Formation Mechanism Of Hydration Microstructure Of Cement-fly Ash Based On Nano-thermal Coupling Effect

As the country vigorously promotes the assembly of buildings,prefabricated concrete components are facing a huge space for development.Prefabricated concrete components have many advantages,such as of convenient construction,stable quality,and cheap.Therefore,prefabricated concrete components have been widely used in the construction industry.Mineral admixtures are important component of concrete which can improve the performance of concrete.However,when incorporation a large amounts of mineral admixtures in concrete,especially fly ash,which is unfavorable to the development of early strength of concrete,make it difficult to achieve the stripping strength,thus affecting the turnover rate of the mold,leading to a lower efficiency of prefabricated concrete components.This paper is based on the Science-Technology Support in Hubei Province,the design and application of long-life concrete surface strengthening materials based on the nano and microscale effect,and National Natural Science Foundation of China,Coupling mechanism of molecular structure between polycarboxylate superplasticizer and hydroxy carboxylic acid salt retarder,the effect of nanomaterials on the hydration properties of the different cementitious materials under steam curing condition was studied.The optimal combination of nanomaterials and cementitious materials was obtained by the test of macroscopic mechanical properties and hydration microstructure.At the same time,we compared the effect of different kinds and content of chemical activators on the fly ash,the excitation mechanism was,in order to provide reference for the application of high volume fly ash in prefabricated concrete components.The conclusions of this paper are listed as follow:1?When mixed with silica sol,after steaming cured,the different cementitious materials mortar stripping strength are higher than the mortar which non-doped silica sol,and with the silica sol content increased from 0% to 4%,the strength of cement-fly ash mortar is always increased,the strength of other cementitious materials mortar is increased first and then decreased;the development of cement-fly ash mortar stripping strength is the most obvious when compare to blank group,incorporation 4% silica sol,the strength increased by about 65%;the silica sol caused more mortar fluidity loss compare with Nano-silica powder,so we need to add more polycarboxylate superplasticizer to maintain the mortar mobility,which is unfavorable to cost.The Nano-silica powder and cement-fly ash system is more suitable for steam curing.2?The influence of Nano-silica powder on hydration microstructure of cement-fly ash system was studied.The stripping compressive strength of cement-fly ash mortar was increased when incorporation Nano-silica powder,when content is 3%,the strength reaches the maximum value of 11 MPa,increasing by about 27.9%;when the content of Nano-silica powder were 0%,1% and 3% respectively,the amount of calcium hydroxide in the hydration products of cement-fly ash system decreases with the increase of Nano-silica powder,which means the chemical activity of silicon oxide is a more important role compare with promote the hydration of cement;Nano-silica powder can react with calcium hydroxide and form a gel,meanwhile Nano-silica particle size is small,it can fill the voids of hydration production,reduce the porosity and make hydration products more dense,the number of harmful holes is reduced and harmless holes is increased,strength and durability performance have been improved.3?The effects of different chemical activators on fly ash were studied.When incorporation 1% sodium sulfate,calcium sulfate and calcium formate in the cement-fly ash system which mixed with 3% Nano-silica powder,sodium sulfate has the best excitation effect due to the dual excitation of sulfate and alkali,its' stripping strength is the highest and porosity is the lowest;the effect of calcium sulfate on fly ash is not as good as that of sodium sulfate,calcium sulfate has some retardation influence,solubility is smaller than that of sodium sulfate which makes the number of sulfate ions in the paste less;calcium formate can play a role in calcium supplementation,promote the hydration of cement,but it also makes the alkalinity decreased which is unfavorable to the stimulate of fly ash,calcium formate has the worst excitation effect,the stripping strength is the lowest and porosity is the highest.