Coefficient Of Thermal Expansion Of Concrete Research Articles

Bridge decks under cold waves: Implications of concrete’s temperature-dependent CTE

Temperature fluctuations within a bridge deck during a cold wave event can cause severe continuity stresses in structures where movement is restrained. Thermal loads are accounted for using thermal gradients that vary depending on bridge location and cross-sectional geometry. However, the effect of temperature change on material properties, particularly on the coefficient of thermal expansion (CTE) is rarely accounted for in the analysis and design. A review of the literature indicates that the CTE of concrete materials can vary significantly with changes in temperature, especially under freezing conditions, whereas saturated or partly saturated concrete exhibits nonlinear expansion at temperatures below freezing, resulting from effective reversal of the CTE sign. This effect has not been considered in the literature, when investigating thermal actions on bridge decks in cold temperatures. The aim of this study is to analyze, using an advanced nonlinear F.E. platform, the structural response of a prestressed concrete box bridge structure subjected to cold wave events, when considering the effect of temperature on the nonlinearity, the magnitude and the sign of the CTE of concrete. Meteorological data from three historical cold events of different intensity is input in the thermal models to simulate the temperature distribution in the bridge deck; the estimated temperature field was then used in a structural model to determine the resulting thermal stresses. The temperature-dependence and nonlinearity of the CTE is modeled after calibration of the mathematical relationships against published data. The results indicate that this behavior has a significant influence on structural response, highlighting the need for pertinent consideration of its effect in the relevant sections of the bridge codes.

Three-dimensional microstructure based model for evaluating the coefficient of thermal expansion and contraction of asphalt concrete

The coefficient of thermal expansion (CTE) and contraction (CTC) are critical parameters for pavement design and thermal analysis. This paper develops a 3-D microstructure-based FE model to evaluate the CTE and CTC of asphalt concrete. The 3-D random microstructure of asphalt concrete was generated with an image-aided algorithm. In the presented algorithm, the random 3-D geometry of a single aggregate was generated with a single 2-D image captured by Aggregate Image System 2 (AIMS2). The randomly generated 3-D aggregates were packaged with PFC 3D to construct the 3-D microstructure for asphalt concrete with prescribed gradation. Then the 3-D microstructure of asphalt concrete was imported into FE software ABAQUS to calculate the CTE and CTC. To validate the results from the numerical simulation, a laboratory experiment was conducted to test the CTE/CTC of the asphalt concrete with the same material composition. With the validated FE model, the effect of aggregate type, shape, and spatial orientation on the CTE/CTE was analyzed. Results show that the relative differences between the average values of numerical and experimental data were 1.63%∼4.64% for the CTE, and 3.01%∼7.20% for the CTC. With the increase of temperature, the CTE first decreased and then increased, while the CTC first increased and then decreased. Compared with the 3-D microstructure-based model, both the 2-D plain stress and plain strain models tended to overestimate the CTE of asphalt concrete. When the aggregate orientation tended to be inclined to a certain direction, the CTC and CTE of the asphalt concrete parallel to that direction tended to be smaller. Asphalt concrete prepared with quartz gravels and sand stones tended to have higher CTC and CTE. While the CTC and CTE of asphalt concrete could be reduced by using limestones.

Autogenous deformation and coefficient of thermal expansion of early-age concrete: Initial outcomes of a study using a newly-developed Temperature Stress Testing Machine

Thermal and autogenous deformations of high-performance concrete at early ages have significant impact on the performance, serviceability, and durability of concrete structures. While substantial past research has significantly improved our fundamental understanding of the autogenous shrinkage and of the coefficient of thermal expansion (CTE) of cement paste and mortar, such understanding for concrete, especially modern types of high-performance concrete at early ages, remains inadequate. Accordingly, a new Temperature Stress Testing Machine (TSTM) capable of generating reliable data on autogenous shrinkage and CTE of concrete from very early ages has been built. After a review of relevant major aspects, key features of the newly-built TSTM are reported, with a focus on advanced thermal regulation and deformation capturing systems. The outcomes of a study using the newly-developed TSTM on autogenous deformation and CTE of early-age concrete (two mixtures with water-to-binder ratio of 0.35 and 0.42) subject to different curing temperatures (23, 35 and 45 °C) are then presented. Higher curing temperatures significantly accelerate the development of autogenous shrinkage at very early ages, whereas after the initial period, the magnitude of autogenous shrinkage cured at the intermediate temperature of 35 °C gradually becomes the largest. Despite this cross-over, the maturity concept appears appropriate to approximate the effect of curing temperature on autogenous shrinkage of concrete at early ages. The linear CTE of early-age concrete, obtained using stepped temperature profiles, follows a clear rising trend after setting. Based on the newly-measured CTE, an attempt was made to separate thermal strain and self-desiccation shrinkage, in which the presence of non-negligible delayed thermal strain became evident.

Evaluation of the Moisture Dependence of Concrete Coefficient of Thermal Expansion and Its Impacts on Thermal Deformations and Stresses of Concrete Pavements

The coefficient of thermal expansion (CTE) is one of the material properties of concrete that has the largest impact on rigid pavement performance. Concrete CTE is typically measured in the laboratory, under saturated conditions, or estimated on the basis of the mix constituents, past experience, or both. Whichever method is used, the mechanistic-empirical design of concrete pavements traditionally assumes a constant value for this material property. This assumption has important consequences in relation to predicting thermal deformations and stresses since the CTE of concrete actually changes with the concrete’s internal moisture conditions. The experimental data presented in this study show that this assumption, together with the way CTE is measured in the laboratory, leads to systematic underestimates of thermal deformations and stresses in concrete pavements. The experimental data come from six concrete overlays of asphalt pavements that were instrumented with thermocouples, relative humidity sensors, and vibrating wire strain gauges to measure the expansion/contraction and bending of the slabs because of temperature and moisture-related actions. The apparent CTE of the overlay slabs reached values up to 65% larger than the CTE measured in the laboratory under saturated conditions. Using finite element method modeling, it was determined that thermal stresses were up to 70% larger than predicted using the saturated CTE.

Predicting Long-Term Coefficient of Thermal Expansion of Paving Concrete

The coefficient of thermal expansion (CTE) of concrete is an important parameter that affects the design and performance analysis of concrete pavements. Higher CTE value results in increased curling and related stresses. A 28-day CTE value is used for designing rigid pavements. Though previous studies have revealed that coarse aggregate mineralogy has substantial effects on the CTE value of paving concrete, it is not known yet how CTE value changes with the age of concrete in the long-term. In this study, seven concrete mixes with different coarse aggregate mineralogy are tested in the laboratory and data is analyzed to examine CTE. Results show that limestone has the lowest CTE values compared with other coarse aggregates. Concrete CTE increases from 6.4% to 12.6% as it ages. This increase in CTE may result in increased thermal distresses as concrete pavement ages. Therefore, a single value of 28-day CTE should not be used in the design of concrete pavements. In this study, a prediction model is developed to determine aged CTE incorporating mixture volumetrics and concrete strength properties. The same can be incorporated in Pavement Mechanistic Empirical (ME) Design software to better predict the rigid pavement performance.

Field evaluation of the impact of environmental conditions on concrete moisture-related shrinkage and coefficient of thermal expansion

This study evaluates the impact of the environmental conditions on the moisture-related shrinkage and the coefficient of thermal expansion (CTE) of concrete. The evaluations are based on the strain measured in a series of unrestrained shrinkage prisms during fifteen months. The prisms included four concrete mixtures containing either portland cement or calcium sulfoaluminate cement. The prisms were fabricated in the field and left outdoors so that they were subjected to natural rainfall, sun radiation, and daily and seasonal changes in air temperature and relative humidity (RH). A strain model was used to divide the deformation measured in the prisms into its thermal and moisture-related components. By doing so, the evolution of concrete moisture-related shrinkage and CTE during the fifteen-month period was back-calculated. A strong correlation (R2 = 0.998) existed between the maximum moisture-related shrinkage that was back-calculated in the outdoor prisms and the ultimate moisture-related shrinkage measured in the laboratory under constant temperature and 50 percent air RH. Because of drying, concrete CTE reached values that were up to 50 percent higher than the CTE determined in the laboratory under saturated conditions. Concrete moisture-related shrinkage and CTE systematically decreased after the rainfall events, except when the concrete was already saturated. Rainfalls, rather than air RH, controlled the re-wetting of the concrete in the field.

Prediction of concrete coefficient of thermal expansion and other properties using machine learning

The coefficient of thermal expansion (CTE) significantly influences the performance of concrete. However, CTE measurements are both time consuming and expensive; therefore, CTE is often predicted from empirical equations based on historical data and concrete composition. In this work we demonstrate the application of linear regression and random forest machine learning methods to predict CTE and other properties from a database of Wisconsin concrete mixes. The random forest model accuracy, as assessed by cross-validation, is found to be significantly better than the American Association of State Highway and Transportation Officials (AASHTO) recommended prediction methods for CTE, denoted as level-2 and level-3.

A new test setup for measuring early age coefficient of thermal expansion of concrete

Coefficient of thermal expansion (CTE) of concrete changes at early ages mainly due to microstructural modifications that occur during cement hydration. This paper proposes an innovative way to assess the CTE of concrete since very early ages, with the original inclusion of an internal heating/cooling system, that allows to speed up the thermal balance cycles, and increase the number of CTE measurements during the early ages. The method comprises a specimen of 154 mm diameter and 300 mm height, submitted to successive heating and cooling steps with thermal variations of 5 °C, right after casting. A spiral heating/cooling tube, embedded in concrete, is used to circulate the controlled temperature water bath inside the specimen. This paper demonstrates the feasibility of the strategy for accelerating thermal equilibrium of the specimen, both experimentally and through numerical simulation. The short duration of the thermal cycle in this proposal strongly increases the ability of the method in capturing the early kinetics of CTE evolution, allowing to measure the CTE as soon as 4.1 h after mixing. With durations of each full temperature cycle of 1.5 h, it was possible to obtain as many as 12 CTE measurements within the first 24 h of testing, which is an important improvement in regard to similarly sized specimens in the literature. Furthermore, when the information obtained from the proposed test method is combined with the continuous feed about E-modulus of concrete that can be obtained through application of the EMM-ARM technique, very definite conclusions can be attained about the expectable stress levels that can be attained in concrete elements at early ages, due to the early variation of CTE. Three concrete mixtures are used to verify applicability of the proposed method for measuring early age CTE of concrete. The calculated values for these concrete mixtures are in agreement with the data found in the literature.

Prediction of Concrete Coefficient of Thermal Expansion by Effective Self-Consistent Method Considering Coarse Aggregate Shape

AbstractThermal cracking is a perennial concern for large-volume concrete projects; for instance, dams and foundations. The concrete coefficient of thermal expansion (CTE) is well recognized as a k...

Finite-Element Modeling and Analysis of Early-Age Cracking Risk of Cast-In-Place Concrete Culverts

Extensive cracking was found in several cast-in-place concrete culverts in Alabama. This condition can decrease the long-term durability of the culverts. Early-age stress development in concrete is influenced by temperature changes, modulus of elasticity, stress relaxation, shrinkage, thermal coefficient of expansion, and the degree of restraint. The objective of this study is to determine means to mitigate early-age cracking in culverts by evaluating the cracking risk. Finite-element analysis was used to model the early-age stress by accounting for the following factors: construction sequencing, support restraint, concrete constituents, temperature effects, and the time-dependent development of mechanical properties, creep/relaxation, and drying shrinkage. Experimental results from restraint to volume change tests with rigid cracking frames were used to verify the accuracy of the finite-element analysis. A parametric study was performed to quantify the effect of changing joint spacing, joint type, construction sequence, concrete coefficient of thermal expansion, placement season, and concrete type on the risk of early-age cracking. The finite-element model results revealed that the use of the following measures will reduce the risk of early-age cracking in cast-in-place concrete culverts: concrete with lower coefficient of thermal expansion, contraction joints, sand-lightweight concrete or all-lightweight concrete, and scheduling the casting of the culvert wall to minimize the difference in its placement time relative to its previously cast base. Alternatively, to minimize the contribution of thermal effects on risk of cracking, the construction schedule should be developed to avoid concrete placement during hot weather conditions.

Thermal expansion prediction of cement concrete based on a 3D micromechanical model considering interfacial transition zone

Thermal expansion of concrete is a main factor of concrete failures especially in underground waterproof engineering, overlong structural engineering and mass concrete construction. Thus, the coefficient of thermal expansion (CTE) of concrete is an important parameter to be determined. A micromechanical model, namely the 3D Two-Layer Built-in Model is developed to obtain the overall CTE of cement concrete. The existence of interfacial transition zone (ITZ) between aggregate and cement paste is considered in the model, and the ITZ model is simplified as a spring layer with a certain stiffness k. According to the existing testing data of three types of cement concrete whose aggregates are siliceous river gravel (RG), dolomitic limestone (DL) and granite (GR) respectively, the CTEs of prediction model are obtained and validated by the measured values. Moreover, the effects of interface, water cement ratio, volume fraction ratio of fine aggregate to coarse aggregate, air voids, CTE of coarse aggregate and elastic modulus of cement paste on the CTE are analyzed.

Effect of Aggregate Mineralogy and Concrete Microstructure on Thermal Expansion and Strength Properties of Concrete

Aggregate type and mineralogy are critical factors that influence the engineering properties of concrete. Temperature variations result in internal volume changes could potentially cause a network of micro-cracks leading to a reduction in the concrete’s compressive strength. The study specifically studied the effect of the type and mineralogy of fine and coarse aggregates in the normal strength concrete properties. As performance measures, the coefficient of thermal expansion (CTE) and compressive strength were tested with concrete specimens containing different types of fine aggregates (manufactured and natural sands) and coarse aggregates (dolomite and granite). Petrographic examinations were then performed to determine the mineralogical characteristics of the aggregate and to examine the aggregate and concrete microstructure. The test results indicate the concrete CTE increases with the silicon (Si) volume content in the aggregate. For the concrete specimens with higher CTE, the micro-crack density in the interfacial transition zone (ITZ) tended to be higher. The width of ITZ in one of the concrete specimens with a high CTE displayed the widest core ITZ (approx. 11 µm) while the concrete specimens with a low CTE showed the narrowest core ITZ (approx. 3.5 µm). This was attributed to early-age thermal cracking. Specimens with higher CTE are more susceptible to thermal stress.

Determination of Coefficient of Thermal Expansion (CTE) of 20MPa Mass Concrete Using Granite Aggregate

Experimental test was carried out to determine the coefficient of thermal expansion (CTE) value of 20MPa mass concrete using granite aggregate. The CTE value was established using procedure proposed by Kada et al. 2002 in determining the magnitude of early-ages CTE through laboratory test which is a rather accurate way by eliminating any possible superimposed effect of others early-age thermal deformation shrinkages such as autogenous, carbonation, plastic and drying shrinkage. This was done by submitting granite concrete block samples instrumented with ST4 vibrating wire extensometers to thermal shocks. The response of the concrete samples to this shock results in a nearly instantaneous deformation, which are measured by the sensor. These deformations, as well as the temperature signal, are used to calculate the CTE. By repeating heat cycles, the variation in the early-ages of concrete CTE over time was monitored and assessed for a period of upto 7 days.The developed CTE value facilitating the verification and validation of actual maximum permissible critical temperature differential limit (rather than arbitrarily follow published value) of cracking potential. For thick sections, internal restraint is dominant and this is governed by differentials mainly. Of the required physical properties for thermal modelling, CTE is of paramount importance that with given appropriate internal restraint factor the condition of cracking due to internal restraint is governs by equation, ΔTmax= 3.663ɛctu / αc. Thus, it can be appreciated that an increase in CTE will lower the maximum allowable differential for cracking avoidance in mass concrete while an increase of tensile strain capacity will increase the maximum allowable temperature differential.

Thermal Expansion Coefficient Testing of Road Concrete Using Optical Lever

The method for determining the coefficient of thermal expansion (CTE) of road concrete with optical lever system was introduced. CTE of 144 concrete specimens was measured with it. The coarse aggregate in these specimens contains 8 types from 19 origins. The measured result was satisfactory verified by AASHTO T 336. The results showed that: CTE of road concrete was ranged from 6 4.76 10  /℃ to 6 12.1 10  /℃. Coarse aggregate type had a great influence on CTE. The higher CTE of the aggregate, the higher CTE of concrete contained that aggregate when aggregate content was equivalent. The sensitivity of concrete for different temperature ranges when the temperature gradient was equal has no significant difference. Meanwhile, amount of concrete expanse when temperature increment was equal with concrete shrinkage when temperature reduction.

Coefficient of Thermal Expansion of Polymer Concrete with Different Polymeric Binders

The coefficient of thermal expansion (CTE) is one of the material factors affecting the behavior of concrete structures. This study reports the typical range of CTE for polymer concrete with different types of polymeric binder based on extensive literature surveys. The results revealed the CTE of polymer concrete generally fell between 12.5 and 28.6 x 10-6/°C, which is about twice or three times higher than that of ordinary cement concrete, because the CTE of polymeric binder is much larger than that of cementitious binders. The findings of this study will provide useful information for the design and analysis of polymer concrete members and repair components.

A systematic optimization technique for the coefficient of thermal expansion of Portland cement concrete

The coefficient of thermal expansion (CTE) of concrete is one of the important concrete properties that is responsible for the deterioration of concrete pavements and structures. A significant savings in repair and rehabilitation cost can be achieved by optimizing the CTE of concrete according to the need of the concrete pavements and structures. CTE reduction also improves the durability and longevity. CTE of concrete is dependent on the CTE of its constituents. Replacing high-CTE aggregates with low-CTE aggregates can significantly reduce the CTE of overall concrete. In addition, concrete CTE can be reduced by reducing the cement paste volume. This study presented systematic guideline to select the concrete constituents to achieve a target CTE.

Testing and modelling of hygro-thermal expansion properties of concrete

This paper investigates the hygro-thermal expansion behavior of concrete as a function of the internal temperature and humidity changes caused by thermodynamics and moisture diffusion. The effects of age and moisture on the Coefficient of Thermal Expansion (CTE) of concrete were evaluated by measuring the temperature, humidity, and strain of cylindrical and prismatic concrete specimens. Based on the measurements, the effects of age and moisture on the concrete CTE were analyzed. In addition, CTE, which depends on moisture, was modeled and validated by comparison with existing research results. The study results indicate that the effect of age on concrete CTE is not significant. CTE was maximized at a concrete humidity of 85% and was about 1.6 times larger than the minimum CTE measured at a humidity of 95~100% or below 50%. The hygro-thermal model developed in this study predicted the measured CTE reasonably well. The CTE of a concrete slab is an important parameter in the design of concrete pavement. More accurate design methodology can be implemented by including the effect of moisture on CTE.

Interlaboratory Study and Precision Statement for AASHTO T 336 Test Method

With the recent release of AASHTOWare Pavement ME Design software, there will be a greater emphasis on measuring the coefficient of thermal expansion (CTE) of concrete because of its significance on predicted distress and design life. The most widely used test method to measure the CTE of concrete is the AASHTO T 336 test method. Data are presented from an interlaboratory (round robin) study conducted by FHWA; this study included 20 CTE units and laboratories representing FHWA, state highway agencies, universities, commercial testing laboratories, and the concrete paving industry. As part of the study, each laboratory tested nine concrete specimens (three concrete mixtures 3 three specimens per mixture) that spanned the typical range of CTE values for concrete. On the basis of this interlaboratory study for the AASHTO T 336 test method, the within-laboratory single operator standard deviation was found to be 0.12 mstrain/°C and the between-laboratory standard deviation was found to be 0.28 mstrain/°C. Data from the study also showed that there was no statistically significant difference between custom-built CTE devices versus commercially available testing devices. This demonstrates the ruggedness of the current test method.

Spalling related to Coefficient of Thermal Expansion (CoTE) of Continuously Reinforced Concrete Pavement in Texas

Concrete volume changes due to temperature and moisture variations (environmental loading) are severely restrained in Continuously Reinforced Concrete Pavement (CRCP) by longitudinal reinforcement and base friction, resulting in numerous transverse cracks, which are held tight by primarily longitudinal steel. Tight transverse cracks provide good load transfer at transverse cracks, ensuring good performance of CRCP. In general, an adequate amount of longitudinal steel and base friction used in CRCP will restrain concrete volume changes to an adequate level, keeping transverse cracks tight and providing good CRCP performance. In Texas, the performance of CRCP is excellent; however, severe spalling problems have been observed in CRCP sections where a certain type of coarse aggregate was used, resulting in costly repairs and traffic delays. This study investigated the causes of severe spalling problems in CRCP in Texas. Fourteen CRCP sections with severe spalling and 10 sections with no spalling distress were identified. A minimum of two cores were taken from each section and concrete material properties, including Coefficient of Thermal Expansion (CoTE) and modulus of elasticity, were evaluated. Test results indicate a strong correlation between spalling and concrete CoTE. Concrete with a CoTE larger than 9.9 × 10-6/°C (5.5 × 10-6/F) is quite prone to severe spalling. On the other hand, CRCP sections with a concrete CoTE smaller than 9.9 × 10-6/°C showed almost no spalling problems.

Effect of Internal Water Pressure on the Measured Coefficient of Thermal Expansion of Concrete

A study was conducted to evaluate the effect of coefficient of thermal expansion (CTE) test procedures and length-change measuring devices on the measured CTE values. Twenty different coarse aggregate sources were tested using the Texas Department of Transportation (TxDOT) and the American Association of State Highway and Transportation Officials (AASHTO) suggested CTE methods. Two different types of length-change measuring devices, linear variable differential transformers (LVDTs) and differential variable reluctance transducers (DVRTs), were used. No significant effects of length-change measuring devices were observed on the CTE values measured by the TxDOT method. However, the test methods have shown effects on the measured values. The TxDOT method yields higher CTE values than the AASHTO method. Data obtained in this study confirmed that the internal water pressure development during the heating and cooling cycles is one of the potential reasons. Internal water pressure can significantly affect the CTE of concrete. Further investigation is needed to determine the effect of internal water pressure on the CTE, which affects the design and service life of concrete pavements.