Integrative Assessment Of Resistance To Frost And Chloride Penetration Of Marine Concrete

The durability deterioration of reinforced concrete structures is severe at middle and high latitude coastland because of the erosion caused by seawater and freeze-thaw damage. Moreover, this kind of area accounts for a large proportion over the world and most regions are developed countries with great amount of infrastructures, industrial and civil architectures.In this research, we made normal concrete, Fly-ash concrete, Silica-fume concrete and Ground granulated blastfurnace slag (GGBS) concrete by simulating and aiming at actual service state of marine concrete (saturated with seawater or with high salt content). At the same time, there were a couple of considerations of different mixture ratios, which include different water binder ratios, different dosages of air entraining agent and mineral admixtures, etc.This thesis is focus on evaluation methodology of resistance to frost and chloride penetration of marine concrete. At first, different changes and developing rules of compressive strength of various kinds of concrete comparing seawater curing with standard curing were carefully investigated, then, to modify the traditional testing method of simulating marine environmant and assure the new testing method of the performance of freeze-thaw and chloride ion permeability. Finally, based on the new testing method, a great amount of systematic experiments on freeze-thaw and chloride ion permeability were done. Besides, the factors that influence the performance on both resistance to frost and chloride penetration were studied.The eddy current method was introduced here to anlysis the relations between early-age shrinkage and resistance to frost and chloride penetration. While seawater corrosive products and their micro-morphology and pore structure characteristic after freeze-thaw cycles were utilized by electron scanning microscope (SEM) and mercury intrusion porosimetry (MIP) to research on the relations between their properties of microstructure and resistance to frost and chloride penetration. Finally, the future developing direction of marine high performance concrete was put forward.The results are listed as follows:(1) Different types of concrete specimens after 3 days moulding were submerged especially in seawater and under standard curing conditions to cure and compared their compressive strength changes. The evaluation of the difference are measured by the changes of their compressive strength. This is the function: Concrete cured for 28d in seawater after moulding for 3d can assure non-deterioration of the strength and performance of inner concrete struture as well as high content of seawater. The testing method correspond with actual service conditions of marine concrete built for a long time which located inside the sea.(2) Testing method of frost resistance and chloride ion permeability in the simulation marine environment are based on the changes of SCF value. Test conditions are: concrete moulded for 3d + seawater curing for 28d, seawater changed every 15d; temprature of seawater curing limited to 20±2℃, all the curing water are natural seawater. Other testing methods accord with JTJ270-98 ?testing code of concrete for port and waterway engineering? and CCES01-2004 (05 revision)'s rules about concrete structure durability design and construction guide.(3) The integrative assessment method of frost resistance - chloride ion permeability was put forward and called R-Value method - a ratio of frost-resisting durability factor (DF)and chloride diffusion coefficient (DNEL) . Definite equcations are given here. Critical durability factor value of concrete's frost damage is represented with DF = 0.75. Here is the formula: Value scope of DF, DNEL and R is set. DF varies in the interval(0,1], the interval of DNEL value is [10-7,10-9], for R value, it's [107,109]. Dimension of R is [s/cm2]. R value reflects concrete's performance in both frost resistance and chloride impermeability, which is the physical significance of this evaluation methodology. Specifically, the bigger the R value, the better performance in both frost resistance and chloride impermeability.(4) No matter what kind of concrete it is, nor the air entraining angent is added or not, R value decends as water binder ratio (W/B) accends. On the contrary, W/B reduces, R value increases.(5) In spite of the kinds of concrete, concrete performs better in both frost resistance and chloride impermeability when the dosage of air entraining agent increases. However, if the content of air entraining agent is too higher, concrete dosn't perform so well in both integrative property.(6) In certain content range of mineral admixtures, silica fume improves the chloride ion impermeability and integrative performance in both frost resistance and chloride ion impermeability of marine concrete, but decreases its frost resistance at seawater, while about 10% of silica fum added in concrete makes the integrative performance perfect. Both fly ash and GGBS decrease the frost resistance at seawater and integrative performance in both frost resistance and chloride ion impermeability of marine concrete, but improve their chloride ion impermeability especially, while about 30% of fly ash added in concrete makes the integrative performance perfect, GGBS dose not have the problem of how much we should add to concrete to improve the integrative performance perfect.(7) For marine concrete whose compressive strength is less than 60MPa, there is no direct relation between its strength grade and integrative performance of both . While for concrete that is more strong than 60MPa, addition of silica fume improves its integrative performance of both.(8) The eddy-current method can be used in freshed concrete, especially for testing the early-age shrinkage of freshed concrete. Early-age shrinkage of concrete mixed with seawater or tap water varies a lot. Concrete mixed with seawater has a very lower early-age shrinkage. The difference (?ε) of their maxium early-age shrinkage value for 3d is inversely proportional to R value which reflects the integrative performance in both frost resistance and chloride impermeability of marine concrete.(9) The micro-morphology and quantity, as well as the patterns of kinds of concrete's seawater corrosive hydration products, in some degree, conincide with the R value.(10) It is the best charateristic parameter of pore structure that the most probable pore size in concrete which has suffered from several freeze-thaw cycles represents its integrative performance of both frost resistance and chloride impermeability, and it is well related with R value. Concrete performs better in integrative performance of both when the most probable pore size is smaller. Air entraining agent and silica fume, as important ingredients for the future marine HPC in high latitude regions, can reduce the most probable pore size of concrete, thus improve concrete's integrative performance of both frost resistance and chloride impermeability.