In this paper, we discuss a deterioration phenomenon of concrete due to sulfuric acid and sodium sulfate attack in environments which contain sulfuric acid and sulfate simultaneously. Specimens were immersed to some kinds of solutions which have different pH and SO42- concentration, and chemical and physical changes of specimens were analyzed. As the result of analyses, we identified that the feature of deterioration can be classified into 3 categories by using the pH value and the SO42- concentration of the solutions. If the SO42- concentration is low, the deterioration of concrete was mild even in the pure sulfuric acid solution of pH2-3. In the case of pH of more than 3 and high SO42-, cracks were generated by ettringite formations. In the case of pH of less than 2-3 and high SO42-, vulnerable gypsum layer was formed, and partial loss became greater. When deterioration velocity and weight loss velocity of the specimens were compared, it became clear that the deterioration became intense synergistically by the simultaneous action of sulfuric acid and SO42-.
In this study, a method was developed to accurately estimate chloride threshold value for corrosion initiation in reinforced concrete. In this method, chlorides are supplied through a part of the specimen surface and half-cell potential between the rebar and reference electrode embedded in a concrete specimen was measured in every ten minutes. A sudden drop of half-cell potential was observed as the continuation of the measurement. At that time, the specimen was broken and corrosion of rebar on its narrow surface was confirmed. The chloride threshold value can be estimated by determining the chloride concentration at the time of the potential drop. The estimated chloride threshold values for ordinary Portland cement concrete with cement content between 254 and 446 kg/m3 are in the range of 1.6 to 3.6 kg/m3.
The surface penetrant is performed for concrete structures as one of the prevention maintenance. The chloride ingress at the reform part in the surface area is different from that at the deeper part where the concrete is not reform. However, there is no established method for determining the chloride ion diffusion coefficient at the reform part. From the above backgrounds, this paper proposes a method for determining the apparent chloride ion diffusion coefficient in an outer layer reformed by silicate type surface penetrants. First, the part reformed with the surface penetrant was investigated from the Vickers hardness distribution. Subsequently, the concrete specimen applied the surface penetrant was exposed to the chloride environment, and the chloride ion concentration distribution was measured. Simultaneously, the chloride ion concentration distribution was measured for the concrete specimen without any penetrant. Thereafter, the chloride ion concentration distributions for the both cases were compared. To determine the diffusion coefficient at the reform part, the cover concrete with the surface penetrant was increased by considering the equivalent cover depth. Herein, the equivalent cover depth implies that the tegmental thickness with the low diffusion coefficient by the surface penetrant is replaced with the cover depth of normal concrete. As a result, the apparent chloride ion diffusion coefficients at the reform part by the four types of the silicate surface penetrant could be estimated. Furthermore, an actual application scenario was demonstrated the effect of delaying the corrosion occurrence time after the surface penetrant was performed as the prevent maintenance. Therefore the chloride ingress was calculated by the investigated reform part and the estimated apparent chloride ion diffusion coefficient in the trial. The results confirmed that the use of the surface penetrant delayed the occurrence of corrosion by 12 years.
It is necessary to cut out the remove of obstructions around reinforced concrete column in the seismic retrofitting construction of existing reinforced concrete columns. Therefore, to widen the space of lateral reinforcement materials is required. However, since the seismic capacity of retrofitted column suddenly deteriorates, it is not able to widen the space of lateral reinforcement materials. So the specimens of reinforced concrete column widened the space of lateral reinforcement materials at base of the column were tested under reverse cyclic loading. Test results showed that the failure mode did not become shear failure mode in this experiment. In addition, the arrangement method of lateral reinforcement material, which dose not decrease the seismic capacity, was showed.
This study focused on inhomogeneity of concrete and influence of material properties of concrete on chloride penetration was analytically investigated. Surface chloride concentration of concrete, porosity and moisture content of both cement paste and interfacial transition zone (ITZ) were assumed to be uncertain. Stochastic FEM analysis involving these variables was carried out and unstable chloride penetration in practice was simulated. Parametric study recognized the variables and its standard deviation as appropriate. Consequently, it was estimated by the FEM analysis involving material variation that apparent diffusion coefficient was considerably affected by the variables of water-cement ratio (W/C) and moisture content and it converged a certain value with the passage of time.
This research proposes a future maintenance plan based on the soundness evaluation through the investigation of concrete and steel properties of 15 years old PC road bridge in severe chloride environment. In this research, investigation of degradation situation from the construction, evaluation of the environmental action of chloride by measuring the salinity of the mortar piece stuck on the concrete surface, measurement of air permeability and water distribution near the concrete surface are performed in order to quantitative evaluation of the properties in connection with the durability of this concrete structure. As a result, although this bridge has some problems resulting from material, or construction, and subsequent maintenance, it was clarified that it is possible to operate this bridge continuously through the future strategic maintenance.
Mechanical shear connectors, such as headed studs and Perfobond ribs, are generally used in steel-concrete composite structures. Such shear connectors may affect negatively on construction as well as increase cost and weight. To improve constructability and to simplify the connecting structures, a composite slab system using a cementitious adhesive has been developed in previous works. The present study aims to examine shear capacity of the composite structure by performing a push-out test. The test results indicate that the developed composite system has almost equal strength to the conventional composite structure using Perfobond. The observation confirms the shear performance can be enhanced by the adhesive and notched stiffeners (half-hole).
It is effective to apply lightweight concrete to reinforced-concrete (RC below) deck in making lighter weight bridge superstructure. It is, however, reported that the fatigue durability of light-weight RC deck is inferior to that of ordinary RC deck with the equivalent design compression strength. On the other hand, the expansive additive is used to reduce initial cracks of RC decks, and it is confirmed that the expansive additive is effective to enhance fatigue durability. The aim of this research effort is to put the lightweight RC bridge deck to practical use, which includes proper amount of the expansive additive in order to induce chemical prestressing within the deck. The hardening characteristic and expansion characteristic of the lightweight concrete combined with expansive additive are confirmed through variety of component tests using small specimens, and it is also confirmed that the deck has superior fatigue durability compared to ordinary RC one through a series of wheel load driving tests using actual-sized deck specimens.