Self-Healing Method For Micro-Cracks Of Cement-Based Materials By Microbial Pre-Coating

Concrete is one of the most widely used building materials in the construction sector.But concrete can easily crack because of the inherent flaws with brittle.Cracks can lead to invasion of harmful substances,the destruction of the structure and reducing of the service life.Currently,in order to improve the durability and service life of concrete,research on the self-healing of cracks in concrete has been widely carried out.Based on the theory of microbial mineralization,microbial technology is used for self-healing of cracks in concrete.Preparing microbes into self-healing paint coating are brushed on the surface of concrete in advance.When cracks appear,the microorganisms induce the Ca2+ to form mineralization products to fill the cracks.Which will achieve the goal of self-healing.In order to simulate the real state of concrete cracks,this paper explored a variety of methods to make cracks,and produced samples to meet the test requirements.The "inline Law" is used to make cracks upon strip specimens,the "repression Law" is used to make cracks upon cylindrical specimens,crack the width of cracks is in the range of 0?m?600?m.And the fracture morphology of crack is close to the real cracks which formed in the natural environment.Using image technology to calibrate the cracks can get the cracks parameters including length,width and area.Then,study the characterization method of crack self-healing effect.Surface characterization method,seepage characterization method and the depth of deposition method can be used to characterize the self-healing effect of cracks.Surface characterization method is simple and versatile.Study the composition of the microbial coating materials,determining the composition and suitable dosage.With reference to national standards and combined with the nature of the coating materials to determine the appropriate coating process.Coating 3 times,the coating time interval is 20min.The thickness of each film is 60?80?m,the overall thickness of the film does not exceed 300?m,the amount of heal solution should be about 1.5mL/cm2.Pre-acidification and coating treatment were conducted and before samples were cracked.The self-healing effect under different conditions was studied,including crack width,cracking age,conservation mode and ambient temperature.The crack width within 300?m can be completely healed,the heal rate of cracks between 300?500?m is about 80%,and the heal rate of cracks above 600?m is only 50%.The self-healing rate of 7d cracks was more than 90%,the self-healing rate of 14d cracks was less than 80%,and the self-healing rate of 60d cracks was less than 40%.Immersion conservation mode has the best self-healing effect.The self-healing rate of wet maintenance is 5%less than the standard conservation.The condition of wet curing is most simple,which is suitable for practical applications.When the ambient temperature is below 10?,the self-healing rate is low.When the temperature of the water environment is above 20?,the rate of self-healing is high.