Study On The Influence Of Fly Ash And Municipal Solid Waste Incineration Fly Ash On Hydration Performance Of Cement Paste Based On Electrical Resistivity Method

The utilization of fly ash and municipal solid waste incineration fly ash(MSWI fly ash)has promoted the development of building materials industry towards green and low-carbon emission.In this paper,the evolution of electrical resistivity and hydration properties of cement paste incorporated with fly ash and MSWI fly ash were studied,and the effect of fly ash on the electrical resistivity and hydration properties of cement paste at different temperatures were investigated.The research shows that the curves of electrical resistivity of cement paste blended with different contents of fly ash will intersect with each other.Before the intersections of the curves of electrical resistivity,the electrical resistivity increases with the increase of fly ash content,while after the intersections,the electrical resistivity is lower when the fly ash content is higher.Within 6 h of hydration,the growth rate of ion concentration of cement paste with high fly ash content is slow,which lead the corresponding curves of electrical resistivity develops slowly.The change of ion concentration plays a dominant effect in the evolution of electrical resistivity.At 72 h,the change of ion concentration in liquid phase of cement paste tends to be gentle,and the pore structure of hardened cement paste plays a dominant effect in the evolution of electrical resistivity.The incorporation of fly ash results the decrease of ion concentration of pore solution and the increase of total porosity of cement paste.At 20 ～ 50 ℃,the initial electrical resistivity of cement paste decreases with the increase of temperature,and then increases rapidly.The increase of temperature significantly accelerates the development of early electrical resistivity.At 1 d,the electrical resistivity of cement paste without or with 20% fly ash at 50 ℃ is lower than that at 35 ℃.The conductivity and p H value of pore solution decrease with the increase of fly ash content.With the increase of temperature,the dissolution and precipitation rate of ions are accelerated,and the conductivity curves of pore solution become smooth earlier.The increase of temperature also accelerates the pozzolanic reaction of fly ash,and the secondary hydration consumes Ca(OH)2,which leads to the decrease of p H value.For cement paste without fly ash,the early compressive strength and chemically bound water content increase with the increase of temperature,while the compressive strength and chemically bound water content decrease with the increase of temperature at 28 d.The addition of fly ash can slow down the adverse effect of high temperature on the later strength.With the increase of age,the effect of high temperature on the activation of fly ash is more obvious,which significantly promotes the increase of strength.The electrical resistivity of cement paste decreases with the increase of the content of MSWI fly ash,and the growth rate of electrical resistivity is slower with the increase of the content of MSWI fly ash.The appropriate content(2.5%)of MSWI fly ash can improve the p H value of pore solution,promote the formation of hydration products and improve the compressive strength of cement paste.When the MSWI fly ash content exceeds 10%,the electrical resistivity and compressive strength will be significantly reduced.It will also affect the formation of dense structure of hydration products.MSWI fly ash can accelerate the setting of cement paste and significantly shorten the setting time.