Experimental Research On Long-term Property Evolution Rule Of High Strength Concrete In Moist Environment

In the moist environment,the strength of high-strength concrete would reach the maximum value when the concrete in service to a certain fixed number of year,and then the strength would decrease and concrete would become brittle.If the earthquake occurred,the damage would be particularly severe.So,the research of strength decreasing and permeability resistance is an urgent requirement in engineering.At home and abroad,the research of high strength concrete on the strength and permeability resistance in the later age was in its infancy.In this paper,we adopted the heat and wet curing to accelerate the hydration of un-hydrated cement particles in the high-strength concrete and accomplished the intention that study the long-term evolvement law of high strength concrete.The standard curing,heat and wet curing(70±1?,RH?95%)and sealed curing(70±1?,RH?95%and the samples were sealed)were used in this paper.The concrete with W/C 0.24,0.27,0.30 and0.40 were cured under the standard curing for 28 days and then taken to the heat and wet curing.During the process of wet and heat curing,some samples with W/C 0.24 were adopted the sealed curing that stopped the outside water from permeating into the concrete.The strength,permeability and water absorption were tested and then analyzed the microstructure of high-strength concrete at different stages.The results showed that the maximum strength value of concrete would reach higher in the shorter time when the water cement ratio(W/C)of concrete is lower.The lower the W/C of concrete is,the higher degree of the strength decrease is when the phenomenon of strength decrease occurred.The lower the w/c of concrete is,the higher strength value the concrete would reach when the strength tends to be stable.The strength value of each team at 28d is higher than the strength value at 28+7d.For Water absorption and chlorine ion permeability,the minimum value of water absorption capacity per unit area and electric flux value of concrete would reach lower in a shorter time when the water cement ratio(W/C)of concrete is lower.The lower the w/c of concrete is,the higher degree of the durability deterioration is when the phenomenon of durability deterioration occurred.The lower the W/C of concrete is,the lower water absorption capacity per unit area and electric flux value the concrete would reach when the strength tends to be stable.The value of each team at 28d is lower than that at28+7d.The durability deterioration lags behind the strength decreasing happened.The concrete performance evolution could be divided into two stages:The first stage,the hydration productions generated newly in the pore and filled it to increase the performance of concrete.The second stage,the tiny cracks and communicating pore generated when the volume of hydration is bigger than the volume of pore in the micro area.This phenomenon causes the loss of various aspect performances.The primary cause of the durability deterioration and strength decreasing is the variation of pore structure caused by the hydration reaction.The most affected factors caused the variation of pore structure are the quantity change of ultra-micro pore(d<10 nm),smaller capillary pore(10 nm<d<10~2 nm)and bigger capillary pore(10~2 nm<d<10~3 nm).Furthermore,the sealed curing can slow down the durability deterioration and strength decreasing.