Preparation And Engineering Application Of Medium-low Strength High-performance Concrete With Manufactured Sand

The mass medium-low strength concrete is used in many civil engineering projects,such as highway and bridge projects,and more attention is paid to its durability.On the other hand,with the excessive consumption of natural sand,the manufactured sand has become an inevitable trend to replace natural sand to prepare concrete.The project of Xiushan-Yinjiang expressway of the fifth company of China construction fourth engineering bureau,which has contracted to build multitudinous tunnels and bridges,and most of the concrete used is medium-low strength concrete of manufactured sand.Therefore,it is necessary to study the application of manufactured sand in the medium-low strength high-performance concrete.Aim at this problem of manufactured sand,the mix proportion of medium-low strength high-performance concrete is investigated systematically,and the optimum mix proportion was determined.In view of the low activity of fly ash,mineral admixture compound and modifiers are used in manufactured sand concrete to improve the concrete function.At the same time,the effects of the shrinkage,water permeability resistance,and freezing and thawing resistance of high-performance concrete with manufactured sand are studied.The major results by this paper are follows:（1）By adjusting the gradations of coarse aggregate,the manufactured sand concretes are prepared.According to its workability and compressive strength,the best gradation of coarse aggregate is determined.（2）By investigating the effects of cement content,fly ash content,manufactured sand ratio,and superplasticizer content on workability and compressive strength of manufactured sand concrete,the reasonable ranges of high-performance are determined.According to the reasonable ranges of high-performance concrete,the orthogonal test are designed to prepare concrete.And the optimum mix proportion are determined according to the range analysis of its workability and compressive strength.（3）In order to improve the performance of high-performance concrete,the technology of mineral admixtures compound is used to increase the content of mineral admixtures,reduce the content of cement.When 15%fly ash and 15%phosphorous slag powder are added,the performance of medium-low strength high-performance concrete is better than the concrete with fly ash alone.The early strength of high-performance concrete is increased by 19.0%and 14.7%respectively when 1%Na₂SO₄is added into the concrete.The 28d compressive strength meets the medium-low strength high-performance concrete requirements.（4）Through the study of the shrinkage,water permeability resistance,and freezing and thawing resistance of the medium-low strength high-performance concrete with manufactured sand,it’s found that the shrinkage of the concrete in 150 days is in the range of（210～270）×10^-6.Under the pressure water,there is no water penetration,and the water penetration height is below 10cm.After 300 freezing-thawing cycles,the frost resistance grade of concrete is F300.According to the situation of the site,the best mix proportion of medium-low strength high performance concrete with manufactured sand mixed by fly ash is used in the project.The concrete mix proportion was adjusted and successfully applied to the piers of Shancha bridge.The workability,compressive strength and surface state of the concrete meet the engineering requirements.