Experimental Study on Mechanical Properties of Coal-Based Solid Waste Nanocomposite Fiber Cementitious Backfill Material.

Backfilling in underground mining is a widely adopted technique, often employing cement-based or geopolymer materials. However, the high cost and logistical challenges associated with these materials in remote mining locations necessitate alternative solutions. Loess materials offer a viable option for reducing production expenses and mitigating environmental impact. Despite this, the mechanical properties of loess-based cemented materials have been insufficiently investigated. This study introduces a novel slag-loess-based cemented backfill material. A three-dimensional model of the backfill material was constructed using Avizo software, and a numerical calculation model, incorporating the actual three-dimensional geometry of aggregate particles, was developed using PFC3D software. The influence of confining pressure σ3, curing temperature TC, and age TA on the crack evolution, force chain evolution, and particle failure characteristics during the loading process of the cemented backfill material was systematically examined. Results demonstrate that increasing confining pressure σ3 accelerates crack initiation and propagation, concurrently increasing the maximum value of the dominant force chain within the specimen at each stage. An increase in age TA has a limited effect on the proportion and quantity of final tensile-shear cracks, though it does intensify the specimen’s ultimate shear failure tendency. At lower curing temperatures (5°C), a significant impact on crack formation is observed, with this effect diminishing as curing temperature TC increases. The macroscopic failure modes of the specimens, across varying temperatures, predominantly exhibit shear failure.

Microstructure and mechanical properties of sustainable cementitious materials with ultra-high substitution level of calcined clay and limestone powder

Cemented backfill coal mining technology is gradually becoming a key technology for green mining of coal resources. And cemented backfill materials generally have congenital defects such as poor crack resistance, poor durability, and high brittleness, which restrict the promotion and application of cemented backfill coal mining technology. Due to the complex stress environment of in situ stress, mining stress, water pressure, and gas pressure, cemented backfill materials need to have good mechanical properties, and glass fiber is usually used to mix into cemented backfill materials to improve its performance, but there are many problems including complex testing process, high cost, and long time-consuming in the study of mechanical properties of glass fiber-modified cemented backfill materials (GFCBM) by laboratory tests. Consequently, this study proposed and compared four artificial intelligence models to forecast the tensile strength of GFCBM. Firstly, the laboratory tests of tensile properties of GFCBM under different influence factors were implemented to supply the prediction model with dataset. The input variables are aeolian sand content, cement content, glass fiber length, and glass fiber content, and the output variable is the tensile strength of GFCBM. The correlation coefficient ( R ), mean absolute error (MAE), and root mean square error (RMSE) are selected to assess the estimated performance of the hybrid intelligent model. The results indicate that the four hybrid artificial intelligence models show a latent capacity for forecasting the tensile strength of GFCBM, and according to the order from high to low, the prediction ability of the four prediction models is as follows: ABC-SVM, GA-SVM, SSA-SVM, and DE-SVM, and the corresponding R values are 0.9555, 0.9539, 0.9413, and 0.9359, respectively. The research findings are beneficial to promote the application of cemented backfill coal mining technology.

Nanomaterials have garnered significant attention in recent years for their potential to enhance the mechanical properties of cementitious construction materials, particularly in high-strength concrete applications. This review aims to explore the effects of various types of nanomaterials on the mechanical properties of concrete materials. Current developments in the synthesis, characterization, and use of nanomaterials in the field of cementitious materials are thoroughly examined in this review. The incorporation of various nanomaterials such as nano-silica, nano-titania, carbon nanotubes, nano-clay, and nano-alumina can significantly enhance the mechanical properties of cementitious construction materials, particularly in high-strength concrete applications. These nanomaterials contribute to denser microstructures, improved hydration products, and enhanced interfacial bonding within the cement matrix, ultimately leading to superior mechanical performance. However, proper dispersion, dosage, and compatibility considerations are essential to realize the full potential of nanomaterials in cementitious materials. The optimum % of NS in cement was reported to be between 1 and 8%, whereas the optimum % of graphene oxide (GO) in cement was reported to be only between 0.05 and 0.5%, imparting high strength characteristics to concrete. The findings of the study promote the use of nanoparticles in cement concrete to enhance the strength of high-rise concrete buildings. The results of various studies are compared, and some significant recommendations are also made. Furthermore, this research underscores the practical applications of nanocomposite-based concrete materials while acknowledging their limitations and opportunities.

Developing green, low-carbon building materials has become a viable option for managing bulk industrial solid waste. This paper presents a kind of all solid waste cementitious material (SWCM), which is made entirely from six common industrial wastes, including carbide slag and silica fume, that demonstrate strong mechanical properties and effectively stabilize aeolian sand (AS). Initially, we investigated the mechanical strength of waste-based cementitious materials in various mix ratios, focusing on their ability to stabilize river sand (RS) and aeolian sand. The results show that it is necessary to use alkaline solid waste carbide slag to provide a suitable reaction environment to achieve the desired strength. In contrast, the low reactivity of coal gangue powder did not contribute effectively to the strength of the cementitious material. Further orthogonal experiments determined the impact of different waste dosages on the strength of stabilized AS. It was found that increasing the amounts of carbide slag, silica fume, and blast furnace slag powder improved strength, while increasing fly ash first increased and then decreased strength. In contrast, higher additions of desulfurization gypsum and coal gangue powder led to a continuous decrease in strength. The optimized mix is carbide slag—desulfurization gypsum—fly ash—silica fume—blast furnace slag powder in a ratio of 4:2:2:3:3. The experimental results using SWCM to stabilize AS indicated a proportional relationship between strength and SWCM content. When the content is ≥20%, it meets the strength requirements for road subbases. The primary hydration products of stabilized AS are C-(A)-S-H, AFt, and CaCO3. Increasing the SWCM content enhances the reaction degree of the materials, thereby improving mechanical strength. This study highlights the mechanical properties of cementitious materials made entirely from waste for stabilizing AS. It provides a reference for the large-scale utilization of industrial solid waste and practical applications in desert road construction.

Cementitious materials are susceptible to cracking and spalling during service by various internal and external factors, while the long setting time and limited initial strength of Portland cement are insufficient for the repair project’s requirements. Cement can be categorized into Portland cement, sulphoaluminate cement, ferroaluminate cement, aluminate cement, phosphate cement, and fluoroaluminate cement based on various water-hardening ingredients. This paper summarized the performance of various cements and discussed the advancements in studying the impact of nanomaterials and major mineral admixtures (fly ash, silica fume, mineral powder, and slag) on the physical properties and mechanical properties of Portland cementitious materials and special cementitious materials. These additives can expedite the setting process, enhance flowability, and boost the strength of cementitious materials. This paper discussed the impact of nanomaterials and mineral admixtures on the hydration mechanisms of various cementitious materials. Mineral admixtures and nanomaterials can regulate the cementitious material hydration process and improve pore structure. On this basis, the problems to be studied in depth in the application of different kinds of cement in repair works were proposed.

The mechanical properties and microstructure of the cemented paste backfill (CPB) in dry-wet cycle environments are particularly critical in backfill mining. In this study, coal gangue, fly ash, cement, glass fiber, and nano-SiO2 were used to prepare CPB, and dry-wet cycle tests on CPB specimens with different curing ages were conducted. The compressive, tensile, and shear strength of CPB specimens with different curing ages under different dry-wet cycles were analyzed, and the microstructural damage of the specimens was observed by scanning electron microscopy (SEM). The results show that compared with the specimens without dry-wet cycles, the uniaxial compressive strength, tensile strength, and shear strength of the specimens with a curing age of 7 d after seven dry-wet cycles were the smallest, being reduced by 40.22%, 58.25%, and 66.8%, respectively. After seven dry-wet cycles, the compressive, tensile, and shear strength of the specimens with the curing age of 28 d decreased slightly. The SEM results show that with the increasing number of dry-wet cycles, the internal structure of the specimen becomes more and more loose and fragile, and the damage degree of the structural skeleton gradually increases, leading to the poor mechanical properties of CPB specimens. The number of cracks and pores on the specimen surface is relatively limited after a curing age of 28 d, while the occurrence of internal structural damage within the specimen remains insignificant. Therefore, the dry-wet cycle has an important influence on the both mechanical properties and microstructure of CPB. This study provides a reference for the treatment of coal-based solid waste and facilitates the understanding of the mechanical properties of backfill materials under dry-wet cycling conditions.

In this article, attempt has been made to improve the performance of self compacting concrete using recycled coarse aggregate with adding of fly ash and glass fiber. Self compacting concrete has significant environmental advantages in compaction to the vibrated concrete. Absence of noise and vibrations during installing provides healthier working environment. In general, there is a scarcity of coarse aggregate throughout the world. Consumption of large amount of coarse aggregate affects the environment. For the purpose of reducing the consumption of coarse aggregate, a need for an alternative coarse aggregate arises. Recycled coarse aggregates are obtained from the demolition of buildings, culverts and also by-products from the industries. Hence, partial replacement of coarse aggregate by recycled aggregate is researched in this article, in view of consuming the ecological balance. SCC can also be used in situation where it is difficult or impossible to use mechanical compaction for fresh concrete, such as underwater concreting, cast in-situ pile foundations, machine bases and columns or wall with congested reinforcement. The self compacting concrete must meet the filling ability and passing ability with uniform composition throughout the process of transport and placing. Hence, Self compacting concrete demands large amount of powder (cementitious and pozzolanic materials) content and fines for its cohesiveness and ability to flow without bleeding and segregation. In this investigation, part of the cementitious material is replaced with pozzolanic material fly ash, and the properties of self compacting concrete in fresh and hardened states were studied. The increase of the percentage of the fly ash influences the bleeding and segregation in SCC. Hence, the addition of glass fibres can improve ductility, post crack resistance, energy absorption capacity and bleeding resistance. Taking these advantages into account a study was done. The various properties of the materials to be used in the experimental programme were determined. The specification of glass fibers and the advantages of using them along with concrete were studied. A detailed review of literature on glass fiber reinforced concrete was also done. The fresh and hardened properties of Self Compacting Concrete (SCC) using recycled coarse aggregate, fly ash with glass fibers were evaluated. The SCC mixtures are prepared with 40% of fly ash, 40% of recycled coarse aggregate and adding of 0.03% glass fiber. The strength test namely, Compressive Strength Test, Split Tensile Strength Test and Flexural Strength Test are carried out in this investigation. To test the characteristics of self compacting concrete, Slump cone test, J-ring test, L-box test were conducted to test the characteristic of self compacting concrete.

In this research, phosphogypsum composite cementing material using phosphogypsum powder, slag powder, fly ash and cement were prepared as the main cementing materials, and sodium silicate was used as the activator. The influence of the cement content of 0 wt.%, 5 wt.%, 10 wt.%, 15 wt.% and the change of 0%, 2%, 4% alkali equivalent on the mechanical properties of cementing materials was studied, the types and content of admixtures suitable for phosphogypsum cementitious materials were also studied. The cost of the materials used was calculated and analyzed. The results showed the increase in cement content and alkali equivalent will improve the mechanical properties of the cementitious material, and the strength can reach 23.0 MPa; the change of alkali equivalent had a more obvious impact on the early (1 d) mechanical properties of the cementitious material than cement; when these two factors synergistically worked, the cement content should not exceed 10 wt.%, or the mechanical properties of the material would decline; the effect of using the naphthalene-based water-reducing agent was better than that of the polycarboxylic acid water-reducing agent, and when cement, sodium silicate and naphthalene water reducer were used together, the maximum compressive strength of 7 d reached 24.4 MPa, which was higher than 39.4% of the sample without water reducer. The ratio used in the experiment was relatively low cost, which had a great reference value for the comprehensive utilization of industrial by-product phosphogypsum.

Experimental study of microwave heating on mechanical properties of fly ash-based cementitious materials

To explore the resource utilization of fly ash, slag, and coal gangue, the composition of hydration products and strength characteristics of fly ash-slag composite cementitious material (FSGF) were studied with NaOH as an alkali activator. First, response surface analysis was used to determine factors influencing the optimal NaOH content, basalt fiber dosage, and length to obtain the complete mix ratio of the composite cementitious material. Microscopic techniques such as XRD, FTIR, TG-DSC, and SEM were employed to analyze the crystal structure, thermal properties, and micro-morphology of the composite cementitious material, and to investigate the mechanism of NaOH-activated fly ash-slag cementitious material. The results indicated that the sensitivity of each factor affecting the mechanical properties of the composite cementitious material followed this sequence: NaOH content > basalt fiber length > basalt fiber dosage, with varying degrees of interaction among them. When the mass ratio of fly ash, slag, and coal gangue was 5:1:4, with 3% NaOH by weight, 2% basalt fiber dosage, and a fiber length of 3 mm, the optimal mix was achieved. The composite material achieved a compressive strength of 8.97 MPa after 28 days of standard curing at room temperature. NaOH, as an alkali activator, provided the strong alkaline environment required for the initial hydration of fly ash-slag composite cementitious materials, promoting the hydration of slag and fly ash. The hydration products in the fly ash-slag composite system were unevenly distributed, primarily consisting of gels like C-S-H, C-A-H, and C-A-S-H. NaOH was highly effective as an alkali activator in the fly ash-slag system.

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

Study on the design method of multi-component industrial solid waste low carbon cementitious material with cement as the activator

Cementitious materials can be considered as consisting of particulate elements on the levels of the microstructure and mesostructure. The mechanical properties of cementitious granular materials were studied by a numerical approach. First, an ellipsoid-based method was developed to generate single aggregate particles of arbitrary shape. The HADES toolbox was then used to form a material structure from aggregate (HADES is a concurrent, algorithm-based program that is designed to simulate the mixing or flow of granular material of arbi- trary shape). Afterwards, an interfacial transition zone (ITZ) between the aggregate particles and the cement paste was enriched and a special tool, Gmsh, was used for forming a mesh of aggregate, cement paste, and ITZ. Finally, the mesh data was transferred into the finite element code FEAP to predict the mechanical properties of the material. Based on these processes, a simulation of concrete was used as an example of a typical cementitious granular material. Additionally, a parameter study was conducted to highlight the influence of aggregate on the mechanical properties. The simulation shows that the method is feasible and effectively predicts the elastic modulus of three-phase cementitious granular materials (cement paste, ITZ and aggregate).

Experimental study on the properties of a polymer-modified superfine cementitious composite material for waterproofing and plugging