Study On Hydration Process And Permeability Evolution Of Concrete By Electrical Resistivity

With the extensive used of concrete in construction engineering, the durability of concrete get more and more attention. The durability of concrete is influenced by early-age hydration process of concrete, and depends on the microcosmic of pore structure and macroscopic permeability.This paper used a non-contact electrical resistivity measurement device and tested the electrical resistivity development of concrete during 0-7d, through which hydration process in early-age of concrete and the influence of mineral admixture on early-age hydration properties of concrete were studied. The experiments studied the 0-7d electrical resistivity development of the concrete which is made out of three mixes:water-cement ratio 0.35, cement only mixed, 50% cement replace with slag mixed and 30% cement replace with fly ash mixed respectively. The experiments test the theory that hydration process in early-age of concrete can be divided into 7 stages which is proposed by Chen Jun doctor of Zhejiang University; the filling effect of both fly ash and slag can slow down the solution of free ion; furthermore, the hydraulicity reaction and secondary hydration reaction of slag have been fiercely reacted since the early-age, and the initial point of secondary hydration reaction of slag is for the first time obtained; the influence of fly ash at the early-age mainly is physical effect.The non-contact electrical resistivity measurement device was used tentatively to measure the permeation rate of concrete by Chen Jun doctor and me. With the electrical resistivity curve measured in the permeating process, the ending time of permeation was obtained, and the solution permeation rate of concrete can be calculated. The solution permeation rate of concretes of water-cement ratio 0.60,0.53,0.45, whose curing time respectively was 12 h,18 h,1 d,2 d,3 d,7 d,14 d, and 28 d, were studied. The pore structure of concretes of the same water cement ratio whose curing time respectively was 12 h,3 d,7 d and 28 d were measured by mercury intrusion porosimetry as well. The experiments show that, in the first 3 days, the solution permeation rate and the amount of pores which is harmful for impermeability of concrete decrease rapidly; and during the 0-28 d curing process, as curing age becomes longer, the solution permeation rate and the amount of pores which is harmful for impermeability is a repetitive process, during which it varies from decreasing to increasing, and then to decreasing again. It can be concluded that,0-3 d is the weak period for impermeability of concrete and needs more attention; the interfacial transition zone of concrete appears during 3-7 d and leads to the phenomenon in which permeation rate increases during 3-7 d.