Effect Of Manufactured Sand On Workability,Mechanical Properties And Durability Of Self-Compacting Concrete

The natural river sand was used to fine aggregate for traditional self-compacting concrete?SCC?.However,in recent years,the ban and restriction for river sand excavation due to environmental grounds caused the shortage of natural sand.So,it has become an inevitable trend for manufactured sand to prepare concrete.The existing research is mainly focused on the preparation method,optimization of the mixing ratio,and the working ability.However,some factors such as raw materials and production processes influenced manufactured sand products,and caused great differences in quality indicators such as lithology,grain shape,and gradation by different production process in different production places.So,it is necessary to analyze the quality indicators of typical manufactured sand products in Shandong and their impact on the performance of SCC in order to guide the production use of manufactured sand in Shandong.In this thesis,the impact crushed limestone manufactured sand which provided by Shandong Luzhu Group is taken as the research object.Based on a comprehensive comparison of differences for lithology,grain shape,and gradation between manufactured sand and river sand,the research studied the effects of manufactured sand on SCC including workability?fillability,passing ability?,mechanical properties?compressive strength,flexural strength?and durability?resistance to chloride ion permeability,resistance to carbonization?.It also studied the influence of stone powder content in mechanism sand on the concrete durability and the SCC pore structure which studied by the mercury intrusion test?MIP?.The main research conclusions are as follows:?1?Compared with river sand,the gap ratio of manufactured sand reduced 7%,and the grain shape is rough and polygonal,which makes the fluidity of concrete slightly lower,and the slump expansion reduced 5%,but the cohesiveness improved significantly and improves the J-ring passing capacity of the manufactured sand SCC by more than 28%;the coarse and angular grain shape of the manufactured sand particles can strengthen the bonding interface between the sand particles and the hardened cement paste.Produce interlocking effect and produce large mechanical meshing force,which can significantly improve the mechanical properties of concrete.The increase in compressive strength and flexural strength are more than10%and 15%,respectively;the interlocking effect between manufactured sand particles makes the increase in the flexural strength of manufactured sand is greater than that of compressive strength;compared to river sand SCC,the total pore volume of hardened slurry,pore volume of more than 50nm,D_RCM,and carbonization depth at 28d of manufactured sand SCC reduced10%,19%,7%,and 5%respectively.It can be seen that the coarse and angular sand is beneficial to the compactness of the concrete,thereby improving the durability of the concrete.?2?The stone powder content in the manufactured sand increased from 8%to 12%after keeping the sand rate unchanged,which increased the powder content of the concrete system,and at the same time increased the water demand of concrete,so that the manufactured sand from the dense concrete cohesion increased,and the J-ring passage capacity increased by about20%.The stone powder content in the manufactured sand from 8%to 12%,will reduce the content of the manufactured sand particles in the SCC,weakening the manufactured sand particles of the skeleton role;the manufactured sand in the stone powder contains more clay minerals,will weaken the adhesion of the gelling material and aggregate interface transition area,not conducive to the mechanical properties of the manufactured sand SCC,so that the compressive strength and flexural strength reduced 3%and 6%respectively,but compared with the SCC of the river sand,the compressive strength and flexural strength increased 3%and 9%respectively.The manufactured sand contains a certain amount of stone powder,which can optimize the pore structure of the hardened slurry,the stone powder content in the manufactured sand increased from 8%to 12%,the total pore volume of the manufactured sand SCC hardened slurry reduced by more than 10%,the pore volume of harmful pores and harmful pores reduced by nearly 20%,which significantly improves the durability of the manufactured sand SCC,D_RCM reduced by about 8%,28d carbonation depth reduced by more than 7%.?3?The total porosity of manufactured sand SCC has a negative correlation with its compressive strength and flexural strength.When concrete is subjected to external load,the greater the porosity,the more likely it is that stress concentration would occur,which would cause the SCC to reduce its bearing capacity and reduce its mechanical properties?compressive strength and flexural strength?.The total porosity of the manufactured sand SCC has a positive correlation with the unsteady chloride ion mobility coefficient and the carbonation depth at 28days.The greater the porosity,the more susceptible the concrete will be to corrosion by chloride ions and CO₂ gas.?4?As the age of concrete increases,the pore volume of less harmful and non-hazardous pores in SCC gradually decreases,and the relative proportion of harmless and harmless pores continues to increase.It shows that as the age increases,the hydration reaction continues,and the pores filled with hydration products gradually transform the harmful pores and multiple harmful pores of the SCC into less harmful pores and harmless pores.