Hongzhu Quan

The recycling of construction waste and the use of a new sintering process in the field of sintered bricks can greatly solve the problems of clay resource depletion, soil structure destruction, and high CO₂ emissions that always limit the development of the sintered brick field. The study was carried out using an orthogonal experiment to derive the optimal mix ratio for the preparation of sintered bricks, and subsequently, the sintered bricks were prepared using the optimal mix ratio. The experimental results show that the maximum compressive strength of construction waste sintered brick (MRB sintered brick) prepared using high-temperature sintering is 8.1 MPa, and the water absorption is 11. When the waste glass slag is mixed with 10%, it can show a better fluxing effect in the preparation of sintered bricks by mixing construction waste with waste glass slag (MGB sintered bricks), so that the MGB sintered bricks have a higher densification. The compressive strength is 32.9% higher and the water absorption is 3.5% lower than that of MRB sintered brick. MGS sintered bricks were prepared by mixing Yellow River sedimentary sand into MGB sintered bricks. The strength of MGS sintered bricks increased with the replacement rate of Yellow River sedimentary sand, and when the replacement rate of Yellow River sedimentary sand reached 16%, the strength of the MGS sintered bricks increased by 88.9%, and the water absorption rate was reduced by 4.6% compared with the MGB sintered bricks. The sintering mechanism had significant effects on the compressive strength, weathering resistance, and frost resistance of the sintered brick. The microwave sintering process has the characteristics of high efficiency, uniform heating, selective heating, and low thermal inertia, which can increase the compressive strength of MGS sintered brick by 4.6%, reduce the water absorption by 12.9%, shorten the sintering time by 43.6%, and improve the frost resistance.

The use of planting concrete (PC) is one of the most prevalent slope protection methods. However, PC offers poor plant growth properties and poor ecological performance due to its high alkalinity. Therefore, in this study we used an orthogonal experimental design to optimize the mix design, and we used three alkali reduction treatments to reduce alkalinity and improve plant growth properties. The compressive strength, interconnected porosity, and pH values were analyzed to obtain the optimal level. Subsequently, the plant growth property test was conducted both indoors and outdoors. Stem length was used to evaluate different plants, which were grown in both natural soil (NS) and construction waste (CW). The experiment results show that the paste–aggregate ratio (PR) has the greatest impact on the above properties and that the optimum levels for PR, water–binder ratio (W/B), and fly ash addition level (FA) are 1/5, 0.29, and 10%, respectively. Additionally, the compound alkali reduction treatments, which combined the use of 0.4% ferrous sulfate in the planting substance and 3% potassium dihydrogen phosphate in the soaking solution, were effective. Furthermore, tall fescue may have potential applications in combination with CW. In conclusion, PC that has undergone alkali reduction treatments shows potential for application in slope protection, and thus may help to improve sustainability.

Poor biological attachment of artificial reef (AR) prepared by the recycled aggregate limit the application in the area of marine engineering. In this study, the waste oyster shell (WOS) was used as raw materials to prepare the recycled aggregate porous concrete (RAPC), the compressive strength, split tensile strength, chloride penetration resistance, freezing-thawing resistance, low temperature resistance, and the biological attachment were tested, aiming to improve the biological attachment and decrease carbon dioxide emission. The experiment results demonstrate that the use of WOS can decrease the compressive and split tensile strength, but the effect of designed porous structure on the mechanical strength is higher than that of WOS. To ensure the durability of RAPC, the contents of WOS should not exceed 20%. Additionally, the addition of WOS and designed porous structure are beneficial to biological attachment. However, the porous structure of RAPC only improves biological attachment in the short term, and the reverse phenomenon is true in the long term. As the partial replacement of cement with WOS is 40%, the total carbon dioxide emission decreases by about 52%. In conclusion, the use of WOS in the RAPC is an eco-friendly method in the artificial reef (AR) with improved ecological attachment and reduced carbon dioxide emission.

Energy efficiency is one of the important indicators for the evaluation of green buildings, and it is also related to the sustainable development of the building industry and energy conservation. Using agricultural waste in concrete to produce biomass recycled aggregates can effectively utilize agricultural solid waste to develop new wall materials with economic and energy-efficient properties. In this study, industrial wastes such as ground, granulated blast-furnace slag (GGBS) and fly ash (FA) were used to replace cement as cementitious material and coconut shell (CC) as lightweight coarse aggregate (LWA) in lightweight concrete. The lightweight coconut shell aggregate concrete with a density of less than 1950 kg/m³ was used as structural concrete. The thermal conductivity of synthesized biomass recycled aggregate concrete (SBRAC) was about 0.47 W/mK, which is 217% and 19% lower than that of natural aggregate concrete (NAC) and crushed coconut shell aggregate concrete (CCSAC), respectively. With the same volume, the costs of SBRAC and CCSAC are 25.1% and 4.9% lower than that of NAC, respectively.

As the first batch of products after the resource utilization of construction and demolition waste, low-grade recycled aggregate (RA) has not been fully utilized, which hinders the development of the comprehensive recycling industry of construction waste. Therefore, this paper studies the mechanical properties of porous concrete (POC) with low-grade RA. An improved relationship between porosity and compressive strength of brittle, porous materials is used to express the compressive strength of POC with recycled aggregate (RPOC), and the prediction for compressive strength of porous concrete with low-grade RA is constructed by analyzing the mechanism of compressive damage. The results show: the compressive strength of porous concrete decreases with the addition of low-grade recycled aggregate, but the effect is not obvious when the replacement rate is less than 25%. The error range of the relationship between porosity and compressive strength of RPOC is basically within 15% after improvement. The prediction model for compressive strength based on the ideal sphere model of aggregate can accurately reflect the compressive strength of porous concrete with low-grade RA. The results of this study can provide a reference for the staff to learn about the functional characteristics of recycled products in advance and provide security for the actual project.

In order to better understand the performance of eco-concrete, this experiment selected three kinds of waterbinder ratio and 4 kinds of aggregates to prepare eco-concrete, and studied the prediction formula of its compressive strength. The results showed that when the aggregate size is fixed, the compressive strength of eco-concrete decreases with the increase of porosity and the decline of cementitious paste strength; the connectivity porosity of eco-concrete is generally about 5% lower than the total porosity, so the total porosity is more suitable to express the strength formula of eco-concrete. The coefficient in the eco-concrete strength formula are mainly affected by the strength of the cementitious paste and the aggregate size. When the target porosity is fixed, the larger the aggregate size, the higher the compressive strength of eco-concrete. When the workability of cementitious paste is constant, the actual porosity of eco-concrete can be expressed by target porosity and paste strength, and the strength prediction formula of eco-concrete expressed by paste strength, aggregate particle size and target porosity shows a good applicability, and has certain reference significance for the practical engineering application of eco-concrete in the future.

At present, not many studies have considered methods to quantitatively evaluate the reaction efficiency of granulated blast furnace slag (GBFS) at different curing temperatures. For high volume slag concrete, when the replacement ratio exceeds a certain ’threshold’ value, the superfluous and ineffective slag will no longer react in concrete but simply behave as a fine aggregate, which may cause the decrement of strength. The ’threshold’ value depends on the reaction efficiency of slag. In this study, experiments on mortars with different replacement ratios by slag were conducted at different curing temperatures (20, 30, and 50 °C, respectively), the threshold values of effective replacement ratio by slag were comprehensively analyzed through the reaction efficiency of slag mortar. The results showed that the turning point of the strength curve with replacement ratio can be considered as the threshold value of the effective replacement ratio by slag in mortar. Along with the curing temperature enhancement, the threshold value of the effective replacement ratio by slag in concrete decreased, whereas the reaction efficiency of slag increased. Meanwhile, the analysis of cement effective coefficient (k value) and basicity was also calculated. Based on the obtained threshold values of effective replacement ratio at different curing temperatures, the formula for the determination of reaction efficiency coefficient of slag in the mortar can be established. Therefore, the reaction efficiency coefficient and upper limit of the effective replacement ratio of slag at different temperatures can be calculated more intuitively and quantitatively, providing a theoretical basis and reference for practical engineering applications.