International Concrete Abstracts Portal

The first edition of ACI CODE-440.11 was published in September 2022, where some code provisions were either based on limited research or only analytically developed. Therefore, some code provisions, notably shear and development length in footings, are difficult to implement. This study, through a design example, aims at a better understanding of the implications of code provisions in ACI CODE-440.11-22 and compares them with ones in CSA S806-12, thereby highlighting a need for reconsiderations. An example of the footing originally designed with steel reinforcement was taken from the ACI Reinforced Concrete Design Handbook and redesigned with GFRP reinforcement as per ACI CODE- 440.11-22 and CSA S806-12. A footing designed as per ACI CODE- 440.11-22 requires a thicker concrete cross section to satisfy shear requirements; however, when designed as per CSA S806-12, the required thickness becomes closer to that of the steel-reinforced concrete (RC) footing. The development length required for a glass fiber-reinforced polymer-reinforced concrete (GFRP-RC) cross section designed as per ACI CODE-440.11-22 was 13% and 92% greater than that designed as per CSA S806-12 and ACI 318-19, respectively. Also, the reinforcement area required to meet detailing requirements is 170% higher than that for steel-RC cross section. Based on the outcomes of this study, there appears to be a need for reconsideration of some code provisions in ACI CODE-440.11-22 to make GFRP reinforcement a viable option for RC members.

Structural lightweight-aggregate concrete (LWAC) has gained a broad range of applications in the construction industry owing to its reduced dead load and enhanced fire resistance. In this study, the potential of using lightweight expanded clay aggregates as a partial replacement for fine and coarse natural aggregates was experimentally and numerically examined. Testing was performed on cylindrical specimens made of normalweight and lightweight concrete incorporating microsilica as a partial replacement for cement to determine the associated stress-strain behavior. Subsequently, three-point bending testing was conducted on reinforced concrete beams to evaluate their structural behavior. Four levels of temperature were considered: 25°C (ambient temperature), and 250, 500, and 750°C (elevated temperatures). The finite element method through Abaqus software was deployed to numerically investigate the behavior at elevated temperatures through a comprehensive parametric study. The experimental and numerical results indicate that under high-temperature exposure, LWAC outperforms its normal counterpart in terms of strength, stiffness, and Young’s modulus. It is also noticeable that LWAC beams retained their load-bearing capacity better than normal weight aggregate concrete (NWAC) after reaching the peak load.

Experiments on seven two-span unbonded post-tensioned beams were conducted under four-point static loading conditions. Variables considered included: strand type (nominal tensile strength); tendon drape (height of tendon profile); and magnitude of prestress. Experimental emphasis was placed on the applicability of using higher-strength 2400 MPa (350 ksi) strands instead of ordinary 1860 MPa (270 ksi) strands in unbonded post-tensioned beam members. Observed results revealed that specimens with 2400 MPa (350 ksi) tensile strength 15.2 mm (0.6 in.) diameter strands developed equivalent tendon stress increment, load-carrying capacity, and flexural ductility while at the ultimate limit state having earlier and wider plastic hinge.

Hollow-core (HC) slabs are the most commonly used and economical precast/prestressed concrete flooring system. HC slabs produced in the U.S. market typically have untopped depth ranging from 6 to 12 in. (152 to 305 mm). Recently, deeper HC slabs (for example, 16 in. [406 mm]) have been produced to satisfy the growing need for longer spans and/or heavier loads. ACI 318-14, Section 7.6.3.1, requires a minimum shear reinforcement to be provided where ultimate shear force is greater than 50% of the factored concrete web shear strength (ϕVcw) for untopped HC slabs deeper than 12.5 in. (318 mm). The 50% modification factor was introduced in 2008 based on a limited testing conducted by HC suppliers on deep HC slabs. This paper briefly summarizes parameters that affect concrete web shear strength of deep HC slabs and presents the results of shear and flexure testing of 16 in. (406 mm) HC slabs. Ten different shear strength provisions adopted by ACI 318-14, AASHTO LRFD 2014, CSA A23.3-04, JSCE 2007, fib MC 2010, AS 3600-2009, EN 1168, and Yang’s method were compared using a database of 51 web shear tests (12 conducted by the authors and 39 obtained from the literature) of deep HC slabs. Comparison results indicated that the 10 shear strength provisions vary significantly with respect to the accuracy and consistency of their predictions and, therefore, different modification factors need to be used.

Replacing cement with limestone and inorganic process additions (IPAs) and increasing the insoluble residue (IR) can aid in reducing the CO2 emission. This paper investigates the effect of adding IPA and increasing IR on the diffusivity characteristics of concrete. Also, the effect of replacing cement with supplementary cementitious materials while batching them with two sand types was demonstrated. To show the effect of these materials, the chloride diffusion test was conducted on 26 concrete mixtures with different proportions that were salt ponded for 90, 180, and 360 days. The IPA addition and increase in IR did not show any notable influence on concrete diffusivity. On the basis of the experimental results, a diffusion model with time-dependent surface chloride and diffusion coefficient was developed. The proposed model was compared with existing service-life prediction software and models, and showed promising results, while the current equations adopted by the software were very conservative.