Properties And Mechanism Of Ground Limestone As Concrete Mineral Additive

With the application of ground limestone in concrete structure project, many problems about concrete workability, mechanics and durability appeared. In this paper, performance and mechanism for concrete with ground limestone were studied.Workability, mechanics, and volume stability of cement containing ground limestones were determined by Marsh cone test, mortar strength and shrinkage test, respectively. The mechanism and microstructure of binder with ground limestones was studied using XRD, SEM-EDS, and IR. The concrete containing ground limestone were prepared by improved absolutely volume method. The durability of concrete containing ground limestones was studied by the acid, alkali, salt erosion test, freezing and thawing test and the chloride ion penetration test. The pore structure of concrete containing ground limestones was studied by MIP and image analysis. The relationship between chloride ion penetration and pore structure was studied by the gray systems theory.The results showed that the compatibility between cement paste with ground limestones and polyaliphatic-type superplasticizers was better than the other superplasticizers, the fluidity of paste gradually increased as ground limestone content increasing. The strength ratio of the sample with 30% ground limestone was 80.3% at 1 day. The drying shrinkage rate of cement mortar increased with ground limestone content increasing, while the drying shrinkage rate was less than 0.1% when the sample containing 30% ground limestone for 28 days. The hydration heat of the cement reduced 21% by mixing 30% ground limestone.There were some hydration products in the cement paste with ground limestone, which was Ca4Al2O6?CO3?11H2O with lamellar crystal and irregular arrange. Some calcites were wrapped by the gel and calcium hydroxide crystals, and some calcites were wrapped by the lamellar crystals. The asymmetric stretching absorption frequency of Si-O of cement containing ground limestone didn't shift to higher wave number within 90 days, and the ground limestones didn't change the polymerization degree of cement hydration products structure.The durability experiments showed that the concrete with finer ground limestone didn't have significant corrosion, but the concrete with coarse one had obviously been corraded by acid. No corrosion was found when concrete dipped in the alkali and high concentration salt solution. The maximum mass loss of concrete was 3.84% after 200 freeze-thaw cycles, but the concrete with complex minerals was less than the 2.0%. The chloride ion diffusibility coefficient reduced to less than 1.0×10-12m2/s as curing time increased, ground limestone fineness increased, or complexed with other mineral addtives.Pore struture of concrete containing ground limestone were studied at one dimension level, two dimensions level, and three dimensions level. The results showed that surface fractal dimension (roughness) ranged from 1.000 to 1.053, the roughness of concrete with ground limestone was larger than that of concrete without mineral additive. The pore axis fractal dimension (tortuousness) ranged from 2.390 to 2.444, the tortuous of concrete with ground limestone was large due to the ground limestone grain characteristic. The pore volume fractal dimension (spatial distribution) ranged from 3.067 to 3.188, the spatial distribution of concrete increased with ground limestone.According to the grey relational theory, the chloride permeability of concrete with ground limestone was closely related to the pore roughness, tortuous and spatial distribution, and the significant sequence of three impact factors were the tortuousness, the spatial distribution, and the roughness.