Study On The Influence Of Manufactured Sand Characteristics On The Working And Mechanical Properties Of Concrete

With the rapid development of infrastructure,concrete dosage increased and the required amount of sand and gravel are also increased dramatically in recent years.Reasonable distribution and quality project of natural sand resources have been difficult to meet the increasing demand.To meet the construction industry of fine aggregate demand rigidity,manufactured sand instead of natural sand gradually become the preferred.However,depending on engineering experience or in accordance with the relevant regulations of natural sand,manufactured sand and natural sand themselves are very different in many aspects,that often lead to the manufactured sand concrete performance may not meet the expectation.In order to fully understand the difference between the effect of manufactured sand and river sand on concrete performance,this paper studies the basic physical properties of manufactured sand and natural river sand that including the analysis of particle grading,particle morphology,angular properties,apparent density and other physical properties of the two kinds of sand.Through experimental study to further reveal the manufactured sand concrete and the influence law of natural river sand concrete performance,in use in the test of coarse aggregate limiting grain size of 40 mm secondary macadam.This paper mainly explores the unit water consumption,sand ratio,water cement ratio,key parameters,such as stone powder content on manufactured sand and river sand secondary concrete and concrete working performance,rheological properties,mechanical properties,dry shrinkage properties,pore structure and interface transition zone,the main contents are as follows:(1)The physical properties of limestone manufactured sand and river sand were tested by image analysis method,angular test and scanning electron microscopy.The differences in particle grading,particle morphology,angular test and apparent density were studied and analyzed.The results show that the screen residual of 2.36mm manufactured sand is 24.7%,which is much higher than 14%of river sand.The sieve size of particles below 0.15mm was 10%,which was 3.6%higher than that of river sand.In the range of 0.3mm to 0.6mm,the screen residual of particles was 27.9%,which was much lower than 41.2%of river sand.The grain size of manufactured sand showed typical gradation characteristics of "larger at both ends"and "smaller in the middle".In addition,there are more needle-rod particles of manufactured sand,the surface is more rough,and the river sand particles are closer to the spherical shape.(2)The effects of stone powder content(0%,5%,8%,12%,15%),unit water consumption(170kg,180kg,190kg,200kg),sand ratio(36%,38%,40%,42%,44%)and water-cement ratio(0.35,0.45,0.55)on the slump of concrete mixture were studied through 50 groups of slump tests of manufactured sand and river sand concrete mixture.The results showed:Along with the increase of the manufactured sand stone powder content in the appropriate improve concrete sheet for water consumption,and reduce sand ratio appropriately,according to the test results and refer to the ordinary concrete unit water use and the calculation method of stone powder content,put forward the suitable for selection manufactured sand concrete unit water use of correction formula and stone powder content and the function relation between the optimal sand ratio.(3)The rheological parameters were used to further characterize the working performance of the mixture.The test results show that under different sand ratios(36%,38%,40%,42%,44%),with the increase of stone powder content(0%,5%,8%,12%,15%),the yield stress decreases at first and then increases,and the plastic viscosity increases slowly and steadily at first and then increases sharply.When the water-cement ratio changes,the rheological parameters of concrete mixture with manufactured sand change more widely than that with river sand.(4)The results show that the strength of concrete with manufactured sand and river sand is significantly higher than that of concrete with river sand at the same water-cement ratio and with appropriate stone powder content and sand percentage.On the basis of the relevant test data in this paper,a total of 10 groups of 120 data in the literature of manufactured sand with water-cement ratio between 0.3 and 0.6 were counted by reference.Through regression analysis,the linear function relationship between the water-cement ratio and the compressive strength was obtained,fcu,0=0.398·fb(C/W+0.276).(5)Combined with the test results of working performance,mechanical performance and drying shrinkage performance of manufactured sand concrete,it is concluded that there is an optimal stone powder content for manufactured sand concrete under different strength grades,and the optimal stone powder content increases with the increase of water-cement ratio.When the water-cement ratio is 0.55,the optimal stone powder content is about 12%.When the water-cement ratio is 0.45,the optimal stone powder content is about 8%.When the water-cement ratio is 0.35,the best content of stone powder is about 5%.(6)Through the drying shrinkage of the manufactured sand and river sand concrete performance test,studied the different stone powder content(0%,5%,8%,12%,15%)and different water cement ratio(0.35,0.45,0.55)influence on drying shrinkage of concrete performance,the results showed that the age 14 days ago,the different stone powder content in the manufactured sand the drying shrinkage of concrete were higher than river sand concrete;Under different water-cement ratios(0.35,0.45),there exists a critical stone powder content(8%,12%),and the drying shrinkage reaches the maximum under this critical stone powder content.During the 7d age,the drying shrinkage of manufactured sand concrete increases gradually with the increase of stone powder content,while after 7d,the drying shrinkage of manufactured sand concrete increases first and then decreases with the increase of stone powder content.