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Alkali-activated slag (AAS) has emerged as a potentially sustainable alternative to ordinary Portland cement (OPC) in various applications since OPC production contributed about 12% of global CO2 emissions in 2020. AAS offers great ecological advantages over OPC at some levels such as the utilization of industrial by-products and overcoming the issue of disposal, low energy consumption, and low greenhouse gas emission. Apart from these environmental benefits, the novel binder has shown enhanced resistance to high temperatures and chemical attacks. However, many studies have mentioned the risk of its considerably higher drying shrinkage and early-age cracking compared to OPC concrete. Despite the abundant research on the self-healing mechanism of OPC, limited work has been devoted to studying the self-healing behavior of AAS. Self-healing AAS is a revolutionary product that provides the solution for these drawbacks. This study is a critical review of the self-healing ability of AAS and its effect on the mechanical properties of AAS mortars. Several self-healing approaches, applications, and challenges of each mechanism are taken into account and compared regarding their impacts.

Concrete is most widely used as an essential building material in the construction industry all over the globe. Concrete deteriorates over time, and cracks eventually form on its surface for many reasons, such as environmental surroundings and extra. This deterioration and cracks might lead to the ingress of water and chemicals that susceptible steel bars or reinforcements to corrosion. Since this deterioration is inevitable, maintenance and repair are also necessary. This process requires skilled labor and is cost-effective. Thus, researchers suggested alternative techniques to enhance concrete's mechanical properties and search for treatments to be applied to concrete's surface for healing and sealing the cracks by producing calcium carbonate precipitation. Therefore, self-healing concrete was introduced; this method is significant as it's proven environmentally friendly. This research aims to investigate the use of liquid bacteria incorporated in concrete mix and assess whether there would be improvements in the mechanical properties of the bacterial concrete compared to the conventional mix and an autogenous self-healing mix. Two different concentrations of an alkaliphile bacterium called Bacillus Subtilis were incorporated into the concrete mixes to test their ability to repair cracks by producing calcium carbonate and sealing them. This experiment showed a remarkable increase in bacterial concrete's compressive and tensile strengths. A visible partial crack sealing was also observed in specimens containing different concentrations of Bacillus Subtilis. Results also indicate that optimum results were obtained when the bacterial solution of concentration 108 cells/ml was incorporated, especially at early ages.

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This paper presents an efficient and reliable computational tool to analyze and reach the optimal design of a high-speed railway pre-stressed box girder bridge. The design and analysis of the simply supported box girder bridge is performed by using CSI bridges and SAP 2000 finite element software according to Eurocode (EN 1991(EN -2, 2003 [5] and the Egyptian Code of Practice (ECP 201, 2012) [3]. Computer spreadsheet applications are developed for design and cost estimation of a full-span precast box girder bridge. The optimal design is achieved by selecting the efficient design variables based on the limit-of-deflection constraint. Development of the optimum design charts was evaluated through cost estimation of all major bridge components, including the foundation and sub-structure. The design variables considered in this study were girder depth, span length and the pre-stressing area. The optimum, i.e. most cost efficient design is attained at a girder depth of 2.9 m, a span length of 32 m and a pre-stressing area of 347 cm 2 .