Research On Performance Of C30 Machine-made Sand Self-compacting Concrete

It is difficult for concrete to vibrate manually in engineering parts such as shallow buried excavation and tunnels.Self-compacting concrete solves the difficult problem of vibrating in these projects through its high fluidity.The amount of cementitious material required for self-compacting concrete is usually higher than that of ordinary concrete,and its strength grade is generally C60 and above.This study explores the self-compacting concrete of C30 strength grade.Natural river sand is generally used to prepare the fine aggregate of self-compacting concrete.However,river sand resources are on the verge of exhaustion in recent years,and people’s awareness of environmental protection has been continuously strengthened.It has become an inevitable trend to replace natural river sand with machine-made sand.The quality of machine-made sand in Chongqing is generally low.The difficulty and innovation of this research are to prepare self-compacting concrete with better workability with machine-made sand.After preparing self-compacting concrete that meets the requirements of workability and mechanical properties,this study explored the influence of six different factors on the work performance and mechanical properties of machine-made sand self-compacting concrete.The main research contents are as follows:(1)Refer to the absolute volume method in the "Technical Regulations for the Application of Self-compacting Concrete"(JGJ/T 283-2012)to design the concrete mix ratio,but the performance of the prepared concrete mixture cannot reach the technical indicators,and the orthogonal test is used to combine the volume Method to optimize the mix ratio;(2)Design an orthogonal test for the fluidity of the pure slurry to determine the optimal ratio of mineral admixtures to replace cement.Take fly ash,slag,and stone powder as the three factors,and perform orthogonal tests with different admixtures as levels to determine The preferred dosages of the three mineral admixtures of fly ash,slag powder and stone powder are 10%,15% and 10% respectively;(3)Substituting the optimal mineral admixture ratio into the self-compacting mortar test,it is found that the fluidity and compressive strength of the mortar are better.After weighting its workability and compressive strength,the mortar volume fractionΦs is selected as 0.45;(4)Substitute the volume fraction of machine-made sand into the volume method to prepare self-compacting concrete with different volume of stones,preferably the volume of the stones is 0.32m3;(5)The study found that the water-binder ratio of C30 machine-made sand self-compacting concrete is 0.46.When the total amount of cementitious materials in the test is 438kg/m3,the concrete slump expansion reaches 650 mm,and its compressive strength exceeds the formulated strength by 38.2MPa.Use this group of concrete mix ratio as the benchmark control group test mix ratio;(6)After preparing self-compacting concrete with machine-made sand with better working performance,this study explored the water-binder ratio,the amount of cementitious material,the powder content,the gradation and sand ratio of machine-made sand,and the coarse aggregate in the concrete.The influence of porosity and other factors on its working performance and mechanical properties;(7)The workability and compressive strength of the 6 different influencing factors will meet the required mix ratio,and 6 self-compacting concretes will be prepared and then the durability test will be conducted;(8)The impermeability and shrinkage performance of C30 machine-made sand self-compacting concrete prepared with 6 different mix ratios in this study can meet the technical requirements.