Nrog ntau tshaj 40 xyoo hauv saw tshuab thiab tsim khoom, peb txoj kev tsim khoom siv los ntawm cov khoom siv asphalt thiab ua tiav rau cov khoom siv asphalt thiab ua tiav rau cov khoom siv asphalt yuav tsum .
Rau txoj kev tsim kev lag luam, zoo heev ntawm txoj kev kev siv cov saw hlau thiab peb cov khoom siv tau ntawm cov khoom siv qub thiab cov khoom siv hluav taws xob .