Sustainability is now a high priority goal in the construction industry. One way of achieving this aim is to use recycled concrete aggregate (RCA) for base courses and other purposes. However, RCA is not widely used in new concrete mixtures largely because RCA concrete has been reported to be of inferior quality relative to concretes produced with virgin aggregates. In this article, a new mixture proportioning method for RCA concrete is outlined, and it is demonstrated that the method results in RCA concrete mixtures suitable for structural applications, with predictable short- and long-term properties, and requiring less cement than a concrete mixture of comparable quality made with only virgin aggregates.
Forst-induced soil-pipeline interaction is modelled using a time-dependent thermo-mechanical process. A simplified one-dimensional frost heave model is used to evaluate frost heave, and a beam on elastic foundation finite element is used to model the buried pipeline. The time-dependent creep displacements of frozen soil are determined based on the elastic theory for the multi-layer half space. The frost-related soil stiffness is obtained using an average elastic modulus and treating the freezing soil as a multi-layer half space. The contact pressure exerted on the pipeline by frost heave and by creep effects in the frozen soil is represented by a simple distributed load. A computer program based on the time-dependent finite element method is developed which can be used to calculate frost-induced stresses and deformations of the pipe. A numerical example is presented which demonstrates reasonable agreement between the results from the proposed analysis and available experimental data.
A hybrid reinforcement system is proposed which consists of a low modulus polymeric reinforcement combined with CFRP, and which is believed to overcome the lack of ductility in FRP reinforced concrete members. Three 4.2 m long and 400 mm deep, high strength concrete inverted T-beams were designed using this new concept and were tested under four point bending. Two of the beams contained hybrid reinforcement while the third contained only CFRP reinforcement (control beam). The control beam failed suddenly, following the rupture of the CFRP reinforcement. The beams with hybrid reinforcement failed in a ductile manner at 63% higher load and they had at least three times more deflection at failure than the control beam. In the later beams, deflections substantially increased following the rupture of CFRP, but the moment of resistance of the beams decreased marginally. Upon release of the load, the hybrid reinforced beams rebounded and had very little deflection under self-weight.
This paper will discuss that every year hundreds of millions of tons of demolition waste is generated throughout the world and concrete constitutes a major portion of this waste. In many countries the demolition concrete is sent either to landfills or is recycled as aggregate to be used for base and/or sub-base of roads, or as bedding for underground pipes. On the other hand, millions of tons of fresh aggregates are annually extracted and processed for making concrete. From both the environmental and economic points of view, it may be difficult to sustain this practice, for fresh aggregate extraction causes land denudation and depletion of a non-renewable resource while it is becoming increasingly expensive to transport it from distant sources to mixing plants and construction sites. Consequently, the need for recycling of old concrete as aggregate in new concrete exists. One reason for the limited use of recycled concrete aggregate (RCA) in new concrete is the perception, substantiated by some experimental data, that concrete made with RCA, termed RCA-concrete, is inherently inferior to concrete made with fresh aggregates. It is the purpose of this paper to demonstrate by means of experimental data that RCA-concrete is not intrinsically inferior, and that the reported inferiorities are the consequence of using inappropriate concrete mixture design methods. To rectify this situation, a new mix design method is proposed which can be applied to conventional or RCA-concrete with practically any fresh aggregate replacement ratio. Using this method, it is demonstrated by testing an extensive number of specimens that the proposed method would result in the production of high quality structural grade RCA-concrete, with predictable fresh and hardened properties (i.e., slump, fresh and hardened density, elastic modulus, compressive strength, creep and shrinkage) comparable to similar concrete made with fresh natural aggregates. The concrete mixes thus designed also show outstanding performance at both service and ultimate states in reinforced beams made of RCA-concrete and no major difference is observed between the cracking and ultimate moment capacities and load-deflection responses of these beams made and of those made of similar conventional concrete.
Effect of temperature on chloride diffusion in concrete has been extensively studied by others and it is found to follow Arrhenius law. However, the lowest exposure temperature studied to date has been −4 °C, but due to supercooling the concrete pore solution is not expected to freeze at −4 °C. It is hypothesized here that below the supercooling temperature, some of the pore water will freeze and pore ice will form, which increases the pores tortuosity, and reduces their connectivity, resulting in reduced diffusivity. To test this hypothesis, concrete samples are subjected to natural diffusion in a 10% NaCl solution under 5, 0, −5, or −15 °C for 3 and 6 months. It is discovered that Arrhenius law can capture the effect of temperature on chloride diffusion, but when the temperature falls below the supercooling temperature, the effect of pore ice must be also considered. A method is proposed for capturing the latter effect. The diffusion coefficients of the frozen specimens computed by the proposed method differ maximum 15% from the corresponding experimental values.
A chloride binding model consisting of physical adsorption and chemical ion exchange was proposed. Chemical binding was quantified based on the thermodynamic equilibrium of the relevant hydrated phases while physical adsorption was modeled by a Freundlich-type isotherm. Comparison of the proposed model results with experimental chloride binding data in the literature was found to be satisfactory. The implementation of the model in the Nernst-Planck-Poisson (NPP) reactive transport NPP model accurately predicted the free and total chloride concentration profiles in the analyzed cement paste and concrete specimens. The results of the traditional chloride diffusion model based on Fick's second law were compared with the NPP model and it was discovered that estimating the apparent diffusion coefficient by a well-established formula and using it in Fick's model gave a significantly erroneous estimation of the free and total chloride profiles compared to the corresponding experimental data. Finally, in the NPP model it was determined that chloride transport by diffusion was limited to the region near the exposed surface while in the concrete bulk it was dominated by electromigration.
A method of analysis is proposed for curved multicell box girder grillages. The method can be used to analyze box girder grillages comprising straight and/or curved segments. Each segment can be modelled by a number of beam elements. Each element has three nodes and the nodal degrees of freedom (DOF) consist of the six DOF for a conventional beam plus DOF to account for torsional warping, distortion, distortional warping, and shear lag. This element is an extension of a straight element that was developed earlier. For a more realistic analysis of the intersection regions of non-colinear box girder segments, the concept of a rigid connector is introduced, and the compatibility requirements between adjoining elements in those regions are discussed. The results of the analysis showed good agreement with the shell finite element results, but the proposed method of analysis needs a fraction of the time and effort compared to the shell finite element analysis.
In this study, 13 typical wide-flange steel columns, each carrying an axial load equal to 25% of its axial capacity, are field tested using live explosives, involving charge size of 50 to 250 kg of ammonium nitrate/fuel oil (ANFO) and ground stand-off distance of 7.0 to 10.3 m. The reflected pressure time histories, time-dependent displacements, accelerations, and strains of the columns are measured, and their postblast damages and failure modes are reported. Maximum deformations, vibration periods, strain-rate, and contributing modes in the dynamic response of the columns are compared to those of companion steel beams (without axial load) tested in the same setup. Results show that columns that exhibit elastic response, due to the elongation of the column vibration period caused by the axial load, the lateral deformation caused by blast load is reduced rather than magnified by the axial load. The axial-bending interaction, or P-δ effect, may be neglected for steel columns with axial load up to 25% of their axial capacity, provided the column response remains within the elastic range—but if it crosses into the plastic range, the interaction cannot be ignored.
Estimating global land surface evapotranspiration (ET) is of great significance for assessing the impact of climate change on the global hydrological cycle and energy balance. In this study, we propose a surface energy balance constrained deep learning (DL-SEB) model for simulating global land surface evapotranspiration (ET). The accuracy of the DL-SEB model in estimating ET was tested using FLUXNET observations. The results suggested that the proposed DL-SEB model significantly enhanced the simulation capability of extreme ET events compared with the original deep learning model (without being coupled with the energy balance equation). The DL-SEB model was further applied to reconstruct global ET changes during 2000–2019 based on meteorological, soil, vegetation, and flux data sets. The annual average global land surface ET was 613 mm/yr during the period 2000–2019 (exclude Antarctica and deserts). The global land surface ET exhibited a significant upward trend with average increase rate of 1.16 mm/yr during the past two decades, which corresponds to approximately 3.8% increase above the mean global ET during 2000–2019. The positive trend of global land surface ET was driven by the combined effect of air temperature (Ta), soil moisture (SM), net radiation flux (Rn) and leaf area index (LAI). The natural climatic events such as El Niño events significantly altered short-term global ET variation, but did not changed the long-term increase trend of global ET. This study enhanced the understanding of the impact of climate change on the global land surface ET. The proposed DL-SEB model achieved a physics-based, smart and reliable ET simulation at global and regional scales.
Seven beams were tested in bending to determine the concrete contribution to their shear resistance. The beams had similar dimensions and concrete strength and were reinforced with carbon fiber reinforced polymer bars for flexure without transverse reinforcement. They were designed to fail in shear rather than flexure. The test variables were the shear span to depth ratio, varying from 1.82 to 4.5, and the flexural reinforcement ratio, varying from 1.1 to 3.88 times the balanced strain ratio. The test results are analyzed and compared with the corresponding predicted values using the American Concrete Institute, the Canadian Standard, and the Japan Society of Civil Engineers (JSCF) fiber reinforced polymer design recommendations. Based on these results and previous experimental data, it is shown that the ACI recommendations are extremely conservative whereas the Canadian and JSCE recommendations, albeit still conservative, are in closer agreement with the experimental data. Overall the Canadian Standard's predictions are in better agreement with experimental data than the JSCE predictions.
