In this paper, an analytical model to predict the service life of reinforced concrete (RC) structures in marine environment is proposed. For constructing a model, the deterioration process of RC structures was assumed to be divided into two stages: the penetration period of chlorides into concrete and the ensuing cracking stage due to corrosion of reinforcement. Two indices, TO and T1, were introduced in this model: the latent period from the beginning of the chloride penetration until the onset of corrosion, denoted as TO, and the progressive period until the initiation of the longitudinal cracking, denoted as Tl. Since the TO model was already described in the previous report, Proposed durability design for RC marine structures CONSEC ‘95 (4) modeling of Tl and a rational service life prediction using a combination of TO and T1 are discussed in this paper. The T1 model was constructed by a parametric study using Finite Element Method, after investigating the effect of finite element layout. In the analytical study, parameters were determined considering the experimental results obtained from exposure tests. The results of parametric study were combined in the regression analysis. An attempt has also been made to discuss some experimental results in the light of the proposed model. Finally, a program (called MS LIFE), which predicts the service life of RC structures in a marine environment was proposed by combining the model for predicting the T1 with that for TO. Some results of the trial calculation using this model were also introduced for verification.

Polymer modified cementitious materials are used in construction for applications such as bridge deck overlays and concrete repair. When using this type of material a wet-dry curing regime is usually recommended in order to give optimum mechanical properties. However, such a curing regime is contrary to that which would be expected for a low porosity surface layer, desirable, e.g., for good resistance to chloride ingress. This paper presents the results of investigations into the influence of curing conditions on the surface porosity of polymer modified cements and its influence on chloride diffusivity. Small cement paste prisms were cast and the top faces exposed to: wet, wet-dry, and wet-dry-wet curing regimes. Pore size distributions were then determined for the top, middle and bottom layers using mercury intrusion porosimetry. Results showed that for all mixture proportions the wet-dry curing regime resulted in a surface layer which was more porous and had a coarser pore structure than the deeper layers The extent of this effect depended on: actual curing regime, W/C, and type of polymer latex used. Results were confirmed by determining the effective diffusivity of chloride ions in similar samples.

The non-linear diffusion equation has been successfully applied to water movement but only during the drying process. As a model which can be applied to both drying and wetting processes, capillary flow is considered to be worth examining as one possibility in order to establish a universal model. In the first step, one-dimensional water movement within mortar was studied both analytically and experimentally. A model consisting of capillaries with various sizes was adopted and water movement was analyzed by assuming that it was caused by capillary action. A good correlation w a s obtained between numerical results and experimental data. Useful information was also obtained from the analysis concerning the behavior of moving water within mortar.

In order to establish durable design of concrete structures, to estimate the service life of the bridges and to obtain data indicating whether the prestressed concrete bridges need repair, the durability of 267 prestressed concrete bridges in service for ten to thirty years in north- east district of Japan was investigated. Furthermore, results of investigation in north-east district were compared with those of Kyushu district. Characteristics of the deterioration of respective parts of prestressed concrete bridge are described from the viewpoints of materials and structures. The results establish the influence of moisture on efflorescence and cracking of superstructures and the influence of frost damage as in snow and cold regions. Furthermore, effective countermeasures for improving durability of concrete structures are discussed and proposed.

Curing of concrete is essential for reliable performance of concrete structures. The recommendations concerning curing of high-strength concrete are contradictory. The traditional ways of curing fail in the case of high strength concrete. A higher porosity in the vicinity of edges, microcracks due to self desiccation and shrinkage, and reduced compressive strength affect the durability of high performance concrete. Therefore, another approach is followed which consists of a new idea for supplying curing water in the interior of the concrete, by using lightweight expanded clay aggregates. When a shortage of water in the hydrating cement paste occurs, the water from the lightweight aggregates is transported by capillary suction or by capillary condensation into the smaller pores of the cement paste, thereby permitting continuous hydration. About 25% by volume of the aggregates are lightweight. The improved durability due to the higher degree of hydration, an improved density of the hydrated cement paste, less drying shrinkage and higher com-pressive strength have been shown by experiments. Test results from differen-tial thermal analyses, X-ray diffraction, mercury porosimetry, water absorp-tion, drying shrinkage and compressive strength are presented and compared with normal weight concrete with 100% natural aggregates.