Improvement In Compressive Strength Research Articles

Influence of Graphene Oxide Concentration and Ultrasonication Energy on Fracture Behavior of Nano-Reinforced Cement Pastes

The aim of this study is twofold. First, to assess the effect of the sonication process on the optimal dispersion of GO sheets for nanostructural reinforcement of cement pastes, as there is currently no clear criterion on this effect in the literature. For this purpose, in the first stage, the GO content in distilled water was fixed at 0.03% by weight, and the sheets were dispersed using different levels of ultrasonic energy, ranging from 0 J/mL to 2582 J/mL. In the second stage, to analyze the modification of pore structure due to the addition of GO sheets in different ratios (0–0.06% by weight) and its relationship with the mechanical and fracture properties of reinforced cement pastes. According to the results, it has been determined that the incorporation of GO sheets into the matrix alters the mechanical and fracture behavior, varying depending on matrix pore size and GO particle size. The addition of GO leads to a reduction in the average size of macropores (greater than 8 µm) of 13% for a dosage of 0.45% in weight and micropores (between 8 and 0.5 µm) in a 64% for the same composition with non-sonicated GO, although the total volume of pores in these ranges only decreased slightly. This reduction is more pronounced when the GO has not been sonicated and has larger particle size. Sonicated GO primarily modifies the range of capillary pores (<0.5 µm). The addition of GO with the highest degree of dispersion (465 nm) did not show significant improvements in compressive strength or Young’s modulus, as the cement used contains a significant volume of macropores that are not substantially reduced in any composition. Adding 0.030% ultrasonicated GO achieved a 7.8% increase in fracture energy, while an addition of 0.045% resulted in a 13.3% decrease in characteristic length, primarily due to the effect of capillary and micropores.

Assessing performance, economic costs and environmental benefits of high-performance ecological geopolymer concrete incorporating excavated rock and soil from tunnelling, fly ash and slag as reclaimed raw materials

Excavated rock and soil from tunnelling (ERST), fly ash (FA), and slag are one of the largest sources of solid waste and play an important role in reducing dependence on natural resources and solving the problem of solid waste accumulation. This study verifies the feasibility of high-performance ecological geopolymer concrete (HPEGC) incorporating ERST, FA and slag for engineering applications. The effects of different binding material to machine-made sand ratio (BMMSR) and SN/FS (the total mass of sodium silicate and NaOH solids to the total mass of the powdered raw material) on the slump, compressive strength, tensile strength, drying shrinkage, salt corrosion resistance of concrete and the microstructural deterioration process before and after salt corrosion were analysed by indoor tests and microscopic tests. The results showed that the hydration products generated at SN/FS of 10, 12, and 15 % could effectively fill the pores of HPEGC and improve the pore structure and interfacial properties of HPEGC by microminiaturisation of the pore size. HPEGC formed a dense three-dimensional reticulated polysilica-aluminate-like structure due to the coexistence of C-S-H gel, C-A-S-H gel, N-A-S-H amorphous gel, and Na2Al2Si3O10. HPEGC with SN/FS of 12 % and BMMSR of 0.36 showed 29.5 % and 18.9 % improvement in compressive and tensile strengths, better resistance to sulfate attack, and 4.5 % and 45 % reduction in economic cost and GHG emission, respectively, compared with ordinary Portland cement concrete (OPCC). The results of the study proved that the engineering application of HPEGC incorporating ERST, FA and slag as raw materials is promising, providing new solutions for global underground excavation materials and industrial solid waste, and effectively promoting the sustainable development of the construction industry.

Characterization and Properties of Binder and Nano-Filler in Geopolymer Paste with Graphene Oxide

Globally, current research has developed new cement-based materials to meet increased demands for performance, energy efficiency, and environmental protection. Geopolymer, cost-effective, and high-early strength concrete binder alternative, has grown in popularity. Geopolymer reduces emissions by 80% during production while maintaining strength levels comparable to Ordinary Portland Cement (OPC). In their natural state, geopolymer binders have a microstructure that is cross-linked and significantly more brittle than OPC. To improve the properties of geopolymer, several approaches were adopted. However, recent study suggests that incorporating nanomaterials such as graphene oxide (GO) to geopolymer has shown an improvement in physical and mechanical properties. Graphene oxide is an inorganic nanomaterial that improves the mechanical characteristics of various composite materials by showing substantial filling effects on composite materials that significantly improve composite material integrity. The investigation into the potential of GO to improve the efficacy of geopolymer composite materials in various engineering applications has garnered considerable attention in recent years. The simplified hummer’s method was employed to synthesise the GO. Various characterization techniques involving SEM, XRD, and FTIR were utilized to understand the crystalline structure and microstructure of GO nanoparticles. GO powder were used as 0.05%, 0.10%, 0.15%, 0.20%, and 0.25% by weight of binder that includes fly ash class F and steel slag with an optimum binder modification of 40% fly ash and 60% steel slag. The influence of GO on Bulk density, microstructure, and mechanical strength were determined. The compressive strength results indicated an improvement of compressive strength by 21.48% in geopolymer paste with 0.15% GO after 28 days of curing.

The effect of Silver addition and deformation parameters on mechanostructure, biodegradation, antimicrobial and mechanical properties of Zn-based biodegradable alloys.

Although low mechanical properties, Zinc (Zn) alloy systems with Copper (Cu) and Silver (Ag) as alloying elements have strong biocompatibility and biodegradability characteristics. This study examined the effects of rolling parameters and Ag alloying on the mechanical, biodegradable, and final structure of an alloy based on Zn. Comparing treated and untreated specimens, the addition of Ag led to a considerable improvement in both hardness and compressive strength. The produced alloys with varying amounts of Ag (between 1 and 4wt%) were cold rolled at 400-800r/min and friction coefficients between 0.3 and 0.5. The alloys' ultimate strength rose with an increase in rolling speed for Zn1Cu4Ag, and hardness and compressive strengths rose to 80HV and 470MPa, respectively. It was demonstrated that rolling force rose somewhat with Ag concentration but significantly increased with rolling speed and friction. E. Coli and S. aureus were used to assess the biodegradable alloys' antibacterial properties. For the Zn-1Cu-2Ag alloy, the inclusion of Ag resulted in a considerable (50%) rise in antibacterial activity that exceeded the effects seen in other alloy systems.

Flexural behaviour of geopolymer concrete beams with hybrid natural–synthetic fibre reinforcement

The requirement of excellent flexural stiffness in construction elements has initiated the use of fibre reinforcement. However, the processing complexity involved in the manufacture of synthetic fibres is environmentally hazardous. The use of natural fibres in geopolymer concrete (GPC) structures was investigated in this work using a hybridisation of natural and synthetic fibre. Natural basalt fibre (BF) was used with synthetic steel fibre (SF) in various proportions in GPC and tests were conducted to evaluate the workability, compressive strength, split tensile strength and flexural strength. It was found that, compared with the plain GPC, the addition of 1.5% BF and 0.5% SF resulted in 45%, 27% and 12% improvements in compressive, split tensile and flexural strengths, respectively. The compatibility between the SF and BF resulted in enhanced post-peak flexural behaviour, with 37% improvements in the modulus of elasticity and stiffness. As BF possesses more tensile strength than SF, the use of 1.5% BF and 0.5% SF provided better flexural and ductility properties than the use of SF alone, which could lead to the development of ductile GPC members under dynamic loading conditions.

Investigation on the compressive strength, chloride migration of MK-FA-LS blended cementitious materials with electrochemical techniques

Blended cementitious materials has become an efficient method to reduce the CO2 emission while improving the long-time performance in construction filed, especially for the application of combined supplementary cementitious materials. However, the microstructure and performance evolution of the new materials need further deep investigation. In this study, metakaolin (MK), fly ash (FA) and limestone (LS) was introduced in cementitious materials to form a complicated quaternary system. The compressive strength and chloride migration performance are evaluated, with different MK/FA proportions. Then through the calorimetry test, X-ray Diffraction (XRD)/Rietveld analysis, free water content measurements, and electrochemical impedance spectroscopy (EIS) test, the phase assemblage and microstructure quantification of the blended systems are compared. Finally, to better understand the performance change, the correlation between the compressive strength/chloride migration coefficient and the electrochemical parameters are established. Results showed that the combination of MK, FA and LS is beneficial for the improvement of compressive strength and the chloride resistance in a proper mix design. EIS is a proper nondestructive method to understand the microstructure evolution of blended systems and even predict the chloride resistance of similar systems. This study shields a light for the application of the quaternary system, with a better durability, higher CO2 emission reduction and lower price.

Comparative Study of Reinforced Concrete Using Human Hair and Aluminum Fibres

This study investigates the efficacy of human hair and aluminum fibres as reinforcements in concrete, analyzing their impact on compressive, flexural, and tensile strengths. Different fibre percentages (0%, 0.5%, 1%, and 1.5% by weight of cement) are systematically incorporated into concrete mixtures. Compressive strength tests on cubes, flexural strength assessments on beams, and tensile strength evaluations on cylinders reveal insights into the material's load-bearing, bending, and stretching capacities. Human hair-reinforced concrete showed significant improvements in compressive strength. Results indicate a gradual strength increase in Human Hair Fibre Reinforced Concrete (HHFRC) up to an optimal percentage. At the same time, Aluminum Fibre Reinforced Concrete (AFRC) shows significant enhancement in higher fibre content. AFRC's superior mechanical properties stem from aluminum fibres high tensile strength and stiffness, enhancing bond formation and resulting in denser, stronger concrete. These findings inform the selection of fibre reinforcement for concrete structures tailored to specific project needs.

Enhanced interface and thermal insulation in cement composites using polydopamine-modified hydrophobic silica aerogels

Silica aerogels (SA) have exceptional thermal insulation capabilities, however, their superhydrophobic nature hinders the formation of a uniform composite when combined with cement slurry. To address this issue, an aqueous solution was employed to disperse SA particles using sodium dodecyl sulfate (SDS). Subsequently, the dispersed micelles were coated with polydopamine (PDA) through in situ polymerization. This approach effectively enhanced the dispersion of SA in cement slurry and improved its connection force with the cement hydration products, thereby mitigating the adverse effects of aggregated SA on the mechanical properties of the cement composite. The successful PDA coating led to the formation of smaller aggregated micelles, resulting in a 30% improvement in compressive strength of cement composites containing modified SA compared to those using unmodified SA, while maintaining the desired thermal conductivity properties. With a strategic increase in the quantity of modified SA, a remarkable thermal conductivity of 0.1351 W/m·K was achieved without significantly compromising the compressive strength, which reached about 13.94 MPa. This enhanced compressive strength surpassed that of conventional thermal insulation materials like expanded polystyrene (EPS) and foam concrete. Consequently, this novel technique has the potential to markedly enhance the thermal insulation of cement composites without excessively impacting their compressive strength, thus contributing to the development of green insulation and energy-saving building materials.

Compressive strength and gel structure improvement in the high-volume calcium carbide residue activated-blast furnace slag system combined with sodium carbonate and silica fume

Calcium carbide residue (CCR) with high alkalinity favorably corresponds to the alkaline activator in the alkali-activated materials (AAMs) production. Its utilization could reduce the carbon footprint and facilitate cast-in-situ applications compared to traditional liquid alkaline activators. A high-volumed CCR from 10 % to 25 % as alkaline activators in an alkali activated-blast furnace slag system was investigated, in which sodium carbonate (Na2CO3) and silica fume were used to improve the mechanical properties of CCR-activated blast furnace slag (CCR activated-BFS) pastes. Isothermal Calorimetry, X-ray diffraction (XRD), 29Si nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) were used to characterize the reaction process, phase transformation, and gel structure. The results show that the highest compressive strength of CCR activated-BFS pastes was obtained when the CCR proportion was 20 %. Na2CO3 addition significantly improved the compressive strength, especially at the CCR to Na2CO3 mass ratio at 1:1.5. However, the compressive strength deterioration appeared at 28 d because of the gel structure decomposition in CCR activated-BFS pastes. The silica fume addition inhibited the structure decomposition, improved the connectivity of gel structure, favored the formation of gel, and thus suppressed the compressive strength deterioration. The study established a sustainable waste recycling from acetylene gas production by using CCR as feedstock to mitigate carbon emissions from AAMs production.

Bulk graphene-based composites with artificial nacre-like laminated structure: Microstructure and mechanical properties

In this study, the bulk Cu/reduced graphene oxide (Cu/rGO) composites featuring an artificial nacre-like laminated structure were successfully fabricated using spark plasma sintering (SPS), and the microstructure and mechanical properties of the resulting composites were investigated. The Cu/rGO composites demonstrated a distinct laminated structure, and their relative densities increase with Cu addition. Moreover, the presence of trace amounts of in-situ interfacial reaction products (CuO and CuO2,) were observed to enhance the adhesive strength at the Cu-rGO interface. Mechanical testing of the composites showed notable improvements in both compressive strength and ductility compared to a bulk monolithic rGO sample. Specifically, the bulk rGO composites with a 35.05 wt% addition of Cu displayed an enhancement of ∼67 % in compressive strength and ∼19 % in ductility relative to the pure rGO sample. These improvements are attributed to synergetic strengthening and toughening mechanisms within the rGO composites. The enhanced strength and ductility of the Cu/rGO composites significantly boost their wear resistance. This research not only demonstrates the effectiveness of incorporating Cu into rGO matrices but also suggests a promising avenue for the development of novel bulk rGO composites with engineered laminated structures.

Study on the Effect of Fly Ash on Mechanical Properties and Seawater Freeze–Thaw Resistance of Seawater Sea Sand Concrete

When using seawater and sea sand as mixes, the mechanical properties and durability of concrete are adversely affected because the raw materials themselves contain harmful ions. Fly ash is the tailings formed in the process of industrial production, the use of which does not require the burning of clinker, reducing CO2 emissions. Moreover, it belongs to a new type of cementitious materials with low emissions and high environmental protection. Fly ash enhances the properties of concrete and reduces the effect of harmful ions on concrete. Based on the above considerations, the corresponding specimens were prepared and subjected to cubic compressive strength, flexural strength, and seawater freezing and thawing resistance tests by using fly ash admixture as the main variable. A combination of macro-analysis and micro-analysis was used to investigate the effect of fly ash on the performance of seawater sea sand concrete. The results showed that fly ash significantly enhanced the mechanical properties and resistance to seawater freezing and thawing of seawater sea sand concrete. The best improvement in compressive strength and resistance to seawater freezing and thawing was achieved at a substitution rate of 20%. The maximum increase in compressive strength was 13.22%. The maximum reduction in mass loss rate was 57.26% and the strength loss rate was 43.14% after the specimens were subjected to seawater freezing and thawing 75 times. The maximum enhancement in flexural strength was 17.06% for a substitution rate of 10%. Through microanalysis, it can be seen that the incorporation of coal ash can enhance the compactness of concrete through the microaggregate effect as well as the volcanic ash reaction to promote the secondary hydration reaction, so as to strengthen the seawater freeze–thaw resistance of seawater sea sand concrete. Finally, the damage prediction model established using the mean GM (1, 1) model of gray system theory meets the requirements of the first level of prediction accuracy and can accurately predict the damage of seawater sea sand concrete under seawater freezing and thawing.

Development of innovative alkali activated paste reinforced with polyethylene fibers for concrete crack repair.

Concrete structures are susceptible to cracking, which can compromise their integrity and durability. Repairing them with ordinary Portland cement (OPC) paste causes shrinkage cracks to appear in the repaired surface. Alkali-activated binders offer a promising solution for repairing such cracks. This study aims to develop an alkali-activated paste (AAP) and investigate its effectiveness in repairing concrete cracks. AAPs, featuring varying percentages (0.5%, 0.75%, 1%, 1.25%, 1.5%, and 1.75%) of polyethylene (PE) fibers, are found to exhibit characteristics such as strain hardening, multiple plane cracking in tension and flexure tests, and stress-strain softening in compression tests. AAP without PE fibers experienced catastrophic failure in tension and flexure, preventing the determination of its stress-strain relationship. Notably, AAPs with 1.25% PE fibers demonstrated the highest tensile and flexural strength, exceeding that of 0.5% PE fiber reinforced AAP by 100% in tension and 70% in flexure. While 1% PE fibers resulted in the highest compressive strength, surpassing AAP without fibers by 17%. To evaluate the repair performance of AAP, OPC cubes were cast with pre-formed cracks. These cracks were induced by placing steel plates during casting and were designed to be full and half-length with widths of 1.5 mm and 3 mm. AAP both with and without PE fibers led to a substantial improvement in compressive strength, reducing the initial strength loss of 30%-50% before repair to a diminished range of 2%-20% post-repair. The impact of PE fiber content on the compressive strength of repaired OPC cube is marginal, providing more flexibility in using AAP with any fiber percentage while still achieving effective concrete crack repair. Considering economic and environmental factors, along with observed mechanical enhancements, AAPs show promising potential for widespread use in concrete repair and related applications, contributing valuable insights to the field of sustainable construction materials.

Spent coffee grounds enhanced compressive strength of cement mortar: an optimization study

This paper presents an optimization study of spent coffee grounds (SCG) as cement mortar additives to enhance mortar strength. In recent years, sustainable materials have begun finding their way into cement mortar, with SCG being one. There is limited optimization study on the SCG addition in mortars, hence this study was performed to optimize the curing time and SCG addition in cement mortar to achieve the highest compressive strength through response surface methodology. Scanning Electron Microscopy (SEM) characterization was carried out on the SCG particles to identify their physical properties. An Energy Dispersive X-ray (EDX) analysis was carried out to identify its chemical properties. Simultaneously, a workability test, the flow table test, is conducted to study the effect of SCG on the flowability of the cement mortar mixes. The synergistic effect between SCG content in cement mortar mixes and the curing period was statistically studied and analyzed. Both parameters were then optimized to obtain the best performance mix of SCG in cement mortar. It was found that 1.1% SCG and a curing day of 68 days produced the highest compressive strength (33.4MPa) of cement mortar. The Response Surface Methodology (RSM)-optimized cement mortar mix presented at least a 12.62% improvement in compressive strength from control cement mortar without SCG additives (28.77MPa). Experimental validation of the optimum condition showed a good agreement with a deviation of 3.12% in three replicates, thus indicating that the optimum model in this work can be used to model the compressive strength of the SCG-cement mortar mixture.

Validating synergistic effects of hybrid nanomaterials and progressive collapse behaviour of UHPC beams: Do particle packing theory, experiments and finite element analysis strongly interconnected?

Ultra-High-Performance Concrete (UHPC), a unique cementitious composite that exhibits an ideal solution for structural reclamation. The significant objective is to develop UHPC with binary nanomaterials (nanosilica and nano clay) using Modified Andreasen and Andersen particle packing theory and examine effect of nano hybridization in flexural and shear behaviour of reinforced UHPC beams. In addition, findings such as load-deflection behaviour and crack pattern are validated with Finite Element Analysis (ANSYS). The synergistic effect of hybrid nanomaterials enhances formation of hydration products that accounts for 27%, 30.7%, and 49% improvement in compressive, splitting tensile, and flexural strength in 2% nanosilica and nano clay (D2 mix Id). Moreover, flexural UHPC beam (D2 F) and shear UHPC beam (D2 S) withstand 9.5% and 10% higher ultimate load than control (A0 F and A0 S mix). The Finite Element Analysis predicts ultimate load in very minimum discrepancy percentage that ranges from 1 to 3%.

Coupled effect of MWCNTs concentration and induced pore structures on compressive performance and elastic modulus of ultra-high toughness cementitious composites: Experimental and theoretical studies

Due to the superior mechanical properties and electrical conductivity of multi-walled carbon nanotubes (MWCNTs), their integration into cementitious composites can improve compressive strength and self-sensing capabilities. However, balancing high mechanical strength with high conductivity is challenging as high MWCNT dosages can impede strength development. We addressed this by studying the effect of MWCNTs concentration (0–1.1 wt% of cementitious binders) and induced pore structures on the compressive performance and elastic modulus of ultra-high toughness cementitious composites (UHTCC), both experimentally and theoretically. It was found that as the MWCNTs concentration increased, the porosity continued to increase, while the compressive strength fluctuated. Two failure patterns were identified, i.e., quasi-brittle failure and ductile failure. Analysis showed MWCNTs could promote cement binder hydration, increasing matrix density but the strength development was curbed by increased porosity. A balance was achieved at 0.7 wt% MWCNTs. Further investigations using the Eshelby-Mori-Tanaka method discussed how MWCNT concentration, mechanical properties, distribution, porosity, and pore geometry influenced the elastic modulus. Ultimately, we developed a UHTCC-MWCNT composite with 1.1 wt% MWCNTs, which exhibited substantial improvements in compressive strength (44.85 MPa) and conductivity (9.78✕10−3 S/m), showing increases of 22.18 % and 18,132.6 % respectively, compared to the reference group.

Compressive Strength of Geopolymer Mortar Reinforced with Rice Husk Fibers

Geopolymer concrete has been proposed to minimize carbon dioxide emissions related to the cement production industry. This environmentally friendly material consists of industry waste materials activated chemically by an activation solution. In this study, the geopolymer mortar has been designed with 70% fly ash and 30% metakaolin. Hydroxide sodium in 14 molar concentrations blended with sodium silicate in a 2.5:1 ratio was used as the activation solution. Rice husk fibers were added as reinforcement in (1%, 1.5%, and 2%), and waste paper (paper pulp and paper ash) was added in (1%, 2%, and 5%) by volume of cementitious material. The geopolymer mortar samples underwent a curing process through exposure to a temperature of 60°C in an oven for 24 hours. The findings indicate that the samples reinforced with 2% rice husk fibers exhibited the most significant improvement in compressive strength, with 59% and 55% increases after 7 and 28 days of curing, respectively. In general, using waste paper and rice husk fibers significantly enhanced the compressive strength of geopolymer mortar.

Effects of enzyme-induced carbonate precipitation technique on multiple heavy metals immobilization and unconfined compressive strength improvement of contaminated sand

Enzyme-induced carbonate precipitation (EICP) has been studied in remediation of heavy metal contaminated water or soil in recent years. This paper aims to investigate the immobilization mechanism of Zn2+, Ni2+, and Cr(VI) in contaminated sand, as well as strength enhancement of sand specimens by using EICP method with crude sword bean urease extracts. A series of liquid batch tests and artificially contaminated sand remediation experiments were conducted to explore the heavy metal immobilization efficacy and mechanisms. Results showed that the urea hydrolysis completion efficiency decreased as the Ca2+ concentration increased and the heavy metal immobilization percentage increased with the concentration of Ca2+ and treatment cycles in contaminated sand. After four treatment cycles with 0.5 mol/L Ca2+ added, the immobilization percentage of Zn2+, Ni2+, and Cr(VI) were 99.99 %, 86.38 %, and 75.18 %, respectively. The microscale analysis results presented that carbonate precipitates and metallic oxide such as CaCO3, ZnCO3, NiCO3, Zn(OH)2, and CrO(OH) were generated in liquid batch tests and sand remediation experiments. The SEM-EDS and FTIR results also showed that organic molecules and CaCO3 may adsorb or complex heavy metal ions. Thus, the immobilization mechanism of EICP method with crude sword bean urease can be considered as biomineralization, as well as adsorption and complexation by organic matter and calcium carbonate. The unconfined compressive strength of EICP-treated contaminated sand specimens demonstrated a positive correlation with the increased generation of carbonate precipitates, being up to 306 kPa after four treatment cycles with shear failure mode. Crude sword bean urease with 0.5 mol/L Ca2+ added is recommended to immobilize multiple heavy metal ions and enhance soil strength.

Enhancing the Durability of Pre-Cracked Concrete: The Crucial Role of Metakaolin and Ground Granulated Blast Furnace Slag

This study conducted a rigorous experiment to assess the strength and durability of pre-cracked concrete modifiedwith metakaolin (MK) and ground granulated blast furnace slag (GBFS). Three categories of hardened concrete werecompared to conventional concrete, focusing on key parameters such as compressive strength, mass loss, openporosity, water penetration, capillary water absorption, and drying shrinkage. The assessments were performed undertwo levels of compression damage and exposure to sulfuric acid (5% concentration). The results demonstrated asignificant long-term improvement in compressive strength by incorporating MK and GBFS, despite a reduction of upto 80% in the presence of sulfuric acid. The F10 formulation exhibited the best performance, highlighting the positiveimpact of additives on concrete durability. Replacing cement with MK and GBFS at a 10% level was identified as theoptimal design for sewer structures due to minimal shrinkage compared to other formulations.

Effect of expanded perlite aggregates and temperature on the strength and dynamic elastic properties of cement mortar

The residential market consumes nearly half of the world’s concrete production, and it is anticipated that 68 % of the global population will reside in urban areas by 2050. Researchers have focused their efforts on exploring alternative options to natural aggregates in concrete and mortar. In line with the principles of circular economy, construction and demolition waste has been repurposed for the manufacture of cement-based materials. Volcanic products, which are abundant but underutilized, have been identified as an alternative to recycled aggregates. They offer several advantages over natural river aggregates, including reduced weight, enhanced thermal and acoustic insulation, improved fire resistance and pozzolanic characteristics. While there has been a significant amount of research on the use of expanded perlite as a supplementary cementitious material, studies involving the use of expanded perlite aggregates (EPA) in cement-based construction materials are relatively limited. This paper seeks to address this knowledge gap by investigating the use of EPA in cement-based mortar at both room and elevated temperatures. The study examines the impact of varying replacement percentages (10 %, 20 % and 30 % - by volume) of natural sand with EPA having a maximum grain size of 4 mm, and the exposure temperature of mortar prisms at the age of 28 days. Specifically, temperatures of 100ºC, 150ºC and 200ºC were selected for analysis. The impact of these parameters on the flexural and compressive strength of mortar, as well as its dynamic elastic properties, was experimentally determined. The findings indicate that, at room temperature, higher replacement percentages of natural sand by EPA result in decreased flexural and compressive strengths, by as much as 50 % and 30.71 %, respectively. However, the dynamic moduli values for replacement percentages up to 20 % are similar to those of the reference mix. Conversely, when subjected to temperatures up to 200ºC, significant improvements were observed in the flexural strength values, e.g. over 20 % for temperatures of 150°C and 200°C, with only marginal improvements in compressive strength, 3 % ÷ 20 % for temperatures of 150°C and 200°C, compared to values obtained at room temperature.

The influence of graphene oxide on the hydration and mechanical properties of cement-based materials with low water-binder ratio

Graphene oxide (GO) has been used as a functional material in cement-based materials. Most of current research suggests that GO effectively enhance the mechanical properties of cement paste with high water-to-binder (w/b) ratios (0.30–0.50). However, due to the high cost of GO, its use in ordinary concrete materials with high w/b ratios is limited. It has shown promising potential for reinforcement in ultra-high performance cement-based materials with low w/b ratios, such as UHPC. Nevertheless, existing studies have paid limited attention to the effects of GO in cement-based materials with low w/b ratio. This study selected cement-based materials with a w/b ratio of 0.17 as a representative example to investigate the changes in the mechanical properties of hardened cement paste after the addition of GO under different curing conditions. Additionally, by combining the results of microstructural analysis of hydration products, the study explored the mechanism by which GO affects the mechanical properties of cement-based materials with low w/b ratios. The research findings indicate that though an appropriate dosage of GO enhances the compressive strength of cement-based materials with low w/b ratios, it significantly reduces their flexural strength. In addition, GO accelerates the dissolution process of Ca2+ in the early stages, enhancing the degree of cement hydration and increasing the thickness of inner hydration products (IP). This action leads to an increase in the calcium-to-silicate (Ca/Si) ratio and a weakening of the microstructure in outer hydration products (OP). Resultantly, these changes lead to the refinement of small pores and the coarsening of large pores within the hardened cement-based material, collectively manifesting as an improvement in compressive strength and a reduction in flexural strength of the cement paste.