Experimental Study On Fracture Performance Of Nano Metakaolin Cement Mortar

In actual engineering,due to some defects of the cement-based material itself,the influence of the design and construction process,the change of the external load or the temperature change may cause the fracture of the cement concrete structure,and thus the durability of the structure And bearing capacity will have varying degrees of impact.Tests and engineering practices have shown that by adding mineral admixtures to cement-based materials,mechanical properties and durability can be improved.nano metakaolin(NMK)is an extremely fine-grained nano-material made of meta-kaolin.It can replace part of the cement clinker,promote the cement hydration reaction,and improve the pore structure by filling the pores between the particles.Combining with the existing domestic and international nano-kaolin clay mechanical properties test research,as well as the three-point bending test of cement concrete materials,this paper carried out the nano metakaolin cement mortar mechanical properties test and three-point bending test research,the main research results are as follows:(1)The prismatic cement mortar flexural test and the cement mortar cube compressive strength and other physical performance tests are used.The prismatic cement mortar bending test and the cubic cement mortar compression test were used.The flexural strength,compression ratio,and cubic compressive strength of ordinary cement mortar and nano metakaolin cement mortar with different dosages were obtained respectively.The effect of nano-sized kaolin on the mechanical properties of cement mortar is also discussed.(2)Based on the three-point bending test,the experimental process of three-point bending test of ordinary cement mortar and nano metakaolin cement mortar at different dosages was studied,and the corresponding load is obtained?The displacement(P??)curve obtains the load peak Pmax and the displacement deformation corresponding to Pmax,and calculates the fracture energy GF of the cement mortar.The notched three-point bending is obtained by the relationship between the strain above the prefabricated crack tip and the sides and the time The cracking load of the beam is Pinr.(3)Calculation of fracture mechanical parameters of nano metakaolin cement mortar.CTODc(Critical Crack Tip Opening Displacement)obtained from P-CTOD curve,CMODC(Critical Crack Opening Position)obtained from P-CMOD curve.The elastic modulus,effective crack length ac and double K fracture parameters of the mortar in the test are calculated according to relevant literature and fracture mechanics related formulas.The relationship between the nano-meta kaolinite dosage and these fracture mechanical parameters is established to obtain the fracture mechanical parameters characterizing the cement mortar.The prediction model of the development law between the amount of nano metakaolin.(4)Calculation of cohesive toughness KIcC of cement mortar.The cement toughness KIcC of cement mortar was calculated by Chebyshev numerical integration method,binary Larangian interpolation method and three-parameter law.Discuss the influence of nanometer metakaolin content on cement mortar cohesive toughness KIcC,and compare the error effects of the three calculation methods,find the better calculation method from Chebyshev.numerical integration method and binary Lagrange interpolation method to make the result The error is minimal.