Study On Mechanical Properties And Durability Of Nano SiO₂ Modified Flyash Ceramsite Concrete

In this paper,the research on nano-materials and ceramsite concrete is summarized.Based on the goal of high strength and light weight of concrete,combined with saline soil conditions and severe cold environment in Northeast China,experimental study on the mechanical properties and durability nano-silica modified fly ash ceramsite concrete was carried out.The experimental studies in this paper include some aspects follows.(1)Orthogonal experiments were designed with water-binder ratio(0.32,0.35,0.38),cementitious material(405 kg/m~3,435 kg/m~3,465 kg/m~3)and sand ratio(30%,35%,40%).The influence of each factor level in the test range was obtained.The following benchmark ratio C1W3S1(water-cement ratio 0.38,cementitious material405kg/m~3,sand ratio 30%)and C2W2S2(water-cement ratio 0.35,cementitious material 435kg/m~3,sand ratio 35%)were selected for the subsequent experiment.(2)The splitting tensile strength,axial compressive strength,static modulus of elasticity and cubic compressive strength at 3d?7d?14d?28d?56d ages of fly ash ceramsite concrete with different nano-silica content were studied.The stress-strain curves are plotted.It is found that the optimum content of nano-silica is 2%.Neural network is used to predict the strength of concrete at different dosage of nano-silica and at different ages.The mechanism of modification of fly ash ceramsite concrete by nano-silica was analyzed by scanning electron microscopy.(3)The salt corrosion resistance and freeze-thaw resistance of fly ash ceramsite concrete with 0%and 2%nano-silica were studied.The concentration of substances in salt solution was 0.35mol/L in the experiment.The complex salt solution is a mixture of sodium sulfate solution and sodium carbonate solution of equal volume.Sixty dry-wet cycling tests were carried out on two groups of concrete specimens in sodium sulfate solution,sodium carbonate solution and compound salt solution,respectively.With the addition of 2%nano-silica,the strength loss rates of concrete after 60 dry-wet cycles in three salt solutions are reduced by 2%,1.75%and 0.72%,respectively.It shows that nano-silica can improve the salt resistance of concrete.The freeze-thaw tests of two groups of concrete were carried out in clear water,sodium sulfate solution,sodium carbonate solution and compound salt solution respectively.With the addition of nano-silica,the relative dynamic elastic modulus loss of concrete in four environments is reduced by 5.9%,6.8%,25.4%and 17.1%,and the mass loss is reduced by 65.6%,36.1%,56.6%and 46.3%,respectively.It shows that nano-silica can effectively improve the frost resistance of concrete.(4)Combining with the deterioration mechanism of freeze-thaw damage of concrete,this paper presents the relative dynamic elastic modulus change model of concrete under water freezing and the mass loss model under salt freezing based on damage probability.These provides a reference for the study of freeze-thaw damage degradation law of fly ash ceramsite concrete modified by nano-silica and other concretes.