Siv ua tus neeg sawv cev sai, roj nplua nyeem thiab tus neeg sawv cev rau lub zog thaum ntxov rau cov cement. Nws yog siv rau hauv kev tsim cov mortar thiab ntau yam concretes kom ua kom cov cement tawv sai dua thiab luv lub sijhawm teeb tsa, tshwj xeeb tshaj yog thaum lub caij ntuj no kev tsim kho kom tsis txhob muaj qhov ceev teeb tsa qeeb dhau ntawm qhov kub qis. ...