Electrokinetic nanopozzolan treatment of cementitious materials has proven to be beneficial for improving durability and rehabilitation outcomes through significant porosity reduction. This study investigated process parameters that enabled control of particle transport effectiveness and cost efficiency as applied to ordinary portland hardened cement paste (HCP). The most significant strength enhancement achieved in this study was 35%, which was provided by a 22 nm silica nanoparticle. This treatment produced a porosity reduction from 25 to 18%. The cost of using this particle was a factor of 2 to 6 lower than the other candidates. An innovative electrode setup was developed to help reduce the particle instability associated with electrolysis-induced pH increases. This new method enabled the use of electric field values that allowed for current densities as high as the concrete damage threshold of 1 A/m2.

A new mixture proportioning method is developed for performance-based concrete with supplementary cementitious materials (SCMs). The method is based on the thermodynamic calculations of the properties for concrete and identifying the mixtures that satisfy a predefined set of performance criteria. This new approach considers the chemical composition and reactivity of SCMs while proportioning concrete mixtures. Performance criteria examples are shown for a bridge deck (corrosion and freezing-and-thawing damage), an unreinforced pavement (salt damage), and a foundation (moderate sulfate and alkali-aggregate reaction). The method is used to proportion concrete mixtures satisfying these three performance criteria using four ashes per mixture. Experiments show that these mixtures met the targets. The proposed approach can proportion mixtures that are optimized for predefined performance using a wide range of SCMs, which can be useful in reducing the cost and carbon footprint of concrete.

This paper investigates the applicability of numerically generated recycled concrete aggregate (RCA) systems by varying the material properties. The methodology was adopted by using a computational algorithm that can generate concrete systems with different RCA replacement levels to numerically simulate recycled aggregate concrete (RAC) systems under mechanical loading. Numerically simulated results are compared with an experimental database that has been established, including a substantial data set on RAC mixture design proportions. RAC geometries and material properties were stochastically generated using Monte Carlo simulation methods, resulting in 200 representative numerical models that were subjected to simulated mechanical loading. The overall variability of the concrete properties was not well-predicted in the numerical models compared to the experimental database results due to modeling limitations and material heterogeneity exhibited in experiments. The variability of tensile strength was governed by the complex strain localization patterns in the interfacial transition zone (ITZ) phases in RAC systems that were simulated.

In this study, an optimal curing method was established for very early-strength latex-modified concrete (VES-LMC), which is frequently used in partial-depth repair (PDR) of deteriorated concrete pavements. The appropriate starting time of curing, when the surface of the VES-LMC was not damaged, was found for various curing conditions such as ambient air, polyethylene (PE) sheet, blanket, curing membrane, PE sheet on curing membrane, and blanket on curing membrane. The hydration characteristics of the VES-LMC and ordinary portland cement concrete (OPCC) were then compared by evaluating their respective properties such as water loss, bleeding, autogenous shrinkage, and compressive strength. In addition, the optimal curing method was investigated by determining the water loss, water absorption, drying shrinkage, and compressive strength of the VES-LMC specimens cured under the aforementioned conditions. The test results revealed that VES-LMC performed better than OPCC as a PDR material. In addition, covering the VES-LMC with a PE sheet 3 minutes after placement was observed to be the most effective curing method in PDR.

The appropriate and efficient design of structural components made with ultra-high-performance concrete (UHPC) requires the establishment of key design properties and material models that engage UHPC’s distinct mechanical properties, as compared to conventional concrete. This paper presents the results of an extensive program of compression and tension property assessment executed according to existing testing methods to assess the mechanical characteristics of several commercially available UHPC products. The experimental results are then used to propose suitable mechanical models and design parameters that are foundational for the structural-level application of UHPC. The models rely on a set of experimentally identified mechanical performance properties that distinguish UHPC from conventional concrete and establish the basis of the material qualification for use in structural design. As such, this work constitutes a fundamental step in ongoing efforts to develop UHPC structural design guidance in the United States.