The Influences And Mechanism Of Corosion Inhibitors On Resistance Of Concrete To Chloride

Chloride ions induce steel corrosion in the reinforced concrete,and further cause concrete cracking,which reduce the bearing capacity of the concrete structures and affect the service safety,shorten the service life.Nanomaterials and hydrophobic materials were used as transport inhibitors to low down the chloride diffusion coefficient and improve the chloride ion penetration resistance to concrete.However,the influences of components and functional groups of transport inhibitors on the chloride transport is not clear,the interaction mechanisms between transport inhibitors and concrete matrix are not well understood,which seriously restricted the research and engineering application of transport inhibitors.In this paper,calcium stearate(Cast),carboxylic acid alkanolamine salt(TIA)and organic carboxylate polymer(HPE)were screened out as representative chloride transport inhibitor materials,and their influence on chloride ion transport was studied,their mechanism of inhibiting chloride penetration was explored,and molecular dynamics simulation were performed to reveal the mechanism of the inhibition chloride transport in concrete due to transport inhibitor materials with different functional groups from the C-S-H gel scale.The effect of calcium stearate on the chloride corrosion resistance of concrete was studied,and the mechanism of hydrophobic effect improving the chloride corrosion resistance of concrete was revealed.Calcium stearate reduced the water absorption,chloride migration coefficient,chloride diffusion coefficient and electric flux of concrete,and lowered down the chloride ion content of concrete in marine environment.The optimum dosage of calcium stearate was about 4% in the test dosage range.The addition of 4% calcium stearate reduced the electric flux of concrete by 15%,the chloride migration coefficient by 7% and the chloride diffusion coefficient by 26%;at the same time,the compressive strength was reduced by about 24%.The addition of calcium stearate increased the contact angle of the cement pastes,deteriorated the pore structure of the cement pastes,and increased the total porosity and the most probable pore size.The contact angle and pore size distribution together determine the transport of water and ions in concrete.The pore water filling factor was proposed to characterize the influences of contact angle and pore size distribution on the water transmission path in concrete.The pore water filling factor is positively correlated with the diffusion of chloride ions.Adding 4% calcium stearate increased the contact angle of the cement paste to 62°,reduced the pore water filling factor by about 19%.The influence of TIA on the chloride corrosion resistance of concrete was studied,and the mechanism of hydrophobic effect improving the chloride corrosion resistance of concrete was revealed.The addition of TIA reduced the water absorption of concrete,and the reduction effect was more obvious with the increase of the amount of TIA;addition of 1.2% TIA reduced the water absorption of concrete by about 44%.TIA reduced the chloride migration coefficient,electric flux and chloride ion content of concrete.Addition of 1.2% TIA reduced the chloride diffusion coefficient of concrete by 48% and the chloride ion content by 30%.TIA participated in the hydration reaction process of cement,slightly diminished the hydration degree of cement,increased the total porosity and the most probable pore diameter of cement pastes,and addition of1.2% TIA reduced the compressive strength of concrete by about 11%.TIA improved the chloride ion corrosion resistance of concrete mainly because TIA increased the contact angle of cement pastes,enhanced the hydrophobicity of concrete,dwindled the connectivity of capillary water path in concrete,and finally inhibited the transmission of water and chloride ions in concrete.The addition of 1.2% TIA increased the contact angle of cement pastes to about 85°,increased the most probable pore diameter of cement pastes from 11 nm to 15 nm,reduced the pore water filling factor by 31% and promoted the resistance of concrete to chloride penetration.The effect of HPE on the chloride corrosion resistance of concrete was studied,and the mechanism of the synergistic effect of hydrophobicity and compaction to improving the chloride corrosion resistance of concrete was revealed.The addition of HPE reduced the water absorption,chloride migration coefficient and electric flux of concrete,and the reduction was more obvious with the increase of the dosage within the test range;HPE had little effect on the compressive strength of concrete.The addition of 1.2% HPE reduced the water absorption of concrete by 52%,the chloride diffusion coefficient by 77%,and the chloride ion content in concrete was about 40%of the reference group.HPE generated hydrophobic films in the cement pastes,which increased the contact angle and augmented the hydrophobicity;meanwhile,HPE reduced the total porosity and the most probable pore size of the cement pastes and optimized the pore structures.Hydrophobicity and compactness work together to reduce water transport and chloride penetration.Molecular dynamics simulations were used to investigate the effect of transport inhibiting materials on the transport properties of C-S-H gel pores.The calcium atoms in the calcium stearate molecule interacted with the oxygen atoms in the silicon-oxygen tetrahedron inside the calcium silicate hydrate,calcium stearate adsorbed on the C-S-H surface,and the hydrophobic long-chain alkanes extended into the gel pores,which increased the contact angle.The amine group in TIA formed a hydrogen bond network with C-S-H.The hydrogen bond was broken under the attack of the hydroxyl group and hydrogen ion in the etching solution,and TIA was desorbed and aggregated at the front of the etching solution to form a water blocking medium;meanwhile,the alcoholamine ion transport inhibitors had a certain complexation with chloride ions to inhibit the migration of ions.The carboxylic acid-ether group of the main chain of HPE formed a calcium-oxygen bond with C-S-H.When there were no water molecules in the C-S-H gel pores,HPE was adsorbed on the surface of the calcium silicate hydrate matrix;when the aqueous solution invaded the gel pores,the hydrophobic groups of HPE were perpendicular to the C-S-H surface and hindered the transport of the solution.