Mitigation of Heat of Hydration with Large Diameter Drilled Shafts: Papers 2018-2021

Boeckmann, El-tayash, and Loehr. Advancements in drilling and concrete technology and increased load demand for bridge foundations have fueled a recent tendency toward larger and larger diameter drilled shafts for support of transportation structures. Concerns over the potential for thermal damage in large concrete elements have led some agencies to impose so-called “mass concrete” provisions on drilled shafts, while other agencies have explicitly exempted drilled shafts from some or all requirements in mass concrete provisions. Opponents of designating drilled shafts as mass concrete correctly point to the lack of recorded evidence of thermal damage to drilled shafts, and to the unique benefits of confinement provided by the ground and heavy reinforcement concentrated near the shaft edges. Proponents of designating drilled shafts as mass concrete correctly note that no one has ever looked for thermal damage, and note the frequent observation of high temperatures in drilled shafts that have been associated with thermal damage in above-ground concrete elements. The objective of this paper, developed out of research for the U.S. Federal Highway Administration (FHWA), is to present rational procedures for establishing thermal requirements for drilled shafts, and to do so in a manner that: (a) is based on research developments in relation to mass concrete and (b) includes consideration of the unique characteristics of drilled shafts compared with above-ground concrete elements. Both aspects of this paper’s consideration of thermal requirements for drilled shafts are in contrast to the approach adopted by some agencies of applying mass concrete provisions developed at least 50 years ago for above-ground applications. Procedures described in this paper are intended to appropriately consider and address thermal requirements without unnecessarily imposing restrictive measures that complicate construction and introduce additional concrete integrity risks.

Sun, Elshafie, et al. 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.

Han. Since the size of foundation increases to support the enormous superstructure, the massive foundation generates the problematic temperature development. This study addresses the use of horizontal construction joint referred to as “layered system” as a curing scheme for alleviating the thermal behavior of foundation. To compare the thermal performance of the layered system, the current curing schemes (e.g., insulation system, post-cooling) also simulated by using the validated finite element model. In the study, the layered system could be the recommended curing method in the foundation element to produce significant savings in time, effort, and cost on an actual construction project.

Riding, Vosahlik, et al. Concrete adiabatic temperature rise is often used to predict temperature development in mass concrete thermal control plans. Several experimental methods are currently being used to obtain the adiabatic temperature rise. This study compared the adiabatic temperature rise from seven concrete mixtures obtained from fully adiabatic, semi-adiabatic, and isothermal calorimetry. The study found a low adiabatic temperature rise difference between semi-adiabatic calorimetry and fully adiabatic calorimetry for ordinary portland cement concrete mixtures for 28 days and for mixtures containing Class F fly ash during the first 10 days after mixing. Semi-adiabatic calorimetry did not match well to fully adiabatic calorimetry results when slag cement was used because the rate of heat development could not be well described by a three-parameter heat of hydration model. Adiabatic temperature rises calculated using isothermal calorimetry results did not compare favorably to measured fully adiabatic results, even when temperature effects on hydration rate were accounted for using an Arrhenius apparent activation energy approach.

Han, Chun, et al. This study focused on the optimization of concrete mixture and geometric design parameters for a drilled shaft to effectively reduce the potential degradation of mass concrete. At concrete’s early hardening stage, the heat of hydration plays a pivotal role that affects the integrity of mass concrete. The Florida Department of Transportation (FDOT) currently designates concrete drilled shafts with a minimum diameter of 1.8 m as mass concrete due to a great concern about high temperature development. In this study, a validated thermal finite-element (FE) model for a drilled shaft with a diameter of 1.8 m was developed for a parametric analysis to determine the effects of concrete property, surrounding soil condition, geometric design, and pipe cooling on temperature development. The results indicated that the use of supplementary cementitious material (SCM) significantly reduced the temperature development in a drilled shaft. The temperature development increased as the placement temperature and volume:surface area (V:A) ratio increased. In particular, the use of a centroid void shaft and a pipe cooling system significantly decreased the maximum temperature and temperature differential, and could be a viable solution to effectively mitigate the temperature development, preventing potential disintegration due to the effects of delayed ettringite formation, strength reduction, or thermal cracking.

Hamid, Chorzepa. The main challenge with mass concrete structures lies in temperature rise and temperature differentials resulting from the heat of hydration of cementitious materials. Therefore, controlling the heat of hydration in mass concrete structures is important in order to minimize and potentially prevent cracks from forming. In this study, a novel material and/or combination of materials were utilized to study the effect on the heat of hydration. An isothermal calorimeter is used to measure the heat of hydration in concrete mixtures including barium oxide (BAO), which is a phase changing material. Different percentages of other supplementary cementitious materials were utilized based on the amount of total cementitious materials in the mixtures. The results were also compared with the heat of hydration of mixtures containing conventional mass concrete mixtures containing cement supplementary materials such as slag and fly ash. It is concluded that BAO significantly retarded the rate of hydration and slightly reduced the magnitude of the heat of hydration peak in concrete mixtures.

Bourchy, Barnes, et al. In the case of massive concrete structures, the heat generated by cement hydration may cause cracking due to thermal strains. The mix design of the concrete used for such structures has to take account of mechanical properties and generated temperatures. Using experimental design principles, the hydration heat and the development of compressive strength are measured in order to determine how the composition of concrete and the presence of SCM influence the characteristics of concrete and to create a mix design protocol. This protocol can help to determine which mix design minimizes the hydration temperature for a given compressive strength.

Boeckmann, Loehr. 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.

Han, Lawrence, Tia, and Bergin. This article presents an investigation on the early-age thermal behavior of drilled shafts with different geometric dimensions through numerical analysis. Finite-element models by using DIANA software were developed to analyze the thermal behavior of drilled shafts. In order to validate the finite-element model, four concrete drilled shafts were constructed and evaluated under Florida conditions for monitoring their actual thermal behavior. The calculated temperatures from the analytical model matched well with the measured values from the constructed shafts. All the drilled shafts with a diameter greater than 1.83 m (6 ft) produced a high maximum temperature and a maximum temperature differential which failed the allowable temperature set by the American Concrete Institute and the Florida Department of Transportation to prevent thermal cracking. Also, it was found that the dimension of the drilled shaft had the greatest influence on the maximum temperature inside a shaft. Analysis was performed to investigate whether the use of drilled shafts with a centroid void in the shaft could reduce the maximum temperature and maximum temperature differential. The results indicated that this is a viable alternate shaft design for controlling the maximum temperature and maximum temperature differential in concrete drilled shafts at an early age.

Schoen, Canivan, & Camp. Thermal integrity profiling (TIP) is a relatively new non-destructive test (NDT) method which can be used to assess the integrity of cast-in-place deep foundations by using the heat of hydration to assess the quality. The heat generated during curing is directly related to the cement content and shaft geometry and is therefore a useful indicator of anomalies. The temperature can be measured at a discreet time with an infrared probe lowered slowly into the shaft through a conduit, or continuously by data loggers attached to thermal wires embedded within the concrete or placed within water filled tubes. Two case studies are presented demonstrating the methods of TIP and their observed effectiveness for determining anomalies in drilled shafts. Based on the case studies, in the authors’ experience, thermal wires embedded within the concrete collects data with the most accurate representation of the integrity of the drilled shaft, and is the preferred method of the three for most applications.

Mullins, Johnson, Winters. Mass concrete defines elements where heat formation due to exothermic hydration reactions can induce tension cracking as a
result of excessive temperature differentials upon cooling. These conditions are anticipated in dams, large footings, and, in some cases, pier columns and caps where internal cooling systems can be used to moderate the effects. Until 2006, drilled shafts were not recognized by the Florida Department of Transportation as mass concrete due to the relatively small diameters (4 ft [1.2 m] diameter being the most common) and/or the perception that the surrounding environment was not conducive to producing mass concrete conditions. This paper presents the results of a full-scale shaft demonstration project where a 9 ft (2.74 m) diameter shaft was constructed with a 3.8 ft (1.17 m) diameter central void to control temperature and reduce costs. Peak and differential temperatures were shown to stay well within specified limits without the need for internal cooling systems

Moon, Ramanathan, et al. Blast furnace slag (SL) is an amorphous calcium aluminosilicate material that exhibits both pozzolanic and latent hydraulic activities. It has been successfully used to reduce the heat of hydration in mass concrete. However, SL currently available in the market generally experiences pre-treatment to increase its reactivity to be closer to that of portland cement. Therefore, using such pre-treated SL may not be applicable for reducing the heat of hydration in mass concrete. In this work, the adiabatic and semi-adiabatic temperature rise of concretes with 20% and 40% SL (mass replacement of cement) containing calcium sulfate were investigated. Isothermal calorimetry and thermal analysis (TGA) were used to study the hydration kinetics of cement paste at 23 and 50 °C. Results were compared with those with control cement and 20% replacements of silica fume, fly ash, and metakaolin. Results obtained from adiabatic calorimetry and isothermal calorimetry testing showed that the concrete with SL had somewhat higher maximum temperature rise and heat release compared to other materials, regardless of SL replacement levels. However, there was a delay in time to reach maximum temperature with increasing SL replacement level. At 50 °C, a significant acceleration was observed for SL, which is more likely related to the pozzolanic reaction than the hydraulic reaction. Semi-adiabatic calorimetry did not show a greater temperature rise for the SL compared to other materials; the differences in results between semi-adiabatic and adiabatic calorimetry are important and should be noted. Based on these results, it is concluded that the use of blast furnace slag should be carefully considered if used for mass concrete applications.

Haung, Liu. Thermal cracks are the main concerns when temperatures increase in mass concrete structures. It is important to explore the temperature rise rules and to find effective methods to control the hydration heat of mass concrete structures. In this study, based on a 1:5 scaled segmental model test of an arch bridge, the temperature field and temperature time histories for the core concrete of the massive pier caused by the hydration heat were measured. The finite element method (FEM) was also used to simulate the hydration temperature field through commercial FEM software. The tested temperature time history curves showed that the temperature of the concrete increases rapidly but decreases slowly. The maximum temperature at the center of the concrete reached 86.6 °C, and the maximum temperature difference from the center to the surface reached 30.6 °C, which may lead to concrete cracks. It was also found that the calculated temperature contours and temperature time history curves agreed well with the tested ones, which verified the accuracy of the FE model. Finally, the verified FE model was used to perform parametric analysis to explore the effects of thermal parameters on thermal behaviors, and an effective heat control method, i.e., the pipe cooling method with cold water, was proposed. Thermal stress analysis was also conducted and results showed that the pipe cooling method is an effective way to reduce both the hydration temperature and thermal stress.

Han, Chun, et al. This study focused on investigating the early-age thermal behavior of drilled shafts under different surrounding soil’s thermal properties. Four 1.8 m (6 ft) diameter drilled shafts were constructed using two different concrete mixes and two different soil conditions. A finite element (FE) model was developed to estimate the temperature development of drilled shafts at early-age and validated using temperatures measured from full-scale drilled shafts constructed in the field. The validated analytical model was then used to perform a parametric analysis to evaluate the effects of the surrounding soils at different moisture conditions on change in thermal behavior of drilled shafts at early-age. Results indicated that the FE model developed was capable of accurately predicting temperature development of drilled shafts at early-age. A drier surrounding soil (i.e., gravimetric moisture content of 0% through 6%) was able to serve as a better insulating material that leads to reduced temperature difference in the drilled shafts. Also, it was identified the use of high-volume fly ash concrete mix in conjunction with relatively low heat of hydration can reduce the temperature difference in the drilled shaft

Hamid, Chorzepa, et al. As the size of modern infrastructure increases, novelties related to mass concrete mixtures including supplementary cementitious materials (SCMs) become critical. The effects of binary and ternary cement replacement mixtures including metakaolin, silica fume, ground calcium carbonate, granulated blast furnace slag, and fly ash on the rate and amount of heat generated in concrete mixtures are investigated. Twenty three binary and ternary mixtures with a water-to-cementitious binder ratio of 0.43 are evaluated. Between 15% and 45% cement replacement by weight is considered. Results indicate that binary mixtures containing metakaolin or silica fume offer no advantage in reducing the amount of heat but increase compressive strength by 20%. On contrary, ternary mixtures, including two pozzolanic materials, provide 15% reduction in the amount of heat evolution without compromising strength. This reduction is observed regardless of alumina (Al) or silica (Si) content in pozzolanic materials when 45% cement is replaced with a combination of slag and metakaolin, or slag and silica fume. Furthermore, the effect of increased calcium (Ca) content is investigated. It is concluded that ternary mixtures with decreased Ca/(Al+Si) ratio reduce internal temperature in mass concrete structures and are less likely to be exposed to the threshold temperature for delayed ettringite formation.

Chorzepa, Hamid, et al. This study focuses on creating mechanistic thermal and structural analysis models for determining thermal stress and cracking in massive concrete structures when alternative, unconventional, or innovative concrete mixtures are considered for design. Current study, funded by the Georgia Department of Transportation, investigates thermal modeling techniques, applying theory to practice, in order to control cracks caused by hydration heat. Thermal cracking caused by hydration heat is detrimental to the long-term durability of large infrastructure such as bridge seals, foundations, and piers. In the proposed analysis, environmental conditions such as convection, weather variation, and solar radiation are considered in a multi-physics model. The thermal model will be validated by an experimental program. Subsequently, a structural model is designed to read in a nonlinear temperature profile and perform a nonlinear cracking analysis of structures based on the boundary and environmental conditions of a bridge seal structure. It is concluded that the proposed evaluation process is efficient and robust in evaluating the effect of innovative and unconventional concrete mixtures that are optimized to control the maximum temperature and temperature variations on mass concrete structures. It is also concluded that the experimental and analysis procedure is highly efficient to validate and streamline the thermal and structural evaluations without a loss of accuracy.

Boeckmann, Loehr, et al. Thermal Integrity Profiling (TIP) methods for evaluating drilled shaft concrete integrity have emerged in recent years as a viable alternative to Crosshole Sonic Logging (CSL) methods. TIP methods use measurements of concrete temperatures along the length of the drilled shaft reinforcing cage to identify potential defect locations from zones of low temperature. TIP methods are appealing because they should be sensitive to defects outside the reinforcing cage, an area not evaluated with CSL. To evaluate the ability to detect defects with TIP methods compared with CSL methods, three 4 ft diameter by 30 ft long drilled shafts with ten intentional defects were installed in Waukesha, Wisconsin. The defects varied in location, size, and material. TIP and CSL tests were performed on all three shafts. The results revealed TIP and CSL to be complementary. Each test is particularly well-suited to identifying certain types of defects but limited or incapable of identifying other types of defects. The alignment of detection abilities attributed to each method is such that virtually any significant defect should be detectable by one or both tests. The results indicated TIP is effective for identifying defects due to weak concrete and defects outside the reinforcing cage. Smaller temperature decreases were observed for tremie breach defects and inclusions within the reinforcing cage, and no TIP effect could be discerned for soft bottom defects. CSL results were sensitive to defects within the reinforcing cage, including inclusions, tremie breach effects, and soft bottom conditions but not weak concrete. CSL results were also not affected by defects outside the reinforcing cage. TIP measurements indicated significantly greater sensitivity to defects at times corresponding to roughly half the time to peak temperature. Improvements to TIP interpretation methods would likely improve defect detection.