Search

Highlights This study fabricated composite materials using waste concrete powder (WCP) and linear low‐density polyethylene via injection molding to improve the resource value of polymer composites of waste concrete. The flexural strength and modulus of the composite material improved with increasing WCP content and did not decrease even at a WCP content of 60 wt%. Moreover, the effect of the WCP particle size on the mechanical properties of the composite was low for composites with a WCP content of 20 wt%. To investigate the effect of the WCP particle size on the mechanical properties of the composite material in detail, the von Mises stress distribution of the composite material with a WCP content of 20 wt% was analyzed using finite element method (FEM). The von Mises stress distributions of the composite materials were almost identical across all WCP particle sizes. The results from the experiment and FEM analysis suggested that the interfacial adhesion between the WCP and LLDPE is in good condition. Therefore, it can be concluded that injection molding using WCP and LLDPE is feasible and WCP shows promise as a reinforcement particle. Fabrication of plastic composite material using the WCP by injection molding. The flexural strength and modulus increased by adding the WCP. The effect of the WCP particle size on the mechanical properties was low. The Mises stress were almost identical at each WCP particle size. The WCP is promising reinforcement of flexural strength and modulus. [ABSTRACT FROM AUTHOR]

To solve the problems on resource utilization and environmental pollution of waste concrete and waste polypropylene (PP) plastics, the recycling of them into asphalt pavement is a feasible approach. Considering the high melting temperature of waste PP, this study adopted a thermal-and-mechanochemical method to convert waste PP into high-performance warm-mix asphalt modifiers (PPMs) through the hybrid use of dicumyl peroxide (DCP), maleic anhydride (MAH), and epoxidized soybean oil (ESO) for preparing an asphalt mixture (RCAAM) containing recycled concrete aggregate (RCA). For the prepared RCAAM containing PPMs, the mixing temperature was about 30 °C lower than that of the hot-mix RCAAM containing untreated PP. Further, the high-temperature property, low-temperature crack resistance, moisture-induced damage resistance, and fatigue resistance of the RCAAM were characterized. The results indicated that the maximum flexural strain of the RCAAM increased by 7.8~21.4% after using PPMs, while the sectional fractures of the asphalt binder were reduced after damaging at low temperature. The use of ESO in PPMs can promote the cohesion enhancement of the asphalt binder and also improve the high-temperature deformation resistance and fatigue performance of the RCAAM. Notably, the warm-mix epoxidized PPMA mixture worked better close to the hot-mix untreated PPMA mixture, even after the mixing temperature was reduced by 30 °C. [ABSTRACT FROM AUTHOR]

A novel multipoint titration coprecipitation method was used to prepare concrete-based layered double hydroxide (CLDH) to uptake phosphorus into slow-release phosphate fertilizer. Both the characteristics and the slow release of CLDH-P were investigated. Results showed that the multipoint titration method was efficient for coprecipitation. P-loaded CLDH under weak acid conditions (CLDH-P1) contained mainly Al-P and Ca-P (CaHPO4·2H2O, DCPD), while the content of Ca-P greatly increased in the product under weak alkaline conditions (CLDH-P2). The slow-release effects of the two samples in soil leaching columns were significantly better than triple superphosphate (TSP). CLDH-P1 was preferably used for mung bean growth promotion due to its better availability. The dry weight of CLDH-P1 mung bean increased by 33% in 40 days, which was obviously better than that of the TSP group. In addition to phosphorus, the nutrient elements Ca and Mg were also enriched in mung bean plants. The results revealed an economical and sustainable candidate for phosphorus recovery. [ABSTRACT FROM AUTHOR]

In this study, the effect of using waste granodiorite powder (WGP) as a cement replacement material in percentages ranging from 1 to 9% on various physical and mechanical properties of ordinary concrete was investigated. The resistance of produced concretes with WGP to the high temperature effects on the 28 days compressive strength were studied as well. Granodiorite is one of the well-known igneous rocks that have been used in previous research as a replacement for coarse or fine aggregates due to the hardness of its grains. However, rare studies have investigated its powder as a partial cement replacement material. Results showed the ability of investigated WGP with high surface area to act as a supplementary cementitious material that contributed to enhance the results of mechanical and physical properties of concrete. At traditional room temperature, the optimal replacement percentage was 7%, where the 28 days compressive and tensile strengths were improved by 28.3% and 17.3%, respectively. The optimal replacement ratio varied between 7 and 9% in the case of high temperatures, according to exposure time and temperature degree. Statistical and sensitivity analysis was conducted on 66 available compressive strength value represents all variables before and after elevated temperature exposure. While the regression equation showed good R2 value of 85.3%, sensitivity analysis indicated that compressive strength value is most sensitive to temperature, followed by WGP ratio and exposure time, with importance values of 56, 26, and 18 %, respectively. Results showed also that the setting times and consistency was decreased with increasing the replacement ratio with WGP, while the workability was slightly improved up to 5% replacement ratio. Furthermore, microstructure analysis showed that WGP can help to densify the concrete matrix due to its small size and ability to fill the interstitial voids in the concrete matrix. [ABSTRACT FROM AUTHOR]

Microwave heating, which is used for pre-treatment of concrete before it is comminuted, stands as a strong candidate for selective liberation of multiphase materials like concrete. This paper is concerned with the selective liberation of concrete's raw constituents (particularly aggregate) for recycling by considering the water content of concrete as a parameter of microwave heating for the first time. The deterioration law of the concrete's performance was characterized by the variation in the splitting tensile strength and relative dynamic modulus after heating by microwave at different water contents. Besides, tests were conducted to evaluate the performance of the interface transition zone (ITZ) between aggregate and mortar as well as to investigate the reasons for the stripping behavior of aggregate-mortar, which included the interface tensile strength test, temperature measurement, and porosity test. The deterioration law of splitting tensile strength and relative dynamic modulus revealed that the performance of concrete was subject to different degrees of damage depending on the water content. Furthermore, experimental results showed that interface bonding strength between aggregate and mortar was dramatically impaired, and a large temperature difference was generated between the aggregate and mortar during microwave heating. Meanwhile, the permeable pores increased considerably even when the specimens were dried. In the presence of water, the intactness of ITZ between aggregate and mortar was destroyed by microwave heating, and its performance was significantly lowered, which led to the occurrence of stripping behavior between aggregate and mortar. This was reaffirmed by the microstructure presented by scanning electron microscopy. Thus, the newly developed microwave pre-treatment improved by providing appropriate water contents for concrete corresponding to different strength grades is a promising method for recycling aggregate from waste concrete.

In order to solve the problem of rapid loss of concrete workability caused by high adsorption of recycled sand, six kinds of recycled sands of C20 ~ C60 were used as objects. The pore structure characteristics of recycled sand were tested by mercury intrusion and low-temperature liquid nitrogen adsorption methods, and the physical composition of recycled sand was tested by X-ray diffraction (XRD). The adsorption law of recycled sand on water, methylene blue, and superplasticizer was explored. The results show that the water absorption rate of recycled sand decreases with the increase of strength grade of waste concrete materials, which is closely related to pore structure. The adsorption of recycled sand on methylene blue decreases with the decrease of clay mineral content, and there is no significant correlation with pore structure. The adsorption of recycled sand on superplasticizer is affected by both pore structure and clay mineral, but mainly depends on clay mineral content. [ABSTRACT FROM AUTHOR]

Copyright of New Building Materials / Xinxing Jianzhu Cailiao is the property of New Building Materials Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study investigated the applicability of siliceous waste concrete powder (WCP‐S) as a reinforcing particle in plastic composite materials for effectively utilizing waste concrete. WCP‐S was obtained by milling waste concrete. Two types of resin materials, polypropylene (PP) and polyethylene (PE), were used as the matrix of the composite material. Composite materials were fabricated via compression molding, and the effect of the WCP‐S content on the mechanical properties of the composite materials was investigated. The flexural strength of the PP‐based material decreased with increasing WCP‐S content, whereas the flexural modulus increased. This result suggests insufficient interfacial adhesion between the matrix resin and WCP‐S in the plastic region with high flexural load. To improve this interfacial adhesion, we investigated the mechanical properties of the PE‐based composite material. The flexural strength remained almost constant on increasing the WCP‐S content in the PE‐based composite material, whereas the flexural strength increased. Therefore, WCP‐S is a promising reinforcement particle with an improved flexural modulus for PP or PE resins. Highlights: Plastic composite material was fabricated using WCP‐S.The flexural strength of PP‐based composite material decreased.The flexural strength of PE‐based composite material remained almost constant.Flexural modulus increased the PP‐ and PE‐based composite material.WCP‐S is a promising reinforcement particle for PP/PE resins. [ABSTRACT FROM AUTHOR]

This study investigated the compression molding of hybrid composite materials using waste concrete powder (WCP) and bagasse fiber (BF) as a novel reuse procedure for waste concrete. The matrix of the composite material was applied to powder-type polyethylene (PE) to facilitate the compression molding of the gas vent. The WCP was obtained by milling siliceous waste concrete using a pot mill procedure. The main constituent of the WCP was quartz. The flexural strength and modulus of the hybrid composite material, in which BF was added to mix the powder with PE and WCP, increased with increasing BF content and exhibited a maximum value at a BF content of 30 wt. %. Next, to improve the mechanical properties of the hybrid composite material, we attempted to improve the adhesiveness between PE and BF by increasing the molding temperature. The mechanical properties of the hybrid composite material with a BF content of 40 wt. % exhibited the highest values at a molding temperature of 413 K. Furthermore, by increasing the WCP content in the hybrid composite material with a BF content of 40 wt. %, the flexural strength exhibited the maximum value at a WCP content of 20 wt. %. Therefore, it was revealed that the composite material using PE powder and WCP could be strengthened by adding BF.

Enhancing the sequestration capacity of waste concrete is crucial for achieving carbon neutrality within the construction industry. Although existing studies primarily focus on theoretical analysis of concrete carbon sequestration, limited attention has been paid to explore the potential of waste concrete sequestration during stockpiling phase under varying environmental conditions. To fill this knowledge gap, we developed a CO 2 uptake calculation model tailored for the stockpiling phase of waste concrete. This model investigates the impact of crush size, stacking method and environmental conditions on the total carbon sequestration capacity and efficiency, identifying the most advantageous approach. Our findings reveal the following: (1) Increasing the crush size of waste concrete enhances its carbon sequestration capacity, albeit extends the sequestration duration. A crush size of 5-20 mm is deemed optimal for achieving the desired sequestration efficiency. (2) The optimal stacking method involves smaller piles with reduced radii and angles. (3) High temperatures and humidity levels accelerate the sequestration rate. Practical measures such as watering and covering can be employed to enhance carbon sequestration. (4) In 2021, China's waste concrete exhibited a declining sequestration potential from the southeast to the northwest and northeast regions. The maximum sequestration potential has the capacity to neutralize up to 4% of the carbon emissions generated by the construction industry in that year. This research provides a foundation for accurate assessment and the development of effective carbon sequestration strategies for waste concrete., Competing Interests: Declaration of conflicting interestsThe authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Plant biomass has been widely used as an exogenous carbon source for constructed wetlands to increase nitrogen removal efficiency, but a convenient and efficient addition strategy is lacking. In this study, a new strategy was developed and tested in full-scale horizontal subsurface flow constructed wetlands, i.e., designing a decomposition zone in front of the constructed wetland, adding plant biomass directly to the decomposition zone, and re-adding the refractory parts to the decomposition zone after removal from the decomposition zone and treatment with alkaline leachate. Adding straw significantly increased the average total nitrogen removal efficiency from 36.0% to 44.9% without a significant increase in the chemical oxygen demand concentration. The refractory straw significantly increased the total nitrogen removal efficiency after it was removed, treated with alkaline leachate, and re-added to the system. Every 1 g of raw straw or refractory straw removed 0.088 g or 0.038 g of nitrate, respectively. The relative abundances of Bacillacea, Gemmatimonadaceae , Blastocatellaceae , and Caldilineaceae , which are associated with denitrification, increased after straw addition. The relative abundances of the functional groups of the bacterial community associated with organic matter degradation increased with straw addition, and the functional groups of the bacterial communities associated with nitrogen cycling were positively correlated with the nitrogen concentration. The strategy developed in this study is convenient and efficient for increasing the nitrogen removal efficiency by increasing plant biomass and can be applied in several scenarios. [Display omitted] • Plant biomass addition requires a decomposition zone in constructed wetlands. • Adding refractory straw after alkaline treatment boosts denitrification. • Every 1 g of wheat straw removed 0.099 g nitrate after two additions. • Straw increases the relative abundance of some denitrification bacteria. [ABSTRACT FROM AUTHOR]

Concrete has been a common building material widely used for decades to build the infrastructure. As a results, considerable amount of waste concrete is produced which is hazardous to the environment. At present, recycling waste concrete is limited to the aggregates for non-structural applications. The low reactivity of waste concrete powder (WCP) limits its use as a binder. Therefore, this study is conducted to enhance the reactivity of WCP to increase its viability as an alkali activated binder. The study was conducted in two phases. In Phase I, the WCP was thermally treated at temperatures ranging between 600 °C and 800 °C and the impact of this calcination on the physiochemical characteristics of thermally treated waste concrete powder (TWCP) was studied. The phase transformation after calcination was analyzed by observing the properties of WCP and TWCP using scanning electron microscope (SEM), X-ray diffractometer (XRD), Fourier transformed infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) techniques. The physical changes were also studied by comparing the density, specific surface area and particle size distribution in WCP and TWCP. It was found that the thermal treatment of WCP resulted in the decomposition of several phases along with a change in quartz structure. Also with temperature increase, the increase in density and particles fineness was observed, which was significant when thermal treatment was performed at 800 °C. The alkali activated WCP and TWCP was prepared to explore the microstructure and strength. The reactivity and strength of TWCP was superior to that of WCP. However, the highest strength obtained after alkali activation of TWCP was less than 10 MPa which is not optimal for a primary binder. Therefore, in Phase II of this study, the performance of TWCP in a binary cement-based mortar was explored by blending it with 0–50 wt% ground granulated blast furnace slag (GGBS) and the series of experiments including compressive strength, flexural strength and drying shrinkage was carried out to characterize the properties of composites. The superior strength and improved drying shrinkage obtained by mortars comprising TWCP-800 were due to the combination of filler effects and increased reactivity. No significant change in the properties of mortar containing 10 wt% TWCP-800 was observed. Study reveals that the thermal treatment of WCP at 800 °C is optimal and a sustainable approach to producing a supplementary binder for alkali activated materials. [ABSTRACT FROM AUTHOR]