Niall Holmes

Developments in Performance Monitoring of Concrete Exposed to Extreme Environments

AbstractThe performance of the surface zone of concrete is acknowledged as a major factor governing the rate of deterioration of reinforced concrete structures because it provides the only barrier to the ingress of water containing dissolved ionic species such as chlorides, which ultimately initiate corrosion of the reinforcement. In situ monitoring of cover-zone concrete is therefore critical in attempting to make realistic predictions as to the in-service performance of the structure. To this end, this paper presents developments in a remote interrogation system to allow for continuous, real-time monitoring of the cover-zone concrete from an office setting. Use is made of a multi electrode array embedded within cover-zone concrete to acquire discretized electrical resistivity and temperature measurements, with both parameters monitored spatially and temporally. On-site instrumentation, which allows for the remote interrogation of concrete samples placed at a marine exposure site, is detailed together wi...

Developments in monitoring techniques for durability assessment of cover-zone concrete

This paper outlines developments in the use of an embedded multi-electrode sensor to study the response of the cover-zone (surface 50mm) to the changing ambient environment. The sensor enables the measurement of the spatial and temporal distribution of the electrical properties of concrete and temperature within the cover-zone thereby allowing an integrated assessment of cover-zone concrete performance. Both laboratory and field results are presented to highlight the information that can be obtained from embedded sensors. When exposed to the natural environment, the temperature dependence of the electrical response is highlighted and standardization protocols are developed to account for this effect. The monitoring system detailed also allows remote interrogation thereby providing (if required) a continuous output of real-time data and developments in this area are presented.

Cement Based Batteries and their Potential for Use in Low Power Operations

This paper presents the development of an innovative cement-electrolyte battery for low power operations such as cathodic protection of reinforced concrete. A battery design was refined by altering different constituents and examining the open circuit voltage, resistor loaded current and lifespan. The final design consisted of a copper plate cathode, aluminium plate anode, and a cement electrolyte which included additives of carbon black, plasticiser, Alum salt and Epsom salt. A relationship between age, temperature and hydration of the cell and the current it produced was determined. It was found that sealing the battery using varnish increased the moisture retention and current output. Current was also found to increase with internal temperature of the electrolyte and connecting two cells in parallel further doubled or even tripled the current. Parallel-connected cells could sustain an average current of 0.35mA through a 10Ω resistor over two weeks of recording. The preliminary findings demonstrate that cement-based batteries can produce sufficient sustainable electrical outputs with the correct materials and arrangement of components. Work is ongoing to determine how these batteries can be recharged using photovoltaics which will further enhance their sustainability properties.

Optimising the Performance of Cement-Based Batteries

The development of a battery using different cement-based electrolytes to provide a low but potentially sustainable source of electricity is described. The current, voltage, and lifespan of batteries produced using different electrolyte additives, copper plate cathodes, and (usually) aluminium plate anodes were compared to identify the optimum design, components, and proportions to increase power output and longevity. Parameters examined include water/cement ratio, anode to cathode surface area ratio, electrode material, electrode spacing, and the effect of sand, aggregate, salts, carbon black, silica fume, and sodium silicate on the electrolyte. The results indicate that the greatest and longest lasting power can be achieved using high proportions of water, carbon black, plasticiser, salts, and silica fume in the electrolyte and using a magnesium anode and copper cathode. This cell produced an open-circuit voltage of 1.55u2009V, a resistor-loaded peak current over 4u2009mA, maintaining over 1u2009mA for 4 days, and a quasi steady current of 0.59u2009mA with a lifespan of over 21 days.

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.

Structural Properties of Concrete Materials Containing RoadCem

This paper presents findings from a preliminary study to assess the structural and material properties of a nonstandard, concrete type mix containing RoadCem, a traditional soil stabilising additive. Two different mixes determined the effect of adding RoadCem in terms of compressive and flexural strengths, breaking strain, thermal expansion and contraction behaviour, permeability using a falling head, and Young’s modulus. RoadCem is a fine powder containing alkali metals and synthetic zeolites which are complemented with a complex activator. RoadCem modifies the dynamics and chemistry of cement hydration by enhancing the crystallisation process and forming longer needle crystalline structures. It reduces the heat of hydration with an early strength development. Varying the volume in the mix varies the viscosity and alters curing times while maintaining the water cement ratio. The results from this study have shown a modest increase in compressive strength and Young’s modulus with improvements in thermal performance, particularly at low temperatures. The flexural strength of the two mixes was similar with a much reduced permeability in the RoadCem mix. The results demonstrate the improved performance of concrete incorporating RoadCem but further improvements are possible by using a better graded aggregate and controlling the maximum dry density and moisture contents.

Using Model Building in Structural Engineering to Enhance Understanding of Construction Principles and Methods

This paper presents a new model building exercise in a second year module in the Department of Civil & Structural Engineering in the Dublin Institute of Technology (DIT). The activity aimed to improve students’ understanding of structural engineering, construction principles and methods. It allowed students to practically apply lecture material and construct a scaled model giving them an opportunity to study and visualise a real structure and generate their own ideas on how it should be assembled within a constructivist active learning environment. As a result, lectures were found to be more interactive and students more engaged in the discussions and provided a pathway to bridge the gap between theory (presented in lectures) and the reality of their professions, which can aid them in their graduate careers. It is hoped that this type of active learning can be used in other engineering programmes to improve student understanding and as an opportunity to better apply lecture material to the real world.

INFLUENCE OF CEMENT TYPE ON THE EFFICIENCY OF ELECTROCHEMICAL CHLORIDE EXTRACTION

The corrosion of steel in concrete due to chlorides is well established. Concrete structures are susceptible to chloride ions ingress when exposed to de-icing salts or seawater which pass through the cover zone to the embedded steel. Erosion of the passive layer leads to corrosion, a reduction in cross-sectional area, cracking and a loss of structural capacity. Electrochemical Chloride Extraction (ECE) has been shown to reduce the chloride concentration in concrete. However, previous work has demonstrated that improper application of the electrical charge has led to adverse side effects such as loss of bond strength and cracking around the steel/concrete interface. This paper presents the effect of a constant voltage and current density on three different cement types and the subsequent rate of chloride ion removal from the cover zone and deeper in the concrete. The findings show how appropriate electrical energy can lead to improved and efficient ECE treatments.

An Overview of the Development of Cement-Based Batteries for the Cathodic Protection of Embedded Steel in Concrete

This paper presents an overview of the cement-based batteries developed in DIT for use in the cathodic protection of embedded steel in reinforced concrete undergoing chloride-induced corrosion. Cathodic protection delivers an external current (approximately 20mA per m of embedded steel) which effectively polarises the internal current generated during corrosion. The batteries developed in DIT comprise of a cement-based electrolyte containing different additives including sand, aggregate, salts, carbon black and plasticiser with protruding anode and cathode metal plates. These batteries produced an initial electrical output of 1.5V and 23mA through a 10x93 resistor as measured using data acquisition units and a custom-built LabVIEW program. By enhancing the ionic conductivity and maintaining the internal moisture content in the cement pores, the batteries power and life span can be improved. Following a concrete ponding regime to initiate corrosion of embedded steel in a concrete block sample, the power required to protect the reinforcement and arrest corrosion current was determined using a DC desktop supply. With the intention of replacing the desktop supply with a battery module ongoing work is focussing on increasing the life span of individual battery modules, improving their recharging capabilities and optimising for different shapes.

Using Photovoltaics to Power Electrochemical Chloride Extraction from Concrete

Corrosion of embedded steel in reinforced concrete (RC) is a world-wide problem, that reduces structural performance and lifespan. Chloride attack may be a result of seawater, de-icing salts or contaminated admixtures, brought on by ingress of chlorides into the concrete. Electrochemical Chloride Extraction (ECE) is a non-destructive treatment for contaminated RC structures, that due to uncertainty of treatment times and applied current densities, is only 50% effective. It is often diesel powered has an environmental impact and often very costly due to the long treatment times. To improve the efficiency of ECE the influences of concrete resistance, cement type and duration of treatment have been investigated in an experimental programme. The use of Photovoltaic (PV) panels to improve the efficiency of ECE is presented which replace fossil fuels as a power source enabling a more environmentally sustainable treatment. These findings will increase the life span of vital infrastructure and reduce expensive ongoing repairs with decreased traffic congestion and inconveniences associated with bridge repairs.