Infrastructures, Volume 6, Issue 7 (July 2021) – 11 articles

The negative environmental impacts associated with the usage of Portland cement (PC) in concrete induced intensive research into finding sustainable alternative concrete mixes to obtain “green concrete”. Since the principal aim of developing such mixes is to reduce the environmental impact, it is imperative to conduct a comprehensive life cycle assessment (LCA). This paper examines three different types of sustainable concrete mixes, viz., alkali-activated concrete (AAC) with natural coarse aggregates, AAC with recycled coarse aggregates (RCA), and bacterial concrete (BC). A detailed environmental impact assessment of AAC with natural coarse aggregates, AAC with RCA, and BC is performed through a cradle-to-gate LCA using openLCA v.1.10.3 and compared versus PC concrete (PCC) of equivalent strength. The results show that transportation and sodium silicate in AAC mixes and PC in BC mixes contribute the most to the environmental impact. The global warming potential (GWP) of PCC is 1.4–2 times higher than other mixes. Bacterial concrete without nutrients had the lowest environmental impact of all the evaluated mixes on all damage categories, both at the midpoint (except GWP) and endpoint assessment levels. AAC and BC mixes are more expensive than PCC by 98.8–159.1% and 21.8–54.3%, respectively. Full article

This article presents the issues and needs for modern solutions in building urban infrastructure, based on the smart city idea to improve the living standards of residents. Particular attention is paid to one of the most important aspects of life, related to road safety of children as pedestrians and cyclists. Pedestrian sidewalks and bicycle paths with high pedestrian traffic are classified as dangerous areas in many countries. More than 3% of the injuries and fatalities among pedestrian road users that are victims of accidents occur due to crossing the road. Therefore, it is necessary to apply various technical infrastructure solutions to improve the safety of this group of inhabitants. The scientific purpose of this article is the assessment of the safety level of children in pedestrian and bicycle traffic and the analysis of road solutions supporting the maintenance of high-level city safety. The research was based on the analysis of statistical data of accidents and the diagnostic survey method determining the safety of the inhabitants of southern Poland. As a result, an analysis of the level of child safety in urban traffic was developed, as well as key factors affecting the levels of road safety, based on the opinions of respondents. Potential places with the greatest risk of collision with minors have also been identified. There are also proposals for infrastructure solutions aimed at minimising accident risk levels in designated areas. Full article

Cold In-place Recycling (CIR) has been widely used in the world since it is easy to apply it in the field at a low cost. However, it is not normally used as a surface layer as a result of its inconsistent quality due to an excessive amount of fine aggregates pulverized during the milling process. Hot In-place Recycling (HIR) can retain the original shape of the aggregates, but it often produces a large amount of Volatile Organic Compounds (VOCs). Therefore, a third in-place recycling technique is introduced in this paper: Warm In-place Recycling (WIR). The WIR technique overcomes the limitations of both CIR and HIR techniques by lowering a heating temperature while adding a Tetraethylenepentamine (TEPA)/Soybean/SBS additive. To identify the effect of the additive on the RTFO-aged binder, viscosity and dynamic modulus values were measured at different temperatures. Based on Hamburg Wheel Tracking (HWT) and Disc-Shaped Compact Tension (DCT) tests, the additive improved the moisture susceptibility and low temperature cracking resistance. The indirect infrared heating equipment reduced the emission by lowering the pavement surface heating temperature by 20 °C from 140 to 120 °C. Compared with the heating at 140 °C, the LPG usage for heating at 140 °C was lowered by 21%. The proposed WIR equipment with an additive would revolutionize the in-place recycling practices. Full article

Smart cities aim to integrate technological development with different functions/components such as mobility, management of energy, natural resources, water, and the waste cycle, air quality, land use, service network, construction, but also the economy, social participation, increased employment, and citizen safety. It includes a series of coordinated and integrated social, environmental and economic interventions to enhance human capital, reduce environmental impacts and solve ecological emergencies. The holistic approach is particular to smart cities, including several mobility aspects in the main European classifications. In particular, the development of smart cities depends on several factors related to transport supply (i.e., mobility service, infrastructure details, ICT) and demand (socio-demographic aspects), and the size of the city. This paper provides an overview of the development of smart cities by defining a methodology that allows the identification of criteria for determining the optimisation of urban mobility with a particular interest in the development of future autonomous mobility. The analysis of current literature on the concept of smart cities and new mobility technologies made it possible to analyse the compatibility between them and possible criticalities. The definition of criteria lays the groundwork for future research steps focused on the application of multicriteria analysis. Full article

In proof-loading of concrete slab bridges, advanced monitoring methods are required for identification of stop criteria. In this study, Two-Dimensional Digital Image Correlation (2D DIC) is investigated as one of the governing measurement methods for crack detection and evaluation. The investigations are deemed to provide valuable information about DIC capabilities under different environmental conditions and to evaluate the capabilities in relation to stop criterion verifications. Three Overturned T-beam (OT) Reinforced Concrete (RC) slabs are used for the assessment. Of these, two are in situ strips (0.55 × 3.6 × 9.0 m) cut from a full-scale OT-slab bridge with a span of 9 m and one is a downscaled slab tested under laboratory conditions (0.37 × 1.7 × 8.4 m). The 2D DIC results includes full-field plots, investigation of the time of crack detection and monitoring of crack widths. Grey-level transformation was used for the in situ tests to ensure sufficient readability and results comparable to the laboratory test. Crack initiation for the laboratory test (with speckle pattern) and in situ tests (plain concrete surface) were detected at intervals of approximately 0.1 mm to 0.3 mm and 0.2 mm to 0.3 mm, respectively. Consequently, the paper evaluates a more qualitative approach to DIC test results, where crack indications and crack detection can be used as a stop criterion. It was furthermore identified that crack initiation was reached at high load levels, implying the importance of a target load. Full article

Due to significant changes in Cairo’s streets today, young children may face difficulties finding opportunities to be safe and active. They can encounter low independent mobility, limiting their access to places in their neighborhoods, and can have poor access to their schools. This study aims to examine governmental primary school children’s access to schools in their neighborhoods after street modifications in Heliopolis, Cairo, seeking to evaluate the potential risks to child pedestrians. This will subsequently aid in developing a methodology for consistently and fairly evaluating hazards along the route to schools. A survey of six governmental primary schools in Heliopolis, Cairo, was conducted through interviews with children and their parents. Furthermore, a behavioral map of the local neighborhood was completed by children (7–12 years old) of six primary schools from the areas surrounding their schools in which the modifications took place. The results indicate that the most common ways of travelling to school, according to the questionnaire, are either by public transportation (30%) or by a small van/private bus (42%). More than half of the children expressed their wish to walk or cycle to school. The result also found that 69% of the children expressed anxiety about crossing streets. In conclusion, for some children, opportunities to be active in the local neighborhood may be limited due to the new modifications to the streets, resulting in limited independent mobility. To promote a sense of neighborhood safety and increase access to neighborhood public spaces, it is important to work with urban planners and local governments. Full article

Deteriorated concrete cover, e.g., spalling or delamination, especially when it occurs at the web of a reinforced concrete (RC) beam within the shear span, can reduce the shear capacity of the beam. Patching of this deteriorated area may be the best option to recover the shear capacity of the beam affected. For this purpose, unsaturated polyester resin mortar (UPR mortar) has been formulated. This research aims to investigate the efficacy of UPR mortar in limiting the shear cracking and so restoring the shear capacity of the deteriorated RC beam. The investigation is carried out by an experimental and numerical study. Two types of beams with a size of 150 × 250 × 1000 mm were prepared. The first type of beams was assigned as a normal beam. The other was a beam with a cut off in the non-stirrup shear span, which was eventually patched with UPR mortar. Two reinforcement ratios were assigned for each type of beams. The results show that UPR mortar is effective to hamper the propagation of diagonal cracks leading to increase the shear failure load by 15–20% compared to the reference (normal) beam. The increase of shear strength with the use of UPR mortar is consistently confirmed at various reinforcement ratios. Full article

This paper presents an experimental investigation into the effects of porosity, dry density and cement content on the unconfined compressive strength and modulus of elasticity of cement-bound soil mixtures. A clayey sand was used with two different proportions of type IV Portland cement, 10% and 14% of the dry mass of the soil. Specimens were moulded with the same water content but using four different compaction efforts, corresponding to four different dry densities. Unconfined compression testing was conducted at seven days of curing time on unsoaked samples. The results showed that the compressive strength increased with the increase in cement content and with the decrease in porosity. From the experimental data, a unique relationship was found between the unconfined compressive strength and the ratio of porosity to volumetric cement content for all the mixtures and compaction efforts tested. The equation developed demonstrates that it is possible to estimate the amount of cement and the dry density to achieve a certain level of unconfined compressive strength. A normalized general equation was also found to fit other authors’ results for similar soils mixed with cement. From this, a cement-bound soil model was proposed for the development of a mixing design procedure for different soils. Full article

The reduction in construction and maintenance costs per MW of renewable energy facilities, together with low interest rates, have led to a significant growth in the purchase prices paid for these facilities in the Spanish market. This trend is shared by other European countries, especially for projects that hedge energy price risk incorporating power purchase agreements with third parties. In this framework, questions arise about the economic rationale of the purchase prices paid for these projects. Consequently, we develop a project evaluation model that forecasts expected cash flow and time-varying required rates of return for a standard photovoltaic plant, in order to study the extent to which foreseeable market conditions—interest rates and equity risk premia, among others—translate into economically viable buyouts. Our results suggest that purchase prices paid for these initiatives often lead to buyer returns below those that would be reasonable according to market conditions. Indeed, we find that only facilities that reach a production 23% higher than the number of hours considered in the base case provide returns that compensate long-term financing costs. However, specialised investors can exploit their relatively low cost of financing to pay prices up to 73% higher than those affordable by classic investors. Full article

It is a universal fact that concrete is one of the most employed construction materials and hence its exigency is booming at a rocket pace, which in turn, has resulted in a titanic demand of ordinary Portland cement. Regrettably, the production of this essential binder of concrete is not merely found to consume restricted natural resources but also found to be associated with emission of carbon dioxide—a primary greenhouse gas (GHG) which is directly answerable to earth heating, resulting in the gigantic dilemma of global warming. Nowadays, in order to address all these impasses, researchers are attracted to innovative Geopolymer concrete technology. However, crack development of various sizes within the concrete is inevitable irrespective of its kind, mix design, etc., owing to external and internal factors viz., over-loading, exposure to severe environments, shrinkage, or error in design, etc., which need to be sealed otherwise these openings permits CO₂, water, fluids, chemicals, harmful gases, etc., to pass through reducing service life and ultimately causing the failure of concrete structures in the long term. That is why instant repairs of these cracks are essential, but manual mends are time-consuming and costly too. Hence, self-healing of cracks is desirable to ease their maintenances and repairs. Self-healing geopolymer concrete (SHGPC) is a revolutionary product extending the solution to all these predicaments. The present manuscript investigates the self-healing ability of geopolymer paste, geopolymer mortar, and geopolymer concrete—a slag-based fiber-reinforced and a variety of other composites that endow with multifunction have also been compared, keeping the constant ratio of water to the binder. Additionally, the feasibility of bacteria in a metakaolin-based geopolymer concrete for self-healing the cracks employing Bacteria-Sporosarcina pasteurii, producing Microbial Carbonate Precipitations (MCP), was taken into account with leakage and the healing process in a precipitation medium. Several self-healing mechanisms, assistances, applications, and challenges of every strategy are accentuated, compared with their impacts as a practicable solution of autogenously-healing mechanisms while active concretes are subjected to deterioration, corrosion, cracking, and degradation have also been reviewed systematically. Full article