Journal of Materials in Civil Engineering

Most of the previous research on the fatigue of reinforcing bars has been based on constant amplitude fatigue tests performed in a noncorrosive environment. Fatigue in a corrosive environment, known as corrosion fatigue, can result in a synergistic damage mechanism that is worse than the combined damage of corrosion and fatigue acting separately. Variable amplitude fatigue loading can lead to fatigue failures even when the majority of cyclic loads are below the constant amplitude fatigue limit. Although engineers have tried to prevent corrosion of reinforcing steel by using alternative materials, there are few published reports on the fatigue resistance of these products. This study presents the periodic overload and corrosion-fatigue resistance of machined specimens made from two corrosion resistant reinforcing steels: MMFX microcomposite and 316LN stainless steel. A series of constant amplitude and periodic overload tests were performed in both laboratory air and in an aqueous 3.5% by weight NaCl solution to compare the fatigue resistance of these materials with conventional reinforcing steel. MMFX had reduced constant amplitude performance in the corrosive environment, whereas 316LN stainless steel showed no environmental reduction under constant amplitude loading (except at high loads). Periodic overload fatigue results in laboratory air were similar to that found with conventional reinforcing steel, with much shorter periodic overload lifespans compared to constant amplitude loading. Corrosion fatigue reduced the periodic overload performance of both materials, although both materials retained their intrinsic fatigue limit ( $250\mathrm{MPa}$ stress range) in the corrosive environment, a drastic improvement over the periodic overload corrosion-fatigue performance of conventional reinforcing steel.

Traditional green oak timber construction, in which frames are connected with the all-timber pegged mortice and tenon joint, is enjoying a revival in the United Kingdom and the United States. However, innovation in design and construction is restricted by a lack of design guidelines or methods for the strength and stiffness analysis of traditional carpentry connections and frames. This paper presents the development of models to predict the stiffness and strength of all-timber pegged mortice and tenon connections as used in traditional green oak carpentry in the United Kingdom. Models developed based upon experimental observations and finite-element modeling are shown to provide simple and effective methods of predicting pegged connection strength and stiffness based upon an energy approach and a four-point beam bending analogy respectively.

Recent studies have shown that potassium acetate based deicers are capable of triggering deleterious expansion and cracking in concrete specimens containing alkali–silica reactive (ASR) aggregates. This paper presents the results and analysis from a research study conducted to evaluate the effectiveness of fly ash and ground granulated blast furnace slag (slag) in mitigating expansions induced by ASR in the presence of a potassium acetate based deicer. Standard and modified ASTM C 1260 and 1567 tests were conducted on mortar specimens prepared with five aggregates to study the mitigation behavior of fly ashes and slag. In this study, fly ash was evaluated at 15, 25, and 35%, and slag at 40 and 50% by mass replacement of cement. Changes in length, dynamic elastic modulus, and microstructure of the mortar bars were studied. Results from these studies indicate that low- and intermediate-lime fly ashes were more effective than high-lime fly ash at 25 and 35% cement replacement levels. High-lime fly ash was ineffective even at a replacement level of 35%. Slag at 50% cement replacement was more effective in mitigating expansions compared to 40% dosage level.

This paper presents the results from an evaluation of a new gradation-based framework developed for identifying and assessing the coarse aggregate structure of dense-graded mixtures for resistance to rutting. A theoretical packing-based analysis procedure was used to evaluate the coarse aggregate structure for hot mix asphalt mixtures. This procedure was applied to an extensive range of mixtures. A key feature of this new framework is the concept of the existence of a dominant aggregate size range (DASR). The porosity of the DASR is calculated based on an interaction diagram to evaluate the degree of particle-to-particle interaction of coarse aggregates between contiguous sieve sizes. In addition, an interaction diagram-based criteria for dense-graded Superpave mixtures are determined, as well as criteria for the porosity of the DASR. Based on the field and laboratory-based rutting performance of the mixtures evaluated in this paper, it was concluded that DASR along with the porosity of the DASR may provide a framework for evaluating the gradation of dense graded mixtures for their likely rutting potential.