Statistical evaluations of field concrete strength

The paper deals with the evaluation of two classes of high strength concrete, C35 and C45, placed on construction sites in Baden-Wurttemberg in the years 1991-1993. The concrete strength was treated as a random variable. The main purpose of this research was to study the variability of concrete strength produced in different concrete-mixing plants then transported on to sites by means of transit mixer trucks. The components in the concrete were determined by computer analysis. Samples of concrete were taken from each construction site and were cured for 7 days in water and then for up to 28 days to the surrounding atmosphere. The strength of each sample was then tested, providing data from which histograms were plotted, their statistical descriptors were estimated and the validity of the assumed normal probability distribution by two goodness-of-fit tests were appraised. The representative coefficients of variations are suggested for use in reliability analysis of structures by level II methods.