With aging, concrete structures exhibit deterioration due to multiple reasons. Consequently, repair processes become overwhelmingly essential to extend the service life of structures. This experimental study investigated nano-modified concrete cast and cured under cyclic freezing/low temperatures, including its applicability to partial-depth repair. Seven mixtures, incorporating general-use cement, fly ash (0 to 25%), and nanosilica (0 to 4%) with a cold weather admixture system (antifreeze/accelerator) were tested. The mixtures were evaluated based on fresh, hardened, and durability properties as well as their compatibility with parent/substrate concrete. In addition, mercury intrusion porosimetry and thermogravimetric analysis were conducted to assess the evolution of microstructure under cold temperatures. The incorporation of 4% nanosilica in the cementitious binder, even with the presence of 15% fly ash, markedly enhanced the performance of concrete cast and cured under low temperatures without protection; thus, it may present a viable option for cold weather applications including repair.

Corrosion performance of reinforced pervious concrete was evaluated through field and laboratory evaluations. Two reinforced pervious cemetery walls in Chicago, IL, were visually evaluated, and samples were investigated through petrographic examination. Corrosion performance of two-layered concrete samples, with an outer layer of conventional concrete and an inner layer of pervious concrete, was evaluated in the laboratory. Results indicated that pervious concrete around the reinforcement can significantly delay the cracking and spalling of samples compared to conventional concrete. Chloride profiles of samples and instantaneous corrosion rate measurements showed that corrosion of reinforcement embedded in two-layered samples was similar to conventional concrete although two-layered samples provided a longer time to cracking. Laboratory results are in agreement with long service life performance observed in the field and with prior pervious concrete corrosion studies.

Reliability-based durability design of reinforced concrete structures requires a probabilistic service life modeling approach. Probabilistic service life modeling of chloride-induced corrosion should consider the statistical distributions of key parameters that influence corrosion initiation and subsequent damage. For typical reinforced concrete structures (such as bridge decks), these are chloride exposure, chloride penetration resistance of the concrete, chloride-induced corrosion threshold, depth of concrete cover, and corrosion propagation time. Assessing the impact of the use of corrosion-resistant reinforcement, such as epoxy-coated reinforcing bars (ECR), is typically performed through a selection of the chloride threshold and/or propagation time. This paper provides recommendations for statistical distributions for the chloride threshold to be used in service life modeling for structures containing carbon steel and ECR based on both experimental work reported in the literature and field investigations of existing structures conducted by the authors.

Magnesium silicate hydrate (M-S-H) formed by the reaction between magnesium oxide and amorphous silica in water imparts strength-binding characteristics similar to that of portland cement (PC). Analysis of both the mechanical and durability parameters of MgO-SiO2 binder is essential for its adoption as an alternative cementitious material. This study investigates the mechanical and transport properties of MgO-SiO2 binder concrete. Silica fume and metakaolin were used as amorphous silica sources in the binder. The implications of the addition of magnesium carbonate in MgO-SiO2 binder concrete was also investigated. Along with the compressive strength, other hardened properties of concrete including elastic modulus, shrinkage, porosity, sorptivity, permeability, and resistivity were measured at 7, 28, and 90 days. The overall performance of the concrete was improved through the use of metakaolin instead of silica fume in terms of compressive strength, elastic modulus, and shrinkage. The transport properties of the magnesium oxide and metakaolin mixture were found to be better or similar compared to PC, which was attributed to the refined pore structure and lower porosity. The addition of magnesium carbonate further helped to improve the overall performance of the concrete through likely the formation of hydrotalcite type phases.