Study On Preparation And Action Mechanism Of B-SMC Cement-based Permeable Crystalline Waterproof Material

Leakage in buildings and structures has long been an important problem that seriously disturbs people’s lives and work.The main cause of leakage in reinforced concrete structures or elements is the presence of cracks in the concrete.With cracks in the work of reinforced concrete components in the case of long-term seepage,will not only affect the normal use of buildings,structures,and even serious will affect structural safety and durability,reducing the life of the building.Cement-based crystalline water penetration waterproofing materials（CCCW）water crystallization is one of the important methods to solve the leakage of concrete structures or components to effectively seal the micro-cracks in the concrete.At present,the CCCW used more often in China is either an imported product,the use of higher costs or domestic,the price is relatively cheap,but also relatively poor quality.Bentonite swells when exposed to water,and can be used as a waterproof material for making bentonite waterproof blankets,waterproof sheets etc.and China’s bentonite reserves rank first in the world,the application cost is low.Sodium methylsilicate can react with silicate materials to form"anti-capillary effect"of water-repellent properties,while micro-swelling,increasing the density and other functions.Based on this,this paper uses sodium bentonite and sodium methylsilicate as the active material to prepare cement-based permeable crystalline waterproofing materials（B-SMC）,the main research content and conclusions are as follows:（1）The chemical composition,mineral composition and composition structure of three existing active masterbatch PLW,TZ and FLW were analyzed by means of XRF,XRD and infrared spectrometer.It was proposed to prepare the R&D active masterbatch with sodium bentonite,sodium methylsilicate,tartaric acid,ethylenediamine tetraacetic acid and citric acid.According to the six CCCW formulas obtained by adding alkaline activator and alkaline penetrant based on WPPFand PLWPFformulas,the flexural and compressive strength tests were carried out on the16 groups of basic formulas of R&D active masterbatch.It was found that the strength of groups 11 and 13 of R&D active masterbatch was higher.Taking group 11 and 13as the objects,the flexural and compressive strength tests were carried out by mixing alkaline activator and alkaline penetrant.The results showed that the compatibility between them was not good.Comparing the results of flexural and compressive tests,it can be considered that the 11th and 13th groups of R&D active masterbatch adding alkaline penetrant according to PLWPFformula is the preferred formula for R&D active masterbatch.（2）Based on the formula of WPPFand plwpf,the flexural and compressive strength tests of eight CCCW formula specimens of three existing active masterbatches PLW,TZ and FLW were carried out respectively.It was found that PLW had the best performance among the three existing active masterbatches,and PLWPFhad the best performance with alkaline penetrant.Comparing the better formula of three existing active masterbatch CCCW with the optimized formula of active masterbatch,it is found that the mechanical properties of the latter are better than TZ and FLW and close to PLW,which proves the feasibility of developing the optimized formula of active masterbatch.（3）Taking the 28 d compressive strength as the evaluation standard,the four factor and four level uniform test was carried out based on the optimized formula of active masterbatch,and the corresponding optimal CCCW formulas B-SMC-1 and B-SMC-2 were obtained.The ratio of B-SMC-1 is:ordinary portland cement:quartz sand:sulphoaluminate cement:talc powder:heavy calcium carbonate:active masterbatch（bentonite:tetrasodium ethylenediaminetetraacetate:tartaric acid:sodium methylsilicate=100:5:20:15）:alkaline penetrant=225:160:35:10:30:22:75;B-SMC-2 ratio:Ordinary portland cement:quartz sand:sulphoaluminate cement:talc powder:heavy calcium carbonate:active masterbatch（bentonite:citric acid:sodium methylsilicate=100:10:5）:alkaline penetrant=225:160:40:15:20:22:75.（4）Comparative tests on mechanics,impermeability and wet base surface of CCCW optimal formula B-SMC-1,B-SMC and its blank group（without R&D active masterbatch）and finished product C were carried out respectively.It was found that the performance indexes of B-SMC-1,B-SMC-2 and finished product C met the specification requirements,while the performance indexes of B-SMC-1 and B-SMC-2were much higher than those of the corresponding blank group and higher than that of finished product C,it shows that it can be used as cement-based permeable crystalline material.At the same time,the self-healing performance test shows that the curing age has a great influence on the self-healing ability of the specimens.The self-healing recovery rate of the specimens at the curing age of 28 days is lower than that at the curing age of 14 days.The self-healing recovery rates at different curing ages increase with the increase of preloading curing time;The self-healing recovery rate of B-SMC-1 and B-SMC-2 specimens at different preloading curing times is greater than100%,and the highest is 117%and 116%when cured for 28 days,which are higher than that of finished product C,while the self-healing recovery rate of corresponding blank specimens at different preloading curing times is basically less than 100%,indicating that B-SMC-1 and B-SMC-2 specimens have excellent self-healing ability.The economic benefit analysis shows that the cost of B-SMC-1 and B-SMC-2 is lower than that of finished product C,and the cost of B-SMC-1 is the lowest.（5）X ray diffraction（XRD）test showed that the strength of B-SMC-1 and B-SMC-2 increased significantly compared with that of the blank group（calcium carbonate,ettringite and C-S-H gel）,which indicated that the addition of the active masterbatch could help to generate more calcium carbonate,ettringite and C-S-H gel crystals,and effectively bridged the gap structure of the specimen.Scanning electron microscope（SEM）was used to observe the micro morphology of B-SMC-1,B-SMC-2 and their blank groups.It was found that there were certain gaps in the initial stage of the test pieces.With the increase of curing age,the gap structure of B-SMC-1 and B-SMC-2 showed a gradual bridging trend,but the corresponding blank group was not obvious,which further proved the excellent self-healing characteristics of B-SMC-1 and B-SMC-2.（6）Analysis of B-SMC-1 formulations for each performance:the mechanism of action:ethylenediamine tetra sodium salt and tartaric acid are forming a calcium ion complex in the calcium ion in the test piece matrix,thereby completing the richness of calcium ions.Set calcium ionic complex can promote the hydration process of unmarked three calcium,silicate,and produce a rich C-S-H gel and calcium carbide;at the same time,the calcium ion complex is The CO₃^2-and HCO₃^-reactions in the gap produce calcium carbonate crystals,and the ingredients can be effectively compromised on the slit structure;In addition,sodium methyl silicate is further enhanced with the silicate crosslinking process.Its hydrolysis bare hydrophobic methyl group also imparts a certain hydrophobic characteristic of the test piece,and the same bentonite can enhance the hydrophobicity of the test piece because there is a good water absorption capacity.