| As a renewable biomass resource,rice straw ash is one of the important agricultural by-products.In view of the environmental pollution caused by the increase of agricultural by-product rice straw at this stage and the increasing demand for composite materials in buildings and structures involved in agricultural engineering,this paper converts rice straw into usable rice straw ash(RSA)to replace cement,and prepares RSA composite material for practical application,to solve the possible environmental pollution caused by crop straw,promote the development of agricultural circular economy and save resources.As a green building material,RSA composite material can be used in solar greenhouse,rice drying pool,farmland canal lining board and other aspects in agricultural construction engineering.Replacing cement with RSA at a reasonable replacement rate can not only reduce the consumption of cement and reduce the pollution and damage to the environment,but also make effective use of the by-products of crops,improve agricultural economic benefits.Around this research purpose,using the research methods of theoretical derivation and experimental comparative analysis,the experimental research on the strength and properties of RSA composite material,the microstructure and strength enhancement mechanism of RSA composite material,and the practical application of RSA composite material were carried out.The main research work in this paper is as follows:1.Study on the properties of cementitious material in RSA composite(1)The calcination test of rice straw was carried out.The results showed that for the same calcination temperature,the amount of RSA decreased with the extension of calcination time;For the same calcination time,the amount of RSA decreased with the increase of calcination temperature,which provided help for the application of RSA.(2)The mechanical property test of RSA cementitious material was carried out.The results showed that with the increase of RSA substitution rate,the water absorption of RSA cementitious material increased and the strength gradually decreased.The decline rate of flexural strength of the test piece was faster than the compressive strength.RSA had a greater impact on the flexural strength than the compressive strength of the cementitious material.Using the characteristics of compressive strength of test piece,RSA cementitious material was applied in practical engineering.(3)Using Matlab software to fit the empirical formula between the amount and strength of RSA,provided reference opinions for the practical engineering application of RSA cementitious material,and provided calculation basis for the decorative surface of farmland canal and farmland drying pool.(4)Through the thermal conductivity test of RSA cementitious material,the results showed that the thermal conductivity of RSA cementitious material was lower than that of ordinary cementitious material,which provided a theoretical basis for the practical application of RSA cementitious material in the decorative surface of solar greenhouse wall.2.Experimental study on mechanical properties of RSA composite(1)The 7-day curing strength test of RSA composite was carried out.It was found that with the increase of substitution rate,the compressive strength of the test piece first increased and then decreased.Among them,the compressive strength of RSA composite with 5% substitution rate increased by 3.2% compared with ordinary composite.When the substitution rate was 10%,15% and 20%,the strength decreased by 7.5%,22.9% and 27.6% respectively.It could be concluded that the general trend of compressive strength change after curing for 7 days was that the compressive strength gradually decreased with the increase of substitution rate.(2)The 28-day curing strength test of RSA composite was carried out.It was found that the compressive strength of RSA composite decreased gradually with the increase of substitution rate,and the compressive strength corresponding to the substitution rate of 5%,10%,15% and20% decreased by 8.3%,16.4%,21.2% and 29.3% respectively.The results showed that the compressive strength and flexural strength of the composite mixed with RSA are lower than those of ordinary composite.RSA composite with a substitution rate of 5% can be used in farmland facility projects such as farmland canal liner.(3)The 128-day curing strength test of RSA composite was carried out.After 128 days of long-term curing,the compressive strength of RSA composite was increased by 14.9% and 9.2%respectively when the replacement rate was 5% and 10%.When the substitution rate was 15%and 20%,the compressive strength decreased by 2.7% and 5.1%.3.Study on mechanical mechanism of RSA composite(1)The stress-strain relationship of RSA composite was studied,and the stress-strain relationship model and damage model of uniaxial tension and compression were established,which provided a theoretical basis for the practical application of RSA composite.(2)Through scanning electron microscope and comparing the micro differences between RSA composite and ordinary composite,it was found that there were more voids in RSA composite than ordinary composite,which was the reason for the low strength.(3)Through the hydration reaction equation of RSA composite,the difference of hydration reaction between RSA composite and ordinary composite was analyzed.Ordinary composite had slightly more hydration reaction products than the former,resulting in slightly lower early strength of RSA composite;However,with the increase of reaction time,additional calcium silicate gel was generated,making the long-term strength of RSA composite prepared by 5% and10% substitution rate higher than ordinary composite.(4)The long-term strength of RSA composite was predicted by Matlab,and the artificial neural network prediction model was established through the test data.Verified by multiple groups of test data,the distribution of the model and the test data basically matched.The prediction model could be effectively applied to the long-term strength calculation of RSA composite,which provided a reference for the actual application proportion.4.Application of RSA composite(1)Based on the application characteristics of RSA composite,the temperature change of solar greenhouse with RSA composite was studied theoretically.The temperature control equation of solar greenhouse was established,the temperature control equation was solved by finite difference method,the simulation program for solving the internal temperature change of solar greenhouse was compiled,and the temperature change law was analyzed.(2)The temperature tests of two kinds of solar greenhouses with different wall decorative surfaces were carried out.Through the mutual verification of the test and numerical calculation results,the daily average temperature of the solar greenhouse with RSA cementitious material as the wall decorative surface was 2-5 ℃ higher than that of the ordinary cementitious material. |
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