Studi Modifikasi Membran Waterproofing Bitumen Menggunakan Polyether Polyurethane Dispersion (PUD) untuk Peningkatan Sifat Mekanik dan Stabilitas Termal = A Study on the Modification of Bitumen Waterproofing Membrane Using Polyether Polyurethane Dispersion (PUD) for the Enhancement of Mechanical Properties and Thermal Stability