Preparation And Mix Proportion Optimization Of High Performance Underwater Anti-washout Concrete

So far,concrete is still one of the most important and used construction materials in underwater engineering.Compared with ordinary underwater concrete,underwater anti-washout concrete overcomes the poor resistance of ordinary concrete to water washing,easily pollutes the environment,and requires special equipment.It can be directly poured in water,and it is not easy to disperse and segregate.And strength,is called "new,ideal,epoch-making concrete" by scholars at home and abroad.At present,the strength of the existing underwater anti-washout concrete at home and abroad is mostly concentrated below C30.With the exploration of the deep sea and the construction of the islands and reefs in the South China Sea in the future,the demand for high-strength and workable underwater anti-washout concrete engineering is increasing.In view of the main problems existing in the research and application of C40 ?C50 underwater anti-washout concrete at present,this paper takes polyacrylamide as the main anti-washout agent and polycarboxylic acid superplasticizer as the auxiliary agent,selects the optimum amount of the main agent and the admixture and the optimum amount of the auxiliary agent through the tests of cement paste,mortar fluidity and anti-washout ability,and explores the mechanism of the action of polyacrylamide The experiment of the fluidity and anti-washout ability of the underwater anti-washout concrete with different forming conditions and different ages adjusts the content of the main agent,and further optimizes the anti-washout ability,strength,anti freezing and anti permeability of the underwater anti-washout concrete by adding mineral admixture;analyzes the action mechanism of the mineral admixture in the underwater anti-washout concrete by SEM and XRD;Finally,2.1adopt to analyzed by fractal theory Based on the theoretical analysis of aggregate bulk density and void ratio in the fractal dimensions of 2.1,2.3,2.5,2.7 and 2.9,the pore structure and void ratio of underwater anti-washout concrete in different gradation fractal dimensions are analyzed by nano X-CT,and the best gradation fractal dimension is selected,and the scientificity of aggregate gradation fractal is verified.The main conclusions are as follows:(1)When the molecular weight of polyacrylamide is low,the fluidity of cement paste increases first and then decreases with the increase of the content of polyacrylamide,and there are different optimal content of different molecular weight,for example,when the content of 8 million molecular weight polyacrylamide is 0.6%of the weight of cement,the fluidity of cement paste reaches the best,when the content of 10 million molecular weight polyacrylamide is 0.4%,the fluidity reaches the best.When the molecular weight of polyacrylamide is high,the fluidity of cement paste decreases with the increase of polyacrylamide content.The possible reason for this phenomenon is that the interaction between the long chain structure of polyacrylamide and free water increases the apparent volume of free water at low molecular weight.In high molecular weight,the long chain of polyacrylamide is connected and twined with each other to form a relatively rigid flocculation network and prevent the movement of free water.(2)The anti-washout ability of cement paste,mortar and underwater anti-washout concrete increases with the increase of polyacrylamide content,and decreases with the increase of water reducing agent content.When the content of polyacrylamide is 0.5% of the quality of cement and the content of water reducer is1.5% of the quality of cement,the anti dispersion and fluidity of slurry are the best.The fluidity of cement paste is very sensitive to the content of high molecular weight polyacrylamide,even if the content of polyacrylamide changes by 0.1%,the fluidity of mixture will change significantly.(3)The compressive strength and anti-washout ability of the underwater anti-washout concrete will be improved by adding silica fume alone,but the fluidity will be reduced significantly.When the content of fly ash is 20% of the quality of cement,and the content of silica fume is 4% of the quality of cement,it can overcome the shortcomings of single mixing.Its workability and early strength are better than that of single mixing.Its slump and slump expansion can reach 220 mm and 458 mm.Its turbidity and p H value are 102 ntu and 11.62.Its fluidity and dispersion resistance are good.The early(7d)compressive strength of the test block formed in water and on land is respectively 5.3MPa?31.5MPa.(4)The aggregate gradation is quantitatively characterized by fractal theory.The porosity of the underwater anti-washout concrete increases with the increase of the fractal dimension of the aggregate;when the fractal dimension of the aggregate grading is 2.5,the aggregate bulk density is the largest and the void ratio is the smallest.Although the porosity is large,most of them are small holes with less large pore structure.It is confirmed by X-CT that the aggregate area of each section is evenly distributed,indicating that when the fractal dimension is 2.5,the aggregate is evenly distributed and well graded.(5)Compared with the existing grading theory,such as Fuller's,Lin Xiuxian's and particle interference's,this paper verifies the scientificity of grading fractal theory,and applies it to the design of underwater concrete mix proportion to prepare high performance water with good fluidity,anti dispersion and compressive strength up to C40 The concrete is not washout and has high strength on land and water.Its frost resistance grade can reach F150.