was added to 20.0 g of an aqueous retarder solution of the appropriate dosage to obtain a w/c ratio of 0.5. The mixture is stirred for 1 min using an overhead stirrer (IKA Nanostar 20 digital, Germany) with a four-blade propeller at 500 rpm. After the mixing, 6.00 g of the cement paste was transferred into a polypropylene ampoule and sealed.