Multi-Functionalization Of Cement-Based Materials Surface Through Nano-Engineered Releasing Agents

Concrete is used for various construction projects,and its quality pays attention to the finishing surface.The concrete surface is crucial to durability because of the onslaught of hazardous materials from the harsh environment.Concrete surfaces were treated to preserve their aesthetic value and resilience while preventing the intrusion of harmful contaminants.For a good quality concrete surface,organic releasing agents were used to ensure that the concrete could easily detach from mold without damaging the concrete surface.However,organic releasing agents negatively impact concrete fundamental qualities.In this work,novel nano-engineered releasing agents have been developed（physical mixing of special nanoparticles with a releasing agent）by taking advantage of nano-engineering on cement to cope with the problems mentioned.In the first work,in order to decrease the inhibition effect of releasing agent on the hydration of concrete surface,the use of nano-silica（NS）and nano-titanium dioxide（NT）was designed to modify releasing agent.These nanoparticles have been used to address the fundamental defects of organic releasing agents in concrete.5wt%releasing agent was added into cement paste/mortar to simulate its effects on cementitious materials at the superficial layer when applied to formwork.Results showed that incorporating nanoparticles into Ra could produce a good dispersion with ultra-sonication.Adding 4wt%NS and 16wt%NT into Ra can improve the compressive strength of mortar by 28.2%and 38.1%.Meanwhile,they decrease the water absorption rate to 41.9%and 46.2%to that of the control sample（mortar with Ra）.Hydration heat calorimetry results demonstrated that the reaction of RA-added cement could be accelerated by nanoparticles,resulting in the microstructure’s enhanced compactness（MIP）.This work shed light on the nano-modification of concrete surfaces in a comfortable,efficient,and economical way.Secondly,the aggressive substances can gain access to the inner structure of cement-based materials through the surface,resulting in the deterioration of the structure.Continuing with simulation work,the positive effects of nano-Si O₂-/nano-TiO₂-engineered releasing agents on cement hydration were used to improve the surface quality of the cement-based samples through its spraying on the mold surface.This work firstly characterized the adhesive properties of these agents on mold surface（contact angle and viscosity measurement）,and then their effects on the surface microstructure and the durability of cement-based materials such as 1)sulfate resistance,2)chloride resistance,and 3)freeze-thaw resistance were determined.Results showed that nanoparticle addition increased the contact angle of releasing agents and helped their adhesion to mold.Applying n SRa/n TRa on cement-based samples benefited the reduction of surface porosity（within 2 mm thick）by 14.2%,19.4%,8.6%,and 18.9%in the n S2Ra-,n S4Ra-,n T4Ra-and n T16Raengineered samples.After 120 days of sulfate attack,mortar samples cast in Ra-,n S4Ra-,and n T16Ra-coated molds showed reductions in compressive strength loss of 1.57%,0.73%,and0.23%.Noticeable reductions in the chloride migration coefficient of 23.9%and 26.6%were found in the n S4Ra-/n T16Ra-modified mortar sample,while their relative dynamic modulus elasticity was 6.72%and 12%higher than Ra-sample after 200 freeze-thaw cycles.This work proved that nano-engineered releasing agents could effectively improve the durability of the concrete structure.Thirdly,environmental pollution such as industrial waste（Organic and Inorganic pollutants）harm the attractiveness of concrete skin,and further toxic elements infiltrate the concrete structure from its surface,limiting the service life.This study considers nano-TiO₂-engineered releasing agents to modify concrete surfaces by brushing the mold surface.As a result,the photocatalytic efficiency of the modified surface was lower due to its larger band gap（3.34 e V）,which activates in the UV region and the agglomeration of particles.Moreover,this study aims a novel MOF-structured composites NH₂-Mil-125（Ti）（MOF）and NH₂-Mil-125@TiO₂ were designed and synthesized via a simple solvothermal method for functionalization of the concrete structure with aid of releasing agent（adding NH₂-Mil-125（Ti）or NH₂-Mil-125@TiO₂ into a vegetable oil-based releasing agent by physically mixing）.The photocatalytic property of the MOF-based derived engineered releasing agents（MOF-Era）was studied after they were brushed on the surface of concrete mold（before casting concrete）.While mechanical properties and hydration degree were analyzed by adding an admixture into white cement paste.Based on the findings of the mechanical strength tests,the addition of Comp-Ra0.4wt%（NH₂-Mil-125/TiO₂0.4wt%of the cement,added into releasing agent）raises the strength by 43.5%compared to Vo-Ra,which contributes to accelerator hydration kinetics.The T-Ra0.05（NT 0.05wt%of the cement,added into releasing agent）,MOF-Ra0.05（NH₂-Mil-125（Ti）0.05wt%of the cement,added into releasing agent）,and Comp-Ra0.05（NH₂-Mil-125/TiO₂0.05wt%of the cement,added into releasing agent）increase the28-day mechanical strength but have a negligible effect at early ages（3,7 days）.After 28 days,the FT-IR results show that T-Ra（NT-based engineered releasing agent）,MOF-Ra(（NH₂-Mil-125（Ti）-based engineered releasing agent）,and Comp-Ra（NH₂-Mil-125/TiO₂-based engineered releasing agent）are present after the harsh weathering process.The excellent performance of Comp-Ra0.4with rhodamine-b degradation is 70%,while MOF-Ra0.4（NH₂-Mil-125（Ti）0.4wt%of the cement,added into releasing agent）and T-Ra0.4（NT 0.4wt%of the cement,added into releasing agent）shows 48%and 59%in UV-visible light.