Research On Mechanical Behaviors And Durability Of Rubber Concrete Under Environmental Conditions

Rubber concrete(RC)is a kind of cement based composite material in which some aggregate replaced by recycling tire rubber powder or rubber particle.As a new green engineering material,durability of RC is one of the key issues to decide whether it could be widely used to civil engineering.An exhaustive research,on the basis of climate condition of concrete engineering,is conducted about the resistance of sulfate attacking,impermeability and freezing resistance of RC.The main investigation contents are the following:(1)Rubber powder and rubber particle are used in the experimental research.The biggest grain size of rubber powder is 0.27 mm and the grain size of rubber particle is 3-4 mm.On the basis of orthogonal experimental design method,the mix proportion is designed and the specimens are made.Mechanical behaviors of RC are detected via the experimental research.The effect of different factors on RC mechanical behaviors is investigated.The optimum mix proportion of RC is proposed for meeting different requirements.The results show that the strength of RC is mostly affected by ratio of water to cement.The subsequent factor is rubber content and ratio of sand is the last factor.By modifying mixing strength formula of the ordinary cement concrete,the strength influence coefficient of rubber content ac is proposed and mixing strength formula of RC is obtained.(2)RC specimens with different mix proportion are soaked into 5%Na2SO4 solution in order to detect erosion effect caused by sulfate attack with the increase of corrosion age.On the basis of mixing strength formula of RC,the strength increasing model and the strength decaying model of RC are established under sulfate attack.The models can well reflect the variation of compressive strength with the corrosion age of sulfate attack.The results indicate that rubber powder can improve resistance to sulfate attack when its content is 5%-15%.The specimens can keep excellent condition.The performance of rubber particle concrete is worse than rubber powder concrete.(3)The permeation depth experiment of RC is conducted under constant hydraulic pressure.It is revealed the effect of rubber content,ratio of water to cement and ratio of sand on impermeability of RC.The research demonstrates that rubber content is the most important factor to permeability of RC.When rubber content is 5%-15%,impermeability of RC is better.When rubber content is 20%or more,impermeability of RC will obviously decrease.Impermeability of rubber powder concrete is better than rubber particle concrete.The effect of water to cement ratio on impermeability of RC is consistent with the ordinary cement concrete.on the basis of artificial neural network theory,BP neural network predicting model of impermeability of RC is established,which input variables are rubber grain size,rubber content,ratio of water to cement and ratio of sand.The BP network model can accurately predict impermeability of RC by testing.(4)Concrete quick freezing-thawing experimental method is used to research on freezing resistance of RC.Dynamic elastic modulus and mass loss rate are introduced to reveal damage and deterioration laws of RC under freezing-thawing cycles.According to concrete damage mechanics theory,relative dynamic elastic modulus is determined as damage variable and theoretical analysis is carried out.The frost resisting factor ?and its expression is proposed for different mix proportion concrete.The freezing-thawing damage model of RC is established.The frost resisting factor ? can be regard as evaluation index of its freezing resistance.The model can appropriately describe damage evolution process of RC under freezing-thawing cycles.(5)The research analyzes damage failure mechanism of RC under different conditions.The results reveal that rubber can enhance resistance to sulfate attack,impermeability and freezing resistance of concrete for which rubber can improve its interior pore structure and anti-cracking performance.Rubber is able to fill,obstruct,entrain air and buffer.So it can reduce larger connected pores and increase smaller closed pores.It can also decrease various internal stresses and restrict generation,expansion and extension of micro cracks.There are correlation between resistance to sulfate attack,impermeability and freezing resistance of RC.Especially,Impermeability directly impacts on other two aspects during initial stages.The resistance to sulfate attack,impermeability and freezing resistance of RC with 5%-15%rubber powder is better ensure that its compressive strength decreasing is less than 17%.Therefore,rubber powder concrete can be further popularized and used.