Study On Preparation And Applications Of Crack Self-healing Materials

The brittleness of concrete makes it easy to produce cracks in the long-term application.The existence and development of these cracks will reduce the durability and service life of concrete.Therefore,the crack healing of concrete has been a major problem in the academic and engineering fields.However,the crack healing is finished after detecting the crack in the traditional method,and the results are not satisfactory.If micro-cracks could be filled before coming into being macro-cracks in the structure of concrete,there would no need for late repair.So,it has an important practical significance to study and develop crack self-healing materials for concrete.In this paper,a variety of components were selected based on the theory of slow expansion,complex-precipitation and carbonation-crystallization,and the best proportion of composite self-healing material was explored by uniform design method firstly.Secondly,the effects of the as-prepared self-healing materials on the micro-cracks in mortar and concrete have been studied,and the influence on the durability of concrete are also determined.Finally,the self-healing mechanism is investigated using X-ray diffraction?XRD?and scanning electron microscopy?SEM?.The conclusions are as follows:?1?The best ratio of composite self-healing material is as follows,complex components: coagulation components: water storage components: plastic components: dense components=1:0.25:2:3.37:13.47.The cement mortar mixed with the composite self-healing material under standard curing for 7 d and 28 d,the compressive strength were increased by 16.9 % and 14.9 % than the control group,and the recovery ratio of compressive strength reached 116 % and 115 %,far higher than 100 % and 90 % of the control group.?2?The self-healing material can not only improve the impermeability of mortar,but also can increase the second impermeability and the overall compressive strength by fully repairing the micro-cracks in the mortar.When the crack self-healing material content is 6 %,it is observed that impermeability of mortar experienced the biggest growth,the first and second impermeability pressure increased by 0.4 MPa and 0.9 MPa respectively than those of the control group;respectively,the compressive strength of the reserved crack mortar increased 1.4 MPa,6.1 MPa and 7.2 MPa respectively compared with the control group after curing for 7 d,28 d and 60 d.?3?The self-healing material can not only improve the basic mechanical properties of concrete,but also repair timely the micro-cracks in concrete and make its strength grow continuously.The compressive strength of 7 d,14 d and 28 d increased by 5.7 %,8.6 % and 9.3 % respectively compared with the control group;and the strength of the recovery rate reached 112 %,108% and 104 % respectively at the second curing age of 7 d,14 d and 28 d.In addition,the durability of concrete is improved by the incorporation of the self-healing material.?4?Crack self-healing mechanism is supposed as follows: self-healing materials promoted the formation of substances,such as the Ca?OH?₂,AFt,CaCO₃ and C-S-H gel,in crack resulting from the slow expansion,complex-precipitation and carbonation crystallization.These substances not only fill,repair cracks,and improve the overall strength of paste.