Novel applications of pulse pre-pump Brillouin Optical Time Domain Analysis for behavior evaluation of structures under thermal and mechanical loading

This study aims to: (1) develop an analytical model for the strain transfer effect of distributed fiber optic sensors in a uniform or non-uniform stress field; (2) develop a measurement approach to monitor strains in concrete and detect damage (e.g. crack and delamination) in bonded and unbonded concrete overlays; (3) characterize the strain and temperature sensitivities of distributed fiber optic sensors at elevated temperatures; (4) develop a thermal annealing approach to enhance the thermal stability and temperature sensitivity of the distributed sensors; and (5) apply the distributed sensors to assess structural behaviors of concrete and steel structures exposed to fire. The pulse pre-pump Brillouin Optical Time Domain Analysis (PPP-BOTDA) was employed to measure strain and temperature distributions along a fused silica single-mode optical fiber. Strain distributions in concrete were measured from the distributed fiber optic sensors embedded in bonded and unbonded concrete overlays. Peaks of the strain distributions represent the effect of concrete cracks and delamination. The strain sensitivity coefficient of distributed sensors was reduced from 0.054 MHz/µε to 0.042 MHz/µε when temperature increased from 22 ⁰C to 750 ⁰C. The temperature sensitivity coefficient of distributed sensors was reduced from 1.349x10-3 GHz/⁰C to 0.419x10-3 GHz/⁰C when temperature increased from 22 ⁰C to 1000 ⁰C. The distributed sensors embedded in concrete beams measured non-uniform temperature distributions with local peaks representing a sudden increase of temperature through concrete cracks. Temperature distributions measured from the distributed sensors attached on steel beams enabled an enhanced thermo-mechanical analysis to understand the structural behaviors of steel beams subjected to fire --Abstract, page iii

Edge curling effect on interface delamination of concrete overlays for bridge decks

Deterioration of reinforced concrete bridge decks caused by various environmental conditions and traffic loads is a problem of significant concern. A protective thin overlay of about 2-inches is typically placed over newly constructed concrete bridge decks. Concrete overlay mixtures offer high resistance to traffic loads and environmental attacks, and often serve as leveling finished surfaces. A critical problem however has been the debonding and delamination propagation of the interface between overlay and substrate concrete, as observed in several bridges in West Virginia. Several studies indicated that during early-age of overlay curing, the debonding usually starts at corners or edges of the slab by curling stresses due to differential shrinkage between newly cast overlays and mature substrate. With time the crack front progressively grows within the interface leading to delamination of the overlay, and further distress cracking and deterioration.;As a part of a large-scale study on bridge deck overlays for the WVDOH, the current investigation focuses on early age curling and delamination behavior of four types of overlays for three substrate surface conditions at two ambient temperatures. A number of bi-layer prismatic specimens were produced and conditioned and tested in an environmentally controlled chamber. A circular interface delamination notch was introduced at the specimen\u27s corner. The corner and edge crack-openings due to possible delamination propagations were continuously monitored using, respectively, a clip-on gage and three displacement transducers (LVDT) connected to a data acquisition system. An ultrasonic pulse velocity method was used to predict the interface crack front propagation. The waveform was recorded with a digital oscilloscope, and through Fast Fourier Transform the amplitude-time history was converted into power spectrum for analysis. The temperature-time gradient across the overlay was measured with thermocouples to evaluate its role on edge curling and delamination.;Results showed that the initial corner crack propagated along the interface edges and within the interface surface. The readings were consistent within and among the specimens. Higher temperature resulted in more delamination and the substrate surface with saturated condition and applied bonding slurry performed best, while the dry surface condition was the worst. Among overlays, the silica fume modified concrete cracked and debonded more than the latex modified concrete. However the use of shrinkage reducing admixtures significantly reduced the curling and delamination. The results of the ultrasonic pulse velocity test to map the crack-front propagation were consistent with the displacement-time data obtained with the transducers. The spectral analysis showed that the highly irregular overlay-substrate delaminated interface surface generated additional frequency components lower than the natural frequency of the transmitting transducer. The time-temperature profile did not appear to affect the curling and debonding as the temperature gradient was nearly stable within 24 hours and before delamination growth was detected

Restrained shrinkage behaviour of rapid hardening fibre reinforced concrete repairs

The functionality and durability of concrete overlays is compromised by delamination and large cracks that result from excessive shear and tensile stresses due to restrained shrinkage. Expansive cements could mitigate shrinkage problems, but as they are usually brittle, they still develop cracks under mechanical loads. Manufactured Steel fibres (MSF) can be used to control crack widths of repairs. However, to promote the sustainability of repairs, recycled fibres extracted from un-vulcanised rubber belt off-cuts can be used. They are also more cost effective than MSF. Currently, there is no accepted design approach to limit crack widths or to accurately quantify the effect of fibres on crack widths and crack spacings of overlays. The aim of this study is to contribute to the understanding of flexural performance and restrained shrinkage and subsequent deterioration of plain and recycled fibre reinforced rapid hardening overlays, especially the fibre effect on crack widths of overlays, and to promote more sustainable, yet efficient solutions. A combination of experimental, analytical and numerical investigation is employed to study: a) the effect of recycled clean steel fibres (RCSF) on the compressive and flexural behaviour of rapid hardening mixes, b) the effect of RCSF on the crack development of overlays and shear stresses at the interface and c) the effect of non-uniform shrinkage distribution across the depth of overlays on the tensile stress development, and therefore, on the risk of cracking in overlays. It was found that the RCSF are efficient in bridging cracks, resulting in flexural hardening properties. The RCSF reduce crack widths in overlays by about 60%. The available methods for predicting crack widths are found to be inaccurate. Therefore, a modified crack width equation is proposed and validated, and a new equation for estimating crack spacing is derived. The fibres are also found to positively contribute in reducing the risk of delamination. They are shown to enhance the shear strength and proven to reduce the shear stress development after crack development and reduce the level of deterioration of shear interface by controlling crack widths. The assumption of uniform shrinkage distribution in overlays underestimates the extent of hygral tensile stresses. An empirical equation to consider this effect is proposed. This work is expected to enable better and more sustainable designs for overlay repairs and strengthening

New innovations in pavement materials and engineering: A review on pavement engineering research 2021

Sustainable and resilient pavement infrastructure is critical for current economic and environmental challenges. In the past 10 years, the pavement infrastructure strongly supports the rapid development of the global social economy. New theories, new methods, new technologies and new materials related to pavement engineering are emerging. Deterioration of pavement infrastructure is a typical multi-physics problem. Because of actual coupled behaviors of traffic and environmental conditions, predictions of pavement service life become more and more complicated and require a deep knowledge of pavement material analysis. In order to summarize the current and determine the future research of pavement engineering, Journal of Traffic and Transportation Engineering (English Edition) has launched a review paper on the topic of “New innovations in pavement materials and engineering: A review on pavement engineering research 2021”. Based on the joint-effort of 43 scholars from 24 well-known universities in highway engineering, this review paper systematically analyzes the research status and future development direction of 5 major fields of pavement engineering in the world. The content includes asphalt binder performance and modeling, mixture performance and modeling of pavement materials, multi-scale mechanics, green and sustainable pavement, and intelligent pavement. Overall, this review paper is able to provide references and insights for researchers and engineers in the field of pavement engineering

Discrete Element Simulation of Bending Deformation of Geogrid-Reinforced Macadam Base

The pavement bending deformation resistance of the existing macadam base structure is poor. The geogrid-reinforced macadam base can effectively strengthen the bending resistance of the pavement, but no international consensus has been reached at present over bending failure laws of reinforced macadam base structure. Discrete element models of semi-rigid base pavement structure, macadam base pavement structure, and geogrid-reinforced macadam base pavement structure were built based on MATDEM discrete element simulation program; loading calculation of the three models was conducted by taking their centers as loading positions; and model displacement nephogram, strain nephogram, and effects of different spans on their bending deformation were analyzed to reveal bending failure laws of reinforced macadam base and improvement effect of the geogrid on the anti-bending performance of the macadam structural layer. Finally, bending deformation laws of the three pavement structures and improvement effect of geogrid reinforcement on bending properties of the macadam base structure were established. The results show that under bending deformation of semi-rigid base, the vertical strain at the contract surface between the baseplate and soil base and horizontal strain at midspan position reach the maximum, which can easily lead to fracture and shear failure, and the macadam base layer can effectively isolate the tensile strain transmitted from bottom up. Through their own deformation, grids can transform surface pressure load into frictional resistance at the geogrid/soil interface and partial kinetic energy in the system into their own elastic potential energy to reduce the kinetic energy at the subbase layer. Geogrid reinforcement can improve the nonlinearity of macadam materials, reduce the fluctuation amplitude of the strain curve and displacement curve, lengthen the service life of the macadam base pavement structure, and improve its structural soundness under bending deformation. This study can provide a theoretical reference for numerical simulation of bending failure of geogrid-reinforced macadam base

On the Use of Interfacial Fracture Mechanics Approaches for Evaluation of the End Movement in Concrete Slabs

This dissertation aims to study effects of different design factors on the end movements in Continuously Reinforced Concrete (CRC) pavements subjected to environmental loads. End movement in CRC pavements is an important distress leading to deterioration of in-service pavement structures. Different models, including closed form solutions and numerical approaches for prediction of the concrete slab displacements, are introduced and discussed. The effect bond strength between the concrete slab and the subbase layer on concrete slab end movement is investigated using interfacial fracture mechanics concepts. First, the theoretical criteria describing the mechanism of interfacial crack propagation are discussed in a general framework. A modified version of the maximum tangential stress criterion is developed for strong interfaces and it is shown that the proposed model provides more accurate prediction of the experimental data. A new fracture test specimen, which covers all mixed mode conditions, is proposed for evaluation of the bond strength between two dissimilar materials. The new test specimen is then employed for evaluation of the bond strength between the asphalt concrete and the Portland cement concrete. As the next step, a series of three dimensional finite element simulations are performed to investigate end movements in CRC pavements. The concrete slab/ subbase layer and concrete slab/ reinforcing steel bar interfaces were modelled using a zero thickness cohesive layer which follows traction-separation constitutive law. The results of the finite element simulations are compared with those measured from experiments by previous researchers. Finally, the effects of CRC dimensions, material properties, bond strength, and environmental loads on the end movements in CRC pavements are explored using three dimensional finite element simulations. The results obtained in the present work can help pavement engineers to better understand the mechanism of end movements in CRC pavements

Mechanical Behavior of Concrete Materials and Structures: Experimental Evidence and Analytical Models

This reprint contains 15 papers published in the Special Issue entitled "Mechanical Behavior of Concrete Materials and Structures: Experimental Evidence and Analytical Models”. Dealing with the broad spectrum of the mechanical behavior of concrete materials and structures, the reprint includes experimental findings and numerical analyses using both conventional and advanced methodologies. This book presents contributions in the field of not only ordinary and prestressed concretes, but also special concretes, including high-strength, recycled, and fiber-reinforced concretes, for both structural and non-structural applications, and for the development of related numerical/analytical predictive models

Review of advanced road materials, structures, equipment, and detection technologies

As a vital and integral component of transportation infrastructure, pavement has a direct and tangible impact on socio-economic sustainability. In recent years, an influx of groundbreaking and state-of-the-art materials, structures, equipment, and detection technologies related to road engineering have continually and progressively emerged, reshaping the landscape of pavement systems. There is a pressing and growing need for a timely summarization of the current research status and a clear identification of future research directions in these advanced and evolving technologies. Therefore, Journal of Road Engineering has undertaken the significant initiative of introducing a comprehensive review paper with the overarching theme of “advanced road materials, structures, equipment, and detection technologies”. This extensive and insightful review meticulously gathers and synthesizes research findings from 39 distinguished scholars, all of whom are affiliated with 19 renowned universities or research institutions specializing in the diverse and multidimensional field of highway engineering. It covers the current state and anticipates future development directions in the four major and interconnected domains of road engineering: advanced road materials, advanced road structures and performance evaluation, advanced road construction equipment and technology, and advanced road detection and assessment technologies