Study On Regulation Mechanism Of Interfacial Transition Zone In Foam Concrete

Foam concrete has the functions of fire proofing,lightweight,porous and thermal insulation.It has less resource consumption,less energy consumption in the preparation process and less toxic emissions during the service process.Now it has developed into the largest application in special concrete.Unlike conventional concrete or lightweight aggregate concrete,the fresh foamed concrete paste is supported by the precast foams formed by liquid film wrapping air,and the aggregate of hardened air is fixed in the cement matrix.There have been a lot of research reports on the structure,performance and their interaction of aggregate,cement mortar and cement slurry aggregate interface transition zone in concrete.The relevant theories are relatively mature and have guiding value for practice.However,for foam concrete,the interaction between precast foam which considered as aggregate and cement paste,and the interfacial transition zone's composition,formation process and macro performance resulting from the interaction between them are still the research difficulties in this field.In this paper,the preformed foam formed by foaming agent was regarded as"aggregate",and the relationship between foaming agent and preformed foam,the interfacial interaction between the preformed foam and cement paste,and the formation and evolution of the interfacial transition zone between the air and cement paste in the hardened foam concrete were studied.The results obtained are as follows:Compared with the properties of foaming agent and cement paste,the interaction between foaming agent and cement paste had greater influence on the state of precast foam in cement paste,the stability of fresh foam concrete and the pore structure of hardened foam concrete.In the fresh foam concrete paste,hydrated ions produced certain hydrophobic protein chelated calcium,calcium dodecyl sulfate and other substances in the surface of liquid membrane of precast foam,which enhanced the film formation performance.On the other hand,the cement particles that had adsorbed the foaming agent had a certain hydrophobicity,which let them firmly adhere to the surface of the precast foam.The precast foam was more stable in the fresh foam concrete,and the denser pore wall in the hardening foam concrete could be obtained through the above two functions.A large increase in surface tension of foaming agent after the mixing of cement paste lead to an increase in density of foam concrete.The low density foam concrete collapsed easily.Prolonging the mixing time may help to improve the stability of fresh foamed concrete paste.When the interaction between foaming agent and cement was weak,the cement paste had little influence on the surface tension of foaming agent,and the density of the foamed concrete was low.The cement was not easily adsorbed on the surface of cationic and non-ionic surfactant solutions.The pores of the new foamed concrete slurry were separated by thin liquid membrane.Ettringite and calcium hydroxide formed and grew in the loose hole wall.When the liquid film was thin enough,the pores of the hardened foam concrete penetrated through each other to form open foam concrete.From foam concrete forming to hardening to use,the pore interface composition and pore structure changed with the hydration of cement and environmental changes.The degree of hydration of cement in the interfacial transition zone of foam concrete and the ratio of pore less than 30 nm had an important influence on the properties of foam concrete.The interface transition zone of ordinary concrete had a similar effect on the properties of concrete.The performance of foamed concrete was also affected by its interface or interfacial transition zone.The dense interface helped to improve the mechanical properties and thermal insulation properties of foam concrete.The performance of foam concrete can be improved by the improvement of its interfacial transition zone.A certain amount of nanoparticles combined with foaming agent improved the stability of precast foam,and also promoted the hydration of cement in the interfacial transition zone,thereby improving the mechanical properties of foam concrete.Solution cure improved the interfacial composition of foam concrete,and effectively improved the adsorption of foam concrete on Sr²⁺and Cs⁺.The adsorption effect of sodium carbonate on foam concrete was the best.By adding OP-10 into the hydrolyzed protein solution,closed-cell foam concrete was transited to open-cell foam concrete.With the increase of OP-10content,the preformed foams had better stability in cement paste.When preparing low volume density foam concrete,the pore in foam concrete was transformed from separate closed pore to connected pore,and the shell structure around the pores became loose until it vanished.