Secondary Efforescence Mechanism Of Portland Cement-based Colorful Decorative Mortar And Its Prevention

Portland cement-based colorful decorative mortar has been widely used in architectural decoration at home and abroad for many years.The decorative mortar has many advantages,for example,the color is rich,it is an environmental-friendly product,the price is low and it is convenient to be used as plaster on the wall.But its efforescence seriously affects the beauty and use of the building.Therefore,studying the anti-efforescence performance of colorful decorative mortar to minimize or reduce effusion is one of the keys to ensuring the overall decorative effect of colorful decorative mortar.Aiming at the secondary efforescence problem of colorful decorative mortar under rain drenched and the change of environmental temperature,the mortar performance is systematically studied in terms of water absorption,porosity,efforescence area and calcium ion concentration;COMSOL software was used to establish a numerical model and the migration process of calcium ions in the mortar was simulated.On this basis,a study on the suppression measures of mortar effusion was carried out.The specific research content and main conclusions are as follows:（1）The XRD and TG-DSC test carried out to determine the composition of efforescence substances and the transmission of efforescence substances in order to analyze the efforescence mechanism of the decorative mortar showed that the main component of the effluent in the decorative mortar is Ca CO₃.The content of Ca（OH）₂ in the depth range of 0-2mm inside the efforescence specimen was higher than that of the specimen without efforescence,and the calcium ion content in the depth range of 2-10mm was lower than that of the specimen without efforescence.The porosity of the mortar was tested by the saturated-weighing method.The test results showed that the porosity of the efforescence specimen was 2.1%larger than that of the non-efforescence specimen.（2）The results of the study conducted on the porosity,efforescence area,calcium ion content of the colorful decorative mortar under different environmental temperature to investigate the efforescence performance of the mortar showed that the porosity and efforescence area of the mortar gradually decrease with increase in temperature.At a temperature of-5°C,the porosity and efforescence area was the largest.The content of Ca（OH）₂in the depth range of 2-10mm was lower than that of the standard group of specimens,within2mm of the surface layer,the content of Ca（OH）₂ was higher than that of the standard group of specimens.（3）The efforescence characteristics of the colorful decorative mortar after rain drenched were studied.The results showed that the calcium ion content in the efforescence specimens gradually decreased with the increase of depth and then stabilized.On this basis,based on the calcium dissolution theory,a migration model（the efforescence mathematical model）of calcium ions in the decorative mortar was established,and the process of forming effluent in the colored decorative mortar was numerically simulated.The results showed that the content of calcium ion content gradually decreases with the increase in the depth of the specimen and then tends to be stable,which is consistent with the law obtained through the experiment.（4）Based on the above research results,starting from the perspective of reducing the porosity,the effect of adding heavy calcium powder and titanium dioxide on the efforescence of the colored decorative mortar was studied.The results showed that the water absorption,porosity,efforescence area and calcium ion concentration of the decorative mortar first decrease and then increase with the increase of heavy calcium powder or titanium dioxide content.When only 4%heavy calcium powder or 1%titanium dioxide was mixed,the minimum water absorption,porosity and efforescence area of the decorative mortar were obtained.The efforescence mathematical model is used to simulate the distribution of calcium ion content in the depth direction of the titanium dioxide-doped decorative mortar after effusion.The simulation results show that with the increase of the titanium dioxide content,the depth value of the Ca（OH）₂ inside the efforescence specimen decreased first and then increased.The simulation results have a good correlation with the efforescence area on the surface of the decorative mortar obtained from the experiment,that is,the smaller the depth value when the Ca（OH）₂ inside the efforescence specimen undergoes significant migration,the smaller the efforescence area of the decorative mortar,and the better the inhibitory effect of efforescence.