Concrete structures cannot efficiently perform their functions over time due to chemical and physical external effects. Thus, enhancing the relationship between repair and aged structures, and also improving the durability properties of concrete is crucial in terms of sustainability. However, high costs, negative environmental effects, and incompatibility problems occur in repair/retrofit applications. Furthermore, three-quarters of the failures in the repaired/retrofitted structures are caused by a lack of repair durability. The need for repair in pavement/bridge decks is also frequently encountered, and early-age performance problems with repair materials cause pavement/bridge decks to be unavailable for certain periods of time. Engineered Cementitious Composite (ECC) can be effectively used as repair/retrofit and pavement/bridge deck material. It also has a minimal need for repair/retrofit thanks to its high durability properties. This article presents state-of-the-art research regarding the application of ECC as a repair/retrofit and pavement/bridge deck material. Studies in the literature show that the repair/retrofit properties of ECC outperform conventional concrete and steel fiber-reinforced concrete. ECC can be a solution to high early strength and drying shrinkage problems frequently encountered in the use of repair materials. It could also be used for different repair applications such as cast, sprayed, and trenchless rehabilitation. Moreover, ECC might fulfill specific requirements for pavement, pavement overlay, tunnel pavement, airfield pavement, and bridge deck. These superior performances are attributed to ECC’s kink-crack trapping mechanism, uniquely large inelastic strain capacity, strain hardening, high tensile strain capacity, and multiple microcracking and ductile behaviors, especially bonding behavior and self-healing.

Production of cement and aggregate used in cement-based composites causes many environmental and energy problems. Decreasing the usage of cement and aggregate is a crucial and currently relevant challenge to provide sustainability. Inert materials can also be used instead of cement and aggregates, similar to pozzolanic materials, and they have positive effects on cement-based composites. One of the inert materials used in cement-based composites is wollastonite (calcium metasilicate-CaSiO₃), which has been investigated and attracted attention of many researchers. This article presents state-of-the-art research regarding fibrous concretes produced with wollastonite, such as mortars, conventional concrete, engineered cementitious composites, geopolymer concrete, self-compacting concrete, ultra-high-performance concrete and pavement concrete. The use of synthetic wollastonite, which is a novel issue, its high aspect ratio and allowing the use of waste material are also evaluated. Studies in the literature show that the use of wollastonite in different types of concrete improves performance properties, such as mechanical/durability properties, and provides environmental–economic efficiency. It has been proven by studies that wollastonite is a material with an inert structure, and, therefore, its behavior is similar to that of a fiber in cementitious composites due to its acicular particle structure.

The acquisition and transportation of aggregate exacerbate the negative impact of concrete on the environment, and waste materials are considered an effective solution to this crucial problem. One of these waste materials is waste ballast (WB), which is needed for new infrastructure along with increasing rail track technology. In this study, the effect of WB aggregate (which is basalt-based) on the mechanical and durability properties of standard concrete was examined. Coarse aggregate was replaced with WB aggregate at the rates of 50%, 75% and 100%. The slump, compressive strength, flexural strength, capillary water absorption, rapid chloride permeability and water penetration tests on the mixtures were performed. According to the results of this study, the utilization of WB improved the compressive strength and flexural strength of the mixtures by about 15% and 7%, respectively. Moreover, the capillary water absorption, rapid chloride permeability and water penetration values of all the concrete mixtures with WB were lower than the control mixture. In addition, the correlation relations between the mechanical and durability properties indicated that they have a strong relationship with each other. All the results of this study demonstrated that the utilization of WB instead of coarse aggregate improved the mechanical and durability properties of concrete. WB can also provide a more sustainable material formation by minimizing the negative environmental effects of concrete production.

The utilisation of waste bricks (WB) and waste marble (WM) in engineered cementitious composites (ECCs), which are high-ductility fibre-reinforced cementitious composites, was investigated in this work. To produce sustainable ECC, WB and WM were used as cement and sand replacements, respectively. Nine ECC mixtures were produced and evaluated through tests for fresh properties, compressive and flexural strength, mid-span beam deflection and ultrasonic pulse velocity, along with microstructural analyses (Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy). The results showed that the irregular shapes of WB and the high surface area of WM reduced the workability of the ECC. WB reduced hydration products (calcium silicate hydrate and calcium hydroxide) owing to its low reactivity, which weakened the matrix and lowered its mechanical strength. The incorporation of WM resulted in enhanced mechanical strength owing to its effective filling of voids. WB enhanced ductility, with the highest value at 30% replacement, whereas WM caused a slight reduction. Microstructural tests confirmed that WB increased internal voids, while the incorporation of WM led to a denser structure. The combined use of WB and WM resulted in lower mechanical performance than their individual use owing to competing microstructural mechanisms. Based on the overall mechanical, microstructural and sustainability performance, the most favourable results were obtained by using 30% WB instead of cement and 100% WM instead of sand.

Financing of public transportation has been a challenge that needs to be concerned because ridership has decreased by up to 90% with the impact of COVID-19. This study presents sustainable policy recommendations and their cost-benefit analyses for the financing problems in public transportation caused by COVID-19. First of all, the public transportation data of Eskişehir-Turkey between the years 2018-2021 were investigated according to different public transportation modes, and financial losses were calculated for municipality. Secondly, within the scope of the study, six policies were recommended as follows: (i) different network and service plans for public transportation, (ii) new or improved low-budget public transportation, (iii) congestion pricing, (iv) bike, bike-sharing and e-scooter, (v) park and ride, (vi) pedestrianization. Crucial points in the implementation of policies and their possible financial impacts were investigated. According to the findings of the study, total ridership decreased 72.94 million in 2020 and 2021 compared to pre-COVID-19. In different modes, it was observed that the decrease buses ridership was higher than in trams. Municipality financial loss was calculated as $19.69-24.87 million. In the cost-benefit analysis results of recommended policies, net present value was calculated as 0.28-23.36 million $ according to different scenarios and sensitivity analyses. It has been foreseen that this is a very suitable period for the implementation of these policies, they could provide sustainable urban transportation and increase the quality of life as well as solving financial problems.