A Remote Interrogation System for Monitoring Concrete Performance Exposed to Environmental Action

The performance of the surface zone of concrete is acknowledged as a major factor governingthe rate of deterioration of reinforced concrete structures as it provides the only barrier to theingress of water containing dissolved ionic species such as chlorides which, ultimately,initiate corrosion of the reinforcement. In-situ monitoring of cover-zone concrete is critical inattempting to make realistic predictions as to the in-service performance of the structure. Tothis end, this paper presents developments in a remote interrogation system to allowcontinuous, real-time monitoring of the cover-zone concrete from an office setting. Use ismade of a multi-electrode array [19] embedded within cover-zone concrete to acquirediscretized electrical resistivity and temperature measurements, with both parametersmonitored spatially and temporally. On-site, instrumentation, which allows remoteinterrogation of concrete samples placed at a marine exposure site, is detailed, together withdata handling and processing procedures. Site-measurements highlight the influence oftemperature on electrical resistivity and an Arrhenius-based temperature correction protocolis developed using on-site measurements to standardize resistivity data to a referencetemperature; this is an advancement over the use of laboratory-based procedures. The testingmethodology and interrogation system represents an additional technique which could beused for intelligent monitoring of reinforced concrete structures

Introducing a New Cement Hydration and Microstructure Model

This paper presents a new cement hydration model (HYDCEM) to predict the microstructure evolution of hydrating tricalcium silicate (C3S). The model is written in MATLAB and employs the continuum approach and integrated particle kinetics relationships to show the change in C3S and the growth of Calcium Silicate Hydrate (C-S-H) and Calcium Hydroxide (CH) in the pore space over time. Cement hydration is a highly complex process. While hydration models should never completely remove experimental analysis, they are an aid to better understand cement hydration and microstructure development by providing a method to analyse a large number of pastes with different cementitious make-ups in a relatively short time. This model uses spherical particles to represent the C3S with customizable input files such as cumulative weight distributions (CWD), to determine the particle size distributions, PSD), w/c ratio, C3S, C-S-H and CH phase densities, kinetics rates, stiochiometries and enthalpy values. The current study presents simulated microstructures and demonstrates the versatility of the model, while still in the development stage, to simulate cement hydration and microstructure development over 100 days. With further development, it can become a flexible tool for both academia and industry that can easily incorporate the inclusion of supplementary cementitious materials etc

Introducing PBL into Civil and Structural Engineering

The benefits of problem based learning for students are a deeper understanding of lecture material, and the development of problem solving and collaboration skills which will greatly enhance their educational experience. This approach has been successful in other programmes as it departs from the traditional ‘what I am told I need to know’ to ‘what I need to know to solve the problem’ promoting self-directed learning. Lecturers in turn transition from the giver of information to the facilitator of learning through support, guidance and monitoring. This project introduced an active learning element into two concrete technology modules by replacing traditional laboratory exercises with a project requiring students to design, test and report on a series of concrete mixes and aggregate samples in the context of a real life assignment. Previously, the details to conduct the laboratory were provided to the students. This project, carried out in groups, required students to apply the theoretical knowledge from lectures thereby increasing their understanding of the material, developing their learning and teamwork skills and appreciating the context in which engineers work

Performance Monitoring of Cover-Zone Concrete

The concrete cover-zone is a major factor governing the degradation of concrete structures as it provides the only barrier to aggressive agents which initiate corrosion of the reinforcement. Knowledge of the protective qualities of cover-zone concrete is critical in attempting to make predictions as to the in-service performance of the structure with regard to likely deterioration rates for a particular exposure condition and compliance with specified design life. To this end, a multi-electrode array was used to study the surface 50mm of concrete specimens thereby allowing a detailed picture of the response of the covercrete to the changing environment. In the current work, CEM I, CEM II/B-V and CEM III/A cements were used and comprised field studies representing a range of exposure conditions

Cathodic Protection for Reinforced Concrete Structures: Present Practice and Moves Toward using Renewable Energy

Abstract: Cathodic protection (CP) limits the corrosion of a metal by making it the cathode of an electrochemical cell. This is achieved either by (i) using more active sacrificial anodes to create a driving current, or (ii) using inert anodes and impressing an external direct current (DC). This paper presents up-to-date CP systems available for reinforced concrete, particularly Impressed Current Cathodic Protection (ICCP) and self-sufficient or renewable energy systems. The potential for overcoming the mismatch in energy provision from renewable sources (intermittent current) with energy needs for CP (constant current) is discussed by exploring novel designs and examining current requirments

First Steps in Developing Cement-Based Batteries to Power Cathodic Protection of Embedded Steel in Concrete

This paper presents the first steps in developing innovative cement-based batteries to power cathodic protection in reinforced concrete structures. Initial electrical outputs of 1.55V and 23mA have been found to be sufficient to polarise prescribed corrosion currents of 20mA per m2 of embedded steel. Cathodic protection is a well-developed and powerful technique to limit the effects of steel reinforcement corrosion. However, as it requires an electrical supply day and night, it is often powered by non-environmentally friendly diesel generators or connected to the electrical grid. This paper focuses on increasing the ionic conductivity of the solution in the cement pores, increasing the porosity of the cement, examining ways of sealing moisture into the cement and comparing different electrode materials and treatments. The batteries presented consist of different combinations of Portland cement, water, carbon black and salt solutions with embedded copper acting as the cathode and magnesium, aluminium or zinc cast as the anode. The preliminary findings demonstrate that cementbased batteries can produce sufficient sustainable electrical outputs with the correct materials and arrangement of cast-in anodes. Work is ongoing to determine how these batteries can be recharged using photovoltaics which will further enhance their sustainability properties

Thermodynamic Cement Hydration Modelling Using HYDCEM

Thermodynamics have been successfully applied to the field of cement hydration science to predict the formation of phase assemblages and pore solution chemistry. For any cement hydration model to be accepted, it must provide accurate forecasts of which solids may form and how the cement will dissolve over time. This is particularly important for the ongoing development of new sustainable cements and understanding their hydration behaviour in service. HYDCEM is a cement hydration model that simulates volumetric changes of cement and gypsum dissolution and product growth that, up to now, assumed which solids would form. In order to improve its usefulness, the PHREEQC geochemical software has been coupled with HYDCEM to provide more sophisticated and flexible predictions of which phases may form under equilibrium conditions and generate their change in volume over time for curing temperatures between 5-45°C, variable w/c ratio and cement oxide compositions. To incorporate the coupling of PHREEQC into the model, HYDCEM was re-written in the C# programming language (previously coded in MATLAB) which also improved overall performance and functionality. This paper presents analysis of a cement system with a w/c ratio of 0.5 at a curing temperature of 20°C and provides predictions of the phase assemblage, phase and product changes in volume and heat evolution over a 1,000-day period in one hour time-steps

HYDCEM: a New Cement Hydration Model

Hydration models are useful to predict, understand and describe the behaviour of different cementitious-based systems. They are indispensable for undertaking long-term performance and service life predictions for existing and new products for generating quantitative data in the move towards more sustainable cements while optimising natural resources. One such application is the development of cement-based thermoelectric applications. HYDCEM is a new model to predict the phase assemblage, degree of hydration, heat release and changes in pore solution chemistry over time for cements undergoing hydration for any w/c ratio and curing temperatures up to 450C. HYDCEM, written in MATLAB, is aimed at complementing more sophisticated thermodynamic models to predict these properties over time using user-customisable inputs. A number of functions based on up to date cement hydration behaviour from the literature are hard-wired into the code along with user-changeable inputs such as the cement chemical (oxide) composition, cement phase densities, element molar mass, phase and product densities and heat of hydration enthalpies. HYDCEM uses this input to predict the cement phase and gypsum proportions, volume stoichiometries and dissolution and growth of hydration products from the silicates, aluminates and ferrites, including C-S-H, calcium hydroxide, hydrogarnet (if applicable) ettringite and monosulphate. A number of comparisons are made with published experimental and thermodynamic model results and HYDCEM predictions to assess its accuracy and usefulness. The results show that HYDCEM can reasonably accurately predict phase assemblages in terms of volume change and behaviour for a range of cements and curing temperatures. It is proposed that HYCEM can complement more sophisticated thermodynamic models to give users a reasonable prediction of cement behaviour over time

Simulating cement hydration using HYDCEM

HYDCEM is a new cement hydration model to simulate volumetric changes and predict phase assemblage, degree of hydration, heat release, compressive strength and chemical shrinkage over time for PC and limestone binders undergoing hydration for any w/c ratio and curing temperatures between 5 and 45 °C. While models should never completely remove experimental analysis, they are an aid to better understand cement hydration and microstructure development by allowing users analyse different binders in a relatively short time. HYDCEM, written in MATLAB®, is aimed at complementing more sophisticated thermodynamic models giving users a reasonable prediction of hydration behaviour over time, using user-customisable inputs. A number of functions based on up to date cement hydration behaviour from the literature are included along with user-changeable inputs such as the cement chemical (oxide) composition, cement phase densities, species molar mass, phase and product densities and heat of hydration enthalpies. HYDCEM uses this input to predict the cement phase and gypsum proportions, volume stoichiometries and growth of hydration products including C-S-H, calcium hydroxide, hydrogarnet (if applicable), hydrotalcite, ettringite, monosulphate, hemicarbonate and monocarbonate if limestone is present. A number of comparisons with published experimental and thermodynamic model results and HYDCEM predictions are provided to demonstrate its accuracy and usefulness. Previous work has shown that HYDCEM can reasonably accurately predict phase assemblages in terms of volume change and behaviour for a range of cements and curing temperatures

Modelling the Addition of Limestone in Cement using HYDCEM

Hydration models can aid in the prediction, understanding and description of hydration behaviour over time as the move towards more sustainable cements continues. HYDCEM is a new model to predict the phase assemblage, degree of hydration and heat release over time for cements undergoing hydration for any w/c ratio and curing temperatures up to 450C. HYDCEM, written in MATLAB, complements more sophisticated thermodynamic models by predicting these properties over time using user-friendly inputs within one code. A number of functions and methods based on up to date cement hydration behaviour from the literature are hard-wired into the code along with user-changeable inputs including w/c ratio, curing temperature, chemical compositions, densities and enthalpies. Predictions of hydration product volumes from the silicate, aluminate and ferrite phases can be determined, including C-S-H, calcium hydroxide, hydrogarnet (if applicable) ettringite and monosulfate. A number of comparisons have been made with published phase assemblages using thermodynamic models and HYDCEM predictions to assess its accuracy and usefulness. This paper presents simulations of cement hydration and microstructure development with and without the additional of ground limestone using the HYDCEM model, both in terms of monocarbonate growth at the expense of monosulfate and ettringite. Comparisons with published phase assemblages show good agreement in terms of volumetric growth and behaviour