A Fundamental Assessment of Graphite Nanoplatelet Effects on Progress of Alkali-Silica Reactions

Abstract

Graphite nanoplatelets were used to control alkali-silica reactions in concrete by enhancing the barrier qualities of cementitious binders and providing local reinforcing effects against the damaging expansive phenomena. Nuclear magnetic resonance (NMR) spectroscopy was used to monitor the changes in chemical environment that reflect upon alkali-silica reactivity. Laboratory experiments were conducted to evaluate the effects of graphite nanoplatelets on alkali-silica reactions (ASRs). Reactive flint aggregates were used to induce ASR. The ²⁹Si MAS NMR spectroscopy technique was employed for evaluating the changes in chemical environment by monitoring different silicate tethrahedra (Qⁿ) as a basis to quantify the progress of ASR in concrete materials prepared with and without graphite nanoplatelets. Quantitative evaluations of different Qⁿ species present in anhydrous cement, calcium silicate hydrate (C-S-H), and ASR products indicated that introduction of graphite nanoplatelets lowered the degree of polymerization of silicate tetrahedral in C-S-H. The reduction in the breakdown of the networked structure of silicate tetrahedra under accelerated ASR indicates that graphite nanoplatelets reduce the extent of ASRs.