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Abstract-Structures built in aggressive environments such as in the sea/marine environment need to be carefully designed, due to possibility of chloride ion penetration into the concrete. One way to reduce the strength degradation in such environment is to use FRP, which is attached to the surface of R/C using epoxy. The study presented is focused on determining the effect of the sea water to the capacity of GFRP as flexural reinforcement elements. Beams of 10×10×40 cm dimension were designed without reinforcing bars. The samples were tested using variation to the distance to the sea and duration of the contact to the sea.The result showed that the use GFRP increased the flexural strength 84,21%, compared to the normal beam, without GFRP. It can also be seen that the closer the distance to the sea, the higher the strength degradation of the beam. The sample rinsed in the water has strength 2.13 kN after 9 months, while sample put at a distance 1 km from the seam has strength 2.53 kN. The result of this study also showed that for areas closer to the sea has a greater effect in terms decreasing flexural capacity of the beam IndexTerms-Flexural strength, GFRP, marine environment.

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Supplies of fresh water in everyday life has increased, but the smaller the potential sources of water so we need to think of alternative uses of water for concrete construction work. This study aims to compare the compressive strength of concrete using sea water and fresh water with water cement ratio of 0.37. An experimental research was conducted by making specimens of concrete cylinder with a diameter of 150 mm and height of 300 mm. The study used specimens of concrete using sea water and fresh water. There were 32 specimens for each kind of concrete. The treatment of each specimen used sea water and fresh water in accordance with the type of mixing water. The immersion periods were 1, 3, 7 and 28 days. Mechanical testing of concrete was conducted by testing the compressive strength and elasticity, while the testing of concrete microstructure was conducted by using X-Ray Diffraction (XRD) and Scan Electron Microscopy (SEM). The results revealed that in the 28-day immersion period. The compressive strength values of the sea water concrete and fresh water concrete were 44.88 MPa and 44.03 Mpa respectively. The difference of compressive strength in the two types of concrete was not significant. The result of microstructure test in the 28-day period revealed that in the sea water concrete, there was a formation of Friedel’s salt (3CaO.Al2O3.CaCl2.10H2O) of 7.71%, tobemorite (3CaO.2SiO2.3H2O) of 58.66% and calcium hydroxide (Ca(OH)2) of 6.18%. In the fresh water concrete, there was a formation of tobermorite (3CaO.2SiO2.3H2O) of 51.35%, and calcium hydroxide (Ca(OH)2) of 22%. There was no formation of Friedel’s salt in the fresh water concrete because there was no mutual reaction between chloride and calcium hydroxide elements. From the regression analysis, showed that the difference of microstructure compressive strength differences caused by differences in the microstructure of the content of the two types of concrete.

Concrete is a construction material that has been used widely in various constructions. For constructions located in seismic areas, require a material that behaves ductile during an earthquake. To obtain ductile concrete behavior, it can be substituted materials such as steel fiber and waste rubber tires. This study aims to determine the flexural toughness of concrete with steel fiber and waste rubber tires substitution. Specimens with dimensions of 100 x 100 x 400 mm with the substitution of 0%, 2.5%, 5%, and 7.5% of Dramix Steel Fiber; 10%, 20%, and 30% of crumb rubber and tire chips. The greater amount of steel fibers in the concrete, the greater value of flexural toughness. The substitution of 7.5% steel fiber, increasing the value of flexural toughness three times than the control specimens. While the number of crumb rubber and tire chips are variations, giving a value of varying flexural toughness. Flexural toughness achieved optimum value for substitution of 10% crumb rubber, where the energy absorption is 6386.225 Nmm.

Concrete curing is an effort made to optimize the results of concrete casting. This action needs to be done because it has a major effect on the quality and strength of the concrete, one of which is so that the concrete does not lose moisture too quickly, because later this condition will lead to excessive shrinkage in the concrete. As a result, the concrete can experience cracks. This will cause the construction work to be less qualified and endanger construction users. The purpose of this study is to determine the effect of concrete treatment methods on the value of normal concrete compressive strength. Concrete curing can be carried out by several methods according to the type and condition of the structural elements to be treated. From the results of the study, it was found that the curing method of concrete had an effect on the value of normal concrete compressive strength, namely that the average compressive strength value in the fresh water immersion treatment method was 23.730 MPa, the treatment method for wrapping concrete with gunny sacks was 22.349 MPa, the treatment method of wrapping concrete with plastic is 22.306 MPa, and in the treatment method of pouring concrete with fresh water is 21.199 MPa. The average value of the maximum compressive strength occurred in the treatment method with fresh water immersion, namely 23.73 MPa, and the minimum compressive strength value that occurred was found in the treatment method with fresh water sprinkling, namely 21.199 MPa. Thus, that concrete curing is good, namely, by soaking the concrete with fresh water.