Creep of SAP modified concrete

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Superabsorbent polymers (SAP) can be used as a new concrete admixture. Due to the high water retention they are capable to create a water reservoir in the concrete, which can be emptied during the hydration of the cement. Thus water is in addition to the mixing water available. Concrete with low water-cement ratio can be cured in this way in the interior (internal curing) or water that evaporates quickly at high temperatures and/or windy conditions, may be replaced. Both effects increase the achievable degree of hydration of the cement paste. Superabsorbent polymers were also used for sealing (micro) cracks with success. In tensile creep tests on concrete was found that concrete with SAP creeps significantly less than without SAP. The research project focuses on analyzing the creep behavior of SAP modified concretes. The approach is based on the hypothesis of P. Rossi who postulated that the basic creep is caused by microcracking. When microcracks occur, they can be cured by SAP and creep can thus decrease. The proposed experiments are not limited to the basic creep, but also the drying creep is included. Creep is examined under compressive as well as under a tensile load. There are two SAP modified concretes and three reference concretes without SAP which are loaded from the 28th day with 40% of the 28 day strength over a period of nine months and the total elongation measured. Also creep recovery shall be determined over two months. The tests are carried out under standard conditions. In parallel, the shrinkage is determined on unloaded samples. It is expected that the crack activity and creep with SAP can be reduced and that the residual strength increases. The results are used to create a rheological model with elastic and viscous components whose parameters are made dependent on the addition of SAP.