Study on the Influence of Accelerators on the Hydration of Portland Cement and Their Applicability in 3D Printing

Abstract

As extrusion based additive manufacturing (AM) has the potential of becoming the largest evolution in the construction industry in the 21^st century, the control of early cement hydration becomes more and more important. This study focuses on the control of the compressive strength development of a CEM I 52.5R via the addition of different dosages of K₂CO₃, Na₂CO₃, Ca(NO₃)₂ and Triethanolamine (TEA) which all act as accelerators in cement hydration. Further, the influence of the above-mentioned substances on the hydration products formed during the first 24 h of hydration and their applicability in extrusion-based 3D printing processes was examined. The initial and final setting time as well as the compressive strength after 1, 2, 7 and 28 d were tested. The formation of hydration products during the first 24 h was studied using continuous in-situ XRD and calorimetric measurements. The early compressive strength development of the accelerated cement was tested, using a newly developed measuring device, starting at 20 min after the initial hydration. It was shown, that by adding the above-mentioned accelerators the initial setting time and the compressive strength development of the cement paste can be precisely adapted to the printing process. It could further be shown that the used accelerators strongly influence the hydration processes of the cement pastes and the crystallinity of some hydration products.