Security :: Put 2 Connectionstrings Inside Aspx.cs?

For example, I have these connectionstrings in my web.config:

<add name="xxx1" connectionString="..."/>
<add name="xxx2" connectionString="..."/>

I want to put 2 connection strings into my aspx.cs page; xxx1 and localsqlserver. I tried to do:

string strConnectionString = ConfigurationManager.ConnectionStrings["LocalSqlServer"].ConnectionString;
strConnectionString += ConfigurationManager.ConnectionStrings["xxx1"].ConnectionString;

but it cannot "detect" the LocalSqlServer. I am trying to populate a GridView with fields from 2 different database, hence I need 2 connectionstrings. Example of my SQL statements:

string strCommandText = "SELECT aspnet_Users.UserName, TableA.Field1, ";
strCommandText += " FROM aspnet_Users, TableA, TableB";
strCommandText += " WHERE aspnet_Users.UserID=TableA.UserID, TableA.ID=TableB.ID";