Search Results (42)

This study investigates the impact of partially replacing cement with fly ash (FA) on the mechanical performance of fiber-reinforced rubberized concrete (FRRC) incorporating waste tyre rubber and recycled macro-synthetic fibers (MSF). FRRC mixtures were prepared with varying fly ash replacement levels (0%, 25%, and 50%), rubber aggregate contents (0%, 10%, and 20% by volume of fine aggregate), and macro-synthetic fiber dosages (0% to 1% by total volume). The fresh properties were evaluated through slump tests, while hardened properties including compressive strength, splitting tensile strength, and flexural strength were systematically assessed. Results demonstrated that fly ash substitution up to 25% improved the interfacial bonding between rubber particles, fibers, and the cementitious matrix, leading to enhanced tensile and flexural performance without significantly compromising compressive strength. However, at 50% replacement, strength reductions were more pronounced due to slower pozzolanic reactions and reduced cement content. The inclusion of MSF effectively mitigated strength loss induced by rubber aggregates, improving post-cracking behavior and toughness. Overall, an optimal balance was achieved at 25% fly ash replacement combined with 10% rubber and 0.5% fiber content, producing a more sustainable composite with favorable mechanical properties while reducing carbon and ecological footprints. These findings highlight the potential of integrating industrial by-products and waste materials to develop eco-friendly, high-performance FRRC for structural applications, supporting circular economy principles and reducing the carbon footprint of concrete infrastructure. Full article

Nickel, as a toxic trace element in fine particulate matter (PM_2.5), has detrimental effects on both air quality and human health. Based on measurements from 2020 to 2021 using a single-particle aerosol mass spectrometer (SPAMS), this study investigates the properties of nickel-containing particles (NCPs) in Guangzhou. The composition, sources, and temporal trends of NCPs were evaluated and the impact of the clean ship fuel policy introduced in 2020 was also examined. The key findings include: (1) Nickel particles account for 0.08% number fraction of PM_2.5, which is consistent with previously reported mass fraction in PM_2.5. (2) Three distinct types of NCPs were identified, including Ni-fresh, Ni-aged, and Ni-ash. Each type exhibits unique characteristics in size distribution, wind direction dependence, sources, and temporal variations. Ni-fresh particles originate from shipping emissions in the Huangpu Port area 2 km away and are the major contributors to fine nickel particles in the region. (3) Ni-aged and Ni-ash particles, which carry secondary components, tend to be larger (>500 nm) and are representative of regional or background nickel particles. (4) The implementation of the clean ship fuel policy has effectively reduced the number concentrations of NCPs and is beneficial to regional and local air quality. Full article

The incorporation of circulating fluidized bed (CFB) fly ash into self-leveling cement-based (SLC) paste production presents significant environmental advantages. However, its addition deteriorates the fresh properties of the paste, posing challenges for practical implementation. This research examined the fresh properties of SLC paste blended with CFB fly ash, emphasizing fluidity, rheological characteristics, and bleeding rate. To enhance flowability, polycarboxylate superplasticizer (PCE) was incorporated, with particular emphasis on its interaction with CFB fly ash. The findings reveal that adding CFB fly ash to cement-based paste significantly decreased fluidity while increasing yield stress and plastic viscosity. Incorporating 20 wt.% CFB fly ash reduced paste fluidity by 51.4%, while plastic viscosity and yield stress increased by factors of 2.3 and 73, respectively. While PCE enhanced the fluidity of the blended paste, its water-reducing efficiency diminished, and the bleeding rate of the paste increased with higher CFB fly ash dosage. The water-reducing capability of PCE in the CFB fly ash-blended cement paste with 20 wt.% CFB fly ash decreased by 40.0%, and the bleeding rate of the paste increased from 0.6% to 6.7%. This effect was primarily attributed to the poor compatibility between PCE and CFB fly ash. The decline in PCE efficiency with higher CFB fly ash content, along with its lower adsorption capacity on CFB fly ash compared to cement particles, further confirmed this incompatibility. Full article

A major challenge in modern infrastructure is the excessive reliance on traditional Portland cement, which contributes significantly to environmental degradation and durability issues. This study addresses the need for sustainable and durable construction materials by investigating geopolymer concrete as an eco-friendly alternative, optimizing its mechanical and microstructural properties to enhance long-term performance in infrastructure applications. The performance of sustainable geopolymer concrete made with silica fume (SF) and fly ash (FA) and utilizing different alkaline activators (AAs) was examined in this study. The alkaline activators included sodium hydroxide (SH), potassium hydroxide (PH), and sodium silicate (SS) solutions. A total of twelve geopolymer concrete mixes were prepared and evaluated. The study considered several variables, including SF content (ranging from 10% to 100%), type of AA (SH+SS or PH+SS), AA concentration, and the AA to cementitious materials (AA/C) ratio. Workability, compressive strength, bending strength, tensile strength, and water absorption were among the mechanical characteristics of the concrete that were assessed, both in fresh and hardened states of the proposed concrete. The geopolymer concrete microstructure was also examined by performing X-ray diffraction (XRD), energy dispersive X-ray (EDX), and scanning electron microscopy (SEM) investigations on a few chosen mixes. The findings showed that when SF content was 10%, 20%, 30%, and 100% as a replacement of FA, the concrete slump rose by 10%, 15%, 15%, and 120%, respectively. However, the compressive strength was increased only with up to 20% SF. Geopolymer concrete with PH as the alkaline activator exhibited up to 13% lower compressive strength compared to SH. The geopolymer concrete microstructure was influenced by the presence of SF, leading to the formation of ettringite. Some FA particles that remained unreacted or were only partially reacted, along with voids, were observed. The findings from this study contribute to the development of sustainable geopolymer concrete, offering a promising solution for green structural applications. Full article

To explore the effect of corn straw biochar on soil water retention, the characterization of corn straw biochar and its application in semiarid loess were investigated. For the corn straw biochars with different preparation conditions, significant differences were observed in elemental composition, specific surface area, pores distribution, surface functional groups, water absorption, and retention performance. The findings demonstrated that while the pyrolysis temperature (300 °C, 500 °C, and 700 °C) had no significant effect, the water absorption performance of biochar increased steadily as particle size increased (<0.25 mm, 0.25–1 mm, and >1 mm). Further, a greenhouse pot experiment with cucumber seedlings was performed using different proportions of biochar application (0.25%, 0.5%, 1%). Compared with no biochar application, the cucumber seedling fresh weight displayed significant improvement (8.89–95.56%), followed by capillary porosity (3.28–30.04%), total porosity (7.91–21.04%), and field water capacity (1.59–11.96%). Conversely, soil bulk density decreased by 3.50–14.69% after the treatments of biochar. Among all the prepared biochars, CSBC700 (particle size > 1 mm, 1% application rate) exhibited the maximum values in both field water capacity (38.78%) and saturated water content (42.25%). Based on the findings of the correlation analysis, the following characteristics may be used to rank the effect of corn straw biochar on soil water retention: application rate, O/C, pH, Ash%, C%, specific surface area, pore volume, and pore width. Biochar with larger particle sizes and abundant hydrophilic functional groups (hydroxyl and carboxyl groups) can greatly improve soil water retention performance. These results provide new insight and support for the utilization of straw and the improvement of soil water retention in semiarid regions. Full article

A fundamental study has been conducted on the effective utilization of rice husk ash (RHA) in concrete. RHA is an agricultural byproduct characterized by silicon dioxide as its main component, with a content of 90% or more and a porous structure that absorbs water during mixing, thereby reducing fluidity. The quality of RHA varies depending on the calcination environment; however, the effect is not consistent. In this study, the pore structure was modified, and fluidity was improved by adjusting the particle size of the RHA. From a quality control perspective, this study aims to classify grades using Luxan values. While the characterization of RHA is based on Luxan values, the methodology for measuring its hydration response has not been reviewed. The test methods used in this study are as follows. To test the raw materials, density, specific surface area, XRF, SEM, and isothermal adsorption–desorption curves were measured, and fluidity was measured in fresh mortar. In a hardened mortar, compressive strength and drying shrinkage length change rate were measured. In addition, XRD and TG were measured for specimens after the compressive strength test. The selective dissolution method was used to measure the hydration rate. By adjusting the particle size of RHA to 45 µm, fluidity was enhanced. The relationship between the Luxan value and the basic properties of the mortar indicates that higher Luxan values correspond to greater compressive strength and drying shrinkage. We believe that the method used in this experiment can be used to quantify RHA. Full article

In response to the environmental pollution caused by transportation and accumulation of large-scale shield muck, the on-site reutilization of shield muck is an effective approach. This study explored the feasibility of silty clay muck to prepare muck grout. Through orthogonal experiments, the effects of cement, fly ash, shield muck, admixture, and the water–solid ratio on the fresh properties and mechanical properties of muck grout were studied. The performance prediction model was established Additionally, the intrinsic relationships between the compressive strength and microstructure of shield muck grouting materials were explored through multi-technology microstructural characterization. The results indicate that the content of muck and the water–solid ratio have a greater significant influence on the bleeding ratio, flowability, setting time, and volume shrinkage rate of muck grout compared to other factors. Cement has a greater significant influence on the compressive strength of muck grout than other factors. An optimal mix proportion (12% for cement, 18% for fly ash, 50% for muck, 0.465 for water–solid ratio, 19.5% for river sand, and 0.5% for bentonite) can produce grouting materials that meet performance requirements. The filling effect of cementitious substances and the particle agglomeration effect reduce the internal pores of grouting materials, improving their internal structure and significantly enhancing their compressive strength. Utilizing shield muck as a raw material for shield synchronous grouting is feasible. Full article

To address the issues of corrosion weakening of solid-waste-based backfill material caused by mine water, a novel hydrophobic solid waste backfill (HSBF) material was developed using polydimethylsiloxane (PDMS) and a silane coupling agent (SCA) as hydrophobic modification additives, and NaOH (SH) and sodium silicate (SS) as alkali activators. Fly ash and slag were chosen as the primary raw solid waste materials. The rheological properties of the hydrophobic-treated backfill slurries were measured, and the resulting physicochemical properties were compared with the unmodified reference group. This study reveals that the fresh HSBF slurry follows a Modified Bingham (M-B) model with shear-thinning characteristics. The addition of PDMS causes an increase in the water contact angle of the hardened HSBF material with F8S2 to up to 134.9°, indicating high hydrophobicity. Morphological observations indicated that PDMS mainly attaches to the inorganic particles’ surface through the bridging action of SCA for the hydrophobic modification of the backfill material. The overall strength of the HSBF materials was further ensured via fly ash–slag ratio optimization, and was found to be enhanced up to 98% by increasing slag content from 20% to 50%. This is mainly attributed to the hydration of slag, forming C-S(A)-H gel, which contributes to the increased strength. The novel HSBF material enables the elimination of cement in mine backfilling applications, demonstrating good economic benefits. Its excellent mechanical and hydrophobic properties can not only prevent overburden displacement in goaf areas, but can also mitigate water resource loss from overlying strata and simultaneously reduce the safety risks associated with long-term mine water deterioration. Full article

Additives such as nano-silica and fly ash are widely used in cement and concrete materials to improve the rheology of fresh cement and concrete and the performance of hardened materials and increase the sustainability of the cement and concrete industry by reducing the usage of Portland cement. Therefore, it is important to study the effect of these additives on the rheological behavior of fresh cement. In this paper, we study the pulsating Poiseuille flow of fresh cement in a horizontal pipe by considering two different additives and when they are combined (nano-silica, fly ash, combined nano-silica, and fly ash). To model the fresh cement suspension, we used a modified form of the power-law model to demonstrate the dependency of the cement viscosity on the shear rate and volume fraction of cement and the additive particles. The convection–diffusion equation was used to solve for the volume fraction. After solving the equations in the dimensionless forms, we conducted a parametric study to analyze the effects of nano-silica, fly ash, and combined nano-silica and fly ash additives on the velocity and volume fraction profiles of the cement suspension. According to the parametric study presented here, larger nano-silica content results in lower centerline velocity of the cement suspension and larger non-uniformity of the volume fraction. Compared to nano-silica, fly ash exhibits an opposite effect on the velocity. Larger fly ash content results in higher centerline velocity, while the effect of the fly ash on the volume fraction is not obvious. For cement suspension containing combined nano-silica and fly ash additives, nano-silica plays a dominant role in the flow behavior of the suspension. The findings of the study can help the design and operation of the pulsating flow of fresh cement mortars and concrete in the 3D printing industry. Full article

This study critically reviews lithium slag (LS) as a supplementary cementitious material (SCM), thereby examining its physiochemical characteristics, mechanical properties, and durability within cementitious and geopolymer composites. The review reveals that LS’s particle size distribution is comparable to fly ash (FA) and ground granulated blast furnace slag (GGBS), which suggests it can enhance densification and nucleation in concrete. The mechanical treatment of LS promotes early hydration by increasing the solubility of aluminum, lithium, and silicon. LS’s compositional similarity to FA endows it with low-calcium, high-reactivity properties that are suitable for cementitious and geopolymeric applications. Increasing the LS content reduces setting times and flowability while initially enhancing mechanical properties, albeit with diminishing returns beyond a 30% threshold. LS significantly improves chloride ion resistance and impacts drying shrinkage variably. This study categorizes LS’s role in concrete as a filler, pozzolan, and nucleation agent, thereby contributing to the material’s overall reduced porosity and increased durability. Economically, LS’s cost is substantially lower than FA’s; meanwhile, its environmental footprint is comparable to GGBS, thereby making it a sustainable and cost-effective alternative. Notwithstanding, there is a necessity for further research on LS’s fine-tuning through grinding, its tensile properties, its performance under environmental duress, and its pozzolanic reactivity to maximize its utility in concrete technologies. This study comprehensively discusses the current strengths and weaknesses of LS in the field of building materials, thereby offering fresh perspectives and methodologies to enhance its performance, improve its application efficiency, and broaden its scope. These efforts are driving the sustainable and green development of LS in waste utilization and advanced concrete technology. Full article

Fly ash is a by-product of coal-fired thermal power plants and offers great potential for the use of resources. To effectively improve the durability of reinforced concrete structures in marine environment and achieve waste to treasure, fly ash is widely used as a pozzolanic material due to its long-hydration characteristics and effects of micro-aggregate, micro-filling and secondary hydration. In this study, both the experimental investigation and numerical simulation are carried out to study the chloride transport characteristics of fly ash cement paste. The variation in chloride diffusivity with fly ash content, water-to-binder ratio and curing age up to 360 days is studied via accelerated conductivity measurement, and it is found that the above three experimental variables have a significant impact on the chloride diffusivity. For the influence of the dosage of fly ash, the optimum dosage is 30%. By introducing specific rules for the particle distribution, the fresh fly ash cement paste is first made. Based on the volume change characteristics of fly ash and cement particles after hydration, the vector hydration model of fly ash cement paste is established by considering the water shortage effect caused by hydration layer interference. After the accuracy of this hydration model is verified by the results from third-party experiments, the random walk algorithm is proposed to calculate the diffusion coefficient of the reconstructed mineral admixture cement paste. By comprehensive comparison with the experimental results from the third-party and self-conducted experiments, the numerical model for predicting the chloride diffusivity of fly ash cement paste is verified. Full article

This study investigates the effects of five different super-plasticizers (SPs): melamine sulfonate (M), naphthalene-based (N), lignosulfonate (L), polyether-type (P-I), and polyester-type polycarboxylate super-plasticizers (P-II), on fly ash through fluidity, viscoelasticity, inter-microstructure, and mechanism of action (adsorption and zeta) experiments. Additionally, the stability of SPs on AAs was investigated in the ATR-FTIR experiment. The results show that most SPs were effective admixtures under high Ms (2.25) of waterglass (WG) alkali activators (AAs), while P-I SPs performed better under low Ms (1.0) of WG AAs in FA-AAM fly ash pastes. Meanwhile, the higher adsorption and zeta values of samples with P-I SPs were useful for the increase of mesh size of inter-particles and consequently promoted the rheology of FA-AAMs fresh pastes. The more stable structure (ether bond) and the formation of small functional groups (carboxylic acid groups) of P-I SPs in the AAs environment may be the main reasons for this. Full article

Fly ash from coal represents the foremost waste product of fossil fuel combustion. These waste materials are most widely utilised in the cement and concrete industries, but the extent of their use is insufficient. This study investigated the physical, mineralogical, and morphological characteristics of non-treated and mechanically activated fly ash. The possibility of enhancing the hydration rate of the fresh cement paste by replacing part of the cement with non-treated and mechanically activated fly ash, and the hardened cement paste’s structure and early compressive strength performance, were evaluated. At the first stage of the study, up to 20% mass of cement was replaced by untreated and mechanically activated fly ash to understand the impact of the mechanical activation on the hydration course; rheological properties, such as spread and setting time; hydration products; mechanical properties; and microstructure of fresh and hardened cement paste. The results show that a higher amount of untreated fly ash significantly prolongs the cement hydration process, decreases hydration temperature, deteriorates the structure and decreases compressive strength. Mechanical activation caused the breakdown of large porous aggregates in fly ash, enhancing the physical properties and reactivity of fly ash particles. Due to increased fineness and pozzolanic activity by up to 15%, mechanically activated fly ash shortens the time of maximum exothermic temperature and increases this temperature by up to 16%. Due to nanosized particles and higher pozzolanic activity, mechanically activated fly ash facilitates a denser structure, improves the contact zone between the cement matrix, and increases compressive strength up to 30%. Full article

The protection of the environment must be a priority in our society, and the construction sector can contribute significantly to this goal. Construction, being one of the industrial sectors that is more demanding in terms of raw materials, must reinforce its effort to implement, in a more profound and systematic way, the paradigm of the circular economy. In this sense, in recent years several studies have been trying to contribute solutions aimed at reintroducing industrial by-products or residues in new products for the construction industry. It should be noted that nowadays it is increasingly important to introduce a higher percentage of recycled materials in concrete. In this context, the present work addresses the appropriateness of a design procedure proposed to maximize the content of electric arc furnace slag (EAFS) and include recycled tire steel fibers (RTSF) in the production of more sustainable structural concretes. For this, the properties of various concrete mixtures at the fresh and hardened state, obtained by the substantial substitution of coarse and fine natural aggregates by EAFS and fly ash (FA), were investigated. The design of EAFS mixtures was based on two conventional reference mixtures (REF1 and REF2), and by using the modified Andreasen and Andersen particle packing model, these were optimized to achieve maximum packing density. Compressive strength, modulus of elasticity behavior, and fresh and physical properties were assessed in order to define the best mix proportions with respect to the predefined requirements of ordinary mixtures. Untreated recycled tire steel fibers (RTSF) were included in the developed sustainable concrete to perform a comparison of the physical properties with unreinforced concretes developed with natural aggregates (REF2) and with EAFS aggregates (EAFS8D1). This incorporation was intended to improve the physical behavior of unreinforced concretes with EAFS aggregates. Mixtures with high percentages of waste aggregates up to 70% (in weight), and 10% (in weight) of FA were obtained, showing competitive mechanical behavior compared to REF1 and REF2. These concrete compositions showed minimum and maximum compressive strengths between 9 MPa and 37 MPa, respectively. This study coverd the two major classes of concrete used as structural material, namely structural concrete and fiber reinforced concrete. Full article

Several studies have investigated the properties of alkali-activated materials (AAM), considering it as a substitute of cementitious concrete. However, the studies on alkali-activated self-consolidating concrete (AASCC) are extremely limited. This paper investigated the properties of AASCCs utilizing ground granulated blast furnace slag (GGBFS) as the main precursor. Single, binary, and ternary AASCCs were produced using fly ash Class-F (FA) and silica fumes (SF) as a replacement for GGBFS. The fresh properties including filing ability, passing ability and stability, as well as the hardened properties including unconfined compressive strength, ultrasonic pulse velocity, electrical resistivity, absorption, and sorptivity of the ambient cured one-part AASCC mixtures with different precursor blends were investigated. In addition, the microstructural properties of 90-day AASCC blends were studied by various microscale analysis methods. This paper demonstrated that the higher fraction of sodium carbonate/silicate activators, ranging from 20% to 25%, contributed to delayed reaction kinetics and satisfactory fresh and mechanical properties in all systems due to their nature. Slag replacement with variable SF or FA class-F ratios, instead, could indeed adjust the particle size distribution of the total binder material and improve the fresh concrete characteristics in binary and ternary systems. Finally, the formation of various reaction products and binding gels, i.e., C-(N)A-S-H, was found to have a significant impact on several transport mechanisms, including capillary sorptivity, permeable pores, and bulk electrical resistivity. Full article