This study presents the encapsulation of mineral compounds as healing materials for cement-based composites. Three liquid (sodium silicate, colloidal silica and tetraethyl orthosilicate) and one powdered (magnesium oxide) minerals were encapsulated in thin walled soda glass capsules. Load regain was obtained for samples healed under three different curing regimes; ambient conditions, high humidity exposure or immersed in water. Water immersion resulted in crack area closure that ranged from 85% to 100% for all mineral treated samples. The measured reduction in both sorptivity and intrinsic gas permeability varied from 18% to 69% depending on the measured parameter and mineral type. Sodium silicate and colloidal silica presented with the best and more consistent response in all applied measurements, both in terms of load and durability recovery. These results demonstrate how self-healing can be achieved by utilising cost effective mineral compounds which are also compatible with the host cementitious matrix.
This study investigates the impact of expansive minerals, namely magnesium oxide, bentonite clay, and quicklime on the early age autogenous self-healing capacity of Portland cement (PC) paste. Individual mineral dosage in PC was studied comprehensively together with several multiple mineral combinations. The study also covers a brief state of the art on autogenous self-healing and the use of minerals. The healing performance was compared using flexural strength recovery, crack sealing, and permeability tests. Materials microstructural investigations were carried out using XRD, TGA and SEM-EDX. The hydrated and swelling products of expansive minerals have effectively contributed to the production of healing materials. Cracks in the range of 150 µm healed efficiently in a mineral containing mixes within 28 days. Self-healing recovery was triggered through the crack bridging (strength recovery), sealing (physical closer of cracks through crystallisation) and durability performance improvement.
7This part of the study presents the optimisation of expansive minerals mix proportions and establishes 8 a quantitative and qualitative correlation between self-healing and the cracking age of cementitious 9 materials. The hydration degree of cementitious materials is considered as a quantitative measure of 10 age and the corresponding healing performance was analysed to establish an age-healing relation. 11Healing performances were assessed in terms of load recovery, crack sealing efficiency and gas 12 permeability. The microstructure of materials was investigated using XRD, TGA and SEM-EDX. The 13 self-healing performance of particular cement mixes shows linearly increasing correlation with the 14 reduction of hydration degree. However, cement mixes containing expansive mineral result in higher 15 healing performance than mixes containing only Portland cement (PC). This observation was 16 confirmed for all cracking ages. Blends containing only PC showed healing materials that were 17 mostly calcite and portlandite, while the optimised use of expansive minerals produced denser healing 18 materials with C-S-H, and complex Ca, Mg, Si, Al combined hydrated and carbonated products in 19 addition to calcite and portlandite. The results further suggest that the proportions of calcite, 20 portlandite and ettringite in healing compounds have an increasing trend with the age of hardened 21 cementitious materials. 22
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