Research Associate in Photonics, Macquarie University
This project aims to develop a sensor system for health monitoring of concrete structures.
Corrosion and corrosion mitigation are the most significant costs faced by Australian water utilities, accounting for about hundreds of millions dollars per annum. Corrosion is the primary factor affecting the longevity and reliability of pipelines. Acid attack has been identified as the prominent concrete ailment in sewer and usually is confined to the cement paste. This results in calcium depletion of concrete surface and leads to corrosion and softening of concrete surface. This is most analogous to the Osteoporosis in human where we have calcium depletion from bones. The water flow and flood can wash away softened concrete ultimately this results in thinner pipes and to an increased risk of structural collapse and failure in long term. Sewer pipes are like human veins and they are crucial part of a healthy city. Since they are underground, health monitoring of these structures is very hard. This silent corrosion pose a significant risk to our city Sewer pipes like Sydney with thousands of kilometers network of pipes. In order to enhance the service life of the expensive and important sewer systems as well as to counter the silent corrosion caused by acid attack, water utilities are following three approaches: (a) continues sewerage treatment to reduce the H2S level; (b) surface treatment of the concrete; and (c) installing corrosion resistant sewer pipes. However, it is still unknown to what extent these mitigation strategies factually contribute to the reduction in corrosion in concrete sewer pipes.Hereby we developed a methodology that could be used to quantitatively measure concrete quality parameters like temperature, humidity, pH, H2S level and strain which are crucial factors in detecting deterioration in concrete sewer pipes. This system is working by adding fiber optic sensors to concrete structures and gives a monitoring dashboard to water utilities to detect any abnormality in underground pipes and enable water utilities to act on time. We have also developed a methodology for periodical structural and mechanical core evaluation by the combination of Neutron Tomography (NT), Scanning Electron Microscopy (SEM) and Microindentation Mapping techniques. Combination of every day sensor readings and periodical core evaluation can be then used as part of asset management strategies in order to address maintenance challenges such as surface treatment of corrosion impacted pipes or sewage chemical dosing in the most efficient manner.
Abstract: Formation of cracks impairs the durability of concrete elements. Corrosion inducing substances, such as chlorides, can enter the matrix through these cracks and cause steel reinforcement corrosion and concrete degradation. Self-repair of concrete cracks is an innovative technique which has been studied extensively during the past decade and which may help to increase the sustainability of concrete. However, the experiments conducted until now did not allow for an assessment of the service life extension possible with self-healing concrete in comparison with traditional (cracked) concrete. In this research, a service life prediction of self-healing concrete was done based on input from chloride diffusion tests. Self-healing of cracks with encapsulated polyurethane precursor formed a partial barrier against immediate ingress of chlorides through the cracks. Application of self-healing concrete was able to reduce the chloride concentration in a cracked zone by 75% or more. As a result, service life of steel reinforced self-healing concrete slabs in marine environments could amount to 60–94 years as opposed to only seven years for ordinary (cracked) concrete. Subsequent life cycle assessment calculations indicated important environmental benefits (56%–75%) for the ten CML-IA (Center of Environmental Science of Leiden University–Impact Assessment) baseline impact indicators which are mainly induced by the achievable service life extension.
Pub.: 23 Dec '16, Pinned: 28 Aug '17
Abstract: It is well known that many reinforced concrete structures are at risk of deterioration due to chloride ion contamination of the concrete or atmospheric carbon dioxide dissolving in water to form carbonic acid, which reacts with the concrete and the reinforcing steel. The environment within the concrete will determine the corrosion product layers, which might, inter alia, contain the oxides and/or hydroxides of iron. Tensile forces resulting from volume changes during their formation lead to the cracking and delamination of the concrete. In the present investigation the handrail of an outside staircase suffered rebar corrosion during 30 year's service, leading to severe delamination damage to the concrete structure. The railings had been sealed into the concrete staircase using a polysulphide sealant, Thiokol®. The corrosion products were identified by means of Mössbauer and SEM analyses, which indicated that the corrosion product composition varied from the original steel surface to the outer layers, the former being mainly iron oxides and the latter iron oxyhydroxide.
Pub.: 01 Jun '03, Pinned: 28 Aug '17
Abstract: The compatibility between a fiber optical sensor and concrete structure in the optic fiber smart concrete is studied. The methods of improving the compatibility are proposed based on theory analysing, and a novel fiber optical sensor was developed. The experimental results show that the novel structure of fiber optical sensor and the scheme of the protecting layer of epoxy resin bed composite not only enable the sensor to be applied in strict environment, but also can monitor the beginning propagation and breaking of concrete craks. The results also indicate that the sensor will maintain its properties in the case of large deformation and that it has the high compatibility with concrete structure and con meet special needs of the intelligent materials and structure.
Pub.: 01 Mar '03, Pinned: 28 Aug '17
Abstract: Based on the advantages of the fiber Bragg grating sensing technology, this paper presents a principle of a novel smart concrete with fiber optical Bragg grating sensor, analyses the theory and characteristics, illustrates the key technology and method to make the fiber Bragg grating sensor for the smart concrete, and proves the feasibility with experiments. The results indicate that the smart concrete with fiber Bragg grating sensors is feasible in the structure monitoring and damage diagnosing in the long run.
Pub.: 01 Jun '04, Pinned: 28 Aug '17
Abstract: An improved sprayable aqueous slurry for inhibiting corrosion in sewer pipe lines comprising an aqueous mixture of about 100% by volume of a metal hydroxide and/or a metal dioxide selected from a class consisting of magnesium hydroxide and titanium dioxide and less than about 1% by volume of sodium hydroxide, the metal hydroxide and the metal dioxide having mixing rates of about 50 to 60% by volume with about 50 to 40% by volume of water and the sodium hydroxide having a mixing rate of about 50% by volume with about 50% of water and the slurry having a pH of 13.0 or more and a useful life of about 15 to about 24 months.
Pub.: 04 Dec '12, Pinned: 28 Aug '17
Abstract: Sewer systems are costly to construct and even more costly to replace, requiring proper asset management. Sewer asset management relies to a large extent on available information. In sewer systems where pipe corrosion is the dominant failure mechanism, visual inspection by closed circuit television (CCTV) and core sampling are among the methods mostly applied to assess sewer pipe condition. This paper compares visual inspection and drill core analysis in order to enhance further understanding of the limitations and potentials of both methods. Both methods have been applied on a selected sewer reach in the city of The Hague, which was reportedly subject to pipe corrosion. Results show that both methods, visual inspection and core sampling, are associated with large uncertainties and that there is no obvious correlation between results of visual inspection and results of drill core analysis.
Pub.: 12 Jun '13, Pinned: 28 Aug '17
Abstract: Concrete is prone to crack formation in the tensile zone, which is why steel reinforcement is introduced in these zones. However, small cracks could still arise, which give liquids and gasses access to the reinforcement causing it to corrode. Self-healing concrete repairs and seals these small (300 µm) cracks, preventing the development of corrosion. In this study, a vascular system, carrying the healing agent, is developed. It consists of tubes connected to a 3D printed distribution piece. This distribution piece has four outlets that are connected to the tubes and has one inlet, which is accessible from outside. Several materials were considered for the tubes, i.e., polymethylmethacrylate, starch, inorganic phosphate cement and alumina. Three-point-bending and four-point-bending tests proved that self-healing and multiple self-healing is possible with this developed vascular system.
Pub.: 08 Jan '17, Pinned: 28 Aug '17
Abstract: Corrosion cracking of reinforced concrete caused by chloride salt is one of the main determinants of structure durability. Monitoring the entire process of concrete corrosion cracking is critical for assessing the remaining life of the structure and determining if maintenance is needed. Fiber Bragg Grating (FBG) sensing technology is extensively developed in photoelectric monitoring technology and has been used on many projects. FBG can detect the quasi-distribution of strain and temperature under corrosive environments, and thus it is suitable for monitoring reinforced concrete cracking. According to the mechanical principle that corrosion expansion is responsible for the reinforced concrete cracking, a package design of reinforced concrete cracking sensors based on FBG was proposed and investigated in this study. The corresponding relationship between the grating wavelength and strain was calibrated by an equal strength beam test. The effectiveness of the proposed method was verified by an electrically accelerated corrosion experiment. The fiber grating sensing technology was able to track the corrosion expansion and corrosion cracking in real time and provided data to inform decision-making for the maintenance and management of the engineering structure.
Pub.: 14 Jul '16, Pinned: 27 Aug '17