188 publications from this institution
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.
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Membrane wetting and fouling are two major challenges in membrane distillation (MD), especially when the feed has components with low surface tension. A series of membranes with different wettability were developed herein to provide rational guidelines for membrane selection to treat these wastewaters. The membranes with different wettability, and Janus membranes composing of same hydrophilic surface but different substrates (hydrophobicity, superhydrophobicity, superomniphobicity), were made by electrospinning and modifications. It was found that when the feeds had anionic and cationic surfactants, the superhydrophobic and superomniphobic modifications improved their anti-fouling/wetting properties. However, both membranes were rapidly wetted when the feeds had nonionic surfactant Tween-20. The Janus membranes could not delay membrane fouling/wetting when treating the feeds with free surfactants. It even worsened membrane performance as the hydrophilic layer absorbed the surfactants and accelerated membrane fouling/wetting. Regarding the emulsified oily wastewaters, the hydrophilic layer on Janus membranes did show obvious improvement in their anti-fouling/wetting abilities. The underwater hydrophobic layer formed a protective layer and impeded oil contact with the underlying substrate, but the choice of the substrate still needed attention. The superomniphobic substrate showed the most excellent stability as it could reject surfactants even if some managed to pass through.
This work utilized fertilizer driven forward osmosis (FDFO) to extract fresh water from acid mine drainage (AMD) wastewater for irrigation, and investigated the effects of draw solutes on membrane fouling behaviours. The carbon nanotubes (CNTs) and polydopamine (PDA) were coated on the thin film nanofibrous composite (TFNC) membrane #FO-0 as anti-fouling modification. When 1 M NH4H2PO4 (MAP) and 500 mg/L copper AMD wastewater (pH=3.0) used as draw and feed solutions, #FO-0 and PDA-coated TFNC membrane (#FO-PDA) exhibited rapid declines of water fluxes due to the dense fouling layer. In contrast, the CNT-coated membrane #FO-CNT exhibited the lowest flux decline of 26.0% attributed to better hydrophilicity, the lowest roughness and neutral surface charge. All the TFNC membranes exhibited insignificant membrane fouling when (NH4)2SO4 (SOA) was used as draw solute. Additionally, the osmotic backwashing could effectively recover water flux. The discharged draw solution promoted plant growth without posed potential health threat.
Five rheological models for conventional concrete are modified to make them suitable for application to recycled aggregate concrete (RAC). The modification involves the inclusion of the effects of the quantity and properties of residual mortar on creep of RAC. The accuracy of the modified models is assessed by comparing their predictions with measured creep strain data from 150 x 300 mm (6 x 12 in.) concrete cylinders made of RAC, proportioned either by the conventional concrete mixture design method or by the Equivalent Mortar Volume (EMV) Method developed by the authors. It is demonstrated that the modified rheological models can be used to obtain reasonable estimates of the creep of RAC, irrespective of the mixture proportioning method and the aggregate type. It is also shown that, for practical applications, the existing ACI Method for calculating the creep of concrete can be applied to RAC via the introduction of a recycled concrete aggregate (RCA) coefficient.
A comprehensive model is presented for predicting the rate of steel corrosion in concrete structures and the consequent formation and propagation of cracks around the steel reinforcement. The corrosion model considers both the initiation and the propagation stages of corrosion. Processes commencing in the initiation stage, such as the transport of chloride ions and oxygen within the concrete and variation in temperature and moisture, are assumed to continue in the propagation stage while active corrosion is occurring contemporaneously. This allows the model to include the effects of changes in exposure conditions on the corrosion rate and the effects of the corrosion reactions on the transport properties of concrete. The corrosion rates are calculated by applying the finite-element solution of the Laplace equation for electrochemical potential, with appropriate boundary conditions. Because these boundary conditions are nonlinear, a nonlinear solution algorithm is used. The results of the analysis are compared with available test data, and the comparison is found to be satisfactory. Key words: reinforced concrete, steel corrosion, finite-element modelling, durability.
A new carbon fiber reinforced polymer (CFRP) anchor is developed and tested to delay debonding in reinforced concrete (RC) beams externally strengthened with FRP laminate/sheet. The C-shape anchor is made from a commercially available CFRP grid. The anchors legs are 95 mm long while the spacing between the legs is adjustable, depending on FRP laminate and beam widths. Nine full scale RC beams, 3.0 m long, 250 mm wide and 400 mm deep, were strengthened with CFRP laminate/sheet, with and without the C-anchor. The main test parameters were the type and amount of FRP laminate and the presence/absence of the anchor. Test results showed that beams with the anchor had generally 5%–10% higher debonding and failure load, and they reached higher deflection at failure than the companion beams without anchors. Although complete separation of the FRP laminate from the concrete was not observed in any of the beams with anchors, there was noticeable slip at failure at one end of the laminate. A significant outcome of the study is that anchors are effective in limiting the extent of debonding along the laminate, thus contributing to the flexural stiffness of the beam by reducing the extent of cracking and limiting the crack width along the beam. Finally, the anchor allowed the FRP to reach or exceed its theoretically allowable strain computed based on the American Concrete Institute (ACI) Committee 440 recommendation while in none of the beams without anchors, the FRP reached its theoretically allowable strain.
The primary objective of this study was to demonstrate that a significant degree of anisotropy may occur in particulate materials that have nearly spherical aggregates (i.e., are typically considered as isotropic) provided there is a bias in the distribution of pore space as a result of the initial densification process. The study included both an experimental and a theoretical component. An experimental program was conducted on dynamically compacted samples of Ottawa standard sand (C109) and incorporated a series of tests performed at different orientations of the specimens. Following the experimental part, a plasticity formulation based on the critical-plane approach was presented. A systematic procedure for identification of material parameters was outlined, and some numerical simulations of a series of triaxial tests were conducted. The last part of this work dealt with a much weaker load-induced anisotropy. Here, the mathematical framework was enhanced by an evolution law for the material fabric. Again, some numerical simulations were conducted, and it was demonstrated that the proposed framework can, at least in a qualitative manner, account for various manifestations of induced anisotropy.
To ensure public safety, existing bridges are often evaluated for their load-bearing capacity. Realistic evaluation must take into account the actual nonlinear stress–strain characteristics of the ...
Due to the large carbon footprint of ordinary Portland cement (OPC) and the rapid corrosion of steel rebars in certain environments, the search for greener, sustainable and more durable reinforced concrete structures is ongoing. In this study, the alkali resistance of basalt- and glass-fibre reinforced polymer (BFRP/GFRP) bars in sulfoaluminate cement (SAC) concrete made with seawater and sea sand is investigated for the first time. Production of SAC involves lower energy consumption and greenhouse gas emission compared to OPC while SAC concrete provides a lower pH environment, which favors the durability of FRP bars. Following ASTM D 7705-D7705M-12 Procedure A, the bars were immersed for three months in simulated pore solution of concrete made with SAC, river sand and fresh water, termed Solution A, and compared their durability to that of companion bars immersed in simulated pore solution of concrete made with SAC, seawater, and sea sand, termed Solution B. Both solutions had the same pH, and their temperature was maintained at 60℃ for the duration of the test. The post-immersion or retained tensile strength of GFRP bars in Solution A and B was 83.0% and 73.6%, respectively, while the corresponding values for the BFRP bars were 52.5% and 67.9%, respectively. It appears that due to the presence of sea salt, Solution B is less damaging to BFRP than Solution A while the opposite is true in the case of GFRP. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) results are utilized to explain the damage mechanisms. Based on image analysis, it is shown that the deteriorated zone within the bar cross-section is not a uniform ring, but its cross-sectional area correlates with the reduction in tensile strength.
The effect of loading and geometric parameters on the transverse and longitudinal redistribution of moments in continuous composite bridges, comprising a concrete slab on parallel steel girders, is investigated with the nonlinear finite element method. Fifty bridges are analyzed over their entire range of loading up to failure, and their moment redistribution factors are determined and compared with the relevant predictions of the Canadian Highway Bridge Design Code (CHBDC) and the AASHTO LRFD Bridge Design Specifications. The parameters studied included truck position along the bridge, number of loaded lanes, bridge width, number of girders, slab thickness, degree of composite action, and presence of diaphragms. The study reveals that among the preceding parameters only the number of loaded lanes and the bridge width significantly affect transverse redistribution of moments at ultimate limit state (ULS). However, most of the preceding parameters affect longitudinal redistribution at ULS. Finally, it is demonstrated that plastic analysis of composite multi-girder continuous bridges, treated as an equivalent beam, provides a reasonable estimate of their longitudinal moment redistribution capacity at ULS. It is demonstrated that the actual load-carrying capacity of a composite bridge may be more than 50% higher than that predicted by the CHBDC or AASHTO code. Such higher predicted capacity may obviate the need for retrofit in some cases.Key words: analysis, bridge, composite, concrete, distribution, finite element, inelastic, load, steel.
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.
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.
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.
One of the most urgent problems related to highway infrastructure is that the cost of maintaining a network of bridges with an acceptable level of service is more than the available budgeted funds. Low prioritization of the available resources allocated to bridge projects exacerbates the situation. About 42 percent of the 574,000 highway bridges in the United States were reported by FHWA to be structurally deficient or functionally obsolete. Traditional management practices have become inadequate as ways to face this serious problem. Priority-setting schemes for bridge projects range from those done on a subjective basis in which engineering judgment is used to those that use very complex optimization models. However, currently used priority-setting schemes do not have the ability to optimize the system's benefits to obtain optimal solutions. The present objective is to show how artificial neural networks (ANNs) can be used to optimize the system's resources to generate the group of bridge improvements that minimizes the loss of the network benefits. ANNs are algorithms with characteristics that are able to solve certain classes of optimization problems. The advantages of using ANNs include improvements in the speed of operation by parallel implementation either in hardware or in software. It is also possible to implement ANNs by optical devices that operate at higher speeds than traditional electronic chips.
