Waste Concrete Powder Research Articles

Integrated utilization of recycled waste concrete powder and waste glass power for preparation of foam ceramics

Integrated utilization of recycled waste concrete powder and waste glass power for preparation of foam ceramics

Fabrication and characterization of foam ceramics from recycled waste concrete powder and waste glass powder

Incorporating multi-solid wastes to prepare foam ceramics has attracted widespread attention due to its excellent characteristics and environmental protection. In this study, foam ceramics were prepared by sintering method using recycled waste concrete powder (RWCP) and waste glass power (WGP) as the major material, Na2CO3 as foaming agent and borax as fluxing agent. The effect of sintering temperature on the physical properties and pore structure of foam ceramics were studied. The phase transformation and reaction mechanism were also discussed. The results reveal that when the RWCP content was 40%, the WGP content was 60% and the sintering temperature was 890 °C, the foam ceramics showed the best overall performance. The compressive strength, bulk density, water absorption and porosity were 2.39MPa, 0.83g/cm3, 8.27% and 66.68%, respectively. At this time, the pore size distribution was optimal, and mesopore occupied the vast majority. The fractal dimension of pore reached the minimum of 1.09. In addition, The XRD results showed that WGP and RWCP gradually depolymerized and reconstructed under the action of flux. Then the foam ceramics with mullite, pyroxene and wollastonite as the main phases were formed. The experimental results showed that it was feasible to prepare foam ceramics using RWCP. This study can provide a new train of thought for the reuse of RWCP.

Experimental Research on the Performance of Recycled Waste Concrete Powder (RWCP) on Concrete.

Waste concrete is a large amount of solid waste produced in the process of urban construction and renewal in China. Its resource utilization is of great significance for saving mineral resources and improving urban environmental quality. The present study was designed to investigate the effects of mechanical grinding time on the particle size distribution and activity of recycled waste concrete powder (RWCP). Combined with unconfined compressive strength, slump, electric flux and chloride ion penetration resistance tests, the effects of RWCP on the mechanical properties, working performance and impermeability of concrete were analyzed, and the phase and microstructure of concrete containing RWCP were analyzed by XRD and SEM. The results showed that the RWCP is mainly composed of quartz, gismondine, C2S, cancrinite and portlandite. The optimum activity of RWCP obtained by ball milling for 45 min was 44.41%. RWCP can improve the fluidity of concrete and shorten the initial setting time of concrete. When the blast furnace slag in the concrete was replaced by the RWCP, the early strength and impermeability of the concrete decreased. When RWCP replaced blast furnace slag by 69.1%, the UCS of the concrete at 1, 3, 7, and 14 d decreased from 9.56, 22.1, 34.1, and 41.2 MPa to 5.9, 14.5, 22.7, and 33.2 MPa, respectively. While RWCP replaced fly ash, the normal strength of concrete increased with the increase in fly ash replacement amount. When RWCP completely replaced FA in concrete, the 28-day strength of the concrete increased from 45.2 MPa to 50.8 MPa. The impermeability results showed that the appropriate substitution of RWCP for fly ash was beneficial to increase the impermeability of concrete while excessive substitution reduced. Based on these results, the RWCP has the potential for large-scale application in the preparation of concrete.

Turning waste concrete powder into high calcium alkali-activated cementitious materials and artificial aggregates

In order to handle the environmental pollution caused by waste concrete powder, recycled concrete powder (RCP) is utilized to prepare high calcium alkali-activated cementitious materials and artificial aggregates. This study first investigates the high calcium alkali-activated cementitious materials, exploring the effects of different mineral admixtures, liquid-to-solid ratios (L/S), RCP/slag, Na2SiO3 modulus, and Na2O content. The results illustrate that slag powder is the best mineral admixture and the most critical factor affecting cementitious materials. Increasing the slag dosage enhances the generation of C-(A)-S-H, improves the microstructure, and increases compressive strength, with a maximum compressive strength reaching 68.42 MPa. According to these test results, the impact of various factors on RCP aggregates is further explored. The results illustrate that the L/S and slag content are primary factors influencing particle size distribution and strength. Increasing these factors leads to larger aggregate particle sizes and higher strength. The compressive strength of the aggregates at 7d reaches 93.24–-99.5 % of that at 28d, with a maximum strength of 8.2 MPa. Additionally, slag content (10–30 %) and Na2O content significantly impact the physical properties of aggregates, improving apparent density and bulk density while reducing water absorption. To verify the applicability of RCP aggregates, they were used in concrete, and the effects of aggregate strength and replacement rate on concrete performance were explored. The results display that as aggregate strength rises, the mechanical properties of the concrete improve. When RCP aggregates are incorporated, the mechanical properties of the natural concrete decline only slightly (<16.70 %). The probability of aggregate damage increases with decreased RCP aggregate strength or increased RCP aggregate content under pressure. RCP aggregate concrete exhibits better shrinkage resistance compared to natural concrete. The process of utilizing RCP is low-energy, non-polluting, and results in high-performance products, making the large-scale effective utilization of RCP feasible.

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.

Collaborative pollution and carbon reduction behaviors of carbonated Pb-contaminated soil stabilized with a low-carbon binder derived from waste concrete

Due to the limited hydration capacity, solidification/stabilization (S/S) with waste concrete powder (WCP) has a low strength. Carbonation can reduce carbon dioxide (CO2) emissions and improve strength of lead-contaminated soil, but its mechanism and environmental behaviors are unclear. In light of this, a comprehensive study was conducted on the compressive strength, lead immobilization, conductivity characteristics, and carbonation mechanism of carbonated Pb-contaminated soils stabilized with WCP compared to calcining 600 °C WCP. Results indicated that with carbonation, the compressive strength of the samples was significantly improved at the early stage (1 d), resulting in increased unconfined compressive strength (UCS) by 2.5-5.2 times due to the filling of pores by calcite. It negatively affected the lead immobilization capacity of highly doped (30%) samples, while this effect reversed after 3 d of carbonating due to the reduced alkaline environment. The lead immobilization capacity decreased after 28 d of carbonating due to the cracking of samples and the influence of a lower pH on the solubility of lead-carbonated hydroxide ((PbCO3)2Pb(OH)2). The water evaporation (saturation <16.8%) led to dry shrinkage cracking and decreased UCS of the samples. Based on this finding, a conductivity model was developed for carbonated and cured samples, accurately predicting changes in saturation levels (R2 = 0.98). A relationship between conductivity and UCS or lead immobilization capacity was proposed. This research proposed an innovative method for the reduction of CO2 emission as well as laid down a theoretical basis for the recovery of WCP and lead-contaminated soils through carbonation.

Reusing thermoactivated waste paste/concrete powder for sustainable alkali-activated materials: Effects of thermoactivated temperature

The construction waste powder encompasses waste paste powder (WPP) and waste concrete powder (WCP), exhibiting an irregular microstructural morphology and containing mineral constituents like portlandite, C-S-H gel, calcite and quartz. Under the influence of thermal activation, certain hydrated products within construction waste powder undergo decomposition, concurrently generating new substances like CaO and C2S, which contribute to enhanced reactivity. Minerals within construction waste powder participate in polymerization reactions under alkali activation. Furthermore, alkali-activated mortar produced from thermally treated construction waste powder generate an increased quantity of C-A-S-H/N-A-S-H gel, resulting in a denser microstructure. When construction waste powder is thermally treated at temperatures ranging from 600°C to 800°C, the resulting alkali-activated construction waste powder mortar (AAWM) exhibits higher compressive strength. For example, the 28d compressive strength of AAWM prepared with WCP subjected to heat treatment at 800°C increased by 195.69 % compared to AAWM prepared with untreated WCP. With the increase in thermal treatment temperature of construction waste powder, the drying shrinkage of the resultant AAWM progressively diminishes, along with a gradual reduction in porosity and water absorption. For instance, the porosity and water absorption of AAWM prepared with WCP treated at 800°C decreased by 15.58 % and 18.67 % respectively compared to AAWM prepared with untreated WCP. At a thermal treatment temperature of 800°C, AAWM exhibits strong resistance to chloride penetration. Particularly, AAWM containing WPP outperforms that containing WCP in terms of chloride resistance. Consequently, this study reveals that alkali-activated materials prepared using thermally treated waste powder exhibit commendable mechanical and durability properties.

The influence of curing methods on the performance of recycled concrete powder artificial aggregates and concrete

In order to address the issues of pollution from waste concrete powder and alleviate the shortage of natural aggregates, recycled concrete powder (RCP) was used to produce artificial aggregates (RCPA). The effects of internal and external addition alkaline activator methods, as well as natural curing (20 °C), heated curing (20/40/60/80/100 °C), and steam curing (20/40/60/80/100 °C) on the properties of RCPA were investigated. It was found that the internal addition method was more effective; the heated curing method yielded the best results, with the optimal temperature being 60 °C. The highest strength of RCPA was 10.24 MPa, with a water absorption rate of 8.68 % at this point. The microstructure of the aggregate under heated curing showed significant improvement compared to that under natural curing. Concrete was prepared using aggregates cured naturally at 20 °C (20 °C NCA) and aggregates cured at 60 °C (60 °C HCA). It was found that the mechanical properties of concrete made with 60 °C HCA were superior to those made with 20 °C NCA. The compressive strength of recycled concrete powder artificial aggregate concrete (RCPAC) at 28d reached 83.73 %-89.97 % of that of natural concrete (NC), with a density lower than NC. When subjected to compression, only mortar and interfaces in NC were damaged, whereas aggregates in RCPAC were also damaged. The resistance drying shrinkage and freeze-thaw of RCPA (ellipsoidal) concrete are better than those of natural aggregate (polyhedron) concrete. The 60 ℃ HCA concrete is optimal, enduring up to 250 freeze-thaw cycles. RCPA can replace natural aggregates in concrete production, and durability is crucial; therefore, future research should explore this area more thoroughly.

Novel utilization of waste concrete powder in alkali-activated binder

This experimental study investigates a novel approach to utilize waste concrete powder (WCP) in conjunction with metakaolin as a precursor in the production of alkali-activated binder for sustainable consumption of construction and demolition waste. A Chapelle test confirms the presence of reactive silica in thermo-mechanically activated WCP. Different alkali-activated mixtures with metakaolin replacement ranging from 0 % to 80 % were prepared. The mixture with 40 % activated WCP, with a sodium silicate to sodium hydroxide ratio of 2, achieved better compressive strength than the reference sample without WCP. Mineralogical analysis of the mixture pastes revealed that activated WCP-based mixtures developed geopolymer gel and C-S-H gel, contributing to better strength properties in the case of the mixture with 40 % activated WCP. Life cycle analysis demonstrated that incorporating 40 % thermo-mechanically activated WCP by replacing metakaolin reduces carbon dioxide emissions by 49.5 % and 2.2 % compared to Portland cement and metakaolin-based binder, respectively.

Novel activation method of waste concrete powder for sustainable clinker-free binder

This study investigates the environmental and mechanical implications of incorporating silica fume into lime-activated thermo-mechanically treated waste concrete powder (TMWCP) to develop a sustainable clinker-free binder. The novel activation method involves thermo-mechanical treatment of WCP, followed by lime and calcium formate chemical activation. The results demonstrated that incorporating silica fume enhanced the pozzolanic reactivity, which led to the formation of C–S–H, pore refinement, and a dramatic increase in compressive strength. For instance, the incorporation of 20 % and 25 % silica fume exhibited compressive strength of 46 MPa and 43 MPa after 28 days of curing. The developed clinker-free binder with the addition of 20 % silica fume demonstrated a reduction in mineral resource consumption of 99.3 % and CO2 emissions of 13 % and 69.3 % compared to the sample without silica fume and ordinary Portland cement, respectively. This study offers a promising avenue for the widespread utilization of WCP as an environmentally friendly clinker-free binder.

Compression molding of polypropylene‐ and polyethylene‐based composite materials using siliceous waste concrete powder

AbstractThis 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.

A comparative life cycle assessment of recycling waste concrete powder into CO2-Capture products

Waste concrete powder (WCP), a byproduct of construction and demolition (C&D), currently has a low degree of recycling despite its potential for environmentally friendly applications. WCP can serve as a valuable substitute for cement, offering advantages for resource conservation and carbon sequestration. However, there are very few studies that quantitatively assess the environmental impact of incorporating WCP into the circular economy as a secondary material instead of disposing of it. The energy-intensive processing of WCP raises questions about the optimal carbonation time using available equipment. This study aims to fill this knowledge gap by employing carbon footprint and life cycle assessments (LCA) to optimize WCP recycling. Three recycling WCP scenarios are analyzed. The first scenario involved the conversion of WCP into compacts that absorb CO2 during the carbonation process. The results of the first scenario revealed that the optimal carbonation time for WCP compacts was 8 h, during which 42.7 kg CO2-e per tonne of WCP compacts was sequestered. The total global warming potential (GWP) was −4.22 kgCO2-e, indicating a carbon-negative recycling process. In the second and third scenarios, LCA was conducted to compare the use of carbonated and uncarbonated WCP as a partial replacement for cement in concrete. In these scenarios, it was found that uncarbonated WCP is a more effective solution for reducing the carbon footprint of traditional concrete mixes, achieving a significant 16% reduction of GWP when 20% of cement is replaced. Conversely, using carbonated WCP as a partial cement replacement in concrete mixtures shows limited potential for CO2 uptake. The sensitivity analysis reveals that the carbon footprint of the WCP compacts production process is strongly influenced by the electricity supplier used.

Quality Improvement Effect of Waste Concrete Fine Powder by Applying Exfoliation Technology

Since the main components of waste concrete fine powder generated in the process of converting waste concrete into recycled aggregate are essentially the same as the main ingredients of cement-clinker, it is possible to use it as a raw material for cement. In addition, because waste concrete fine powder is a decarbonated salt, using it as a raw material for cement clinker is a very important carbon-neutral technology that can be expected to reduce process-derived carbon emission generated during cement manufacturing. However, waste concrete fine powder has a low calcium oxide content of around 10%, so its usability as a clinker raw material is very low. In order to use waste concrete fine powder as a raw material for clinker, the calcium oxide content must be increased to more than 35%. Separating the hardened cement paste from the aggregate while reducing the crushing ration of the aggregate during the crushing process is an important means of increasing the calcium oxide content of waste concrete fine powder. Accordingly, this study conducted an experimental study to increase the calcium oxide content of waste concrete fine powder using exfoliation grinding technology. The characteristics of waste concrete fine powder recovered through the exfoliation grinding technology were examined for waste concrete collected from a domestic intermediate processing company, model concrete manufactured in a laboratory, and commercially available cement bricks. As a result of the experiment, it was possible to recover the waste concrete fine powder with a higher CaO content by applying exfoliation grinding technology, compared to the dust collection fine powder that could be recovered through the crushing and grinding process.

Influence of elevated temperature on waste concrete powder and its application in alkali activated materials

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.

Life cycle assessment of waste materials in deep cement mixing for land reclamation in Hong Kong

In recent years, researchers have shown increasing concern on the environmental impact attributed to traditional binders like cement, especially in mega-scale reclamation projects utilizing Deep Cement Mixing (DCM). The substitution of cement with alternative binders derived from construction and demolition waste as well as industrial slag waste is viewed as a potential strategy for mitigating the carbon footprint of this construction sector. In this study, the potential of using ground granulated blast furnace slag (GGBS), steel slag (SS), and waste concrete powder (WCP) to partially replace cement in construction projects involving DCM is assessed based on a case study in Hong Kong. A detailed comparison through Life Cycle Assessment (LCA) is conducted to examine the carbon footprint of alternative binders. Various scenarios that involve substituting cement to different extents with alternative binders generated from waste materials have been considered. The results reveal that the grinding process is the main contributor to the Global Warming Potential (GWP) for GGBS and SS, accounting for over 57% in each case. For WCP, the GWP is distributed across separation, sieving, and loading. Utilizing alternative waste leads to a GWP reduction in all scenarios, primarily due to lower emissions from these secondary raw materials. Overall, substituting 60% of Portland cement with GGBS, SS, or WCP in DCM construction resulted in GWP reductions of 34.7%, 34.5%, and 35.8% of greenhouse gas emissions, respectively. Various transportation scenarios are explored when moving the supply of construction materials from a local to a regional level by considering various material suppliers and the associated transportation distance. The sensitivity analysis highlighted the significant impact of transportation distance on GWP. This underscores the importance of logistics analysis in land reclamation projects and the benefits of integrating alternative binders into DCM projects.

Influence mechanism of Nano-SiO2 on geopolymer recycled concrete: Change mechanism of the microstructure and the anti-carbonation mechanism

To improve the durability of geopolymer recycled aggregate concrete based on waste concrete powder (WCP), and realize its application and promotion, this study utilized WCP, fly ash (FA), and ground granulated blast-furnace slag (GGBS) as raw materials, and recycled concrete aggregate (RCA) as aggregate, with Nano-SiO2 as the modifying material to prepare WCP-based geopolymer recycled concrete (WCPGRC). The carbonation depth, uniaxial compressive strength (UCS), and dynamic elastic modulus (DEM) of WCPGRC without Nano-SiO2 (P-WCPGRC) and with Nano-SiO2 (NS-WCPGRC) were investigated. The phase composition, microstructure morphology, and pore distribution characteristics of the two WCPGRCs were investigated using XRD, SEM, and MIP tests. The mechanism of influence of Nano-SiO2 on the carbonation effect and microstructure of WCPGRC was revealed. The findings demonstrate that: (1) The carbonation depth of P-WCPGRC was higher than that of NS-WCPGRC, and both increased linearly with the carbonation times. (2) Both UCS and DEM of P-WCPGRC were lower than those of NS-WCPGRC, and both showed a two-phase change, with the inflection point from a rapid to a slow increase in UCS and DEM occurred on day 7 for P-WCPGRC, while the inflection points for NS-WCPGRC occurred on the day 14. (3) The addition of Nano-SiO2 generated more geopolymer gels, changed the microstructure, reduced the porosity, changed the pore size distribution, and enhanced the physical and mechanical properties and carbonation resistance of WCPGRC. It is feasible to improve the durability of WCPGRC by adding Nano-SiO2.

Valorization of waste concrete powder (WCP) through silica fume incorporation to enhance the reactivity and hydration characteristics

The aim of this study is to utilize the bulk proportion of waste concrete powder (WCP) as cementitious material in the fabrication of binder, and to investigate the impact of silica fume on the reactivity and hydration characteristics of thermomechanical activated WCP. A 29 Silicon Nuclear Magnetic Resonance (NMR) analysis confirmed the presence of reactive silica in the activated WCP. Various blends were prepared with a 50%–80% substitution of type CEM I 52.5 N cement. The combination of activated WCP and silica fume improved the reactivity of the binder blend and achieved a compressive strength comparable to cement. Mineralogical analysis revealed the development of secondary C–S–H gels in mixtures containing silica fumes and activated WCP, which is the result of a secondary hydration reaction between portlandite and reactive silica. The use of life cycle analysis software for the replacement of 60 wt % of cement with activated WCP was found to reduce carbon dioxide emissions by 80.42% due to the use of less cement, an environmentally friendly WCP activation process, even when considering the addition of 10% silica fume. This innovative approach not only enhances WCP reactivity and mechanical strength but also significantly contributes to the reduction of carbon emissions. By elucidating the formation mechanisms and environmental benefits, this study paves the way for a more eco-conscious and efficient construction methodology, promoting the vision of a greener future.

Effectiveness of waste concrete powder in fabricating compressed stabilized earth blocks: Strength, durability and thermal assessment

The construction industry's rapid expansion has led to the accumulation of substantial quantities of waste concrete powder (WCP), which constitutes a significant portion of construction and demolition waste. This study seeks to explore the potential of utilizing WCP in conjunction with cement to manufacture compressed stabilized earth blocks (CSEB) with enhanced mechanical properties. CSEB has long been recognized as an environment-friendly and viable alternative to traditional building blocks that harm the environment. By incorporating WCP into the production process, we can achieve recyclability and sustainability in our construction practices. In order to identify the optimal amount of stabilizers, 15 different combinations of cement and WCP were considered. These included three cement contents (4%, 6%, and 8% by weight of dry soil) and five waste concrete powder (WCP) contents (0%, 5%, 10%, 15%, and 20% by weight of dry soil). Compressed stabilized earth blocks (CSEB) performance was evaluated in terms of strength, durability, and thermal properties. Strength characteristics were determined through unconfined compression and flexure tests, while durability characteristics were evaluated using water absorption, wet compressive strength, submersion, and efflorescence tests. CSEBs without WCP displayed a maximum dry compressive strength of 6.67 MPa, while those with optimal WCP replacement reached a higher strength of 10.68 MPa using the same cement amount. Comparable outcomes were seen in the flexure test, with optimal WCP replacement resulting in a peak strength of 1.92 MPa compared to 1.12 MPa without WCP. In terms of durability, WCP-absent samples showed 13% water absorption, reduced to 10.5% with higher WCP content. Wet compressive strength was relatively lower for all samples, but those with optimal WCP performed best at 4.83 MPa. These fabricated samples also exhibited no efflorescence or damage from submersion. Thermal conductivity, determined using the simplified Lee's method, demonstrated a gradual increase in conductivity as WCP content was increased. However, the obtained values remained within comparable range of fired clay bricks. Furthermore, to investigate the supplementary cementitious behavior of WCP in CSEB, microstructural and thermal analyses were conducted. Scanning electron microscope images revealed a higher concentration of C–S–H gels in the 20% WCP-8% cement combination. The findings suggest that CSEB blocks stabilized with WCP could help to reduce construction and demolition waste while also providing a more stable and sustainable alternative to traditional building blocks.

Utilization of Blast Furnace Slag as an Enhancer in Masonry Mortars Made with Thermally Treated Waste Concrete Powder

Every year, a massive amount of natural materials are subjected to high temperatures during cement production, resulting in 5% to 8% of total global carbon dioxide (CO2) emissions. The employment of supplementary cementitious materials (SCMs) for developing construction materials could reduce the use of natural materials and CO2 emissions during cement manufacturing. One option to accomplish this is to examine the possibility of producing masonry mortars using thermally treated waste concrete powder (WCP) and ground granulated blast furnace slag (GGBFS). The main objective of the present study is based on this. The study was conducted in two phases. In Phase I, WCP was thermally treated at various temperatures of 0 °C, 300 °C, 500 °C, and 700 °C and then used to prepare mortars at a binder-to-fine aggregate ratio of 1:3. From the strength results obtained in Phase I, a mortar mixture made with 500 °C WCP was selected for Phase II investigation. Mortars were produced by replacing the 500 °C WCP with GGBFS at 0%, 25%, 40%, 60%, 70%, and 85%. It was found that the performance of the mortars was enhanced when GGBFS was used up to 60%. The mortar mixture containing 60% thermally treated WCP and 40% GGBFS produced the optimal physical and mechanical properties. Also, material characterization was carried out on the binders using X-ray fluorescence, scanning electron microscopy, and thermogravimetric analysis. The results indicate that the thermally treated WCPs and GGBFS contain oxides similar to cement, making them suitable for mortar production. In conclusion, the study has shown the feasibility of producing masonry mortars using thermally treated WCP and GGBFS.

Development of Sustainable Cement-Based Materials with Ultra-High Content of Waste Concrete Powder: Properties and Improvement

The recycled powder (RP) of construction waste, as a kind of silica–aluminum waste, can have a certain gelling effect after alkali activation modification. Sodium silicate (water glass) and NaOH are used as composite alkali activators to stimulate RP to prepare alkali-activated mortar. The different micro and macro properties of RP are studied under the ultra-high substitution rates of 70%, 80%, 90%, and 100% of cementation-based materials. The results show that the mechanical properties of the regenerated powder mixture decrease gradually with the increase in the substitution rate. When the replacement rate of RP is 70%, the 3 d and 28 d compressive strength decreases by 73.63% and 69.46%, respectively. When the replacement rate reaches 100%, the 3 d and 28 d compressive strength decreases by 96.98% and 93.74%, respectively. The cement-based material after alkali excitation has the characteristics of early strength and the mechanical properties are greatly improved, and the mechanical properties of cement-based materials can be effectively increased by increasing the modulus of water glass. At 70%RP substitution rate, the compressive strength of 28 d increases by 3.59% and 107.71% when the modulus of sodium silicate is 1.0 M and 1.6 M, compared with the unactivated groups. At 100%RP substitution rate, the 28 d strength of the unexcited specimen is 0.92 MPa, and the 28 d compressive strength reaches 6.15 MPa and 12.86 MPa when the modulus of sodium silicate is 1.0 M and 1.6 M. The results show that the alkali-activated mortar has good application potential.