Research On Design,Performance And Mechanism Of Polymer Powders Modified High Toughness Concrete

Cement concrete is a kind of brittle material with high compressive strength but poor flexural strength and toughness,which can not meet the higher requirements of flexural strength and toughness of cement concrete for long-span bridges and other projects.At the same time,the toughness of cement concrete slab is insufficient,which is inconsistent with the deformation of bridge deck bonding layer,and the slab bottom is void,which will also aggravate the occurrence of various diseases of cement concrete structures.Therefore,improving the toughness of cement concrete has important practical significance for enhancing the flexural tensile strength of cement concrete structures,improving the cracking phenomenon caused by shrinkage stress,reducing the risk of slippage and delamination of bridge deck pavement,and prolonging the service life of cement concrete structures.In this paper,three different types of polymer powder（ethylene vinyl acetate polymer powder,styrene butadiene polymer powder and styrene acrylate polymer powder）were selected.The proportion of different types of polymer powder modified cement-based composites was designed by orthogonal test.The effects of three kinds of polymer powder on the mechanical strength and physical properties of cement-based composites were studied,and the optimal proportion of different polymer powder modified cement-based composites was determined;Using polymer powder modified cement-based composites,river sand,fiber and polycarboxylate superplasticiser as raw materials,the mix proportion of polymer powder modified high toughness concrete（HTC）was designed by orthogonal experiment.The effects of three kinds of polymer powder on mechanical properties and durability（frost resistance,salt frost resistance,drying shrinkage,sulfate corrosion resistance,chloride ion penetration resistance and carbonation resistance）of HTC were studied;Through comparison,the mix proportion of HTC modified by polymer powder with better comprehensive performance was put forward;the micro morphology and internal pore structure of HTC modified by polymer powder were analyzed by scanning electron microscope（SEM）and mercury intrusion porosimetry（MIP）,combined with the macro performance of polymer powder modified HTC,the action mechanism of polymer powder modified HTC was discussed.The results show that the flexural strength of cement increases significantly with the addition of three kinds of polymer powder,but the compressive strength decreases.Among them,the flexural strength of cement-based composites with styrene butadiene polymer powder is the highest,followed by ethylene vinyl acetate polymer powder and styrene acrylic polymer powder.Polycarboxylate superplasticizer is used in concrete preparation,and the amount of sand is reduced,which makes HTC modified by polymer powder different from that of cement-based composites modified by polymer powder.The results show that the compressive strength of HTC decreased and the flexural strength and the folding-compression ratio increased with the addition of three kinds of polymer powder;the flexural strength,the flexural compression ratio and the toughness coefficient of HTC modified by styrene acrylic were the highest,followed by those modified by styrene butadiene and ethylene vinyl acetate.The optimal mix proportion of HTC modified by styrene acrylic polymer powder is:cement of 680 kg/m³,silica fume of 200 kg/m³,polymer cement ratio of 10%,NS of 1%,water binder ratio of 0.2,sand binder ratio of 1.1,polycarboxylate superplasticizer of 2%and fiber of 2.5%.The results show that the polymer powder can obviously improve the frost resistance,salt frost resistance,drying shrinkage,sulfate corrosion resistance,chloride corrosion resistance and carbonization performance of HTC.The reason is that the polymer powder can form a network structure with ettringite and fill the loose structure of Ca（OH）₂ to make it more dense.At the same time,polymer powder particles can play the role of bonding and filling to HTC matrix,reduce the gap between cement matrix and river sand interface transition zone,improve the pore structure,reduce the number of harmful holes,and make HTC matrix more dense.