International Concrete Abstracts Portal

Geopolymer concrete (GPC) is a progressive material with the capability to significantly reduce global industrial waste. The combination of industrial by-products with alkaline solutions initiates an exothermic reaction, termed geopolymerization, resulting in a carbon-negative concrete that lessens environmental impact. The fly ash-based GPC (FA-based GPC) displays noticeable variability in its mechanical properties due to differences in mix design ratios and curing methods. To address this challenge, we optimized the constituent proportions of GPC through a meticulous selection of nine independent variables. A thorough experimental database of 1242 experimental observations was assembled from the available literature, and artificial neural networks (ANN) were employed for compressive strength modeling. The developed ANN model underwent rigorous evaluation using statistical metrics such as R-values, R₂ values, and mean square error (MSE). The statistical analysis revealed an absence of a direct correlation between compressive strength and independent variables, as well as a lack of correlation among the independent variables. However, the predicted compressive strength by the developed ANN model aligns well with experimental observations from the compiled database, with R₂ values for the training, validation, and testing datasets determined to be 0.84, 0.74, and 0.77, respectively. Sensitivity analysis identified curing temperature and silica-to-alumina ratio as the most crucial independent variables. Furthermore, the research introduced a novel method for deriving a mathematical expression from the trained model. The developed mathematical expressions accurately predict compressive strength, demonstrating minimal errors when using the tan-sigmoid activation function. Prediction errors were within the range of (-0.79 – 0.77) MPa, demonstrating high accuracy. These equations offer a practical alternative in engineering design, bypassing the intricacies of the internal processes within the ANN.

This paper investigates the seismic performance of exterior beam-column joints in special moment frames (SMFs) with varying axial load ratios. Cyclic testing of four additional specimens with an axial load ratio of 0.45 is compared with four companion specimens at 0.10. Each specimen was designed and constructed with Gr.60 (420), Gr.80 (550), or Gr. 100 (690) reinforcement in accordance with ACI CODE-318 provisions for special moment frame joints, except for the provisions of joint shear and confinement. While ACI CODE-318 tightens confinement requirements for SMF columns and joints, especially under high axial loads, this study reveals that increasing the axial load ratio benefits joint behavior. The study also demonstrates the feasibility of using high-strength reinforcement in exterior beam-column joints of SMFs, provided that appropriate modifications are made. The findings in this study have influenced modifications from ACI CODE-318 to the Building Code Requirements for Concrete Structures in Taiwan.

Subjected to either tensile or compressive loads, concrete is susceptible to the effect of sustained loading. To address this, common practice in building guidelines typically involves applying a sustained loading factor ranging from 0.6 to 0.85. Given that the shear capacity of structural members without shear reinforcement is linked to the concrete strength, one might question whether there is a comparable sustained loading impact on shear. To address this inquiry, a total of 18 reinforced concrete beams without shear reinforcement were subjected to prolonged sustained loading, with a load intensity factor (ratio of applied sustained shear load to short-term shear resistance) ranging from 0.88 to 0.98. Several beams endured the sustained loading test for an extended period, close to a decade, before the test was terminated. Interestingly, in contrast to concrete subjected to direct compression or tension, it was observed that sustained loading did not affect the shear capacity. Some early results of this experimental study, where concrete beams were subjected to up to 4 years of sustained loading, have been previously published by Sarkhosh and Sarkhosh et al. This paper concludes the results of the testing campaign of up to a decade of sustained loading, with additional results and findings.

Pourbacks and overlays are commonly used in bridge elements and repairs, as it is crucial to corrosion protection that the bond between grout and concrete in these regions is carefully constructed. The integrity of the bond is crucial to ensure a barrier against water, chloride ions, moisture, and contaminants; bond failure can compromise the durability of concrete structures’ long-term performance. This study examines the influence of surface preparation methods on the bond durability and chloride permeability between concrete substrate and grouts, including both non-shrink cementitious and epoxy grouts. A microstructural analysis of scanning electron microscopic (SEM) images was conducted to characterize the porosity of specimen interfaces. Pulloff testing was performed to quantify tensile strength. Results show that a water-blasted surface preparation technique improved the tensile bond strength for cementitious grout interfaces and reduced porosity at the interface. In contrast, epoxy grout interfaces were less affected by surface preparation. The study establishes a relationship between chloride ion permeability, porosity, and bond strength. The findings highlight the importance of surface preparation in ensuring the durability of concrete-grout interfaces.

Past investigations showed that the one-way shear strength of reinforced concrete members exhibits “size effect,” a phenomenon whereby shear strength does not increase in direct proportion to member size. However, it is unclear if the reduction in the two-way shear strength of reinforced concrete members due to size effect applies in the same magnitude as one-way shear strength. To investigate size effect in two-way shear, 12 three-pile caps were tested in three size groups: small, medium, and large. Specimens were doubly scaled from small to medium and medium to large groups, with all other key nondimensional structural parameters such as span-depth ratio, reinforcement ratio, and so on kept constant. The test results supported the existence of size effect in deep pile cap members, although the observed rate of unit shear strength reduction with depth was less severe than that predicted by size effect provisions in American and Japanese design codes. Capacity estimations made using sectional and strut-and-tie approaches prescribed by design codes, as well as the proposed analytical procedure using the softened strut-and-tie model, are presented. The proposed method produced reasonably accurate estimations at all size ranges, capturing the effect of reinforcement more efficiently resulting in an overall mean test-to-calculated capacity ratio of 1.15 with a low coefficient of variation of 11%.