Novel biochar-concrete composites: Manufacturing, characterization and evaluation of the mechanical properties

Coal-derived char as new sand replacement material in cement mortars: A comprehensive experimental study

Coal char is a coal-derived product produced by pyrolysis of char, which has valuable applications in the production of building materials. This paper presents the use of coal char in developing coal char-based cement mortar. Coal char is used to replace the sand, partially, at different proportions in cement mortar, and the change in properties is studied. Four cement types are used in the initial study, and one is selected for a detailed study based on the water retention, density, and compressive strength of the mortar. The properties of coal char-based mortar for the selected cement are comprehensively evaluated in terms of flow, water retention, air content, density, compressive strength, flexural strength, porosity, water absorption, drying shrinkage, thermal conductivity, thermogravimetric and differential thermal analysis, and scanning electron microscopy. The addition of coal char at an optimum sand replacement content of 5 % increases the compressive strength of mortar by 17.55 % and the flexural strength by 17.57 %, compared to conventional cement mortar. The thermal conductivity reduces by a maximum of 20 %, compared to traditional cement mortar. This paper also presents a study to compare the addition of coal char and commercial biochar on the properties of masonry cement mortar. The compressive strength of mortar with coal char is 44.39 % greater than that of mortar with the same content of biochar. The addition of coal char as a new sand replacement material shows good potential in improving the engineering properties of mortar.

Evaluation of Rheological Properties of Asphalt Binder Modified with Biochar from Oat Hulls

In this study, the effect of biochar from oat hulls (BO) on the rheological properties of a PG 64-22 asphalt binder was evaluated using a full factorial design, which included the following factors: pyrolysis temperature (PT) (300 °C and 500 °C), BO particle size (<20 µm and <75 µm), and the amount of BO (2.5%, 5%, and 7.5%). First, the morphological and physicochemical properties of BO were analyzed by comparing it with graphite powder (CFG) and commercial activated carbon (CAC). The physicochemical properties of the modified asphalt binder were then evaluated using confocal laser microscopy, scanning electron microscopy (SEM-EDX), and Fourier-transform infrared spectroscopy (FTIR). Its storage stability was also evaluated. Subsequently, the rutting parameter G*/sin(δ) and the Fraass breaking point were analyzed to select asphalt binders that extended their viscoelastic range. The asphalt binders selected were those with 2.5%, 5%, and 7.5% BO, produced at a PT of 300 °C with a particle size <20 µm (BO300S). Next, the rheological properties of the selected samples were evaluated by testing for rotational viscosity, rutting parameter G*/sin(δ), multiple stress creep recovery (MSCR), fatigue parameter G*·sin(δ), and creep stiffness by bending beam rheometry (BBR). The rheological aging index according to rutting parameter G*/sin(δ) (RAI) was also evaluated. These tests were conducted in different states of the asphalt binder: original, short-term aged, and long-term aged. According to the results, the application of BO300S significantly increased the resistance of the asphalt binder to rutting and rotational viscosity, proportional to the amount added to the asphalt binder. Moreover, low modifier percentages improved fatigue resistance, outperforming CFG and CAC. In addition, it performs well at low service temperatures, registering better resistance than the control asphalt binders.

Development of lightweight structural concrete with artificial aggregate manufactured from local clay and solid waste materials

The partial replacement of conventional natural coarse aggregate (NCA) with artificial light weight aggregate (LWA) manufactured from local clay and solid waste to develop a lightweight aggregate concrete (LWAC) for the structural use was studied in this paper. Red clay and Savar clay were used individually with solid wastes like rice husk ash (RHA) and waste glass to produce LWA. The suitability of raw materials and LWA was evaluated by investigating various properties. The mechanical, thermal and durability properties of manufactured LWAC were explored. The results of physical, chemical, thermal and geotechnical properties revealed that Red clay is better than Savar clay for the preparation of LWA. All the physical and mechanical properties of LWA prepared from Red clay are suitable for the preparation of LWAC compared to Savar clay. The test results demonstrated that the concrete manufactured by replacing 30 % of NCA with LWA produced a concrete of lightweight properties. The compressive strength of LWAC for 7 and 28 days was observed as 28 and 48 MPa, respectively. The results of modulus of elasticity, splitting tensile strength, flexural deformation, and creep test of LWAC revealed that these mechanical properties meet the requirements for the structural concrete. The RCP test proves that chlorine permeability of LWAC is comparable with NCA. It was observed that the superior performance of LWAC can be achieved only when the optimized mix designed is followed strictly. The suitability of the replacement of natural aggregate by LWA may be helpful for Bangladesh due to the scarcity of natural coarse aggregate and reusability of solid waste materials.

Multiple objective energy optimization of a trade center building based on genetic algorithm using ecological materials

It is crucial to optimize energy consumption in buildings while considering thermal comfort. The first step here involved an EnergyPlus simulation on a trade center building located in Tehran, Bandar Abbas, and Tabriz, Iran. A multi-objective optimization was then performed based on non-dominated sorting genetic algorithm II (NSGA-II) in jEPlus + EA to establish the building in the selected city where would benefit the most from implementing the radiant ceiling cooling system. Efforts were undertaken to choose environmentally-friendly materials. The final solution by Pareto charts resulted in a 52% reduction in energy consumption, a 37.3% decrease in cooling load, and a 17.4% improvement in comfort hours compared to the original design. Annual emission of greenhouse gas reduced as 167.67 tone of CO2 equivalent emission, 25.77 ton of CH4, and 0.2 ton of NO2. The mentioned algorithm was conducted for the first time on a trade center, including a DOAS system and radiant ceiling cooling system. Simultaneously, the environmental-friendly materials were dealt with. The procedure holds significant relevance for the design and optimization of buildings in Iran, especially wherever the climate is hot and humid. This approach offers advantages to the environment by reducing the impact on energy resources and utilizing environmentally-friendly materials.

A holistic framework of biochar-augmented cementitious products and general applications: Technical, environmental, and economic evaluation

In the context of the circular economy, the development of innovative and low-carbon concrete that incorporates different kinds of waste materials is gaining attention among the research community, regulatory agencies, and policymakers. These materials can be incorporated into concrete mixtures as aggregates or as fillers for improvement of product properties. This study aims to identify reliable designs for biochar-augmented cementitious products and general applications through technical, environmental, and economic assessments. The outcomes demonstrate that 5 wt% biochar addition could enhance the compressive strength of the final products. Using biochar, together with other recycled materials, can enormously reduce the environmental impacts, especially for global warming, enabling biochar-augmented cementitious products and general application as carbon-negative resources. The highest GWP reduction reached -720 kg CO2/tonne, equal to a 200% saving. A high quantity of biochar could be included in several specific applications (up to 60 wt%). The economic assessment highlights that the proposed designs are cost-effective and carbon tax can be significantly reduced. Carbon credits can also be earned for some carbon-negative designs. These findings can serve to mitigate GHG emissions and provide decision-makers with a reliable and holistic framework towards the goal of carbon neutrality.

Biochar affects compressive strength of Portland cement composites: a meta-analysis

One strategy to reduce CO2 emissions from cement production is to reduce the amount of Portland cement produced by replacing it with supplementary cementitious materials (SCMs). Biochar is a potential SCM that is an eco-friendly and stable porous pyrolytic material. However, the effects of biochar addition on the performances of Portland cement composites are not fully understood. This meta-analysis investigated the impact of biochar addition on the 7- and 28-day compressive strength of Portland cement composites based on 606 paired observations. Biochar feedstock type, pyrolysis conditions, pre-treatments and modifications, biochar dosage, and curing type all influenced the compressive strength of Portland cement composites. Biochars obtained from plant-based feedstocks (except rice and hardwood) improved the 28-day compressive strength of Portland cement composites by 3-13%. Biochars produced at pyrolysis temperatures higher than 450 °C, with a heating rate of around 10 C min-1, increased the 28-day compressive strength more effectively. Furthermore, the addition of biochar with small particle sizes increased the compressive strength of Portland cement composites by 2-7% compared to those without biochar addition. Biochar dosage of < 2.5% of the binder weight enhanced both compressive strengths, and common curing methods maintained the effect of biochar addition. However, when mixing the cement, adding fine and coarse aggregates such as sand and gravel affects the concrete and mortar's compressive strength, diminishing the effect of biochar addition and making the biochar effect nonsignificant. We concluded that appropriate biochar addition could maintain or enhance the mechanical performance of Portland cement composites, and future research should explore the mechanisms of biochar effects on the performance of cement composites.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s42773-024-00309-2.

Possible Options for Utilization of EU Biomass Waste: Pyrolysis Char, Calorific Value and Ash Content

The application of biomass as a co-feed in coal power plants and in standalone biomass power plants, as well as in char production for soil remediation, is a currently important issue. This paper reports on the investigation of biochar formation from agricultural waste crops that are used for soil upgrading, but which do not meet the standards of EU crops, as well as largescale food processing waste. These were compared to test results from basket willow, which is commonly used for energy generation. Food industry waste is often produced in cities on a large scale and is generally easier to process due to lack of other stream components. The key parameters, namely, the content of volatiles, energy content of the formed biochar and the composition of the ash, were determined for a number of herbaceous materials locally available in the European Union. All of them can be used as a cheap source of biochar. A novel procedure of capturing volatiles and hence minimizing the PAH content in the biochar, as well as enabling the recovery of energy from the volatiles is presented. Knowledge of the composition and form of elements in ash is very important for designing ash management systems if co-combustion is implemented. The aim of this study was to determine if the types of biomass are better suited for biochar production or energy generation.

Enhancing road performance of lead-contaminated soil through biochar-cement solidification: An experimental study

The effectiveness of cement-based solidification for remediating heavy metal-contaminated soil diminishes at high levels of contamination. To overcome this limitation, the potential of a biochar-cement composite curing agent to enhance the properties of Pb 2+ contaminated soil was investigated in this study. The permeability, unconfined compressive strength (UCS), and leaching characteristics of the biochar-cement composite material were assessed under varying biochar contents. The results revealed that the addition of 1-5 wt% biochar in cement significantly improved the UCS of the solidified soil. However, excessive biochar contents had a detrimental effect on the strength of samples. Additionally, the incorporation of 3.0% biochar reduced the hydraulic conductivity and porosity to 7.75 × 10-9 cm/s and 43.12%, respectively. Moreover, the biochar-cement composite material exhibited remarkable efficiency in treating highly concentrated Pb2+ contaminated soil, with leaching concentration decreasing significantly with increasing biochar content, falling below the Chinese hazardous waste identification standard. Overall, the utilization of a biochar-cement composite curing agent in the solidification of heavy metal-contaminated soil could be considered a promising subgrade filler technique.

Converting coastal silt into subgrade soil with biochar as reinforcing agent, CO2 adsorbent, and carbon sequestrating material

Large amounts of coastal silt produced annually is urgent to be treated with a feasible strategy. This study converted it into subgrade soil by cement solidification for resource utilization. Biochar was used as exogenous additive for enhancing compressive strength of the product, simultaneously achieving carbon sequestration. Three biochars derived from peanut shells (PSBC), cow dung (CDBC) and sewage sludge (SSBC) at 300 °C, 500 °C and 700 °C pyrolysis, were added into raw materials with 1%, 2% and 5%, respectively. All biochars significantly improved the compressive strength of the subgrade soil by 20-110%. Biochar catalyzed cement hydration reactions to produce more Ca(OH)2, CaCO3 and calcium silicate hydrates (C-S-H gel). The catalytic capacity of different biochars followed the order of SSBC > PSBC > CDBC. Addition of 2% SSBC500 induced the greatest increase in 28 d-strength from only 1.0 MPa-2.1 MPa, which was due to that 500 °C biochar had a suitable specific surface area and porosity. Biochar facilitated CO2 capture (absorption) during the hydration reactions at the initial 48 h with 55-70 mg g-1. The high alkalinity and water holding capacity of biochar contributed to the absorption of CO2; the high content of minerals in SSBC compared to CDBC and PSBC promoted chemical conversion of CO2 to carbonate. Besides, the biochar itself as carbon rich material was encapsulated in the subgrade soil, which can be regarded as a long-term carbon sequestration strategy. Carbon budget analysis demonstrated that converting one ton dry silt into subgrade soil with addition of 2% biochar could increase CO2 sequestration from 11 kg to 36-94 kg. This study proposes a novel strategy of using biochar to strengthen the subgrade soil simultaneously achieve long-term carbon sequestration.

Performance of biochar mixed cement paste for removal of Cu, Pb and Zn from stormwater

Using biochar as a partial replacement of Portland cement in cementitious materials is a promising solution to mitigate negative environmental impacts. However, current studies in available literature primarily focus on the mechanical properties of composites made with cementitious materials and biochar. Therefore, this paper reports the effects of the type of biochar, the percentage of biochar addition, and the particle size of the biochar on the removal efficiency of Cu, Pb, and Zn, as well as the effect of contact time on the removal efficiency of Cu, Pb, and Zn, along with the compressive strength. The peak intensities of OH^-, CO₃^2- and Calcium Silicate Hydrate (Ca-Si-H) peaks increase with increasing biochar addition levels, reflecting increased hydration product formation. The reduction of particle size of biochar causes the polymerization of the Ca-Si-H gel. However, no significant changes were observed in heavy metal removal, irrespective of the percentage of biochar addition, the particle size of biochar, or the type of biochar added to the cement paste. Adsorption capacities above 19 mg/g, 11 mg/g and 19 mg/g for Cu, Pb and Zn were recorded in all composites at an initial pH of 6.0. The Pseudo second order model best described the kinetics of the Cu, Pb, and Zn removal. The rate of adsorptive removal increases with the decrease in the density of the adsorbents. Over 40% of Cu and Zn were removed as carbonates and hydroxides through precipitation, whereas over 80% of Pb removal was via adsorption. Heavy metals bonded with OH^-, CO₃^2- and Ca-Si-H functional groups. The results demonstrate that biochar can be used as a cement replacement without negatively impacting heavy metal removal. However, neutralization of the high pH is needed before safe discharge.

Research Progress with Membrane Shielding Materials for Electromagnetic/Radiation Contamination

As technology develops at a rapid pace, electromagnetic and radiation pollution have become significant issues. These forms of pollution can cause many important environmental issues. If they are not properly managed and addressed, they will be everywhere in the global biosphere, and they will have devastating impacts on human health. In addition to minimizing sources of electromagnetic radiation, the development of lightweight composite shielding materials to address interference from radiation has become an important area of research. A suitable shielding material can effectively reduce the harm caused by electromagnetic interference/radiation. However, membrane shielding materials with general functions cannot effectively exert their shielding performance in all fields, and membrane shielding materials used in different fields must have specific functions under their use conditions. The aim of this review was to provide a comprehensive review of these issues. Firstly, the causes of electromagnetic/radiation pollution were briefly introduced and comprehensively identified and analyzed. Secondly, the strategic solutions offered by membrane shielding materials to address electromagnetic/radiation problems were discussed. Then, the design concept, technical innovation, and related mechanisms of the existing membrane shielding materials were expounded, the treatment methods adopted by scholars to study the environment and performance change laws were introduced, and the main difficulties encountered in this area of research were summarized. Finally, on the basis of a comprehensive analysis of the protection provided by membrane shielding materials against electromagnetic/radiation pollution, the action mechanism of membrane shielding materials was expounded in detail, and the research progress, structural design and performance characterization techniques for these materials were summarized. In addition, the future challenges were prospected. This review will help universities, research institutes, as well as scientific and technological enterprises engaged in related fields to fully understand the design concept and research progress of electromagnetic/radiation-contaminated membrane shielding materials. In addition, it is hoped that this review will facilitate efforts to accelerate the research and development of membrane shielding materials and offer potential applications in areas such as electronics, nuclear medicine, agriculture, and other areas of industry.

Waste to energy: A review of biochar production with emphasis on mathematical modelling and its applications

United Nations charter to build a sustainable future has paved the way for the introduction of the Sustainability Development Goals (SDGs) at a global forum. In particular, SDG 11 is aligned with the idea of developing cities and communities that provide quality human life, by attaining net-zero discharge and self-sustainability. In line with the efforts of the global community, biochar has emerged as a viable solution due to its ability to convert waste into value. Finding applications in a spectrum of domains, biochar is being studied for use as an adsorbent, a co-catalyst to promote industrial-grade reactions and as a feed for fuel cells. Moreover, the inclusion of biochar as a soil enhancement material advocates the implementation of closed-loop nutrient cycles. Hence, it is imperative to have a proper understanding of the biomass characteristics, the hydrothermal treatment and the process parameters to be adopted for the production of char in order to identify biomass feedstock based on the application. The current work provides insight into the key factors and conditions employed for the production of biochar based on the plethora of applications. In order build a basic framework to aid in the production of char, the development of a statistical correlation was undertaken to determine the feed and optimum process parameters for the production of biochar based on its applications.

Biochar application for greenhouse gas mitigation, contaminants immobilization and soil fertility enhancement: A state-of-the-art review

Rising global temperature, pollution load, and energy crises are serious problems, recently facing the world. Scientists around the world are ambitious to find eco-friendly and cost-effective routes for resolving these problems. Biochar has emerged as an agent for environmental remediation and has proven to be the effective sorbent to inorganic and organic pollutants in water and soil. Endowed with unique attributes such as porous structure, larger specific surface area (SSA), abundant surface functional groups, better cation exchange capacity (CEC), strong adsorption capacity, high environmental stability, embedded minerals, and micronutrients, biochar is presented as a promising material for environmental management, reduction in greenhouse gases (GHGs) emissions, soil management, and soil fertility enhancement. Therefore, the current review covers the influence of key factors (pyrolysis temperature, retention time, gas flow rate, and reactor design) on the production yield and property of biochar. Furthermore, this review emphasizes the diverse application of biochar such as waste management, construction material, adsorptive removal of petroleum and oil from aqueous media, immobilization of contaminants, carbon sequestration, and their role in climate change mitigation, soil conditioner, along with opportunities and challenges. Finally, this review discusses the evaluation of biochar standardization by different international agencies and their economic perspective.

Life Cycle Assessment (LCA) of Biochar Production from a Circular Economy Perspective

Climate change and environmental sustainability are among the most prominent issues of today. It is increasingly fundamental and urgent to develop a sustainable economy, capable of change the linear paradigm, actively promoting the efficient use of resources, highlighting product, component and material reuse. Among the many approaches to circular economy and zero-waste concepts, biochar is a great example and might be a way to push the economy to neutralize carbon balance. Biochar is a solid material produced during thermochemical decomposition of biomass in an oxygen-limited environment. Several authors have used life cycle assessment (LCA) method to evaluate the environmental impact of biochar production. Based on these studies, this work intends to critically analyze the LCA of biochar production from different sources using different technologies. Although these studies reveal differences in the contexts and characteristics of production, preventing direct comparison of results, a clear trend appears. It was proven, through combining life cycle assessment and circular economy modelling, that the application of biochar is a very promising way of contributing to carbon-efficient resource circulation, mitigation of climate change, and economic sustainability.

The Capture and Transformation of Carbon Dioxide in Concrete: A Review

Concrete is one of the most commonly used engineering materials in the world. Carbonation of cement-based materials balances the CO2 emissions from the cement industry, which means that carbon neutrality in the cement industry can be achieved by the carbon sequestration ability of cement-based materials. Carbon dioxide is a symmetrical molecule and is difficult to separate. This work introduces the important significance of CO2 absorption by using cement-based materials, and summarizes the basic characteristics of carbonation of concrete, including the affected factors, mathematical modeling carbonization, and the method for detecting carbonation. From the perspective of carbon sequestration, it mainly goes through carbon capture and carbon storage. As the first stage of carbon sequestration, carbon capture is the premise of carbon sequestration and determines the maximum amount of carbon sequestration. Carbon sequestration with carbonization reaction as the main way has been studied a lot, but there is little attention to carbon capture performance. As an effective way to enhance the carbon sequestration capacity of cement-based materials, increasing the total amount of carbon sequestration can become a considerably important research direction.

Current trends in production, morphology, and real-world environmental applications of biochar for the promotion of sustainability

Biochar has sparked a lot of interest in recent years for various applications such as contaminant removal, carbon sequestration and soil amendment. However, laboratory scale studies dominates over the real-world applications. In this study, we first enumerated on the various ongoing uses of biochar along with adsorption mechanism; and then identified the most suitable source, and efficient method for biochar production; and finally proposed real-world practical applications of biochar as an additive to control diffuse micropollutant pollution along the highways and railway tracks; as well as the pollution through agricultural runoff. We demonstrated that directly or indirectly, biochar can definitely help to achieve all the 17 Sustainable Development Goals. The study on the practical use of biochar is an emerging area, because a lot of research needs are there to realise the full-potential of biochar with ways of attaining sustainable development goals towards waste, energy and pollution management.

Biochar Produced from Saudi Agriculture Waste as a Cement Additive for Improved Mechanical and Durability Properties-SWOT Analysis and Techno-Economic Assessment

The Kingdom of Saudi Arabia generates an enormous amount of date palm waste, causing severe environmental concerns. Green and strong concrete is increasingly demanded due to low carbon footprints and better performance. In this research work, biochar derived from locally available agriculture waste (date palm fronds) was used as an additive to produce high-strength and durable concrete. Mechanical properties such as compressive and flexural strength were evaluated at 7, 14, and 28 days for control and all other mixes containing biochar. In addition, the durability properties of the concrete samples for the mixes were investigated by performing electric resistivity and ultra-sonic pulse velocity testing. Finally, a SWOT (strengths, weaknesses, opportunities, and threats) analysis was carried out to make strategic decisions about biochar’s use in concrete. The results demonstrated that the compressive strength of concrete increased to 28−29% with the addition of 0.75−1.5 wt% of biochar. Biochar-concrete containing 0.75 wt% of biochar showed 16% higher flexural strength than the control specimen. The high ultrasonic pulse velocity (UPV) values (>7.79 km/s) and low electrical resistivity (<22.4 kΩ-cm) of biochar-based concrete confirm that the addition of biochar resulted in high-quality concrete free from internal flaws, cracks, and better structural integrity. SWOT analysis indicated that biochar-based concrete possessed improved performance than ordinary concrete, is suitable for extreme environments, and has opportunities for circular economy and applications in various construction designs. However, cost and technical shortcomings in biochar production and biochar-concrete mix design are still challenging.

Waste Management for Green Concrete Solutions: A Concise Critical Review

Reinforced concrete based on ordinary Portland cement (OPC) is one of the most commonly used materials in modern buildings. Due to the global growth of the building industry, concrete components have been partially or completely replaced with waste materials that can be used as binders or aggregates. Besides the ecological aspects, modern architecture widely needs materials to make the concrete durable, resisting large loads and various detrimental forces in the environment. This opens the possibilities of managing waste materials and applying them in practice. This paper presents a concise review of the green solutions for ecofriendly materials in the building industry that deal with the practical application of materials commonly treated as waste. The main emphasis was placed on their influence on the properties of the building material, optimal composition of mixtures, and discussion of the advantages and disadvantages of each of the “green” additives. It turned out that some solutions are far from being ecofriendly materials, as they leech and release numerous harmful chemicals into the environment during their presence in concrete. Finally, the paper suggests a research direction for the development of an ecofriendly structural material for a sustainable future.

Potential of biochar use in building materials

A critical review of the articles dealing with biochar in terms of the reuse of biomass waste in building materials and its impact on material properties was conducted using five different electronic databases; thirteen articles were selected for this critical review. Biochar was used as a replacement for cement and aggregate in cementitious composites and as an addition in wood polypropylene composites and plasters. The biochar dosages ranged from 0.5% to 40%; in most composites, the addition of biochar increased strength and reduced thermal conductivity and the bulk density of fresh mortars. Also, biochar dosages of 0.5-2% decreased, while dosages of 10-40% increased water absorption and penetration on cementitious composites. The selected studies mainly introduced biochar use in building materials as a means of biomass waste reduction and its reuse for various purposes, while carbon footprint reduction was addressed in only a few of them. Biochar-containing building material's capability of capturing CO₂ from the air was also observed (0.033 mmol CO₂ g_biochar^-1 to 0.138 mmol CO₂ g_biochar^-1). The results also showed that mortars with CO₂-unsaturated biochar had better mechanical and physical properties than mortars with CO₂-saturated biochar. Selected studies showed biochar-containing building materials have a great potential for carbon footprint reduction. However, there is a lack of comprehensive studies about biochar use in building materials concerning climate change mitigation.

Damage Management of Concrete Structures with Engineered Cementitious Materials and Natural Fibers: A Review of Potential Uses

The importance of the safety and sustainability of structures has attracted more attention to the development of smart materials. The presence of small cracks (<300 µm in width) in concrete is approximately inevitable. These cracks surely damage the functionality of structures, increase their degradation, and decrease their sustainability and service life. Self-sensing cement-based materials have been widely assessed in recent decades. Engineers can apply piezoresistivity for structural health monitoring that provides timely monitoring of structures, such as damage detection and reliability analysis, which consequently guarantees the service life with low maintenance costs. However, concrete piezoresistivity is limited to compressive stress sensing due to the brittleness of concrete. In contrast, engineered cementitious composites (ECC) present excellent tensile ductility and deformation capabilities, making them able to sense tensile stress/strain. Therefore, in this paper, first, the ability of ECC to partly replace transverse reinforcements and enhance the joint shear resistance, the energy absorption capacity, and the cracking response of concrete structures in seismic areas is reviewed. Then, the potential use of natural fibers and cellulose nanofibers in cementitious materials is investigated. Moreover, steel and carbon fibers and carbon black, carbon nanotubes, and graphene, all added as conductive fillers, are also presented. Finally, among the conductive carbonaceous materials, biochar, the solid residue of biomass waste pyrolysis, was recently investigated to improve the mechanical properties, internal curing, and CO2 capture of concrete and for the preparation of self-sensing ECC.

Water treatment sludge conversion to biochar as cementitious material in cement composite

Water treatment sludge was successfully thermally converted to obtain biochar as a stable material with resource potential. This research explored the application of sludge biochar as a supplementary cementitious material. The cement paste samples incorporating different amounts of sludge biochar were prepared, hardened, and analyzed for performance. The results show an improvement in hydration kinetics and mechanical properties of cement paste incorporating biochar, compared to raw sewage sludge. The mineralogical, thermal and microscopic analyses show evidence of pozzolanic activity of the biochar. The samples with 2% and 5% biochar showed higher heat release than the reference material. Specimens with 1%, 2% and 5% biochar showed a slightly higher compressive strength at 28 days compared to the reference material. Sludge conversion to biochar will incur an estimated cost of US$398.23/ton, which is likely to be offset by the substantial benefits from avoiding landfill and saving valuable cementitious materials. Therefore, this research has demonstrated that through conversion to biochar, water treatment sludge can be promoted as a sustainable and alternative cementitious material for cement with minimum environmental impacts, hence contributing to circular economy.

Carbonaceous admixtures in cementitious building materials: Effect of particle size blending on rheology, packing, early age properties and processing energy demand

Application of biochar, produced from locally generated wastes, as admixture in cement is a strategy to upcycle biomass waste and produce durable building materials. This research explores the influence of particle size and porosity of biochar, prepared from coconut shell and wood waste, added at 2 wt% of cement, on rheology, setting time, hydration and early age strength of cement mortar. For each biochar type, three particle size gradations are explored - coarser biochar (d₅₀ = 45-50 μm) (obtained by sieving), finer biochar (d₅₀ = 10-18 μm) (obtained by ball milling) and combination of coarser and finer biochar (d₅₀ = 15-25 μm). Experimental findings suggest that combination of coarser and finer biochar improves workability and rheological properties of binder pastes compared to that with (only) coarser biochar. Depending on biochar type, hydration and rate of setting are accelerated compared to control. Inclusion of finer biochar and combination of finer and coarser biochar improve packing density and degree of hydration of pastes compared to coarser biochar and control, leading to 12-19% enhancement in compressive strength at 7-day age. Micro-structural investigations show that the macro-pores of coarser biochar can be filled with dense hydration products, although some macro-pores may remain unfilled. This offsets improvement in strength that can be achieved through enhancement in packing density. The approach of blending coarser and finer biochar reduces the energy demand and cost associated with ball-milling by 23-37% and SGD 2.30-4.80 per ton respectively compared to only finer (ball-milled) biochar per cubic meter of concrete. Overall, the findings from this research demonstrate that blending of biochar of different particle size distributions can enhance physical properties of cement-based materials, while reducing associated energy consumption.

Viscoelastic Properties, Rutting Resistance, and Fatigue Resistance of Waste Wood-Based Biochar-Modified Asphalt

The purpose of this study is to explore the viscoelastic properties, rutting resistance, and fatigue resistance of waste wood-based biochar-modified asphalt. The biochar with 2%, 4%, and 8% mixing amounts and two kinds of particle size, 75–150 μm and <75 μm, were used as modifiers of petroleum asphalt. Meanwhile, in the control group, a graphite modifier with a particle size of 0–75 μm and mixing amount of 4% was used for comparison. Aged asphalts were obtained in the laboratory by the Rolling Thin Film Oven (RTFO) test and the Pressure Aging Vessel (PAV) test. The viscoelastic properties, rutting resistance, and fatigue resistance of biochar-modified asphalt were evaluated by phase angle, critical high temperature, and fatigue cracking index by the Dynamic Shear Rheometer (DSR) test. In addition, the micromorphology of biochar and graphite was compared and observed by using the scanning electron microscope (SEM). The results show that increasing the mixing amount of biochar gave a higher elastic property and significantly better rutting resistance of the modified asphalt at high temperature. Compared with graphite, the biochar has a rougher surface and more pores, which provides its higher specific surface area. Therefore, it is easier to bond with asphalt to form a skeleton network structure, then forming a more stable biochar–asphalt base structure. In this way, compared to graphite-modified asphalt, biochar-modified asphalt showed better resistance to rutting at high temperature, especially for the asphalt modified with biochar of small particle size. The critical high temperature T(G*/sinδ) of 4% Gd, 4% WD, and 4% Wd was 0.31 °C, 1.57 °C, and 2.92 °C higher than that of petroleum bitumen. In addition, the biochar asphalt modified with biochar of small particle size had significantly better fatigue cracking resistance than the asphalt modified with biochar of large particle size. The fatigue cracking indexes for 2% Wd, 4% Wd, and 8% Wd were 29.20%, 7.21%, and 37.19% lower by average than those for 2% WD, 4% WD, and 8% WD at 13–37 °C. Therefore, the waste wood biochar could be used as the modifier for petroleum asphalt. After the overall consideration, the biochar-modified asphalt with 2%–4% mixing amount and particle size less than 75 μm was recommended.

Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review

In the context of climate change and the circular economy, biochar has recently found many applications in various sectors as a versatile and recycled material. Here, we review application of biochar-based for carbon sink, covering agronomy, animal farming, anaerobic digestion, composting, environmental remediation, construction, and energy storage. The ultimate storage reservoirs for biochar are soils, civil infrastructure, and landfills. Biochar-based fertilisers, which combine traditional fertilisers with biochar as a nutrient carrier, are promising in agronomy. The use of biochar as a feed additive for animals shows benefits in terms of animal growth, gut microbiota, reduced enteric methane production, egg yield, and endo-toxicant mitigation. Biochar enhances anaerobic digestion operations, primarily for biogas generation and upgrading, performance and sustainability, and the mitigation of inhibitory impurities. In composts, biochar controls the release of greenhouse gases and enhances microbial activity. Co-composted biochar improves soil properties and enhances crop productivity. Pristine and engineered biochar can also be employed for water and soil remediation to remove pollutants. In construction, biochar can be added to cement or asphalt, thus conferring structural and functional advantages. Incorporating biochar in biocomposites improves insulation, electromagnetic radiation protection and moisture control. Finally, synthesising biochar-based materials for energy storage applications requires additional functionalisation.

Bio Discarded from Waste to Resource

The modern linear agricultural production system allows the production of large quantities of food for an ever-growing population. However, it leads to large quantities of agricultural waste either being disposed of or treated for the purpose of reintroduction into the production chain with a new use. Various approaches in food waste management were explored to achieve social benefits and applications. The extraction of natural bioactive molecules (such as fibers and antioxidants) through innovative technologies represents a means of obtaining value-added products and an excellent measure to reduce the environmental impact. Cosmetic, pharmaceutical, and nutraceutical industries can use natural bioactive molecules as supplements and the food industry as feed and food additives. The bioactivities of phytochemicals contained in biowaste, their potential economic impact, and analytical procedures that allow their recovery are summarized in this study. Our results showed that although the recovery of bioactive molecules represents a sustainable means of achieving both waste reduction and resource utilization, further research is needed to optimize the valuable process for industrial-scale recovery.

Behavior of Biochar-Modified Cementitious Composites Exposed to High Temperatures

In this study, the effect of biochar on the high temperature resistance of cementitious paste was investigated using multiple experimental methods. The weight loss, cracks, residual compressive strength, and ultrasonic pulse velocity (UPV) of biochar cementitious paste with 2% and 5% biochar exposed to 300, 550 and 900 °C were measured. The products and microstructures of biochar cementitious paste exposed to high temperatures were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The results showed that the cracks of specimens exposed to high temperatures decreased with increasing biochar content. The addition of 2% and 5% biochar increased the residual compressive strength of the specimens exposed to 300 °C and the relative residual compressive strength at 550 °C. As the exposure temperature increased, the addition of biochar compensated for the decreasing ultrasonic pulse velocity. The addition of biochar contributed to the release of free water and bound water, and reduced the vapor pressure of the specimen. The addition of biochar did not change the types of functional groups and crystalline phases of the products of cementitious materials exposed to high temperatures. Biochar particles were difficult to observe at 900 °C in scanning electron microscopy images. In summary, because biochar has internal pores, it can improve the high-temperature resistance of cement paste.

Biochar-Added Cementitious Materials—A Review on Mechanical, Thermal, and Environmental Properties

The enhanced carbon footprint of the construction sector has created the need for CO2 emission control and mitigation. CO2 emissions in the construction sector are influenced by a variety of factors, including raw material preparation, cement production, and, most notably, the construction process. Thus, using biobased constituents in cement could reduce CO2 emissions. However, biobased constituents can degrade and have a negative impact on cement performance. Recently, carbonised biomass known as biochar has been found to be an effective partial replacement for cement. Various studies have reported improved mechanical strength and thermal properties with the inclusion of biochar in concrete. To comprehend the properties of biochar-added cementitious materials, the properties of biochar and their effect on concrete need to be examined. This review provides a critical examination of the mechanical and thermal properties of biochar and biochar-added cementitious materials. The study also covers biochar’s life cycle assessment and economic benefits. Overall, the purpose of this review article is to provide a means for researchers in the relevant field to gain a deeper understanding of the innate properties of biochar imparted into biochar-added cementitious materials for property enhancement and reduction of CO2 emissions.

Remediation of noxious pollutants using nano-titania-based photocatalytic construction materials: a review

Nano-titania (n-TiO₂), due to its unique photocatalytic and hydrophobic properties, can be used to prepare self-cleaning cement-based smart building materials. The n-TiO₂ degrades organic and inorganic pollutants through its photocatalytic action and convert them into non-toxic byproducts, i.e., improves the air quality. In this review, aspects such as methodologies of n-TiO₂ synthesis, approaches for n-TiO₂ loading on cementitious materials, photocatalytic properties, self-cleaning mechanism, and application of n-TiO₂ in cement-based materials have been overviewed. Further, the n-TiO₂ can be used either as coatings or admixtures in pavement blocks, mortars/concrete at zebra crossings, road dividers and linings, and high rise buildings. Moreover, the implications and economic aspects of n-TiO₂ usage in cement-based materials revealed that n-TiO₂ increases the material cost by ~ 27%, (101 to 128.1$) in comparison to conventional building materials. Furthermore, the low-cost carbonized materials such as biochars have been suggested to be used as support of n-TiO₂ to lower the cost and improve the remediation efficiency of photocatalytic concrete.

Towards Sustainable Soil Stabilization in Peatlands: Secondary Raw Materials as an Alternative

Implementation of construction works on weak (e.g., compressible, collapsible, expansive) soils such as peatlands often is limited by logistics of equipment and shortage of available and applicable materials. If preloading or floating roads on geogrid reinforcement or piled embankments cannot be implemented, then soil stabilization is needed. Sustainable soil stabilization in an environmentally friendly way is recommended instead of applying known conventional methods such as pure cementing or excavation and a single replacement of soils. Substitution of conventional material (cement) and primary raw material (lime) with secondary raw material (waste and byproducts from industries) corresponds to the Sustainable Development Goals set by the United Nations, preserves resources, saves energy, and reduces greenhouse gas emissions. Besides traditional material usage, soil stabilization is achievable through various secondary raw materials (listed according to their groups and subgroups): 1. thermally treated waste products: 1.1. ashes from agriculture production; 1.2. ashes from energy production; 1.3. ashes from various manufacturing; 1.4. ashes from waste processing; 1.5. high carbon content pyrolysis products; 2. untreated waste and new products made from secondary raw materials: 2.1. waste from municipal waste biological treatment and landfills; 2.2. waste from industries; 3. new products made from secondary raw materials: 3.1. composite materials. Efficient solutions in environmental engineering may eliminate excessive amounts of waste and support innovation in the circular economy for sustainable future.

Biochar industry to circular economy

Biochar, produced as a by-product of pyrolysis/gasification of waste biomass, shows great potential to reduce the environment impact, address the climate change issue, and establish a circular economy model. Despite the promising outlook, the research on the benefits of biochar remains highly debated. This has been attributed to the heterogeneity of biochar itself, with its inherent physical, chemical and biological properties highly influenced by production variables such as feedstock types and treating conditions. Hence, to enable meaningful comparison of results, establishment of an agreed international standard to govern the production of biochar for specific uses is necessary. In this study, we analyzed four key uses of biochar: 1) in agriculture and horticulture, 2) as construction material, 3) as activated carbon, and 4) in anaerobic digestion. Then the guidelines for the properties of biochar, especially for the concentrations of toxic heavy metals, for its environmental friendly application were proposed in the context of Singapore. The international status of the biochar industry code of practice, feedback from Singapore local industry and government agencies, as well as future perspectives for the biochar industry were explained.

Biochar admixtured lightweight, porous and tougher cement mortars: Mechanical, durability and micro computed tomography analysis

Currently, the global carbon footprint of cement industry is nearly 7 to 8% and this number is expected to grow in the near future given the continued global demand of cement usage in the construction and other sectors. Additionally, extraction of sand from the coastal and riverine environment is detrimental to ecosystem health and also gives rise to sand mafia in many developing countries. Biochar has the potential to sequester CO₂ in cement mortars. The purpose of this study was to valorise a waste biomass (poultry litter) to carbon-rich biochar and utilise as filler material to replace the sand in the range of 10-40% of the total weight in cement. A total of four mix designs each with three replicates at 10%, 20%, and 40% replacement of sand and control (0% biochar addition) were investigated for their mechanical, durability and micro-computed tomography (CT) analysis. The results showed that the flexural strength of the composites at 20% biochar replacement of sand was improved by 26% when compared to control. Biochar addition lowered the thermal conductivity of the cement mortars and was optimised at 10% addition. The density of the mortars decreased ~20% with 40% biochar addition. Micro-CT analysis showed nearly a five-fold increase in the 2-dimensional porosity of the samples, from 2.5% (control) to 12% for samples which had 40% biochar; however, no marked changes were noticed for samples at 20% biochar addition. Taking mortar plastering as an example for 100 m² area with standard 12 mm thickness revealed that CO₂ emissions decreased 20% when sand was replaced with 40% biochar as compared to control specimen. It was concluded that biochar has the potential to replace the sand in the mortars for improving toughness, lowering thermal conductivity and density of the cement composites.

Current Sustainable Trends of Using Waste Materials in Concrete—A Decade Review

Concrete is the most used construction material in the world. Consequently, the mass extraction of virgin materials required for concrete production causes major environmental impacts. With a focus on promoting sustainability, numerous research studies on incorporating waste materials to replace virgin substances in concrete were undertaken. Despite this vast volume of published literature, systematic research studies on these sustainable concrete mixes that inform various stakeholders on current research trends, future research directions, and marketability options products are seldom conducted. This paper presents a decade review on sustainable concrete with a focus on virgin materials being replaced with waste materials. It aims to inform researchers of current research trends and gaps in the research area of waste material use in concrete. The review also identifies key parameters that restrict the marketability of these sustainable concrete products. The three-step research methodology involves a bibliometric assessment, a key review of selected waste materials, and an interview with a panel of experts focusing on impediments towards the transition of sustainable concrete products into the industry market. Bibliometric assessment was based on 1465 research publications in which five key materials (plastic, glass, fly ash, slag) and construction and demolition waste were selected for the review. The interview was conducted with ten industry experts to discuss the industry limitations in the commercial establishment of materials. The review of existing knowledge and the findings on sustainable concrete presented in this paper provide directions for both research academics and industry stakeholders to systematically focus on sustainable concrete products that are market-ready.

Biochar-red clay composites for energy efficiency as eco-friendly building materials: Thermal and mechanical performance

Biochar and red clay were used to develop eco-friendly building materials with improved thermal and mechanical performance. Rice husk, coconut shell, and bamboo were prepared by thermally decomposing as biochar. Thermal conductivity measurements, scanning electron microscopy imaging, compressive strength measurements, and an infrared heat transfer experiment were performed, and the results showed that the mixture of biochar tends to lower the thermal conductivity. The compressive strength of specimens mixed with rice husk decreased, but that of specimens mixed with coconut shell and bamboo tended to increase. The infrared heat transfer test showed that the thermal performance of the mixed rice husk specimens was significant, while the specimen mixed with coconut shell and bamboo showed thermal performance improvement. A comprehensive evaluation of the improvement in thermal performance and strength indicated that a 10 wt.% mixture of bamboo was the most effective. Therefore, it was possible to effectively determine the type and weight ratio of biochar to red clay binder an important step in the study of biochar and red clay building materials.

Enhancement of high temperature performance of cement blocks via CO2 curing

Carbonation for the curing of cement-based materials has been gaining increased attention in recent years, especially in light of emerging initiatives to reduce carbon dioxide (CO₂) emissions. Carbonation method or CO₂ curing is founded on the basis of the reaction between CO₂ and cement products to form thermally stable and denser carbonate, which not only improves the physical and mechanical properties of cement-based materials, but also has the ability to utilize and store CO₂ safely and permanently. This study aims to assess the effect of CO₂ curing technology on the high-temperatures performance of cement blocks. Upon molding, dry-mix cement blocks were cured under statically accelerated carbonation condition (20% CO₂ concentration with 70% relative humidity) for 28 days, followed by exposure to elevated temperatures of 300 °C to 800 °C in order to comprehensively study the principal phase changes and decompositions of cement hydrates. The results indicated that CO₂ curing improved the performance of cement blocks, such as enhancement in the residual compressive strength and reducing the sorptivity. At 600 °C, the scanning electron microscopy (SEM) revealed a denser microstructure while thermal analisis and X-ray diffraction (XRD) analysis also clearly demonstrated that higher amounts of calcium carbonate were present in the cement blocks after CO₂ curing, suggesting better high-temperature performance compared to natural cured cement blocks. In general, an improved high-temperature performance, specifically at 600 °C of the dry-mixed cement blocks was demonstrated by adopting the CO₂ curing technology. This confirms the potential of utilizing CO₂ curing technology in not only improving quality of cement blocks, new avenue for storing of CO2 in construction material can be realized at the same time.

Carbonaceous micro-filler for cement: Effect of particle size and dosage of biochar on fresh and hardened properties of cement mortar

This study explores influence of biochar particle size and surface morphology on rheology, strength development and permeability of cement mortar, under moist and dry curing condition. Experimental results show that the flowability and viscosity of cement paste is more affected by macro-porous coarser (or 'normal') biochar particles of size 2-100 μm (NBC) compared to fine (or 'ground' biochar), which is in the size range of 0.10-2 μm (GBC). Addition of both GBC and NBC accelerated hydration kinetics and improved early (1-day) and 28-day strength by 20-25% compared to the control. Water permeability, measured by capillary absorption was reduced by about 50% compared to control mortar, due to the addition of 0.50-1% NBC and GBC respectively. GBC is found to be more effective in minimizing loss in strength and water tightness under dry curing condition compared to the control and mortar with NBC and quartz filler respectively. In summary, findings from the study show that finer biochar particles offer superior performance in improving early strength and water tightness compared to normal biochar (with macro-pores), while 28-day properties are similar for mortar with both GBC and NBC respectively.

The impact of crop residue biochars on silicon and nutrient cycles in croplands

Croplands are subjected to nutrient loss mainly due to agricultural harvest. Silicon has beneficial effect on alleviating nutrient imbalance-induced stress. Addition of crop residue biochars to cropland can import both silicon (Si) and nutrients (e.g. nitrogen, phosphorus and potassium) directly and enhance their availability. Nevertheless, how the concentrations of Si and nutrients vary among the biochars derived from different feedstocks, and how crop Si and nutrients respond to addition of biochars to croplands have not yet been clarified comprehensively and quantitatively. Total and essentially available Si and nutrients in crop residue biochars and their relationships with crop Si and nutrient uptake were investigated by using data collected from peer reviewed papers. Biochars derived from rice husk, rice straw, corn stover, sugarcane residues, and wheat straw, which were produced by thermal pyrolysis at 150-900 °C under oxygen-limited conditions, averagely contained 20.03% (n = 10), 12.39% (n = 16), 10.25% (n = 7), 7.40% (n = 9), and 3.34% (n = 3) of total Si, respectively. By contrast, crop residue biochars contained, on average, 1.23% nitrogen (n = 461), 0.32% phosphorus (n = 209), 0.56% sulfur (n = 187), 2.73% potassium (n = 197), 1.17% calcium (n = 123), and 0.54% magnesium (n = 111), which largely depended on and varied widely with their feedstocks and pyrolysis conditions. On average, 32.6%-54.9% of the total Si and nutrients (excluding nitrogen) in crop residue biochars were essentially available. Hence, addition of crop residue biochars to croplands may contribute a considerable amount of total and available Si and nutrients, except available inorganic nitrogen. The increasing amounts of Si and nutrient input with addition of biochars had positive and statistically significant (p < 0.05) relationships with the increment of crop Si and nutrient uptake, respectively. In conclusion, addition of crop residue biochars can be beneficial to sustainable agriculture system through concerting Si and nutrient cycling in croplands.

Outlook of carbon capture technology and challenges

The greenhouse gases emissions produced by industry and power plants are the cause of climate change. An effective approach for limiting the impact of such emissions is adopting modern Carbon Capture and Storage (CCS) technology that can capture more than 90% of carbon dioxide (CO₂) generated from power plants. This paper presents an evaluation of state-of-the-art technologies used in the capturing CO₂. The main capturing strategies including post-combustion, pre-combustion, and oxy - combustion are reviewed and compared. Various challenges associated with storing and transporting the CO₂ from one location to the other are also presented. Furthermore, recent advancements of CCS technology are discussed to highlight the latest progress made by the research community in developing affordable carbon capture and storage systems. Finally, the future prospects and sustainability aspects of CCS technology as well as policies developed by different countries concerning such technology are presented.

Influence of biochars on the accessibility of organochlorine pesticides and microbial community in contaminated soils

Biochar can be used as a promising potential substance to reduce the availability of toxic elements and compounds in contaminated soils but its effects on the accessibility of pesticides and microbiological interactions still remain unclear. Here, 65 day incubation experiments were conducted to investigate the efficacy of biochars on the accessibility of 21 different organochlorine pesticides (OCPs), and also to evaluate their influence on soil microbial community. The tested soil was collected from an agricultural field, containing loamy sand texture, and historically contaminated with high concentrations of OCPs. The soil was amended with four different kinds of biochars: sewage sludge biochar (SSBC), peanut shells biochar (PNBC), rice straw biochar (RSBC), and soybean straw biochar (SBBC). The results indicated that biochar-amendments had strong effects upon OCP accessibility over time and can act as super sorbent. Despite greater persistence of OCPs in soil, the application of selected biochars significantly (p < 0.01) reduced the accessibility of ∑OCPs in the amended soil in the order of SSBC (8-69%), PNBC (11-75%), RSBC (6-67%), and SBBC (14-86%), as compared to the control soil during 0-65 d incubation period. Moreover, the findings from total phospholipid acid (PLFA) and Illumina next-generation sequencing revealed that the incorporation of biochar have altered the soil microbial community structure over time. Higher abundances of Proteobacteria, firmicutes, Gemmatimonadetes, and Actinobacteria were found in biochar amendments. However, the relative abundances of Acidobacteria and Chloroflexi decreased, following biochar addition. The findings of these experiments suggest that biochar addition to soil at the rate of 3% (w/w) could be advantageous for decreasing accessibility of OCPs, enhancing the soil microbial communities, and their subsequent risk to environment and food chain contamination.

High volume fly ash mortar containing nano-calcium carbonate as a sustainable cementitious material: microstructure and strength development

The mechanisms underlying the effects of nano-calcium carbonate (NC) on the strength of high volume fly ash (FA) mortar are discussed. Two NCs are used as 2%, 4%, 6%, and 8% by weight of cementitious materials. Hydrated products of fly ash mortar containing NC was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG) and differential thermal gravity (DTG) analysis. Results indicate that NC could improve strength of FA mortar due to the more rapid growth of hydrated products induced by NC through additional nucleation sites. Corresponding to the highest measured strength of FA mortar, the optimal contents of NC are around 2%. In addition, the presence of 2% NC improved the microstructure of FA mortar after 180 days due to the formation of calcium carbonaluminate hydrate.

Rheological Performance of Bio-Char Modified Asphalt with Different Particle Sizes

To improve the performance of petroleum asphalt, bio-char was used as a modifier for a petroleum asphalt binder, in this study. The rheological properties of bio-char modified asphalt binders were compared with different particle sizes and contents, with one control and one flake graphite modified asphalt binder. Specifically, the bio-char modifiers with two particle sizes (ranging from 75 μm–150 μm and less than 75 μm) and three contents of 2%, 4%, and 8% were added into the asphalt binder. A flake graphite powder with particle sizes less than 75 μm was used as a comparison modifier. The Scanning Electron Microscopy (SEM) image showed the porous structure and rough surface of bio-char as well as dense structure and smooth surface of flake graphite. A Rotational Viscosity (RV) test, Dynamic Shear Rheometer (DSR) test, aging test, and Bending Beam Rheometer (BBR) test were performed to evaluate the properties of bio-char modified asphalt in this study. Both modifiers could improve the rotational viscosities of the asphalt binders. The porous structure and rough surface of bio-char lead to larger adhesion interaction in asphalt binder than the smooth flake graphite. As a result, the bio-char modified asphalts had better high-temperature rutting resistance and anti-aging properties than the graphite modified asphalt, especially for the binders with the smaller-sized and higher content of bio-char particles. Furthermore, the asphalt binder modified by the bio-char with sizes less than 75 μm and about 4% content could also achieve a better low-temperature crack resistance, in comparison to other modified asphalt binders. Thus, this type of bio-char particles is recommended as a favorable modifier for asphalt binder.