 1] = DateTime.Parse("2008-1-1");
            }

            this.Repeater1.DataSource = _tbl;
            this.Repeater1.DataBind();            

<asp:Repeater ID="Repeater1" runat="server">
        <ItemTemplate>
            <li><%# Eval("F_Name") + "，" + Eval("F_Age") + "，" + Eval("F_Time")%></li>
        </ItemTemplate>
    </asp:Repeater>