Use of Natural Zeolite and Glass Powder Mixture as Partial Replacement of Portland Cement: The Effect on Hydration,Properties and Porosity

The study investigates effect of the additive consisting of natural zeolite (clinoptilolite) and soda lime glass powder on the hydration, mechanical properties and porosity of Portland cement concrete. The effect of mineral additive on the technological, physical-mechanical properties and porosity of the mortar was investigated by increasing the content of natural zeolite and glass powder added to the mortar up to 20% by weight of cement in increments of 5% and different particles size of natural zeolite. The mixes with the best technological and mechanical properties were identified and further studies were conducted by replacing 10% and 15% of cement with natural zeolite and soda lime glass with an average grain size of 59.3 μm, 29.0 μm or 3.6 μm of zeolite, and 29.6 μm of glass powder. The hydration process and microstructure of hardened cement paste modified with the aforementioned mineral additives was analysed by microcalorimetry, X-ray diffraction tests and thermogravimetric analysis. The optimal composition of cement paste and particle size distribution of natural zeolite were determined to achieve the higher flexural and compressive strength and lower open porosity. The mixture of mineral additives has the highest effect in terms of flexural and compressive strength and open porosity when added at the proportion 75:15:10 (cement:natural zeolite:soda lime glass) and when zeolite with an average particle size of about 3.6 μm is used     

Properties of Chemically Combusted Calcium Carbide Residue and Its Influence on Cement Properties

Calcium carbide residue (CCR) is a waste by-product from acetylene gas production. The main component of CCR is Ca(OH)₂, which can react with siliceous materials through pozzolanic reactions, resulting in a product similar to those obtained from the cement hydration process. Thus, it is possible to use CCR as a substitute for Portland cement in concrete. In this research, we synthesized CCR and silica fume through a chemical combustion technique to produce a new reactive cementitious powder (RCP). The properties of paste and mortar in fresh and hardened states (setting time, shrinkage, and compressive strength) with 5% cement replacement by RCP were evaluated. The hydration of RCP and OPC (Ordinary Portland Cement) pastes was also examined through SEM (scanning electron microscope). Test results showed that in comparison to control OPC mix, the hydration products for the RCP mix took longer to formulate. The initial and final setting times were prolonged, while the drying shrinkage was significantly reduced. The compressive strength at the age of 45 days for RCP mortar mix was found to be higher than that of OPC mortar and OPC mortar with silica fume mix by 10% and 8%, respectively. Therefore, the synthesized RCP was proved to be a sustainable active cementitious powder for the strength enhanced of building materials, which will result in the diversion of significant quantities of this by-product from landfills.     

Recycling Blast Furnace Ferronickel Slag as a Replacement for Paste in Mortar: Formation of Carboaluminate,Reduction of White Portland Cement,and Increase in Strength

Blast furnace ferronickel slag (BFFS) is generated in the production of ferronickel alloys and is used as cement replacement in concrete or mortar. The effectivity in reducing cement consumption and improving performance are limited. By referring to the paste replacement method, this work used BFFS to replace an equal volume of the white Portland cement paste to obtain greater performance enhancement. BFFS was used with five levels of replacement (0%, 5%, 10%, 15%, 20%) and four water-to-cement ratios (0.40, 0.45, 0.50, 0.55) were designed. Fluidity, mechanical strength, hydration products, and pore structure of every mixture were measured. The results showed that the workability of the mortars decreased due to the reduced volume of water, but the 28-day compressive strength of the mortars increased, and the cement content of the mortars was also reduced by 33 wt %. The X-ray diffraction (XRD) patterns revealed that there existed a carboaluminate phase, and the presence of the ettringite was stabilized, indicating that the accumulating amount of the hydration products of the mortar increased. Furthermore, the BFFS could consume the portlandite and free water to form a higher amount of chemically bound water due to its pozzolanic activity. A high degree of hydration and a large volume of the hydration products refined the porosity of the hardened mortars, which explained the enhancement of the strength of the mortars. Compared to the cement replacement method, the paste replacement method was more effective in preparing eco-friendly mortar or concrete by recycling BFFS for reducing the cement content of the mortar while improving its strength.     

Destructive and Non-Destructive Testing of the Performance of Copper Slag Fiber-Reinforced Concrete

Concrete technology is adopted worldwide in construction due to its effectiveness, performance, and price benefits. Subsequently, it needs to be an eco-friendly, sustainable, and energy-efficient material. This is achieved by replacing or adding energy-efficient concrete materials from industries, such as ground granulated blast furnace slag, steel slag, fly ash, bottom ash, rice husk ash, etc. Likewise, copper slag is a waste material produced as molten slag from the copper industry, which can be used in concrete production. Copper slag can perform roles similar to pozzolans in the hydration process. This paper extends the comparative study of copper slag concrete with polypropylene fiber (PPF) subjected to destructive and non-destructive testing. Under destructive testing, compressive strength of concrete cubes, compressive strength of mortar cubes, splitting tensile tests on cylindrical specimens, and flexural tests on plain cement concrete were conducted and analysed. Ultrasonic pulse velocity and rebound hammer tests were performed on the samples as per IS13311-Part 1-1992 for non-destructive testing. The 100% replacement of copper slag exhibited a very high workability of 105 mm, while the addition of 0.8% PPF decreased the flowability of the concrete. Hence, the workability of concrete decreases as the fiber content increases. The density of the concrete was found to be increased in the range of 5% to 10%. Furthermore, it was found that, for all volume fractions of fiber, there was no reduction in compressive strength of up to 80% of copper slag concrete compared to control concrete. The 40% copper slag concrete was the best mix proportion for increasing compressive strength. However, for cement mortar applications, 80% copper slag is recommended. The findings of non-destructive testing show that, except for 100% copper slag, all mixes were of good quality compared to other mixes. Linear relationships were developed to predict compressive strength from UPV and rebound hammer test values. This relationship shows better prediction among dependent and independent values. It is concluded that copper slag has a pozzolanic composition, and is compatible with PPF, resulting in good mechanical characteristics.     

Investigating the Potential Use of Date Kernel Ash (DKA) as a Partial Cement Replacement in Concrete

The palm and date sector is one of the most important sectors in Saudi Arabia. The total number of fertile palm trees in Saudi Arabia is about 31 million. In the production of pitted dates, date molasses, date paste, and date confectionery, a considerable number of date kernels are usually discarded as waste. This study reports experimental investigations conducted to evaluate the potential of waste date kernel ash (DKA), obtained by the calcination of date pits at 800 °C, as a partial cement replacement in concrete. DKA has low silica oxide and does not qualify as a pozzolanic material. The effect of DKA partially replacing the cement and acting as a filler material in concrete was investigated, and its properties were compared with two pozzolanic materials, fly ash (FA) and natural pozzolan (NP). Twelve concrete mixes in which cement was replaced with different proportions of calcined DKA (5%, 10%, 15%, 20%, and 30%), NP (10%, 20%, and 30%), and FA (10%, 20%, and 30%) were investigated in the experimental program. The properties of DKA, FA, and NP concrete mixes were evaluated in fresh and hardened states, including the heat of hydration, mechanical characteristics, and thermal properties. The results show that replacing cement with 5% date kernel ash increases the compressive strength by 0.42%, 3.2%, and 2.5% at 3, 7, and 28 days, respectively, while the 28-day compressive strength decreases by 2.4%, 5.4%, 16.3%, and 26.69% when the cement is replaced with 10%, 15%, 20%, and 30% DKA, respectively. Date kernel ash concrete mixes with 10%, 20%, and 30% replacement levels demonstrated higher compressive and tensile strengths and lower thermal conductivity, density, and workability when compared to natural pozzolan and fly ash. DKA is a promising partial cement replacement material; nevertheless, additional research is required to assess the durability of DKA in concrete.     

Enhanced Metakaolin Reactivity in Blended Cement with Additional Calcium Hydroxide

This study aims to increase the pozzolanic reactivity of metakaolin (MK) in Portland cement (PC) blends by adding additional calcium hydroxide (CH_add) to the initial mixture. Cement paste samples were prepared with PC, MK and water with a water-to-binder ratio of 0.6. Cement replacement ratios were chosen from 5 to 40 wt.% MK. For higher replacement ratios, i.e., 20, 30 and 40 wt.% MK, CH_add was included in the mixture. CH_add-to-MK ratios of 0.1, 0.25 and 0.5 were investigated. Thermogravimetric analysis (TGA) was carried out to study the pozzolanic reactivity after 1, 7, 28 and 56 days of hydration. A modified mass balance approach was used to normalize thermogravimetric data and to calculate the calcium hydroxide (CH) consumption of samples with CH_add. Results showed that, without CH_add, a replacement ratio of 30 wt.% or higher results in the complete consumption of CH after 28 days at the latest. In these samples, the pozzolanic reaction of MK turned out to be restricted by the amount of CH available from the cement hydration. The increased amount of CH in the samples with CH_add resulted in an enhanced pozzolanic reaction of MK as confirmed by CH consumption measurements from TGA.     

Correlation between the Compressive Strength and Ultrasonic Pulse Velocity of Cement Mortars Blended with Silica Fume: An Analysis of Microstructure and Hydration Kinetics

The effect of the replacement rate of silica fume (SF) on the correlation between the compressive strength and ultrasonic pulse velocity (UPV) of cement mortar was experimentally analyzed. Specimens were fabricated with different replacement rates of SF, the compressive strength and UPV were measured, and isothermal calorimetry and mercury intrusion porosimetry tests were conducted to analyze the effects of replacement on the hydration kinetics and microstructures on these properties. Field emission scanning electron microscopy analysis was performed to observe SF particles and microstructure. The substitution of SF changed the cement mortar’s hydration kinetics and microstructures, resulting in different strengths and UPVs depending on the replacement rate. The compressive strength and UPV for cement mortars blended with SF also showed a different exponential relationship depending on the SF replacement rate.     

Exploring the Influence Factors of Early Hydration of Ultrafine Cement

This work intends to contribute to the understanding of the influence factors of early hydration of ultrafine cement by focusing on the different fineness, different kinds of hardening accelerators, and different curing temperatures. Isothermal calorimetry, thermogravimetry, and X-ray diffraction (XRD) were performed to compare the hydration and chemical evolution of pastes containing accelerators with different fineness and curing temperatures; meanwhile, mechanical properties and water absorption were tested. The results showed that the cement fineness had a significant effect on the early hydration process; the smaller the cement particle size, the higher the early compressive strength. The 24 h compressive strength of ultrafine cement with a particle diameter of 6.8μm could reach 55.94 MPa, which was 118% higher than the reference cement. Water absorption test results indicated that adding 1% Ca(HCOO)₂ to ultrafine cement can effectively reduce the water absorption, and it was only 1.93% at 28 d, which was 46% lower than the reference cement. An increase in curing temperature accelerated the activation of ultrafine cement in terms of the strength development rate, and the content of Ca(OH)₂ in the ultrafine cement paste could reach 13.09% after being mixed with water for 24 h, which was 22% higher than that of the reference cement.     

The Effect of Fine-Ground Glass on the Hydration Process and Properties of Alumina-Cement-Based Composites

This paper discusses studies regarding the impact of fine-ground glass additives on the hydration and properties of alumina cement pastes and mortars. Fine-ground glass was added to pastes and mortars instead of high-alumina cement and calcium aluminate cement in quantities of 5% and 10%. The findings are inconclusive as to the impact of glass on the properties of tested alumina cement types. The effect produced via the addition of glass instead of cement depends on the type of alumina cement used. Adding fine-ground glass to high-alumina cement enhances the paste’s density while improving paste and mortar strength. Using the same additive for calcium aluminate cement reduces its density and strength. The addition of glass to high-alumina cement adversely affects its strength at higher temperatures.     

Research on the Working Performance and the Corresponding Mechanical Strength of Polyaluminum Sulfate Early Strength Alkali-Free Liquid Accelerator Matrix Cement

Liquid accelerating agents have the advantages of simple operation and fast construction, and have become indispensable admixtures in shotcrete. However, most liquid accelerating agents in the market at present contain alkali or fluorine, which adversely affect concrete and seriously threaten the physical and mental health of workers. Therefore, in view of the above deficiencies, it is necessary to develop a new type of alkali-free fluorine-free liquid accelerating agent. In this paper, the polyaluminum sulfate early strength alkali-free liquid accelerator is prepared using polymeric aluminum sulfate, diethanolamine, magnesium sulfate heptahydrate and nano-silica. The influence of this agent on the setting time of fresh cement paste and compressive strength of the corresponding cement mortar is determined. Thermogravimetric analysis curves, X-ray diffraction and scanning electron microscopy images are obtained to investigate the mechanism. Findings show that the initial setting time and the final setting time of cement paste are 2 min 30 s and 7 min 25 s. The compressive strengths of cement mortar cured for 1 d, 28 d and 90 d are 2.4 MPa, 52.2 MPa and 54.3 MPa respectively. Additionally, the corresponding flexural strengths are 3.4 MPa, 9.8 MPa, 11.8 MPa. When the mass rate of accelerator is 7%, the mechanical strengths of cement mortar are the highest. The additions of fly ash and blast furnace slag can affect the mechanical of cement mortar mixed with accelerator. When the mass ratio of the fly ash and blast furnace slag is 15%, the mechanical strengths of cement mortar reach the highest. Moreover, the hydration heat release rate of cement is increased by the accelerator and the corresponding time of hydration heat peak is decreased by the accelerator. The accelerator can decrease the amount of needle-like hydration products and improve the compactness. The mechanical strengths are improved by consuming a large amount of Ca(OH)₂ and forming more compact hydration products. It is recommended that the optimum dosage range of the polyaluminum sulfate early strength alkali-free liquid accelerator is 7%.     

Study on the Influence of Nanosilica Sol on the Hydration Process of Different Kinds of Cement and Mortar Properties

Compared with nanosilica collected in a gaseous state, nanosilica sol has great economic value and application significance for improving the performance of concrete and mortar. In this study, the influence of nanosilica sol on the hydration process of different kinds of cement is studied by means of hydration heat analysis, X-ray diffraction analysis (XRD) and other methods, and the properties of mortar such as setting time, mechanical properties and porosity are also studied to characterize the influence of nanosilica sol on the macroscopic properties of mortar. The experimental results show that nanosilica sol can accelerate the hydration rate of two kinds of cement and promote the hydration reaction degree of cement, and this promotion effect increases with the increase in nanosilica sol content. At the same time, nanosilica sol can significantly shorten the setting time of the two kinds of cement, and it is more obvious with the increase in content. Excessive content of nanosilica sol will adversely affect the permeability resistance of mortar. It may be caused by the weak interval formed by nanosilica particle clusters in the mortar matrix, which can be supported by the mortar pore structure distribution test. At the same time, the influence of nanosilica sol on the hydration of the two kinds of cement is different, and the compressive strength of HBSAC cement mortar increases first and then decreases after adding nanosilica sol; However, the compressive strength of P·O 42.5 cement mortar increases gradually after adding nanometer silica sol. This shows that nanosilica sol does not effectively promote the hydration of β-C2S in high belite sulfoaluminate cement (HBSAC) mortar. Based on the above experimental results, it can be concluded that when the content of nanosilica sol is about 1%, it has the best promotion effect on the hydration of the two kinds of cement and the performance of mortar.     

Effect of Limestone and Quartz Fillers in UHPC with Calcined Clay

Ultra-high-performance concrete (UHPC) is a material developed to maximize the engineering characteristics of hydraulic concrete, in terms of durability and mechanical properties, but the adoption of this technology in practice has not turned out as desired, mainly due to the high amounts of cement and silica fume required for its production, and for its consequences on both economic and ecological costs. As an option to improve the impact of UHPC, both on costs and on sustainability, this work evaluates four UHPC series with metakaolin additions of 5%, 10%, 15% and 20%, and the substitution of 37.5% of the Portland cement volume by limestone or quartz filler. The compressive strength, the bulk electrical resistivity and a set of tests for microstructural characterization (TGA, XRD and quantitative EDS) were utilized to better understand the role of calcite on the hydration and pozzolanic reactions in ternary Portland cement-metakaolin-limestone filler. Results indicate that the reaction of calcite is scarce and should be considered as a mere filler, as no increase in AFm phases were found. Nevertheless, the ternary mixture with 15% of metakaolin in addition to cement, and with 37.5% of the Portland cement volume substituted by limestone filler, was the one that presented the best performance in terms of compressive strength and bulk electrical resistivity. The results of the microstructural characterization indicate that the high kaolin content in the metakaolin originated the most significant hydration and pozzolanic reactions development between the ages of 7 and 28 days, as between 28 and 91 the reaction remained dormant. In general, the whole set of results included in this work indicate that limestone filler doesn’t act as a better filler than other kind of powders when used in ternary Portland cement-metakaolin- filler systems.     

Contribution to Understanding of Synergy between Red Mud and Common Supplementary Cementitious Materials

Recently, much attention has been paid to the reuse of bauxite residues from alumina production, also known as red mud, in the cement industry. Red mud bears the potential to improve concrete properties due to its favourable chemical composition and particle size. In this work, the synergy between locally available red mud and common supplementary cementitious materials such as fly ash, slag, calcined clay and limestone in cement mixes is investigated. All materials used were sourced from the immediate vicinity of the cement plant. The study of synergy involved the evaluation of the individual chemical reactivity of each material using the R3 test by isothermal calorimetry as well as their joint contribution to the heat of hydration and the composition of the reaction products of the paste and the compressive strength of the mortar. The results show how, by understanding the synergy between the materials, a higher level of cement substitutions can be achieved without compromising the mechanical properties of the mortar.     

Prediction of Ultrasonic Pulse Velocity for Cement,Mortar, and Concrete through a Multiscale Homogenization Approach

Ultrasonic testing (UT) is an important method for concrete, and ultrasonic pulse velocity is commonly used to evaluate the quality of concrete materials in existing studies. The ultrasonic pulse velocity of concrete materials is affected by many factors; therefore, it is necessary to establish a quantitative prediction model for the ultrasonic pulse velocity of concrete materials. Based on the multiscale homogenization method, concrete material is divided into different scales of homogenized materials, namely cement paste, mortar, and concrete. Then, a multiscale ultrasonic pulse velocity model is established through a combination of elasticity formulation and the hydration model. At the three scales of cement paste, mortar, and concrete, the elastic parameters and ultrasonic pulse velocity were predicted with the water-to-cement ratio of 0.35, 0.5, and 0.65, respectively. The ultrasonic pulse velocity of concrete with different water-to-cement ratios and different ages were measured in the test and predicted by the model. The results show that the predicted value of ultrasonic pulse velocity is within the error range of ±1.5% of the measured ultrasonic pulse velocity, suggesting that the established prediction model of ultrasonic pulse velocity can reliably predict the velocity change in concrete materials.     

Effect of Mechanically Treated Recycled Aggregates on the Long Term Mechanical Properties and Durability of Concrete

The objective of this research was to study the effect of an optimal mechanical treatment method to reduce the mortar adhered on recycled aggregates (RCA) on the long-term mechanical properties and durability of concretes containing RCA at different replacement levels. It was found that concretes incorporating treated RCA exhibited sharper and more significant increase on 90- and 365-day compressive strengths than any other investigated mixture. The same mixtures also benefitted from a ‘shrinkage-controlling’ effect, where strains and mass losses were reduced by almost 15% and 10%, respectively, compared to the reference concrete. While sulfate resistance and carbonation resistance are predominantly defined by the hydration products available within the cement paste and not to a large extent by the aggregate type and quality, the incorporation of either treated or untreated RCA in concrete did not appear to expose RACs to significant durability threats.     

Study on Carbonation Resistance of Polymer-Modified Sulphoaluminate Cement-Based Materials

The use of tricyclic copolymer latex (AMPS) can effectively improve the carbonation resistance of sulphoaluminate cement. This paper investigated polymer AMPS and polycarboxylic acid to modify sulphoaluminate cement materials by exploring the carbonation level of sulphoaluminate cement paste and mortar and the strength before and after carbonation. Then, the optimal dosage of polymer and polycarboxylic acid was obtained so that the carbonation resistance of sulphoaluminate cement reached the best state. The compressive strength was significantly improved by adding AMPS for sulphoaluminate cement paste and mortar. After carbonation, the strength decreased and combined with the carbonation level; it was concluded that the carbonation resistance of sulphoaluminate cement materials was the best when the optimal dosage of AMPS and polycarboxylic acid was 5% and 1.8%, respectively. Due to the addition of AMPS, the hydrated calcium aluminosilicate (C-A-S-H) and hydrated calcium silicate (C-S-H) gels, generated by the hydration of sulphoaluminate cement and the surface of unreacted cement particles, are wrapped by AMPS particles. The water is discharged through cement hydration. The polymer particles on the surface of the hydration product merge into a continuous film, which binds the cement hydration product together to form an overall network structure, penetrating the entire cement hydration phase and forming a polymer cement mortar with excellent structural sealing performance. To prevent the entry of CO₂ and achieve the effect of anti-carbonation, adding polycarboxylic acid mainly improves the sample’s internal density to achieve the anti-carbonation purpose.     

Mechanical Strength and Hydration Characteristics of Cement Mixture with Highly Concentrated Hydrogen Nanobubble Water

In this study, highly concentrated hydrogen nanobubble water was utilized as the blending water for cement mortar to improve its compressive and flexural strengths. Highly concentrated nanobubbles can be obtained through osmosis. This concentration was maintained by sustaining the osmotic time. The mortar specimens were cured for 28 days, in which the nanobubble concentration was increased. This improved their flexural strength by 2.25–13.48% and compressive strength by 6.41–11.22%, as compared to those afforded by plain water. The nanobubbles were densified at high concentrations, which caused a decrease in their diameter. This increased the probability of collisions with the cement particles and accelerated the hydration and pozzolanic reactions, which facilitated an increase in the strength of cement. Thermogravimetric analysis and scanning electron microscopy were used to confirm the development of calcium silicate hydrate (C-S-H) and hydration products with an increase in the nanobubble concentration. Quantitative analysis of the hydration products and the degree of hydration were calculated by mineralogical analysis.     

Properties of Foamed Mortar Prepared with Granulated Blast-Furnace Slag

Foamed mortar with a density of 1300 kg/m³ was prepared. In the initial laboratory trials, water-to-cement (w/c) ratios ranging from 0.54 to 0.64 were tested to determine the optimal value for foamed mortar corresponding to the highest compressive strength without compromising its fresh state properties. With the obtained optimal w/c ratio of 0.56, two types of foamed mortar were prepared, namely cement-foamed mortar (CFM) and slag-foamed mortar (SFM, 50% cement was replaced by slag weight). Four different curing conditions were adopted for both types of foamed mortar to assess their compressive strength, ultrasonic pulse velocity (UPV) and thermal insulation performance. The test results indicated that utilizing 50% of slag as cement replacement in the production of foamed mortar improved the compressive strength, UPV and thermal insulation properties. Additionally, the initial water curing of seven days gained higher compressive strength and increased UPV values as compared to the air cured and natural weather curing samples. However, this positive effect was more pronounced in the case of compressive strength than in the UPV and thermal conductivity of foamed mortar.     

Hardening and Fresh State Behaviour of Ternary Cement for Marine Environments: Modification through Nanoadditives

The use of nanomaterials to enhance the physical and mechanical properties and durability of cement materials in their hardened state has been studied for a long time in many investigations. In comparison, fewer studies focus on nanomaterials’ influence on the fresh state when the cement reaction starts. In addition, if we consider ternary blended cement (as those used for applications in marine environments), this has been rarely studied. Severe stresses in the marine environment require high durability, which is achieved by using pozzolanic additions, to the detriment of a rapid achievement of the properties. The addition of nanomaterials could contribute to increasing the durability and also accelerating the setting of the concrete. In this work, we performed a systematic and comparative study on the influence of adding graphene oxide (GO), nanosilica (NS), and microfibrillated cellulose (MFC) during the setting mechanisms of cement (CEM V/A suitable for concrete subjected to external attacks in marine environments) blended with fly ash and slag. Cement hardening was examined through setting time and rheology within mini-slump tests. The effect of nanoadditives on the cement hydration was analysed by heat flow calorimetry to evaluate the acceleration potential. Exploring the three nanoadditives on the same formulation, we could establish that the retention of mixing water significantly decreased workability for MFC. In contrast, NS increases the hydration of cement particles, acting as nucleation nodes and promoting supplementary cement hydrates (pozzolanic reactions) and accelerating setting time. Finally, GO showed a reduction in workability. We also investigated the dosage effects on mechanical behaviour at an early age and discovered an improvement even at low GO (0.006%) and NS (3%) dosages. We have also analysed the dosage effects on mechanical behaviour at an early age.     

Bio-Based Admixture (Black Tea Extraction) for Better Performance of Metakaolin Blended Cement Mortars

With high pozzolanic reactivity, metakaolin (MK) is a popular supplementary cementitious material (SCM), which can be used to partially replace Portland cement in concretes. Due to its small particle size, however, MK can agglomerate, resulting in a nonuniform matrix and underperformance of the produced concrete. To address this issue, this paper exploits a low-cost, bio-based admixture—black tea extract (BTE)—to replace the traditional petroleum-based chemical admixture to enhance the dispersion and workability of MK blended cement mortars. Major biomolecules in the BTE such as caffeine, catechin, theanine, and theaflavin are rich in polyphenol, hydroxyl, and carboxylic acid groups, which can interact with cement particles and have profound effects on the hydration process and microstructure of the hydration products. Experimental studies showed that BTE does improve the workability of the MK blended cement mortar. More importantly, the BTE introduces significant change on the microstructure of the hardened pastes. Both the pores with size less than 50 nm and the total porosity of the hardened paste were significantly reduced, leading to a significant improvement in the micro- and macro-mechanical properties of the hardened paste. Experimental results suggest that up to 35% greater improvement in the compressive strength at 28 days was achieved using the proposed bio-admixture. Economic and environmental advantages of using the BTE as a renewable admixture were also illustrated through analyzing the cost–benefit, embodied carbon, and eco-efficiency of the MK blended mortars.