Online Prediction of Strength Development in Precast Production Based on Cement Reaction Model

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Title: Online Prediction of Strength Development in Precast Production Based on Cement Reaction Model

Author(s): E. Nordenswan and A. Kappi

Publication: Special Publication

Volume: 241

Issue:

Appears on pages(s): 133-140

Keywords: heating control; maturity; precast production; strength prediction.

Date: 4/1/2007

Abstract:
The throughput of precast concrete plants can be improved by controlled heating of the cast products. Presently many systems do measure maturity or degree-hours providing information about the strength development, but not sufficient data for accurate decisions for the control of heating. A heat control system has been developed based on an on-line predictive calculation of the temperature behavior of concrete and a maturity-strength model. The temperature is measured continuously and every minute a complete prediction calculation up to the target maturity and strength is made. If the target strength cannot be reached without heating by the target time limit, the system opens the valve for heating the mould, until the temperature is high enough. The predictive algorithm also provides an accurate estimation of the time when the prestress release or demoulding strength is going to be reached. The parameters for the cement heat generation model are obtained by semiadiabatic measurements of the production concrete. The system has been in use since 1999 and applied in over ten precast factories in Europe in hollow-core and railroad sleepers production. The system has reduced significantly the heating costs; reduced rejections caused by too early demoulding and improved production planning in the factories.