Experimental Study On Cracking Performance Of Cement Based Material With The Addition Of Nanoclay

Cracks are common in concrete structures such as construction,transportation,ocean,and national defense,which seriously affect the structural bearing capacity and durability.In order to prevent early cracking,adding mineral admixture to cement-based materials is one of the main technical ways to improve crack resistance and durability.Nano metakaolin(NMK),nano Attapulgite Clay(NMA),nano-montmorillonite,and other nano-materials are extremely fine,reaching nanometer scale,can fully fill the pores between the cement particles,promote the cement hydration reaction,enhance the structural compactness and improve the crack resistance of the material.Based on the research status of cracking properties of nano-clay cement mortar(NCM)and nano-clay concrete(NCC)at home and abroad,this paper studies the cracking performance of nano-clay cement-based materials.The main research contents include:(1)Experimental study on dispersibility of nanoclay in water.The uniformity and sedimentation rate of nanoclay in water were observed and analyzed.Combined with TEM experiment,a method for quantitatively describing the gray value of nanoclay suspension was proposed.The particle size relationship of nanoclay agglomerated particles was obtained.(2)Study on mechanical properties of nano-clay cement-based materials.150 specimens of mortar flexural test and mortar and concrete cube compression test were completed.The influence of nanoclay on the mechanical properties of cement-based materials was analyzed,and the relationship between elastic modulus,tensile strength,compressive strength and flexural strength was established.And the strength prediction model for characterizing the strength development of nano-clay cement-based materials was obtained.(3)Experimental study on cracking performance of NCM.The influence of different kinds and different particle sizes of nano-clay on the crack resistance of cement mortar was studied by using the flat blade-induced restraint and ring restraint test.The fractal theory was used to describe the irregularity of the surface crack of the flat specimen,and the relationship between fractal dimension and its mechanical properties was established.It can be used as a non-destructive test for strength.The BP neural network was also used to predict the crack resistance of NCM.(4)Experimental study on mixing process of nanoclay in cement mortar.Using the three mixing processes of ultrasonic dispersion,mechanical agitation and direct dry mixing,45 flat test specimens were produced by the flat blade edge-induced restraint crack test.The effects of different mixing processes on the cracking performance of nano-clay cement mortar were compared and analyzed.The ultrasonic dispersion mixing process is optimal and significantly improves the NCM crack resistance.