Kieran Owens

Fiber-Optic Strain Sensor System With Temperature Compensation for Arch Bridge Condition Monitoring

This paper presents an innovative sensor system, created specifically for new civil engineering structural monitoring applications, allowing specially packaged fiber grating-based sensors to be used in harsh, in-the-field measurement conditions for accurate strain measurement with full temperature compensation. The sensor consists of two fiber Bragg gratings that are protected within a polypropylene package, with one of the fiber gratings isolated from the influence of strain and thus responding only to temperature variations, while the other is sensitive to both strain and temperature. To achieve this, the temperature-monitoring fiber grating is slightly bent and enclosed in a metal envelope to isolate it effectively from the strain. Through an appropriate calibration process, both the strain and temperature coefficients of each individual grating component when incorporated in the sensor system can be thus obtained. By using these calibrated coefficients in the operation of the sensor, both strain and temperature can be accurately determined. The specific application for which these sensors have been designed is seen when installed on an innovative small-scale flexi-arch bridge where they are used for real-time strain measurements during the critical installation stage (lifting) and loading. These sensors have demonstrated enhanced resilience when embedded in or surface-mounted on such concrete structures, providing accurate and consistent strain measurements not only during installation but subsequently during use. This offers an inexpensive and highly effective monitoring system tailored for the new, rapid method of the installation of small-scale bridges for a variety of civil engineering applications.

Retrofit versus new-build house using life-cycle assessment

This paper reports the findings of research on the environmental performance of two case-study houses, a retrofit and new build. The retrofit was completed to a Passivhaus standard while the new build was completed to current Irish building regulations. Environmental performance of the retrofit and new build was measured using life-cycle assessments, examining the assembly, operational and end-of-life stage over life spans of 50 and 80 years. Using primary information, life-cycle assessment software and life-cycle assessment databases the environmental impacts of each stage were modelled. The operational stage of both case studies was found to be the source of the most significant environmental damage, followed by the assembly and the end-of-life stage respectively. The relative importance of the assembly and end-of-life stage decreased as the life span increased. It was found that the retrofit house studied outperformed the new build in the assembly and operational stage, whereas the new build performed ...

Use of nanocrystal seeding chemical admixture in improving Portland cement strength development: application for precast concrete industry

Abstract This paper summarises an investigation into the potential advantages to the precast concrete industry of using a new ‘seeding’ type of chemical admixture in Portland cement (PC) based concrete mixes. Results indicated that the addition of 2–4% nanocrystal seeding chemical (NCS) admixture by weight of PC can provide a doubling of early strength, particularly at 6 and 12 h. This strength gain could lead to the turnover of moulds in precast concrete plants being completed twice in 24 h, thus increasing production capacity. Isothermal conduction calorimetry, X-ray diffraction and thermogravimetric analysis techniques were used to investigate the reasons for the improvement in compressive strength development. Results indicated that the increase in early compressive strength is due to an acceleration of early hydration of PC in presence of the NCS. Indeed, after 6 h, the degree of hydration was more than 50% greater when NCS was used. This paper also highlights the possibility of the NCS chemical admixture being used in conjunction with supplementary cementitious materials (SCMs) in PC blended concrete mixes. 2% NCS was added to a blend containing 70% PC and 30% ground granulated blast furnace slag (GGBS). Results indicated that early strength values were greater compared to the blend without NCS and comparable to the 100% PC mix.

Arch-bridge Lift Process Monitoring by Using Packaged Optical Fibre Strain Sensors with Temperature Compensation

This paper presents a novel sensor design and packaging, specifically developed to allow fibre grating-based sensors to be used in harsh, in-the-field measurement conditions for accurate strain measurement, with full temperature compensation. After these sensors are carefully packaged and calibrated in the laboratory, they are installed onto the paragrid of a set of flat-packed concrete units, created specifically for forming a small-scale, lightweight and inexpensive flexi-arch bridge. During the arch-bridge lifting process, the sensors are used for real-time strain measurements to ensure the quality of the construction. During the work done, the sensors have demonstrated enhanced resilience when embedded in concrete structures, providing accurate and consistent strain measurements during the whole installation process and beyond into monitoring the integrity and use of the structure.

CO2 Sequestration in Cement-Based Materials During Mixing Process Using Carbonated Water and Gaseous CO2

This paper presents selected findings from a recently completed research project, aimed at the investigation of CO2 sequestration in cement-based materials during the early stages of hydration when the cement paste is being mixed. Portland cement pastes were carbonated during the mixing process, using both carbonated water and gaseous CO2, and their properties were compared to the control non-carbonated mix. All mixes were prepared in a purpose-designed chamber that permitted carbonated water and gaseous CO2 to be mixed with the cementbased materials during the mixing process, without losses of CO2 to the external environment. Temperature measurements taken of the samples during mixing were used to evaluate the influence of carbonation on the properties of fresh pastes and their early hydration. Changes in the composition of the hardened pastes, due to the above- mentioned processes, were studied using thermogravimetric (TG) analysis, X ray diffractometry (XRD), and Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDXS) were used to investigate physical (morphological) and chemical differences between non-carbonated and carbonated samples. It was found that, when compared to the non-carbonated mixes, the rate of the initial hydration of carbonated pastes increased, but the later hydration rate was decreased dramatically. TG, XRD, and FTIR spectroscopy revealed a substantial increase in the CaCO3 content and decrease in the Ca(OH)2 content in carbonated pastes. SEM showed substantial differences in the microstructure of the carbonated mixes when compared to the noncarbonated ones; needle- and lichen-like hydrates, with a high content of CO2, covered the surface of the fractured carbonated samples.