Abstract
This study focuses on the effects of superabsorbent polymers (SAP) and belite-rich Portland cement (BPC) on the compressive strength, autogenous shrinkage (AS), and micro- and macroscopic performance of sustainable, ultra-high-performance paste (SUHPP). Several experimental studies were conducted, including compressive strength, AS, isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TGA), attenuated total reflectance (ATR)–Fourier-transform infrared spectroscopy (FTIR), ultra-sonic pulse velocity (UPV), and electrical resistivity. The following conclusions can be made based on the experimental results: (1) a small amount of SAP has a strength promotion effect during the first 3 days, while BPC can significantly improve the strength over the following 28 days. (2) SAP slows down the internal relative humidity reduction and effectively reduces the development of AS. BPC specimens show a lower AS than other specimens. The AS shows a linear relationship with the internal relative humidity. (3) Specimens with SAP possess higher cumulative hydration heat than control specimens. The slow hydration rate in the BPC effectively reduces the exothermic heat. (4) With the increase in SAP, the calcium hydroxide (CH) and combined water content increases, and SAP thus improves the effect on cement hydration. The contents of CH and combined water in BPC specimens are lower than those in the ordinary Portland cement (OPC) specimen. (5) All samples display rapid hydration of the cement in the first 3 days, with a high rate of UPV development. Strength is an exponential function of UPVs. (6) The electrical resistivity is reduced due to the increase in porosity caused by the release of water from SAP. From 3 to 28 days, BPC specimens show a greater increment in electrical resistivity than other specimens.
Highlights
Ultra-high-performance concrete (UHPC) has a high cementitious material content, low water–cement ratio (w/c), dense microstructure, and very low porosity [1]
superabsorbent polymers (SAP) releases the absorbed water to the surrounding area in the reaction process (w/c decreases), which plays the role of internal curing, increases hydration, improves the microstructure, and promotes the development of strength [17,23]
We found that hours 1–7 represented the dormant period, which was due to the increase in the effective w/c of samples ordinary Portland cement (OPC)–0.25SAP and OPC–0.5SAP [39,40]
Summary
Ultra-high-performance concrete (UHPC) has a high cementitious material content, low water–cement ratio (w/c), dense microstructure, and very low porosity [1]. It has superior mechanical properties and durability performance. To achieve a high-strength and dense structure in UHPC, the mechanical properties and rheology can be improved by adding microfillers [2]. Limestone fillers and blast-furnace slag are used to increase UHPC sustainability. The addition of limestone and slag can increase cement’s degree of hydration, improve mechanical strength, and lower CO2 emissions [3,4,5]. AS and autogenous cracking limit the application of UHPC in practical engineering [7]
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