The objective of this research is to understand the hydration and engineering performance of superabsorbent polymers as an internal curing agent in ultra-high performance concrete.Two different types of superabsorbent polymers of acrylic acid and acrylic amide with similar particle size profiles were systematically tested.To estimate the water absorbent capacity of the polymers, tea-bag tests using distilled water were performed.Isothermal calorimetry and x-ray diffraction experiments revealed the impact of polymers with different chemical bonds on cement hydration, in terms of hydration degree and hydration products.To test its feasibility as a shrinkage reducing admixture for ultra-high performance concrete, compressive strength,flowability, and autogenous shrinkage profile were measured.Lastly, scanning electron microscopy and computed tomography showed a multi-scale porosity network of the concrete with superabsorbent polymers.While both polymers showed a reduction in autogenous shrinkage, it has been concluded that the particle size and chemical form of each polymer affected its role as an internal curing agent in concrete.This also significantly affects cement hydration and mechanical strength.While acrylic acid polymer has more absorption capacity of distilled water, acrylic amide polymer shows better performance in low water-to-cement concrete systems.