Development of a Practical Heat of Hydration Model for Concrete Curing for Geotechnical Applications

Thermal integrity profiling (TIP) is a common non-destructive technique to evaluate the quality of construction of piles by analysing the temperature fields due to heat of hydration from freshly cast concrete piles. For this process to be accurate, a reliable concrete heat of hydration model is required. This paper proposes a practical and simple to calibrate four parameter model for the prediction of concrete heat of hydration. This model has been shown to be able to reproduce the evolution of heat of hydration measured in laboratory tests, as well as field measurements of temperature within curing concrete piles, as part of a thermal integrity profiling (TIP) operation performed at a site in London. With the simplicity of the model and the small number of model parameters involved, this model can be easily and quickly calibrated, enabling quick predictions of expected temperatures for subsequent casts using the same concrete mix.

Fiber Optic-Based Thermal Integrity Profiling of Drilled Shaft: Inverse Modeling for Spiral Fiber Deployment Strategy

The current state of practice to interpret the thermal integrity profiling (TIP) data of drilled shaft is the so-called effective radius method. It uses the concrete pouring log and average temperature to construct a relationship between temperature distribution and effective radius that can be used to reconstruct a drilled shaft model. While this effective radius method is computationally inexpensive and has good operationality, it is not good at predicting the dimensions and shape of shaft defects. Upgrading the sensor used in conventional TIP from thermocouples/thermal wires to fiber optic sensors, the spatial resolution of the measured temperature will be enhanced. By using the newly proposed spiral fiber deployment strategy, we can improve the reconstruction of shaft defects in the integrity testing of drilled shafts. The corresponding inverse modeling of defected shaft reconstruction for spiral deployment is proposed in this paper based on the temperature distribution pattern that is learned from forward modeling. Through inverse modeling, the details of defects in drilled shafts can be reconstructed numerically. An analysis of the results shows that the prediction by inverse modeling has good agreement with the forward modeling set up initially. This work helps the evolution of the TIP from the nondestructive testing stage to the quantitative nondestructive evaluation stage.

QUALITY ASSURANCE OF DIAPHRAGM AND PILE WALLS BY GEOPHYSICS

Underground structures like diaphragm and pile walls are constructed to organize waterproof curtains, protect pit sides, and transfer loads from the structures. Violations of the construction technological process can lead to the formation of defects. To prevent adverse consequences, before excavation, it is necessary to control the integrity of the slurry walls using non-destructive geophysical methods. A review of geophysical slurry wall quality control methods based on the excitation and registration of physical fields through access tubes installed in the reinforcement cage, in wells drilled near the structure or on the surface of the structure, is presented. The main capabilities and limitations of the methods are given. Cross-hole ultrasonic logging was used to study the section of the slurry wall during the construction of the Moscow Metro station. The results of parallel soundings made it possible to identify anomalous zones, interpreted as defects. The geometric dimensions of one of the major defects were refined by ultrasonic tomography. For the first time in Russian testing practice, thermal integrity profiling was applied to study the diaphragm wall at the base of a residential building. The results of temperature monitoring during the concrete hardening are presented. According to the method, a major flaw, excess of the design mark of the wall bottom and bulging of the structure were revealed. The results of thermal integrity profiling were verified by ultrasonic logging. The combined use of thermal and ultrasonic methods can be recommended as a reliable tool for integrity testing of diaphragm and pile walls. To carry out the measurements, the access tubes shall be included in the reinforcement cage of the structure at the design stage.

Thermal integrity testing of cast in situ piles: An alternative interpretation approach

Integrity testing of deep cast in situ concrete foundations is challenging due to the intrinsic nature of how these foundations are formed. Several integrity test methods have been developed and are well established, but each of these have strengths and weaknesses. A relatively recent integrity testing method is thermal integrity testing. The fundamental feature is the early age concrete release of heat during curing; anomalies such as voids, necking, bulging and/or soil intrusion inside the concrete body result in local temperature variations. Temperature sensors installed on the reinforcement cage collect detailed temperature data along the entire pile during concrete curing to allow empirical identification of these temperature variations. This article investigates a new approach to the interpretation of the temperature variations from thermal integrity testing of cast in situ concrete piles and presents a field case study of this approach. The approach uses the heat of hydration and heat transfer theory and employs numerical modelling using the finite element method. The finite element model can be customised for different concrete mixes and pile geometries. The predicted temperature profile from the numerical model is then compared, in a systematic manner, to the field test temperature data. Any temperature discrepancies indicate potential anomalies of the pile structure. The proposed new interpretation approach could potentially reduce construction costs and increase the anomaly detection accuracy compared to traditional interpretation methods.