International Concrete Abstracts Portal

Reinforced concrete members derive flexural strength from reinforcing steel, which acts together with concrete to reach the required capacity. Design standards stipulate mandatory norms that must be complied with during the design process. Noncompliance with these provisions can increase the risk of corrosion, compromising the safety and integrity of the structure. Concrete provides protection to the reinforcing steel against corrosion, but it can also become a contributing factor when its microstructure is poor due to noncompliance with these norms. Assessing the residual flexural capacity is essential for making informed decisions regarding repair or demolition. The proposed model in this paper enables computation of the reduction in flexural strength based either on gravimetric mass-loss percentage or on measured corrosion current density. A design chart is also proposed to facilitate practical application, enabling engineers to assess residual capacity and decide on repair or demolition.

This article presents results from ten tests on reinforced concrete (RC) columns strengthened with post-tensioned clamps. The test columns were subjected to displacement reversals at increasing drift ratios and approximately constant axial loads. The transverse reinforcement consisted of post-tensioned clamps made of steel angles and high-strength steel rods. A key feature of the proposed clamps is their capacity to provide active confinement by exerting lateral pressure, which can delay concrete cover spalling, crushing, and the formation of inclined shear cracks. The test results showed the effectiveness of the clamps in enhancing both shear strength and drift capacity. This paper focuses on measured drift capacities, which are compared with drift capacities listed in a database of conventional RC columns compiled by ACI Committee 369, Seismic Repair and Rehabilitation. The comparison is made using existing empirical equations and a machine-learning algorithm calibrated to estimate the drift capacity of conventional RC columns without lateral prestress. Consistently, the results suggested that columns with post-tensioned clamps had drift capacities exceeding estimates obtained for similar columns reinforced with conventional ties. The proposed clamps offer a practical alternative for mitigating the seismic vulnerability of older RC columns with insufficient transverse reinforcement. Their ease of design and implementation makes them a feasible retrofit and repair solution, especially for mass retrofitting efforts and emergency repairs after strong ground motion.

Limestone calcined clay cement (LC3) has the potential to provide high clinker replacement in cement blends while providing excellent engineering properties and durability with low environmental impact, but such blends of clinker, limestone, and calcined clay are still in the industrial trial stage in the United States (US). In this study, it is proposed that sources of calcined clay (C), Type IL portland cement (IL), and additional limestone powder (L) can be blended into a “CC·I·L” cement to speed up the implementation of LC3-like systems in the US by combining already commercially available components during concrete mixing. In this investigation, regional CC·I·L blends were prepared using ASTM C595 Type IL cements and calcined clays, replacing 20% - 30% of the cement, from suppliers in the east, west, central, and mountain areas of the US, with additional ground limestone to reach a total limestone content of up to 15% by mass of the total cementitious system. To investigate the feasibility of this approach, fresh properties, early and late age performance, and durability of pastes and mortars made with the CC·I·L blends were examined and compared to ASTM C595 standard performance requirements and performance of regionally available Type IL cements. The results showed that 30% calcined clay and 15% limestone can be used to produce CC·I·L blends in each studied region to meet the ASTM C595 strength requirements. However, gypsum adjustment up to 5.0% was necessary to address undersulfation of CC·I·L blends in some of the regional blends. The results demonstrate the feasibility of using CC·I·L in the US without intergrinding, by taking into account key design factors such as the reactivity of calcined clays, sulfate balance, performance, durability, and possible environmental impact.

This study evaluated the performance of recycled brick-concrete aggregate concrete (RB-CAC) incorporating both recycled brick aggregate (RBA) and recycled concrete aggregate (RCA). It further examined the reinforcement effects of polypropylene macrofibers (PPMF) on the composite and assessed its mechanical properties and frost resistance. The results showed that incorporating 15% RBA reduced the compressive and splitting tensile strengths of concrete by less than 20%, while the peak load decreased by 28.8%. Fiber incorporation effectively mitigated compressive strength degradation and significantly enhanced tensile strength, with the optimum fiber dosage at 0.9% by volume. However, RBA incorporation reduced frost resistance, resulting in a 37.6% strength loss and a 40.6% mass loss after 100 freeze-thaw cycles. In contrast, a 0.6% fiber admixture improved frost resistance, reducing strength loss and increasing the relative dynamic elastic modulus by 26.7%. Finally, the study established a frost-resistance durability prediction model based on PPMF and RBA content.

This paper presents an experimental and analytical study conducted on concrete cores extracted from the Hungry Horse Dam, located in Montana, United States. The dam, constructed over a five-year period (1948–1953), represents the first major application of fly ash as a pozzolan for the partial replacement of portland cement in structural and mass concrete. Two cores were obtained from the same borehole at different depths, representing the interior and exterior mixtures. The measured mechanical properties of both concretes are largely consistent with values reported in the literature. Bulk electrical resistivity tests reveal significant differences in concrete quality, which are subsequently substantiated by microstructural and analytical investigations that identify variations in both the cementitious materials used and the current condition of the concretes. Microstructural examination exhibits evidence of deleterious alkali-silica reaction in the exterior concrete, while both interior and exterior concretes are found to contain reactive aggregates, as confirmed by petrographic analysis and gel pat testing. The study highlights and attempts to explain the remarkable long-term concrete durability enabled by a pozzolan after more than 70 years of deterioration-free field service offered by the Hungry Horse Dam concrete.