Penetration of pressure-injected lithium nitrite in concrete and ASR mitigating effect

Abstract

The objective of this study is to clarify optimal conditions for suppressing the expansion of ASR-deteriorated concrete by pressure-injecting a lithium nitrite solution. To investigate the ASR-mitigating effect of lithium nitrite, concrete mixtures with two types of reactive aggregates were impregnated with lithium nitrite by pressurized injection at three steps of ASR. The effects of different timings on the penetration of lithium nitrite driven by the pressure gradient and on the suppression of expansion were examined through tests.The expansion rate started to decrease immediately after injecting a lithium nitrite solution into the concrete in the propagation period (PP) with severe ASR cracking and an expansion strain of 2000 micro. With a lithium-sodium molar ratio of 0.6 or more, further expansion was significantly reduced. On the other hand, expansion continued even after application of lithium nitrite when the solution was injected into the concrete in the early propagation period (EPP) with slight ASR cracking and an expansion strain of 400 micro, and the final strain eventually exceeded that of the concrete that had been subjected to the lithium injection in the PP.It is assumed that the lithium nitrite solution migrates through ASR cracks first because of the pressure gradient and then diffuses into the bulk mortar. The degree of expansion could also be affected by at which stage of ASR the lithium ions reach the reactive aggregates and the ASR gel.