Demand For Concrete Research Articles

Mitigating Drying Shrinkage in High-Strength Concrete Using Glass and Polypropylene Fibers with Diatomaceous Earth as Cement Substitute

Abstract In recent decades, the demand for high-strength concrete has surged due to its enhanced workability and durability. However, the high cement content in such concrete impacts its hardening properties, particularly causing drying shrinkage strain, which affects structural performance and durability. Adding fibers like glass and polypropylene can mitigate this drying shrinkage by improving tensile and flexural strength, ductility, and crack control. High cement content also raises environmental concerns, including increased CO2 emissions. Diatomaceous earth, an eco-friendly and cost-effective cement substitute, can address these issues. This study explores the effects of glass and polypropylene fibers on concrete drying shrinkage and the impact of diatomaceous earth. Concrete specimens (100 mm × 100 mm × 400 mm) with 0% and 10% diatomaceous earth and varying fiber contents (0%, 0.2%, 0.4%, 0.8%, 1%) were tested. Drying shrinkage data over 60 days were recorded using dial gauges. Results indicate that both types of fibers effectively reduce drying shrinkage, with glass fibers being more effective. Additionally, the usage of 10% diatomaceous earth also reduces drying shrinkage. A modified B4-Bazant model incorporating coefficients for diatomaceous earth (Kd), fiber type (Kf), and fiber volume (Kvf) was developed. Further research with different fiber proportions is recommended for more accurate modeling.

Research on the Durability of Composite Epoxy Resin Modified Repair Mortars Based on Water-Oil Gradient Phase Change: From Macroscopic to Nanoscopic Scales

With the rapid pace of urbanization, global demand for concrete is increasing, shifting focus from construction to repair and maintenance. Traditional cement-based repair materials generally suffer from brittleness and poor durability, failing to meet the growing demand for durable repair solutions. We developed a water-oil gradient composite epoxy resin (CEP) modified cement-based repair mortar (MCEP) using self-synthesized water-based epoxy resin (WEP) and oil-based epoxy resin (EP). Durability tests showed that CEP-modified cement mortar exhibited improved resistance to solution penetration, shrinkage, acid corrosion, and freeze-thaw cycles, with increased CEP content positively affecting mortar durability. Notably, the addition of CEP not only enhanced the interface bonding strength between MCEP and old concrete but also maintained good bonding stability under moisture erosion. X-CT and SEM microstructural tests revealed that CEP is evenly distributed in the cement paste, forming a cement-polymer interpenetrating network structure, which improves crack resistance and reduces solution penetration in MCEP. Molecular dynamics simulations explored the adsorption of CEP on calcium aluminate hydrate (AFt), a key cement hydration product, and the moisture transport mechanisms in AFt and CEP-modified AFt nanopores. Results indicated that CEP molecules adsorb onto AFt via ionic and hydrogen bonds, demonstrating good stability. During moisture penetration, CEP reduced water transport efficiency in the nanopores. CEP modification improved the crack resistance and durability of cement repair mortars, providing valuable insights into molecular-scale enhancements in water permeability resistance. This study aims to contribute to the design and practical application of water-oil gradient epoxy resins and other polymer-modified cement-based repair materials.

Tactical Activities to Improve the Effectiveness of Concrete Batching Plant Based on Overall Equipment Effectiveness Analysis

The growth of infrastructure projects has led to an increased demand for ready-mix concrete. A company that produces ready-mix concrete using a batching plant encountered difficulties in fulfilling customer orders due to the high rate of machine downtime. Overall equipment effectiveness (OEE) was employed to examine these issues at the tactical activities, where the root causes of losses that occur in the OEE components of availability, performance, and quality were addressed. The OEE analysis was extended to encompass maintenance effectiveness measures, as the anticipated solution to the problem was not the replacement of the machine, but rather an enhancement of its operational efficacy. The effectiveness of maintenance activities was measured using MTTF (mean time to failure), MTTR (mean time to repair), and MTBF (mean time between failure). A review of the OEE components revealed a necessity to reduce losses, as evidenced by the availability and performance rates. Although the performance rate has the lowest value, based on the frequent occurrence of failures to the availability component, the improvement process was carried out to overcome problems in the availability variable. The implementation of scheduled maintenance at the beginning of each month and the implementation of daily checks before and after the machine was used resulted in an increase in the OEE value from 56.62% to 71.15%. The incorporation of maintenance analysis into OEE has been shown to result in increased OEE values, as evidenced by a longer mean time between failures, a reduced time for process adjustments, and a decreased asset repair time.

Investigation of strength, durability, and microstructure properties of concrete with waste marble powder as a partial replacement of cement

Purpose Cement plays a significant part in concrete, and with the increasing demand for concrete, cement output varies day by day, allowing production to carbon dioxide emissions. As well as marble processing creates stone slurry and solid discards. These are often dumped irresponsibly on open land, polluting the soil. This improper disposal of marble waste is a major environmental concern. This study aims to propose a sustainable solution for reusing this waste material as a concrete additive. Design/methodology/approach A total of 135 concrete cubes of size 150 × 150 × 150 mm, 54 concrete cylinders of size 150 mm dia. and 300 mm height and 54 concrete beams of size 150 × 150 × 700 mm were cast. The replacement was 0%, 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 17.5% and 20% by weight of cement with marble dust to create M30 concrete with a water-cement ratio of 0.45. The test was performed to find the compressive strength (CS), flexural strength (FS) and split tensile strength. Also, durability tests like rapid chloride penetration test (RCPT), acid attack, ultrasonic pulse velocity (UPV) and water permeability test were performed. Findings After 7 and 28 days of curing, it was found that replacing 5% of cement with marble powder led to an initial strength improvement of up to 25% for both curing periods. However, further increases in marble dust resulted in an inconsistent decrease in strength for all the mixtures. Also, durability properties like acid attack test, water permeability test and RCPT, showed good performance at the optimum percentage of waste marble powder (WMP) as cement replacement. The microscopic analysis revealed a denser pore structure at lower WMP replacement levels, likely due to the powder filling in gaps. Originality/value This study reveals that by substituting 5% (optimum) of cement with WMP, there was CS improvement up to 8.4% and 17% for both 7 and 28 days of curing. WMP is typically finer than cement particles and fills the voids in the concrete more effectively, resulting best performance at optimum percentage against RCPT, UPV, acid attack and water permeability.

Sulfate activation of wheat straw ash to enhance the properties of high-performance concrete with recycled aggregates and waste tire steel fibers.

A sustainable alternative to conventional concrete involves using recycled aggregates (RA) instead of natural aggregates (NA) and incorporating wheat straw ash (WSA) as a partial replacement for Portland cement. The demand for high-performance concrete (HPC) is rising due to the need for architecturally complex structures and long-span bridges, but HPC's low ductility necessitates reinforcement. Waste tire steel fibers (WTSFs) are gaining popularity for their tensile strength. However, WSA-RA concrete's low early strength is a challenge. Chemical activators like sodium sulfate can enhance early-age strength. This study evaluated the durability and strength of fiber-reinforced concrete with both inactivated and activated WSA. Tests included compressive strength, indirect tensile strength, modulus of rupture (MOR), acid attack resistance, chloride penetration, sorptivity, and water absorption. Activated WSA-RA concrete showed significantly improved early strength. The mixture with 30% RA, 40% WSA, WTSFs, and activator exhibited the highest strength at 90 days. At 60% RA content, activated concrete with 40% WSA and 2.5% WTSFs outperformed the control. Durability was enhanced with a 14-17% reduction in water absorption and sorptivity and a 25.2% decrease in chloride penetration. Acid resistance improved by 26%. X-ray diffraction (XRD) confirmed these findings with elevated hydration product peaks. This study demonstrates that chemical activation of WSA optimizes the engineering properties of WSA-modified HPC with WTSFs and RA, providing a sustainable solution to their challenges.

Long-Term Care in Germany in the Context of the Demographic Transition—An Outlook for the Expenses of Long-Term Care Insurance through 2050

Demographic aging results in a growing number of older people in need of care in many regions all over the world. Germany has witnessed steady population aging for decades, prompting policymakers and other stakeholders to discuss how to fulfill the rapidly growing demand for care workers and finance the rising costs of long-term care. Informed decisions on this matter to ensure the sustainability of the statutory long-term care insurance system require reliable knowledge of the associated future costs. These need to be simulated based on well-designed forecast models that holistically include the complexity of the forecast problem, namely the demographic transition, epidemiological trends, concrete demand for and supply of specific care services, and the respective costs. Care risks heavily depend on demographics, both in absolute terms and according to severity. The number of persons in need of care, disaggregated by severity of disability, in turn, is the main driver of the remuneration that is paid by long-term care insurance. Therefore, detailed forecasts of the population and care rates are important ingredients for forecasts of long-term care insurance expenditures. We present a novel approach based on a stochastic demographic cohort-component approach that includes trends in age- and sex-specific care rates and the demand for specific care services, given changing preferences over the life course. The model is executed for Germany until the year 2050 as a case study.

Exploring Sustainable Construction: Utilizing Printed Circuit Board Waste as a Partial Sand Replacement in Concrete Production

The escalating demand for concrete in construction, coupled with the environmental degradation caused by sand extraction, necessitates the exploration of alternative materials for sustainable construction practices. This study investigates the potential of utilizing Printed Circuit Board (PCB) waste as a partial replacement for sand in concrete production. This investigation is presented through experimental work to replace the sand by 10%, 20%, and 30% by volume. The applicability of the proposed mixes is demonstrated through a comparative analysis of the concrete fresh and hardened properties. This research contributes to the field of sustainable construction by offering a novel use for electronic waste, thereby mitigating the environmental impact of both the electronics and construction industries.

Development of a learner model tool for predicting strength and embodied carbon for lightweight concrete production

The demand for sustainable concrete in meeting the net zero carbon target places a burden in optimizing concrete response to structural strength that satisfy acceptable embodied carbon. In most cases, a low carbon concrete is deficient in structural requirement and vice versa. This dilemma informs the need for a tool that can predict compressive strength as well as embodied carbon using the same input data. Since the use of alternative materials as cement replacement to enhance sustainability is emerging in the quest for a sustainable concrete, an optimal material that satisfy both conditions of structural integrity and sustainability is still lacking. Paucity of data in the emerging lightweight low carbon concrete using alternative materials, portends an upheave in the bias for prediction of the behaviour of lightweight low carbon concrete. This study therefore uses concrete data of lightweight low carbon concrete from laboratory experiment for the prediction of compressive strength and embodied carbon with their performance evaluated using eight machine leaning regression models. The results obtained indicates that the XG boost regression model exhibited excellent performance with a low Mean Squared Error (MSE) of 50.15, Mean absolute error(MAE) = 5.26, Mean absolute percentage error(MAPE) = 11.76 %, Explained variance score = 0.97, Root mean square error(RMSE) = 7.08 and a high R squared value of 0.96. The tool predicted compressive strength and embodied carbon for lightweight carbon concrete using multiple output regression such that the output can be limited to the yearly structural embodied carbon threshold to achieving 2050 net zero target. The developed tool when compared with concrete of similar mix ingredients performed more than 95 % in predicting concrete compressive strength and associated embodied carbon. In line with the inclusion of embodied carbon in carbon regulations of buildings in the UK as suggested by the professionals in the construction industry, the developed learner model and prediction tool has integrated concrete strength and embodied carbon to initiate a holistic approach to design and construction, balancing performance, cost, and environmental impact.

Destructive and non-destructive strength performance of iron slag recycled aggregate concrete using regression and grey correlation analysis

The future construction industry will demand for sustainable concrete, either by recycling or direct incorporation of industrial by-products for effective solution of ecological concerns. The paper covers, outcomes of an investigation conducted to assess the ‘performance of iron slag (0–30 %) recycled aggregate concrete (ISRA) with different levels of recycled (0–100 %) concrete aggregates (RCA)’ using destructive (DT) ‘(compressive, split-tensile and flexure strength)’ and non-destructive ‘(pulse velocity, electrical resistivity and rebound hammer)’ testing (NDT). The strength characters were evaluated to develop statistical regression and grey co-relations. ISRA concrete resulted majorly in decrease of pulse velocities, electrical resistance (up to 28 %) and rebound numbers (by 10) at higher alteration levels. The correlation coefficients were evaluated using linear regression and grey analysis. The grey correlations resulted in visible variations, indicating disparity in magnitude of ISRA concrete. The higher regression (>0.75) and grey coefficients (GRG>0.8) postulates higher probability of accuracy, successfully validate the outcomes.

Mechanical, microstructural, and thermal characterization of geopolymer composites with nano‐alumina particles and micro steel fibers

AbstractCement production is responsible for 5%–7% of global CO2 emissions, highlighting the need for sustainable alternatives like geopolymer composite (GCOMP) to meet the growing demand for concrete. This study investigates the mechanical, microstructural, and thermal properties of GCOMP by incorporating nano‐alumina (n‐alumina) and MSF (MSF). The n‐alumina content was varied at 1%, 2%, and 3% by weight of the mix, while the MSF content remained fixed at 0.5% by weight. Thermal characterization was conducted up to 800°C. The performance of GCOMP blends with n‐alumina was compared to a control blend consisting of only 0.5% MSF. Various mechanical properties were evaluated for all GCOMP blends. Microstructural and mineralogical characteristics were analyzed using scanning electron microscopy (SEM), X‐ray diffraction (XRD), and Fourier‐transform infrared spectroscopy (FTIR). Thermogravimetric and differential thermal analysis were performed up to 800°C for the thermal analysis of the GCOMP mix. The results indicate that the optimal mechanical properties were achieved with 2% n‐alumina (compressive and flexural strength increased by 35.65% and 77.7%, respectively). Additionally, the incorporation of n‐alumina improves the interfacial zones and results in a denser structure. GCOMP mortars portrayed a mass loss between 25°C and 250°C, with a marginal mass loss occurring between 250°C and 715°C. No mass loss was observed between 715°C and 800°C. The MSF‐reinforced GCOMP mortars experienced an ultimate mass loss of approximately 12%, with the MSF showing negligible influence. The addition of n‐alumina particles to MSF‐reinforced GCOMP resulted in the development of stronger samples characterized by the presence of C–S–H, calcium aluminate oxide hydroxide, and quartz.

Calculation of Productivity Loss at Batching Plant Due to Production Decline

The Batching Plant owned by PT Semen Indogreen Sentosa was established in the Binjai-Langsa Section on the Trans Sumatera Toll Road Project specifically to handle the demand for ready-mix concrete in the project. However, several obstacles in the project have caused a decrease in production from the batching plant, necessitating an evaluation of productivity loss due to these issues. The productivity loss calculation was conducted by sampling one of the batching plants over a 1-month working period using three approaches/methods: Zink’s Method, Thomas Baseline Technique, and Ibbs Statistical Approach. The calculation results from these three approaches provided a range of minimum daily productivity values, which should be 4.40 w-h/m3 - 2.48 w-h/m3, which can then be used as a reference for evaluation purposes, claims, etc.

Physical and mechanical properties of lightweight concrete with the incorporation of waste disposal polyurethane foam as coarse aggregate

<p>Industrial waste in engineered concrete mixes is an enormous step towards sustainable development. Polyurethane foam waste (PUFW) is mainly generated by the refrigeration, automobile, and construction industries. Day by day, large amounts of PUFW are incinerated and disposed of in landfills, which not only affects the environment but also leads to the loss of land usage. On the other hand, with the improvement of financial benefits, environmental benefits, and structural style, the demand for lightweight concrete (LWC) is also increasing. This study investigated the incorporation of rigid PUFW as coarse aggregate in LWC. Various proportions of PUFW replacement by volume (40%, 50%, 60%, 70%, and 80%) were examined to formulate the LWC mixtures. The physical and mechanical properties of the LWC were tested and compared with conventional concrete. The results showed that the compressive strength reached more than 17 MPa when LWC was made with 40%, 50%, and 60% PUFW content, satisfying the compressive strength of structural LWC. At 70% PUFW content, the compressive strength was satisfactory for semi-load bearing strength, and at 80% PUFW content, it was suitable for insulation concrete. In all mix proportions, the density value was less than 2000 kg/m3, which was satisfactory for LWC.</p>

Assessment of the opportunities of demolition waste using as a building material of the future in Ukraine

The object of research is the potential of secondary use of waste from the destruction of buildings and structures, which were formed as a result of the military aggression of the Russian Federation on the territory of Ukraine. For Ukraine, the issue of demolition waste is critical at the level of environmental safety and ensuring the demand for building materials for the reclamation of Ukraine according to the principles of the circular economy. To date, there are no official methods that would allow to determine the exact amount of destruction and the quality of the material formed, which complicates the development of mechanisms for its utilization in production. The key industry considered during the research for disposal of demolition waste is the industry of construction materials production. In the course of research, it was determined that most of the generated waste is waste from the destruction of buildings and structures made of precast concrete, however, considering that these wastes are generated by the action of explosions from shells. It is very difficult to ensure their compliance with the requirements of current standards due to the inclusion that such waste can contain. Therefore, the problem considered by this study is the determination of the nature of waste from the destruction of buildings and structures, their physical, mechanical and chemical characteristics, in the context of the final applications of products based on them. The results of the study showed that when reproducing the concrete mix for tared concrete for civil purposes, which do not have high requirements for stability in aggressive operating conditions, when replacing natural aggregate crushed to a fraction of 5 to 20 mm, the requirements for concrete strength are achieved in the level of C40/50 strength class. But the rheological characteristics deteriorate due to the high absorption of water from the concrete mixture by the studied material. Research has shown that for further use in the production of ready-mixed concrete and precast concrete products, it is necessary to prepare demolition waste with a wide particle size distribution and low dust content. This can ensure a high level of recycling and meet the demand for concrete in the reconstruction of Ukraine. The fine aggregate from the demolition waste crushing process can be considered as secondary cementitious material for cement production.

Optimized transportation scheduling for precast concrete components considering heterogeneous vehicle-size matching

Recently, prefabricated construction has been vigorously promoted, resulting in high demand for precast concrete (PC) components. The transportation scheduling optimization problem of PC components with various kinds from multiple projects arises. Unlike conventional cargo, PC components are characterized by shape heterogeneity, large volume, and strict delivery time limits. Based on three characteristics, a heterogeneous fixed fleet vehicle routing problem (HFFVRP) for PC components is introduced, where heterogeneous vehicles, allocation of PC components to size-matching vehicles, and hybrid time windows are considered. Then a two-stage solution strategy based on the improved ant colony optimization (ACO) and Dijkstra algorithm is designed to obtain optimal vehicle routes under minimum transportation costs. The results indicate that the improved ACO-Dijkstra algorithm outperforms in obtaining optimal transportation plans for heterogeneous vehicles compared with manual decision-making and other heuristic algorithms. Sensitivity analysis denotes that utilizing heterogeneous vehicles contributes to reductions in transportation costs, and vehicle configuration should be adjusted along with demand scales. The proposed model and algorithm extend the theoretical basis of construction industrial applications.

Enhancing Concrete Durability: Sustainable Ternary Blends Incorporating Agricultural and Industrial Wastes

<p>The demand for sustainable concrete in civil infrastructure operations grows by the day, resulting in the use of agricultural and industrial byproducts and controlling high-cost nanomaterials. Ternary blended concrete is an excellent alternative to conventional concrete for long-term development by lowering carbon footprint. Ternary blended concrete is a green and sustainable concrete made from three separate source components to make a binder. The fundamental benefit of ternary mixed concrete is its densely packed particles of various shapes and sizes, resulting in superior characteristics. This study discusses experimental studies that were conducted to assess the durability properties of regular ordinary Portland cement (OPC) concrete and ternary blended concrete containing 1% nano-SiO2 and industrial or agricultural byproducts. Concrete durability is defined as its capacity to sustain a safe degree of serviceability and various environmental exposure circumstances without requiring considerable repair or rehabilitation during its service life. Conventional concrete is prone to cracking because of its low tensile and durability properties. Six potential mixes were investigated in this work: three blends based on industrial byproducts (fly ash, ground granulated blast furnace slag, and metakaolin) and three mixes based on agricultural byproducts (rice husk ash, corncob ash, and sugarcane bagasse ash). This study investigated the durability characteristics such as water permeability, sorptivity, resistance to sulphate, acid attack, and alkaline attack. The experimental test findings were determined to be well within limitations when compared to the requirements specified in the standard/literature. The study also shows that ternary blended concrete with regulated nano-SiO2 enhances durability metrics significantly. Furthermore, energy dispersive spectrophotometry (EDS) measurements show dense phases with high proportions of Si atoms in the substrate's penetration layer. As a result, ternary mixed concrete is strongly advised in structural repair works.</p>

DEVELOPMENT OF A SELF-LEVELING FLY ASH-SLAG GEOPOLYMER MORTAR

Exponential growth in the world population and increase in demand for concrete are pressing researchers and scientists to find sustainable alternative materials for Portland cement and natural aggregates. Self-leveling mortar is extensively used in construction applications, such as floor leveling, repair, resurfacing, or adhesion. Yet, limited research has been carried out on enhancing this material’s sustainability. This paper aims to produce a geopolymer mortar produced with fly-ash (FA), ground granulated blast furnace slag (BFS), and desert dune sand. Geopolymer mortar samples were produced with different binder-to-sand (B:S), FA-to-slag (FA:BFS), and alkali-activator solution-to-binder (AAS/B) ratios. Alkaline solution was blended with sodium silicate and sodium hydroxide with a molarity of 8 M (ratio of 1.5). Fresh and hardened properties of the developed self-leveling mortars were assessed. Experimental results showed that the flow, initial and final setting time, and 7-and 14-day compressive strength were in respective ranges of 17.3-40.3 cm, 21-155 minutes, 42-221 minutes, 6.0-70.3 MPa, and 5.2-78.7 MPa. Furthermore, an increase in FA:BFS, B:S, and AAS/B ratios enhanced flowability and prolonged setting time but reduced compressive strength at both ages. These research findings advocate the use of a self-leveling, cement-free geopolymer mortar to be utilized in various buildings and repair applications.

DEVELOPMENT OF A SELF-LEVELING FLY ASH-SLAG GEOPOLYMER MORTAR

Exponential growth in the world population and increase in demand for concrete are pressing researchers and scientists to find sustainable alternative materials for Portland cement and natural aggregates. Self-leveling mortar is extensively used in construction applications, such as floor leveling, repair, resurfacing, or adhesion. Yet, limited research has been carried out on enhancing this material’s sustainability. This paper aims to produce a geopolymer mortar produced with fly-ash (FA), ground granulated blast furnace slag (BFS), and desert dune sand. Geopolymer mortar samples were produced with different binder-to-sand (B:S), FA-to-slag (FA:BFS), and alkali-activator solution-to-binder (AAS/B) ratios. Alkaline solution was blended with sodium silicate and sodium hydroxide with a molarity of 8 M (ratio of 1.5). Fresh and hardened properties of the developed self-leveling mortars were assessed. Experimental results showed that the flow, initial and final setting time, and 7-and 14-day compressive strength were in respective ranges of 17.3-40.3 cm, 21-155 minutes, 42-221 minutes, 6.0-70.3 MPa, and 5.2-78.7 MPa. Furthermore, an increase in FA:BFS, B:S, and AAS/B ratios enhanced flowability and prolonged setting time but reduced compressive strength at both ages. These research findings advocate the use of a self-leveling, cement-free geopolymer mortar to be utilized in various buildings and repair applications.

Fresh and mechanical properties of ground granulated blast furnace slag-based concrete: A review

The surge in global urbanization and developmental activities has led to a significant increase in the worldwide demand for concrete. Cement composites, such as concrete and mortar, are among the world's most extensively used construction materials. Cement manufacturing accounts for about 90% of overall carbon footprints in concrete that leads to demand for alternate binding materials derived from industrial by-products. Steel manufacturing is one of the fastest expanding sectors in construction, resulting in massive slag creation. Slag, a solid waste generated during the extraction of iron from its ore, exhibits varying qualities determined solely by the cooling process employed. One of its forms, Ground Granulated Blast Furnace Slag (GGBFS), has characteristics comparable to cement and hence it is a possible alternative. This study gives a comprehensive report on GGBFS as a cement substitute based on previously published research on the effect of GGBFS on various concrete qualities as well as its manufacture. The impact of GGBFS on concrete characteristics such as workability, setting time, flexural strength, compressive strength, and split tensile strength is explored in this study. It has been determined that integrating GGBFS up to a particular level successfully matches the characteristics of standard concrete. The current state-of-the-art evaluation aims to provide a consolidated, complete source that incorporates the general trends, discoveries, areas of study that require additional investigation, and prospective future applications of concrete based on GGBFS.

Mechanical properties of silica fume based concrete: A review

The significant industrial growth accompanying rapid urbanization has spurred a heightened demand for concrete. Cement production, a primary ingredient of concrete, results in substantial carbon dioxide (CO2) emissions. To mitigate this impact, alternative pozzolanic materials like silica fume (SF) can be incorporated. SF, an industrial byproduct, serves as a supplementary cementitious material (SCM), offering benefits of waste recycling. This study aims to comprehensively review the addition of SF as an SCM replacement, with a specific focus on the mechanical properties of concrete. Numerous scientific papers were analyzed and carefully examined from the period of 1998 to 2023, which forms the bibliometric core of this study. The entire scopus database was examined for co-occurrence of keywords and actively contributing countries and results were shown through network diagrams. The effect of SF addition on fresh properties as well as mechanical properties were discussed. The inclusion of SF in range of 10–25% by quantity of cement was found to have increased split tensile strength, compressive strength and flexural strength. However, the addition of SF beyond 25% replacement level can have an adverse impact on the overall characteristics of the composite mix. The present study summarizes the major trends as reported in the available literature where SF has been used as SCM. Apart from finding the general trends, various research gaps have been identified.

Reinforcing effect of CNT on the microstructure and creep properties of high-strength lightweight concrete

Demand for precast high-strength lightweight concrete (HSLC) has recently increased for cost benefits. This study aims to explore the reinforcing effect of carbon nanotube (CNT) on the microstructure and creep properties of HSLC. A total of four types of HSLC mixture were applied by securing two target properties (a compressive strength of 120 MPa and a density of 2000 kg/m3; a compressive strength of 80 MPa and a density of 1600 kg/m3) through steam curing with high temperature (90℃), considering a combination of lightweight materials and CNT utilization as variables. Lightweight aggregates operated internal curing (IC) more effectively than hollow microsphere, improving the pore structure of HSLC and leading to the formation of hydration products, especially calcium silicate hydrate (C-S-H). The efficiency of lightweight aggregate on IC was proven through nanoindentation testing, identifying that no unhydrated particles were observed in the specimen incorporating only lightweight aggregate as lightweight material, while unhydrated particles made up 8–19% of the total phase volume with hollow microsphere incorporation. The utilization of CNT enhanced the microstructure of the cement matrix by filling pores and inducing formation of ultra-high-density (UHD) C-S-H, improving the creep resistance of HSLC. Furthermore, CNT bridging suppressed redistribution of C-S-H caused by C-S-H slip, resulting in approximately 49% of the total specific creep compared to conventional high-strength concrete (HSC). The fédération internationale du béton (fib) model is considered to derive the creep properties of HSLC, since it indirectly applies the impact of lightweight material utilizing its oven-dried density.