International Concrete Abstracts Portal

The efficacy of ultra-high performance concrete (UHPC) overlays holds great promise for mitigating chloride-induced corrosion in reinforced concrete bridges. This research examines the corrosion resistance of a bridge structure through the application of simulation techniques to better understand the effectiveness of ordinary concrete and UHPC overlays. To represent the three-dimensional microstructure of ordinary concrete and UHPC, the Virtual Cement and Concrete Testing Laboratory (VCCTL) program is utilized. Additionally, an agent-based model is developed to investigate chloride penetration mechanisms within the concrete overlays. Furthermore, the structural response of the overlayed bridge under a corrosive condition is studied.

Corrosion of steel reinforcement is one of the primary contributing factors to bridge deck deterioration. Based on the extent of corrosion, different corrosion mitigation strategies can be used to extend the service life of a bridge deck. Bridge deck overlays are efficient tools in reducing active corrosion. While there are multiple overlay solutions that are commonly deployed, including concrete-based and polymer-based systems, ultra-high performance concrete (UHPC) overlays have gained interest from bridge owners in recent years. Another corrosion mitigation strategy is the application of corrosion-inhibiting chemicals and sealers to a concrete surface to reduce the ingress of deleterious ions. The purpose of this paper is to compare different corrosion mitigation strategies and study the effects of such techniques on the bond between the UHPC overlay and the substrate concrete. UHPC overlays were found to be effective in reducing corrosion rates by more than 50 percent. Sealers and corrosion inhibitors applied to the concrete substrate in combination with placing a UHPC overlay reduced the corrosion rates even further. However, sealers and corrosion inhibitors appeared to negatively affect bond strength, potentially increasing the likelihood of overlay delamination.

The presence of chloride ions is one of the most widespread causes of corrosion initiation in reinforcing steel in concrete. Trace chlorides present in cementitious materials or admixtures typically result in very low fresh chloride contents in normal-strength concrete that do not present a danger of corrosion. UHPC mixture designs, however, use much higher dosages of cementitious materials and admixtures that can result in non-negligible total fresh chloride contents. These high chloride values are likely to occur more frequently in the future as more UHPC mixtures are made with locally available materials and alternative cementitious materials and may result in concrete mixtures failing to meet specifications for fresh chloride content limits that are based on mixture proportions used in normal-strength concrete mixtures. UHPC and normal concrete samples were made without fibers and with increasing levels of internally admixed chlorides for four different levels of strength to determine chloride thresholds for internally added chlorides. The chloride threshold for fresh concrete was measured using a slightly modified version of the accelerated test EN 480-14. The water-soluble and acid-soluble chloride ion content of UHPC mixtures tested were measured according to ASTM C1218 and Florida Method FM 5-516 to determine the bound chlorides and fresh chloride limits for corrosion. The results demonstrate that the UHPC had ~ 25% higher chloride threshold than the control mixture when measured as an absolute content per unit volume of concrete. When the UHPC chloride content is normalized by mass of cementitious material, it was found that the amount needed to initiate corrosion may be lower than fresh chloride limits given in ACI-318 and ACI 222. Therefore, the ACI-318 water-soluble chloride limits as a % by mass of cementitious materials were found to be non-conservative for the two of the UHPC mixtures tested and should be re-examined for UHPC.

Using particle packing models (PPMs) in combination with limestone fillers has been shown to be effective in proportioning eco-efficient concrete mixtures with reduced Portland cement content, resulting in suitable performance in fresh and short-term hardened states. However, the decrease in Portland cement and increase in limestone fillers may lower the pH of concrete, raising concerns about durability and long-term performance, potentially leading to increased corrosion of steel reinforcement in the presence of carbonation or chlorides. In this study, the performance of three eco-efficient concrete mixtures with varying cement (250, 200, and 150 kg/m³) and inert filler contents is evaluated against accelerated chloride exposure. The findings highlight the influence of the mixture proportioning and water-to-cement ratio on the resistance to chloride ingress. Ultimately, it is verified that the distance between cement particles is a major contribution towards chloride ingress.

This article presents the characterizations of mechanical and durability properties on diverse concrete formulas with a lower carbon footprint. The contribution of mineral additions in the binder is currently limited by the NF EN 206/CN (2022) standard with the concept of the equivalent binder. It is now necessary to change these normative provisions to expand low-carbon concrete solutions and accelerate their development in construction. The objective of this study is to formulate concretes based on ternary binders and to evaluate their use properties compared to traditional concrete defined today in the normative context. Several types of addition have been used to form ternary binders: limestone addition, blast-furnace slag, and flash metakaolin. The results obtained with substitution rates ranging from 40% to 60% of clinker have allowed positioning these different concretes regarding the thresholds defined for the performance-based approach according to FD P 18-480 (2022).