Simon Foo

Flexural Performance of Steel-Reinforced Recycled Concrete Beams

A new method of mixture proportioning is used to investigate the flexural performance of reinforced concrete beams made with coarse recycled concrete aggregate (RCA). In this method, RCA is treated as a two-phase material comprising residual mortar and natural aggregate; therefore, when proportioning the mixture, the relative amount and properties of each phase are considered separately. Several reinforced concrete beams are built and tested using concrete mixtures designed by the new method and their deflection; cracking, yielding, and ultimate moments; crack spacing; cracking patterns; and failure modes are studied. The results show that at both the serviceability and ultimate limit states, the flexural performance of beams made of RCA-concrete proportioned by the new method is comparable to that of beams made of conventional natural aggregate concrete; and the general flexural theory and current code provisions for flexural design are applicable, without alteration, to the reinforced recycled concrete beams.

Proposed Method for Determining the Residual Mortar Content of Recycled Concrete Aggregates

Recycling concrete from demolition of existing structures and using it as recycled concrete aggregates (RCAs) in structural-grade concrete have significant economic and environmental benefits. Currently, only a small portion of the concrete waste is reused in building construction, while most of it is used as either pavement base course or sent to landfills for disposal. The lack of confidence in the material properties of the concrete produced with RCAs is generally the main reason for its under-utilization in structural concrete. It has been demonstrated in the literature that the amount of residual mortar attached to the original (or “virgin”) aggregate particles is one of the factors affecting the material properties of RCAs. Therefore, before using RCAs in new concrete, it is crucial that the residual mortar content (RMC) is determined accurately; however, currently there is no standard procedure to determine this quantity. In this paper, an experimental method is proposed to determine the RMC of RCAs. The method comprises a combination of mechanical and chemical stresses that disintegrate the residual mortar and destroy the bond between the mortar and the natural aggregates. The mechanical stresses are created through subjecting RCA to freeze-and-thaw action, while the chemical degradation is achieved through exposure of the RCA to a sodium sulphate solution. The results of the proposed test procedure are validated by means of comprehensive image analysis. With the proposed approach, the attached residual mortar can be adequately removed, and the residual mortar content can be determined.

Thermal Behavior of Fire-Exposed Concrete Slabs Reinforced with Fiber-Reinforced Polymer Bars

This paper describes the results of experiments carried out to investigate the performance in fire of concrete slabs reinforced with carbon or glass fiber fiber-reinforced polymer (FRP) bars. Several variables were examined to determine which were critical to the fire resistance of these slabs. The parameters examined included the reinforcement type, slab thickness, concrete cover thickness to the reinforcement, the aggregate type, and the effectiveness of other fire insulation. The thickness of the concrete cover to the reinforcement and the type of reinforcement were found to be the key parameters in determining the fire resistance of FRP-reinforced slabs. Overall, the results indicated that the qualitative and heat transfer behavior of FRP-reinforced slabs was similar to that of steel-reinforced slabs.

Environmental Benefits of Green Concrete

Of the approximately 11 million tonnes of annual solid concrete and demolition waste (C&D) in Canada, concrete accounts for about 52% by weight. However, most of this concrete is used as highway base or sent to landfills for disposal; only a very small portion of the concrete waste is reused in building construction. Considering the fact that usable natural aggregate (NA) supplies are diminishing, there will be a high demand for recycled concrete aggregates (RCA) to be used in the so called ldquogreen concrete (GC)rdquo. Using recycled concrete as aggregate will help reduce the total cost of concrete production because aggregates need not be hauled from remote locations, but obtained locally. The combination of RCA with significant quantities of fly ash or slag as replacement for Portland cement is particularly attractive from both economic and environmental perspectives. GC will reduce the demand for natural resources, the associated energy consumption, and green house gas (GHG) emissions required to produce aggregates and cement. These reductions can be considered as one of the construction industrys major contributions to Canadas GHG emission reduction objective. Although there are some guidelines/specifications established by different countries such as the UK and Japan, currently, there are no established guidelines for producing GC in Canada. This paper presents the environmental and economic benefits of increasing the use of GC in the construction industry and highlights the objectives of an ongoing research by the authors on GC.

Response of Arching Unreinforced Concrete Masonry Walls to Blast Loading

New standards for blast protection of buildings are currently being developed in the United States and Canada. In this regard, both standards are considering unreinforced masonry (URM) walls as particularly vulnerable to blast events and may not be used in blast-resisting structural systems. In this paper, the effectiveness of enforcing arching action as a cost-effective hardening technique for vertically spanning one-way URM walls under blast loads is investigated. A total of eight full-scale concrete-block URM walls were subjected to blast loads generated by high explosives. Enforcing URM walls arching between rigid supports significantly enhanced their out-of-plane blast resistance compared to similar nonarching (flexural) URM walls. Moreover, no fragments or debris were observed on the leeward side of the arching walls, indicating the potential of the proposed hardening technique in reducing the hazard level on the occupants of buildings with exterior URM walls. The improved performance is attributed ...

Experimental Performance of Steel Beams under Blast Loading

In this study, the dynamic response of typical wide-flange steel beams was experimentally evaluated under blast loading. A total of 13 beams were field tested using live explosives, where the charge size ranged from 50 to 250 kg of ammonium nitrate-fuel oil mixture, and the ground stand-off distance was from 7.0 to 10.3 m. Blast wave characteristics, including incident and reflected pressures, were recorded. In addition, time-dependent displacements, accelerations, and strains at different locations along the steel members were measured, and the postblast damage and mode of failure of the test specimens were observed. The blast load characteristics were compared with those obtained using the Technical Manual UFC 3-340-02 results. The displacement response results were used to validate the results obtained from a nonlinear dynamic analysis based on a single degree-of-freedom (SDOF) model. Results showed that the UFC 3-340-02 pressure predictions compare reasonably well with the measured pressure in the positive phase in terms of both the peak pressure and overall time variations. The SDOF model predicted the maximum displacements of beams in the elastic range reasonably well, but it overestimated them in the plastic range.

Time-Response Analysis of Arching Unreinforced Concrete Block Walls Subjected to Blast Loads

The new ASCE59-11 standards currently limit the use of unreinforced masonry (URM) walls in blast-resistant construction, regardless of the wall boundary conditions. This is attributable in part to the lack of experimental and analytical studies focusing on evaluating the response of URM walls under blast when the walls are forced to arch between the surrounding frame members. In this paper, the out-of-plane displacement response and structural stability of one-way vertical arching URM walls subjected to blast loads are investigated. A simple bilinear moment-rotation relationship is developed to simulate the arching wall responses. The model takes into account the masonry material strength, thrust forces, and wall geometry. Time-response analyses were performed using both single-degree-of-freedom (SDOF) and two-degrees-of-freedom (2DOF) models. Both models take into account the rocking phenomenon and second-order effects. Responses generated by both models were validated using experimental data reported previously. For preliminary design, performance charts were developed to correlate the effects of the wall slenderness ratio, masonry strength, and block size to the wall response under different levels of blast loads. The developed model and charts can be used as simple and quick calculation tools to estimate the required thickness, height, and strength of the wall under an expected blast threat when hardening of URM walls is necessary, with arching being considered as one of the alternatives.

Modeling the Nonlinear Behavior of Concrete Masonry Walls Retrofitted with Steel Studs under Blast Loading

This paper presents the results of an analytical investigation of one-way unreinforced masonry (URM) walls retrofitted with externally anchored steel studs and subjected to blast loads. Using the wall geometrical and material properties, deflected shape, and crack pattern as input, a nonlinear model is developed to predict the inward force-displacement relationship of the retrofitted walls. In addition, using a rigid body analysis, a simple bilinear force-displacement relationship is developed to model the outward force-displacement relationship of the walls. Utilizing these two force-displacement relationships (resistance functions), a generalized single-degree-of-freedom (SDOF) model is developed to capture the nonlinear out-of-plane dynamic response of the retrofitted walls under blast loads. The SDOF model captured the experimentally observed displacement responses of the tested walls with reasonable accuracy. The model was also used to investigate the influence of block thickness, wall slenderness ra...

Strain Rate Effect on Development Length of Steel Reinforcement

Accidental or premeditated explosions have detrimental effects on the infrastructure near the center of explosion and pose major threats to human life. Thus, research is currently underway to study the effects of explosions on infrastructure systems with the ultimate goal of minimizing infrastructure damage and saving lives. Because reinforced concrete is the most common building material used in blast-resistant infrastructure design and construction, understanding the effect of blast loads on reinforced concrete components is essential to reaching this goal. The prevailing design philosophy for blast-resistant structures is energy dissipation through reinforcement yielding (ductility) and large bending deformations without the incidence of nonductile failure modes such as shear and bond. However, information regarding the bond behavior and strength of steel reinforcement–concrete bonds under blast loads is rather scant; therefore, this paper reports on an experimental program designed to investigate the strain rate effect on steel reinforcement–concrete bond. Reinforced concrete beams longitudinally reinforced with 15M, 20M, or 25M were tested in a shock tube under simulated blast loading. The test results show that high strain rate increases the steel reinforcement–concrete bond strength and thus, that the static load development lengths of these bars are adequate for developing their dynamic yield strengths at high strain rate. The dynamic increase factor for bond stress is determined to be 1.11 for 15M, 2.24 for 20M, and 3.68 for 25M bar.

Investigation of the Use of Solar Thermal Buffer Zone in Buildings

This paper presents results of a collaborative study that is being carried out by the Thermal Processing Laboratory (TPL), the Department of Civil Engineering and Public Works and Government Services Canada (PWGSC). The main objective of this study is to investigate the feasibility of passive means to achieve net-zero energy (NZE) in federal buildings in Canada.