International Concrete Abstracts Portal

Reinforced concrete (RC) members undergoing shrinkage are susceptible to cracking when restrained; however, studies on this behavior are limited. Thus, the main objective of this paper is to present crack-widths, crack-patterns, and shrinkage strains from an experimental study on three RC walls with aspect ratios of 3.26 and 1.08, and horizontal reinforcement ratios of 0.2% and 0.35%, as well as a rectangular tank with 0.24% reinforcement. A 3-D nonlinear finite element (FE) analysis is conducted, and the results reveal that although the model predicts strains and maximum crack-widths reasonably well, the crack-pattern differs from the experiments. The possible reasons for this difference are discussed, and a parametric study is done to propose design equations to estimate restraint factors along the wall centerline for different aspect ratios. These equations can be used to estimate the cracking potential in the design stage without the need for a nonlinear FE analysis. For L/h above four, horizontal reinforcement has a negligible effect on the restraint, and for L/h above eight, full-height cracks can be expected due to almost uniform restraint. Finally, the design codes are compared, and it is found that ACI 207.2R-07 and CIRIA C766 predict shrinkage-induced crack-widths conservatively and reasonably accurately.

The aim of the current research is to investigate the distinctive geometry of deep box girders under horizontal curvature. Six specimens were cast and tested to investigate the effect of both web and flange thickness and section height under horizontal curvature conditions. It was found that when using strut and tie modelling (STM) as is, i.e., with the struts passing through both box girder webs, the results differed from the experimental data by 45 to 53%. However, when the STM was modified to include the influence of both flanges and the counteracting torsional shear resulting from the horizontal curvature on both webs, the results of the STM aligned more closely with the experimental results, reducing the difference to 7 to 32%. The shear generated by torsion had a minimal effect compared to the conventional shear, particularly due to the box girder’s geometry, especially when its span-to-effective depth ratio is low.

This paper summarizes the results of an experimental study investigating interface shear resistance through slant shear tests. A total of 54 tests were conducted on 6×12 in. (150×300 mm) cylinders with inclined cold joints. Five key test parameters were investigated: cold joint inclination, interface roughness, variation in concrete compressive strength between layers, casting age difference, and aggregate size. The test results demonstrated that the most influential parameters affecting interface shear resistance were interface roughness, casting age difference between layers, and aggregate size. Conversely, cold joint inclination and variations in compressive strength between layers were identified as comparatively less influential factors. A comprehensive analytical study was conducted, including the comparison of five current design codes. A modified approach is proposed for calculating the interface shear resistance, compatible with current design codes’ expressions. The proposed approach was validated using the experimental results generated from this study and a database of 124 slant shear test results from different research programs. Overall, the proposed approach resulted in more accurate estimations for the interface shear resistance, particularly for specimens with intermediary levels of amplitude at the interface.

The production of Ordinary Portland Cement (OPC) is a major contributor to carbon emissions. One immediate and viable solution is the use of optimized concrete mixtures that employ a decreased quantity of cement and increased dosage of high-range water-reducing (HRWR) admixtures. This study investigates five different concrete mixtures with varying w/c (0.37 to 0.42) and reduced cement contents. The mixtures with “low cement + high dosage HRWR admixture” content had over 30% increase in mechanical strength and presented 40% lower water absorption, and 68 to 97% higher formation factor, indicating enhanced durability. The optimized concrete mixtures with reduced cement and lower w/c have a service life increase of up to 117% and a life-cycle cost reduction of 29%. The application of “low cement + high dosage HRWR admixture” mixtures can improve the sustainability of concrete mixtures by reducing cement and water contents and increasing the service life of concrete in severe environments.

Portland Limestone Cement (PLC) 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 in the concrete industry has primarily relied on Ordinary Portland Cement (OPC). In this study, PLC Type II/B-L was partially replaced with clay pozzolana at levels ranging from 10% to 50% by weight. The investigation included compressive strength testing, non-destructive evaluations using electrical surface resistivity, pulse velocity, and chloride penetration tests, targeting a characteristic strength of 30 MPa. Additionally, an environmental impact assessment based on the carbon footprint of both control and clay pozzolana concretes was conducted. The mix design followed the EN 206 standard. A total of 72 cubic moulds were produced for the strength test. The results showed that clay pozzolana concretes with between 10 and 20% replacement achieved strength values of 35 and 33 MPa, 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, 10-50% clay pozzolana replacement attained strength between 32 and 41 MPa. Non-destructive 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 CSi and a 19 to 36% increase in CRi with 10 to 50% clay pozzolana (for CSi) and 10 to 40% (for CRi). The thermodynamic modelling also revealed that pozzolana contents below 30% primarily promoted pozzolanic reactions, enhancing performance compared to the control mix. Based on these results, 20–30% clay pozzolana replacement is recommended to ensure reliable performance, while higher levels (>30%) require further durability evaluation for long-term use.