Slab Samples Research Articles

Assessing the Ageing Impact on Fatigue Life of Asphalt Concrete

The fatigue life of asphalt concrete is often related to environmental condition, loading condition, ageing, material composition and properties. This work investigates the influence of short and long term ageing of laboratory beam specimens, asphalt content, and testing temperature on fatigue life of asphalt concrete wearing course. Slab samples of (30 x 40x 6) cm have been prepared, beam specimens of (40x 5x 6) cm were cut from the asphalt concrete slab samples. Beam specimens were tested for fatigue life under the influence of three levels of micro strain (250, 400, and [3]750) at (5, 20, and 30) °C before and after practicing long-term aging. It was observed that the fatigue life decreases by (85 and 97) %, (87.5 and 97.4) %, (71.4 and 95.2) % after increasing the applied microstrain from (250 to 400 and 750) μƐ for control mixture and for mixtures subjected to short-and long-term ageing processes respectively. The fatigue life increases by (142.8 and 257.1) %, (34.4 and 57.8) % and (10 and 30) % when the asphalt content increases from (4.4 to 4.9 and 5.4) % for specimens practicing the applied microstrain of (250, 400 and 750) μƐ respectively. It was concluded that the fatigue life increases by a range of (two to fifteen) folds when the testing temperature increases from (5 to 20 and 30)°C respectively.

Influence of effective texture depth on pavement friction based on 3D texture area

Pavement texture significantly affects the anti-skid performance. This study applied 3D laser technology to measure the texture of asphalt pavement surfaces with an objective to explain the variation in the friction measured using a portable pendulum tester. Pavement slab samples were prepared for six different types of asphalt mixtures (SMA-Top5, AC-10, AC-13, AC-16, SMA-13, and OGFC-13). High-precision surface texture data of the samples were then collected using a portable laser scanner (LS-40), and the friction values (BPN) were measured. The 3D image reconstruction and segmentation of the pavement texture were realized through a digital image processing technology, and the texture surface area at different depths was calculated. Finally, we performed a correlation analysis between the texture surface area at different depths and the pavement friction values. The results showed that the pavement anti-skid value and the texture surface area have a significant positive correlation in the texture depth range of 0.5–2 mm, with the lowest determination coefficient value of 0.6836. Our research confirms that the effective texture depth influencing pavement friction is 2 mm and that the texture surface area can be used as an indicator of pavement friction during its service life.

Benchmark experiment for bismuth by slab samples with D-T neutron source

A benchmark experiment is carried out with slab sample to validate nuclear data of bismuth by measurement of leakage neutron spectra from 0.8–16 MeV. The measured experiments are performed at China Institute of Atomic Energy with the integral benchmark facility established on the D–T neutron generator. The neutrons leaking from the sample are recorded at the measuring angle of 60° and 120° by time-of-flight technique. To make understanding of the impact of accuracy of data files in evaluated library on the neutron transport simulation, the calculation is carried out by MCNP-4C code with a series of latest available evaluated libraries. The calculated spectra are analyzed by comparing with experimental ones in neutron spectrum shape and C/E values. The result indicates that the theoretical simulation with different data libraries overestimated or underestimated the measured ones in some energy ranges, and the secondary neutron energy distribution and angular distribution in data files have been present to explain it.

Computation of Core Floor Slabs of Different Length

The purpose of this research is to study what the crosscurrent representation format of core slabs is for samples of different length, by investigating the effect of the above factors on the load-bearing and stress-related properties, as well as the cracking load. The authors examined samples of slabs of different length, freestanding and working in bending, with a cross-section in a natural form, in comparison with samples of similar length in an I-beam shape. The samples were systematically loaded an interval of one kN until the yield point of reinforcement in the tension area was reached. The authors completed a numerical study of core slabs in a nonlinear setting. The researchers designed load-deflection plots when modeling the corresponding lengths of samples with a natural and I-beam form of section. The scholars received and compared results with loading of the cracked condition, midspan deflections with a rupturing load. They found out that the length of the slab affects the calculation results of the shapes issued: the shorter the length, the more highlighted deviation in the load-deflection plots. The authors suggested correction coefficients to perform a refined calculation of slabs for cracking, deflection, and rupturing loads.

Thermal diffusivity measurement of microscale slabs by rear-surface detection thermoreflectance technique

A new approach to measure the cross-plane thermal diffusivity of a microscale slab sample, which can be fabricated by the focused ion beam and attached to a substrate, is proposed. An intensity-modulated pump laser is applied to heat the front surface of the sample uniformly, and the thermoreflectance signal is observed at the rear surface to evaluate thermal wave transport in the material. The thermal diffusivity can be obtained by fitting the phase lags of the experimental data with a theoretical model. The model was developed for the sample with thin-film coatings and heat transfer to the substrate. Although the absorbed heat can cause a significant DC temperature increase in the microscale sample, a thin-film coating with high thermal conductivity can effectively reduce the DC temperature increase within low thermal conductivity samples. To validate the method, we conducted measurements of a fused silica sample of 2.16 µm thickness, coated with 95 nm Ti film on the front surface and 120 nm Au film on the rear surface. The measured thermal diffusivity is in good agreement with the literature value. The uncertainty analysis shows that the measurement uncertainty is within 6%. This proposed approach, designed for microscale samples, offers a unique option for thermal property measurements of special materials, such as irradiated nuclear fuel or other irradiated materials, to enable microscale property determination while minimizing sample radioactivity.

Hollowcore slab with alternative cementitious materials for winter conditions

The precast industry, due to its specific early-age strength requirements for hollowcore (HC) slab products, has been reluctant to introduce alternative cementitious materials such as ground granulated blast-furnace slag (GGBS) due to the slower strength development of such materials. This paper reports on a study undertaken at a precast production facility to examine how to overcome the consequences of strength loss due to the replacement of up to 50% of CEM I (42·5R), as usually used in cold weather conditions, with GGBS, for environmental or durability reasons. The GGBS concrete slabs were activated using thermal, chemical and mechanical means to enhance their early-age strength gain. The results were compared at early ages in terms of the temperature profile during curing, cube compressive strengths, load-carrying capacities for transportability requirements, ultimate load and short-term creep. In addition, 28 d densities and strengths were compared for in situ cubes and cores extracted from HC slab samples. The experimental results showed a favourable potential for replacing CEM I (42·5R) cement with up to 50% GGBS in winter without compromising on factory productivity.

Time-dependent flexural performance and design procedures for steel-bars truss slabs

Thin-walled steel decks have been generally treated as permanent formwork in the routine design of steel-bars truss slabs, and their effects on the time-dependent behaviour of steel-bars truss slabs have not been quantified. The objective of this study was to propose design procedures for the time-dependent behaviour of steel-bars truss slabs accounting for the effects of soffit steel decks. For this purpose, two full-scale slab samples were tested for 9 months, with one slab subjected to non-uniform shrinkage and sustained loading and the other slab subjected to only non-uniform shrinkage. Typical design equations for reinforced concrete slabs and composite steel–concrete slabs were benchmarked against available test results to verify their applicability. Non-linear finite-element models were established to describe the time-dependent behaviour of steel-bars truss slabs, and simplified design procedures were proposed. It was found that the steel-bars truss sample subjected to non-uniform shrinkage had a mid-span deflection accounting for 52·4% of the total deflection; that the design methods in available composite structure standards significantly underestimated the long-term deflections; and that the proposed design procedures well predicted the time-dependent deflections of steel-bars truss slabs by considering the influence of the shrinkage gradient.

Magnon-polaritons in graphene/gyromagnetic slab heterostructures

We present a theoretical study for the surface magnon-polaritons in structures formed by graphene layer(s) on an insulating gyromagnetic medium (that can be either ferromagnetic or antiferromagnetic) surrounded by vacuum. We consider different doping levels to vary the Fermi energies in the graphene, including both semi-infinite and slab magnetic samples. Our results reveal a strong influence, exerted by the presence of graphene, on the surface magnon-polariton modes. The effects include control of the group velocities for the modes as the Fermi energies of the graphene sheet are varied, modified nonreciprocal and reciprocal mode propagation properties depending on the type of magnetic material, and distinct localization properties for the emerging surface modes.

Improving calculating theory of multiple-cavity reinforced concrete floor panels

It is a known fact that core slabs are introduced as I-shaped beams (T-beams) to simplify calculations and are considered according to the beam theory. However, such a view may cause erroneous calculation results. This is particularly evident when calculating the second group of limit states. The aim of this survey is to examine the influence of the cross current representation of core slabs for samples of various length by defining the impact of these factors (the shape of the cross-section and length) on the bearing and nonrigid capacity as well as a cracking load. The paper makes the calculating theory of reinforced concrete framing clear, in particular, core slabs according to the limit states. The author dwells upon samples of slabs of various lengths with a natural cross-sectional shape in comparison with I-shaped samples of similar length. The author should emphasize that it is assumed both in analytical calculations and in software based on FE analysis in order to save time and computing resources. The author performs a computational investigation of core slabs in a nonlinear setting with forming a plastic centroid in the middle of a slab in the study. It is found out that the slab length affects the calculation results of the considered shapes. The shorter the length, the clearer cut the deviation in the load deflection plots.

An experimental study on corrosion initiative of infused reinforcing bar in concrete

Durability of concrete is the essential property for the lifespan of concrete structures. Rusting of steel is the major factor responsible for the loss of durability property. In order to study the corrosion behaviour of three types of reinforcing bars like Thermo-mechanically treated bar(TMT), Corrosion resistant steel (CRS), Epoxy coated rebar(ECR) were experimentally studied. The reinforcing bars having 12 mm diameter were infused in 300×300×75 mm size of concrete slab samples were kept under room temperature and certain samples are spraying with 3% of NaCl solution to attain a simulated marine exposure condition. There are various techniques including Open circuit potential (OCP), Linear polarisation resistance (LPR), Electrochemical impedance spectroscopy (EIS) are used to monitorize the corroding performance of samples. On analysing the results of the electrochemical studies, it could be inferred that the efficient rebar to withstand the corrosive nature by improving the life expectancy of the concrete structure.

Retrieval of Particle Size of Natural Granite From Multiangular Bidirectional Reflectance Spectra Using the Hapke Model (June 2020)

Quantitative determination of the physical properties of natural granite has been attempted from remotely sensed information, for which the Hapke model is a popular method. However, using the model to retrieve the photometric properties of terrestrial rocks (slab or particulate samples), especially for those with complex surface conditions such as natural granite, remains a challenge. In this study, we have approached the dilemma by coupling both radiative transfer (Hapke’s isotropic multiple scattering approximation (IMSA) model) and an empirical relationship between particle sizes with its critical parameter, the single-scattering albedo (SSA, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\omega$ </tex-math></inline-formula> ), determined from bidirectional reflectance (BDR) measurements. The results clearly indicated that the particle size of natural granite systematically controlled the BDR, which can be well fit by the Hapke model with varying parameters. The retrieved photometric parameters of the coefficients in the phase function ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$b$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$c$ </tex-math></inline-formula> ) can effectively indicate the scattering behavior of natural granite, but the variations in their values did not strongly correlate with the change in particle sizes. Instead, a good linear relationship between the SSA values and particle sizes has been established. By coupling the relationship into the Hapke model, we found a practical approach to estimate the particle size for measured samples from inversely retrieved SSA. Through this method, we are able to retrieve the physical properties of granite under natural surface conditions, and we foresee that the approach will be widely used in the future.

Influence of Ageing on Flexible Pavement Interface Bond under Repeated Shear Stresses

The durability of interface bond was not sufficiently taken into consideration, and the research work in this field is scares and scattered. The interface bond usually practices dynamic shear stresses throughout its service life while ageing due to volatilization provide stiffness at the interface. In this investigation, an attempt has been made to assess the durability of the interface bond in terms of resistance to ageing under repeated shear stresses. Two types of tack coat (Rapid Curing cutback RC-70 and Cationic Medium setting emulsion CMS) and three application rates have been implemented in the preparation of two layers slab samples (base overlaid by binder, and binder overlaid by wearing) courses using roller compactor. Asphalt concrete core specimens were obtained from the roller compacted slab samples and subjected to long term ageing, then the specimens were subjected to 1200 repeated shear stress cycles. The accumulation of permanent deformation was monitored. Afterwards, the specimens were tested for interface shear strength at 20 °C. Control specimens were also tested for comparison. It was concluded that ageing reduces the total microstrain for RC-70 tack coat by (43.6, 25.6, and 29.5) % and (50, 51.3, and 30.2) % for (binder-base) and (wearing-binder) interfaces for the application rate of (0.15, 0.33, 0.5) l/m2 respectively. However, ageing reduces the total microstrain for CMS tack coat by (37, 35.5, and 40.3) % and (45.2 , 49, and 46.8) % for (binder-base) and (wearing-binder) interfaces for the application rate of (0.1, 0.23, 0.35) l/m2 respectively. Ageing increases the interface bond shear strength by a range of (8-27)% for various interfaces, tack coat type and application rates.

Manufacture of porcelain insulators from locally available materials

This study discusses the local production, electrical characteristics and performance in service of porcelain insulators for outdoor low-voltage apparatus. Concern was given to the identification, beneficiation, characterization and utilization of locally available raw materials in Nigeria for the production of electrical porcelain insulators, taking benefits of the availability of these raw materials. The process control presents figures, tables, simulations. The basic raw materials were separately prepared using a 200-µm sieve. The composition of the triaxial constituents was varied to produce samples for testing. Altering the percentage content of silica and the alumina recorded a change in the mechanical strength and the sintering temperature; this was handled by adding fluxes suitable for improving tensile strength without increasing sintering temperature of the paste. Porcelain slab samples of different triaxial composition were formed. Tests on mechanical resistance, porosity and water absorption were carried out. Sample A, with specific percentage composition of 38% feldspar, 18% quartz, 32% kaolin and 12% ball clay, was used to produce porcelain suitable for the 480 V pin insulators. The produced sample possess an electrical dielectric constant of 9.80, a dissipating factor of 0.060, flashover voltage of above 5 kV all at 50 Hz of supply voltage frequency and a mechanical load support of 13.85 kN.

Influence of Surface Texture on Interface Bond Shear Strength of Asphalt Concrete

The bonding strength provided by the tack coat between asphalt concrete layers at the interface is considered as an essential issue in the performance of the flexible pavement throughout its service life. However, the surface texture of the pavement surface exhibits another essential issue in the bond strength. In this investigation, three layers of asphalt concrete (base, binder and wearing) courses with (25, 19, and 12.5) mm of nominal maximum size of aggregates have been prepared using roller compactor. Rapid curing cutback RC-70 and cationic medium setting emulsion CMS have been implemented as tack coats with three application rates. The slab specimens were subjected to mean texture depth determination using sand patch method. Core specimens of 102 mm diameter were obtained from the prepared slab samples and subjected to interface bond strength test with the aid of a special manufactured mold. Test results were analyzed and compared. It was concluded that when RC-70 tack coat was implemented, asphalt concrete binder course laid on base course exhibited the highest shear strength of 1600 kPa at an application rate of 0.33 liter/m2 when compared to other application rates. Asphalt concrete wearing course laid on binder course exhibited the highest shear strength of 1515 kPa at an application rate of 0.15 liter/m2 when compared to other application rates. When CMS tack coat was implemented, asphalt concrete binder course laid on base course exhibited the highest shear strength of 1620 kPa at an application rate of 0.23 liter/m2 when compared to other application rates. Finally, the asphalt concrete wearing course laid on binder course exhibited the highest shear strength of 2272 kPa at an application rate of 0.23 liter/m2 when compared to other application rates.

Ignition risk analysis of common building material cylindrical PMMA exposed to an external irradiation with in-depth absorption

The Poly methyl methacrylate (PMMA) material with a cylindrical shape are widely used for the building components. Under external irradiation, it may be ignited by a pilot ignition. Previous studies focused more on a flat surface sample, while for a cylindrical configuration, the heat flux distribution, solid-phase temperature profile and ignition time establishes different aspects induced by the cylinder curvature. Therefore, this study investigated the ignition behaviors of the cylindrical PMMA samples with various radius exposed to an external irradiation by experimental and numerical methods. Firstly, decomposition gases of PMMA samples under the irradiation were observed to evidently accumulate on the top surface of the cylinders, after which an incipient ignition occurred in conjunction with blue flames, quickly followed by sustained ignition. With varied cylinder radius, the characteristic parameters of solid-phase temperature profile and thermal penetration depth changed, which are dependent upon sample radius. While for thermal-thick slabs, these parameters have no changes to be independent of the sample thickness. Furthermore, two absorption heat flux coefficients were introduced to analyze the in-depth heat absorption by considering the effects of angle and sample radius. Finally, the critical mass flux and ignition time were given. The cylindrical samples were easier to be ignited than slab samples. With smaller sample radius, the ignition time is established to be shorter. With increasing sample radius, the critical mass flux is lower. This investigation will provide a tractable way to obtain a comprehensive evaluation of fire risk of the commonly used cylindrical components in construction and buildings.

Benchmark experiment with iron slab by Time-of-flight technique at CIAE

In order to validate the evaluated nuclear data, leakage spectra in the range of 0.8 to 15 MeV from samples were measured by time-of-flight (TOF) technique using a D-T neutron source. An experimental system for benchmark validation of nuclear data with slab samples has been set up at China Institute of Atomic Energy (CIAE). In this study, test samples are iron slabs, of which the thickness are 5cm, 10cm and 15cm, and the measured angles were chosen to be about 60° and 120°. By comparing measured leakage spectrum with calculated ones by MCNP-4C code, using the data from the CENDL-3.1, ENDF/B-VIII.0, JENDL-4.0 and JEFF-3.3 nuclear data files, and the comparison was made by the spectrum shape and by the C/E values in different energy regions.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ПРЕДВАРИТЕЛЬНО НАПРЯЖЕННЫХ БЕЗ СЦЕПЛЕНИЯ ЖЕЛЕЗОБЕТОННЫХ ПЛИТ ПРИ ПРОДАВЛИВАНИИ

In this paper there are results of a punching shear test of slab samples, which were modeling post-tensioned reinforced concrete floor slabs when they are punched by columns. Geometrical dimensions of slab samples and properties of used materials are listed as well. There were 4 series of samples which differed to each other by level of prestress. Load have been applied through stamps of several types, which have allowed to research different positions of tensioned reinforcement relatively to the punching pyramid. Obtained results are discussed. Recommendations, which compliance may allow to obtain positive effect in ultimate punching shear loads for unbonded post-tensioned slabs are given.

Effect of Flow Field on Surface Slag Entrainment and Inclusion Adsorption in a Continuous Casting Mold

A water model of slab mold was established to analyze the flow field behaviors. Particle image velocimetry measurement, fluctuation sensors, and industrial experiments were adopted to analyze the slag entrainment and inclusion adsorption. The risk of surface slag entrainment was discussed from the perspectives of flow patterns, surface fluctuation, and velocity. The ability of mold slag to adsorb inclusions was discussed by electrolysis on slab samples. The results reflected that the flow field determined the fluctuated amplitude, surface pattern and flow velocity of the mold surface, playing an important role in the slag entrainment and inclusion adsorption. Uneven surface fluctuations and downward vertical velocity lead to high slag entrapping risk. High surface horizontal velocity in mold leads to a higher inclusion concentration gradient at the slag‐steel interface, which leads to a stronger ability of mold slag to adsorb inclusions.

Strength of two-way Semantan Bamboo reinforced concrete slabs

Steel has been widely known as the essential material for reinforcement. However, many researches have been conducted in order to find an alternative sustainable material to replace steel. In this study, bamboo has been chosen to replace steel as reinforcement is introduced as one of the alternative material for reinforcement of concrete. The Semantan Bamboo (Gigantochloa Scortechinii) splint with a size of 20 mm x 10 mm (Thickness) was used as the main reinforcement. Three samples of two-way concrete slabs were prepared with a dimension of 1200 mm x 1200 mm x 100 mm. One sample will be constructed without reinforcement, while the remaining two samples will be reinforced with 1.5%, 2.5%, 3.5% and 4.5% of bamboo. All the samples will undergo concentrated punch loads and control slab without reinforcement. The results show that the maximum punching shears that the slabs can sustain more 60 kN. The slabs fail by the cracking of concrete at the bottom of the slab under the concentrated load.

Durability of Stone Cladding in Buildings: A Case Study of Marble Slabs Affected by Bowing

Bowing is an uncommon pathology that can affect marble stone cladding of building façades, causing a large permanent deflection and the degradation of the flexural and anchoring strength of the stone slabs, which can lead to the cladding falling from the façades. Moreover, the combination of bowing with wind pressure effects on the building façades can increase the risk of fracture and collapse of the stone slabs, especially if this combination is not properly evaluated during design. Motivated by a case study, this work describes a stability evaluation of a 15-year-old building façade coated with marble stone cladding affected by bowing and subjected to wind pressures. This evaluation was focused on the stone slabs, and was performed through finite element model (FEM) numerical simulations of these slabs submitted to wind pressures and through lab tests using samples of stone slabs removed from the building façade. The results obtained demonstrated stability problems on the stone slabs caused by wind pressure-induced stresses combined with the loss of strength due to aging and bowing effects, especially for slabs with larger dimensions.