Does a dissolution-precipitation mechanism explain concrete creep in moist environments?

TL;DR

This study proposes that concrete creep in moist environments results from a nanoscale dissolution-precipitation process, supported by experiments and simulations linking creep rates to dissolution rates and identifying compositions with higher resistance.

Contribution

It introduces a dissolution-precipitation mechanism at the nanoscale as the origin of concrete creep, supported by experimental and molecular dynamics evidence.

Findings

Creep rates correlate with dissolution rates in C-S-H.

Certain C-S-H compositions resist dissolution and creep.

Topological constraint theory explains limited relaxation in resistant compositions.

Abstract

Long-term creep (i.e., deformation under sustained load) is a significant material response that needs to be accounted for in concrete structural design. However, the nature and origin of creep remains poorly understood, and controversial. Here, we propose that concrete creep at RH (relative humidity) > 50%, but fixed moisture-contents (i.e., basic creep), arises from a dissolution-precipitation mechanism, active at nanoscale grain contacts, as is often observed in a geological context, e.g., when rocks are exposed to sustained loads, in moist environments. Based on micro-indentation and vertical scanning interferometry experiments, and molecular dynamics simulations carried out on calcium-silicate-hydrates (C-S-H's), the major binding phase in concrete, of different compositions, we show that creep rates are well correlated to dissolution rates - an observation which supports the dissolution-precipitation mechanism as the origin of concrete creep. C-S-H compositions featuring high resistance to dissolution, and hence creep are identified - analysis of which, using topological constraint theory, indicates that these compositions present limited relaxation modes on account of their optimally connected (i.e., constrained) atomic networks.