The nanomaterial graphene oxide (GO) has been investigated as a way to improve concrete strength, but reported results of GO’s effects have been inconsistent and detailed understanding of the mechanisms of its strength-enhancing effects has been elusive. New studies by a multidisciplinary team led by scientists at the University of California at Los Angeles (UCLA; www.ucla.edu) have revealed new insight on these mechanisms and illuminated a path toward more effectively applying GO in commercial concrete.
“The findings of our research offer practical guidance for the effective use of GO, at very low dosage, in concrete,” says Gaurav Sant, the Pritzker professor of sustainability at UCLA and one of the project’s leaders.
Source: UCLA
Concrete strength is governed by the cement clinker content and the water-to-cement ratio, and GO at dosages of 0.05 wt.% of binder material can improve concrete’s 28-day compressive strength by more than 20%. The research investigated the factors that influence the reinforcing effectiveness of GO in concrete, including GO dosage, physical treatments (such as sonication) and chemical treatment (such as the use of the superplasticizer polycarboxylate ether (PCE)). In addition to the conventional role as a superplasticizer to enhance the workability of concrete, PCE could also serve as a surfactant that modifies the dispersion state of nanomaterials, including GO.
Sant and his team found that the strength-enhancing effects of GO are governed by the balance between its hydration-seeding and pore-refinement effects. “GO’s high specific surface area provides abundant nucleation sites that accelerate cement hydration and contribute to early-age strength development,” Sant explains. “In contrast, its nanoscale dimensions enable pore filling and microstructural densification, which enhances later-age strength,” he says.
Sonication and PCE additions regulate how the GO disperses in the concrete mixture and determine the effective surface area of GO. “Specifically, while sonication exfoliates multilayer GO sheets into single-layer GO sheets, increasing their available surface area, PCE adsorption decreases the surface area,” Sant says. “This allows these two manipulations to be co-optimized to ensure a balance between hydration-seeding and microstructural densification, thereby maximizing the use of GO at any dosage.”