Concrete Waste Research Articles

Poly(allyl alcohol-co-vinyl acetate)-grafted concrete waste for adsorptive removal of As(III)

This study focused on the synthesis of concrete waste grafted with a polymer of allyl alcohol and vinyl acetate as a novel nano adsorbent and the investigation of its ability in the adsorptive removal of Arsenic (As(III)) from aqueous solutions. The prepared nano adsorbent was characterized using X-ray diffraction, thermogravimetric analysis, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. Various parameters were optimized by response surface methodology and central composite design model to achieve the highest As(III) removal efficiency, including the solution's temperature, contact time, and pH. The model predicted a maximum removal efficiency of 92 % under the optimal conditions (temperature = 25 °C, contact time = 24 min, and pH = 7), resulting in a sorption capacity of 6.81 mg g−1. The zero point of charge for the nano adsorbent was obtained at about 6.5. The experimental data for As(III) sorption onto the nano adsorbent was well-fitted by the Freundlich isotherm and pseudo-1st-order kinetic models. This suggests that the adsorption process involves the formation of a multilayer of As(III) on the adsorbent surface, and it occurs through physical interactions rather than chemical reactions. The reusability of the nano adsorbent was evaluated, demonstrating a removal efficiency exceeding 72 % even after seven recycling cycles. The presence of interfering cations influenced the removal efficiency in the following order: Pb2+>Mn2+>Cu2+>Zn2+>Ni2+. The prepared nano adsorbent showed significant efficiency in removing As(III) from well water and river water samples, with a repeatability range of 1.09–2.51 %.

Assessing environmental impacts of utilizing recycled concrete waste from the technosphere: a case study of a cement industry in West Java, Indonesia

Assessing environmental impacts of utilizing recycled concrete waste from the technosphere: a case study of a cement industry in West Java, Indonesia

Influence of Recycled Coarse Aggregate and Steel Fiber on the Workability and Strength of Self-Compacting Concrete

Abstract Waste materials pose a significant threat to both the environment and human health. On a global scale, the quantity of recyclable material is steadily growing, and its proper disposal is a significant focus of modern study. Concrete debris is a recyclable material that poses challenges for reutilization. Concrete waste refers to the fragments or remains of ready-mix concrete plants and the debris from destroyed structures, including historic buildings and those affected by earthquakes. The objective of this study is to reuse and utilize coarse aggregate formerly used in concrete constructions to create self-compacting concrete (SCC). The purpose is to assess the performance of this recycled aggregate in both its fresh and hardened states. Natural coarse aggregate (NCA) was switched out for recycled coarse aggregate (RCA) at 0, 50, and 100% volume ratios. In contrast, concrete was mixed with steel fibers (SF) at volume percentages of 0 and 0.44. Workability tests, including V-funnel, slump flow, and L-box tests, were conducted to assess the consistency of the mixes in their fresh condition. Additionally, the tensile and compressive strength of the concrete specimens were measured to evaluate their strength in the hardened state. Overall, the experimental findings showed that the fresh qualities of almost all SCC mixes fell within the required range, as outlined in the EFNARC standards. While the steel fiber harmed the fresh characteristics, it resulted in a proportionate enhancement in tensile strength. The findings indicated that including recycled aggregates into the concrete mixture enhanced its strength. The results showed that adding (0.44%) of steel fibers to concrete reduced the decline in compressive strength when the coarse aggregate was replaced entirely with recycled aggregate. In contrast, an equivalent proportion of fibers resulted in a significant improvement in tensile strength, rising from 26% to 54%, when using recycled coarse aggregate as the replacement of natural coarse aggregate. Thus, it can be concluded that using recycled aggregates and steel fibers in concrete production results in a higher quality product than regular concrete. Removing concrete waste has other benefits, such as enhanced financial return and preservation of the environment.

Effect of curing conditions on cement based self-compacting mortar produced with mortar waste aggregate

Concrete and mortar wastes, which have a large volume and economic value among construction demolition wastes, are the most targeted demolition waste group to be recycled. An important area where construction demolition waste can be utilized is self-compacting mortar (SCM) systems. SCMs are innovative and economical systems designed to minimize the labor requirements that are difficult to meet in the production process. In this study, mortar waste aggregate (MWA) obtained by mechanical crushing and grinding was used in SCM elements by substituting different ratios (5-10-20-30-40 %) by mass to aggregate. In this way, it was aimed to evaluate both the sustainability of MWAs and the usability of MWAs in SCMs, which are considered as a new production technology. The fresh and hardened mortar tests performed in the study are presented comparatively. The physical (dry unit volume weight, porosity), durability (capillary water absorption) and mechanical properties (flexural tensile, compressive strength) of the hardened SCM elements are based on the determinations made at 3, 7 and 28 test days and according to different curing conditions (water curing, air curing and heat curing).In addition, X-ray Diffractometer (XRD) analysis was performed on specimens obtained from 0 %, 10 %, 20 % and 40 % MWA substituted specimens after heat curing (after 7 days water curing) and 28 days water curing. In the light of the data obtained, it is reported that SCM production with 10 % MWA substitution is feasible in terms of sustainability and engineering properties evaluated in this study.

Effect of silica fume on the microstructural and mechanical properties of concrete made with 100% recycled aggregates

Recycled concrete aggregate can be utilized in structural concrete in order to reduce the use of natural resources and the harmful impacts of waste concrete on the environment. This present research aimed to assess the effectiveness of using recycled aggregate concrete with the partial replacement of cement by silica fume (SF) to analyze the microstructural and mechanical properties of recycled aggregate concrete (RAC). In this study, recycled stone was used as coarse aggregate. The main variables of the study included the dosage of silica fume that was employed as a partial replacement of ordinary Portland cement (OPC) with four different percentages: 4%, 8%, 12%, and 16% by weight. Five different mixes were prepared, with four mixes created by varying amounts of silica fume, which were designated as RSACSF4, RSACSF8, RSACSF12, and RSACSF16. The other mix was created as a reference mix without silica fume and designated RSACSF0. Slump test was conducted to investigate the workability of concrete mixes. From the test result, a decreasing trend was found after adding more percentage of SF. Compressive and splitting tensile tests were conducted to analyze the mechanical properties of RSAC at 7 and 28 days. The results showed that the addition of SF improved the performance of RSAC at early and later curing ages, and a 12% addition of SF showed the best result. Scanning electron microscopy and X-ray diffraction analysis were performed to explore SF's microstructural performance and effect on RSAC. The results showed that silica fume showed a positive pozzolanic impact, and when combined with calcium hydroxide, it underwent a secondary hydration reaction that boosted the generation of calcium silicate hydrate and improved the parameters of the interface transition zone. X-ray diffraction analysis showed that silica fume and silica fume have similar pattern intensities. Finally, 12% SF is recommended as a partial replacement for cement in RSAC.

Improving geopolymer concrete performance with hazardous solid waste phosphogypsum

Recycling the hazardous solid waste phosphogypsum (PG) in concrete is a popular trend. However, the inherent properties of PG used alone in concrete tend to limit the strength of the concrete. In this study, PG was used as a precursor for the production of phosphogypsum-based geopolymer concrete (PGC), which effectively improved the performance of geopolymer concrete by utilising the synergistic effect of different solid wastes in geopolymer concrete. The effects of PG content (0, 10, and 20 %) and alkali modulus (0.8, 0.95, 1.1, and 1.25) on the axial compressive properties and resistance to chloride penetration of PGC were investigated. The results show that 10 % PG improved the properties of geopolymer concrete the most, with a maximum increase in axial compressive strength of 17 %. Due to the addition of SO42−, the PG content also affected the optimal alkaline modulus of PGCs. Chemical composition and microstructural analyses revealed that the promotion of the geopolymer reaction by PG is crucial for PGC performance enhancement. In addition, leaching tests and carbon emission assessment, confirmed that PGCs are an environmentally friendly option. Based on the analysis of axial compression behaviour, resistance to chloride ion permeability and environmental impact, PGC with 10 % PG content and 1.1 alkali modulus is an environmentally friendly alternative to conventional concrete. This study shows that hazardous solid waste PG can improve the performance of geopolymer concrete and create a new type of solid waste concrete.

Experimental study on impact performance of seawater sea-sand concrete with recycled aggregates

On islands distant from the mainland, obtaining raw materials for concrete production is often more challenging. To achieve sustainable development in island reef engineering, using discarded marine concrete and coral waste generated during island construction as recycled aggregates are of considerable significance. The preparation of Recycled Coral Aggregate Concrete (RCAC) for island reef engineering thus holds substantial importance. In this study, RCAC and Natural Aggregate Concrete (NAC), both designed with a compressive strength of C60, were prepared. Initially, the fundamental physical properties of the recycled coarse aggregate, such as apparent density, water absorption, and crushing index, were determined. Subsequently, a comparative analysis of the quasi-static mechanical properties of RCAC with varying proportions of recycled coral coarse aggregate (RCCA) was conducted. Furthermore, the impact compression mechanical properties of different RCAC specimens under various strain rates were examined using the Ф100mm Split Hopkinson Pressure Bar (SHPB) apparatus. The microstructure and long-term drying shrinkage performance of RCAC were also analyzed using Scanning Electron Microscopy (SEM) and a drying shrinkage apparatus. The finding indicated that the 28-day compressive strength of RCAC specimens with 100% coarse aggregate replacement reached a maximum of 62.4 MPa. The quasi-static compressive strength of RCAC specimens with 50% and 100% RCCA replacement was only 11.5% and 14.2% lower than that of NAC, respectively. Under impact loading, the dynamic compressive strength of RCAC specimens increased with the strain rate, with peak stress exhibiting an approximately linear relationship with the strain rate. The energy dissipation of RCAC specimens generally occurred in three stages, with the reflected and absorbed energies of the specimens increasing linearly with strain rate. At the same strain rate, the transmitted energy of RCAC specimens was higher than that of NAC specimens. Microstructural analysis revealed that the morphology of recycled coral aggregate is characterized by its porous and rough surface. The interfacial transition zone between the recycled coral aggregate and the cement mortar was relatively dense. Incorporating recycled coarse aggregate significantly affected the drying shrinkage properties of the concrete, with higher contents of RCCA leading to greater drying shrinkage rates.

Structural implementation of recycled lump prepared from waste concrete after elevated temperatures: Mechanical and environmental performances

To find a sustainable treatment for construction and demolition waste, the utilization of recycled lump (RL) prepared from waste concrete after elevated temperatures as coarse aggregate in concrete was investigated. The mechanical and environmental properties of recycled lump concrete (RLC) and reinforced recycled lump concrete (RRLC) were discussed with three RL replacement ratios and five treatment temperatures. The results show that increasing the RL replacement ratio would reduce the slump, and axial compressive performance of RLC, resulting from the presence of old adhered mortar on RL. The treatment of elevated temperature for RLC would improve the adverse effect of increasing the RL replacement ratio, resulting from the decreasing amount of old adhered mortar and interfacial transition zone on RL. The prediction formulas for the mechanical model of RLC were proposed while the design method for the axial compressive strength for RRLC was modified against the existing standard to conduct the full-range parametric analysis. The environment assessment indicates that the sustainable utilization of RL as coarse aggregate could reduce the environmental impact and global warming from concrete production whilst the RL prepared from waste concrete after 400 °C treatment is an appreciated option for the production of RLC and RRLC products from a mechanical and environmental perspective. In addition, the increase in external diameter would remarkably dwindle the environmental impact caused by the utilization of RL in structural members.

Alkalinity control in sludge propels the conversion of concrete slurry waste into micro- and nano-sized biogenic CaCO3.

The utilization of Bacillus sp. for the production of bio-CaCO3 in concrete crack repair and strength enhancement has attracted considerable attention. However, microbial-induced calcium carbonate precipitation (MICP) has yet to be explored as a precedent with activated sludge. Here calcium sourced from concrete slurry waste (CSW) and carbon from sludge microbial β-oxidation under alkaline were used to generate micro/nano CaCO3. The results indicate that the main crystalline form of the generated precipitated particles is calcite, with a particle size ranging from 0.7 to 10 μm. Minimal heavy metals were found in the supernatant following settling. And at the optimum pH of 8.5-9, carbon capture reached 743 mg L-1, and CaCO3 production reached 1,191 mg L-1, and dominant phylum were Proteobacteria and Bacteroidota, with Thauera being a prevalent genus adept in β-oxidation. Mass balance analysis showed that alkali promotes microbial β-oxidation of organisms to produce CO2 and facilitate storage. Thus, the alkaline regulation of metabolism between microbe and CSW provides a novel way of sludge to initiate MICP.

Multi response optimization of recycled aggregate based alkali-activated concrete using Taguchi-Grey Relational Analysis Method

The use of cement in construction causes large amounts of CO2 emissions into the atmosphere. Moreover, the use of large amounts of natural coarse aggregate causes environmental damage, and the availability of such natural aggregate is also depleting. The present experimental study explores and optimizes the impact of various parameters on the fresh, mechanical, and durability properties of recycled waste concrete coarse aggregate (RWCA)-based geopolymer concrete (GPC) in combination with ground-granulated blast furnace slag (GGBFS) and fly ash (FA) using the Taguchi-Grey Relational Analysis Method (TGRAM). The coarse aggregates in GPC were fully replaced with RWCA produced by crushing waste concrete. The effects of FA inclusion (%), Na2SiO3/NaOH ratio (SS/SH), molarity of NaOH (SH), dosages of superplasticizer (%), and alkaline solution to binder (Al/Bi) ratio are investigated under ambient curing conditions. The obtained maximum compressive strength and split tensile strength along with minimum water absorption of GPC at 28 days were 67.90 MPa, 3.85 MPa and 2.92 % respectively. The microstructural studies of GPC having low, high, and optimal strength are carried out using XRD, FE-SEM, and EDAX analysis. These studies confirmed the presence of calcium-based hydration products such as CSH and N(C)ASH, which makes the matrix of optimized GPC more compact.

Elucidating the role of recycled concrete powder in low-carbon ultra-high performance concrete (UHPC): Multi-performance evaluation

Reusing recycled powder as an alternative binder for ultra-high performance concrete (UHPC) offers a highly value-added approach to recycling concrete waste. This study shows the multi-performance evaluation of low-carbon UHPC containing recycled powder as a substitution of cement and silica fume. Recycled powder, which includes recycled concrete powder (RCP) and recycled paste powder (RPP), contains massive SiO2, CaCO3 and hydration products. Substituting recycled powder for cement reduces the cumulative hydration heat per gram binder, while increasing the cumulative hydration heat per gram cement of UHPC. Replacing high-volume cement and silica fume with recycled powder negatively impacts the micro-characteristics, increasing the drying shrinkage and transport properties. When using recycled powder as cement replacement, incorporating a moderate dosage of recycled powder has negligible impact and can even confer some beneficial effects on the mechanical strength. Substituting recycled powder for high-volume cement reduces the mechanical strength, yet the blended UHPC retains good mechanical strength. The compressive strength of UHPC containing RCP as 0 %, 30 %, 50 % and 70 % of cement is 157.6 MPa, 154.6 MPa, 145.0 MPa and 129.9 MPa, respectively. Due to its good dilution and active effects, the replacement of cement with recycled powder causes a significant increase in compressive strength per unit cement, and the mix of 70 % RCP increases the compressive strength per unit cement by 174.7 %. Besides, incorporating recycled powder as silica fume replacement causes a limited reduction in the mechanical strength of blended UHPC. The RCP-UHPC generally has better micro-macro properties than the RPP-UHPC. By optimizing recycled powder type and replacement rate, UHPC with excellent micro-macro performance can be achieved.

Physico-Mechanical Characterization of Masonry Mortars for Sustainable Construction: Experimental Study with Four Different Aggregates

The construction sector generates a strong environmental impact every year as a result of the high consumption of raw materials and the large waste volumes associated with this productive activity. In this sense, the search for alternative and sustainable solutions that allow progress towards responsible economic growth has become a priority activity. This work presents an exhaustive characterisation of masonry mortars made with four different types of aggregates: standard sand, natural sand, concrete waste recycled sand and ceramic components recovered sand. Differently from other studies, this research addresses the previous characterisation of the aggregates as raw material for the manufacture of masonry mortars, and, afterwards, a study of the most relevant properties for these cement composites in the fresh and hardened state is carried out. The most relevant properties of the mortars made with these raw materials are presented, and the repercussion of aggregate washing on their physical-mechanical characteristics is analysed. The results show how mortars made with 100% recycled aggregate can be competitive in the industry, presenting excellent properties in the fresh state and achieving an optimal mechanical strength. In addition, it has been observed that the introduction of a previous washing step of the aggregates improves their physical-mechanical properties and results in a higher quality of the cement mortars finally produced. In this way, the most representative properties of this type of materials have been collected in a well-structured and complete way, thus showing their possibilities of application in the construction industry.

CO2-Accelerated Carbonation Modification for Recycled Coarse Aggregate with Various Original Concrete Strengths and Coarse Aggregate Sizes.

The increasing demand for concrete reduces natural resources, such as sand and gravel, and also leads to a sharp increase in the amount of waste concrete produced. Due to the fact that the physical and mechanical properties of waste concrete made of recycled aggregates (RAs) differ greatly, it is difficult to use directly as a raw material for reinforced concrete (RC) components, which greatly restricts the popularization and application of RAs in actual projects. Utilizing the alkali aggregate properties of RAs to capture CO2 from industrial waste gases is an innovative way of enhancing their properties and promoting their application in real projects. However, the extent of the influence of original concrete strength (OCS) and coarse aggregate size (CAS) on the accelerated carbonation modification of RA is not clear, and a quantitative description is still required. For this purpose, accelerated carbonation tests on recycled coarse aggregate (RCA) samples under completely dry condition were carried out, and the variation laws for the physical property indicators of RCA samples before and after accelerated carbonation versus the OCS and CAS were revealed. Moreover, the influence degrees of the two factors, OCS and CAS, on the property enhancement of RCAs after accelerated carbonation were clarified, and the results of OCS and CAS corresponding to the best accelerated carbonation effects of RCAs were determined. By analyzing the micromorphology of RCA before and after accelerated carbonation, the reasons for property enhancement of RCAs with various OCSs and CASs under the best carbonation modifications were clarified. The findings will contribute to the development of basic theoretical research on accelerated carbonation modification of RA and have important scientific value.

Effect of Recycled Concrete Aggregate Utilization Ratio on Thermal Properties of Self-Cleaning Lightweight Concrete Facades

In today’s environment, where energy is desired to be used more efficiently, it has been understood that the interest in the use of lightweight concrete with superior performance in terms of thermal insulation properties has increased. On the other hand, it has been stated that construction waste increases rapidly, especially after severe earthquakes. In this context, encouraging the use of recycled concrete waste and efficient disposal of construction and demolition waste is of great importance for the European Green Deal. It is also known that pollutants such as COx and NOx stick to facades over time, causing environmental pollution and visual deterioration. It has been reported that materials with photocatalytic properties are used in lightweight concrete facade elements to prevent such problems. This study examines the effect of using recycled concrete aggregates on the thermal properties of self-cleaning lightweight concrete mixtures (SCLWC). For this purpose, an SCLWC containing 1% TiO2 and 100% pumice aggregate was prepared. By replacing pumice aggregate with recycled concrete aggregate at the rates of 15%, 25%, 35%, 45% and 50%, four different SCLWCs with self-cleaning properties were produced. High-temperature resistance, thermal conductivity performance, microstructure analysis and photocatalytic properties of the produced mixtures were examined. It has been understood that the unit volume weight loss of SCLWC mixtures exposed to high temperatures generally decreases due to the increase in the recycled concrete-aggregate substitution rate. However, it was determined that the loss of compressive strength increased with the increase in the amount of recycled concrete-aggregate replacement. Additionally, it was determined that the thermal-conductivity coefficient values of the mixtures decreased with the use of pumice. After SCLWC mixtures were exposed to 900 °C, small round-shaped crystals formed instead of C–S–H crystals.

Carbonation of waste concrete: An effective and green strategy for enhancing its heavy metals removal from wastewater

Water pollution, especially Pb2+, Cd2+, Co2+, and Ni2+ released from industrial and mine wastewater, harms human health and is a global environmental concern. At the same time, the effective disposal of waste concrete originating from constructs is a global challenge. In this study, carbonated recycled concrete powder (CRP) is efficiently prepared by carbonizing waste concrete powder, which not only might enhance its adsorptive performance but also sequestrate CO2 in the form of mineral carbon. Characterization techniques revealed CRP forms calcium carbonate and highly polymerized silica gel. Batch adsorption experiments indicate that the CRP is found to have strong adsorption properties. The maximum equilibrium adsorption capacities calculated by the Langmuir model were determined as 997.03, 199.56, 148.85, and 76.69 mg/g for Pb2+, Cd2+, Co2+, and Ni2+, respectively, outperforming most waste concrete and industrial wastes reported. The adsorption mechanism mainly includes electrostatic interactions, precipitation, and ion exchange. This study proposes a method to synthesize low cost, good performance, high chemical stability, and facile preparation adsorbent using waste concrete powder, with promising applications in wastewater treatment.

Investigation of Physical-Mechanical Properties and Microstructure of Mortars with Perlite and Thermal-Treated Materials.

This study aimed to obtain and characterize a mortar with perlite aggregate and thermal-treated materials that could substitute for Portland cement. First, the thermally treated materials were obtained by calcinating old Portland cement (OC-tt) and concrete demolition waste (CC-tt) at 550 °C, for 3 h. Second, plastic mortars with a perlite: cement volume ratio of 3:1 were prepared and tested for water absorption, mechanical strength, and thermal conductivity. The microstructure was also analyzed. Portland cement (R) was partially substituted with 10%, 30%, and 50% OC-tt. Thermal-treated materials negatively influenced the compressive and flexural strengths at 7 and 28 days. With an increase in the substitution percentage to 50%, the decrease in the compressive strength was 40% for OC-tt and 62.5% for CC-tt. The presence of 10% OC-tt/CC-tt positively influenced the water absorption. The thermal conductivity of the tested mortars was in the range of 0.37-0.48 W/m·K. SEM analysis shows the expanded perlite pores remained unbroken.

REVIEW: AN EXPERIMENTAL STUDY ON EFFECT OF NANO MATERIALS ON STRENGTH OF CONCRETE AND PLANE STRESS ANALYSIS USING ANSYS SOFTWARE

These days, making efficient and cost-effective use of resources has taken precedence. The main ingredient in concrete, cement has been under criticism in recent years for the quantity of CO2 released during production. Although cement has better mechanical properties, it hasn't been able to live up to the expectations in terms of durability. Owing to cement's shortcomings, scientists started looking into additives that would enhance concrete's qualities while also making it stronger and lighter. Fly ash, silica fume, and other micro particles were added to cementitious materials to improve their compactness, strength, and durability. These additives were also selected because they are eco-friendly by products of industrial waste that may be handled ethically. Fly ash has significant disadvantages because it is not good for initial strength increase and setting time. Because silica fume affects cementitious material performance, researchers have recently become interested in combining it with ceramic waste and rice husk ash. A more effective way to utilize rice husk ash, a by-product of rice cultivation, would be to replace 10% to 15% of cement. Studies have shown improvements in the durability performance of recycled ceramic waste concrete and rice husk ash concrete. There are issues since the RHA production process is quite time-consuming. With the discovery of nano-particles (NP) smaller than 100 nm, researchers have advanced the field of nanotechnology to new levels. The mechanical properties of many materials, including polymers and cementitious materials, can be enhanced by NP. NP is also helpful in the fields of food, engineering, and medicine. This led researchers to investigate the effects of nano-silica (NS) on concrete in further detail. Nano materials can improve the compressive strength and ductility of concrete. In this project an effort will be made to increase the compressive strength of concrete using Nano materials and waste product like GGBS. Also plane stress analysis of concrete cubes and cylinders is to be done using Ansys Software to find deformation, principal stresses and shear stresses. Keywords: Nano –Silica, Nano Titanium dioxide, Ansys, GGBS, Compressive strength

Elucidating the role of recycled concrete aggregate in ductile engineered geopolymer composites: Effects of recycled concrete aggregate content and size

Utilizing recycled fine aggregate (RFA) as silica sand replacement for ductile engineered geopolymer composites (EGC) provides a high value-added approach to recycling concrete waste and reduces the needs for high-cost silica sand. RFA contains abundant active alkaline substances which can promote the secondary geopolymerization of EGC. Substituting RFA for silica sand can improve EGC micro-characteristics, and the micro-structure of RFA-EGC is further refined with the decreased RFA size. The compressive/flexural strength of EGC is elevated as RFA is incorporated, and the decreased RFA size further enhances the compressive/flexural strength of RFA-EGC. Attributed to the micro-pores and micro-cracks in RFA, including RFA benefits the formation and development of crack, leading to an enhancement in the uniaxial tensile behavior of EGC. The tensile strength and tensile strain capacity of 100 % RFA blended EGC are 5.7 % and 8.6 % higher than those of 100 % silica sand blended EGC. The decreased RFA size can enhance the tensile strength, and an appropriate increase in RFA size improves the tensile strain capacity of RFA-EGC. When RFA size is 0.15–0.3 mm and 0.3–0.6 mm, the tensile strain capacity of 100 % RFA blended EGC is 8.6 % and 12.9 % larger than the reference EGC with 100 % silica sand (0.15–0.3 mm). A moderate increase in silicate modulus can further improve the tensile behavior, and the RFA-EGC with 1.5 M shows the best tensile behavior; besides, the longer fiber length results in the higher tensile strength of RFA-EGC. By optimizing the replacement rate and size of RFA, adjusting the silicate modulus and fiber characteristics, one can achieve a sustainable high-ductility RFA-EGC with exceptional mechanical behavior.

Consequential life cycle assessment of demolition waste management in Germany

ContextBulk mineral waste materials such as construction and demolition waste are Germany’s largest waste stream. Despite the availability of high-quality recycling pathways such as road base layers, waste concrete is predominantly recycled into lower-quality recycling pathways like earthworks or unbound road construction. This is due to low demand for recycled aggregates in road base layers and frost protection layers, especially in public procurement.PurposeThis study assesses the environmental consequences of increasing high-quality recycling of waste concrete in the near future to provide decision support for public procurement in Germany. The focus lies on climate change due to its importance for decision-makers. However, 17 other impact categories were assessed to avoid problem shifting.MethodsLife cycle assessment (LCA) is applied with background data from ecoinvent 3.9.1. Impact assessment was conducted at midpoint level using IPCC 2021 and ReCiPe Midpoint (H). Foreground data were taken from literature and expert interviews. In line with the goal of this LCA, a consequential modeling approach was followed to account for changes in the material flow system. Substitution creates a cascade effect previously omitted in consequential LCA studies, in which lower quality recycling materials replace higher quality recycling materials in their respective utilization pathways.Results and discussionIncreasing the high-quality recycling of waste concrete into road base layers causes a reduction in environmental impacts for all 18 impact categories, as it replaces natural aggregate and avoids backfilling of mixed mineral waste and excavated earth through substitution effects. Transport distances and ferrous metal recovery were identified as hot spots. Sensitivity analyses show that only transport is a significant issue.ConclusionIncreasing the high-quality recycling of waste concrete in Germany is recommended in terms of environmental impacts. Lower-quality recycling is environmentally feasible only in cases where the avoided transport distances for natural aggregates and backfilling are significantly lower than the additional transport distances for high-quality recycling.

Valorization of a high-sulfur petroleum coke for energy and fuels through its co-processing with a forest waste, using concrete wastes for sulphur and carbon dioxide capture under mild conditions

Current work provided a comprehensive assessment on the pyrolysis, combustion and gasification of a high-sulfur pet coke (PEC) and its blends with a forest waste (FOP). The potential of waste concrete fractions to capture SO2 and CO2 emissions was explored. The experiments were conducted in a fixed bed system and a thermogravimetric-mass spectrometric unit. Thermal behavior, reactivity, conversion, synergy, structural and chemical characteristics of solid materials, quantitative analysis of products and heating value, chemical, mineralogical and fusibility analysis of ashes were studied as a function of temperature, blending ratio and sorbent/fuel ratio. Addition of sorbent at a ratio Ca/S = 2 resulted in a desulfurization extent of 76–81 % during combustion. Quarry dust sorbent captured up to 95.4 % of CO2 emitted below 700 °C. At 1000 °C H2 content was 64.8–72.9 % mol and syngas yield 1.1–1.8 m3/kg. The gasification performance of PEC was improved upon blending with FOP.