Effects Of Mineral Admixtures On The Self-healing Capability Of Mortar Incorporating Crystalline Additive

With the development of urbanization and the expansion of infrastructure in China,because of the porous structure,internal microcracks and surface cracking of concrete,the leakage often occurs in construction projects.Cementitious capillary crystalline waterproofing materials reacts with calcium hydroxide to make concrete obtain structural waterproofing and crack self-healing properties,have been increasingly used in construction projects.The mineral admixtures such as fly ash and granulated blast furnace slag powder have been used widely,they can reduce the content of calcium hydroxide,unhydrated cement particles and capillary pores in the cement system.However,it is unclear whether these factors will affect the effect of crystalline admixture.Therefore,based on practical engineering applications,the influences of crystalline admixture on the mechanical properties,impermeability and water absorption of Portland cement,fly ash-portland cement,granulated blast furnace slag power-portland cement cementing system were studied.And then,the self-healing properties of mortars containing mineral admixtures and crystalline admixture under different curing conditions and crack ages were studied by the compressive strength recovery rate,water absorption and crack closure,and the self-healing products were studied by X-ray diffraction(XRD),scanning electron microscopy and energy spectrum analysis(SEMEDS).The main conclusions are drawn as follows:(1)Crystalline admixture have no negative impact on the performance of cement-based materials.The content of crystalline admixture was 1.2 wt.%,which had the best effect on the improvement of mechanical properties,water absorption and permeability of cement matrix.Appropriate amounts of mineral admixtures and crystalline admixture can improve the mechanical properties,water absorption and permeability of mortars.The amount of fly ash or granulated blast furnace slag powder in engineering applications should not exceed 20 wt.%.(2)Under the conditions of water immersion(WI),water contact(WC)and air exposure(AE)curing condition,the self-healing capability of OPC-CA specimens containing crystalline admixture is higher than that of OPC,indicating that crystalline admixture are beneficial to the self-healing properties of mortar specimens.The order of self-healing effect of the specimens under different curing conditions is: WI> WC> AE,indicating that moisture is a necessary condition for mortar self-healing.(3)Incorporation of an appropriate amount of fly ash or granulated blast furnace slag powder can improve the self-healing properties of the specimens containing crystalline admixture,and the healing efficiency of the structural cracks was higher than the early age cracks,the healing effect is best when the amount is 10 wt.%.In combination with the practical application of the project,it is recommended that the content of fly ash and slag powder not exceed 20 wt.%.(4)According to the results of XRD and SEM-EDS,the analysis shows that there are healing products on the surface of the cracks,and the main component is calcium carbonate,but the pozzolanic reaction of granulated blast furnace slag powder has little contribution to the self-healing property of specimens.