Sustainable road surfaces: Evaluating eco-friendly additives on bitumen penetration gradeArman Alibayeva, Yerik Amirbayev, Dinmukhambet Alizhanov, Manarbek Zhumamuratov and Mariya SmagulovaE3S Web Conf., 614 (2025) 04013DOI: https://doi.org/10.1051/e3sconf/202561404013