International Concrete Abstracts Portal

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.

Alkali–silica reaction (ASR) is a major concrete durability problem. The occurrence of ASR results in significant maintenance and reconstruction costs to concrete infrastructures all over the world. Current market solutions are not always sustainable, such as hauling non-reactive aggregates or fly ash from long distances; or use of a lithium-based admixture that has availability, and lead time challenges. The current article will present an ASR mitigating admixture, which is based on the abundant water-soluble calcium salts, such as Ca(NO3)2. The current ASTM C1567 test method is not suitable for evaluating this new ASR mitigating technology due to the potential for leaching of soluble Ca(NO3)2 into the soak solution. A slight modification to the ASTM C1567 test using additional Ca(NO3)2 in soak solution to buffer any potential leaching has been developed for evaluating this new ASR preventing technology. Twenty-seven aggregates have been evaluated with this innovative technology. Depending on the reactivity of the aggregate and the alkali content of the cement, the dosage of this new admixture required to inhibit ASR ranges from 32 to 81 mL/kg of cement for aggregates tested. This new admixture is formulated to be set neutral, provides water reduction, and significantly improves the compressive strength of concrete in addition to preventing ASR expansion.

Returned concrete is the residual amount of fresh concrete that is not placed at the jobsite and comes back to the ready-mixed plant in the truck mixer. This amount is estimated from 3 to 5 per cent of the overall ready-mixed concrete production and represents the main waste at the ready-mixed concrete plants. Returned concrete can be treated by washing with large amounts of water, whereby coarse and fine aggregates are recovered with the heavy burden of producing a large amount of wastewater, which can be recycled into new concrete production. In addition, the production of sludge always accompanies this process.

Recently, a new dry reclaiming method not using water has been developed, based on the addition of special additives to returned concrete, which are capable of instantaneously transforming fresh concrete into a dry material, from which reclaimed aggregates can be easily recovered. The main advantage of the dry method is that concrete can be fully recovered as aggregates without generating any waste, both in liquid or solid form, and therefore can be considered more sustainable compared to the wet methods.

In this study, different technologies to treat returned concrete by the dry method are compared with a focus on the quality of resulting aggregates to produce new concrete. The results indicate that the reclaimed aggregates obtained by the dry process can be conveniently used up to 30 per cent by weight as a replacement of natural aggregates without affecting concrete performance.

The use of lithium-based admixtures is one of the options to prevent deleterious alkali-silica reaction (ASR) in concrete. In 1992, the Canadian Centre for Mineral and Energy Technology (CANMET) initiated a comparative laboratory-versus-field ASR study. About 700 concrete blocks were cast with various aggregates susceptible to ASR, different binders including supplementary cementitious materials, and lithium-based admixtures. The blocks have been exposed outdoors near Ottawa, Canada, and their expansion has been monitored over time. Out of those, a set of blocks was made with two lithium-based products: lithium hydroxide (LiOH) and lithium nitrate (LiN). They were used with high alkali Portland cement (PC) and in “ternary” concrete systems with PC and Class F fly ashes. The Li-to-(Na+K) molar ratios in the mixtures ranged from 0.37 to 1.10.

This paper presents the expansion of the concrete blocks after 25-30 years of outdoor exposure, for 20 different mixtures. The efficacy of LiOH and LiN to limit the expansion depends on the aggregate type and the dosage. Overall, lithium-based products reduced the expansion caused by ASR. However, there are indications that lithium may only have a retarding effect on ASR expansion - not a prevention effect - at least for some aggregates. Finally, two 30-year blocks with and without Li were cored to better characterize the condition of the concrete. The paper presents the results of in-depth investigations, including the damage rating index and stiffness damage test.