Strength Of Mortar Research Articles

Optimal Limestone Content on Hydration Properties of Ordinary Portland Cement with 5% Ground Granulated Blast-Furnace Slag.

In this study, the effect of limestone content on the mechanical performance and the heat of hydration of ordinary Portland cement (OPC) was investigated. Changes in the phase assemblage were analyzed through XRD and thermodynamic modeling. The purpose of the study was to identify the optimal limestone content in OPC. As a result of the experiment, all samples were found to have equal fluidity. Increasing the limestone content accelerated the hydration of the cement before approximately 13 h and shortened the setting time due to the acceleration of the initial hydration reaction. The compressive strength of the cement mortar showed a dilution effect, with lower compressive strength compared to the reference sample at an early age, but it gradually recovered at a later age. This is because, as shown in the XRD and thermodynamic modeling results, the carboaluminate phases formed due to the chemical effect of limestone contributed to the development of compressive strength. As a result, within the scope of this study, it is believed that maintaining the limestone content in OPC within 10% is optimal to minimize quality degradation.

Low-carbon microwave curing of limestone calcined clay cement (LC3): Performance and mechanism

Limestone calcined clay cement (LC3) incorporates calcined clay and limestone as supplementary cementitious materials that can replace up to 50 % of conventional cement, significantly reducing the carbon emissions associated with cement production. However, challenges remain, including the inefficiencies of traditional curing methods and suboptimal early strength properties. Consequently, this study presents the low-carbon microwave curing approach for LC3 mortar. A comparative analysis of 15 different microwave curing systems was carried out. The results show that the optimum microwave curing efficiency is 300 W of heating power, 5 minutes of heating, 25 minutes of rest, and eight cycles. Three curing methods, including microwave curing, standard curing, and steam curing, were also compared. Microwave curing significantly increased the early strength of LC3 mortar, with 1-day compressive strength 1.78 times greater than standard curing and 1.26 times greater than steam curing. Microscopic studies show that the “thermal effect” of microwaving increases the internal Hc content of LC3, promotes the secondary hydration reaction of Ca(OH)2 within the LC3 material, and reduces the porosity of LC3, achieving reductions of 37.8 % and 8.9 % compared to standard and steam curing, respectively. This helps to improve the efficiency of the curing process. The results of this research will advance the use of low-carbon LC3 in building structures.

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.

Strength and Acid Resistance of Mortar with Different Binders from Palm Oil Fuel Ash, Slag, and Calcium Carbide Residue

This study deals with the use of ground palm oil fuel ash (GPOFA) in combination with ground granulated blast furnace slag (GGBFS) and ground calcium carbide residue (GCR) to produce the binary and ternary binders-based alkali activated mortar. The appropriate content of materials in each binder type was determined as a function of compressive strength. The results revealed that both GPOFA:GGBFS and GPOFA:GCR binders had an optimum blending ratio of 70:30 wt%, while the GPOFA:GGBFS:GCR binder was 55:30:15 wt%. An alkaline catalyst of NaOH was admixed to the best mixture in each binder type to stimulate the mortar's compressive strength. The sulfuric acid (H2SO4) resistance of the mortar in terms of weight change was also examined. The addition of 1M NaOH in both binary and ternary binders could enhance the compressive strength and H2SO4 resistance of the mortar. The highest compressive strength and lowest weight change due to soaking in H2SO4 solution were found in the ternary binder mortar with a 1 M NaOH. The mortar with GCR immersed in H2SO4 solution resulted in an increased weight, which was different from that of the mortar without GCR. The microstructural analysis of the alkali-activated pastes indicated more reaction products than in the case of the pastes without alkali activator. However, a higher concentration of 2 M NaOH resulted in a poor microstructure, which had a negative effect on the compressive strength and H2SO4resistance. Doi: 10.28991/CEJ-2024-010-07-08 Full Text: PDF

Effect of fiber characteristic parameters on the synergistic action and mechanism of basalt fiber asphalt mortar

Basalt fiber has been shown to significantly improve the performance of asphalt mixtures and extend the lifespan of roads. However, more research is needed to investigate the characteristic parameters of basalt fiber when used in asphalt mortar and asphalt mixture. In order to enhance the reinforcing effect of basalt fiber on asphalt mixture and understand how it works, this study examines the properties of asphalt mortar mixed with basalt fiber with different characteristic parameters. Nine types of basalt fibers with varying characteristic parameters were selected for this work, including three lengths (3 mm, 6 mm, 12 mm) and three diameters (7 μm, 16 μm, 25 μm). The properties of asphalt mortar mixed with basalt fiber with different characteristic parameters were tested. High-temperature properties were characterized using the ZSV and MSCR tests; medium-temperature properties were characterized using the LAS test; low-temperature properties were characterized using the BBR and direct tensile tests. In addition, the effects of fiber characteristics on the viscosity, structural integrity and interfacial properties of asphalt mortar were analyzed through the bond strength test, Rigden porosity test and fiber monofilament drawing test. The results demonstrate that basalt fiber can improve high-temperature properties significantly in asphalt mortar while being greatly influenced by its characteristic parameters. Specifically, fibers with a length of 6 mm and a diameter of 7 μm exhibit superior reinforcement effects. Fatigue life results indicate that basalt fiber enhances fatigue resistance in asphalt mortar as well; furthermore, the influence exerted by fiber characteristic parameters aligns consistently with that observed for high-temperature performance. Although the BBR test results indicate that fiber incorporation has minimal impact on its enhancement, the direct tensile test results demonstrate a significant improvement in the toughness of asphalt mortar due to fiber reinforcement. The addition of basalt fiber enhances the bond strength of asphalt mortar. According to Einstein viscosity formula, the viscosity of asphalt mortar decreases with shorter fiber lengths and larger diameters. Incorporating basalt fiber can enhance the proportion and strength of structural asphalt in asphalt mortar. When comparing fibers with equal diameter or length, an increase in either parameter initially improves the strength of structural asphalt but eventually leads to a decline. Results from monofilament fiber drawing tests and theoretical critical embedding length confirm that a 6 mm fiber length is most beneficial for enhancing the performance of asphalt mortar. Basalt fiber exhibits significant potential for improving various properties of asphalt mortar and provides a favorable reference for optimizing the selection of basalt fiber.

Synergistic Effect of Early-Strength Agents on the Mechanical Strength of Alkali-Free Liquid Accelerator Mortar

Synergistic Effect of Early-Strength Agents on the Mechanical Strength of Alkali-Free Liquid Accelerator Mortar

The possibility of partial substitution of cement in cement mortars with the use of spent fluid catalytic cracking catalyst from polish oil refinery: mechanical performances and impact of the addition of superplasticizer

This paper presents the results of a study of the effect of spent catalytic cracking catalyst derived from polish oil refinery used as a partial replacement of cement (in the amount of 20, 40, 60 and 80% of cement mass) in the binder on the mechanical strength of cement mortars, prepared without and with superplasticizer. It was shown that the replacement of 20% of cement, by mass, with spent catalyst increased the compressive strength of mortars without and with superplasticizer dosage by 16.7% and 24.4%, respectively, and did not deteriorate the flexural strength of samples prepared with superplasticizer. With the increasing amount of spent catalyst (above 40% by weight of cement), a decrease in the strength of mortars was observed. This indicates that spent catalyst from catalytic cracking might be a promising material as a binder replacement in cementitious composites when used in smaller amounts (less than 40%).

The Multifaceted Comparison of Effects of Immobilisation of Waste Imperial Smelting Furnace (ISF) Slag in Calcium Sulfoaluminates (CSA) and a Geopolymer Binder.

Using waste materials as replacements for sand in building materials helps reduce waste and improve the properties and sustainability of the construction materials. Authors proved the possibility of using imperial smelting furnace (ISF) slag granules as a 100% substitute for natural sand in self-compacting (SCC) cement-based mortars of calcium sulfoaluminates (CSA). The study proved that ISF slag's radioactive properties meet this area's requirements. CSA cement eliminates the noted problem in the case of concrete with Portland cement, which is the extended setting of the cement binder. The research findings indicate that using slag to replace sand up to 100% in mortars without grains smaller than 0.125 mm allows high flowability, compaction, low porosity and mechanical parameters. The compressive strength of the CSA cement mortars was about 110 MPa, and more than 140 MPa for geopolymer mortar. Unfortunately, the alkaline pH of a geopolymer causes high leachability of barium and sodium. Thus, the CSA cement is in a more favourable binder to achieve high strength, is environmentally friendly, and is a self-compacting mortar or concrete.

Variations in the physical and mechanical behavior of basalt fiber reinforced NHL mortars exposed to different curing conditions

This paper investigates experimentally the short-term behavior of natural hydraulic lime (NHL) mortars reinforced with ballast fiber for use as structural repair mortars in historic and contemporary buildings. The physical and mechanical properties of mortar mixes reinforced with 0.143–0.215 mm equivalent thick and 12 mm long fibers in volumetric percentages of 1 %, as well as of unreinforced mortars, produced with different compaction methods and cured under different environmental conditions, have been evaluated. A cost-effectiveness analysis has also been carried out to determine the economic impact of these factors in their practical application. It is found that basalt fiber reinforcement provides lower water absorption coefficients and significantly improves the shore hardness, compressive strength, and post-critical flexural behavior of NHL mortars at early ages. Furthermore, it is observed that the compaction procedure can improve the packing density of the mortars providing higher densities, lower water absorption coefficients and higher mechanical strength values. Finally, it is verified that the curing parameters affect unevenly the basalt fiber reinforced NHL mortars and unreinforced NHL mortars, with greater deterioration being observed in the former when sufficient moisture is not ensured. Decreases in hardness, flexural and compressive strength, as well as increases in the water absorption coefficient are important. Consequently, the economic profitability of basalt fiber reinforcement depends on ensuring optimal moisture conditions during curing, especially when the mixes have already lost excess water after the first 2–3 days. The study provides quantitative and qualitative data to determine the appropriate curing parameters for basalt fiber reinforced NHL mortars that are viable in practice for their industrial performance.

Enhancement of the tensile properties of cement mortar composites with nanoadditives produced by chemical vapor deposition

While graphene effectively enhances the performance of cement-based materials, its current production methods are characterized by environmental unfriendliness and high energy consumption. To investigate a large-scale and eco-friendly graphene preparation approach, Carbon Nano Sheets (CNS) were synthesized via chemical vapor deposition (CVD). The influence of CNS content on the tensile strength of cement mortar was assessed through the Brazilian splitting test. Concurrently, the mechanism of CNS was examined using acoustic emission monitoring and scanning electron microscope. The experimental results revealed that methane can be effectively decomposed into high-quality CNS at 1080 ℃ when using fly ash, silica fume, and sand as substrates. The Brazilian splitting test revealed that CNS effectively enhances the tensile strength of cement mortar, with improvements ranging from 9 % to 58.7 %. Acoustic emission results indicated that the inclusion of CNS reduces the occurrence of micro-fractures during the failure of cement mortar specimens. Furthermore, nano-mechanical testing and microstructural characterization demonstrate that CNS can reduce micro-cracks and pores in the interface transition zone and hydration products, playing a role in dense hydration products. Furthermore, it can decrease the width of the interface transition zone and enhance the micro-mechanical properties of cement pastes. This study offers a novel approach for the eco-friendly production of cement nano additives.

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.

Enhancing the strength, microstructural integrity, and shrinkage performance of cement-based mortar using pulverised carbon and glass FRP composite waste

Adopting sustainable materials is a pressing concern for the construction industry to achieve net-zero carbon emissions, driving ongoing research to address environmental challenges. With a particular focus on the fibre-reinforced polymer (FRP) byproducts and wastes generated by various industries, this paper investigates the viability of pulverising and repurposing waste materials from electrical cross-arms and aerospace composite parts in cementitious materials as a partial substitute for cement. Micro fibres with crushed resin particles (passing through a 600 μm sieve) were incorporated into the mortar, up to 10 % relative to the mass of cement. A series of tests was conducted to evaluate the effects of varying FRP recyclates on the mechanical, durability and electrical performance of mortars. The results indicated that at the 28-day curing age, the inclusion of FRP recyclates led to a 19 % reduction in water absorption and significant enhancement in the compressive (up to 67 %) and flexural strength (up to 43 %). The optimal restraint of drying shrinkage was observed when replacing 5 % by weight of cement with FRP recyclates from electrical cross-arms. The inclusion of FRP recyclates from aerospace offcuts resulted in a 25 % reduction in electrical resistivity, indicating a potential for reusing aerospace recyclates for electrically conductive cementitious composites (ECCCs). Further analyses were conducted to assess the effects of FRP recyclate addition on the microstructural properties of the cementitious matrix. This research offers a promising pathway to repurpose composite wastes from utility and aerospace industries as valuable additions to construction materials.

Investigating correlations between microstructural characteristics and mechanical properties of coral sand mortar with different silica fume contents

The use of coral sand in concrete and mortar for ocean engineering has led to significant reductions in construction costs and improved construction efficiency. However, this approach poses challenges such as low strength, high brittleness, and high porosity. To address these challenges, this study incorporated silica fume to enhance the mechanical properties of the mortar and investigated the effects of different silica fume contents on the hydration process, pore structure, and strength of coral sand mortar. Additionally, this study introduced a novel iterative approach combining low-field nuclear magnetic resonance and scanning electron microscopy image analysis to determine transverse relaxivity (ρ2). During the early hydration process, the intensity spectrum of coral mortar exhibited three peaks at 298, 1841, and 299 au, corresponding to transverse relaxation times (T2) of 0.64, 6.83, and 83.10 ms, respectively. Over a 6 h hydration period, the spectrum of the specimen prepared with white cement exhibited an additional peak that gradually merged with the main peak. As the curing period extended from 7 to 28 days, the porosity of coral sand mortar decreased by 3.77–4.55 %, while the strength increased by 7.43–14.35 MPa across silica fume contents ranging from 6 % to 24 %. With increasing silica fume content, the calcium–silicon ratio of the samples gradually decreased, promoting the formation of more floccus C–S–H gels. Consequently, the sample porosity first decreased slightly. After 28 days of curing, the coral sand mortar containing 12 % silica fume exhibited the highest strength owing to the increased amount of floccus C–S–H gels. These gels gradually filled the pores between the fibrous C–S–H gels, forming a compact spatial reticular structure. This structure mitigated the adverse impact of high porosity on mortar strength.

Investigation of hydration kinetics, microstructure and mechanical properties of multiwalled carbon nano tubes (MWCNT) based future emerging ecological economic ultra high-performance concrete (E3 UHPC)

In recent years, attest to the growing prominence of sustainable buildings and the integration of advanced materials like nanomaterials in construction practices. Among these advancements, the strategic application of multi-walled carbon nanotubes (MWCNTs) alongside dispersion techniques such as surfactant agents, functionalization, and ultrasonication is pioneering. These techniques are instrumental in elevating the mechanical strength and durability of cement paste and mortar. The approach involves gradually introducing nanomaterials to create a cementitious composite, allowing for a systematic analysis of their effects on each type and determination of the optimal dosage. The influence of MWCNT with various dosage combination on rheological, mechanical and microstructural properties of ultra high-performance concrete (UHPC) were investigated in this study. According to test results, the UHPC MWCNT 0.06 % mix can be considered as the best UHPC mix due to discussed specifications. The outcomes of the research demonstrate that the optimal dosage of MWCNT enhances various mechanical properties of UHPC significantly. At 28 days of curing, the addition of MWCNT resulted in improvements of 32.97 % in compressive strength, 49.72 % in split tensile strength, 40.41 % in flexural strength, and 9.09 % in dynamic modulus. The observed enhancements in mechanical properties can be attributed to the pore-filling, bridging, and densification effects of MWCNT within the calcium-silicate-hydrate structure of UHPC. Moreover, the incorporation of MWCNT facilitates the development of a more sustainable and environmentally friendly UHPC, thereby supporting sustainable construction practices.

Analysis of the Influence and Mechanism of Diatomaceous Earth Internal Curing on the Autogenous Shrinkage and Early Crack Resistance of Cement-Based Materials with Low Water–Binder Ratio

Diatomaceous earth (DE), a kind of natural and environmentally friendly concrete admixture with good pozzolanic and water absorption properties, is a potential high-quality internal curing material. DE internal curing agent was prepared by calcining excavated diatomaceous earth and applied in cement-based materials with a low water–binder ratio of 0.35 to study its effects on the autogenous shrinkage and early crack resistance of the materials. The results showed that DE was a kind of microfine powder with a unique and orderly microporous structure, and its main component was SiO2, which had good water-holding and -releasing properties. Pre-absorbed DE could effectively improve the internal relative humidity of cement-based materials with a low water–binder ratio. Under the standard of not reducing the 28 d compressive strength of mortar, compared to the benchmark group without DE, when 1% of cement is replaced by DE of equal mass, DE could effectively reduce the 7 d autogenous shrinkage of mortar by about 36.7% and delay the initial cracking time of mortar under the restraint condition of the ring by 10.7%. Therefore, it is an internal curing material with excellent performance.

The Applicat ion of Super Absorbent Polymer in Self-Healing Morta r: The Effect on Mechanical Properties

Super Absorbent Polymer (SAP) were used in various application, including in mortar production. The ability of SAP to absorb a high amount of water made this material become a promising water reservoir in the mortar that can later mitigate micro-cracks in concrete. Besides SAP, a nutrient must be embedded into self-healing mortar to support metabolism in bacteria-based self-healing mortar. However, adding SAP and nutrient was reported to decrease the mechanical properties of the resulting self-healing mortar. Thus, in this research, the modification in the mix design of mortar containing SAP and nutrient were observed. The water to cement ratio was decreased up to 0.3. The amount of SAP and entrained water added is based on its swelling capacity. The swelling capacity of SAP, the workability of fresh mortar, and the compressive strength of mortar were examined. The results show that the swelling capacity of SAP was affected by the pH and the presence of calcium ions in the solution. The higher the pH and the calcium ion in the solution, the lower SAP’s swelling capacity. Applying the modified mortar mix design containing SAP and nutrient proofed to mitigate the reduction in workability and compressive strength of the resulting self-healing mortar.

Effect of Wet Grinding Concrete Slurry Waste on Hydration and Hardening Properties of Cement: Micro-Nano-Scale Modification.

The concrete slurry waste (CSW) produced by concrete mixing plants is a type of hazardous waste that is difficult to handle. To better recycle the CSW separated from the aggregates, this study uses a variety of wet-grinding processes to refine the solid in it, replaces some of the cement with the solid particles in wet grinding concrete slurry waste (WCSW), and investigates the properties of WCSW and its effect on the hydration and hardening properties of cement. The results show that a suitable wet-grinding process can ensure that the particle size in WCSW is less than 10 μm, the particle morphology is more flat, and the degree of hydration is higher. The WCSW particles can promote early cement hydration; after adding WCSW, the heat release peak of cement hydration appears earlier and more early hydration products are produced, and with the increase in the substitution amount, the promoting effect on early cement hydration will be more significant. The WCSW particles have a great effect on improving the strength of mortar, especially in the early stage. At 1 d, when the substitution amount is 7.5 wt.%, the compressive and flexural strength is increased by 43.67% and 45.04%; this is related to the filling of matrix pores and the improvement of the interface transition zone by micro- and nanoparticles. After the wet grinding of CSW, fine WCSW particles are obtained, which can improve the performance of cement-based materials by replacing cement.

Experimental Study on the Effect of Environmental Water on the Mechanical Properties and Deterioration Process of Underground Engineering Masonry Mortar

Urban underground engineering is generally buried at a shallow depth and suffers long-term environmental water effects such as rainfall, rivers, underground pipeline leakage, and groundwater. The mechanical properties of the structures are affected by constant deterioration, which seriously hinders the safe, healthy, and sustainable development of the city. On the basis of on-site investigation of civil defense engineering, this article simulates the water environment conditions of mortar in underground engineering in the laboratory and conducts manual sample preparation in the laboratory. Then, water, H2CO3, NaCl, and Na2CO3 solution or wet–dry cycles are used to corrode the sample, respectively. A uniaxial compression test, Brazilian splitting test, analyses of the acoustic emission signals and electromagnetic signals, and magnetic imaging testing are performed, respectively. The results show that an increase in the action time of environmental water leads to a gradual increase in the uniaxial compressive strength, tensile strength, and elastic modulus of cement mortar, but it will decrease over a long period of time. Different environmental water components can also lead to a different performance of soaked mortar. The uniaxial compressive strength R, tensile strength σt, and elastic modulus E of mortar samples exhibit values in different solutions in the order of H2CO3 solution < NaCl solution < Na2CO3 solution < water. A moderate solution soak time can enhance the mechanical properties of the mortar, but this effect decreases at long time scales. The effect of wet–dry cycles on the mechanical properties and degradation process of mortar is significant. With the increase in wet–dry cycles, the porosity of mortar continuously increases. The cumulative ringing count, energy, amplitude, and impact number of acoustic emission signals always increase when the samples are loaded to failure. The uniaxial compressive strength, tensile strength, and elastic modulus first increase and then decrease. The experimental results lay the foundation for further investigating the performance changes in mortar under complex water environments in underground engineering.

Enhancing alkali resistance of recycled GFRP fibers and mechanical performances of cement mortars with microbial induced carbonate precipitation

Applying the recycled glass fiber reinforced plastic (rGFRP) fiber to reinforce cement-based materials is a promising way to reuse this massively waste material. However, rGFRP fiber is prone to be corroded in the alkali environment of cement. To solve this problem, the rGFRP fiber was treated with microbial induced CaCO3 precipitation (MICP) technique. The effects of MICP treatment on the rGFRP fiber and the reinforced mortar were investigated. It was revealed that the alkali resistance of the rGFRP fiber was significantly modified by CaCO3 deposition, which was increased with the concentration of mineralizing solution and treating time. The tensile strength and aging resistance of the rGFRP fiber reinforced mortar were all improved by MICP treatment, since fiber-cement friction, fiber-cement compatibility, microstructural compactness and cement hydration degree were enhanced by the properly precipitated CaCO3 crystals on fiber surface. However, excessive MICP treating process was detrimental for effective CaCO3 precipitation. The rGFRP fiber treated in the mineralizing solution of 1.0 mol/L for 3 times with 24 h/time (1−24−3) had the most promising modification effect on the rGFRP fiber and the reinforced mortar in this study. The 1–24–3 rGFRP fiber had similar alkali resistance to the alkali resistance glass fiber, which increased the tensile strength of mortar by 34.1 % and improved the bending strength of mortar by 10.8 % after accelerated aging. The MICP technique was used on modifying rGFRP fiber and the reinforced mortar for the first time, which would benefit the durability of rGFRP fiber and its wider application in cement-based materials, while the long-term performance of rGFRP fiber reinforced mortar should be studied in the future.

Fresh and hardened properties for a wide range of geopolymer binders – An optimization process

The objective of this study was to identify the optimal geopolymer binder compositions produced from local industrial by-products and compare them with commercially available materials. The first part investigated the optimal binder composition by studying 27 mixtures. In this part of the research, three series of binders were created: the first series of 18 mixtures was Na-based fly ash-slag, the second series consisted of 8 mixtures of K-based fly ash-slag, and the third series were a mixture of metakaolin-slag based geopolymer. The compressive strengths of the mixtures at the age of seven days ranged from 2.18 to 96.23 MPa. The strength development is clearly defined by the components and proportions of the blends. Geopolymers reach about 80% of their 28-day strength in seven days. The 25% water content was optimal for slag-fly ash geopolymers. The strength of the material increased from 68.08 to 96.23 MPa when the Blaine surface area of the slag increased from 3500 to 4500 cm2/g. The optimal proportions of the alkali solution were the intermediate ratios: SiO2/Na2O = 2.0 and SiO2/K2O = 1.5. In the case where Visonta fly ash is prepared for blending, the fly ash content can be maximized by 30%–50% in addition to the blast-furnace slag. In the second part of the research, mortars were prepared from the selected binders: 4 mixtures were prepared with two different binders. In one of these mortars, the solid part of the binder consisted of local raw materials originating from Hungary. This mixture was prepared with 43 m% fine aggregates. The optimal composition of the tested 27 binders tested was selected as the geopolymer matrix for the production of three further mortar mixtures. In these geopolymer mortars, 55, 65, and 75 m% of aggregate applied. The flowtable values of fresh mortars decreased when the proportion of sand increased. The lower the additive content was, the higher the strength of the geopolymer mortar. The 28-day compressive strengths of filtered fly ash-slag mortar sample with 55%, 65%, and 75% of fine aggregate (F–S-a55, F–S-a65, and F–S-a75) made with the selected optimised filtered fly ash-slag geopolymer binder of group A-I.3 (F–S-A-I.3) varied between 11.39 and 40.15 MPa, whereas the Visont fly ash-slag mortar sample with 43% of fine aggregate (V–S-a43) has been 25.05 MPa. For 28 days, the density ranged between 1870 and 2204 kg/m3. The V–S-a43 is found to be the lowest-density blend. The chloride migration test revealed that geopolymer mortars with higher slag content have higher resistance to Cl− ions.