Cement-sand Ratio Research Articles

Effect of bottom ash powder replacement rate, water cement ratio and sand cement ratio on alkali activated slag mortar

The main objective of this study is to clarify the effect of bottom ash (BA) powder replacement rate, water-cement ratio, and sand-cement ratio on alkali-activated slag mortar (AASM) by comprehensively investigating the following parameters: fluidity, consistency, setting time, pH, compressive strength, and flexural strength, as well as observing the microstructure by XRD and SEM. Finally, the relationship between the parameters was explored by means of correlation coefficient heatmaps in concert with scatter plots (including quadratic polynomial linear fitting). The results show that it is feasible to use up to 60% of BA powder to replace slag for AASM. Meanwhile, it is suggested that the AASM with a water-cement ratio of 0.44 and a sand-cement ratio of 2.6 can obtain better workability, mechanical properties, and a denser microstructure. The incorporation of BA powder produces the unique hydration product Magadiite. In addition, the mechanical models of compressive strength and flexural strength of AASM were proposed . This study provides a reference for the application of BA powder in the alkali-activated system, which is beneficial for resource recycling.

Effect of Polypropylene and Straw Fiber Materials on the Unconfined Compressive Strength of Tailings and Wasted Stone Mixed Backfill.

Ensuring the mechanical performance of backfill materials while reducing cementation costs is a key challenge in mine backfill research. To address this, fiber materials such as polypropylene (PP) fiber and rice straw (RS) fiber have been incorporated into cement-based mixtures for mine backfilling. This study investigates the effects of PP and RS fibers on the mechanical properties, flow characteristics, and microstructure of Tailings and Wasted Stone Mixed Backfill (TWSMB). A series of orthogonal experiments were designed to evaluate the influence of variables, including the cement-sand ratio, solid mass concentration, wasted stone mass concentration, fiber content, and fiber length on the TWSMB properties. The results indicate that the influence of cement-sand ratio and solid mass concentration have a more significant impact on strength than fibers, though the fibers show a stronger effect than the wasted stone mass concentration. Both fiber types enhanced the strength of the specimens, with PP fiber exhibiting a stronger reinforcing effect than RS fiber. Furthermore, the effect of PP fiber content was more pronounced than that of fiber length, whereas the opposite trend was observed for RS fiber. The optimum fiber parameter levels were determined for each type: PP fiber performed best at a mass concentration of 1.5% and a length of 6 mm, while RS fiber showed optimal performance at a mass concentration of 1.0% and a length of 5-10 mm. Macroscopic damage analysis indicated that the structural integrity and residual compressive strength of the TWSMB specimens were preserved even after surpassing the ultimate compressive strength, due to the crack-bridging effect of the fibers. Microstructural analysis showed that PP fiber-reinforced specimens exhibited a dense structure formed through reactions with other hydration products. In contrast, the surface of RS fibers was nearly fully encapsulated by hydration products, resulting in the formation of a physical skeleton structure. This study provides new insights into minimizing cement consumption and reducing backfilling costs in mining operations.

Utilizing residual waste particles from polyethylene terephthalate (PET) waste pellet production in cement mortar

ABSTRACT Polyethylene terephthalate (PET) bottle waste management is a global challenge, with PET pellet production generating 20-23% waste particles (PWP). These particles, when deposited in landfills, do not decompose and can disperse, posing health risks, while burning them releases hazardous gases. This study explores the use of PWP in masonry mortar by replacing sand at 0%, 5%, 10%, and 15% levels. Mortar mixtures with cement-sand ratios of 1:4 and 1:6, and a water-cement ratio of 0.50 were tested. The results showed that 5% PWP content improved mortar properties, including flow table value, water absorption, compressive strength, flexural strength, and splitting tensile strength, while reducing density and elastic modulus. Specifically, the 28-day compressive strength increased by 14.0% and 7.1% for the 1:4 and 1:6 mixes, respectively. The enhanced workability is attributed to the smooth, round shape, and zero water absorption of PWP particles, while the increase in mechanical strength is due to the pozzolanic properties of PWP. This solution addresses PWP waste management while improving mortar properties, contributing to sustainable construction practices, reducing sand usage, and promoting eco-friendly mortar and concrete production.

Experimental study on creep characteristics of cemented coal gangue backfill under uniaxial compression

ABSTRACT The uniaxial compression creep test is used to study the cemented coal gangue backfill body specimens with different cement-sand ratios (1:4,1:6,1:8, respectively). Through the processing and analysis of the creep curve, we discussed the influence of different cement-sand ratios, stress load and loading time on the strain, creep rate and long-term strength of the backfill body. These studies have revealed the creep law of the backfill body and obtained accurate conclusions. The results show that: (1) Different proportions of cemented coal gangue backfill body under the action of the set step by step axial loading stress, the strain is positively correlated with the change of loading stress. (2) With the increase of axial stress, the instantaneous deformation of cemented coal gangue backfill with three kinds of cement–sand ratio increases with the decrease of cement–sand ratio under the same axial stress. (3) With the increase of the axial stress of the three kinds of cement–sand ratio cemented coal gangue backfill body, the strain rate of the deceleration creep speed and the constant creep stage increases, and the duration of the deceleration creep stage increases. The average creep strain rate of the three kinds of cement–sand ratio cemented coal gangue backfill materials before entering the accelerated creep stage is determined. (4) Using an improved steady-state creep rate inflection point method, the long-term strength of three kinds of cement–sand ratio of cemented coal gangue backfill is determined, and it is concluded that the long-term strength decreases with the decrease of cement–sand ratio, which is positively correlated.

Recycling gold mine tailings into eco-friendly backfill material for a coal mine goaf: Performance insights, hydration mechanism, and engineering applications

Recycling gold mine overflow tailings for coal mine filling is crucial for sustainable mining. In this work, an eco-friendly, performance-controllable overflow tailings-fly ash-based backfill material is developed for coal mine filling. The effects of three critical factors, namely, the slurry concentration (SC), cement-sand ratio (C:S), and tailings-fly ash ratio (T:F), on the workability and uniaxial compressive strength (UCS) properties of the novel backfill material are thoroughly investigated, and an optimization of the corresponding formulation is conducted. The optimal formula for the backfill is determined to be a CS of 60 %, a C:S of 0.10, and a T:F of 6:6. The hydration mechanism of the chosen typical mixtures is analyzed via X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy, and the results show that a needle-like Aft gel, identified as the major gelatinous product, is intricately intertwined to create an intricate network structure. As the T:F increases, the content of calcium and silicon oxide initially decreases but then increases, and the optimal mixture reaches a minimum value of 63.66 %. The optimum specimen exhibits a peak wavenumber at 1109.46 cm−1 involving a Si-O stretching vibration bond. A comprehensive filling program at the Liangjia Coal Mine is successfully implemented. Approximately 0.27 tons of overflow tailings are utilized for every ton of backfills. The underground core-pulling backfill achieves a peak uniaxial compressive strength (UCS) of 7.56 MPa after 28 d, surpassing design requirements and showing promise for coal mine filling applications. This study is expected to achieve the transformation of a coal mine goaf into a gold mine tailings pond.

Study on Crushed-Stone Cementation Properties and Bottom Stope Stability of Goaf by Open Stope Mining in Inclined Ore Bodies

The mining of the part of the inclined ore body below a goaf is crucial for improving resource extraction and safe production. In this study, the cementation properties of crushed stone during the mining of the inclined ore body were investigated by means of laboratory experiments, theoretical analysis, and numerical simulation. Additionally, orthogonal experiments were performed to assess how factors like water–cement ratio, crushed-stone particle size, and cement–sand ratio affect the strength of the grouting concretion body (GCB). Furthermore, the fluidity of the slurry under different ratios was also measured. Considering both the fluidity of the slurry and the strength of the GCB, the optimal ratios of the slurry were determined to be a water–cement ratio of 2.5:1 and a cement–sand ratio of 1:4. This ratio was then used for crushed-stone cementing under the poorest crushed-stone particle size conditions, based on which mechanical parameters were obtained from experiments. Theoretical analysis equated the problem of the grouting range to the width of the plastic zone of surrounding rock, and a conclusion was reached that the width of the GCB should be at least 29 m. The numerical simulation results reveal that among 30 mining rooms formed below the GCB, 24 mining rooms are in a stable state and 6 mining rooms are partially damaged on a small scale. As a whole, the GCB formed by grout filling into the goaf manages to effectively support the stope below, and it is verified that the theoretical calculation method of the width of the GCB is feasible.

Estimating the compressive strength of lightweight foamed concrete using different machine learning-based symbolic regression techniques

The development of concrete with excellent water and frost resistance providing high level of sound and thermal insulation has triggered the formulation of foamed concrete. However, multiple laboratory studies are required to produce reasonable data to design the relevant codes and mathematics with which design of mixes is made easier at low cost. In this research paper, the artificial intelligence (AI)-based symbolic regression technique estimation of the compressive strength of foamed concrete has been reported. Foamed concrete has been a subject of serious research in sustainable built-environment due to its lightweight and structural functionality. In this research work, data gathering method was applied to gather a globally representative data base comprising concrete density to water density (concrete density g/cm3) (γ/γw), water-cement ratio (W/C), and sand-cement ratio (S/C) as input variable and the compressive strength (Fc) as the study output. The dimensionless factors have been derived to eliminate data handling complexities and improve model performances. The 230 data entries from foamed concrete mixes were partitioned into 75% and 25% for training and validation data, respectively. At the end of the model execution, it was found that the response surface methodology (RSM) produced a symbolic closed-form equation like the genetic programming (GP), evolutionary polynomial regression (EPR), and the group method of data-handling-neural network (GMDH-NN). Even though the RSM closed with a minimum error, the GP, EPR and GMDH-NN were faster in runtime. The overall outcomes show that the GP outclassed the EPR, RSM and the GMDH-NN, though with minor margin. Meanwhile the EPR produced the highest outliers from the ±25% test of accuracy envelope. Overall, the present models outperformed those reported in the literature due the parameter reduction through dimensionless factors derivation and provided a decisive model to predict the Fc of foamed concrete.

Optimum Design of Mix Ratio of Premixed Iron Tailings Mortar Based on Response Surface Method

To study the influence of cement-sand ratio, fly ash content, steel slag content, and fiber content on the performance of iron tailings premixed dry mixed mortar based on Box-Behnken, the regression model of compressive strength and fiexural strength and the above four factors was established, and the optimized mix ratio parameters were obtained. The results showed that the significance of the effect on compressive strength is ranked as follows: cement-sand ratio is greater than fly ash content than steel slag powder content than fiber content, and the significance of the effect on flexural strength is ranked as follows: cement-sand ratio is greater than fiber content than steel slag powder content than fly ash content.

Experimental Study for the Matching of Explosives and Rocks Based on Rock Hydrophysical Properties

The study of the hydrophysical properties of rocks is indispensable for the development of hydraulic engineering, especially for blasting operations in water. Reasonable matching between explosives and rocks increases the utilization of explosive energy and improves the blasting performances. Based on the energy law in the rock blasting process, the matching relationship between explosives and rock is studied by combining experimental and theoretical methods for the hydrophysical properties of the rock itself. Firstly, the theoretical solutions for crushing-zone energy, fragmentation energy and fragment-throwing energy are derived. Subsequently, concrete blocks are prepared with four types of cement–sand ratios, and four types of emulsion explosives are used to carry out single-hole blasting tests in which a high-speed camera is used to capture the trajectory of the blasting fragments that are later collected. Finally, the crushing energy, fracturing energy and fragment-throwing energy are calculated according to the test results and the basic parameters of the used explosives and concrete models. The results show that the size and distribution pattern of blasting blocks are significantly affected by the hydrophysical properties of concrete and explosive properties; the higher the energy consumption in the rupture zone, the smaller the size of the fragments and the more uniform the distribution. Moreover, the median utilization efficiency of explosive energy on rock breaking is 26.4%, the energy consumption in the crushing zone is approximately 8.4%, that in the rupture zone is approximately 10.9%, and that in the throwing energy of fragments accounts for approximately 7.1%. It is also found that the traditional wave impedance matching theory fails to obtain the best explosive energy utilization. On the contrary, the concrete specimen had the best fracturing effect and the highest energy utilization of 30.77% when the impedance ratio of concrete to explosives is 1.479.

Comparative analysis of selected machine learning techniques for predicting the pull-off strength of the surface layer of eco-friendly concrete

With recent trends reducing the carbon footprint of concrete, more novel materials are designed. It's mostly done by replacing cement with admixtures that are wastes in industrial processes. There is a need to provide reliable and accurate models to estimate the properties of the material. In this case the selected ML algorithms such as ANN, RF and DT were used for estimating the pull-off strength of the surface layer of cement mortar containing granite powder, fly ash and ground granulated blast furnace slag. The focus was on the cement-sand ratio of 1:3, replacing up to 30 % of the binder. Ultrasonic pulse velocity and pull-off strength of the surface layer. The analyses were performed in comparative manner and proved the accuracy of the designed models. The error values (MAPE, NRMSE and MAE) of the most effective model is below 3,5 %, indicating an extremely high success rate in prediction. An R2 ratio of 0.9436 confirms the very good fit of the model. Parametric tests were performed and SHAP analysis gave a better understanding of the models. The main conclusion of the study is to identify the possibility of replacing destructive testing with non-destructive testing supported by machine learning and material information to determine the pull-off strength of the subsurface layer at a selected depth for cement mortars containing waste materials. A particular advantage of the presented approach is the possibility of reducing the time to determine selected desired material parameters and the amount of testing required compared to the traditional approach.

Strength and Crack Propagation Analysis of Layered Backfill Based on Energy Theory

The strength of backfill is greatly influenced by its inclination angle and interlayer concentration. In order to study the influence of inclination angle and interlayer mass concentration on the strength of backfill, a group of layered cemented backfill with cement-sand ratio of 1:4, interlayer mass concentration of 66%, 67% and 68% and inclination angles of 0°, 10°, 20° and 30° were prepared by using tailings as aggregate. The uniaxial compression test was carried out to analyse the effect of interlayer mass concentration and inclination angle on layered cemented backfill. The crack propagation and energy change law of the specimen during compression were analysed by J-integral and energy conservation law. The relationship between the crack initiation and propagation and strain energy of two representative three-layer backfill specimens was analysed by numerical modelling. The results show that the increase in the layer number and the inclination angle of the backfill can weaken the strength of the backfill. In a certain range of inclination angles, the weakening coefficient of the backfill caused by the inclination angle is very consistent with the cosine value of the corresponding angle. Due to the release of crack energy and the existence of interface J integral, the uniaxial compressive strength of different mass concentration backfill is different at various positions. When the displacement reaches a certain value, the crack and strain energy no longer increase.

Enhancing performance and structural integrity of cemented paste backfill: Rheological behavior, strength characteristics, and microstructural dynamics

In order to improve the mechanical properties of backfill, steel slag and straw fiber were used as materials to prepare backfill. The law of sand-cement ratio, mass concentration, steel slag content and straw fiber on strength and rheological parameters of backfill was analyzed by orthogonal test method, and the influence mechanism of steel slag content and straw fiber on physical properties of backfill was revealed. The results show that mass concentration exerts the most substantial impact on rheological parameters, emerging as a significant determinant. Moreover, the yield stress diminishes with escalating tailings-cement ratio, while it escalates with higher mass concentration, steel slag content and straw fiber content. Augmenting the tailings-cement ratio and steel slag content serves to impede the amplification effect of mass concentration on yield stress. Notably, the tailings-cement ratio emerges as the most influential factor affecting the uniaxial compressive strength (UCS) of the backfill, albeit the UCS diminishes with rising tailings-cement ratio. Elevating the mass concentration and steel slag content can counteract the debilitation caused by an increase in the tailings-cement ratio on the UCS of the backfill. Furthermore, heightened mass concentration can bolster the reinforcing impact of steel slag content on early UCS. The increase of tailings-cement ratio increases the size and range of the void inside the backfill, subsequently leading to the degradation of its macroscopic compressive strength. The adhesion between straw fiber and mortar matrix constitutes a pivotal factor in improving the integration of backfill, whereas steel slag contributes to improving the mechanical properties by enhancing the distribution of void structures within the backfill. This research not only offer data support and scientific guidance for the design of backfill ratio parameters but also facilitate the broader application of straw fiber and steel slag in mine backfilling operations.

Eupatorium Adenophorum Spreng as a green additive in cementitious materials for sustainable infrastructure

The use of natural admixtures as a sustainable alternative to cement and chemical admixtures in concrete has gained significant attention. Eupatorium adenophorum Spreng (EAS), commonly known as the ‘forest killer’ in Nepal, is a perennial and herbaceous invasive plant. This prompted an experimental investigation aimed at assessing the potential utilization of its liquid and burnt ashes as additives in cement mortar. EAS leaves were dried, burnt at wooden coal fire, and sieved through a 90 μm sieve to obtain EAS powder. EAS liquid was produced by hammering the fragmented leaves, followed by squeezing and filtering. The control mortar had a water-cement ratio of 0.35 and a cement-sand ratio of 1.0. EAS powder content ranged from 0 % to 15 % and EAS liquid from 0 % to 0.4 %, by weight of cement. The optimal content (10 %) of EAS powder resulted in decreases in flow table value, density, and elastic modulus of mortar by 2.3 %, 4.2 %, and 10.6 %, respectively, while increasing compressive strength and water absorption by 2.3 % and 14.6 %, respectively. As for EAS liquid, its optimal content (0.3 %) led to increases in flow table value, density, compressive strength, elastic modulus, flexural strength, and splitting tensile strength by 11.0 %, 1.4 %, 13.0 %, 25.4 %, 28.4 %, and 33.0 %, respectively, while decreasing water absorption by 2.7 %. The observed increase in the compressive strength of mortar with the incorporation of EAS powder suggests its potential to substitute mineral admixtures. This can be achieved through improvements in the burning process, grinding to finer particles, and thorough micro-characterization, followed by detailed investigations into mortar properties. Additionally, the effectiveness of EAS liquid in replacing chemical admixtures to enhance various mortar properties has been confirmed. The collaborative use of EAS powder and liquid holds promise for supporting future sustainable infrastructure development, facilitating the production of eco-friendly green concrete.

Effect of Strength and Durability of Sand Cement Brick Containing Recycled Concrete Aggregate and Cold Bottom Ash

Introduction The market price of brick has risen sharply due to the insufficient brick supply. Therefore, implementing RCA as one of the alternative materials for sand replacement is significant. The consumption of natural aggregate (NA) can be reduced by using the RCA. It is a good step to utilize recycled concrete to minimize the problem of excess waste materials. The results of using RCA and CBA as sand replacements contribute to better performance in compressive strength as compared to the normal brick. The density of the brick was also reduced by 4.95% as the RCA and CBA took place in the brick. Besides that, the water absorption was decreased when incorporating RCA and CBA in the cement brick due to less free water in the mix and fewer voids. Aims This study aims to ascertain the performance, strength, and durability characteristics of sand cement bricks incorporated with RCA and CBA as partial replacements for sand. Methods Percentages of 1.5%, 3.0%, 4.5%, and 6.0% of CBA and 15%, 30%, 45%, and 60% of RCA were chosen for partial sand replacement. The brick had dimensions of 215 mm in length, 65 mm in depth and 105 mm in width. Density, compressive force, and water absorption tests were undertaken after each of the three varied ratios of water to cement (1:5, 1:6, and 1:7). Results The finding indicates that with the optimum RCA and CBA replacement and the correct water to cement ratio, the performance of the new brick is better than the normal brick. Conclusion The optimum sand-to-cement ratio is 1:6, according to the overall results of selecting the optimal sand-to-cement ratio by density, compressive strength, and water absorption test. However, the result for the density value shows that the average brick density is inferior to the control brick. For all of the sample bricks, the compressive strength was best at a sand cement ratio of 1:6. However, as each of the samples complies with the British Standard criterion of less or equal to 15% absorption, it was determined that the sand cement brick's capacity for water absorption was sufficient.

Mechanical Properties of Bricks Containing Sago Fine Waste as Cement Replacement Material

Due to the country's expanding population and the resulting growth of the building industry, brick is one of the most crucial materials used in construction projects in Malaysia. Producing large amounts of bricks requires a lot of cement yet this method has environmental consequences due to increasing carbon emissions into the atmosphere. Therefore, this study aims to use partial Sago Fine Waste (SFW) to replace the cement. About 60 tonnes of sago trash are dumped into the closest river every day during the production of sago starch. To protect the environment and contributing to sustainable development, this study has been conducted on the production of bricks from waste materials. For this study, the brick specimens were prepared using 0%, 1%, 3%, 5%, 7% and 9% of SFW with a water-cement ratio of 0.6 fixed at 1:3 sand cement ratio. The total specimens that were produced for testing are 72 bricks. The water curing for concrete has been conducted at 7 and 28 days. The overall results revealed that both density and compressive strength are decreases as the percentages of SFW increases. The initial rate of absorption increases due to the increasing percentage of SFW. However, all the results obtained are still met the requirements. Based on the findings, the optimum percentage SFW are SFW1W0.6 with strength 5.18 MPa. The optimum brick properties of SFW1W0.6 is normal weight with density 2092.86 kg/m3 and lowest initial rate absorption with 0.91 kg/m3.min.

Mechanical and energetic properties of rock-like specimens under water-stress coupling environment

AbstractSoft rock has the properties of low strength, poor integrity, and difficulty in core extraction. In order to study the deformation and failure of soft rock, this study used fine river sand as aggregate, cement and gypsum as bonding materials, and borax as a retarder to produce cylindrical rock-like samples (RLS) with a sand cement ratio of 1:1. Uniaxial compression tests were conducted on RLS under DIT (different immersion times) (0, 4, 8, 12, 24, and 48 h) in the laboratory. The mechanical and energy properties of RLS under water-stress coupling were analyzed. The results showed that the longer the IT of the RLS, the higher their water content (WC). As the moisture time increases, the uniaxial compressive strength, elastic modulus (EM), and softening coefficient (SC) of the sample gradually decrease, while the rate of change of EM is the opposite. The fitted sample SC exhibits a good logarithmic function relationship with WC. During the loading process of the sample, more than 60% of the U (total energy absorbed) during the loading process of the sample is accumulated in the form of Ue (releasable elastic energy), while less than 40% of U is dissipated by the newly formed micro cracks during the compaction, sliding, and yield stages of the internal pores and cracks of the sample. The U before the peak and the Ue of the RLS decrease exponentially with the moisture content; the relationship curves of Ue/U (released elastic energy ratio) and Ud/U (dissipated energy ratio) of RLS during uniaxial compression with the σ1/σmax (axial stress ratio) can be divided into three stages of change, namely the stage of primary fissure compaction and closure (σ1/σmax < 0.25), continuously absorbing energy stage (0.25 < σ1/σmax < 0.8), and energy dissipation stage (σ1/σmax > 0.8); the D (damage variable) was defined by the ratio of Ud (dissipated energy) to the Udmax (maximum dissipated energy) at failure time of RLS, the fitting of the relationship between the damage variable and axial strain conforms to the logistic equation.

Feasibility Study of Material Deformation and Similarity of Spatial Characteristics of Standard Coal Rocks

The comparison between similar materials and original coal rock is the basis for similar simulation experiments in coal mines. The differences in mechanical properties, acoustic characteristics, and damage laws between similar materials and the original coal rock are of great significance for similar simulation research, to reveal objective laws. First, materials similar to coal rock with similar theoretical ratios were taken as the object of research, and the sand–cement ratio, the carbon paste ratio, and the water content were determined by multivariate linear regression to accurately match the ratios. Second, by using acoustic emission and digital scattering technology to explore the acoustic law, deformation characteristics, and spatial feature similarities of the materials similar to coal rock, the acoustic emission evolution law of the original rock was found to be the same as that of the similar materials. Digital scattering was able to describe the localization of strain in the similar materials, and the correlation between the overall deformation and the local deformation was explored. This indicates that materials similar to coal rock can effectively simulate the deformation of actual coal rocks. Lastly, these materials were found to allow effectively simulating the deformation characteristics and spatial properties of actual coal rock, which provides an important experimental means and method for similar research in the field of coal rock engineering.

Influence of macadamia nutshell particles on the apparent density and mechanical behavior of cement-based mortars

The production of cement mortar has resulted in significant environmental issues. Many scientists have attempted to reduce environmental pollution by using agricultural waste as a substitute for mortar raw materials. This study creatively investigated the physical and mechanical properties of the new green cement mortar made from macadamia nutshell(MN), including compressive strength, flexural strength, and apparent density of 7d, 14d, and 28d. The effects of cement-sand ratio (c/s), nutshell particle size, and MN substitution rate on cement mortar's physical properties were studied using three-factor and three-level orthogonal test design methods. The digital image correlation (DIC) technique was used to analyze the crack development of macadamia nutshell cement mortar (MNM) at different loading stages. The analysis of variance (ANOVA) showed that the cement-sand ratio was the most significant factor affecting the strength of MNM. In addition, adding MN can increase the compressive strength of the mortar compared to the control group. The apparent density of the mortar decreases with the increase of MN addition.

Comparative prediction performance of the strength of a new type of Ti tailings cemented backfilling body using PSO-RF, SSA-RF, and WOA-RF models

The uniaxial compressive strength (UCS) of the backfilling body plays a crucial role in backfilling safety. To study the feasibility of preparing new cementitious materials by Ti tailings, 90 sets of backfilling ratio tests and UCS tests with different Ti tailings replacement ratios were carried out. The test results showed that the UCS tended to decrease as the ratio of Ti tailings replacing cement increased, and the UCS decreased sharply after the ratio of Ti tailings replacing cement exceeded 80%; however, the UCS increased at 28 days when the ratio of Ti tailings replacing cement did not exceed 10%. Meanwhile, to accurately predict the UCS, the whale optimization algorithm and random forest (WOA-RF), particle swarm optimization and random forest (PSO-RF), and sparrow search algorithm and random forest (SSA-RF) hybrid models were constructed. Moreover, the input parameters of the models include the ratio of Ti tailings, concentration, curing age, ratio of P.O42.5 cement and cement-sand ratio. In addition, a single RF model was constructed for comparative analysis, the four models (RF, WOA-RF, PSO-RF, and SSA-RF) were trained and tested, and the root mean square error (RMSE), coefficient of determination (R2), and mean absolute error (MAE) of the four models were obtained: (0.532, 0.922, 0.416), (0.254, 0.975, 0.209), (0.367, 0.961, 0.300) and (0.318, 0.965, 0.258), respectively. The research showed that the WOA-RF model achieves better performance (R2 = 0.975), which proves that it is a better prediction model for predicting the USC of new cementitious filler with Ti tailings replacement.

Variation characteristics of key dynamic measurement signals of anchor bolts with different anchorage qualities under pull-out loads

Pull-out load and the cement-sand ratio (CSR) can affect the non-destructive testing (NDT) results of anchor bolts. Therefore, in this article, NDT experiments were conducted on both fully and defectively grouted anchor bolts, and variation patterns of key dynamic testing signal parameters were analyzed. A longitudinal vibration model of defectively grouted anchor bolts considering dynamic and static damping was proposed, and simulated NDT of anchor bolts with varying qualities. The results indicated that grouting defects resulted in an increase in wave velocity, along with a decrease in the fundamental frequency and dynamic stiffness of anchor bolts. When grouting defects and pull-out load acted concurrently, the fundamental frequency, and dynamic stiffness of the defectively grouted anchor bolts were consistently smaller than those of fully grouted ones during the initial loading phase. With pull-out load increasing, wave velocity decreased first, then increased; fundamental frequency increased, followed by a decrease; dynamic stiffness rose. When the CSR of defectively grouted anchor bolts was reduced, wave velocity decreased, fundamental frequency increased slightly, and a substantial increase in dynamic stiffness was observed. Pull-out loads were more sensitive to anchor bolt key dynamic signals than defects and CSR. Simulated validation demonstrated the reliability of the proposed theory.