Study On Manufactured Sand Concrete Of Composite Cement Material System:Performance And Mix Proportion Design

The research of manufactured sand concrete is beneficial to promote the application of manufactured sand in concrete,and effectively solves the impact of river sand resource shortage on infrastructure construction.In addition,the admixtures in manufactured sand concrete is very commonly used.The impact of various admixtures on the performance of concrete is also an urgent problem to be solved.There is a lack of systematic research on the influence of mix proportion factors on the performance of manufactured sand concrete.The conventional design methods of concrete mix proportion fail to consider the influence of manufactured sand ratio,stone powder content,etc.on concrete.A proper design method for modern manufactured sand concrete is of great significance to the practical engineering.Therefore,the influence rules of mix proportion factors including water-binder ratio,sand ratio,manufactured sand gradation,stone powder content,fly ash content,mineral powder content,etc.on the performance of manufactured sand concrete were studied,and a design method for the mix proportion of manufactured sand concrete of composite cement material system was proposed in the thesis.The main work and conclusion of the study are as follows:(1)The influence rules of water-binder ratio on the workability and compressive strength of manufactured sand concrete were investigated,through which the increased water-binder ratio within a certain range is found to be favorable to the workability of manufactured sand concrete,but adversely affects the concrete strength.As a result,the preferred water-binder ratios for C30 and C50 manufactured sand concrete are 0.40 ? 0.42 and 0.30 ? 0.32 respectively.Meanwhile,to accurately calculate the water-binder ratio in manufactured sand concrete mix proportion design,the C30 and C50 manufactured sand concrete strength were combined with the analysis of water-binder ratio test results,the conventional Bolomy equation was modified,and the stone powder influence coefficient was innovatively proposed.(2)The proper range of sand ratio was determined through studying the influence rule of sand ratio on the workability and mechanical properties of manufactured sand concrete,which are 46% ? 48% and 43% ? 45% for C30 and C50 manufactured sand concrete,respectively.In addition,to ameliorate the gradation property “a large portion at both ends and a small portion in the middle” of the manufactured sand,different portions of 0.30 mm ? 2.36 mm intermediate particle sized manufactured sand(medium sand)were added to replace the original manufactured sand,which results in an optimized gradation.It is concluded that the increase of the medium sand substitution ratio within a certain range is advantageous to the concrete workability,however,has little effect on the mechanical properties of concrete.As a result,the proper substitution ratio of medium sand is 66%.(3)The influence of the mixing amounts of stone powder,fly ash and mineral powder composite cement material system on the workability and mechanical properties of manufactured sand concrete were studied,it shows that when the mixing amounts of stone powder,fly ash and mineral powder increase,the workability and mechanical properties of manufactured sand concrete improve.When the proper range is exceeded,however,the performance of concrete is undesirable.The properly selected mixing amounts of stone powder,fly ash and mineral powder for C30 and C50 manufactured sand concrete were analyzed to be: 8% ? 16%,5% ? 10%,10% ? 20%,respectively.(4)Considering the particularity of stone powder as an admixture,a modified equation of unit water consumption for manufactured sand concrete was proposed,by studying the influence rule of the mixing amount of stone powder on the slump of manufactured sand concrete.A modified equation of the sand ratio for manufactured sand concrete was proposed,according to the influence rule of the mixing amount of sand ratio on the slump of manufactured sand concrete.Finally,a design method for the mix proportion of manufactured sand concrete of composite cement material system were developed.