This study aims to understand how moisture, CO2, and chloride ions penetrate usable postfire concrete by using electrical resistivity data. Mortar and concrete specimens with water-to-cement ratios (W/Cs) of 0.35 and 0.45, respectively, were prepared for testing. Polypropylene (PP) fibers were added to the specimens with W/C of 0.35. One surface of each specimen was placed on a hot plate and exposed to 350°C for 15 min. The moisture transfer in the specimens stored at 20°C and 60% relative humidity was assessed by measuring their electrical resistance. Then, the penetration of CO2 and Cl ions in the mortar specimens was examined. The electrical resistance of the specimen surfaces was found to be greater than that at greater depths, and the unheated specimens were found to have the lowest resistance. This implies that the regions of the specimens heated with and without PP fibers were drier than those of the unheated specimens. In addition, the heated mortar specimens exhibited greater penetration of CO2 and chloride ions compared to the unheated specimens. Thus, PP fibers and high W/C increased the rate of carbonation and chloride penetration into the mortar specimens after heating.
Stagnant water on reinforced concrete (RC) decks shortens their fatigue life significantly compared to dry conditions. By using a multi-scale simulation together with the pseudo-cracking method, the remaining fatigue life of real RC bridge decks covered by stagnant water is estimated based upon their site-inspected surface crack’s patterns. For quick diagnosis for deterioration magnitude of RC decks, two assessment methods are proposed. A predictive correlation of the remaining fatigue life and a mechanics-based parameter (cracks density) considering both cracks length and width is introduced as a speedy judgment for the deterioration-magnitude. For comprehensive judgment for the deterioration-magnitude, an artificial neural network (ANN) model is further introduced by means of machine learning. Bayesian regularization technique was conducted to the training scheme to reduce the misguided ANN’s evaluation caused by overlearning. Finally, deck’s bottom surface map of reference is introduced to show the location of comparatively problematic cracks based upon the weights assigned with the synapses of the neuron of the built ANN model.
The porosity of concrete affects the mechanical properties and durability, during its exposure to extreme temperatures where the chemical and physical changes in PC affect the integrity of concrete as a whole because of its binding properties. An attempt is made to analyze the porosity in hydrated PC using synchrotron micro-tomography at temperatures of 27°C, 100°C, 400°C, 500°C, and 800°C. These temperatures are significant in the context of the mass loss and phase changes taking place during the thermal analysis. Image analysis is carried out to estimate porosity, radius, and circularity of pores for all the individual 2D slices. 3D analysis is carried out to estimate the diameter, area, and volume of pores present in the sample. The number of pores in the 2D slices has increased from 5974 to 11564 at 27°C and 800°C; while the total number of pores present in the sample at 27°C is 317 and at 800°C it is 3361. With the increase in temperatures, the area of pores 947 µm2 contributed to 44.16 volume percent at 27°C, whereas at the temperatures of 800°C the area of 136 µm2 pores volume percent is 41.
In the mountainous area of the Hokuriku region, bridges are experiencing early deterioration caused by salt damage, alkali-silica reaction (ASR), and frost damage. Survival time analysis was carried out using the inspection data to study the relationship between the degradation tendency of bridges and the regional characteristics. In addition, the causes of the degradation of the reinforced concrete (RC) slab of a road bridge, which deteriorated early, were investigated using cylindrical core extraction. Polarizing microscopic observation of the specimens collected from the slab confirmed that ASR was the cause of the deterioration. The reduction in the mechanical properties of concrete due to ASR was also studied and reported. Moreover, vehicle running tests using a test truck were carried out. Then, long-term monitoring of the responses of the test bridge due to live load based on the bridge weigh-in-motion method was also performed for ordinary vehicles. The stiffness of the RC slab was evaluated by comparing the results obtained from the tests and the numerical analyses. It was found that the current stiffness of the slab remarkably decreased as compared with the results when the slab was sound. Finally, this study proposes an approach for the soundness evaluation of RC slabs.
Until now, the influence on the thermal and mechanical properties of concrete of SO3 and calcium carbonate as minor constituents contained in binder used for concrete made with blast furnace slag rich cement was not clearly known, and neither was the optimum mixing ratio most effective for control of thermal cracking. To evaluate the influence of these minor constituents on the temperature and crack resistance properties of concrete, a simple adiabatic temperature rise test and examination by thermal stress testing machine (TSTM) were carried out in this study. The simple adiabatic temperature rise test evaluated mainly the thermal characteristics of the minor constituents under investigation, while the test using a TSTM, which is a test device that can simulate the behavior inside the member of a real structure, investigated mechanical properties such as creep characteristics, and crack resistance. Further, using the results of the simple adiabatic temperature rise test and the test using a TSTM, thermal stress analysis using a wall structure was carried out to determine the influence of minor constituents on crack resistance. As a result, as determined within the scope of this study, we found that the formation of ettringite and monosulfate accompanying the addition of SO3 has an influence on the adiabatic temperature rise characteristic and the apparent mechanical properties, and that the addition of calcium carbonate has only a small influence on thermal properties.