International Concrete Abstracts Portal

This paper presents the durability modeling of bridge piers subjected to corrosive environments including atmospheric, splash, and submerged conditions for a service period of 100 years. Two types of reinforced concrete columns are used—cast-in-place and accelerated bridge construction (ABC)—and their time-dependent performance is predicted by von Neumann’s square lattice in conjunction with a novel evolutionary mathematics approach called cellular automata. The capacity of the corrosiondamaged columns is upgraded using carbon fiber-reinforced polymer (CFRP) sheets. Depending on the concrete strength and construction method, chloride migration mechanisms are evaluated to elucidate the variation of diffusion coefficients, chloride concentrations, and other corrosion-related issues for those columns with and without CFRP confinement. For the first 30 years, the chloride diffusion of the ABC column is slower than that of the cast-inplace column; otherwise, no difference is noticed. Under the splash condition incorporating periodic wetting-and-drying cycles, chloride concentrations remarkably increase relative to other exposure environments, particularly for the cast-in-place column. The development of corrosion current density is dominated by the pore structure of the concrete, and the corrosion initiation of the ABC column takes 4.3 times longer compared with its cast-in-place counterpart. At 100 years, the capacity of the cast-in-place and ABC columns decreases by 28.1% and 23.2%, respectively, primarily due to the impaired concrete near the degraded reinforcing bars in a corrosion influence zone. The columns’ responses are enhanced by CFRP confinement in terms of toughness, energy dissipation, loadcarrying capacity, and load-moment interactions.

Autoclaved aerated concrete (AAC) is a cellular concrete with consistent material properties. AAC structures have many advantages including ease of construction, low density, and high fire and thermal resistance. In this study, a suite of 14 scaled floor diaphragms were tested to determine physical behavior of the system subjected to either monotonic and cyclic loads. Next, a simple strut-and-tie model (STM) was used as a mechanism to predict the strength of floor diaphragms subject to in-plane lateral loads. Testing validated that although the model violates the minimum angle of 25 degrees, individual panel movement and nodal confinement permit sufficient rotation. Test results indicate that the STM provides conservative predictions for the strength of floor diaphragms.

Foam concrete is a highly cellularized cementitious material that undergoes extensive plastic deformation when loaded to failure. Under compression, the microstructure of low-density foam concrete gets progressively crushed at a steady stress stage, accompanied by substantial energy dissipation. Understanding foam concrete crushing behavior is of special importance for its engineering applications. However, the current studies are insufficient to define key attributes that are important for material characterization and design. This study focuses on low-density foam concrete ranging from 0.4 to 0.8 g/cm3 (25 to 50 lb/ft3), with the crushing behavior investigated using a penetration test and dynamic Young’s modulus determined using a resonant frequency test. Four distinct crushing phases—linear elastic, transitional, plateau, and final densification—are observed for the samples. Furthermore, the yield strength and plateau strength are identified to characterize the foam crushing behavior. Using the experimental inputs, the modulus-strength constitutive relationship is established for predicting the crushing behavior with fundamental material properties. The findings significantly facilitate subsequent foam concrete studies, as well as the engineering design of this material.

This paper presents the stress-strain behavior of structural synthetic fiber-reinforced cellular lightweight concrete (CLC) stack-bonded prisms under axial compression. Masonry compressive strength is typically obtained by testing stack-bonded prisms under compression normal to its bed joint. CLC prisms with cross-sectional dimensions of 200 x 150 mm (7.87 x 5.90 in.) with an overall height of 470 mm (1.54 ft) were cast with and without different dosages of synthetic fiber reinforcement. Polyolefin was used as a structural fiber reinforcement at different volume fractions (vf) of 0.22, 0.33, 0.44, and 0.55% with and without microfiber dosage of 0.02%. Experimental results indicate that the presence of fibers helps in the improvement of strength, stiffness, and ductility of CLC stackbonded prisms under compression. Test results also signify that the hybrid fiber reinforcement provides better crack bridging mechanism both at micro and macro levels when compared to only macrofibers. Simple analytical models were developed for stress-strain behavior of CLC blocks and stack-bonded CLC prisms based on the experimental results with and without fibers under compression.

Rice husk ash (RHA) has significant potential to be used as a supplementary cementing material (SCM). However, RHA contains a cellular, honeycomb-like morphology of amorphous silica and this morphology results in high water absorption. Due to this morphology, the use of RHA in concrete results in reduced workability and higher water demands. Reduced workability and higher water demands can be mitigated by using smaller RHA particles. These smaller particles can be obtained by mechanical grinding. However, this grinding requires significant energy. This paper presents a novel method to transform RHA morphology using a chemical transformation process; specifically, an alkali transformation method. Results indicate that the process can effectively reduce RHA particle size and eliminate the cellular and honeycomb-like morphology.