Influence Of Dry-wet And Freeze-thaw Cycles On Mechanical Properties Of Reactive Powder Concrete In Marine Environment

In the coastal areas of China, durability deficiency problems are widespreadwhich are located in the marine environment long-term. A new type of composite material who based on cement, reactive powder concrete has ultra-high strength, high toughness and excellent durability. It is very suitable service for the severe marine environment. Since in the concrete structures are highly vulnerable to seawater erosion, dry-wet cycles and freeze-thaw cycles, in this paper, through the simulation test of the seawater dry-wet cycles, the seawater freeze-thaw cycles and the seawater without sulfatefreeze-thaw cycles, we study the change rules of mechanical propertiesof RPC in the coupling effects. On the other hand, combined with SEM, XRD micro method, we analyze the microstructure and corrosion product inside in the coupling effect. The main work and conclusions are as follows:(1) The reactive powder concrete underthe of seawater erosion and dry-wet cycles indicate that:as the increase of cycle number, the compressive strength of the material increased first and then decreased, tensile strength first decreased and then increased and last decreased. The micro experiment indicates that:the reactive powder concrete be corroded inside by seawater, hasmagnesium salt andsulfate erosionreaction,chloride ion in seawater has also led to the steel fiber rusted.(2) The reactive powder concrete underthe coupling effect of seawater erosion and freeze-thaw cycles, the compressive strength and splitting tensile strength on the whole with freeze-thaw cycles increases. The SEM and XRD test show that:in the seawater freeze-thaw cycles, the reactive powder concrete in the coupling effect of the seawater erosion and the freeze-thaw cycles, we can observeettringite and gypsum, and a small amount of magnesium salt and sulfate erosion product.(3) The reactive powder concrete inthe coupling effect of seawater without erosion and freeze-thawcycles, as the increase of cycle number, the compressive strength and splitting tensile strength still decreased. But comparewith sulfate seawater erosion, the compressive strength of the material decreases slowly. The SEM and XRD test show that:no large amount erosion products, only a small amount of ettringite and sulfate product can be observed due to the material and hydration in the later stage. Based on the above results, we believe thatin the coupling effect ofthe seawater freeze-thaw cycle, SO42-is one of the important factors causing reactive powder concrete durability deterioration.