International Concrete Abstracts Portal

Hybrid cements contain a small amount of Portland cement; the rest of the binder is made up of pozzolanic or latent hydraulic admixtures. Another component is an alkaline activator. These binders, therefore, combine the advantages of alkaline activation and Portland cement. In this work, a combination of Portland cement, ground granulated blast furnace slag (GBFS), siliceous fly ash (FA), and ground recycled masonry (GRM) is chosen. The GRM mainly contains ground bricks - i.e., heat-treated clay with potential pozzolanic properties and usually about 7-8% CaCO3 from the original mortar. Sodium water glass modified with potassium hydroxide is used as an activator. Potassium ions improve the workability of the mixture and limit the efflorescence of the hardened mixture. The dose of cement was optimized, as well as the dose of the activator. Furthermore, mixtures with different GBFS or FA and GMR ratios were tested. With an optimal composition and a water-to-binder ratio of 0.50, it is possible to achieve compressive strengths between 15 and 20 MPa at the age of 28 days, with the expectation of further improvement.

Concrete specimens containing iron sulfide-bearing aggregates were investigated under electrochemical acceleration to evaluate potential damage mitigation strategies. Cylinders were prepared with different aggregate sizes, sulfide contents, water-to-cement ratios, cement types, and pozzolanic replacements, and subjected to controlled electrochemical exposure to reproduce field-like deterioration within weeks. Damage progression was monitored using resonance frequency measurements, visual crack quantification, and microstructural analysis. Results showed that higher sulfide contents accelerated modulus loss and crack initiation, with coarser aggregates producing visible cracking and greater stiffness reductions, while finer aggregates largely avoided macrocracking. Higher water-to-cement ratios further accelerated deterioration, whereas lower ratios delayed both onset and propagation. Cement type and pozzolanic additions also influenced deterioration, with all mixtures exhibiting damage under electrochemical acceleration. Specimens containing Type I white Portland cement demonstrated greater resilience against rapid failure, while partial cement replacement with glass powder delayed early crack propagation. These findings demonstrate that electrochemical acceleration provides a reliable platform for evaluating potential mitigation strategies and show how mixture design parameters influence deterioration progression in iron sulfide-bearing concrete, offering insights that support the development of practical approaches to manage this durability problem.

With the reduced availability of traditional supplementary cementing materials (SCMs), a need arises for alternatives. This study presents an investigation into the reactivity of powders derived from reactive siliceous aggregates, some of which demonstrated pozzolanic potential by reducing concrete expansion associated with alkali-silica reaction (ASR). A dissolution test was conducted to quantify the amounts of soluble silica and alumina available for pozzolanic reaction. The aggregate powders were immersed in an alkaline solution designed to simulate the alkalinity of concrete pore fluid and tested at four different temperatures to evaluate the effect of temperature on the dissolution behavior. These tests were performed in parallel with ASR expansion testing to determine whether dissolution data could serve as a rapid indicator of pozzolanic potential, reducing the need for long-term monitoring. The results indicated that dissolution kinetics varied significantly with temperature, raising concerns about the use of high-temperature methods to evaluate pozzolanic activity. Aggregate powders containing calcium exhibited notable physical changes, suggesting reactions involving both silica and calcium in the solution. A strong inverse relationship was observed between dissolved silica and aluminum concentrations; all solutions exhibited either high aluminum and low silica, or high silica and low aluminum, but never elevated levels of both simultaneously. Finally, the powders were analyzed using X-ray diffraction (XRD) to assess mineralogical changes following alkaline exposure. Cryptocrystalline quartz, muscovite, and kaolinite phases were altered during the dissolution test, whereas other phases, including crystalline quartz, did not.

Over the past four decades, significant advances have been achieved in material science and construction technologies for the construction of dams. Among these, MgO concrete, rock-filled concrete, and roller-compacted concrete have been applied on an increasing trend in the construction of concrete dams. The application of these innovative materials and technologies in arch dam construction makes it possible to omit transverse and longitudinal contraction joints, which can speed up construction progress and reduce project costs. This paper discusses the design and construction features of arch dams constructed without contraction joints, highlighting the role of innovative materialsand associated construction methods.

Spray-based 3D-printed concrete (3DPC) is gaining popularity due to its ability to realize complex geometries, optimize materials, and reduce labor and construction costs. Anchorages are widely used in concrete to connect structural or non-structural elements to the concrete. However, there are currently no tests that evaluate the behavior of anchorages in 3DPC. In this pilot study, steps were taken to assess the behavior and performance of anchorages in 3DPC.