International Concrete Abstracts Portal

The aging reserve of bridges in the United States needs load rating assessment to ensure sufficient load-carrying capacity and safety. Bridges without sufficient capacity to carry the legal loads are load posted. These load limits reroute traffic that may result in traffic congestion and longer routes and, thus, impose inconvenience to travelers and significant cost to society. This paper investigates the potential for improvement in the load rating process for simple-span concrete slab bridges. Such bridges are load rated by the Texas Department of Transportation using simplified load rating procedures, which are intended to be conservative and can have varying degrees of accuracy compared to the actual behavior of bridges. Finite element modeling was conducted to simulate the expected behavior of a representative concrete slab bridge, and the model was calibrated using experimental test data. The equivalent width results were compared with estimates from established design specifications and empirical guidelines. The methods developed for concrete slab bridges with integral curbs provided accurate estimates of moment demand for curb sections. In addition, an established analytical approach in the literature accurately predicted the moment demand for interior slab sections under one-lane loading, while the equations in current design specifications performed well for the two-lane loading case.

Repeated vehicle loading causes a decrease in transverse joint stiffness in concrete pavements due to damage accumulation around dowel bars. The relationship between key design parameters and damage accumulation is not well established due to limited faulting performance data and a lack of experimental data from expensive full-slab testing. A novel laboratory test setup was developed to characterize damage development caused by repeated vehicle loads. This setup was used to characterize damage for a range of key parameters at a lower cost and level of effort compared to full-scale slab testing. The concept of beam deflection energy, DE_Beam, is also introduced. Experimental results were used to develop a DE_Beam prediction model. The novel test setup developed in this study enables the rapid evaluation of a variety of dowel materials and geometries, and experimental results can be used to improve current faulting prediction performance.

Traditional analytical models have commonly been employed to assess the progressive collapse performance of building structures subjected to seismic loads. However, few studies addressed the effect of initial damage to adjacent components following the failure of a key component under explosion loads. In this paper, a damage assessment method for reinforced concrete structures was proposed based on the component analytical model, taking into account damage to adjacent members caused by close-in explosive scenarios. The reliability of the proposed analytical model was validated through comparison with experimental results in the existing literature. Besides, comparing the damage levels of a five-story reinforced concrete frame with those predicted by the proposed component models, the proposed assessment method based on components for predicting the damage degree of a reinforced concrete frame was validated to be reliable under a close-in explosion. The results indicated that the proposed analytical model can offer the advantage of not requiring a complex modelling process or the consideration of safety concerns associated with field explosion testing by comparing to numerical models of equivalent accuracy and experimental results.

Portland-limestone cement (PLC) currently has gained widespread use as the most accessible and sustainable blended cement in the market. However, in many African countries, including Ghana, the use of clay pozzolana (CP) in the concrete industry has primarily relied on ordinary portland cement (OPC). In this study, PLC Type II/B-L was partially replaced with CP at levels ranging from 10 to 50% by weight. The investigation included compressive strength testing, nondestructive evaluations using electrical surface resistivity, pulse velocity, and chloride penetration tests, targeting a characteristic strength of 30 MPa (4351.13 psi). Additionally, an environmental impact assessment based on the carbon footprint of both control and CP concretes was conducted. The mixture design followed the EN 206 standard. A total of 72 cubic molds were produced for the strength test. The results showed that CP concretes with between 10 and 20% replacement achieved strength values of 35 and 33 MPa (5076.4 and 4786.32 psi), respectively, higher than the target of 30 MPa (4351.13 psi) strength at 28 days. However, mixtures with 30 to 50% replacement required extended curing periods of 60 to 90 days to reach the desired strength. At extended curing, 10 to 50% CP replacement attained strength between 32 and 41 MPa (4641.28 and 5946.64 psi). Nondestructive test results showed no direct correlation with compressive strength, confirming that different factors govern strength, resistivity, and pulse velocity. The environmental impact assessment revealed a 14 to 51% reduction in carbon strength index (CSi) and a 19 to 36% increase in carbon durability index (CRi) with 10 to 50% CP (for CSi) and 10 to 40% (for CRi). The thermodynamic modeling also revealed that pozzolana contents below 30% primarily promoted pozzolanic reactions, enhancing performance compared to the control mixture. Based on these results, 20 to 30% CP replacement is recommended to ensure reliable performance, while higher levels (>30%) require further durability evaluation for long-term use.

This paper presents the implications of variable bond for the behavior of concrete beams with glass fiber-reinforced polymer (GFRP) bars alongside shear-span-dependent load-bearing mechanisms. Experimental programs are undertaken to examine element- and structural-level responses incorporating fully and partially bonded reinforcing bars, which are intended to represent sequential bond damage. Conforming to published literature, three shear span-depth ratios (av/d) are taken into account: arch action (av/d < 2.0), beam action (3.5 ≤ av/d), and a transition from arch to beam actions (2.0 ≤ av/d < 3.5). When sufficient bond is provided for the element-level testing (over 75% of 5db, where db is the reinforcing bar diameter), the interfacial failure of GFRP is brittle against a concrete substrate. An increase in the av/d from 1.5 to 3.7, aligning with a change from arch action to beam action, decreases the load-carrying capacity of the beams by up to 40.2%, and the slippage of the partially bonded reinforcing bars dominates their flexural stiffness. Compared with the case of the beams under beam action, the mutual dependency of the bond length and shear span is apparent for those under arch action. As far as failure characteristics are concerned, the absence of bond in the arch-action beam prompts crack localization; by contrast, partially bonded ones demonstrate diagonal tension cracking adjacent to the compression strut that transmits applied load to the nearby support. The developmental process of reinforcing bar stress is dependent upon the av/d and, in terms of using the strength of GFRP, beam action is favorable relative to arch action. Analytical modeling suggests design recommendations, including degradation factors for the calculation of reinforcing bar stresses with bond damage when subjected to arch and beam actions.