The Use of Superabsorbent Polymers in High Performance Concrete to Mitigate Autogenous Shrinkage in a Large-Scale Demonstrator

Abstract

High performance concrete (HPC) is a high strength concrete that undergoes a lot of early-age autogenous shrinkage (AS). If shrinkage is restrained, then micro-cracks arise and threaten the durability of the structure. Superabsorbent polymers (SAPs) can reduce/mitigate the autogenous shrinkage, due to their promising application as internal curing agents. In this paper, large-scale demonstrators were built to investigate the efficiency of SAPs to mitigate autogenous shrinkage in HPC. For this purpose, different measurement techniques were used like embedded fiber optic sensors and demountable mechanical strain gauges, complemented by AS measurements in corrugated tubes and restrained ring tests. The SAP wall showed an AS reduction of 22%, 54%, and 60% at the bottom, middle, and top, respectively, as recorded by the sensors (in comparison with the reference wall (REF)). In the corrugated tubes, mitigation of AS was shown in the SAP mixture, and under restrained conditions, in the ring test, the reference mixture cracked after two days, while the SAP mixture had not cracked at the end of the measurement period (20 days). Cracks were shown on REF wall after one day, while the SAP wall was crack-free. Water flow tests performed on the main crack of the REF wall confirmed that the flow rate is related to the third power of the crack width. All tests showed that SAPs could highly reduce AS in HPC and avoid cracking.

Effect of Cement Types and Superabsorbent Polymers on the Properties of Sustainable Ultra-High-Performance Paste

“…At the initial ages, the AS contraction of all samples was significantly greater, while the AS of samples with SAP was significantly lower than that of the control group. This was due to the release of water from SAP during the reaction process, slowing down the decrease in internal relative humidity and effectively reducing AS development [ 12 ]. This decrease became more pronounced as the SAP content increased.…”

“…Moreover, SAP affects the technological processes of concrete mixing. The mixing procedure of SAP-blended concrete is slightly more complex than that of traditional concrete, because the presoaked SAP turns into a hydrogel and is difficult to disperse in the mixture [ 12 ]. As shown in the mixing procedure ( Figure 3 ), Step 2 involves adding 50% of water, SP, and/or additional water and mixing for 60 s, and Step 3 involves adding dry SAP powder into the mixer.…”

“…In addition, the water absorption of SAP was measured using the “tea bag” method [ 27 ]. In water, the swelling capacity of SAP was equal to 295.5 g/g SAP after 10 min and 291.5 g/g SAP after 12 h. The swelling capacity of SAP in cement paste was much lower than when in water [ 12 ]. In cement paste, the swelling capacity of SAP was approximately 10.4 g/g SAP .…”

“…Step 1: dry mix all the binding materials for 30 s. Step 2: add 50% of water, SP, and/or additional water, mixing for 60 s. Step 3: add the dry SAP, mixing for 60 s. Considering that the presoaked SAP turns into a hydrogel, it is difficult to disperse in the mixture [ 12 ]. Therefore, it is reasonable to add the dry SAP directly [ 12 ]. Step 4: add the rest of the water, SP, and/or additional water; mix slowly for 120 s; and then mix quickly for 180 s.…”

Chemical Shrinkage of Low Water to Cement (w/c) Ratio CEM I and CEM III Cement Pastes Incorporating Silica Fume and Filler

“…The superplasticizer Sika ViscoCreteUHPC2 (Sika AG, Baar, Switzerland) with a density of 1.08 ± 0.02 kg/liter and 40% of active materials was used with a dosage of 1.1% by weight of cement. This value was chosen based on the amount added in the related HPC concrete composition under study [ 21 ] to aim at a slump flow of 700 mm (SF2). De-aerated water was used to fill the vials in the test.…”