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Research paper thumbnail of The use of novel Non-Destructive methods for quality control and performance evaluation of concrete structures

Concrete cover provides the first line of defense against the ingress of many deleterious substan... more Concrete cover provides the first line of defense against the ingress of many deleterious substances into the concrete. Therefore, a measure of its transport properties is vital in assessing its long term performance in a given exposure condition. In new structures the rate of ingress of the deleterious substances could be monitored using array of electrical sensors that are embedded in the cover concrete. For structures that are currently in service, tests can be performed by removing cores from the structure (lab based tests) or by using tests that can be performed on the surface (in situ tests). Results relating to few of the most commonly used lab based test methods are presented here along with two in situ permeability apparatuses, viz. Autoclam Permeability System (for measuring gas/water permeability and water absorption) and Permit Ion Migration Test (for determining rate of ionic ingress). Data from these test methods are further exploited using numerical models to predict ...

Research paper thumbnail of Conductivity Sensors to Monitor Cover-zone Performance

This paper presents developments in the use of an embedded, multi-electrode conductivity sensor t... more This paper presents developments in the use of an embedded, multi-electrode conductivity sensor to study the response of the concrete cover-zone to environmental action. The sensor enables an evaluation of the temporal and spatial variation of electrical conductivity thereby allowing an integrated assessment of the cover-zone. Conductivity sensors were embedded within concrete samples to study the cover-zone response to cyclic wetting and drying under laboratory conditions. This work was extended to include the use of remote interrogation methods to study samples placed at a marine exposure site and preliminary results are presented.

Research paper thumbnail of Real-time monitoring of covercrete response to environmental action

International Journal of Modelling, Identification and Control, 2009

ABSTRACT Currently, the most predominant process associated with the deterioration of reinforced ... more ABSTRACT Currently, the most predominant process associated with the deterioration of reinforced concrete structures is corrosion. Since it is the cover-zone concrete which protects the steel from the environment, the ability to study the protective qualities of the covercrete could assist in assessing the current and future performance of the structure. To this end, a multi-electrode array was used to study the surface 50 mm of concrete specimens, thereby, allowing a detailed picture of the response of the covercrete to the changing environment, both in the short- and long-term. In the current work, CEM I, CEM II/B-V and CEM III/A cements were used and comprised field studies on both 'mini slabs' and monoliths.

Research paper thumbnail of Electrical behaviour of chemically activated fly ash

Journal of Materials Science, 2005

ABSTRACT The temporal change in electrical properties is used to study the hydration kinetics of ... more ABSTRACT The temporal change in electrical properties is used to study the hydration kinetics of chemically activated fly-ash systems at room temperature. Four low-lime ashes and one high-lime ash were used in the experimental programme and the electrical response was measured in terms of the in-phase (i.e. conductance) and quadrature (i.e. capacitance) components of the sample admittance. The low-lime ash and high-lime ash exhibited markedly different electrical response. The work highlights the applicability of the testing methodology as a non-invasive, non-destructive technique in the assessment of the efficacy of a particular activator or combination of activators.

Research paper thumbnail of Rheology of Carbon Fibre Reinforced Cement-Based Mortar

… Part Two(AIP …, 2008

ABSTRACT Carbon fibre reinforced cement based materials (CFRCs) offer the possibility of fabricat... more ABSTRACT Carbon fibre reinforced cement based materials (CFRCs) offer the possibility of fabricating 'smart' electrically conductive materials. Rheology of the fresh mix is crucial to satisfactory moulding and fresh CFRC conforms to the Bingham model with slight structural breakdown. Both yield stress and plastic viscosity increase with increasing fibre length and volume concentration. Using a modified Viskomat NT, the concentration dependence of CFRC rheology up to 1.5% fibre volume is reported.

Research paper thumbnail of Testing and monitoring concrete using novel methods for predicting their long term behaviour

It is widely recognised that durability of concrete depends on its transport properties, viz. abs... more It is widely recognised that durability of concrete depends on its transport properties, viz. absorption, diffusion and permeability. As concrete cover provides the first line of defence against the ingress of many deleterious substances into the concrete, a measure of its transport properties is vital in assessing its long term performance in the given exposure condition. In new structures the rate of ingress of the deleterious substances could be monitored using array of electrical sensors which are embedded in the cover concrete. For structures which are currently in service, two in situ permeability apparatuses, viz. Autoclam Permeability System (for measuring gas/water permeability and water absorption) and Permit Ion Migration Test (for determining the ionic diffusion) could be employed. These instruments can be mounted on the concrete surface for carrying out the tests. Typical results are presented for these two novel testing systems to illustrate their usefulness for the condition assessment of reinforced concrete structures.

Research paper thumbnail of Monitoring and characterisation of sand-mud sedimentation processes

Ocean Dynamics, 2016

Estuaries and tidal inlets are often characterised by the presence of both cohesive and non-cohes... more Estuaries and tidal inlets are often characterised by the presence of both cohesive and non-cohesive sediments. Knowledge of the sedimentation behaviour of sand-mud mixtures is therefore crucial to the understanding and prediction of the time-dependent structure (i.e. mixed or segregated), composition and erodibility of sediment bed deposits developing within these environments. In the current study, a series of settling column tests are conducted to investigate the hindered settling and initial bed consolidation phases of a range of sandclay mixtures to determine the parametric conditions under which bed segregation occurs. A new, non-invasive, electrical resistivity measurement technique is employed to capture both temporal and spatial changes in the density, porosity and composition of the evolving sand-clay bed deposits, complimented by time-lapsed images of the sedimentation process within the column. The results show that the formation of segregated (sand-clay) bed layers with bed deposits is largely controlled by the initial fractional composition (i.e. relative sand and clay concentrations). Specifically, mixtures with low clay contents are shown to form well-defined (sandclay) layer segregation within the resulting deposits, while higher clay contents result in more transitional segregation patterns or no layer segregation (for very high clay concentrations). The physical mechanisms under which these different segregation types can be generated are illustrated through predictions from an existing polydisperse hindered settling model. This model indicates that the degree of bed segregation, and time scale over which this occurs, correlates well with the difference in predicted hindered settling characteristics and upward displacements associated with the sand and clay fractions, respectively. In this regard, the new experimental dataset provides validation for the polydisperse model (for the first time), with the combined data and model predictions providing new insight into mixed (sand-clay) sedimentation processes.

Research paper thumbnail of Activation energy and conduction in carbon fibre reinforced cement matrices

Journal of Materials Science, 2007

Research paper thumbnail of The complex impedance response of fly-ash cements revisited

Cement and Concrete Research, 2004

It has been reported in a previous study [Cem. Concr. Res. 29 (1999) 377; Cem. Concr. Res. 33 (20... more It has been reported in a previous study [Cem. Concr. Res. 29 (1999) 377; Cem. Concr. Res. 33 (2003) 197] that when a low-lime fly ash is introduced as a cementitious component, there are significant changes in the electrical response of the system, most notably, an enhancement in dielectric constant and the emergence of a plateau region in the complex plane. The changes in electrical behaviour were attributed to the spherical nature of the fly-ash particle, resulting in an enhancement in the double-layer polarization effects on the particle surface. In this paper, data are presented for three low-lime ashes, each displaying differences in their electrical behaviour. Through a systematic series of tests, a new interpretation for the origin of the characteristic electrical response is presented. D

Research paper thumbnail of Hydration and drying of Nirex Reference Vault Backfill

Building and Environment, 2004

ABSTRACT The short-term hydration and drying response of Nirex Reference Vault Backfill (NRVB) gr... more ABSTRACT The short-term hydration and drying response of Nirex Reference Vault Backfill (NRVB) grout is presented. Low-frequency electrical conductance measurements were used in conjunction with gravimetric and internal temperature measurements to study NRVB grout from initial mixing up to 7 days hydration. The grout was subjected to ambient temperatures of 25°C, 55°C and 70°C at relative humidities of 50–55% and 85–90%. By taking measurements at discrete depths from the exposed surface, the influence of the external environment on setting and hardening and drying effects could be studied. An empirical relationship, based on a simplified electrical model, was established between moisture loss and electrical measurements.

Research paper thumbnail of Sensor systems for use in reinforced concrete structures

Construction and Building Materials, 2004

Whole-life costing and residual service-life prediction of structures require quantitative inform... more Whole-life costing and residual service-life prediction of structures require quantitative information on cover-zone properties and threshold values for corrosion initiation and, once initiated, the rate of corrosion. It is clear that there exists a need to determine those near-surface characteristics of concrete, which promote the ingress of gases and liquids containing dissolved contaminants. In addition, in-situ monitoring of the seasonal change in such properties could assist in making realistic predictions as to the in-service performance of the structure, likely deterioration rates for a particular exposure condition, or compliance with the specified design life. To this end, this paper presents a review of sensors and associated monitoring systems from which information concerning corrosion activity, concrete (electrical) resistivity, oxygen availability, carbonation and chloride ingress can be obtained at strategic locations within a structure. This paper is based upon a draft of a RILEM Technical Recommendation 'Measurements with embedded sensors' prepared for RILEM Technical Committee TC-154 'Electrochemical methods for measuring metallic corrosion in concrete'. The work also formed part of the European research programme COST 521 -'The Corrosion of Steel in Reinforced Concrete Structures'.

Research paper thumbnail of The use of novel Non-Destructive methods for quality control and performance evaluation of concrete structures

Concrete cover provides the first line of defense against the ingress of many deleterious substan... more Concrete cover provides the first line of defense against the ingress of many deleterious substances into the concrete. Therefore, a measure of its transport properties is vital in assessing its long term performance in a given exposure condition. In new structures the rate of ingress of the deleterious substances could be monitored using array of electrical sensors that are embedded in the cover concrete. For structures that are currently in service, tests can be performed by removing cores from the structure (lab based tests) or by using tests that can be performed on the surface (in situ tests). Results relating to few of the most commonly used lab based test methods are presented here along with two in situ permeability apparatuses, viz. Autoclam Permeability System (for measuring gas/water permeability and water absorption) and Permit Ion Migration Test (for determining rate of ionic ingress). Data from these test methods are further exploited using numerical models to predict ...

Research paper thumbnail of Conductivity Sensors to Monitor Cover-zone Performance

This paper presents developments in the use of an embedded, multi-electrode conductivity sensor t... more This paper presents developments in the use of an embedded, multi-electrode conductivity sensor to study the response of the concrete cover-zone to environmental action. The sensor enables an evaluation of the temporal and spatial variation of electrical conductivity thereby allowing an integrated assessment of the cover-zone. Conductivity sensors were embedded within concrete samples to study the cover-zone response to cyclic wetting and drying under laboratory conditions. This work was extended to include the use of remote interrogation methods to study samples placed at a marine exposure site and preliminary results are presented.

Research paper thumbnail of Real-time monitoring of covercrete response to environmental action

International Journal of Modelling, Identification and Control, 2009

ABSTRACT Currently, the most predominant process associated with the deterioration of reinforced ... more ABSTRACT Currently, the most predominant process associated with the deterioration of reinforced concrete structures is corrosion. Since it is the cover-zone concrete which protects the steel from the environment, the ability to study the protective qualities of the covercrete could assist in assessing the current and future performance of the structure. To this end, a multi-electrode array was used to study the surface 50 mm of concrete specimens, thereby, allowing a detailed picture of the response of the covercrete to the changing environment, both in the short- and long-term. In the current work, CEM I, CEM II/B-V and CEM III/A cements were used and comprised field studies on both 'mini slabs' and monoliths.

Research paper thumbnail of Electrical behaviour of chemically activated fly ash

Journal of Materials Science, 2005

ABSTRACT The temporal change in electrical properties is used to study the hydration kinetics of ... more ABSTRACT The temporal change in electrical properties is used to study the hydration kinetics of chemically activated fly-ash systems at room temperature. Four low-lime ashes and one high-lime ash were used in the experimental programme and the electrical response was measured in terms of the in-phase (i.e. conductance) and quadrature (i.e. capacitance) components of the sample admittance. The low-lime ash and high-lime ash exhibited markedly different electrical response. The work highlights the applicability of the testing methodology as a non-invasive, non-destructive technique in the assessment of the efficacy of a particular activator or combination of activators.

Research paper thumbnail of Rheology of Carbon Fibre Reinforced Cement-Based Mortar

… Part Two(AIP …, 2008

ABSTRACT Carbon fibre reinforced cement based materials (CFRCs) offer the possibility of fabricat... more ABSTRACT Carbon fibre reinforced cement based materials (CFRCs) offer the possibility of fabricating 'smart' electrically conductive materials. Rheology of the fresh mix is crucial to satisfactory moulding and fresh CFRC conforms to the Bingham model with slight structural breakdown. Both yield stress and plastic viscosity increase with increasing fibre length and volume concentration. Using a modified Viskomat NT, the concentration dependence of CFRC rheology up to 1.5% fibre volume is reported.

Research paper thumbnail of Testing and monitoring concrete using novel methods for predicting their long term behaviour

It is widely recognised that durability of concrete depends on its transport properties, viz. abs... more It is widely recognised that durability of concrete depends on its transport properties, viz. absorption, diffusion and permeability. As concrete cover provides the first line of defence against the ingress of many deleterious substances into the concrete, a measure of its transport properties is vital in assessing its long term performance in the given exposure condition. In new structures the rate of ingress of the deleterious substances could be monitored using array of electrical sensors which are embedded in the cover concrete. For structures which are currently in service, two in situ permeability apparatuses, viz. Autoclam Permeability System (for measuring gas/water permeability and water absorption) and Permit Ion Migration Test (for determining the ionic diffusion) could be employed. These instruments can be mounted on the concrete surface for carrying out the tests. Typical results are presented for these two novel testing systems to illustrate their usefulness for the condition assessment of reinforced concrete structures.

Research paper thumbnail of Monitoring and characterisation of sand-mud sedimentation processes

Ocean Dynamics, 2016

Estuaries and tidal inlets are often characterised by the presence of both cohesive and non-cohes... more Estuaries and tidal inlets are often characterised by the presence of both cohesive and non-cohesive sediments. Knowledge of the sedimentation behaviour of sand-mud mixtures is therefore crucial to the understanding and prediction of the time-dependent structure (i.e. mixed or segregated), composition and erodibility of sediment bed deposits developing within these environments. In the current study, a series of settling column tests are conducted to investigate the hindered settling and initial bed consolidation phases of a range of sandclay mixtures to determine the parametric conditions under which bed segregation occurs. A new, non-invasive, electrical resistivity measurement technique is employed to capture both temporal and spatial changes in the density, porosity and composition of the evolving sand-clay bed deposits, complimented by time-lapsed images of the sedimentation process within the column. The results show that the formation of segregated (sand-clay) bed layers with bed deposits is largely controlled by the initial fractional composition (i.e. relative sand and clay concentrations). Specifically, mixtures with low clay contents are shown to form well-defined (sandclay) layer segregation within the resulting deposits, while higher clay contents result in more transitional segregation patterns or no layer segregation (for very high clay concentrations). The physical mechanisms under which these different segregation types can be generated are illustrated through predictions from an existing polydisperse hindered settling model. This model indicates that the degree of bed segregation, and time scale over which this occurs, correlates well with the difference in predicted hindered settling characteristics and upward displacements associated with the sand and clay fractions, respectively. In this regard, the new experimental dataset provides validation for the polydisperse model (for the first time), with the combined data and model predictions providing new insight into mixed (sand-clay) sedimentation processes.

Research paper thumbnail of Activation energy and conduction in carbon fibre reinforced cement matrices

Journal of Materials Science, 2007

Research paper thumbnail of The complex impedance response of fly-ash cements revisited

Cement and Concrete Research, 2004

It has been reported in a previous study [Cem. Concr. Res. 29 (1999) 377; Cem. Concr. Res. 33 (20... more It has been reported in a previous study [Cem. Concr. Res. 29 (1999) 377; Cem. Concr. Res. 33 (2003) 197] that when a low-lime fly ash is introduced as a cementitious component, there are significant changes in the electrical response of the system, most notably, an enhancement in dielectric constant and the emergence of a plateau region in the complex plane. The changes in electrical behaviour were attributed to the spherical nature of the fly-ash particle, resulting in an enhancement in the double-layer polarization effects on the particle surface. In this paper, data are presented for three low-lime ashes, each displaying differences in their electrical behaviour. Through a systematic series of tests, a new interpretation for the origin of the characteristic electrical response is presented. D

Research paper thumbnail of Hydration and drying of Nirex Reference Vault Backfill

Building and Environment, 2004

ABSTRACT The short-term hydration and drying response of Nirex Reference Vault Backfill (NRVB) gr... more ABSTRACT The short-term hydration and drying response of Nirex Reference Vault Backfill (NRVB) grout is presented. Low-frequency electrical conductance measurements were used in conjunction with gravimetric and internal temperature measurements to study NRVB grout from initial mixing up to 7 days hydration. The grout was subjected to ambient temperatures of 25°C, 55°C and 70°C at relative humidities of 50–55% and 85–90%. By taking measurements at discrete depths from the exposed surface, the influence of the external environment on setting and hardening and drying effects could be studied. An empirical relationship, based on a simplified electrical model, was established between moisture loss and electrical measurements.

Research paper thumbnail of Sensor systems for use in reinforced concrete structures

Construction and Building Materials, 2004

Whole-life costing and residual service-life prediction of structures require quantitative inform... more Whole-life costing and residual service-life prediction of structures require quantitative information on cover-zone properties and threshold values for corrosion initiation and, once initiated, the rate of corrosion. It is clear that there exists a need to determine those near-surface characteristics of concrete, which promote the ingress of gases and liquids containing dissolved contaminants. In addition, in-situ monitoring of the seasonal change in such properties could assist in making realistic predictions as to the in-service performance of the structure, likely deterioration rates for a particular exposure condition, or compliance with the specified design life. To this end, this paper presents a review of sensors and associated monitoring systems from which information concerning corrosion activity, concrete (electrical) resistivity, oxygen availability, carbonation and chloride ingress can be obtained at strategic locations within a structure. This paper is based upon a draft of a RILEM Technical Recommendation 'Measurements with embedded sensors' prepared for RILEM Technical Committee TC-154 'Electrochemical methods for measuring metallic corrosion in concrete'. The work also formed part of the European research programme COST 521 -'The Corrosion of Steel in Reinforced Concrete Structures'.