Try out
System.Web.VirtualPathUtility.ToAbsolute("yourRelativePath");
There are various ways that are available in ASP.NET that we can use to resolve relative paths to a resource on the server-side and making it available on the client-side. I know of 4 ways –
1) Request.ApplicationPath
2) System.Web.VirtualPathUtility
3) Page.ResolveUrl
4) Page.ResolveClientUrl
Good article : Different approaches for resolving URLs in ASP.NET