Study On Performance And Mechanism Of Concrete With Rice Husk Ash

Rice husk ash(RHA),as a kind of renewable biomass resource,is one of the most important agricultural wastes.There is about more than 40 million tons per year in China.But in the past,rice husk was usually used as fuel,which is burning directly to provide heat.However,the utilization grade is relatively low.The biomass rice husk ash used for improving the high temperature resistance of concrete and insulation material is one of hot issues at present.Through controlling the temperature and burning time,the rice husk can be transformed into highly active mineral admixture,so it has high added value in the water conservancy and civil engineering construction industry,which has large engineering demand.The common mineral admixtures are silica fume(SA),slag(SS),fly ash(FA)and so on.These components mixed with concrete can reduce the dosage of cement and make the production cost lower.Meanwhile,it can improve the durability of concrete.But producing these source with large-scale economic construction is not only a shortage of resources,but also has a potential energy crisis.Therefore,it is an urgent need to find a new type of material,which is easy to obtain and has high quality and low cost and high activity.Rice husk ash is a kind of Reclaimed biomass products from agricultural waste.RHA,the product of burned raw rice husk has a SiO2 content greater more than 90%.Compared with conventional mineral admixtures such as fly ash(FA)and slag,RHA has a huge specific surface area and high activity,which is preferable for active mineral admixture.A huge number of agricultural waste biomass,rice husk in our country can give full play to its inherent potential value,then it can be reused by applying in the production of concrete,not only alleviate the pressure of pollution of rice husk ash in the environment,but also realize the development of circular economy in building materials industry.Thus it has a broad market prospect and important economic significance of environmental protection.In this paper,the industrial and agricultural wastes such as rice husk ash and fly ash in Ningxia were used as the concrete admixture.Based on the particle size distribution,chemi cal composition and microstructure of rice husk ash,using the research methods of combinat ion of macroscopic and microscopic,the physical and mechanical properties of cement mixe d with rice husk ash and mechanical properties,durability,high temperature resistance proper ty,thermal conductivity and the change of microstructure of concrete mixed with rice husk ash are studied.The conclusions are as follows:(1)that water demand of cement increases and setting time extends when higher amou nts of cement were replaced by RHA.It is determined that the best grinding time is 45 mi nutes by testing the strength of the cement mortar.The combination of rice husk ash,fly ash and silica fume can not improve the early strength of cement mortar,but adding a proper amount of admixture can improve the strength of 28d cement mortar.(2)Through the study on the mechanical properties of concrete,the early strength of concrete can not be improved by adding mineral admixtures,but it has significant increase in late strength.The optimum mix proportion of concrete is determined by orthogonal test:water binder ratio is 0.3,rice husk ash content is 10%,the content of fly ash is 15%and the content of silica fume is 5%.And the effects of single rice husk ash,rice husk ash/fly ash,rice husk ash/silica fume and three mineral admixtures on the strength of concrete are analyzed.The 128d intensity of rice husk ash concrete is predicted by using neural network technology.The microstructure of cement paste was tested by SEM microscopic technique.The result show that the microstructure of past with RHA is compacter than that of JZ.Adding RHA can reduce the content of C-H in the paste and refine the C-H crystal in large size.By means of Artificial Neural Network(ANN)method,the strengths of of RHA concrete in 128 days'period are predicted..The predicted results are in good agreement with the measured values.(3)Rice husk ash can improve the sulfate resistance of concrete,and the effect of rice husk ash mixed with fly ash and silica fume is better.The effect of rice husk ash,fly ash and silica fume on the corrosion resistance of concrete was analyzed,and the improvement mechanism is discussed.Based on the experimental results,the concrete strength degradation model of sulfate attack was established and the service lives of various concretes are calculated using this model.(4)The frost resistance of JZ concrete is better than that of concrete with RHA,RHA/FA,RHA/SA,FA/SA and concrete with RHA/FA/SA,but frost resistance of RHA/FA concrete is better than that of concrete with other mixed with mineral admixture,the greater the water binder ratio is,the relative dynamic elasticity modulus and mass loss of concrete is serious declined,and the frost resistance is worst.In three kinds of freezing and thawing medium,the mass loss ratio of concrete in 3.5%NaCl solution is the largest,The loss ratio of the relative dynamic elastic modulus in different solutions ranges in a descendant sequence,from 5%Na2SO4 solution to 3.5%NaCl and then to water.(5)Rice husk ash,fly ash and silica fume used as mineral admixtures can significantly reduce the electric flux of the concrete,With the increase of water cement ratio,the electric flux of the concrete was increased.The electric flux of the concrete with water binder ratio of 0.35 is 2 times of concrete with water binder ratio of 0.3 and the electric flux of the concrete with water cement ratio of 0.4 is nearly 5 times as many as concrete with water binder ratio of 0.3.The electric flux of R20F15S5(20%RHA +15%FA +5%SA)concrete is the lowest,only 160.6 Coulomb and its anti-permeability is the best.(6)The addition of rice husk ash can significantly improve the high temperature performance of concrete.At 800?,the compressive strength of R20F15S5 concrete reaches 36.1 MPa,which is about 2 times of JZ concrete,The effect of rice husk ash on the mechanical properties and heat resistance of concrete was analyzed,and by means of microscopic methods(SEM,XRD,DSC-TG)to reveal the micro morphology and after phase change of concrete after different temperature.(7)The thermal conductivity of concrete is reduced when adding rice husk ash to concrete.With the increase of water cement ratio,the coefficient of thermal conductivity of rice husk ash concrete was decreased.When the rice husk ash amount is 10%,fly ash amount is 15%,the water ratio is 0.3 and the coefficient of thermal conductivity value rice husk ash concrete is 0.2390W/(m·K),reduced by 32.1%.The energy consumption of rice husk ash concrete was analyzed by PKPM software.The building energy consumption is reduced significantly when concrete with rice husk ash as the maintenance of structural materials.This paper enriches the basic characteristics of rice husk ash,the performance of rice husk ash concrete and the mechanism of high temperature thermal reaction,and the research results can provide guidance and basis for further research and application of rice husk ash in water conservancy and civil engineering.