Superabsorbent biopolymers for mitigating autogenous shrinkage in cement-based materials

Abstract

Availability of water plays an essential role in the hydration of ordinary portland cement. At low water-to-cement (w/c) ratios, for example, hydration processes can rapidly deplete water. The increased demand for more water exacerbates surface tension-induced stresses within fine capillary pores, which causes shrinkage of the cement paste. This phenomenon, termed autogenous shrinkage, is often prevented with sufficient curing, namely by keeping the surface of the concrete continuously wet. However, such conventional curing methods are not sufficient for ultra-high-performance concretes, which are produced with very low w/c ratios. In these applications, autogenous shrinkage is mitigated via the use of internal curing approaches, either by inclusion of prewetted lightweight aggregates or superabsorbent polymers (SAPs). SAPs are ultra-hydrophilic polymer networks capable of absorbing 100,000% of their dry weight in water. A variety of acrylic-based monomers are typically employed in the preparation of SAPs, as are a number of aggressive solvents and time- and energy-intensive polymerizations. This paper presents recent experimental efforts on synthesizing and characterizing superabsorbent polymers from biorenewable resources and principles of green chemistry. In this work, the chemical synthesis and physical swelling of superabsorbent biopolymers are investigated in (a) water and (b) synthetic concrete pore solutions. Results demonstrate that biobased SAPs that absorb in excess of 20,000% their weight in water can be synthesized using ambient-condition polymerizations and green solvents, thus offering a potential biobased solution to successfully mitigating autogenous shrinkage in ordinary portland cement paste and mortars.