You will need to write the result Replace(the lines are immutable) and ensure that character escaping is used for \:
string path = Directory.GetCurrentDirectory();
path = path.Replace("\\", "/");
For information; most of the built-in methods will be accepted either, and if you are on Windows, it \will be more common anyway. If you want to get uri use Uri:
string path = Directory.GetCurrentDirectory();
Uri uri = new Uri(path);
string abs = uri.AbsolutePath;