Effect Of Overlayer Thickness Research Articles

Effect of overlay thickness, fiber volume, and shrinkage mitigation on flexural behavior of thin bonded ultra-high-performance concrete overlay slab

This study investigated the flexural performance of 10 reinforced concrete slabs rehabilitated using thin ultra-high-performance concrete (UHPC) bonded overlay. The performance was compared to two slabs repaired using latex-modified concrete (LMC) that is widely used for bridge deck rehabilitation. Test parameters included the overlay thickness (25, 38, and 50 mm), fiber volume (2% and 3.25%), and shrinkage mitigation methods for the UHPC. The overlay slab specimens were stored outdoor for 30 months before conducting the four-point bending test. Experimental results indicated that the overlay slabs exhibited flexural failure pattern with yield of reinforcing steel, concrete crushing of the reinforced concrete substrate, and multiple cracks in the overlay. The use of UHPC thin bonded overlay enhanced cracking load by 295%–395% and flexural capacity by 35%–75% compared to the LMC overlay slabs. The maximum crack width of UHPC overlay slabs at the stage of the yield of reinforcement was less than 0.1 mm compared to 0.25–0.3 mm for the LMC overlay slabs. No slip occurred at the interface between the UHPC overlay and substrate, whereas the slip initiated following LMC overlay cracking. The increase of overlay thickness from 25 to 50 mm and fiber volume from 2% to 3.25% enhanced the flexural load capacity of the UHPC overlay slabs by 30%–40% and 10%–25%, respectively. These two strategies also reduced crack opening and propagation before the yield of reinforcing steel. The use of pre-saturated lightweight sand and CaO-based expansive agent was effective in mitigating autogenous and drying shrinkage without significantly influencing the flexural capacity of UHPC overlay slab.

An Ultrathin Compact Polarization-Sensitive Triple-band Microwave Metamaterial Absorber

In this study, an ultra-compact metamaterial absorber (MMA) has been proposed for microwave applications comprising two modified square-shaped resonators printed on a dielectric substrate and terminated by a metallic plane. The proposed MMA exhibits perfect absorption at 3.36 GHz, 3.95 GHz and 10.48 GHz, covering S- and X-band applications. The absorber is ultra-compact (0.112 λ) in size and ultra-thin (0.018 λ) in thickness at the lowest resonating frequency. The normalized impedance, constitutive electromagnetic parameters, electric field and surface current distribution have been studied to understand the physical mechanism of the triple-band absorption. Furthermore, the absorber is analyzed with different polarization and incident angles for transverse electric waves. The proposed MMA has been experimentally demonstrated to verify the results obtained from simulations. Moreover, the effect of over-layer thickness is investigated to examine the sensing application of the absorber.

移动荷载作用下水泥混凝土基层沥青加铺层力学分析

为了研究移动荷载作用下水泥混凝土路面沥青加铺层裂缝中点的应力状态，应用abaqus软件分析加铺层厚度、加铺层模量、水泥板厚度、基础模量对沥青加铺层路面应力状态的影响。结果表明：基础模量对沥青加铺层裂缝中点应力影响最大，加铺层厚度和加铺层模量影响次之，但水泥板厚度对裂缝中点应力几乎没有影响。 In this paper, the abaqus software is used to analyze the stress state of the midpoint of the cracks in the asphalt overlay of the cement concrete pavement under the moving load, and the most un-favorable load position is obtained. The effects of overlay thickness, overlay modulus, cement board thickness and base modulus on the stress state of pavement pavement were studied. The influence factors of pavement overlay structure were analyzed. The results showed that the basic modulus Asphalt overlay cracks at the midpoint of the maximum stress, followed by the thickness of the overlay and overlay modulus, the thickness of the cement board basically did not affect.

Sensitivity enhancing of transition mode long-period fiber grating as methane sensor using high refractive index polycarbonate/cryptophane A overlay deposition

A highly sensitivity long-period fiber grating (LPFG) methane sensor system is presented, which was working in transition mode with high refractive index overlay deposition of polycarbonate/cryptophane A. The transparent composition coating of polycarbonate/cryptophane A was used as high refractive index overlay deposition based on automatically dip-coating technique to tune the working point of the sensor in the transition region. Effects of overlay thickness and refractive index (RI) on the LPFG's resonant wavelength were studied in order to obtain the optimal overlay thickness. For the overlay thickness of 530nm, the overlay RI of 1.5605 and the grating period of 520μm, the maximal RI sensitivity of the designed LPFG sensor could reach 3.56×103nm/RIU. The experimental results demonstrate that the new sensor has the features of high sensitivity (∼2.5nm%−1) and low detection limit of 0.2% (v/v).

Coated long-period fiber gratings as high-sensitivity optochemical sensors

In this paper, the numerical and the experimental analyses of coated long-period fiber gratings (LPFGs) as a high-sensitivity optochemical sensor are presented. The proposed structure relies on LPFGs coated with nanoscale high refractive index chemical-sensitive overlays. The deposition of overlays with refractive index higher than the cladding one leads to a modification of the cladding-mode distribution. If the overlay features are properly chosen, a strong field enhancement within the overlay occurs, leading to an excellent sensitivity of the cladding-mode distribution to the coating properties. The effects of overlay thickness and cladding-mode order on sensor performances have been numerically and experimentally investigated. In order to provide a high-sensitivity and species-specific optochemical sensor, this mechanism has been proved with nanoscale overlays of syndiotactic polystyrene (sPS) in the nanoporous crystalline /spl delta/ form. The sensitive material has been chosen in light of its selectivity and high sorption properties towards chlorinated and aromatic compounds. Sensor probes were prepared by using dip-coating technique and an adequate procedure to obtain the /spl delta/-form sPS. Experimental demonstration of the sensor capability to perform subparts-per-million detection of chloroform in water at room temperature is also reported.

In Situ Criteria of Pull-Off Test for Measuring Bond Strength of Latex-Modified Concrete Overlay

This study evaluated the factors influencing a pull-off test on latex-modified concrete (LMC) overlay by finite element analysis (FEA) and experimental verification and provided field engineers and project managers a guideline for measuring the bond strength in the field. The purpose of FEA was to predict stresses at the interface between the substrate and the overlay and between the disk and the overlay. Good agreement has been obtained between the theoretical and experimental results to confirm the following: the steel disc thickness did not affect the stress concentration factor (SCF) at the concrete interface but significantly influenced that of the steel disc. To prevent failure at the steel disc interface, the normalized steel disc thickness (T/D) should be at least 0.3. The effect of overlay thickness was significant to the stress distribution at the concrete interface. The normalized overlay thickness should be larger than 0.4. SCFs at all diameters decreased rapidly as the substrate coring depth increased from 0.05 to 0.2 of normalized cutting depth relative to core diameter. Those with a 75-mm diameter (D75) and a 100-mm diameter (D100) became stabilized immediately after reaching 0.2 of normalized cutting depth relative to core diameter. Stress distributions at concrete interfaces were not affected by the distance of the core from the edge of the slab (le), the distance between cores (lc), and the typical elastic modulus ratio of LMC to conventional concrete. The experimental results with the major influencing factors (steel disc thickness, core diameter, and partial cutting depth) showed good agreement with FEA results. For theoretical as well as for practical purposes, 100-mm (4-in.) core diameter is optimum; cutting depth should be between 25 mm (1 in.) and 40 mm (1.7 in.).

Effect of overlayer thickness on electron emission from Si:Cs-O NEA surfaces

Experimental and theoretical studies of the variation in photoresponse of the Si:Cs-O negative electron affinity (NEA) photocathode with thickness of the Cs-O overlayer and acceptor concentration in the Si bulk, are reported. Resonance transmission peaks in the variation of photoyield with increasing overlayer thickness are predicted and observed. From a comparison of theoretical and experimental curves, the electron attenuation length in the overlayer is estimated to be about 50 AA. The theoretical analysis indicates that the optimum overlayer is metallic with a carrier concentration of about 2*1021 cm-3, varying slightly with bulk acceptor concentration.

Thickness Effects in Overlay Guides for Elastic Surface Waves

The analysis here is concerned with waveguides for elastic surface waves where the guiding structure consists of an overlay of rectangular cross section on the surface of an infi- nite substrate. When the overlay is thin with respect to the wavelength various perturbation techniques can be used to determine the dispersion curves of such guides. By using an approach which treats the overlay and the region under the overlay in a manner similar to the polynomial variational ap- proaches which have been used for propagation modes of rods and plates, the analysis here allows an investigation of the effects of overlay thickness on the dispersion curves and on the displacement distributions in the overlay and in the sub- strate. The infinite series introduced into the displacement distribution can be truncated at different orders depending on the accuracy desired and on the tolerable computational complexity. Two different orders of truncation are discussed and numerical results for several different modes are presented showing both the dispersion and displacement behaviour for a gold overlay on a fused quartz substrate.