Experimental Study On The Mix Design Of PK-3 Composite Slab Concret

The continuous acceleration of urbanization of our country drives the development of assembly building and pushes the innovation of assembly building.The new PK-3 type steel tube truss prestressed concrete composite slab（PK-3 composite slab for short）has been popularized nationwide due to its advantages of free formwork,good integrity,convenient construction,short construction period,less support,no filling empty slab and so on,which puts forward higher requirements for concrete mix ratio design of composite slab production.In actual production,there are problems such as the reduction of concrete strength due to the addition of more water for rapid construction,or the poor working performance and low production efficiency of concrete due to the reduction of water consumption for ensuring the strength.Therefore,it is of great significance to prepare concrete with excellent workability,economy,durability and mechanical properties by designing the mix according to local raw materials and studying its workability and mechanical properties.TThis subject relies on Shandong One Stare Construction Technology Co.,Ltd.,for the actual production of raw materials and according to the production demand design mix ratio,and the admixture optimization,the workability and mechanical properties of a series of studies.Firstly,the effects of sand replacement rate with different mechanism on slump,compressive strength,tensile strength and high temperature performance of concrete were studied.It is found that with the increase of the replacement rate of machine-made sand,the slump and expansion of concrete gradually increase,the empting time is gradually shortened,the strength of concrete gradually increases at the 1st and 3rd days,and the strength increases first and then decreases at the 7th and 28th days.The strength is the highest when the replacement rate is 60%.The high temperature test shows that the addition of machine-made sand has no obvious effect on the hydration process,and the concrete strength can be improved mainly by improving the aggregate strength and optimizing the mixing of granulator.The comprehensive analysis shows that it is feasible to replace river sand with machine-made sand in the production of PK-3 composite slab.The influence of concrete mix parameters（water-binder ratio,sand rate,fly ash content and mineral powder content）on workability（slump,spread degree and slump cylinder inverted emptying time）and mechanical properties（compressive strength and splitting tensile strength）of concrete is further studied.The single factor test results show that the properties are best when the water-binder ratio is 0.36,the sand rate is 47～49%,the fly ash content is15%and the mineral powder content is 10～15%.Through the design of four factors and four levels(L₁₆（4）⁴)orthogonal test,according to the range analysis and comprehensive consideration of workability,strength and engineering production needs,finally determined the water-binder ratio of 0.36,sand rate of 47%,fly ash content of 15%（78 kg/m³）,mineral powder content of 10%（52 kg/m³）.Aiming at the problem of poor workability of concrete in the process of mix ratio design,the compound optimization of admixtures was carried out.Three factors and four levels(L₁₆（3⁴）)orthogonal test was designed to study the effects of the mixing amount of 6-carbon water-reducing mother liquor（6C-PC）,6-carbon slump-proof mother liquor（6C-BT）and concrete viscosity regulator（ZN-Z）prepared from new EPEG macromonomer on slump,elongation,time loss and 28-day compressive strength of newly mixed concrete.Through range analysis and comprehensive consideration of various properties,it was determined that the substitution rate of 6C-PC and 6C-BT were 75%and the content of ZN-Z was 4%.The synergistic effect of the three admixtures could improve the initial and 30 min slump and expansion,reduce the time loss,optimize the workability,and improve the 28 d compressive strength.In this thesis,the final mix ratio is applied to the production line of Shandong One Star Construction Technology Co.,Ltd.The field use shows that the concrete has good fluidity,no bleeding subsidence phenomenon,the material cutting machine is convenient,the construction difficulty of workers is low,the speed is fast,the strength of the field sample after the test block meets the requirements,the mix ratio is successfully applied to the production.Cost analysis shows that the cost of the mix ratio in this thesis is reduced by 71.56 yuan,and the economy is better.The MIP test shows that the internal pores of the concrete in this thesis are more dense.The carbonization test shows that the mass growth rate and strength growth rate of the original concrete after carbonization are greater than that in this thesis.After 28 days of carbonization,both of them have about 1%mass growth,and the strength growth rate after 28days of carbonization is 12.07%and 10.07%,respectively.On the whole,the carbonation depth of the original mix ratio concrete is slightly larger than the mix ratio in this thesis.SEM microcosmic results show that the longer the carbonation time,the denser the internal structure of concrete,and the smaller the difference in the internal structure of concrete under two mix ratios.