Jacek Kwasny

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.

Selection and characterisation of geological materials for use as geopolymer precursors

Geopolymer binders are generally formed by reacting powdered aluminosilicate precursors with alkali silicate activators. Most research to date has concentrated on using either pulverised fuel ash or high purity dehydroxylated kaolin (metakaolin) in association with ground granulated blast furnace slag as the main precursor material. However, recently, attention has turned to alternative calcined clays that are abundant throughout the globe and have lower kaolinite contents than commercially available metakaolins. Due to the lack of clear and simple screening protocols enabling assessment of such geological resources for use as precursors in geopolymer systems, the present paper presents results from experimental work that was carried out to develop a functional binder using materials containing kaolinite taken from the Interbasaltic Formation of Northern Ireland. The influence of mineralogy has been examined, and a screening process, using three Interbasaltic materials as examples, that will assist in the rapid selection of suitable geopolymeric precursors from such materials is outlined.

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.

Optimization of Self-Consolidating Pastes Containing Limestone Powder and Chemical Admixtures

This paper describes how the performance of self-consolidating pastes was optimized by studying the effect of three mix composition parameters, limestone powder (LSP) content, dosage of superplasticizer (SP), and that of viscosity-modifying admixture (VMA), in a statistically designed experiment. Four properties of the pastes were measured: fluidity (mini-slump flow), Vicat setting times, volume change in the fresh state, and 28-day compressive strength. The optimization was preceded by the evaluation of the response surfaces of all chosen properties in the specified ranges of the three variables. The response surface results emphasized the primary and secondary effects on the properties of cement paste. The optimization indicated that pastes with properties acceptable for self-consolidating applications could be obtained with a moderate LSP content (for example, 19.5% by mass of total powder) and low dosage of the chemical admixtures (for example, 0.64% of SP and 0.01% of VMA by mass of total powder).