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A study was conducted to determine if the current design formulas can adequately predict the capacity of reinforced concrete beams tested at early ages and to determine the effectiveness of stirrups in young beams. Three sets of reinforced concrete beams were tested-with the main variables being beam age and stirrup spacing. It was found that the ACI-318 ultimate strength design method provides a lower bound to flexural strength of young reinforced concrete beams. For beams failing in shear, however. the current code provisions appear unsatisfactory. For example,the contribution of shear reinforcement was observed to be less than that predicted by the code when beams failed in shear at early ages. A change in mode of failure was often observed at early ages and the ductility of young reinforced concrete beams , was less than that for the 28 day old beams.

Thermal analysis was made of the effects of hydration of cylindrical configuration specimens of a slightly expansive cementitious mixture. This simulated a cylindrical borehole plug, and with modification, may be applied to other cylindrical configurations. Inputs were made to the computer program ATHENAN developed to assess the thermal history of cylindrical domains with symmetrical thermal loads. Inputs to the program were the experimental isothermal rates of heat-evolution of the cementitious mixture measured at several temperatures. Using the temperature history from ATHENAN and experimental data from the volume change and mechanical properties of the cementitious mixture in the computer program SAPIV, a stress analysis was performed, which showed that tensile stresses at the interface may arise at the early stages of hydration when the cementitious mixture tends to shrink, while small compressive stresses are present at long times in such materials when the cementitious mixture tends to expand.

The DITEX computer program was developed to predict the temperature distribution in a concrete structural element during manufacture and to evaluate the resulting stresses. This program takes account of several types of boundary conditions : variable ambient temperatures, and various kinds of formwork and heat treatment. A simple and inexpensive specific test has been developed to determine the heat of hydration of the cement, the kinetics of which are a function of position. The test consists of recording the temperature during setting of a concrete sample subjected to adiabatic conditions. These tools have recently been applied to actual cases (bridges, tunnels, pressure vessels, etc.) and have demonstrated the variety of their applications: - optimization of the temperature cycle, making possible a significant reduction in fuel consumption; - better distribution of heating resistors to avoid cracks completely; - selection of the type of cement based on quantitative analysis - a judicious staging of the casting of large structures.

The construction of the Faroe Bridges between Sealand and Falster in Denmark was completed early 1985. The project inclu-ded the placement of about 42,000 m3 of concrete for the substruc-tures of the bridges. Monitoring the curing of the concrete was an essential part of the efforts invested to assure satisfactory dura-bility of the structures. The operations included: I. Pre-calculations of the heat and strength (maturity) develop-ment after placing concrete in critical sections. The require-ments to be complied with were (1) maximum temperature, (2) maximum temperature differences in the concrete, and (3) at-tainment of sufficient maturity before form-removal. II. Site-control with continuous recording of the temperature de-velopment at essential positions in the concrete, including assessment of the strength development. Means for moderating the predetermined course of the curing, in case of unacceptab-le deviations, were used. The expenses for monitoring curing technology were deemed reason-able in view of the directly documented assurance that the requi-red quality of the concrete in the structures was obtained.

Early age concrete is subject to a temperature rise due to the hydration of the cement. Cube or cylinder reference specimens stored alongside a structure will not exhibit this temperature rise to the same degree and therefore will not have the same maturity as the concrete in the structure. Temperature matched curing is a method whereby cubes or cylinders of a similar maturity to the structure are produced, and is an extremely efficient method of determining minimum formwork striking and prestressing time. This paper gives a brief account of the history behind temperature matched curing in the United Kingdom, where the recent issue of a British Standard Institution document has focussed attention to the subject. Details are presented of the design and construction of a portable matching system for use on site. The system which is extremely robust, (but light enough to be carried by control cube temperatures to within -+, temperature within a structure. Results are given which show the advantages and disadvantages of such a system and illustrate the difference of maturity and hence strength between reference cubes stored in the curing bath and reference cubes placed next to the structure itself. one man), is able to 1oC of the concrete