Microstructure Design Of Aggressive Ion Transport Inhibitors And Their Property Modulation Of Cementitious Materials

In the harsh marine environment,aggressive ions such as chloride ions invade the surface of steel bars,induce corrosion of steel bars and deterioration of concrete,and eventually lead to failure and damage of reinforced concrete structures in service.Therefore,delaying the transport rate of aggressive ions in concrete is essential to improve the durability of reinforced concrete structures,and the development of efficient and controllable aggressive ion transport inhibition technology applicable to reinforced concrete systems has become a hot research topic in the field of concrete durability.Aggressive ion transport inhibitors are a class of amphiphilic polymers that modulate the water and ion transport properties of cement concrete,and are an innovative way to enhance the durability of concrete.In this paper,the design of aggressive ion transport inhibitors is deepened to the micro and nano levels,and the model of aggressive ion transport in the pores of cement-based materials is constructed using molecular dynamics,and the mechanism of aggressive ion inhibition of amphiphilic polymers is investigated to establish the correlation between molecular conformation and inhibition efficiency and propose optimized molecular structure conformations.On this basis,the composites of calcium silicate hydrate gel（C-S-H）and inhibitors were synthesized,and the microstructure and interaction mechanism of C-S-H and inhibitors were characterized by comprehensive use of modern testing techniques.Finally,the inhibitor was incorporated into the cement paste to comprehensively evaluate the modification effect on the mechanical properties,hydrophilicity and hydrophobicity,pore structure and transport properties of the cement paste.The main results of this paper are as follows:（1）Based on the molecular dynamics technique,the nano-action mechanism of the aggressive ion transport inhibitor was revealed,the correlation between the molecular structure of the inhibitor and the ion transport performance was established,and the optimization method of the inhibitor based on the number of amphiphilic polymer carboxyl groups was proposed.Molecular simulation studies have shown that the oxygen atom（Op）in the deprotonated carboxyl group of the inhibitor and the calcium ion(Ca²⁺)in the matrix can bond strongly,allowing the inhibitor molecule to adsorb firmly to the C-S-H surface,while the hydrophobic group acts as a"water-repellent brush",preventing the penetration of aggressive ions and water molecules.The number of oxygen-containing deprotonated carboxyl hydrophilic groups in the inhibitor polymer molecule determines the water-blocking effect of the aggressive ion inhibitor.With the increase of the number of deprotonated carboxyl groups,the water-blocking effect of the inhibitor was enhanced,and the best inhibition was achieved when the polymer contained two deprotonated carboxyl groups.However,polymers containing a higher number of hydrophilic groups did not consistently improve the corrosion inhibition effect.The reason for the molecular configuration is that with an increased number of hydrophilic groups,the inhibitor molecules tend to interact more with water molecules and free themselves from the solution,and the anchoring effect of the inhibitor at the C-S-H interface is weakened,thus failing to exert sufficient water-blocking effect.Considering the inhibition efficiency and the cost of multihydrophilic group development,the inhibitor is the most cost-effective when the number of deprotonated carboxyl groups is 2.（2）Based on the optimal molecular configuration,an inhibitor of ion transport（TIA401）was designed,and a composite of C-S-H gel and inhibitor（C-S-H/T）was synthesized.The mechanism of the influence of the inhibitor on the chemical composition,microstructure and morphological characteristics of the synthesized C-S-H was systematically investigated by a combination of SEM,XRD,TG,XPS and other tests.XRD,TG and XRF tests showed that the synthesized hydrated product C-S-H was C-S-H（I）with a purity of over 96%.The degree of stacking and aggregation of the hydration product of C-S-H/T after the introduction of inhibitor is more dense compared to that of the undoped C-S-H gel,the[002]crystalline surface spacing of the C-S-H layer spacing becomes smaller,the layer spacing is reduced,and the degree of crystallization is increased.Meanwhile,the introduction of TIA401 affects the reaction process and phase composition of the hydration products,and the calcium ions in the C-S-H gels combine with the inhibitor hydrophilic group,which promotes the dissolution of calcium ions and further induces the formation of calcium hydroxide crystals.（3）TIA401 inhibitor was incorporated into the cement paste,and the macroscopic mechanical and transport properties of the cement paste were investigated from 0%to 10%of TIA401 inhibitor,and the mechanism of the effect of TIA401 on the cement paste was analyzed in depth by microscopic experimental studies.It was found that the water absorption of net cement paste decreased significantly with the increase of inhibitor admixture.Compared with the control group,the initial water absorption of net cement paste at 28 days of age could be reduced by up to 92.1%and the saturation water absorption could be reduced by up to 83.6%.At the same time,the admixture of the inhibitor did not significantly change the strength of the net cement paste,with the 28-day compressive strength fluctuating within 7Mpa,under the premise of significantly improving the impermeability of the cement paste.The internal contact angle between water and cement paste gradually increased to 82.6°with the admixture amount,and no significant change occurred after the admixture amount reached 6%.The microscopic morphology study found that the microscopic morphology of the paste did not change significantly under the low inhibitor dosing.With the increase of inhibitor doping,the gel paste tends to be dense,but excessive inhibitor doping will lead to a decrease of the dense surface of the paste.The hydration product content was quantified by thermogravimetric analysis,and it was found that the inhibitor doping could promote the generation of calcium hydroxide,resulting in a lower calcium-silica ratio of C-S-H in the paste.Finally,the pore structure of the inhibitor modified slurry was characterized by BET method,and it was found that the hydrophobic part of the inhibitor has air-entraining effect,which makes the net cement paste introduce smaller pores and reduces the average pore size of the cement paste,and the average pore size reaches the lowest at 6%of inhibitor admixture,which is 46.127（?）.When the admixture is relatively large,the pore capacity and average pore size of the slurry increase,and considering the performance and structure comprehensively,6%is the best amount of inhibitor doping.In this paper,the constitutive relationships and microscopic mechanisms of action of aggressive ion transport inhibitors are investigated comprehensively and the inhibitory effects of modified cementitious materials are evaluated by means of molecular simulations,microscopic characterization and macroscopic tests.The research results are useful as a guide for the design of highly durable reinforced concrete materials under harsh marine environments.