155 / 2022-04-29 20:25:12

Preparation and properties study of expansive mineral-based artificial aggregates for self-healing concrete

MgO Expansive Agent,Artificial Aggregates,Preparation,Cracks,Self-healing

Expansive minerals are commonly used to promote the self-healing capacity of cracked concrete. But they are gradually consumed with the progress of hydration, decreasing the self-healing efficiency of later cracks. In this paper, an expansive mineral-based artificial aggregate was prepared, and its basic properties were investigated. It was found that the expansive mineral could not react with water during the preparation process, ensuring its later healing potential. Meanwhile, the aggregates had a slightly negative effect on the mechanical property of mortar specimens, whereas the self-healing efficiency could be significantly improved.



The artificial aggregates were prepared by the disc granulation method, using magnesium oxide (MgO) expansive agent as the self-healing agent and geopolymer materials consisting of fly ash, sodium hydroxide and sodium silicate solution as the binder. Then the aggregates were coated with polyvinyl alcohol solution and fine sand to prevent MgO from reacting prematurely. After being sieved, the aggregates with a diameter of approximately 3.5 mm were obtained (Fig. 1).



The mineral components of artificial aggregates were identified by X-ray diffraction (XRD). For comparison, the compositions of the MgO expansive agent and the reacted MgO were also examined (Fig. 2). Results showed that the mineral composition of aggregates was mainly periclase rather than brucite, indicating that the aggregates had the potential to heal later cracks. In addition, with the increase of MgO content, the crushing load of aggregates showed a decreasing trend (Fig. 3). This revealed that there was an optimal content of MgO in terms of ensuring aggregates strength and self-healing efficiency.



Compared with natural aggregates, MgO-based artificial aggregates had lower strength. Therefore, they had a negative impact on the compressive strength of mortar specimens. With the increase of aggregates content, the compressive strength of mortar specimens decreased more and more (Fig. 4). In this study, the aggregates content of 10% was selected to investigate its effect on the self-healing properties of specimens, which were evaluated by the water absorption test (Fig. 5). After healing in wet-dry cycles for 20 days, the self-healing rate of the specimens mixed with artificial aggregate reached about 60%, which was three times higher than that of the control specimens. This research provides some guidance for the application of expansive mineral-based artificial aggregates in practical engineering.