This annotated bibliography is aimed at provid- . ing the concrete technologist and the construction engineer information about the recently developed, but not yet adequately used, accelerated methods of testing concrete. This will also be of value to any researcher in the same or similar area of concrete technology research. It covers the development of accelerated curing techniques, and the influence of temperature on strength development. Some references on maturity of concrete which are integrally connected with accelerated testing are included. However, this bibliography is not intended to be exhaustive; it is a selective bibliography chronologically arranged. Annotations are provided for selected entries, and have been omitted when there are repetitions in listed references, unavailable references, and foreign language references. When titles alone are sufficiently indicative of the content, annotations are omitted.

This paper contrasts the statistical properties of two statistical techniques for predicting the ultimate strength of concrete, using data from two preliminary calibration experiments. The techniques are: (1) prediction from the mean early strength by the usual regression line; (2) prediction from a conservative estimate of early strength by a conservative relationship of early strength to ultimate strength. It is shown that the latter method guarantees (for almost all calibration experiments) a, high percentage of conservative predictions of ultimate strength -- as concrete users desire -- and that the former method, which is commonly used, does not. The use of the techniques is illustrated by predictions of 28-day cylinder strength from the strength of cylinders autogenously cured for 48 hours.

Description is presented of a new method and apparatus for accelerated strength testing of concrete. The method consists of subjecting the fresh concrete mixture to pressure and elevated temperature to accelerate curing. In a preferred embodiment, prediction of the 28-day strength is provided in about 5-hours. The apparatus comprises a cylindrical container with piston closures, a means to pressurize and seal the container and heating means to heat the sample within the container. Preliminary tests show that the relationship between the accelerated cured (X) and 28-day standard cured strength (Y) can be represented by the linear equation: Y = 1570 + 1.42X 500< X < 3400 psi Y = 105.9 + 1.42X 35< X < 239 kgf/cm 2 with an accuracy of + 15%. This relationship appears to be independent of the type of aggregates and admixtures used.

A study of the method for prediction of potential strength of concrete based on the maturity concept is presented. The maturity which is expressed as the integral of the curing temperature with respect to time, is related to the compressive strength of standard cylinders cured at 33 oF (1.7 "C), 55 OF (12.8 "C), 73 OF (22.8 "C), and 90 OF (32.2 "C). The relationship between the compressive streng and maturity is obtained by regression analysis. Other published dat are also used in the analysis of the relationship. It is shown that the function relating the compressive strength to the logarithm of maturity is nonlinear and that the relationship is dependent on the strength-gain characteristics of cement and on water/cement ratio.

An accelerated-curing method to predict the 28-day strength of concrete, from 2-day self-cured test results was evaluated in the field. All concrete samples were collected at the job-site as a part of normal field control work. The method consists of casting and curing the concrete in expanded polystyrene molds which accelerates the rate of strength gain at early age and of testing the cylinders at 48 hours (24 hours). A total of 37 different mixes and 18,908 cylinders test results from four suppliers using different brands and types of cements and admixtures were studied. Particular attention was given to the influence of initial concrete temperature on thestrength prediction. Under the conditions prevailing during this study, the evaluation of the field test results indicate that with Type I cement, a) the 28-day strength can be predicted with a high degree of confidence, from the 2-day self-cured accelerated concrete strength test, when the relationship has been established with several cement factors or strength levels; ` within standard temperature placing limits of concrete 50 to 9OoF (10 to 32oC), the predicted results are consis-tent with the behaviour of concrete under those conditions; c) the addition of initial concrete temperature as a variable allows a better estimate of the 28-day strength although the improvement is not very significant from a quality control stand point. With Type II cement, prelim-inary test results obtained indicate that the strength prediction is not suitable without modification of the present method. Further studies are required for low heat cements.