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The hydration process of cementitious materials involves a thermally activated reaction that depends on the composition of the mixture and the curing temperature. The main parameter affecting the temperature variation of cast-in-place concrete is the apparent activation energy, which can be used for the efficient prediction of the temperature evolution and maturity index of hardening concrete. This paper discusses two methods to determine the activation energy of mortar specimens, whose mixture proportions are based on standards. The first approach is based on isothermal calorimetry measurements, and the second involves compression tests of mortar samples stored under four different temperature conditions. Mortar mixtures with ordinary portland cement and two rates of cement substitution with siliceous fly ash (10% and 20%) are investigated. The values of the activation energy obtained using the two approaches are compared. Finally, the effectiveness of different tests in determining the activation energy, and thus, maturity index is highlighted. [ABSTRACT FROM AUTHOR]

• Prediction of early-age concrete temperature of cast-in-place stemwall of the bridge abutment. • The in-situ measurements using novel temperature monitoring system working on 1-wire digital sensors. • Numerical simulation conducted using the own finite element code for nonlinear thermal problem. • The recorded thermal data highly consistent with FE results. • Recommendations regarding the measurement system and maintenance of massive walls of bridge abutments. The paper deals with the prediction of early-age concrete temperature of cast-in-place stemwall of the bridge abutment. The considered object is an arch bridge located in Gdańsk. In the case of massive structures, it is particularly important to not exceed the temperature difference between the core and the concrete surface. Too high temperature gradient generates an increase in thermal stresses, what could be the reason of exceeding the tensile strength and as a consequence cracking occurrence. Therefore, the numerical simulations of concrete hardening were conducted using own codes of finite difference and finite elements method. Based on numerical results the project of monitoring system was developed. The concrete temperature of stemwall was registered during 12 days by using fifteen 1-wire digital sensors. The recorded thermal data are highly consistent with FE results, which confirms the accuracy of the finite element model. The conducted calculations and in-situ measurements allowed to determine guidelines for proper curing of massive abutment's wall. [ABSTRACT FROM AUTHOR]

• Augmented maturity method using FEM-based numerical tests in addition to the usual laboratory and field experimental methodology. • Recommendations for an effective laboratory research program and a reliable temperature measurement system. • FEM analysis of compressive strength distribution in the concrete deck of extradosed bridge. • The complex system of concrete monitoring improves the confidence of decisions on prestressing tendons or formwork removal and provides economic benefit. The work is devoted to the implementation of a monitoring system for high performance concrete embedded in the span of an extradosed bridge deck using a modified maturity method augmented by numerical simulations conducted by the authors' FEM code. The paper presents all research stages of bridge construction and considers the conclusions drawn from the results of laboratory tests, field measurements, and numerical calculations. The monitored structure is the largest extradosed bridge in Europe in terms of the span's length. Due to the considerable size and duration of the investment, it was beneficial to use an alternative method for estimating the compressive strength of concrete based on the maturity function. The bridge sections were investigated in three stages: in summer, autumn, and early spring (in June, September, and March). The monitoring of in-place concrete provided information on the actual temperature of the concrete and its gradients. Based on recorded temperatures and proposed numerical procedures, the actual strength of the cast-in-place concrete and the optimal dates of prestressing were determined. This contributed to shortening the work cycle and speeding up the work schedule. [ABSTRACT FROM AUTHOR]

The paper deals with a concept of a practical computation method to simulate the temperature distribution in an extradosed bridge deck. The main goal of the study is to develop a feasible model of hardening of concrete consistent with in-situ measurement capabilities. The presented investigations include laboratory tests of high performance concrete, measurements of temperature evolution in the bridge deck and above all, numerical simulations of temperature field in a concrete box bridge girder. A thermal conductivity equation in the author's program, using finite difference method has been solved. New approach for identification of the model parameters and boundary conditions (heat transfer coefficients) has been proposed. The numerical results are verified by means of a wide set of experimental tests carried out on three stages of the extradosed bridge studies. A high agreement between the concrete temperature distribution in the time and space domain was obtained. The temperature history of concrete hardening, supplemented with maturity method equations, made it possible to estimate an early-age compressive strength of the cast-in-place concrete. The proposed solution could be applied in a Structural Health Monitoring system for concrete objects. [ABSTRACT FROM AUTHOR]