The reference Pittsburg Ontario alkali carbonate-reactive (ACR) aggregate source was characterized using a holistic approach to identify and quantify mineral phases, particularly reactive forms of silica and expansive types of clays in the aggregate which may have a role in the controversial ACR mechanism and resulting expansion and cracking of concrete. This research was performed using state-of-the-art analytical techniques and methods that included polarized light microscopy (PLM), quantitative image analysis (QIA) of backscattered electron (BSE) scanning electron microscope (SEM) images, acid-insoluble residue (AIR) tests, X-ray diffraction (XRD), X-ray fluorescence (XRF), and a chemical ratio method of identifying alkali-reactive carbonate rocks. Three types of silica phases were identified through PLM examination: upper silt-sized quartz grains both in the virgin aggregate and acid insoluble residue (AIR); cryptocrystalline silica dispersed and hidden in the fine-grained rock matrix and identified only in the AIR; and cryptocrystalline-to-microcrystalline silica occupying interstitial spaces of dolomitic limestone particles which lacked clay in their matrix. PLM findings were confirmed through QIA of the AIR. Particle size distribution of silica phases through QIA showed that silica phases in sizes of 0.5 to 2 μm (0.00002 to 0.00008 in.) occur in high abundance. QIA of AIR identified illite as the major clay mineral in the aggregate. While this clay type is not known to be expansive, microcrystalline to cryptocrystalline silica phases are potentially alkali-silica reactive (ASR) in concrete as opposed to ACR.

Alkali-silica reaction (ASR) is one of the most harmful distress mechanisms affecting concrete infrastructure worldwide. ASR is a chemical reaction that generates a secondary product, which induces expansive pressure within the reacting aggregate material and adjacent cement paste upon moisture uptake, leading to cracking, loss of material integrity, and functionality of the affected structure. In this work, a computational homogenization approach is proposed to model the impact of ASR-induced cracking on concrete stiffness as a function of its development. A representative volume element (RVE) of the material at the mesoscale is developed, which enables the input of the cracking pattern and extent observed from a series of experimental testing. The model is appraised on concrete mixtures presenting different mechanical properties and incorporating reactive coarse aggregates. The results have been compared with experimental results reported in the literature. The case studies considered for the analysis show that stiffness reduction of ASR-affected concrete presenting distinct damage degrees can be captured using the proposed mesoscale model as the predictions of the proposed methodology fall in between the upper and lower bounds of the experimental results.

Alkali-silica reaction (ASR) and freezing and thawing (F/T) cause premature deterioration and reduce the service life of concrete structures, and both are difficult to mitigate in existing concrete pavements once deterioration occurs. The objective of this research program was to evaluate the efficacy of silane surface treatments used to reduce the moisture state of concrete pavements, thereby reducing further deterioration from ASR and F/T and increasing the remaining useful life of the pavement. The pavement test section evaluated contained a borderline-reactive fine aggregate and marginal air entrainment. The efficacy of silane was evaluated by instrumenting a pavement test section with devices for monitoring strain and internal RH. Core samples were extracted before and after treatment. The core samples were evaluated using the damage rating index (DRI). Results indicate silane may reduce the rate of deterioration in the concrete pavement compared to untreated control sections.

Producing concrete requires considerable quantities of natural aggregates, and contributes to large amounts of solid waste in both production and when removed from service. With many structures reaching the end of their service life, a means of concrete disposal is needed that is both practical and eco-friendly. Reusing concrete waste as recycled concrete aggregate (RCA) in new concrete is a promising solution. However, the current use of RCA is generally limited to backfill and road base. Additionally, alkali-silica reaction (ASR) can pose a substantial obstacle to highly durable concrete and with limited research on ASR behavior in RCA, effective design recommendations are lacking. Current methods of ASR mitigation depend on experimental testing for aggregate classification. Therefore, a multi-laboratory study was done using ASTM C1260 with nine laboratories and 10 operators to determine within- and between-laboratory variation on ASR expansions. The result of this investigation suggests a small change to the existing precision statements of ASTM C1260 to allow the standard to incorporate RCA into the accelerated mortar bar test (AMBT). In addition, testing revealed that expansions using RCA and natural aggregates produced nonreactive or moderately reactive mortar mixtures far more frequently than highly reactive mixtures.

Alkali-silica reaction (ASR) and reinforcement corrosion are wellknown deterioration mechanisms in concrete structures. This research investigates how ASR affects corrosion in reinforced concrete specimens. Concrete specimens containing aggregate susceptible to ASR (reactive) and aggregate not susceptible to ASR (nonreactive) were cast. Expansion of the specimens, corrosion potential, macrocell current, and chloride diffusivity were measured for each specimen until the embedded reinforcement began to actively corrode. Scanning electron microscopy (SEM) results indicate that ASR gel can fill the interfacial transition zone (ITZ) and cracks, which can reduce the transport of the chlorides in concrete. The presence of ASR gel at the HCP-steel interface likely reduces the pH at the interface, which can reduce the critical chloride threshold level (CT). The results indicate that ASR expansion does not significantly influence the time to corrosion initiation of reinforced concrete systems for laboratory specimens exposed to wetting/drying cycles at 100°F (38°C).