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Prefabricated lightweight concrete building fascade can improve the energy efficiency of buildings and reduce the carbon emission of transportation. However, it is essential to maintain the dimensional stability of the full scale element. The drying shrinkage of lightweight foamed concrete was investigated in this study. The hypothesis of using the drying shrinkage of normal weight concrete to approximate that of lightweight foamed concrete of dry density about 1500 kg/m3 counterpart was verified. Three different strategies of reducing drying shrinkage were studied. The drying shrinkage of common ingredients of ordinary Portland cement (OPC) and ground granulated blast-furnace slag (GGBS) was commonly up to 2000–3000 μ e . The use of magnesium expansive agent with different calcination conditions could not reduce the drying shrinkage. The use of calcium sulfoaluminate (CSA) cement with OPC and GGBS could significantly reduce the drying shrinkage within 1000 μ e in standard testing environment. The formulation developed in laboratory was scaled up in a concrete production plant for prefabricated concrete elements. A lightweight full scale panel (the wet density was about 1700 kg/m3) was fabricated. The drying shrinkage of the developed formulation with CSA cement was only 161 μ e in the field test. A hygro-mechanical model was developed to model the diffusion, shrinkage and plastic strain evolution. The incremental stress-strain constitutive relationship of the hygro-mechanical model was derived for incorporating it into general finite element routine. The model parameters were calibrated by the drying shrinkage measurements in this study. The calibrated model demonstrated the cracking potential of three typical reinforced concrete panels of three different formulations studied in this study.

Characterization of surface cracks is one of the key steps towards condititional assessment and understanding the durability of strain hardening cementitious composites (SHCCs). Under laboratory conditions, surface crack statistics can be obtained from images of specimen surfaces through manual inspection. This is subjective, time consuming and laborious. In order to automate this process a framework encompassing a deep learning model for rapid identification and computation of crack parameters of thin SHCC cracks in presented in this work. A tailored deep convolutiontional neural network (TDCNN) was trained to detect thin cracks and then crack parameters were computed using image processing technique. The proposed technique does not require optimal lighting conditions, proper surface treatment, and prior (manual) selection of the correct region for proper inference.. The results from the controlled study suggest that the inference ability of TDCNN is reasonably good, resilient against epistemic uncertainty and tunable for completely independent but adverse observations. From the crack pattern computed using TDCCN, crack parameters-average crack width (ACW) and crack density (CD) can be calculated to facilitate conditional and durability assessment in a practical environment.

Rapid identification of structural damage positions is essential to the post-disaster rehabilitation of structures and infrastructures. Large shear deformation, e.g., shear failure of bridge piers, shear-slip of slopes, and shear cracking of structural walls, is often the cause of structural instability. Distributed optical fibre sensing (DOFS) techniques have an advantage over point-based sensors in terms of spatial continuous structural condition monitoring. This paper presents the development of new measurement theory and algorithm to evaluate the structural shear deflection based on the large beam deflection and optical bend loss theories. The proposed technique adopted a photon-counting Optical Time Domain Reflectometer (&nu, OTDR) with polymer optical fibres (POFs) which has a large deformation measurement range and high spatial resolution. In the experiment, shear deformation events can be successfully detected and evaluated from the proposed technique. When the normalised shear deformation is larger than 0.2, both the event locations and the magnitudes can be accurately determined. When normalised shear deformation is lesser than 0.2, the error in the magnitude evaluation increased, but the event location can be found with an absolute error &lt, 0.5 m. Multiple shear events can be treated as independent events when they are separated by more than 5 m. Various configurations of POFs attached to concrete beam specimens for rupture failure monitoring were also studied. The configuration that could maximise the POF curvature at the beam failure produced the largest &nu, OTDR signals. In other configurations in which the POFs were only stretched at failure, the signals were less strong and were influenced by the POF-structure bonding strength.

Backsheet degradation is key to maintaining the lifetime of photovoltaic (PV) modules. Cracking, delamination, bubbling, and discoloration are main types of degradation. PV modules were collected from PV installations in multiple climatic zones. Multiple types of backsheets were obtained with poly(ethylene teraphlate) (PET) and polyamide air side layers being the largest number of backsheets retrieved. Multiple commercial PV backsheets were exposed to multiple accelerated exposures and key degradation mechanisms were identified. Polyamide backsheets showed cracking in retrieved modules and under accelerated exposures. Poly(vinylidene fluoride) (PVDF) and poly(vinyl fluoride) (PVF) showed the highest stability in retrieved and accelerated exposures. While polyamide had the largest amount of large scale degradation.

The annual construction and demolition waste (CDW) generated from EU construction sector was 850 million tons, which represented 31% of the total waste generation and about 28% of CDW was ceramics (bricks and tiles). In this study, the feasibility of using CDW brick powder as the precursor of alkali activated mortar (AAM) and extruded polystyrene (XPS) as the lightweight aggregates to form lightweight brick powder AAM (LW-BP-AAM) for non-structural applications was investigated. The thermal conductivity of LP-BPAAM was 0.112 W/m·K with density of about 1,135 kg/m3 which was lower than the counterparts with similar density in literature. The acid resistance of LW-BP-AAM is comparable to conventional fly ash based AAM and superior than ordinary Portland cement. From the scanning electron microscopy with energy dispersive X-ray spectroscopy, there was no severe damage on the surface of LW-BP-AAM but aluminate was removed from the matrix which was further verified in Fourier transform infrared spectroscopy. The mass and strength loss of LP-BP-AAM was 1.5% and 33%, respectively. Although the compressive strength of the LP-BP-AAM was low (about 1.8 MPa), it can be improved by optimising the particle size of the XPS aggregates.

In this paper, a low-cost 3 × 3 coupler Mach–Zehnder interferometric optical fibre vibration sensor is proposed. Unlike the traditional Mach–Zehnder interferometer with a strain free reference arm, two parallel optical fibres with different strain transfer sensitivities are adopted. With the proper demodulation algorithm, the time rate of change in strain can be computed from the light signal of the outputs of a 3 × 3 coupler. The proposed optical fibre vibration sensor is verified by experiment. The vibrating frequency spectrum of a two-layer metal frame is measured by both the proposed optical fibre vibration sensor and micro-electro-mechanical system (MEMS)-based accelerometers. It was found that the proposed vibration sensor is more sensitive compared to the MEMS-based accelerometer, unless it is located near a zero-strain region. Several proposed sensors can easily be multiplexed to minimise the overall cost.

Optical fiber strain sensors, in particular, the fiber Bragg grating (FBG) type, are widely applied in different applications. The most common installation method is surface-attached. In principle, the optical fiber strain sensor with adequate sampling and signal processing techniques is usually more accurate than electrical resistive strain gauge. However, the strain of the surface of structure may not transfer to the sensing element perfectly. The ratio between the measured and actual strain can be correlated by a strain transfer factor (STF). However, it depends on the material and geometrical properties of the optical fiber and adhesive. It is noneconomical and impractical to measure the STF for every installed sensor. It is desirable to identify the most of the sensitive parameters on the variation of the STF so that the quality control and assurance procedure can be performed more efficiently. In this paper, a quantitative global sensitivity analysis, called extended Fourier amplitude sensitivity test will be performed to compute the first-order and total sensitivity indexes based on a well-established semi-analytical/empirical mechanical model of three material and five geometrical parameters of both integral and optical FBG type optical fiber strain sensor with two different kinds of polymeric coating under three types of strain field in 16 different configurations. From the detail analysis, the most of the sensitive parameters on the STF are bond length, the thickness of adhesive beneath the optical fiber and the deviation of grating position, which are related to workmanship instead of the material properties of the optical fiber and adhesive.

Steel corrosion resulting from the penetration of chloride ions or carbon dioxide is a major cause of degradation for reinforced concrete structures,. The objective of the present investigation was to develop a low-cost sensor for steel corrosion, which is based on a very simple physical principle. The flat end of a cut optical fiber is coated with an iron thin film using the ion sputtering technique. Light is then sent into a fiber embedded in concrete and the reflected signal is monitored. Initially, most of the light is reflected by the iron layer. When corrosion occurs to remove the iron layer, a significant portion of the light power will leave the fiber at its exposed end, and the reflected power is greatly reduced. Monitoring of the reflected signal is hence an effective way to assess if the concrete environment at the location of the fiber tip may induce steel corrosion or not. In this paper, first the principle of the corrosion sensor and its fabrication are described. The sensing principle is then verified by experimental results. Sensor packaging for practical installation will be presented and the performance of the packaged sensors is assessed by additional experiments.

Many masonry building structures are vulnerable to a seismic event. There are many structural retrofitting technologies available, such as glass/carbon fibre reinforced polymeric matrix composite. However, it is difficult to protect the polymeric matrix from fire in building structures. To fundamentally improve the fire resistance of retrofitting material, it can simply change the polymeric matrix to cement based matrix. This kind of composite is called fibre reinforced cementitious matrix (FRCM). It consists of high performance manmade fibre such as AR glass, carbon, basalt or Kevlar and it is extensively investigated by different researchers. It provides an excellent alternative for engineers to structural retrofit building structures for which fire is one of major design concerns. Ironically, most of the earthquake active zones are in the poorest region in the world because of continuous attack by natural disasters. In those regions, the building structures are the most vulnerable to an extreme event such as earthquake and there is a need for structural retrofitting. Due to poor economic development of those regions, it is unaffordable to apply high performance manmade fibre to achieve the purpose. One practical solution is to develop a technically feasible,economically viable and environmentally sustainable is to replace high performance manmade fibre by locally available natural fibre in FRCM. A technical challenge is the durability of natural fibre in the high alkalinity environment of cementitious matrix. In this presentation, the effects of different treatment methods on sisal fibre as well as how to extract the mechanical and bond parameters of treated fibre from pull-out test under accelerated ageing test will be discussed.

Cracks in structures may open in mixed mode under general loading conditions. In other words, there are both opening and shearing displacements along the crack. In our former work, a distributed fiber optic sensor has been developed for the detection and monitoring of purely opening cracks (or Mode I cracks). The sensing principle is based on the bending loss of an optical fiber intersecting the opening crack at an angle other than 90°. In the present work, the sensing concept is extended to the monitoring of mixed mode cracks. To obtain both the opening and shear displacements at the crack, two independent measurements are required. Based on theoretical simulation, the feasibility of various sensing strategies, including the use of two wavelengths and two fibers, are first investigated to identify the most promising approach. A method to solve the inverse problem of obtaining the crack displacements from the measured signal losses is then derived. Experiments are performed under controlled crack opening/shearing history to verify the sensing approach. Good agreement between derived opening/shearing displacements and imposed displacements has been obtained.

The degradation of concrete structures is always accompanied by the formation of cracks. If cracks are detected at an early stage before significant degradation occurs, life of the structure can be extended by the performance of relatively low cost but timely maintenance measures. To detect and monitor cracking in concrete structures, where the crack locations are often not known in a-priori, a distributed optical crack sensor based on OTDR measurement of bend loss has been developed. In this paper, the sensing principle will be discussed and the fabrication of sensors for surface attachment and internal embedment is described. Experimental results are shown to demonstrate that the optical power loss versus crack opening relation at a particular point of bend loss is independent of the number of bends along the fiber. Then, the monitoring of single and multiple cracks under quasi-static loading is illustrated, followed by the detection of cracks under restrained dimensional change (caused by shrinkage or thermal effects). Finally, the sensor performance under cyclic loading is studied. Based on the test results, the potential of the sensor for practical applications is demonstrated.

The degradation of concrete structures is always accompanied by the formation of cracks. Crack monitoring is hence useful in assessing the “health condition” of the structure. In our previous investigation on an optical-fiber crack sensor, we have successfully demonstrated the possibility of crack detection and monitoring without requiring prior knowledge of crack locations. Also, a single fiber can be employed to monitor a number of cracks. In practical applications, the signal loss versus crack opening relationship of the sensor needs to be properly “designed” to satisfy performance requirements on sensitivity to small cracks and/or the total number of detectable cracks (which is limited by the maximum loss at each crack). In this paper, a theoretical model for the signal loss versus crack opening relationship is developed through a combination of mechanical and optical analyses. Using concrete beams with embedded sensors, crack monitoring experiments are conducted. Test results are found to be in reaso...

Optical fiber sensor (OFS) technologies have developed rapidly over the last few decades, and various types of OFS have found practical applications in the field of civil engineering. In this paper, which is resulting from the work of the RILEM technical committee “Optical fiber sensors for civil engineering applications”, different kinds of sensing techniques, including change of light intensity, interferometry, fiber Bragg grating, adsorption measurement and distributed sensing, are briefly reviewed to introduce the basic sensing principles. Then, the applications of OFS in highway structures, building structures, geotechnical structures, pipelines as well as cables monitoring are described, with focus on sensor design, installation technique and sensor performance. It is believed that the State-of-the-Art review is helpful to engineers considering the use of OFS in their projects, and can facilitate the wider application of OFS technologies in construction industry.

The relation between the component strain and the strain on a surface-attached optical fiber is governed by the effectiveness of shear transfer through the adhesive and the polymeric coating(s) on the optical fiber. A classical shear lag model can predict the strain transfer through a soft layer well. However, experiments showed that the results are unsatisfactory for bare fiber with stiff adhesive case. A 3D-FEM is established to model the strain transfer of a surface-mounted strain sensor and it is verified by experiments. Then, it is used to investigate the influence of four geometric parameters of the adhesive: (1) side width, (2) top thickness, (3) bond length, (4) bottom thickness, on the strain transfer. By sensitivity analysis, it is revealed that the bond length and the bottom thickness are dominant factors. Based on finite element results, the parameter of the analytical model is modified to suit stiff layer cases. Important considerations for practical installation of surface-attached optical interferometric and FBG strain sensors will be discussed.