The Effect Of Viscosity Modifier Agent On The Early Age Strength Of The Limestone And Calcined Clay-Based Sustainable And 3D Printable Cementitious Material

Abstract

Recently, our group attempted to develop the ternary blended (Portland cement, calcined clay and limestone) cementitious material for 3D concrete printing (3DCP). Due to the elimination of formwork during the layer-by-layer casting process, the printed material should have favorable elastic properties and green strength at the fresh state. A small amount of Hydroxypropyl methylcellulose (HPMC) based viscosity modifier agent (VMA) is used in the printable mixture to enhance the printing shape stability during the printing process. However, adding VMA may delay the hydration of cement-based materials and affect the strength development at an early age. It is necessary to determine how the VMA additions affect the early age strength development of a 3D printable cementitious material. In this paper, three mix designs with different amounts of VMA were selected to perform the uniaxial compression test at different early ages (30 min, 1, 2, 3, 4, 6h). The setting time and compressive strength tests at 1, 7 and 28 days of those mix designs were also measured. Besides, the heat flow of different mix designs was recorded by using the isothermal calorimeter. Finally, it has been found that: (1) adding VMA could contribute to increase the green strength within the first 2h after mixing water and weaken the strength development from 2h to 6h; (2) the VMA additions mainly delayed the initial set and small effects on the final set; (3) about 50% of compressive strength at 1, 7 and 28 days were reduced for the specimens with VMA. (4) the more amounts of VMA was used in the mixture, the more retarding effects on cement hydration.