Study On Physical And Freeze-Thaw Resistance Properties Of Rice Straw Mortar Composites

Crop straw resources are rich and widely distributed,with an annual collection and utilization of 900 million tons,in China.There are still many problems in treatment and utilization of straw.The straw has high tensile strength,as a kind of aggregate,combined with cement,gypsum and other bonding materials,which can improving the flexural strength,impacting resistance of the benchmark materials and controlling the initiation and propagation of microcracks.However,it is necessary to study the main factors affecting the physical performance of composite materials systematically;due to the influence of factors such as the properties of straw,the bonding properties of the matrix material and the environmental conditions,the physical properties of straw composite building materials are quite different.In this paper,cement and gypsum were used as basic cementing materials,adding amounts of sand and rice straw fiber mixed to rice straw mortar composites.The three factors of gypsum content（₁x）,straw length（x₂）and straw content（₃x）were taken as the influencing factors of response surface analysis,and the three-factor and three-level regression analysis was carried out by using Design-Expert software to obtain the optimal mix ratio of materials.At the same time,the quadratic polynomial fitting regression equations was established to obtain the optimal material mix ratio.In addition,considered the special environment in winter of northeast China,the materials exposed to the natural environment will be eroded by snow water,causing damage.In this case,the freeze-thaw cycle test was carried out,the mass loss rate and the compressive strength loss rate are taken as two main indicators to determine the frost resistance of materials.The relevant conclusions are shown:（1）The optimal mix ratio of rice straw mortar composites was following:the ratio of rubber to sand was m（cement）:m（sand）=1:3,gypsum content was 15%,straw length was 20mm,straw content was 15%,the compressive strength was 3.06 MPa,the density was 1340kg/m³,and the water absorption rate was 20.8%,which met the building requirements of mortar M2.5 and by calculating the wall constructed by the material blocks can support the gravity load and can be used as the non-load-bearing wall to meet the practical application.（2）The mass loss rate and compressive strength loss rate of the rice straw mortar composites increased with the increasing of freeze-thaw cycles,and the straw content had an impact on the mass loss rate and loss rate of compressive resistance of the materials.When the ratio of rubber to sand was m（cement）:m（sand）=1:3,gypsum content was 13.3%,straw length was 20mm and straw content was 16.3%,the quality loss rate and strength loss rate of the materials were the lowest,which were 2.2%and 34.2%respectively.The strength loss rate of the material under this condition was too much,but it still retained a certain strength,which could be used as a non-load-bearing wall.