Mix Design And Performance Research Of Ultra-high Strength Self-compacting Concrete

In the 21st century,with the rapid expansion of urban scale,continuous development of infrastructure and acceleration of urbanization,ordinary concrete can no longer fully meet the needs of high-rise,super high-rise,super span,irregular structure and complex engineering,ultra-high strength self-compact concrete has become one of the development directions of concrete technology.The preparation of ultra-high strength self-compacting concrete is difficult,and the properties of raw materials in different regions are different.Most of the preparation is based on experience,and no systematic theoretical method has been formed.In the preparation of ultra-high strength concrete,in order to meet the requirements of ultra-high strength,blindly reduce the water binder ratio,so the water consumption is very low.The fluidity of newly mixed concrete mainly depends on the strong adsorption dispersion lubrication effect of high efficiency water reducing agent,which is easy to produce problems such as high viscosity,slow flow and difficult pumping,and even cause dangerous accidents such as pipe blocking and pipe bursting,which seriously affect the construction safety.In view of the large amount of cementing materials,low water-binder ratio,high viscosity and poor construction performance of ultra-high strength self-compacting concrete,this paper studies the compounding technology of water-reducing water reducing agent,the composition of cementing materials of ultra-high strength self-compacting concrete and the lithology selection of sand and stone aggregate.At the same time,the influences of water-binder ratio,slurry bone ratio,sand rate and water consumption on the performance of ultra-high strength self-compacting concrete are also studied.Finally,the microstructural characteristics of ultrahigh strength self-compacting concrete and ordinary concrete at different ages are compared,and the following conclusions are drawn:Based on the mother liquor of polycarboxylic acid highly adaptable water reducing agent,single-component test and orthogonal test were carried out by using the method of"elimination before introduction"to determine the air entraining agent as the key viscosity reducing component,and the optimal mix ratio of viscosity reducing water reducing agent was obtained:mother liquor of polycarboxylic acid highly adaptable water reducing agent:defoamer:air entraining agent:rheological agent=1000:0.4:0.4:15,its solid content is 40%,water reduction rate is 35.8%.The effects of different dosage of silica fume,microbeads,gradeⅠfly ash and grade S105 ore powder on viscosity,fluidity of cement paste and bending and compressive strength of 3d and 28d mortar were studied.The results show that silica fume and S105 grade mineral powder can increase the viscosity of cement paste and reduce the fluidity.Microbeads and GradeⅠfly ash can reduce the viscosity of cement paste and increase the fluidity,which are the key viscosity reducing components.All the four mineral admixtures can improve the 28d strength of cement sand,and silica fume is the key strengthening component.Combined with the orthogonal test,the optimal proportion relationship of superhigh strength self-compposing concrete cementing materials is obtained:P·Ⅰ52.5 cement:silica fume:microbeads:Ⅰgrade fly ash=60%:10%:15%:15%.The influence of limestone machine-made sand,granite machine-made sand and basalt machine-made sand on the fluidity and strength of mortar is studied.The results show that limestone machine-made sand has the best fluidity and strength.The MB values of the three lithologic sand were studied,and it was found that the MB values of the limestone sand were the lowest and the adsorbability was the lowest under the same content of stone powder.The influence of limestone machine-made sand with different content of limestone powder on mortar fluidity and strength is studied.It is concluded that mortar fluidity and strength are the best when the content of limestone machine-made sand is 4%.In the design of ultra-high strength self-compactness concrete mix,the fine aggregate should choose limestone machine-made sand,and the content of stone powder should not exceed 4%.The influence of coarse aggregate of limestone,granite and basalt on the workability and compressive strength of concrete is studied.Combined with the apparent texture and basic performance indexes,it is found that granite has the highest strength,less surface defects,dense structure,and more similar to the strength of hardened slurry.The deformation of the two rocks is similar,and the overall force is uniform,and the prepared concrete has the highest strength.In the mix design of ultra-high strength self-compacting concrete,granite should be selected as the coarse aggregate,and its suitable size range is 5mm～16mm.The effects of water binder ratio,slurry bone ratio,sand rate and water consumption on the performance of ultra-high strength self-compacting concrete were studied.When the water-binder ratio is in the range of 0.18～0.22,with the increase of water-binder ratio,the workability of concrete gradually increases,the compressive strength gradually decreases,and the shrinkage rate gradually increases.When the ratio of pulp to bone is between 30:70 and40:60,the workability and shrinkage of concrete gradually increase with the increase of pulp to bone ratio.The 28d compressive strength first increases and then decreases,and reaches the highest point when the ratio of pulp to bone is 36:64.When the sand rate is 36%-44%,the workability and compressive strength of concrete first increase and then decrease with the increase of sand rate,and the shrinkage rate has no obvious change.When the water-binder ratio is 0.18 and the unilateral water consumption is 116kg/m~3～132kg/m~3,as the unilateral water consumption increases,the workability,shrinkage rate and compressive strength of concrete gradually increase,but the increase is not obvious.When the unilateral water consumption exceeds 130kg/m~3,the 28d compressive strength hardly increases.Ultra-high strength self-compacting concrete mix ratio:The amount of cementing material should be within 640kg/m~3～760kg/m~3;The ratio of plasma to bone should be 34:66～37:63;Sand rate should be 40%～42%;When the water-binder ratio is 0.18,the water consumption should be 116kg/m~3～130kg/m~3.For concrete with cementing material content ranging from 640kg/m~3 to 700kg/m~3,the water-binder ratio should not exceed 0.21,and for concrete with cementing material content ranging from 700kg/m~3 to 760kg/m~3,the water-binder ratio should not exceed 0.22.Eight groups of ultra-high strength self-compacting concrete were selected for the chloride ion penetration test and sulfate attack resistance test.It was found that the electric flux of concrete was between 300C and 800C,and the sulfate corrosion resistance coefficient was much higher than 75%,which met the durability requirements.Through scanning electron microscopy(SEM),X-ray diffraction(XRD)and mercury injection test(MIP),it can be seen that the 28d hydration products of ultra-high strength self-compactous concrete are more,forming a dense whole with cementing materials.The total pore volume,total pore area,porosity and harmful porosity are far less than ordinary strength grade concrete.