Hydration, reinforcing mechanism, and macro performance of multi-layer graphene-modified cement composites

Multi-layer graphene (MLG) has excellent mechanical properties and a unique stacked structure. In this paper, sulphoaluminate cement replaced ordinary portland cement to prepare low-carbon ecological ultra-high-performance-concrete (UHPC); the effects of MLG on the hydration, microstructure, and mechanical properties of UHPC were investigated, revealing the hydration mechanism and reinforcing mechanism of MLG on UHPC. Results show that adding MLG can significantly enhance the macro performance of UHPC. When the MLG content is 0.08%, UHPC has better macro performance. Compared with the M0 group, the flexural strength and compressive strength of the M3 group increased by 31.6%, 35.3%, 43.3%, 50.9%, and 9.5%, 13.5%, 22.2%, 21.7% after curing for 1 d, 7 d, 28 d, and 56 d, respectively. We quantitatively characterized the content of hydration product changes in UHPC. Various characterization analyses showed that the adsorption effect and nucleation effect of MLG promoted the hydrolysis and ions exchange of Ca2+ and Al3+, which provided sites for the growth of hydration products and accelerated the hydration process of cement, forming more hydration products, including AFt (ettringite) and AH3 (gibbsite). AFt, AH3, and MLG are closely connected, filling the pores and reducing the porosity of the matrix, optimizing the pore structure, and the medium and large pores transformed into micro-nano pores. Revealing the multi-level reinforcing mechanism, namely hydration products (AFt, AH3) and MLG filling the pores; MLG prevented the extension of micro-cracks and changed micro-cracks development path through filling effect, deflection effect, pulling out, and bridging effect.