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In this study, the macro-cell induced corrosion behavior of steel bars embeded in concrete members was experimentally investigated specially for the influence of the permeation of oxygen and chloride ions throught joints. Steel bars composed of 7 elements were embedded in mortar or concrete, and repair materials such as polymer cement mortar. The electric current flowing in the steel bars, the polarization resistances, and the potentials of the steel bars, as well as the macro-cell and micro-cell current densities of the steel bars were measured. The differences between the type of joints and the permeation of oxygen and chloride were then studied. The influence of the quality of repair materials on the macro-cell corrosion was also investigated. Results showed that the permeation of oxygen and chloride ions through the joint and the qualities of the repaired concrete members played important roles in macro-cell corrosion behavior. Results showed that the permeation of oxygen and chloride ions through the joint and the qualities of the repaired concrete members played important roles in macro-cell corrosion behavior.Results showed that the permeation of oxygen and chloride ions through the joint and the qualities of the repaired concrete members played important roles in macro-cell corrosion behavior.

A network of lift stations forms an integral part of a city’s wastewater disposal system. These underground concrete pits through which the sewage is pumped, are known to represent an environment highly conducive for chemical attack of concrete. Apart from the acidic state created by the sewage, gases emanated due to microbial reactions can cause the concrete to deteriorate rapidly. Fifteen lift stations were investigated to determine the deterioration depth profile of the concretes. Cores from strategic locations inside each lift station were tested and analyzed using different techniques, including petrography and scanning electron microscopy. Based on these results, a cost-effective yet practical means of evaluating the present state of the concrete, and the precise depth to which the concrete must be removed for effective rehabilitation has been developed. These results are presented in this paper.

This paper presents the results of several studies carried out on the parameters affecting the durability and serviceability performance of concrete water-retaining structures. It has been identified that one of the main causes for the early deterioration of concrete water-retaining structures is the occurrence of strain-induced loadings arising from temperature changes, shrinkage, and swelling. However, a majority of the current design guidelines and recommendations are quite cursory in this regard. The evaluation of induced strains, as well as stresses generated by the restraining effects, is quite complex compared with the effort needed for much-familiar dead and live loads. It was shown that the strain-induced loadings are as significant as the hydrostatic loading. The inevitable cracking of concrete relaxes the strain-induced loadings and this aspect should be considered if economical and practical designs are to be achieved. Swelling of concrete, occurring after filling the reservoir, generates a differential strain gradient across the wall thickness. A comprehensive analysis method was developed to predict the wall structural behaviour from basic moisture transfer modeling. Creep of concrete would relax the induced stresses by about 50% generally. Concretes with low W/C have been introduced recently in order to achieve improved impermeability properties and strength parameters. An inherent property of low W/C concrete is the autogenous shrinkage taking place during hydration. When restrained, this could cause through-depth cracking, thus making the structures unserviceable.

paper summarises results of studies carried out at the Building Research Establishment on the performance and longer term durability at 5 years of two concretes, which contained different normal portland cements, designed to give equal 28-day compressive strength by adjusting the cement contents and water/cement ratios. The two cements were chosen to provide examples of normal Portland cements with the widest difference in tricalcium silicate (C3S) content. It was necessary to obtain the low C3S cement from Israel to satisfy this requirement. The cements originating from the UK and Israel, had C3S contents of 67 and 33.5%, and tricalcium aluminate (C3A) contents of 8.4 and 12.3%, respectively. The concretes assessed were of similar mixture proportions, although an extra 25 kg of the low C3S cement and a lower water/cement ratio were required compared with the high C3S cement, to achieve equal 28-day strength concretes of 40 (-+ 2) MN/m2. Several types of concrete specimens were prepared using two curing regimes (wet and dry-curing), before carrying out a range of long-term tests. These included: compressive strength, seawater attack rating, carbonation, oxygen permeability, chloride ingress, and corrosion of rebar. This study showed that by designing concretes to give equal 28-day strengths, but using high-early strength cements, concrete performance should be quite satisfactory in most indoor and outdoor environments. However, concrete durability may be compromised, even with good curing, if the cement content is not sufficient or the w/c is too high for certain severe exposure conditions, such as in the marine tidal zone. In such cases the reduced cement content and higher w/c could result in discernible loss in long term strength development and reduced durability. These data are of direct relevance to the UK concrete industry practice and support the approach adopted in the current British Standards and Codes of Practice of specifying concrete in terms of minimum cement content and maximum W/C, as well as by minimum strength grade, rather than by 28-day strength attainment.

Results of an investigation of the deterioration of Portland cement products due to deleterious ettringite formation are described. The effects of thermal-drying on internal-sulfate attack in different concrete products is discussed. Comment on the relative significance of deterioration mechanisms is given. Delayed ettringite formation usually occurs in high-temperature cured products. It is usually associated with products exposed to conditions favorable to cracking (e.g. thermal-drying/re-wetting cycles).