Urban Mining of Bivalve Shell Waste as a Sustainable Alternative to Limestone Exploitation: A Review on Alkali-Activated Cements and Mortars

Construction spoil (CS), a prevalent type of construction and demolition waste, is characterized by high production volumes and substantial stockpiles. It contaminates water, soil, and air, and it can also trigger natural disasters such as landslides and debris flows. With the advent of alkali activation technology, utilizing CS as a precursor for alkali-activated materials (AAMs) or supplementary cementitious materials (SCMs) presents a novel approach for managing this waste. Currently, the low reactivity of CS remains a significant constraint to its high-value-added resource utilization in the field of construction materials. Researchers have attempted various methods to enhance its reactivity, including grinding, calcination, and the addition of fluxing agents. However, there is no consensus on the optimal calcination temperature and alkali concentration, which significantly limits the large-scale application of CS. This study investigates the effects of the calcination temperature and alkali concentration on the mechanical properties of CS–cement mortar specimens and the ion dissolution performance of CS in alkali solutions. Mortar strength tests and ICP ion dissolution tests are conducted to quantitatively assess the reactivity of CS. The results indicate that, compared to uncalcined CS, the ion dissolution performance of calcined CS is significantly enhanced. The dissolution amounts of active aluminum, silicon, and calcium are increased by up to 420.06%, 195.81%, and 256.00%, respectively. The optimal calcination temperature for CS is determined to be 750 °C, and the most suitable alkali concentration is found to be 6 M. Furthermore, since the Al O bond is weaker and more easily broken than the Si O bond, the dissolution amount and release rate of active aluminum components in calcined CS are substantially higher than those of active silicon components. This finding indicates significant limitations in using CS solely as a precursor, emphasizing that an adequate supply of silicon and calcium sources is essential when preparing CS-dominated AAMs.

In this work, bioceramic hydroxyapatite (HAp) was synthesized based on sand lobster shells (Panulirs homarus) as a source of calcium using the precipitation method. Sand lobster shell powder was calcinated with temperature variations of 600, 800, and 1000 °C for 6 hours. The effect of calcination temperature on sand lobster shell powder was characterized to determine the optimal temperature for the synthesis of HAp. Based on the XRF (X-Ray Fluorescence) characterization, the highest calcium content (Ca) was 93% at a calcination temperature of 1000 oC. This result was supported by FTIR (Fourier Transform Infrared) spectrum that increasing the calcination temperature will reduce the intensity of carbonate ion (CO32-). These results showed that 1000 °C was the best calcination temperature on sand lobster shells to synthesize HAp. The characterization result of HAp using EDX (Energy Dispersive X-Ray) revealed that the molar ratio of Ca/P was 1.73. The FTIR and XRD (X-Ray Diffractometer) spectral pattern indicate that HAp had been successfully synthesized with minor-TCP, which is also a calcium phosphate with high biocompatibility.

Fly ash-based geopolymer as A4 type soil stabiliser

Farmers’ perceptions and willingness to adopt egg and snail shells as alternative calcium sources for poultry production in the Western region of Ghana

Biological methods of soil stabilization are emerging as potential futuristic solutions for repair and maintenance of built infrastructure. However, development of a sustainable solution requires reliable supply of raw materials with added privileges in the context of circular economy. This study investigates the potential of waste egg shells as an eco-friendly source of calcium for microbially induced calcium carbonate precipitation (MICP) using Sporosarcina pasteurii MTCC 1761, with the aim of enhancing the geotechnical properties of Sea Shore Sand (SSS) and Dry Clayey Soil (DCS). The collection and utilization of the raw materials were administered with minimum processing steps. The mechanical and biochemical properties of SSS and DCS using Sporosarcina pasteurii were compared in the presence of two alternative calcium sources (eggshell powder (ESP) and calcium hydroxide (CH)). The results showed an increase in shear strength up to 0.35 kg/cm2 for SSS-CH and 0.29 kg/cm2 for SSS-ESP. Similarly, the unconfined compression strength for cohesive soil (DCS) reached up to 0.41 kg/cm2 under the test conditions. Further, an adaptive mechanistic framework is proposed for selecting an optimal implementation strategy for MICP using recycled materials such as ESP. For this, a correlation matrix is developed describing the relationship between cause, evidence and effect of soil stabilization based on biocementation. We propose that ESP can be a promising source of calcium for enhancing the sustainability of biocementation irrespective of the soil type.

The stabilization of sulfate-bearing soils with traditional calcium-based stabilizers is not recommended, as reactions between the calcium and sulfates in the presence of water could lead to soil heave. Alternative stabilization methods are therefore required, and this paper proposes innovative alkali-activated cements (AACs), whose use for soil stabilization and especially sulfate-bearing soils is little researched. To fill this knowledge gap, AAC systems with a ground granulated blast-furnace slag precursor and different alkaline activators, including commercial lime, wastepaper sludge ash (PSA), potassium hydroxide (KOH) and potassium carbonate (K 2 CO 3 ), were used to treat an artificial sulfate-bearing clay. AAC-treated clay specimens cured for 7 and 28 days, respectively, were soaked in water for 45 days; their one-dimensional swelling, unconfined compressive strength (UCS), pH and ultrasonic pulse velocity (UPV) were measured and compared to those of specimens not exposed to water. Material characterization (scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR)) was performed to attest cementation and detect ettringite. In AAC systems, CaO/Ca(OH) 2 did not lead to specimen heave and damage, and developed the highest strengths. Potassium-based activators performed less well but combined PSA–K 2 CO 3 in time led to strength gain. Overall, AACs lead to greater strengths than lime only or lime and admixtures, and show promise as sulfate-bearing soil stabilizers. Thematic collection: This article is part of the Leading to Innovative Engineering Geology Practices collection available at: https://www.lyellcollection.org/topic/collections/leading-to-innovative-engineering-geology-practices

To study how calcination temperature influences the structural properties and catalytic performance of a novel amorphous NiP/Hβ catalyst, amorphous NiP/Hβ catalysts calcined at different temperatures were prepared for n-hexane isomerization. The optimum calcination temperature was determined, and the effect of calcination temperature on the structural properties of the catalysts was investigated using different characterization methods, such as XRD, TPD and so on. It was found that the optimum calcination temperature was 200 °C. Simultaneously, the amorphous NiP/Hβ catalyst showed good application potential as a non-noble metal catalyst. Calcination temperatures from 100 to 400 °C had almost no effect on pore properties. Meanwhile, the acid properties of the amorphous NiP/Hβ catalyst were affected very little by calcination temperature. By increasing calcination temperature, the dispersion state of amorphous NiP became worse at 300 °C, and then the structure of NiP changed from an amorphous structure into a crystalline structure at 400 °C. In addition, the catalyst became more difficult to reduce with the increase in calcination temperature. Combined with the results of n-hexane isomerization catalyzed by different samples, the mechanism by which calcination temperature affects n-hexane isomerization over catalyst was revealed. It was shown that for the amorphous NiP/Hβ catalyst, calcination temperature influences the catalytic performance mainly by affecting the dispersion degree and structure of active components.

The technology of microbially induced carbonate precipitation (MICP) provides a promising approach of improving the durability and the safety of concrete structures. CaCl2, the common calcium source of MICP, may be detrimental for the steel bars and significantly affects the durability of the reinforced concrete. Therefore, alternative calcium sources and their feasibility are investigated in the paper. The uniaxial compressive strength tests and the water absorption ratio tests are carried out for the biogrouted sand columns treated with different calcium sources, and the mineralogical compositions, the microstructure morphology and the pore size distribution of the MICP of the samples are analysed in detail. Results show that the samples using Ca(CH3COO)2 as the calcium source possess a higher strength and a wider distribution of pore size than those using CaCl2 or Ca(NO3)2. The crystal type of the MICP of the samples treated with Ca(CH3COO)2 is mainly aragonite, while that of the others is mainly calcite. It is believed that Ca(CH3COO)2 is a suitable alternative calcium source to replace CaCl2 for the MICP technology applied in the reinforced concrete structures.

The growing concern with carbon dioxide emissions from the cement industry has driven the search for alternative binders with lower environmental impact. Among these, alkali-activated cements (AACs) stand out due to their ability to produce cementitious matrices from aluminosilicate precursors and alkaline activators. However, comparisons between One-Part and Two-Part systems remain limited. This study evaluated the technical feasibility of producing AAC using sugarcane bagasse ash (SCBA) as precursor, carbide lime (CL) as calcium source, and sodium hydroxide (NaOH) as activator. Different parameters were tested, including NaOH molarities (1.0–2.5 M), SCBA/CL ratios (9.00–1.50), curing times (3, 7, and 28 days), and preparation methods. Mortars were produced at constant water/solid ratio of 1.40 and cured at room temperature (23 °C). Unconfined compressive strength (UCS) and leaching tests were performed, along with statistical analysis and Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) analyses. ACC synthesized by the Two-Part method (2.0 M NaOH, SCBA:CL 70:30) reached an UCS of 1.60 MPa at 28 days, compared to 1.39 MPa for the One-Part method. Curing time was identified as the most significant factor, followed by SCBA/CL ratio and activator molarity, while preparation method had minimal effect. The material developed alkali-activated gels, and leaching tests indicated no toxicity, although Ba concentrations exceeded regulatory limits for water quality. Potential applications include mine tailings stabilization, soil improvement, shallow foundations, and urban furniture production.

This study was aimed to investigate the potential use of pre-treated cuttlebone powder (CBP) as an alternative calcium source by evaluating the physicochemical properties of CBP pre-treated with distilled water (CBP1), 1% acetic acid (CBP2), and 2% sodium hydroxide (NaOH) solutions (CBP3). Proximate analysis revealed ash as the major component of all samples. The presence of phenols, flavonoids, alkaloids, and glycosides were detected but tannins appeared to be absent in cuttlebones. Mineral analysis indicated that CBP was rich in calcium, which means the material may be considered as a potential calcium source for food products or calcium supplements. The bulk density of CBP2 was significantly lower (p < .05) than those of CBP1 and CBP3, and the water holding capacity (WHC) of CBP1 was significantly higher (p < .05) than those of CBP2 and CBP3. The high bulk density, water and oil holding capacities of CBP demonstrated its potential use as a functional food ingredient.

Eco-friendly soil stabilization method using fish bone as cement material

Microbial induced carbonate precipitation for immobilizing Pb contaminants: Toxic effects on bacterial activity and immobilization efficiency

Aim/Background: Calcium is an essential mineral in poultry nutrition, crucial for skeletal development and eggshell quality. Marine shell extraction is labor-intensive and costly, so alternative calcium sources are necessary to reduce feed costs and preserve aquatic ecosystems. This study assesses the efficacy of Figuil limestone, shellfish, and quail eggshells as dietary calcium sources, primarily focusing on improving animal welfare. Materials and Methods: Advanced analytical techniques, including X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDX), used to conduct a comprehensive assessment of Figuil limestone, shellfish, and quail eggshells. A total of 195 (21-day-old) Cobb500 chicks with comparable live weights were divided into 15 batches, each containing 13 mixed-gender chicks housed within low-meshed cages at a density rate set at 13 chicks/m². Five experimental diets were formulated, substituting shellfish meal with limestone powder at levels set at 0%, 25%, 50%, 75%, and 100% within a basal diet containing 20.14 % crude protein and 3069.50 kcal/kg metabolizable energy. Each diet was randomly assigned across three batches utilizing a completely randomized design where five treatments were repeated three times. Results: Results indicate that Figuil limestone and quail eggshells are predominantly composed of calcite calcium, while shellfish primarily contain aragonite calcium. The calcium oxide (CaO) content was determined to be 50% in Figuil limestone, 42% in shellfish, and 26% in quail eggshells, with varying concentrations of magnesium (Mg), aluminum (Al), silicon (Si), and iron (Fe). Substituting shellfish meal with limestone powder notably influenced broiler feed consumption at six weeks of age, positively affecting live weight and average weekly weight gain. Treatment T4 (100% limestone) notably demonstrated promising outcomes, with significant differences (P ≤ 0.05) detected in feed consumption (FC), weight gain (WG), and feed conversion ratio (FCR) among the treatment groups. Conclusion: Findings advocate for Figuil limestone powder as a sustainable and ethically sourced alternative to shellfish meal in broiler diets, capable of complete replacement up to 100%. This study highlights Figuil limestone's potential as a viable calcium source in animal feed formulations, offering environmentally friendly options for poultry nutrition while promoting animal welfare and delivering economic benefits to both developed and developing regions.

Alkali-activated cement (AAC) cured at ambient temperature conditions have a wider application area compared to heat cured AAC. High calcium precursor materials such as ground granulated blast furnace slag (GGBS) are commonly used to achieve ambient curing behavior. However, the GGBS results in a short setting time. Hence setting adjustment is critical in such AAC systems. This paper reviews state-of-the-art in the area of retarders for AAC systems. The most promising prospective retarders such as zinc salts, borax, sucrose, and phosphates are investigated. The retarder’s effect is dependent on the precursor materials and alkaline activators used. Consequently, in the review, these are identified for each retarder discussed. Some of the retarders were then tested in AAC with a blended precursor system containing fly ash (FA) and GGBS activated with sodium hydroxide and sodium silicate. The results showed that each borax percentage, with respect to the total solid binder, increases the setting time by about 50% of the mix without borax. Sucrose, sodium acetate, acetic, and phosphoric acids have no significant effect on the investigated AAC’s setting time.

Co-disposal of MSWI fly ash and spent caustic through alkaline-activation: Immobilization of heavy metals and organics