Activation of autogenous self-healing in pozzolanic natural hydraulic self-compacting lime concrete under cyclic compressive loading

Abstract

This study investigates the activation of autogenous self-healing in pozzolanic natural hydraulic lime concrete subjected to cyclic compressive loading. Several concrete mixtures were formulated incorporating various mineral pozzolanic additions, including one reinforced with steel fibers, to evaluate their influence on fatigue performance and healing capacity. Fatigue tests revealed significant variability in the fatigue life of specimens, effectively modeled by the Weibull distribution. Fibers did not reduce fatigue life variability nor produce surviving specimens after testing, despite their expected role in crack control and damage stabilization. Mixes with runout specimens exhibited greater scatter in fatigue life, with cyclic loading inducing notable self-healing in specific lime-based concretes, particularly in the metakaolin-enriched mixture. Runout specimens from this mix showed marked increases in compressive strength and stiffness, confirming successful autogenous healing. The strain-cycle behavior displayed stable secondary strain phases, which correlated with fatigue life through a log–log relationship, highlighting the interaction between microstructural damage and healing. Microstructural analyses using thermal techniques – thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) – as well as X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP), provided comprehensive insights into the self-healing mechanisms. TGA–DSC results demonstrated increased calcium carbonate and portlandite contents in specimens subjected to higher fatigue cycles, supporting self-healing through carbonation, hydration, and rehydration. XRD identified crystalline phases linked to ongoing hydration and carbonation reactions, while MIP revealed densification of the pore network, contributing to enhanced mechanical properties. These processes facilitate crack filling and matrix consolidation, improving stiffness and strength retention over time. The findings suggest that fatigue-induced microcracking primarily activates carbonation reactions, supplemented by hydration, resulting in progressive microstructural recovery and durability enhancement under cyclic loading. This work underscores the potential of combining pozzolanic additives and cyclic mechanical loading to promote sustainable, low-carbon lime-based concretes with intrinsic self-healing capabilities. Such materials are promising for eco-efficient construction and the restoration of heritage structures, providing increased lifespan and reduced maintenance needs.