Thermal Integrity Profiling Research Articles

Thermal integrity profiling of cast-in-situ piles in sand using fiber-optic distributed temperature sensing

Defects in cast-in-situ piles have an adverse impact on load transfer at the pile‒soil interface and pile bearing capacity. In recent years, thermal integrity profiling (TIP) has been developed to measure temperature profiles of cast-in-situ piles, enabling the detection of structural defects or anomalies at the early stage of construction. However, using this integrity testing method to evaluate potential defects in cast-in-situ piles requires a comprehensive understanding of the mechanism of hydration heat transfer from piles to surrounding soils. In this study, small-scale model tests were conducted in laboratory to investigate the performance of TIP in detecting pile integrity. Fiber-optic distributed temperature sensing (DTS) technology was used to monitor detailed temperature variations along model piles in sand. Additionally, sensors were installed in sand to measure water content and matric suction. An interpretation method against available DTS-based thermal profiles was proposed to reveal the potential defective regions. It shows that the temperature difference between normal and defective piles is more obvious in wet sand. In addition, there is a critical zone of water migration in sand due to the water absorption behavior of cement and temperature transfer-induced water migration in the early-age concrete setting. These findings could provide important insight into the improvement of the TIP testing method for field applications.

Transient 3D-thermal-analysis of bored piles - Comparison of two software tools and validation using a test pile

Thermal integrity profiling (TIP) has become increasingly important as a test method for checking the integrity of bored piles in recent years. The application and the evaluation are very complex, which is why transient 3D thermal analyzes were carried out. Two software tools were compared and the results validated using real measurements on a test pile. A recommendation for the application and evaluation of thermal integrity profiling, and for the assessment of pile integrity is based on this work. After a brief description of the bored pile production and the test methods for checking the pile integrity, 3D thermal analyzes follow on different pile variants with the help of the software tools Thermaly and MATLAB®. The temperature measurements on the test pile are then analyzed. All results are then linked, evaluated and assessed. The evaluations show that the size and position of the thermal anomaly (here considered as “defect”) cannot be deduced from the temperature difference alone. The type of concrete and the pile diameter influence the measurement results. The limit values for the classification of the defects are to be selected taking the influencing factors into account. However, they must not be chosen too low (too sensitive), because otherwise unavoidable deviations within the measurement tolerances would be accidentally classified as defects. In addition, it must be taken into account that the arrangement of the measuring sensors and the point in time of the evaluation have a significant influence on the temperature differences at defects, or at any kind of thermal anomaly.

Orally Administered, Biodegradable and Biocompatible Hydroxypropyl-β-Cyclodextrin Grafted Poly(methacrylic acid) Hydrogel for pH Sensitive Sustained Anticancer Drug Delivery.

In the current study, a pH sensitive intelligent hydroxypropyl–β–cyclodextrin-based polymeric network (HP-β-CD-g-MAA) was developed through a solution polymerization technique for site specific delivery of cytarabine in the colonic region. Prepared hydrogel formulations were characterized through cytarabine loading (%), ingredient’s compatibility, structural evaluation, thermal integrity, swelling pattern, release behavior and toxicological profiling in rabbits. Moreover, the pharmacokinetic profile of cytarabine was also determined in rabbits. New polymer formation was evident from FTIR findings. The percentage loaded into the hydrogels was in the range of 37.17–79.3%. Optimum swelling ratio of 44.56 was obtained at pH 7.4. Cytarabine release was persistent and in a controlled manner up to 24 h. In vitro degradation of hydrogels was more pronounced at intestinal pH as compared to acidic pH. Toxicity studies proved absence of any ocular, skin and oral toxicity, thus proving biocompatibility of the fabricated network. Hydrogels exhibited longer plasma half-life (8.75 h) and AUC (45.35 μg.h/mL) with respect to oral cytarabine solution. Thus, the developed hydrogel networks proved to be excellent and biocompatible cargo for prolonged and site-specific delivery of cytarabine in the management of colon cancer.

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 technique to calibrate a 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 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.

Selection of Thermal Integrity Data Regression Parameters

Abstract Thermal integrity profiling (TIP) is a nondestructive method of evaluating the as-built features of cast-in-place concrete foundation elements such as bored piles, drilled shafts, continuous flight auger piles, barrettes, dams, or diaphragm walls. The technology measures the temperature of curing concrete along the length of the element to detect the presence (or absence) of hydrating cement, alignment of the reinforcing steel, and rebar cover thickness. Like many integrity methods used for drilled shafts, direct comparison of local concrete conditions are made relative to the overall normal or average concrete conditions with two exceptions: the top and bottom of the element, which cannot be directly compared with the rest of the shaft temperature without adjusting those measurements to account for end effects. This paper outlines the selection of the end adjustment parameters to ensure the top and bottom shapes are properly defined. The presented data regression process is based on both numerical model findings as well as the statistical findings from 232 TIP-tested shafts on the same project.

Full-Scale Load Testing and Extraction of Augered Cast-in-Place (ACIP) Piles in Central Florida

A full-scale field demonstration project consisting of installation, instrumentation, testing, and extraction of augered cast-in-place (ACIP) piles located in central Florida was undertaken in conjunction with the Florida Department of Transportation and the University of South Florida. Seven instrumented ACIP piles, with a nominal diameter of 457 mm (18 in) or 610 mm (24 in), were installed in mainly sand and silty sand. Load testing was performed on six ACIP piles: two in compression, two in tension, and two laterally. In addition, one of the ACIP piles was extracted for visual inspection and comparison to predictions and measurements. The program demonstrated the fully monitored installation and load tested performance of instrumented ACIP piles, along with the use of manual and automated monitoring; use and accuracy of embedded instrumentation, including thermal integrity profiling (TIP) and embedded strain gages; load-displacement behavior of tested ACIP piles; and the integrity and as-constructed geometry of an exhumed ACIP pile. This paper presents the details, results from the different testing performed, and observations from the experimental field program.

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.

Influence of Aggregates in Concrete on Fiber-Optic Based Thermal Integrity Profiling Analysis of Concrete Structures

Fiber-optic sensor has drawn wide attention in the nondestructive testing and evaluation of civil engineering materials due to its high accuracy and resolution as well as cost-efficiency. Currently, using optical fiber as the temperature sensor is proposed to conduct the thermal integrity profiling (TIP) of concrete structures. However, concrete is not a thermally homogeneous material as assumed in current studies of concrete TIP. Its essential components, such as aggregates may cause thermal inhomogeneity problems when implementing fiber-optic sensors for TIP. In this paper, we use the concrete structures with different grades of aggregates to conduct numerical simulation for nondestructive thermal testing. The goal is to investigate how the thermal inhomogeneity caused by aggregates would influence the testing result. Firstly, we establish three concrete structure models with three different grades of aggregates based on the scenarios where these concrete structures will be used. Then, we numerically simulate the thermal process on these models and extract the temperature at the location where optical fiber would be installed. The influence caused by the inhomogeneity of aggregate size and distribution as well as the possible method to minimize the effect are evaluated in the paper. Overall, aggregates of concrete have a significant influence on the accuracy of TIP analysis, and defects could be veiled if no proper treatment to the data is implemented for TIP analysis.

Evaluation of Thermal Integrity Profiling and Crosshole Sonic Logging for Drilled Shafts with Concrete Defects

Thermal integrity profiling (TIP), which uses temperatures measured along drilled shafts during concrete curing to identify defects, has recently gained favor as an allowable concrete integrity test method for drilled shafts. Drilled shaft concrete temperatures are theoretically sensitive to defects anywhere within the shaft, which presents an opportunity for improving detection over the widely used crosshole sonic logging (CSL) method. This paper describes investigations conducted to compare detectability from TIP and CSL measurements for various types of defects. TIP and CLS measurements are presented for three full-scale drilled shafts constructed with ten intentional defects varying in location, character, and size. Comparison of these measurements indicates TIP and CSL tests are generally complementary with regard to their detection abilities. Each test method is effective for identifying certain types of defects, but limited or incapable of identifying other types of defects. The paper also includes an evaluation of the role of time on the detectability of TIP interpretations, demonstrating that the temperature effect of defects generally peaks around the time of the maximum rate of temperature rise and decreases significantly thereafter.

Optical‐Fiber‐Based Smart Concrete Thermal Integrity Profiling: An Example of Concrete Shaft

Concrete is currently the most widely used construction material in the world. The integrity of concrete during the pouring process could greatly affect its engineering performance. Taking advantage of heat production during the concrete curing process, we propose an optical‐fiber‐based thermal integrity profiling (TIP) method which can provide a comprehensive and accurate evaluation of the integrity of concrete immediately after its pouring. In this paper, we use concrete shaft as an example to conduct TIP by using the optical fiber as a temperature sensor which can obtain high spatial resolution temperature data. Our method is compared with current thermal infrared probe or embedded thermal sensor‐based TIP for the concrete shaft. This innovation makes it possible to detect defects inside of the concrete shaft with thorough details, including size and location. First, we establish a 3D shaft model to simulate temperature distribution of concrete shaft. Then, we extract temperature distribution data at the location where the optical fiber would be installed. Based on the temperature distribution data, we reconstruct a 3D model of the concrete shaft. Evaluation of the concrete integrity and the existence of the potential defect are shown in the paper. Overall, the optical‐fiber‐based TIP method shows a better determination of defect location and size.

Integrity Testing of Pile Cover Using Distributed Fibre Optic Sensing

The integrity of cast-in-place foundation piles is a major concern in geotechnical engineering. In this study, distributed fibre optic sensing (DFOS) cables, embedded in a pile during concreting, are used to measure the changes in concrete curing temperature profile to infer concrete cover thickness through modelling of heat transfer processes within the concrete and adjacent ground. A field trial was conducted at a high-rise building construction site in London during the construction of a 51 m long test pile. DFOS cables were attached to the reinforcement cage of the pile at four different axial directions to obtain distributed temperature change data along the pile. The monitoring data shows a clear development of concrete hydration temperature with time and the pattern of the change varies due to small changes in concrete cover. A one-dimensional axisymmetric heat transfer finite element (FE) model is used to estimate the pile geometry with depth by back analysing the DFOS data. The results show that the estimated pile diameter varies with depth in the range between 1.40 and 1.56 m for this instrumented pile. This average pile diameter profile compares well to that obtained with the standard Thermal Integrity Profiling (TIP) method. A parametric study is conducted to examine the sensitivity of concrete and soil thermal properties on estimating the pile geometry.

Analyzing thermal integrity profiling data for drilled shaft evaluation

Thermal integrity profiling (TIP) is the most recent non-destructive test method to gain widespread popularity in post-construction evaluation of drilled shafts. The allure lies in its ability to detect anomalies across the entire cross-section of a shaft as well as provide a measure of lateral cage alignment. Similarly remarkable, early developments showed that the shape of a temperature profile (with depth) matched closely with the shape of the shaft, thus allowing for a fairly straightforward interpretation of data. Immediately apparent however, was that the relationship between shape and temperature was with two major exceptions: (1) near the ends of the shaft where heat can escape both radially and longitudinally and (2) where drastic changes in the surroundings are encountered (e.g. soil to water, soil to air). Today, methods for analyzing these portions of data exist, but can often involve tedious levels of parameter iterations and trial-and-error thermal modeling. This is particularly true when th...

Advancements in Drilled Shaft Construction, Design, and Quality Assurance: The Value of Research

For the past 20 years, researchers at the University of South Florida have been striving to bridge the gap between research and practice and to speed the process by which academic findings are implemented by the foundations industry. Their aim is and has been to solve on-going construction problems, enhance usable capacity, and assure quality foundation elements. This article addresses the findings of several research projects and how they are in use today. The topics include: seal slab construction, rapid hydration of mineral slurry, tip-grouted drilled shafts, and quality assurance using Thermal Integrity Profiling.

Thermal Integrity Profiling of Drilled Shafts

AbstractThe construction of drilled shafts as well as other cast in place foundation alternatives relies heavily on good practices from the contractor, engineer, and inspector in order to produce a quality foundation element. As many of the installation methods involve blind concreting processes, it is difficult to be certain of an intact concrete mass of the intended dimensions. A new integrity test has been developed that provides additional insight into the integrity of drilled shaft concrete. By measuring the temperature throughout the shaft via standard access tubes, the measured temperature profile can be compared to the normal signature associated with a shaft of the specified size. This article provides an overview of the new method development, test procedure, analysis, and results.