Viscoelastic Behavior of Concrete Containing Super Absorbent Polymers


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Title: Viscoelastic Behavior of Concrete Containing Super Absorbent Polymers

Author(s): E.A.B. Koenders, H.W.M. van der Ham and K. van Breugel

Publication: Special Publication

Volume: 278


Appears on pages(s): 1-12

Keywords: early-age concrete, super absorbent polymers (SAP), viscoelastic properties

Date: 3/1/2011

Concrete mixtures, having a water/cement ratio below 0.4, may exhibit a considerable autogenous shrinkage induced by internal drying of the capillary pore structure. In order to compete with this issue and to avoid or compensate for the development of autogenous shrinkage of concrete, either the mix proportions have to be adapted or additional (internal) water has to be supplied with emphasis on the moisture state of the capillary pore system. Until recently, one of the most frequently used methods used to retain internal self-desiccation of concretes was by adding water saturated porous light weight coarse aggregates (i.e. Lytag) or wood pulp fibers to the cementitious matrix. One of the latest innovations in this area is the addition of shrinkage reducing additives such as Super Absorbent Polymers (SAP). In order to examine the pros and cons of SAP addition to a concrete mix, an extensive experimental programme considering eight different concrete mixtures have been tested at Delft University of Technology. It is investigated how the Super Absorbent Polymers influence the mechanical and viscoelastic properties of hardening concrete. Experiments are performed for water/cement ratios of 0.32, 0.39 and 0.5, for Portland cement as well as Blast Furnace Slag cement, with addition of three different percentages of SAP, i.e. 1, 1.5 and 2 kg/m3 (1.68, 2.53 and 3.37 lb/yd3). The mixtures are tested at isothermal conditions of 20 ºC and the early-age autogenous shrinkage strains are measured over a testing period of about 300 hours. Besides, the tensile strength, compressive strength, the elastic modulus and the creep strains have been measured for the different mixtures as well. The tensile, compressive strength and elastic modulus are tested at 28 days of age. The early age creep of the mixtures was measured from prisms and tested under a sustained compressive load of 40% of the compressive strength and were loaded at an age of 3 and 7 days. In this paper, the results of the experimental program are described in detail. A significant effect of the reduction of autogenous shrinkage due to SAP addition was observed. However, results also show that SAP affects the tensile and compressive strength and the viscoelastic properties like elastic modulus and the early age creep.