Mohamed Sonebi

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.

Performance of Reinforced Columns Cast with Self-Compacting Concrete

This paper compares the structural performance of full-scale (300 x 300 x 3000 mm) columns cast using ordinary concrete and self-compacting (SCC) concretes with stirrup configurations representing different degrees of confinement. SCC and ordinary concretes having compressive strengths of 35 MPa (housing) and 60 MPa (civil engineering) were used to cast a total of eight columns. Two pairs of columns were cast using ordinary concrete and SCC. For each pair of the reinforced columns, one column was tested in uniaxial compression to determine its load carrying capacity, while the other one was used to take core samples to determine the distribution of in-situ compressive strengths along its height. The core results were compared to strengths determined on control cubes cured in standard conditions (water) and in air. In general, the in-situ compressive strengths or SCC were closer to standard cube strength than those of ordinary concrete. The distribution of in-situ properties was found to be more uniform in the case of SCC than that of the ordinary concrete. The compressive strength and the ductility of SCC and the ordinary concrete obtained from the 3-m column tests are also compared in this paper.

Effect of Mixture Composition on Relative Strength of Highly Flowable Underwater Concrete

Concrete used for underwater repair is often proportioned to spread readily into place and self-consolidate, and to develop high resistance to segregation and water dilution. A study was conducted to determine the effect of the dosage of antiwashout admixture, water-cementitious materials ratio (w/cm), and binder composition on the relative residual strength of highly flowable underwater concrete. Two types of antiwashout admixtures and 4 binder compositions were used. Results indicate that for a given washout mass loss and slump flow consistency, greater relative residual strength can be secured when the dosage of antiwashout admixture is increased, the w/cm reduced, and a binary binder with 10% silica fume substitution or the ternary binder are employed.

Mechanical Properties of Self-Compacting Concrete: State-of-the-Art Report of the RILEM Technical Committee 228-MPS on Mechanical Properties of Self-Compacting Concrete

The State-of-the-Art Report of RILEM Technical Committee 228-MPS on Mechanical properties of Self-Compacting Concrete (SCC) summarizes and extensive body of information related to mechanical properties and mechanical behaviour of SCC. Due attention is given to the fact that the composition of SCC varies significantly. A wide range of mechanical properties are considered, including compressive strength, stress-strain relationship, tensile and flexural strengths, modulus of elasticity, shear strength, effect of elevated temperature, such as fire spalling and residual properties after fire, in-situ properties, creep, shrinkage, bond properties, and structural behaviour. A chapter on fibre-reinforced SCC is included, as well as a chapter on specialty SCC, such as light-weight SCC, heavy-weight SCC, preplaced aggregate SCC, special fibre reinforced SCC, and underwater concrete.

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.

Effect of Free-Fall Height in Water on Performance of Highly Flowable Concrete

This study presents the results of a laboratory investigation that aimed to evaluate the effect of free-fall height (FFH) of concrete in water on in-place properties of high-performance concrete made with various water/cementitious materials and binder types. The variations of in-place compressive strength, splitting tensile strength at 28 and 56 days, and mean of thickness of washed-out and sedimentation materials are evaluated for concrete subjected to FFHs ranging between 250 and 600 mm. The effect of washout resistance on residual strength is also evaluated for an optimized concrete of a fixed slump flow consistency of 500 mm.

Effect of Freezing-Thawing Cycles on the Resistance of Self-Consolidating Concrete to Sulfate Attack

SCC has been used in various applications, such as pavements, marine structures, shallow foundations, etc. that can be concomitantly exposed to sulfaterich environments and frost action. To evaluate the resistance of SCC mixtures to sulfate attack considering the effect of frost action, the present study introduces accelerated testing procedure combining the exposure to aggressive magnesium and mixed magnesium-sodium sulfate solutions with freezing-thawing cycles. After five months of exposure, the results showed that SCC mixtures incorporating high dosage of fillers (limestone and ultrafine kaolin) had inferior physicomechanical properties relative to the other SCC mixtures. Thermal and microscopy analyses indicated that mutual effects of sulfate attack and freezing-thawing cycles caused severe distress in such cementitious systems.

Structural Behaviour of SCC

The State-of-the-Art Report of RILEM Technical Committee 228-MPS on Mechanical properties of Self-Compacting Concrete (SCC) summarizes and extensive body of information related to mechanical properties and mechanical behaviour of SCC. Due attention is given to the fact that the composition of SCC varies significantly. A wide range of mechanical properties are considered, including compressive strength, stress-strain relationship, tensile and flexural strengths, modulus of elasticity, shear strength, effect of elevated temperature, such as fire spalling and residual properties after fire, in-situ properties, creep, shrinkage, bond properties, and structural behaviour. A chapter on fibre-reinforced SCC is included, as well as a chapter on specialty SCC, such as light-weight SCC, heavy-weight SCC, preplaced aggregate SCC, special fibre reinforced SCC, and underwater concrete.

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).

Design and testing of self-compacting SIFCON produced with low strength slurry

ABSTRACT Slurry Infiltrated Fibre Concrete (SIFCON) is produced by a process in which fibres are put into an empty mould, after which the fibre mass is infiltrated by a cement slurry. Generally, the infiltration of the slurry into the layer of fibres is carried out under intensive vibration. Recent research has investigated the development of slurries which do not require to be vibrated when SIFCON is produced. Samples of self-compacting SIFCON were produced and tested for flexural and compressive strength. Three different orientations of fibres in testing samples were obtained. A three-point bending test with displacement control system was used for testing the beams. Basically, the results showed higher flexural strength and energy absorption compared with plain cement slurry. The anisotropy of SIFCON was shown from results of samples which had different orientation of fibres.