Mortar Specimens Research Articles

Early estimation of 28-day compressive strength of mortars using regression and neural network-based models

Concrete, the most commonly used construction material, presents a challenge in determining its compressive strength (CS) after 28 days of manufacture. This study aims to predict the compressive strength of conventionally cured (CC) mortar specimens using data from accelerated microwave-cured (MC) specimens. Two hundred and seventy-six specimens with different mixes and admixtures were divided into two groups: one half was subjected to MC and the other to CC. The CSs of the CC specimens were determined after 28 days, while the MC specimens were subjected to additional tests such as ultrasonics pulse velocity and three-point bending after microwave curing. Regression and artificial neural network models (ANN) were developed using the obtained data. While the data of the specimens subjected to MC were used as independent variables of the developed models, the compressive strength of the conventionally cured specimens (CC) was used as the dependent variable. In the models, 60% of the data were used for training, 20% for validation, and 20% for testing. The predictive capabilities of the developed models were compared using performance statistics such as root mean square error (RMSE), root mean absolute error (MAE), and Nash-Sutcliffe efficiency coefficient (NSE). As a result of the study, it was found that compared to all models, the highest performance values were obtained by the ANN-based models. Among the regression-based models, the multivariate adaptive regression splines method (MARS) obtained the highest performance values. Considering the calculated NSE values, it was determined that the ANN-based model gave similar results to the MARS model for the training and validation data sets but provided performance values approximately 25% higher than the MARS model for the test data set. In addition, the results obtained from the modeling studies showed that the CSs of concrete could be predicted very accurately and well in advance.

Study on improvement of waterproofing performance of CCCW with silicone waterproof material and waterbased capillary inorganic waterproofer

The silicone waterproof material and waterbased capillary inorganic waterproofer possess the advantages of rapid film formation and significant hydrophobic effect. In this study, the material composition and mixing ratio of the silicone waterproofing material and waterbased capillary inorganic waterproofing were investigated by multiple performance tests. The results indicated that a white coating was formed on the surface when the mixing ratio of isobutyl-triethoxy-silane and isooctyl-triethoxy-silane was more than 69 %. When the content of sodium and potassium methyl silicate exceeded 0.5 %, respectively, there was an upward trend of contact angle while the reduction in water absorption gradually decreased. Meanwhile, the contact angle and water absorption height of silicone waterproof material were tested. The results showed that the coating performance and hydrophobicity were the best when the mixing ratio of isobutyl-triethoxy-silane, isooctyl-triethoxy-silane, sodium methyl silicate, and potassium methyl silicate was 1.5:0.2:1:0.5. When the matrix mortar specimen was made of Cementitious Capillary Crystalline Waterproofing Materials (CCCW), the lowest water absorption height and water absorption of the experimental group consisted of sodium silicate, sodium tetraborate, sodium phosphate, and sodium hydroxyethyl cellulose were 316.7 % and 39%, respectively. The lowest water absorption height and water absorption of the experimental group consisted of sodium silicate, sodium tetraborate, nano-silica, and sodium hydroxyethyl cellulose were 215.4 % and 28 %, respectively. The results showed that CCCW combined with the experimental group consisted of sodium silicate, sodium tetraborate, sodium phosphate, and sodium hydroxyethyl cellulose had better waterproofing effect.

Smart Inhibition Action of Amino Acid-Modified Layered Double Hydroxide and Its Application on Carbon Steel.

Surface impregnation of concrete structures with a migrating corrosion inhibitor is a promising and non-invasive technique for increasing the lifetime of existing structures that already show signs of corrosion attack. The main requirement for inhibitors is their ability to diffuse the rebar at a sufficient rate to protect steel. The use of smart nanocontainers such as layered double hydroxides (LDH) to store corrosion inhibitors significantly increases efficiency by providing an active protection from chloride-induced corrosion. The addition of LDH to reinforced mortar can also improve the compactness and mechanical properties of this matrix. Here, we report the synthesis of a magnesium-aluminum LDH storing glutamine amino acid as a green inhibitor (labeled as Mg-Al-Gln), which can be used as a migrating inhibitor on mortar specimens. The corrosion behavior of the specimens was determined via electrochemical techniques based on measurements of corrosion potential and electrochemical impedance spectroscopy. A cell containing a 3.5% NaCl solution was applied to the mortar surface to promote the corrosion of embedded rebars. The specimens treated with Mg-Al-Gln presented an improved corrosion protection performance, exhibiting an increase in polarization resistance (Rp) compared to the reference specimens without an inhibitor (NO INH). This effect is a consequence of a double mechanism of protection/stimuli-responsive release of glutamine and the removal of corrosive chloride species from the medium.

Influence of thermal activation on the properties of non-ferrous slag blended cement mortar

In this paper, the influence of different thermal activation methods, namely the hot water curing method and steam curing method on the properties of cement mortar blended with low-volume non-ferrous slag (NFS) (15% cement replacement) is investigated. Therefore, mortar specimens are intrinsically prepared and cured at a controlled temperature of 60 °C in the different curing methods for a short period of 6 hours. Results showed that the steam curing method can significantly improve the compressive strength, reduce the water absorption level and densify the morphology of NFS blended cement mortar. The findings may contribute to accelerating the strength gain of NFS in cement-based material and reduce the amount of cement used.

Effect of type and quantity of inherent alkali cations on alkali-silica reaction

In this study, the macroscopical expansion induced by alkali-silica reaction (ASR) and its corresponding ASR products are investigated using ordinary Portland cement (OPC) mortar specimens with a gradient of boosted alkalis. Experimental results show that the expansion increases with the concentration of inherent alkalis. Sodium-boosted samples expand approximately three times as much as potassium-boosted samples. ASR gels that are present in aggregate veins are calcium-free and amorphous; the atomic ratios of ASR gels are nearly independent of the type and quantity of alkali cations. Aggregate ASR gel exudation occurs in high (≥2.5 %) sodium cases and produces potential Na-shlykovite. Crystalline and amorphous calcium-containing ASR products are present in aggregate vicinities in either Na- or K-boosted samples. The higher hydrophilicity of Na-gel in aggregate veins accounts for the larger expansion. Boosted alkali cations are more effective in ASR products formation than in exposing solution. A new observation that NaOH exposure inhibits ASR in K-boosted samples (zero expansion) is reported.

AN EXPERIMENTAL RESEARCH CONTRIBUTION TO THE USE OF CARBON NANOTUBES IN CEMENT COMPOSITES

Indeed, cement is the second most widely used material after water, with annual global cement production exceeding 4 billion tons in each of the last ten years. Cementitious composites are favored in construction because of their high compressive strength, low cost of preparation, simple manufacturing method, and ease of usage. However, these composites have several drawbacks, including a low tensile capacity, poor deformation performance, and a high cracking tendency, all of which impact the long-term durability of constructions. Carbon nanotubes can reinforce at the nanoscale, which was not possible before. Experimental work was conducted, and specimens of cement pastes and mortars were cast toward testing the carbon nanotubes’ dispersion within the matrix. Carbon nanotubes are known for being very cohesive in their raw form and difficult to disperse into the water. Using ultrasonic energy (bath sonication) along with incorporating a polycarboxylate high-range water-reducing agent to disperse the multiwalled carbon nanotubes helped to achieve about an 18% gain in compressive strength for cement pastes compared to plain cement pastes. This observed gain in strength was evidence of reinforcement. Several aspects explain the restricted work of carbon nanotubes on the industrial scale, including the high price of carbon nanotubes, the absence of standards and confirmations, and the complexity of dispersions, mixing, transporting, casting, and sufficient curing procedures. However, these practical difficulties could be partially resolved by improving the dispersion method or using pre-dispersed carbon nanotubes, which would be encouraging and useful for further exploration at the laboratory scale and the industry floor.

Comparative study on the electric resistance of mortars made of low carbon binders

Against the background of the high CO2 emissions generated in the production of Portland cement (OPC), research is being carried out worldwide into alternative binders that can be produced with lower energy consumption. These have a lower clinker-cement factor or contain no Portland cement at all. To enable these binders to be used on a large scale, also in reinforced concrete structures, their performance in terms of durability must be ensured. The specific electric resistance is a parameter for characterizing different binders. At a young age, the hydration progress and the formation of the pore structure can be observed based on the specific electric resistance. In connection with the electrical conductivity of the pore solution, statements about the pore structure and the resistance to the penetration of corrosion-promoting substances are possible. Finally, the electric resistance is an influencing factor for estimating possible corrosion rates after depassivation of the steel reinforcement. In this study, a wide range of mortars produced with different alternative binders were characterized in terms of their resistivity as a function of age and water content. From the group of clinker substitutes (SCMs), calcined clays and modified steel slag were investigated. The other binders included in the investigation program are produced entirely without Portland cement: In addition to a calcium sulfoaluminate (CS̅A) cement and the C-S-H binder Celitement®, alkali-activated materials (AAMs) in the form of geopolymers and alkali-activated slags were also investigated. The results show a wide range of specific electric resistances in a naturally water-saturated state of the mortar specimens between 5.5Ωm for an alkali-activated metakaolin and 971Ωm for the Celitement®. Clinker replacements with calcined clays metakaolin, or metaillite result in increased specific electric resistances. In addition, the different binders show a very different influence on the dependence of the resistivity on the water content.

ENCAPSULATION OF GROUND BOTTOM ASH AS SUPPLEMENTARY CEMENTITIOUS MATERIALS FOR CEMENT MORTAR

Excessive carbon dioxide (CO2) emissions due to the Portland cement manufacturing process have encouraged the industry to look for more sustainable alternatives to cement. Supplementary cementitious material (SCM) has been widely used to improve concrete performance through considerable research. By-product waste, such as fly ash, has been utilized in many construction projects. It is an effective solution to solve long-term environmental pollution. As one of the coal industry by-products, bottom ash has similar chemical properties compared to fly ash, but it is rarely used as SCM because of its size. Therefore, this research aims to modify the regular bottom ash and observe the strength development of cement mortar incorporating bottom ash as SCM. The pre-treatment process of bottom ash was performed by 4 hours of milling to produce micro-size particles. The chemical and physical properties of modified bottom ash were evaluated before being cast into cement mortar specimens. Various percentages of cement replacement using modified bottom ash were used in this research. The evaluations include X-ray fluorescence (XRF) analysis, specific gravity, particle size analysis, scanning electron microscope-energy dispersive X-ray (SEM-EDX), normal consistency, and setting time. The compressive strength and strength activity index were evaluated to obtain the strength development and optimum composition of cement mortar incorporating bottom ash, caused by pozzolanic activity. The results indicate that bottom ash positively affects the strength development of cement mortar, and it can be used as SCM to produce more sustainable cement-based construction materials.

Effect of Curing Temperature on Mechanical Properties of Sanitary Ware Porcelain based Geopolymer Mortar

The objective of this study was to investigate the effect of curing temperature on the mechanical properties of sanitary ware porcelain powder-based geopolymer paste and mortar under various curing temperatures. The setting time, porosity, water absorption, and compressive strength of specimens mixed with alkaline concentrations of 8M, 10M, 12M, and 14M were compared. All mortar cube (50×50×50 mm) specimens were placed into drying ovens for 24 hours at 60°C, 75°C, 90°C, and 105°C, respectively. The specimens were then air-cured for 1, 3, 7, 14, and 28 days. The results showed that the elevated curing temperature accelerated the polymerization process of the porcelain geopolymerization reaction. The setting time varied between 89 mins and 380 mins. It showed variability depending on alkaline concentration and initial curing temperature. The setting time of pastes decreased when alkaline concentrations increased. An increasing temperature in the drying oven decreased the initial and final setting times. Similar to this, the rate of water absorption and permeability of porcelain-based geopolymer mortar specimens decreased with drying oven temperatures and increments in alkaline concentration. The lowest water absorption and porosity of the specimen were 2.1% and 15.7%, respectively. The compressive strength increased as drying oven temperatures and alkaline concentrations increased. The highest 28 day compressive strength was found in 14M specimens with 105°C curing temperatures. The ultimate compressive strength was 64.45 N/mm2. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were investigated to study the microstructural properties of the geopolymers. Doi: 10.28991/CEJ-2023-09-08-01 Full Text: PDF

철강산업 부산물의 재활용에 관한 연구

In this study, an experiment was conducted to reduce carbon dioxide emission which is the main cause of global warming in the construction industry. Blast furnace slag is used to replace cement that emits a large amount of carbon dioxide in the manufacturing process, and alkaline water was electrolyzed with potassium carbonate (K2CO3) as an electrolyte instead of an alkali activator to solve the problem of deterioration of initial strength and neutralization resistance of blast furnace slag. In other words, a series of experimental studies were conducted to reduce the amount of cement used by analyzing the compressive strength, micro structure analysis and neutralization test of concrete using blast furnace slag and electrolysis alkaline water. As a result, the compressive strength of mortar using alkaline water as the mixing water showed higher strength improvement than the mortar using general mixing water, and as a result of SEM analysis, more hydration products were generated inside the mortar test specimen using alkaline water as the mixing water. This is judged to be(by) the destruction of the glassy film through alkaline water and the elution of reactive substances from the blast furnace slag. In addition, as a result of the accelerated carbonation test, it was confirmed that the mortar using alkaline water as the mixing water had higher carbonation resistance than the mortar using general mixing water.

A bio-inspired mineral precipitation method to improve the freeze-thaw resistance of cement concrete pavement

Mineral precipitation has been proven to be an effective surface treatment for reducing the porosity of Portland cement concrete (PCC), leading to significant improvement in its freeze-thaw (F-T) resistance. Inspired by human teeth, this study proposes to produce a protective surface layer for PCC through in-situ precipitating hydroxyapatite (HAP), the same mineral found in the tooth enamel, on the concrete surface to improve its freeze-thaw resistance. This protective layer was generated by simply treating the mortar surface with a diammonium hydrogen phosphate (DAP) solution. Experimental results reveal that the F-T resistance is significantly improved, with the DAP-treated specimens surviving three times as many cycles as the control group. The proposed treatment also enhances the compressive strength of the mortar specimens by 35% and reduces saturated water absorption by up to 50%. Analysis of mineralogy suggests that DAP reacts with calcium ions from hydrated cement, leading to HAP precipitation and calcium phosphate on the cement mortars' surface. Particularly, the nanoindentation results indicate that the mineral phase with a lower density tends to react more readily with DAP, leading to its conversion into minerals with significantly higher packing density. Quantitative backscattered scanning electrons (BSE) images and mercury intrusion porosimetry (MIP) analysis verify that the microstructure of the cement mortar surface was densified by the formation of HAP and calcium phosphate induced by the proposed treatment. The proposed method exhibits great potential in enhancing the longevity of PCC pavements in cold regions.

Dynamic enhancing effect of free water on the dynamic tensile properties of mortar

This study investigates free water effect on the dynamic tensile properties of mortar. Fully saturated and saturated-then-redried mortar specimens with two porosities, namely common and high-porosity, are prepared and tested under quasi-static and dynamic split-tension states covering strain rates between 1.49e−06s−1 and 5.29s−1. The split-tensile strength and elastic modulus at different strain rates are quantified. Comparing the dynamic increase factor (DIF) for mortar tensile strength, a maximum difference of 1.2 at strain rate 5 s−1 is found between saturated and dried high-porosity mortars revealing the influence of free water. The testing data is compared with other existing data which shows the mortar water effect is more similar to concrete than limestone and sandstone. The high-speed camera images during the dynamic tests are analysed which revealed a water retarding effect on the dynamic split-tension failure process, resulting in an initial crack delay of up to 0.4 ms due to free water. The wave speed for different mortar specimens at different strain rates is analysed, which shows that higher porosity is more sensitive to the water effect. Possible mechanisms leading to this water effect is discussed. Overall, the study provides a quantitative measure of the water enhancing effect on the dynamic tensile strength of mortar and offers insights into the practical use of water in the design and construction of mortar structures.

Influence of Spanish Broom Fibre Treatment, Fibre Length, and Amount and Harvest Year on Reinforced Cement Mortar Quality

The use of natural materials, such as natural fibres, in the construction industry is becoming more frequent. The source of natural fibres should be sought in local plants, such as Spanish Broom in the Mediterranean area. The fibre treatment process was carried out in 8 different ways with alkali 4%, 5%, 6%, 8%, 10% and 15% NaOH solution, and 5% NaOH and 2% Na2SO3 mixture solution and seawater. The fibres were tested for tensile strength. No relationship was established between the concentration of the solution and the tensile strength of the fibres. The influence of the reuse of treatment solution on fibre quality was monitored by X-ray diffraction (XRD), ATR-FTIR, and TG/DTG analysis. Fibres with lengths of 1, 2, and 3 cm were added to cement mortar specimens in amounts of 0.5 and 1 vol%. The flexural and compressive strengths were tested on mortar specimens after 28 days. For fibres 1 and 3 cm long, 0.5% natural fibre content gives higher strength results: about 9% for flexural strength and 13.5% and 11.7% for compressive strength in regard to mortar reinforced with fibres of the same length but with a proportion of 1%. For mortar reinforced with fibre 2 cm long, better results are achieved with 1% fibre content, namely 9% higher flexural strength and 11.2% higher compressive strength compared to mortars with 0.5% fibre content. SEM/EDS analysis showed that the fibres are integrated into the cement matrix but that there is no strong interaction with the binder. For examination and 3D visualisation of mortar specimens, a medical device MSCT (Multi-slice Computed Tomography) was also used. For three consecutive years of Spanish Broom harvesting, an analysis of meteorological conditions and the results of the mechanical strength of reinforced mortars is given. For the examined years, the meteorological conditions did not affect the obtained results. Additional knowledge about the Spanish Broom fibres can introduce this plant to the application of new sustainable building materials.

Dynamic Mechanical Behavior of Rock Specimens with Varying Joint Roughness and Inclination under Impact Load

The influence of joint roughness and inclination on the dynamic mechanical properties of rocks is a prominent research area. In order to investigate the effects of joint roughness and inclination on the dynamic mechanical properties of jointed rocks, impact tests were conducted using a spilt Hopkinson pressure bar (SHPB) apparatus for prefabricated serrated joint cement mortar specimens with varying joint roughness and inclination. The failure mode, stress wave propagation characteristics, peak stress, and stress wave energy transfer law under impact load were analyzed. The results indicate that both joint inclinations and joint roughness coefficients (JRC) have a strong influence on the failure mode, peak stress, and stress wave energy transfer of jointed specimens. The jointed specimens exhibit three distinct failure modes under impact load, namely splitting tensile failure, shear slip failure, and compound failure of splitting tensile and shear. The peak stress initially decreases then increases with the increase in joint inclination angle, namely a V-shape variation, while it gradually increases with JRC increasing from 0 to 20. Jointed specimens exhibit the lowest peak stress at an inclination angle of 45° and JRC of 0. The variation of transmitted energy coefficient is similar to the peak stress, while the variation of reflected energy coefficient is opposite to the peak stress. At joint inclination angles of 0° or 90°, the reflected energy coefficient increases with the increase of JRC from 0 to 20, while the transmitted energy decreases. However, when the joint inclination angle is in the range of 30° to 60°, the reflected energy coefficient gradually decreases with JRC increasing, while the transmitted energy coefficient gradually increases.

Novel production of macrocapsules for self-sealing mortar specimens using stereolithographic 3D printers

The use of capsule-based technology for self-sealing and self-healing cementitious systems has been extensively investigated for both macro- and microencapsulated additions. In this study, macrocapsules, produced using a novel technique were characterised and compared, evaluating mechanical triggering, bonding with the cementitious matrix, and self-sealing efficiency upon integration into cementitious mortar specimens. Macrocapsules containing a commercially available water repellent agent were produced in two ways. Stereolithographic additive manufacturing (3D printing) was used to produce novel rigid acrylate macrocapsules as well as alumina ones. Cementitious macrocapsules produced with a rolling technique were also used as a comparison. The capsules were characterised in terms of watertightness, water uptake, and shell morphology. Following this, the capsules were integrated into cement mortar prisms and subjected to controlled cracking by three-point bending to evaluate the triggering and subsequent self-sealing effect. The results highlighted influential process parameters that can be optimised and explored for further capsule-based self-sealing in structural applications.

Influence of Electromagnetic Inductive Microcapsules on Self-Healing Ability of Limestone Calcined Clay Cement (LC3) Mortar.

In order to promote the sustainability of cementitious materials, it is imperative to reduce the level of environmental pollution and energy consumption during their production, as well as extend the service life of building elements. This study utilized limestone, calcined clay and gypsum as supplementary cementitious materials to prepare LC3 mortar, replacing 50% of ordinary silicate cement. Three types of microcapsules (M1, M2 and M3) were prepared using IPDI as a healing agent and polyethylene wax, polyethylene wax/nano-CaCO3 or polyethylene wax/ferrous powder as shell materials. The microcapsules were added to the LC3 mortar and tested for their effects on the mechanical properties, pore structure and permeability of mortars. Pre-loaded and pre-cracked mortar specimens were subjected to room temperature or under an applied magnetic field to evaluate the self-healing ability of the microcapsules on mortars. The kinetics of the curing reaction between IPDI and moisture were investigated using quasi-first-order and quasi-second-order reaction kinetic models. The experimental results showed that the mortar (S3) mixed with electromagnetic inductive microcapsules (M3) exhibited the best self-healing ability. The compressive strength retention, the percentage of pores larger than 0.1 μm, recovery of chloride diffusion coefficient and maximum amplitude after self-healing of S3 were 92.2%, 42.6%, 78.9% and 28.87 mV, respectively. Surface cracks with an initial width of 0.3~0.5 mm were healed within 24 h. The curing reaction between IPDI and moisture during self-healing followed a quasi-second-order reaction kinetic model.

The Effects of Crystalline Admixture on the Self-Healing Performance and Mechanical Properties of Mortar with Internally Added Superabsorbent Polymer.

Crystalline admixture (CA) can be incorporated into concrete to achieve self-healing of concrete cracks. In this study, both CA and superabsorbent polymer (SAP) were used as self-healing agents to investigate the effects of CA on the self-healing performance and mechanical properties of mortar with internally added SAP at different self-healing ages. The healing effect of cracks in mortar is assessed by crack observation and impermeability. The structure and composition of the filler in the cracks were analyzed by microscopic experiment. The experimental results indicate that CA enhances the healing of cracks in mortar specimens. The chemical reactions of CA primarily contribute to significantly improving the early-age crack-healing ability of the specimens, and the water absorption and expansion ability as well as the internal curing effect of SAP also facilitate the crack-healing process. Increasing the CA content leads to an increase in the Ca/Si ratio of C-S-H, causing a transition from a layered structure to a more compact needle-like structure. When 4% CA was added to the mortar, it resulted in an adequate formation of needle-like C-S-H structures, which eventually penetrate and fill the pits formed by SAP, compensating for the strength loss caused by SAP.

Effect of Embedded Depth of Copper-Nickel-Plated Sensor Probes on Compressive Strength Development of Mortar

Embedded sensors are widely employed for the structural health monitoring of structures constructed with concrete or mortar. Despite embedded sensors being actively used, there has been no study on whether or not the sensor probe placement within structures made of concrete or mortar influences their structural stability. The strength of small structures in particular could be affected by sensor probes embedded within them. To address the lack of research in this area, this study analyzed the effect of embedding positions of sensor probes on the compressive strength development of mortar. After the production of mortar specimens with the depth of the embedded sensor being controlled by the developed mold, compressive strength tests were conducted, and then test results were verified through finite element analysis. For testing, copper–nickel-plated sensor probes were embedded within the mortar because these sensor probes are popular commercial probes. The test results show that the compressive strength was 7.1 MPa when the sensor probe was embedded at a depth of 5 mm. In contrast, the compressive strength was 28.2 MPa at a depth of 30 mm. Since the compressive strength without the embedded sensor probe was 29.8 MPa, considering the results of this study, it is highly recommended that copper–nickel-plated sensor probes be embedded at least 30 mm from the surface of mortar structures.

The Deformation Behavior and Failure Modes of Surrounding Rock after Excavation: A Experimental Study

The deformation and failure of the surrounding rock during roadway excavation often determine the choice of supporting methods. To study the deformation behavior and failure modes of the surrounding rock after excavation under unloading stress, structural model tests were carried out with a novel experimental device. The present structural model test using partial hollow thick-walled cylinder cement mortar specimen φ200 mm × 280 mm with a horizontal central circular hole of 60 mm diameter and the hollow height of 160 mm was conducted to investigate the deformation, failure characteristics, and AE response of a whole testing process from excavation to postunloading state. Experimental results revealed that the amount of deformation behind the surface is significantly higher than that in front of the surface, and the radial strain increases with the increase of the distance from the surface within the range affected by unloading. Furthermore, the unloading rate has a little effect on the radial deformation of the surrounding rock in front of the surface, but has a substantial effect on the radial deformation behind the excavation surface. The peak value of the strain rate at the unloading rate of 2 MPa/s is much higher than that at the unloading rate of 0.1 MPa/s. According to AE results and the failure of opening the boundary, the increase of unloading rate triggers and exacerbates the damage of the specimen under high in situ stress conditions. The surrounding rock expanded to the inner hollow, accompanied by large dilation and volume changes, and it resulted in the shrinkage of the hole diameter. A large number of rock slices are generated at the opening curved free surface and then fell off, whose morphology is similar to the rock blocks that fell off after caving failure and rock burst in situ field. The results show that the system can accurately simulate the mechanical response and acoustic emission response of the excavated surrounding rock, which provides a new experimental method for further study of the unloading response of the surrounding rock.

Mechanical properties of eco-friendly cement based composite mortars plastic fiber reinforced partially replaced by natural pozzolan and marble waste

This research presents a study on the mechanical properties of mortar specimens reinforced with plastic fibers incorporating natural Moroccan pozzolan and marble waste as partial substitutes for cement. Cement is a widely used material, but its production contributes significantly to CO2 emissions. And reducing the carbon footprint of materials without increasing costs is a critical challenge. Hence, numerous studies have investigated the partial or complete substitution of cement. Moroccan pozzolan, a natural pozzolanic material, offers an alternative to energy-intensive cement production. Marble waste, an industrial byproduct generated during the sawing, shaping, and polishing of marble, poses a significant environmental threat. Likewise, the issue of environmental pollution caused by plastic has received lot of attention, and the ideal solution recommended is recycling. In this sense, twenty-one mixes were synthesized and evaluated to explore the mechanical properties of the fiber-reinforced mortars based on natural pozzolan and marble waste added at different weight percentages (5–5/10–5/5–10/15–0/0–15/7.5–7.5) as a partial replacement for cement and 1% and 2% plastic fibers, based on the mortar volume. The hardened mortar mixtures were tested for compressive strength determined after 7 and 28 days, and flexural strength by a three point bending machine. The test results revealed that the mortar specimens containing marble waste and natural pozzolan exhibited the highest compressive strength. The addition of plastic fibers positively influenced the compressive and flexural strength of the mortars. Optimal percentages of natural pozzolan, marble waste, and plastic fibers were identified. The best-performing mixture achieved a compressive strength of 18.67 MPa with 5% pozzolan, 5% marble waste, and 2% plastic fibers added to the mortar mix. This approach not only addresses the uncontrolled disposal of plastic and marble waste but also provides an opportunity to utilize abandoned natural resources, creating more durable and environmentally friendly composite mortars.