Vinh Dao - Academia.edu (original) (raw)

Papers by Vinh Dao

Research paper thumbnail of Evaluation of zero-stress temperature and cracking temperature of high performance concrete at early ages

Materials and Structures

Assessing the risk of cracking of high performance concrete induced by restrained volume changes ... more Assessing the risk of cracking of high performance concrete induced by restrained volume changes from early ages is of considerable significance. To estimate and control such cracking risk of high performance concrete, two characteristic temperatures, namely zero-stress temperature (Tz) and cracking temperature (Tx) are crucial. In this study, the two temperatures are investigated in-depth by both theoretical analysis and experimental studies. For predicting the evolutions of Tz and Tx from early ages, rigorous yet practical models are proposed, which crucially take the visco-elastic behaviour of concrete into account. The reliability and predictive capability of the proposed models are demonstrated through a series of comparisons between the predicted and the measured results. Based on the predicted Tz and Tx profiles, practical thermal control criteria for preventing concrete from cracking caused by restrained strain are put forward. In principle, the actual temperature (T) of con...

Research paper thumbnail of Evolution of Coefficient of Thermal Expansion of Concrete at Early Ages

Lecture Notes in Civil Engineering, 2019

Together with drying shrinkage and autogenous deformations, thermal strain is one of the driving ... more Together with drying shrinkage and autogenous deformations, thermal strain is one of the driving force of cracking of cement-based materials at early ages. However, current understanding of these early-age deformations remains unsystematic and further studies are needed. In this paper, evolution of thermal strain and coefficient of thermal expansion (CTE) are reviewed. Based on a newly built test setup at The University of Queensland, the development of the CTE of concrete at early ages was measured and investigated. It is found that CTE shows a clear rising trend after setting, meaning that CTE cannot be seen as constant even though this has often been done for modelling and design purpose. Based on newly-measured CTE, the separation process of self-desiccation shrinkage and thermal strain was studied. It is noted that the separation process is rather complicated due to the effects of delayed thermal strain. Through literature review, it is demonstrated that the delayed thermal strain is closely linked to relative humidity change inside concrete. Since the development of self-desiccation shrinkage is also affected by such relative humidity change, there appears a coupling effect between self-desiccation shrinkage and delayed thermal strain, which should be further studied in the future.

Research paper thumbnail of Constitutive models of concrete at elevated temperatures: studying the effect of temperature gradients

The outbreak of fire can have serious consequences in the structural performance of a load-bearin... more The outbreak of fire can have serious consequences in the structural performance of a load-bearing concrete structure. To assure adequate fire performance, detailed knowledge of fundamental mechanical properties of concrete at elevated temperatures is crucial. This paper first highlights limitations of existing knowledge regarding the mechanical response of concrete at elevated temperatures, including the inconsistent thermal boundary conditions and intentionally-minimised temperature gradients in “standardized” conventional concrete material testing. Accordingly, it is argued that the effect of temperature gradients within concrete on its fire performance has not been extensively or directly addressed. On this basis, the paper outlines key features of an ongoing research programme at The University of Queensland aimed at studying the performance of concrete in fire using a novel medium-scale testing method. By heating using radiant panels, welldefined and consistently-controlled he...

Research paper thumbnail of Deformation capturing of concrete structures at elevated temperatures

Procedia Engineering, 2017

Reliable deformation measurement is required for proper quantification of fire performance of con... more Reliable deformation measurement is required for proper quantification of fire performance of concrete structures. Predictive capability of models for many critical properties, including Young's moduli, stress-strain relationships and load-induced thermal strains, is first and foremost dependent on such reliable deformation capturing. This paper first presents a state-of-the-art review of existing methods for capturing deformation of concrete structures at elevated temperatures. Key merits, limitations and challenges associated with each measuring technique are discussed. It is shown that existing testing facilities and measuring instruments generally do not allow reliable direct measurement of deformation and strain of high-temperature concrete. As a result, the deformation has typically been captured either indirectly or outside the heated zones, inevitably introducing additional uncertainty and errors that are difficult to be adequately quantified. On the basis of that review, the paper details a new test setup for reliable non-contact full-field deformation capturing of concrete structures at high temperatures using 3D Digital Image Correlation technique. Key features of the new setup that enable to successfully address major challenges of thermal boundary condition, thermal stability of speckle pattern, contrast of image and hot air movement are presented; together with evidences giving confidence to the reliability of such setup. With its combined advantages of reliable full-field deformation capturing and thermal boundary conditions on test specimens, the new setup allows to generate required reliable data on performance of concrete at elevated temperatures, thereby facilitating the development of effective rational fire design and analysis of concrete structures.

Research paper thumbnail of Properties of cement-based materials containing fly ash

Proceedings of the Second International Conference on Performance–based and Life-cycle Structural Engineering (PLSE 2015), 2015

Fly ash has been increasingly used in concrete structures due to both environmental and technical... more Fly ash has been increasingly used in concrete structures due to both environmental and technical benefits. Despite significant past research, our understanding of thermal and physical properties of fly ash mortar and concrete remains incomplete and thus needs further investigation. This paper presents results of a study into important fundamental thermal and physical properties of both fly ash mortar and fly ash concrete. Replacement levels of Portland cement by fly ash investigated were30%, 50% and 60% by mass. In cement-fly ash mortar tests, increasing fly ash content was found to delay setting times, decrease both compressive and flexural strengths and reduce hydration heat. The effect of fly ash on hydration heat evolution of cement binder was quantitatively analysed. The obtained reduction coefficient (k) would allow reasonable prediction of temperature rise in concrete structures, which is of particular interest for mass concrete construction. In cement-fly ash concrete tests, thermal properties, including thermal diffusivity, conductivity and specific heat, were also measured and reported. There also appeared a linear relationship between compressive and flexural strengths of

Research paper thumbnail of Effects of micro-fibres on early-age properties of concrete

Proceedings of the Second International Conference on Performance-based and Life-cycle Structural Engineering (PLSE 2015), 2015

Proper control of early-age cracking risk in concrete as well as optimisation of relevant process... more Proper control of early-age cracking risk in concrete as well as optimisation of relevant processes in precast industry requires an adequate knowledge of tensile and fracture properties of concrete at relevant ages. Despite significant past research, such knowledge is currently lacking. This paper presents the recent results of an ongoing research program aimed to address that important knowledge gap. After briefly outlining notable features of an improved direct tensile testing system, the paper presents key results of an experimental investigation into the tensile properties of concrete of age between 2.5 and 9 hours after mixing, both with and without fibres. Compared to concrete without micro-fibre, micro-fibre concrete is found to have more bleeding, considerably lower and more scattered tensile strength and Young's modulus, and higher fracture energy and characteristic length. Possible explanations for such differences are also given. Importantly, the roles of microfibres in mitigating the risk of plastic shrinkage cracking are shown to be complex, prompting the need for further study: Although a decreased tensile strength heightens such risk, an increased bleeding helps reduce the risk while the higher fracture energy and characteristic length implies higher ductility.

Research paper thumbnail of Temperature and stress in concrete cylinder specimen subject to uniform heat flux: a numerical solution

Proceedings of the Second International Conference on Performance-based and Life-cycle Structural Engineering (PLSE 2015), 2015

The outbreak of fire in a concrete infrastructure can have disastrous consequences, including sev... more The outbreak of fire in a concrete infrastructure can have disastrous consequences, including severe structural damage, total loss of contents, and loss of life. Adequate structural fire design is therefore critical. Despite significant past studies, our understanding of concrete performance in fire remains inadequate. This paper will first highlight major limitations of conventional testing and accordingly of resulting constitutive models for concrete at elevated temperatures. The paper will then detail results of a thermal-stress coupling analysis as part of an ongoing research at The University of Queensland that aims to develop more realistic constitutive models through studying performance of concrete cylinders subject to known consistent heat flux boundary conditions. It is clearly shown that (i) Different levels of incident heat flux causes significantly different evolution of temperature and stress profiles within the specimen; and (ii) Such profiles and their nature may be considerably modified by mechanical loading. Accordingly, heat flux, and temperature gradient by extension, may have nonnegligible influence on thermal and structural behaviour of concrete and concrete structures-Such influence has not been captured in currently available models.

Research paper thumbnail of Pile cap design using strut-and-tie modelling

Research paper thumbnail of A novel method for tensile testing of very early-age concrete

Early-age cracking can seriously compromise the performance and aesthetics of concrete structures... more Early-age cracking can seriously compromise the performance and aesthetics of concrete structures, and is thus an ongoing major concern to the concrete construction industry. More effective control of this form of cracking requires an improved knowledge of concrete properties. In this paper, currently available test methods for complete stress-strain curves of early-age concrete are first briefly reviewed. A new system specifically designed for early-age tensile testing of concrete is then described. The novel use of digital image correlation in this system enables the desired deformation to be reliably captured in a non-contact way – a significant improvement compared to previous studies. The more reliable data to be collected would result in improved knowledge of concrete at early ages, including the tensile strength, Young’s modulus, strain at peak stress, and fracture mechanics characteristics, as well as their interrelationships and development with time. This improved understanding would form a solid basis for more effective control of early-age cracking in concrete.

Research paper thumbnail of Performance of concrete in fire

Concrete in Australia, Sep 1, 2014

Research paper thumbnail of Plastic shrinkage cracking of concrete - Roles of osmotic suction

Plastic shrinkage cracking of concrete occurs when the stresses arising in the concrete, due to a... more Plastic shrinkage cracking of concrete occurs when the stresses arising in the concrete, due to a combination of suction and restraints of deformation such as reinforcement or formwork, equal its strength. However, three different types of suctions should be distinguished, namely total, matric and osmotic suctions. Although the total suction comprises matric and osmotic suctions, it is often used interchangeably with matric suction, with the underlying unconfirmed assumption that either the osmotic suction or its effect is negligible. In this paper, after a discussion of the pore moisture suctions and strength of unsaturated early-age concrete, experimental investigations of the suctions arising in, and the tensile strength and shear strength of, fly ash mixed with solutions of different osmotic suctions are described. It was found that osmotic suction has negligible effect on the shear and tensile strength, and hence, by inference, the inter-particle stresses in the fly ash mixture and early-age concrete. This strongly suggests that the role played by osmotic suction in the plastic shrinkage cracking of concrete is minimal and, accordingly, justifies the focus of earlier researchers on matric suction only.

Research paper thumbnail of A novel approach to estimate the evolution of fracture energy and tensile softening curve of concrete from very early age

Engineering Fracture Mechanics, 2018

Concrete fracture properties and their evolution over time are critical inputs for numerous engin... more Concrete fracture properties and their evolution over time are critical inputs for numerous engineering aspects. Despite substantial efforts invested, there exists a crucial need to establish a comprehensive model for reliable estimation of such evolution. In this paper, combining reliable experimental data and in-depth analyses, a novel approach for estimating of the evolution of fracture energy and tensile softening curve of concrete from early age is proposed. Fundamentally, the approach relies on three criteria, namely (i) Tensile strength, (ii) Tensile strength-fracture energy correlation and especially, (iii) Centroid coordinates of the area under actual stress-crack opening curve. Through detailed assessment of all mentioned criteria and with provided examples of direct applications, the capability and reliability of the approach are clearly demonstrated.

Research paper thumbnail of EASEC16

Lecture Notes in Civil Engineering, 2021

Research paper thumbnail of Crack propagation in concrete at very early ages

Magazine of Concrete Research, 2014

Surface defects and cracks in early-age concrete slabs have been observed to propagate under adve... more Surface defects and cracks in early-age concrete slabs have been observed to propagate under adverse conditions, impairing the performance and service life of these structures. However, the underlying mechanism of this form of crack propagation has remained largely unexplained, with very limited literature available. In this paper, simple yet sufficiently rigorous theoretical analyses of crack propagation in early-age concrete slabs, based on combined geotechnical engineering and fracture mechanics models, are presented. The results obtained clearly show how surface cracks can become unstable and propagate further, and either become stable again or develop through the full depth of the slab. They also convincingly demonstrate the roles of surface cracks and defects, pore moisture suctions and exposure conditions in this process. Importantly, the critical role of good construction practices in minimising this form of cracking is highlighted. These include proper compaction and effect...

Research paper thumbnail of On equations for the total suction and its matric and osmotic components

Cement and Concrete Research, 2008

A clear fundamental understanding of suctions is crucial for the study of the behaviour of plasti... more A clear fundamental understanding of suctions is crucial for the study of the behaviour of plastic cement mortar and concrete, including plastic shrinkage cracking. In this paper, the expression relating the change in free energy of the pore water with an isothermal change in pressure is first derived. Based upon definitions of suctions, it is then shown that total, matric, and osmotic suctions can all be expressed in the same thermodynamic form. The widely accepted, but not yet satisfactorily validated, assumption that the total suction comprises matric and osmotic components is then confirmed theoretically. The well-known Kelvin equation for matric suction, and Morse and van't Hoff equations for osmotic suction are subsequently derived from the corresponding thermodynamic equations. The applicability of latter two equations in evaluating the osmotic suctions of cement mortar and concrete is highlighted.

Research paper thumbnail of Evaluation of zero-stress temperature and cracking temperature of high performance concrete at early ages

Materials and Structures

Assessing the risk of cracking of high performance concrete induced by restrained volume changes ... more Assessing the risk of cracking of high performance concrete induced by restrained volume changes from early ages is of considerable significance. To estimate and control such cracking risk of high performance concrete, two characteristic temperatures, namely zero-stress temperature (Tz) and cracking temperature (Tx) are crucial. In this study, the two temperatures are investigated in-depth by both theoretical analysis and experimental studies. For predicting the evolutions of Tz and Tx from early ages, rigorous yet practical models are proposed, which crucially take the visco-elastic behaviour of concrete into account. The reliability and predictive capability of the proposed models are demonstrated through a series of comparisons between the predicted and the measured results. Based on the predicted Tz and Tx profiles, practical thermal control criteria for preventing concrete from cracking caused by restrained strain are put forward. In principle, the actual temperature (T) of con...

Research paper thumbnail of Evolution of Coefficient of Thermal Expansion of Concrete at Early Ages

Lecture Notes in Civil Engineering, 2019

Together with drying shrinkage and autogenous deformations, thermal strain is one of the driving ... more Together with drying shrinkage and autogenous deformations, thermal strain is one of the driving force of cracking of cement-based materials at early ages. However, current understanding of these early-age deformations remains unsystematic and further studies are needed. In this paper, evolution of thermal strain and coefficient of thermal expansion (CTE) are reviewed. Based on a newly built test setup at The University of Queensland, the development of the CTE of concrete at early ages was measured and investigated. It is found that CTE shows a clear rising trend after setting, meaning that CTE cannot be seen as constant even though this has often been done for modelling and design purpose. Based on newly-measured CTE, the separation process of self-desiccation shrinkage and thermal strain was studied. It is noted that the separation process is rather complicated due to the effects of delayed thermal strain. Through literature review, it is demonstrated that the delayed thermal strain is closely linked to relative humidity change inside concrete. Since the development of self-desiccation shrinkage is also affected by such relative humidity change, there appears a coupling effect between self-desiccation shrinkage and delayed thermal strain, which should be further studied in the future.

Research paper thumbnail of Constitutive models of concrete at elevated temperatures: studying the effect of temperature gradients

The outbreak of fire can have serious consequences in the structural performance of a load-bearin... more The outbreak of fire can have serious consequences in the structural performance of a load-bearing concrete structure. To assure adequate fire performance, detailed knowledge of fundamental mechanical properties of concrete at elevated temperatures is crucial. This paper first highlights limitations of existing knowledge regarding the mechanical response of concrete at elevated temperatures, including the inconsistent thermal boundary conditions and intentionally-minimised temperature gradients in “standardized” conventional concrete material testing. Accordingly, it is argued that the effect of temperature gradients within concrete on its fire performance has not been extensively or directly addressed. On this basis, the paper outlines key features of an ongoing research programme at The University of Queensland aimed at studying the performance of concrete in fire using a novel medium-scale testing method. By heating using radiant panels, welldefined and consistently-controlled he...

Research paper thumbnail of Deformation capturing of concrete structures at elevated temperatures

Procedia Engineering, 2017

Reliable deformation measurement is required for proper quantification of fire performance of con... more Reliable deformation measurement is required for proper quantification of fire performance of concrete structures. Predictive capability of models for many critical properties, including Young's moduli, stress-strain relationships and load-induced thermal strains, is first and foremost dependent on such reliable deformation capturing. This paper first presents a state-of-the-art review of existing methods for capturing deformation of concrete structures at elevated temperatures. Key merits, limitations and challenges associated with each measuring technique are discussed. It is shown that existing testing facilities and measuring instruments generally do not allow reliable direct measurement of deformation and strain of high-temperature concrete. As a result, the deformation has typically been captured either indirectly or outside the heated zones, inevitably introducing additional uncertainty and errors that are difficult to be adequately quantified. On the basis of that review, the paper details a new test setup for reliable non-contact full-field deformation capturing of concrete structures at high temperatures using 3D Digital Image Correlation technique. Key features of the new setup that enable to successfully address major challenges of thermal boundary condition, thermal stability of speckle pattern, contrast of image and hot air movement are presented; together with evidences giving confidence to the reliability of such setup. With its combined advantages of reliable full-field deformation capturing and thermal boundary conditions on test specimens, the new setup allows to generate required reliable data on performance of concrete at elevated temperatures, thereby facilitating the development of effective rational fire design and analysis of concrete structures.

Research paper thumbnail of Properties of cement-based materials containing fly ash

Proceedings of the Second International Conference on Performance–based and Life-cycle Structural Engineering (PLSE 2015), 2015

Fly ash has been increasingly used in concrete structures due to both environmental and technical... more Fly ash has been increasingly used in concrete structures due to both environmental and technical benefits. Despite significant past research, our understanding of thermal and physical properties of fly ash mortar and concrete remains incomplete and thus needs further investigation. This paper presents results of a study into important fundamental thermal and physical properties of both fly ash mortar and fly ash concrete. Replacement levels of Portland cement by fly ash investigated were30%, 50% and 60% by mass. In cement-fly ash mortar tests, increasing fly ash content was found to delay setting times, decrease both compressive and flexural strengths and reduce hydration heat. The effect of fly ash on hydration heat evolution of cement binder was quantitatively analysed. The obtained reduction coefficient (k) would allow reasonable prediction of temperature rise in concrete structures, which is of particular interest for mass concrete construction. In cement-fly ash concrete tests, thermal properties, including thermal diffusivity, conductivity and specific heat, were also measured and reported. There also appeared a linear relationship between compressive and flexural strengths of

Research paper thumbnail of Effects of micro-fibres on early-age properties of concrete

Proceedings of the Second International Conference on Performance-based and Life-cycle Structural Engineering (PLSE 2015), 2015

Proper control of early-age cracking risk in concrete as well as optimisation of relevant process... more Proper control of early-age cracking risk in concrete as well as optimisation of relevant processes in precast industry requires an adequate knowledge of tensile and fracture properties of concrete at relevant ages. Despite significant past research, such knowledge is currently lacking. This paper presents the recent results of an ongoing research program aimed to address that important knowledge gap. After briefly outlining notable features of an improved direct tensile testing system, the paper presents key results of an experimental investigation into the tensile properties of concrete of age between 2.5 and 9 hours after mixing, both with and without fibres. Compared to concrete without micro-fibre, micro-fibre concrete is found to have more bleeding, considerably lower and more scattered tensile strength and Young's modulus, and higher fracture energy and characteristic length. Possible explanations for such differences are also given. Importantly, the roles of microfibres in mitigating the risk of plastic shrinkage cracking are shown to be complex, prompting the need for further study: Although a decreased tensile strength heightens such risk, an increased bleeding helps reduce the risk while the higher fracture energy and characteristic length implies higher ductility.

Research paper thumbnail of Temperature and stress in concrete cylinder specimen subject to uniform heat flux: a numerical solution

Proceedings of the Second International Conference on Performance-based and Life-cycle Structural Engineering (PLSE 2015), 2015

The outbreak of fire in a concrete infrastructure can have disastrous consequences, including sev... more The outbreak of fire in a concrete infrastructure can have disastrous consequences, including severe structural damage, total loss of contents, and loss of life. Adequate structural fire design is therefore critical. Despite significant past studies, our understanding of concrete performance in fire remains inadequate. This paper will first highlight major limitations of conventional testing and accordingly of resulting constitutive models for concrete at elevated temperatures. The paper will then detail results of a thermal-stress coupling analysis as part of an ongoing research at The University of Queensland that aims to develop more realistic constitutive models through studying performance of concrete cylinders subject to known consistent heat flux boundary conditions. It is clearly shown that (i) Different levels of incident heat flux causes significantly different evolution of temperature and stress profiles within the specimen; and (ii) Such profiles and their nature may be considerably modified by mechanical loading. Accordingly, heat flux, and temperature gradient by extension, may have nonnegligible influence on thermal and structural behaviour of concrete and concrete structures-Such influence has not been captured in currently available models.

Research paper thumbnail of Pile cap design using strut-and-tie modelling

Research paper thumbnail of A novel method for tensile testing of very early-age concrete

Early-age cracking can seriously compromise the performance and aesthetics of concrete structures... more Early-age cracking can seriously compromise the performance and aesthetics of concrete structures, and is thus an ongoing major concern to the concrete construction industry. More effective control of this form of cracking requires an improved knowledge of concrete properties. In this paper, currently available test methods for complete stress-strain curves of early-age concrete are first briefly reviewed. A new system specifically designed for early-age tensile testing of concrete is then described. The novel use of digital image correlation in this system enables the desired deformation to be reliably captured in a non-contact way – a significant improvement compared to previous studies. The more reliable data to be collected would result in improved knowledge of concrete at early ages, including the tensile strength, Young’s modulus, strain at peak stress, and fracture mechanics characteristics, as well as their interrelationships and development with time. This improved understanding would form a solid basis for more effective control of early-age cracking in concrete.

Research paper thumbnail of Performance of concrete in fire

Concrete in Australia, Sep 1, 2014

Research paper thumbnail of Plastic shrinkage cracking of concrete - Roles of osmotic suction

Plastic shrinkage cracking of concrete occurs when the stresses arising in the concrete, due to a... more Plastic shrinkage cracking of concrete occurs when the stresses arising in the concrete, due to a combination of suction and restraints of deformation such as reinforcement or formwork, equal its strength. However, three different types of suctions should be distinguished, namely total, matric and osmotic suctions. Although the total suction comprises matric and osmotic suctions, it is often used interchangeably with matric suction, with the underlying unconfirmed assumption that either the osmotic suction or its effect is negligible. In this paper, after a discussion of the pore moisture suctions and strength of unsaturated early-age concrete, experimental investigations of the suctions arising in, and the tensile strength and shear strength of, fly ash mixed with solutions of different osmotic suctions are described. It was found that osmotic suction has negligible effect on the shear and tensile strength, and hence, by inference, the inter-particle stresses in the fly ash mixture and early-age concrete. This strongly suggests that the role played by osmotic suction in the plastic shrinkage cracking of concrete is minimal and, accordingly, justifies the focus of earlier researchers on matric suction only.

Research paper thumbnail of A novel approach to estimate the evolution of fracture energy and tensile softening curve of concrete from very early age

Engineering Fracture Mechanics, 2018

Concrete fracture properties and their evolution over time are critical inputs for numerous engin... more Concrete fracture properties and their evolution over time are critical inputs for numerous engineering aspects. Despite substantial efforts invested, there exists a crucial need to establish a comprehensive model for reliable estimation of such evolution. In this paper, combining reliable experimental data and in-depth analyses, a novel approach for estimating of the evolution of fracture energy and tensile softening curve of concrete from early age is proposed. Fundamentally, the approach relies on three criteria, namely (i) Tensile strength, (ii) Tensile strength-fracture energy correlation and especially, (iii) Centroid coordinates of the area under actual stress-crack opening curve. Through detailed assessment of all mentioned criteria and with provided examples of direct applications, the capability and reliability of the approach are clearly demonstrated.

Research paper thumbnail of EASEC16

Lecture Notes in Civil Engineering, 2021

Research paper thumbnail of Crack propagation in concrete at very early ages

Magazine of Concrete Research, 2014

Surface defects and cracks in early-age concrete slabs have been observed to propagate under adve... more Surface defects and cracks in early-age concrete slabs have been observed to propagate under adverse conditions, impairing the performance and service life of these structures. However, the underlying mechanism of this form of crack propagation has remained largely unexplained, with very limited literature available. In this paper, simple yet sufficiently rigorous theoretical analyses of crack propagation in early-age concrete slabs, based on combined geotechnical engineering and fracture mechanics models, are presented. The results obtained clearly show how surface cracks can become unstable and propagate further, and either become stable again or develop through the full depth of the slab. They also convincingly demonstrate the roles of surface cracks and defects, pore moisture suctions and exposure conditions in this process. Importantly, the critical role of good construction practices in minimising this form of cracking is highlighted. These include proper compaction and effect...

Research paper thumbnail of On equations for the total suction and its matric and osmotic components

Cement and Concrete Research, 2008

A clear fundamental understanding of suctions is crucial for the study of the behaviour of plasti... more A clear fundamental understanding of suctions is crucial for the study of the behaviour of plastic cement mortar and concrete, including plastic shrinkage cracking. In this paper, the expression relating the change in free energy of the pore water with an isothermal change in pressure is first derived. Based upon definitions of suctions, it is then shown that total, matric, and osmotic suctions can all be expressed in the same thermodynamic form. The widely accepted, but not yet satisfactorily validated, assumption that the total suction comprises matric and osmotic components is then confirmed theoretically. The well-known Kelvin equation for matric suction, and Morse and van't Hoff equations for osmotic suction are subsequently derived from the corresponding thermodynamic equations. The applicability of latter two equations in evaluating the osmotic suctions of cement mortar and concrete is highlighted.