To alleviate the heavy burden on landfilling, construction and demolition wastes (C&DWs) are recycled and reused as aggregates in cementitious materials. However, the inherent characteristics of recycled fine aggregates (RFA), such as the high crushing index and high-water absorption, magnify the reusing difficulty. Nevertheless, attributing to the high porosity and high level of calcium hydroxides existing in the old mortar, RFA is featured with a high specific surface area and a high alkalinity. These features are useful to augment the total photo-degradation of SO₂ by nano-TiO₂ (NT) intermixed mortar, leading RFA to be an excellent potential carrier to load nano-TiO₂ and prepare the composite photocatalyst. Hence, this study proposed to load NT onto the surface of RFAs and river sands (RSs) (the control) by the soaking method, preparing composite photocatalysts denoted as NT@RFA and NT@RS, respectively. The prepared composite photocatalysts were then utilized as sands in photocatalytic mortar to evaluate for SO₂ degradation. Experiments identified a 50% higher amount of NT was loaded onto the surface of FRA relative to the control. This higher loading amount plus higher alkalinity ultimately translated into a higher photocatalytic activity. In addition, the mortar containing NT@RFA exhibited 46.3% higher physiochemical absorption and 23.9% higher photocatalytic activity than that containing NT@RS. In addition, the durability, embodied by the reuse and anti-abrasive properties, of NT@RFA exceeded that of NT@RS. The overall findings reveal that the NT@RFA not only garners beneficial effect from the high porosity but also generates positive effect from the high alkalinity. Though a number of studies deal with building materials with NT, this study is the first to load NT onto RFA and prepare composite photocatalysts which were then used as fine aggregates in building materials. Consequently, this study proves the potential high-added-value reusability of RFA in green construction materials and provides a low-cost, high-efficiency approach to degrade atmospheric SO₂.

This research attempted to develop an environmentally-friendly functional building mortar by the combined use of agriculture wastes (agro-wastes) and construction wastes in magnesium oxychloride cement (MOC). The agro-wastes referred to corn stalk (CS) and saw dust (SD), which were used to improve the flexural properties of host cementitious material, whilst the construction wastes referred to recycled clay brick powder (CBP), which was employed to enhance compressive strength and water resistance. Moreover, tourmaline powder (TP) was added as a negative ion-inducing admixture, at a fixed dosage of 10% by weight of MgO, to bestow air-improving functions on the end products. Results showed the flexural strength of MOC was enhanced by the addition of CS and SD. Besides, the incorporation of CBP improved the water resistance in a dosage-dependent way. In addition, the specimens containing CS and SD also had better negative ion-inducing performance due to their higher porosity. Overall, the study provided a feasible and attractive approach to recycle agro- and construction wastes for the production of air purifying mortar. The developed mortar possesses an eco-friendly nature (simultaneous reuse of various waste materials and improvement of the air quality).

The increasing excavated soil from construction projects has become a big problem in the sustainable development of megacities worldwide. Even though excavated soil management concerns are receiving increased attention, low rates of excavated soil recycling remain a barrier to the continuous improvement of the construction industry. Nowadays, Building Information Modeling (BIM) technology has gained popularity for construction and demolition (C&D) waste management purposes. However, few studies and cases of recycling excavated soil using BIM technology have been found. This paper gives a BIM-GIS-IoT-based excavated soil recycling system to effectively integrate BIM and Internet of Things (IoT) technologies into a geographic information system (GIS) to achieve scientific and reasonable recycling for excavated soil. The system mentioned above could collaboratively manage information from the government, developers, construction enterprises, transportation companies, and recycling facilities to meet the requirement for the specific communication, analysis, decision-making, and recycling plan preparation of the excavation project. In addition, it provides a systematic method and applies relevant information technology required to recycle the excavated soil effectively in the excavation project. The system is intended to provide a fundamental digital construction model for excavated soil recycling, regardless of whether it is invoked by the existing application software or a program tailored to the demands of a specific organization or stakeholders. It makes excellent use of the rich information stored in digital information models, may create a mapping to the input data required by the application, or automatically convert the basic model to facilitate the specific analysis. This system can not only serve as an excavation project simulation tool before construction, but also serve as a tool to recycle the excavated soil and cost evaluation. The developed model is applied via case studies within an excavation project. Different plans are described and compared in detail in several aspects of the schedule, revenue, and contract, finding that actual benefits will differ depending on the project’s limiting conditions. The result indicates ample opportunity for the advantages of the BIM-GIS-IoT-based excavated soil recycling system in the excavation project.

Recycled aggregates have high water absorption and crushing index. In order to improve the properties of recycled aggregates in concrete production, various treatments were used to modify the aggregates. In recent years, bio-deposition as a new treatment method of recycled aggregates was environmentally friendly. An improved method of bio-deposition was implemented to modify the properties of recycled mortar aggregates (RMA). O-bio-deposition is based on aerobic bacteria induced CaCO₃ precipitation by respiration by varying the distance between the RMA and the bottom of the container and by adding an oxygen release compound to the culture solution that contains bacteria to promote the induction of CaCO₃. First, the physical properties, including water absorption, crushing value, and apparent density, of the coarse RMA under different treatment methods were determined, and an o-bio-deposition treatment method was obtained. The fine RMA was treated and compared with the untreated RMA. Concretes were then prepared from the treated coarse RMA, and compressive strength and slump were determined. In addition, the effect of the o-bio-deposition treatment on the RMA surface and the micro-cracks of concretes were observed by scanning electron microscopy (SEM). It was found that the water absorption and crushing index of the coarse RMA treated by o-bio-deposition were reduced by 40.38 and 19.76% compared with untreated RMA, respectively. Regarding the concrete, the slump and the compressive strength (28 d) of concrete were increased by 115% and 25.3%, respectively compared with the untreated concrete.

The existing recycling chain of construction and demolition waste generally considers soil inert solid waste to be sent to landfills. As the most significant component of C&D (construction and demolition) waste, excavated soil occupies approximately half of landfills. Currently, excavated soil is a big issue in China’s Pearl River Delta. This paper investigated the composition and quantity of excavated soil in Shenzhen, China. In particular, the potential market demand for critical recycled sand (a key recycled material extracted from the excavated soil) was estimated. Furthermore, the technical analysis for excavated soil recycling takes an entire excavated soil recycling process’s perspective, delving into the process flow for the excavated soil and the recycled sand’s physicomechanical properties. Then, two mainstream and legitimate models of excavated soil recycling were considered: stationary plant recycling and on-site recycling. Each model’s financial and economic viability was assessed. The financial analysis focuses on investors’ perspectives, whose primary goal is to assess their investment profitability. The economic feasibility of the excavated soil stationary plant recycling and on-site recycling models in Shenzhen were then compared via benefit and cost analysis during the lifetime of the recycling equipment. A comprehensive, complete cost calculation and investment analysis revealed that Shenzhen’s excavated soil recycling business is profitable under the current market conditions. This study investigates scaled and effective excavated soil recycling and gives a technically and economically viable reference to the global excavated soil issue.

The incorporation of circulating fluidized bed (CFB) fly ash into self-leveling cement-based (SLC) paste production presents significant environmental advantages. However, its addition deteriorates the fresh properties of the paste, posing challenges for practical implementation. This research examined the fresh properties of SLC paste blended with CFB fly ash, emphasizing fluidity, rheological characteristics, and bleeding rate. To enhance flowability, polycarboxylate superplasticizer (PCE) was incorporated, with particular emphasis on its interaction with CFB fly ash. The findings reveal that adding CFB fly ash to cement-based paste significantly decreased fluidity while increasing yield stress and plastic viscosity. Incorporating 20 wt.% CFB fly ash reduced paste fluidity by 51.4%, while plastic viscosity and yield stress increased by factors of 2.3 and 73, respectively. While PCE enhanced the fluidity of the blended paste, its water-reducing efficiency diminished, and the bleeding rate of the paste increased with higher CFB fly ash dosage. The water-reducing capability of PCE in the CFB fly ash-blended cement paste with 20 wt.% CFB fly ash decreased by 40.0%, and the bleeding rate of the paste increased from 0.6% to 6.7%. This effect was primarily attributed to the poor compatibility between PCE and CFB fly ash. The decline in PCE efficiency with higher CFB fly ash content, along with its lower adsorption capacity on CFB fly ash compared to cement particles, further confirmed this incompatibility.