Compared to point estimate, interval estimate of compressive strength of concrete from limited test data would give a better confidence on the evaluated statistics, which can be obtained with Normal approximation theory. In this study, a non-parametric methodology based on bootstrap re-sampling for interval estimate was found to be more suitable. Optimal numbers of bootstrap samples and optimal number of data in each bootstrap sample in such analysis demand attention. Using cube test results, these aspects of bootstrap re-sampling as applied to interval estimate from concrete test data are investigated in this paper. It is recommended that for evaluation of mean or standard deviation of concrete compressive strength, optimum number of bootstrap samples should be between 1,000 and 2,000 with equal to or more than 25 data in each sample. The corresponding numbers for estimation of characteristic strength of concrete was advocated as 4,000 to 5,000 bootstrap samples, each of 30 or more data. Normal approximation theory might yield slightly higher estimate of characteristic strength, which could be detrimental in case of health evaluation or safety margin assessment of important existing structures.

This paper reviews the literature available on the subject of the durability of concrete sewer pipes and the corresponding rehabilitation technologies. An introduction related to the importance of the sewer system in urban life and its durability issues was first discussed as most people did not recognise the scale and complexity of the underground sewer system. Then the recent development of alternative binder materials or filler materials to improve the acid resistance of concrete was specified. For instance, the effects of alternative binders on the hydration products and the mechanism of biogenic corrosion were discussed in detail. The paper ends with the current rehabilitation technologies and the structural performance of rehabilitated sewer pipes. Also, some suggestions associated with future research were made.

Before taking up seismic re-qualification and retrofitting of an existing concrete structure, if required, assessment of the current strength of structure is an important aspect. Health assessment ascertains variation in properties of concrete, particularly strength, attained over the initial development phase when subjected to service exposure for a long time. It further tries to assess the deterioration of the reinforcing steel and degradation of the concrete through the various mechanisms over time. Health assessment of a reinforced concrete (RC) Nuclear Fuel Cycle Facility was taken up through Non-destructive (NDT) and Partiallydestructive testing (PDT) in the recent past. The RCC framed-cum-shear wall structure was of dimensions 98 m by 84 m and had been constructed around 15 years back. From the results the various material properties of concrete like compressive strength and density were determined. The health of the concrete was found to be in satisfactory condition with chloride and sulphate content within permissible limits specified by International standards. The paper provides an overview of the different tests performed for health assessment and further provides a brief account of the results and inferences therefrom.

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