Effect Of Graphene Oxide On Structure And Properties Of Cement-based Composite

Cement-based composites is the most versatile and has the greatest consumption in construction engineering field at present,and the development trend is high performance(high strength,high toughness,high volume stability,high crack resistance,high permeability)and high durability.The main weakness of present cement-based composite is the existence of cracks,pores and leakage in its structure,affecting the strength and durability of the composites,and so how to solve this problem has been a hot topic in this field.The cracks,pores and leakage of the composites are caused by the irregular morphology and aggregation mode of its hydration products,which results in the inhomogeneity and uncompactness of microstructure and macrostructure.At present,no feasible method has been found to eliminate cracks and leakage.However,the main components and hydration products of cement have the inherent nature of crystalline materials,and it is possible to form regular crystalline material through regulating cement.Therefore,it is of great significance for solving the existing problems of cement-based composites and achieving high performance and durability to adjust the morphology and aggregation structure of hydration products to form a regular,compact and defect-free microstructure and macrostructure with crystal structure characteristics.Graphene oxide(GO)is a kind of layered two-dimensional nanomaterial and there are a large number of oxygen-containing groups on the surface and edge of the layer.These groups could react with cement and so GO can be incorporated into cement-based composites to regulate the morphology and structure of cement hydration products.Previous studies have found that GO has the capability to regulate cement-based composites to form regular structure and significantly improve its strength and durability.On the basis of our group's previous research,this study focused on the effects of sheet layer size,oxygen level and dispersion degree of GO on cement hydration products,microstructure and properties of cement-based composites,and the formation mechanism of microstructure of the composites under GO control was explored.Meanwhile the treatment scheme of wastewater from Hummers method preparation process of GO was put forward and the treatment effect and benefit were also analyzed.The main content of this study is as follows:(1)Three kinds of GO solutions(GO size are respectively 5-140,5-260 and 5-410 nm)were prepared by using the Hummers method and ultrasonic stripping procedure,and then three kinds of cement-based composites with the different size of GO were also prepared at 0.03% GO dosage.The influence of GO size on the hydration products,microstructure and mechanical properties of the composites was studied by employing scanning electron microscope(SEM),thermogravimetric analyzer(TG),X-ray diffractometer(XRD),Fourier transform infrared spectrometer(FTIR),flexural and compressive strength tester and mercury injection tester.The results of SEM test show that GO with a size of 5-140 nm could transform cement hydration products into regular acicular crystals,the microstructure and macrostructure presenting regular interwoven morphology formed by acicular crystals.The GO with the size of 5-260 nm or 5-410 nm enables hydration products to form flower-like and polyhedral crystals,and the microstructure and macrostructure are regular and dense structure morphology formed by the interlacing of flower-like crystals.TG examination results show that the regular structures of calcium silicate gel(C-S-H)and calcium hydroxide(CH)in the composites increase as the size of GO increases from 5-140 nm to 5-260 nm and to 5-410 nm.XRD investigation results show that the grain size of CH decreases and the crystallization degree of C-S-H increases with increasing GO size.The results of FTIR test show that the regularity and compactness of the microstructure of cement-based composites increase with an increase of GO size.The test results of pore structure,mechanical property and durability of cement-based composites show that the adding of GO is conducive to improving the pore structure of the composites,reducing porosity,and enhancing the strength,toughness and durability.The composites with 5-410 nm GO has better structural regularity,strength,toughness,pore structure and durability than those with the composites with GO of 5-260 nm or 5-410 nm.(2)GO with the oxygen levels of 18.50%,22.50% and 26.85% as well as the size of 5-140 nm were prepared by using Hummer method and controlling potassium permanganate dosage.The cement-based composites containing GO with oxygen content of 18.50%,22.50% and 26.85%,were prepared at 0.03% GO dosage,and the influence of GO oxygen content on the hydration products and their aggregate structures as well as compressive strength,flexural strength and durability of the composites was studied.The results show that GO with the oxygen content of 18.5% enables the hydration products to form nanometer acicular crystals,presenting regular,uniform and compact microstructure through the growth and aggregation of the acicular crystals.GO with the oxygen content of 22.50% or 26.85% enables hydration products to form flower-like and rod-like crystals,which grow and aggregate to form regular structural morphology.With the increasing of GO oxygen content,the crystal hydration products in cement increase,and the regularity and compactness of cement-based composites increase.The cement-based composites with GO significantly has more superior pore structure and pore distribution as well as more advanced strength,toughness and durability.The GO with a size range of 5-410 nm and an oxygen content of 26.85% has the most significant effect on the improvement of the pore structure,strength,toughness and durability of cement-based composites.(3)The intercalatin composite GO/P(AA-AM)was prepared by free radical polymerization using GO(size is 5-410 nm and oxygen content is 26.85%),acrylic acid(AA)and acrylamide(AM)as raw materials,and GO dispersion solution with the GO of small size and few layers was obtained.The GO in the intercalated composite had a size range of 5-200 nm and was mainly single-layer and double-layer.GO/P(AA-AM)was used for the preparation of cement-based composites,and the influence of GO/P(AA-AM)on the structure and performance of the composites was studied.The results show that GO/P(AA-AM)has a significant effect on the hydration products and their crystals as well as the microstructure of the composites.When directly adding GO dispersion solution into cement-base composites,the cement hydration products mainly exhibit acicular and polyhedron crystals.The crystals are uneven,and their aggregate forms weak regularity and order of microstructure with more pores.This illustrates the unideal dispersion of GO in the cement.On the contrary,when adding GO/P(AA-AM)into cement-base composites,the cement hydration products mainly form rod-shaped and polyhedral hydration crystals having more quantity and uniform distribution.The aggregates of the hydration crystals show regular and orderly microstructure with high regularity and order,which indicates that GO is well dispersed and evenly distributed in the composites.Compared with cement-based composites with GO dispersion solution,the composites with GO/P(AA-AM)exhibits more superior strength,toughness and durability.(4)GO/P(AA-AM)cement-based composites(GO content is 0.03%)was prepared and the mechanism of GO regulating cement microstructure was studied.The results show that under the control of GO sheet the cement hydration products mainly form regular polyhedral hydration crystals,and the compact,regular microstructure and macrostructure with flower-like morphology are formed through the growth,interlacing and cross-linking of hydration crystals.GO nanosheets play template and regulation role to hydration products and microstructure.Finally the mechanism of GO regulating microstructure was put forward.(1)GO can join and promote hydration reaction through many active chemical groups in its molecule.GO nano sheet layer plays a template role to the structure and morphology of hydration products and furthers hydration products to form compact and uniform microstructure with regular morphology.Eventually GO can adjust the growth of hydration products to form interlaced and crosslinked cement-based composites with regular and compact structure.(2)The large strength and toughness of GO as well as its regulation function to cement structure can improve the mechanical properties and durability parameters of cement-based composites.So GO can significantly improve the performance of the composite by regulating the formation of regular,compact and even microstructure.(5)The physicochemical method was adopted to treat the wastewater generated in the preparation process of GO by Hummers method,mainly including the removal of sulfates and nitrates in the wastewater and the recovery of manganese oxides,and the treatment effect and benefit were analyzed.The results show that nitrates are mainly removed by neutralization reaction tank,and the removal rate is 82.5%.Manganese salts are mainly removed from the neutral reaction sedimentation tank,and the removal rate is 81.5%.Sulfate are removed in alkaline reaction sedimentation tank,and the removal rate is 81.0%.The operation cost of the whole process is 43.5 yuan/ton of water,and the treated wastewater meets the three-level discharge standard.