This paper presents the prediction of bond strength between ultra-high performance concrete (UHPC) and fiber reinforced polymer (FRP) reinforcing bars using an artificial neuronal network (ANN) approach. A large amount of datasets, consisting of 183 test specimens, are collected from literature and an ANN model is trained and validated. The ANN model includes six variable inputs (bar diameter, concrete cover, embedment length, fiber content, concrete strength, and rebar strength) and one output parameter (bond strength). The model performs better than other models excerpted from existing design guidelines and previously published papers. Follow-up studies are expected to examine the individual effects of the predefined input parameters on the bond strength of UHPC interfaced with FRP rebars.

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 Production of Portland cement used in concrete and the large amount of industrial waste generated worldwide represent critical environmental and economic issues. The reuse of bauxite residue generated during alumina production by Bayer’s process to replace Portland cement and produce sustainable and environmentally friendly geopolymer concrete is a promising solution. This paper presents the development and characterization of bauxite residue and class F fly ash-based geopolymer mortar and concrete. The parameters studied for the mixture proportions are the bauxite residue to class F fly ash ratio, the water-to-binder ratio, and the curing condition, in terms of duration and temperature. Then, the compressive strength of the geopolymer mortar and concrete is characterized with experimental tests. Results show that, with appropriate mixture proportions and curing conditions, a large amount of bauxite residue (up to 70%) can be used to replace fly ash and obtain geopolymer concrete with improved quality characteristics that meet the construction field’s sustainable development criteria.

The use of recycled aggregates in concrete has gained popularity due to its contribution to the reduction of primary resource extraction. In Germany, the use of recycled fine aggregates is not standardized while recycled aggregates larger than 2 mm can be used in concrete depending on their origin, exposure class, and humidity class. In this research framework, we investigated the workability, mechanical, and durability performance of low-clinker mortars using recycled fine aggregates compared to natural sands. Three polycarboxylate ether-based superplasticizers, differing in their polymer structure (chain lengths and charging density) were tested to achieve a comparable initial workability. Four mortar test series with recycled fine aggregates were analyzed with different supplementary cementitious materials to keep the clinker amount low. The initial water demand, presoaking of recycled aggregates, and the workability over time were tested. The workability of low-clinker mortars with recycled aggregates, analyzed through slump flow measurements, proved comparable results to natural aggregates once mixture proportions and superplasticizer type and content were adjusted. However, mechanical tests on mortars with optimized workability properties showed decreased compressive strength and increased capillary suction when using recycled fine aggregates and supplementing cement. An optimized workability procedure for enhanced mechanical properties is still ongoing research. The results are the basis for further mortar and concrete mixture optimizations to reach high-performance low-clinker mortars and concrete with recycled aggregates.

The ecological and health issues of construction and demolition waste (CDW) accumulation, as well as the depletion of virgin raw materials from the increased use of concrete are pushing the drive for the reuse of this waste in more construction-related applications. The objective of this study is to investigate the production of geopolymer mortars (GM) prepared with maximum amounts of CDW materials such as concrete, red clay bricks, and ceramic tiles, along with smaller contents of supplementary cementitious materials like Fly ash C, ground granulated blast-furnace slag, and metakaolin. The study also examined the effects of concrete waste aggregates (CWA) on the flowability and compressive strengths of GM prepared with CDW- binders and exposed to three exposure conditions of ambient environment, water immersion, and high temperature. An algorithmic mixture design method was used to determine the ideal composition ratios of silica oxide to alumina oxide, sodium oxide to silica oxide, and liquid to solid binders. Although the use of concrete waste aggregates resulted in lower compressive strengths compared to silica sand and natural sand, it was possible to achieve appropriate structural strengths and dimensional stability for highly sustainable mortars combining both CDW-binders and CWA-aggregates.