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Recently, nano silica (NS) has gained the attraction of academic researchers and the construction industry because of enhancing the properties of cementitious composites. Although there have been some related reviews, the comprehensiveness and advancedness need to be further improved. This paper is a detailed review of previously conducted studies to explore the influence of NS in cementitious composites for evaluating mechanical properties and durability. The impact of NS on the fresh state, i.e. setting time and workability, and in the hardened state, i.e. compressive, flexural, and split tensile strengths is considered. Besides, the long-term durability is discussed that include permeability, resistance against acid and base attack, abrasion resistance, and carbonation resistance. Furthermore, volume stability and microstructure of concrete with NS are presented. A huge number of studies showed the positive effect of NS with optimized content for improving the concrete properties, while a negative effect was observed with the use of excess NS content. The inclusion of NS in cementitious composites substantially enhances the mechanical properties, durability and microstructure. Meanwhile, better dispersibility is the key to ensure the strengthening effect of NS, which can be improved by changing the morphology/size of NS, optimizing the stirring method, and adding surfactants. Further investigation of the application of NS in special concrete is its development direction, and the effect of NS on the microstructure of main hydration products needs to be further explored. [ABSTRACT FROM AUTHOR]

This paper aims to study the effect of using modified nano‐TiO2 with fly ash (FA) on ultra‐high performance concrete's (UHPC) mechanical, transport, and microstructure properties (UHPC). A ball mill was used to disband the nano‐TiO2 and distribute it uniformly within the FA powder. In this research, 20% of the cement weight was replaced by FA, and nano‐TiO2 was added by 0.4%, 0.8%, 1.2%, 1.6%, and 2% of the FA weight. To investigate the effect of the ball mill period on the UHPC properties, periods of 10, 20, 30, and 40 min were applied to a binder of 20% FA and with 6% nano‐TiO2. In addition, a 30‐min ball mill period on a binder of 20% FA and 0.4%, 0.8%, 1.2%, 1.6%, and 2% nano‐TiO2 was also investigated. Tests of compressive strength after 1, 7, 28, and 91 days of curing in tap water, splitting tensile strength, flexural strength, and modulus of elasticity were performed after 28 days of curing in tap water. Tests of chloride permeability, sorptivity coefficient, water permeability, and microstructure were also performed after 28 days of curing in tap water. The results showed that the addition of higher percentages of nano‐TiO2 led to a decrease in workability. The addition of nano‐TiO2 improved the mechanical properties. The highest compressive strength of 208.9 MPa was achieved for the mixture of 20% FA with 1.2% nano‐TiO2 at the age of 28 days. The 30‐min period of application of the ball mill achieved the best performance compared with the other periods. The results of using a ball‐mill to re‐mix nano‐TiO2 between 1.2% and 2% by weight with FA showed impressive comparative results. [ABSTRACT FROM AUTHOR]

Seawater concrete (SWC) is an environmentally friendly construction material that addresses freshwater scarcity concerns by utilising seawater as a mixing water source. This review study comprehensively examines SWC by focusing on its fresh properties, hardened properties, seawater composition, microstructure and porosity, hydration process, durability, test methods and electrical resistivity. The study analyses the influence of additives and admixtures on SWC's performance by considering constituents such as cement, aggregates and seawater. It also explores the impact of manufacturing techniques, including mix design. The potential of SWC is revealed and compared with that of conventional concrete by evaluating and comparing their mechanical properties, such as compressive strength, modulus of elasticity, stress-strain behaviours, tensile strength and flexural strength. This study primarily aims to thoroughly examine the characteristics of SWC in its fresh and hardened states. It also assesses the advantages and drawbacks of seawater as a mixing water source. Moreover, this study delves into the impact of seawater composition on crucial aspects, such as the hydration process, microstructure and porosity of concrete. It also used various test methods to explore SWC durability, including resistance to chloride ingress, sulphate attack and carbonation. Furthermore, the importance of electrical resistivity for corrosion prevention is discussed in this study. The carbon-negative cement production and carbonation curing of seawater concrete underscore groundbreaking advancements, emphasizing sustainability and climate mitigation in the construction industry. Overall, this study aims to enhance the comprehension of SWC and provide valuable insights for engineers, researchers and policymakers in concrete technology. • Utilisation of seawater in concrete for sustainable construction. • Supplementary cementitious materials of seawater concrete. • Seawater in concrete and hydration of concrete materials. • Microstructures properties and Chloride penetration of concrete incorporated with seawater. • Fresh and hardened, Mechanical and durability properties of concrete made with seawater. • Recommendations and observations are advanced for future research. [ABSTRACT FROM AUTHOR]

Advances in recycling can exceed traditional practice in that a non-renewable resource can at least become a partially renewable resource. This research attempts to support the cradle-to-cradle concept by testing the effect of reused recycled concrete aggregates (RRCA) on the fresh, physical, mechanical, and microstructure properties of self-compacting high-strength concrete (SCHSC). Two generations of recycled aggregate concrete (RAC) are produced; the first and second are created by recycled concrete aggregate (RCA) and by RRCA, respectively. For each generation, two replacement amounts are used (25% and 50% by mass). Results show that using RRCA does not affect the fresh properties of SCHSC, and up to 50% RRCA replacement amount by mass can be adopted for enhancing the mechanical and microstructure properties of reused recycled aggregate concrete (RRAC). Computed tomography indicates that the porosity of RRCA is less than that of RCA. [ABSTRACT FROM AUTHOR]

• Volcanic pumice powder (VPP) could contribute to the compressive strength of concrete. • Utilization of 10% of VPP produces the optimum high strength concrete (HSC). • VPP contributes to pore filling (HSC) thereby lowering the permeability of HSC. • Strength of 70 MPa or more could be achieved with VPP replacement of OPC in HSC. • Ionic and fluid transport reduces with increase in VPP-OPC replacement in HSC. In this study, the potency of volcanic pumice powder (VPP) as a supplementary cementitious material at varied levels (0%, 10%, 20%, and 30%) in high strength concrete (HSC) was investigated for its pozzolanic reactivity as a basis for strength and durability enhancement. Workability, transport properties and mechanical properties were tested in addition to the characterization of the products. X-ray florescence and strength activity index established the VPP oxides (SiO 2 + Al 2 O 3 + Fe 2 O 3 = 76.01%) and pozzolanicity while diffraction techniques revealed the presence of anorthite (Al 2 CaO 8 Si 2), and clinopyroxene (AlCaMgSiO 6). Despite the paucity of calcium oxide and the excess of silica and alumina in VPP in contrast to OPC, yet it contributes significantly to the microstructural density and tortuosity of HSC pores thereby improving the strengths and transport properties as evidenced in the reduction of rapid chloride ions penetration (RCPT), and low initial surface (water) absorption (ISA) values. The maximum 180-day tensile, flexural and compressive strengths of the HSC-VPP sample were 6.22, 10.5 and 78.9 MPa, respectively. [ABSTRACT FROM AUTHOR]

The performance of any repaired concrete structure, and thus its service life, depends on the quality of the interfacial transition zone of the composite system formed by the repair material and the existing concrete substrate. In this work, the properties of the interfacial transition zone between normal concrete (NC) substrate as an old concrete and ultra-high performance fiber-reinforced concrete (UHPFC) as a repair material was investigated. Pull-off and splitting cylinder tensile tests were performed to quantify the bond strength in direct and indirect tensions, respectively. The microstructure of the interfacial transition zone was also studied using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS). Different types of NC substrate surface preparation methods were used. An optical three-dimensional surface metrology device was used to estimate the substrate roughness parameters. Based on the results, high interfacial bond strength was achieved on the 3rd, 7th, and 28th days. The pull-off test results revealed that all failures occurred in the substrate, regardless of the substrate surface roughness. The majority of failures in the split tensile test also occurred in the substrate. SEM/EDS proved that the use of UHPFC as a repair material chemically, physically, and mechanically improved the repaired interfacial transition zone to become stronger and denser, as well as more uniform, and durable. Moreover, the use of UHPFC increased the service life of repaired structures and minimized the number and extent of interventions to the lowest possible level. [ABSTRACT FROM AUTHOR]

Recent advancements in recycling have transformed nonrenewable resources into partially renewable resources. In line with these advancements, the application of wastes, including ceramics, as substitute aggregate materials for construction has elicited considerable research interest. Ceramic waste aggregates can be used to address complex problems, such as the shortage of materials in construction sites, and reduce environmental wastes. This study aims to investigate the effectiveness of replacing silica fume (SF) and metakaolin (MK) with cement to improve ultrahigh-performance concrete (UHPC) prepared using ceramic wastes as coarse aggregates. Eleven UHPC mixes with 10%, 20% and 30% proportions of either SF or MK were designed. The fresh, physical, mechanical and microstructure properties of these mixes were evaluated, and test results showed that replacing cement with either SF or MK can improve the mechanical and physical properties of UHPC. The use of this waste as construction material will yield substantial technical, economic and environmental benefits, particularly from the perspective of sustainable development. The results showed that replacing SF or MK is effective in improving the strength of UHPC, particularly when the SiO 2 /CaO ratio was increased to 2.98. The 28-day compressive strength of UHPC with SF increased from 133.1 MPa to 146.6 MPa due to the improved microstructure and denser matrix. Image 1 • Ceramic waste aggregates (CWA) from reject the production line were evaluated. • Natural coarse aggregates of Ultra-high performance concrete (UHPC) mixes were fully replaced by CWA. • The evaluation results revealed that replacing cement with 20% silica fume can optimise the strength of UHPC made from CWA. • The interfacial transition zone between CWA and cement paste was evaluated via scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Concrete material is one of the most widely used construction materials in Indonesia due to its high compressive strength and adaptability to various construction needs. Despite its benefits, concrete has limitations, notably its weakness in tension and tendency to crack under tensile stress. This research focuses on High-Performance Concrete (HPC) with compressive strength exceeding 80 MPa, reinforced with 3D Dramix steel fibers to enhance both compressive and tensile strength. The study aimed to evaluate the compressive strength and splitting tensile strength of HPC mixed with varying percentages (0%, 3%, 6%, and 9%) of Dramix 3D steel fibers. Additionally, the methodology involved microstructure analysis using Scanning Electron Microscopy (SEM) and mechanical testing on HPC samples cured at 7, 14, and 28 days. Results indicate that the compressive strength reached a maximum of 94.776 MPa, and tensile strength reached 6.599 MPa with a 9% fiber addition at 28 days, highlighting the material's potential application in high-performance structural elements. The findings suggest that 3D Dramix steel fibers significantly enhance the mechanical properties of HPC, making it a viable option for durable construction. [ABSTRACT FROM AUTHOR]

Due to the growing need for sustainable and ultra-high-strength construction materials, scientists have created an innovative ultra-high-performance concrete called Geopolymer based ultra-highperformance concrete (GUHPC). Besides, in the last few decades, there have been a lot of explosions and ballistic attacks around the world, which have killed many civilians and fighters in border areas. In this context, this article reviews the fresh state and mechanical properties of GUHPC. Firstly, the ingredients of GUHPC and fresh properties such as setting time and flowability are briefly covered. Secondly, the review of compressive strength, flexure strength, tensile strength and modulus of elasticity of fibrous GUHPC. Thirdly, the blast and projectile impact resistance performance was reviewed. Finally, the microstructural characteristics were reviewed using the scanning electron microscope and X-ray Powder Diffraction. The review outcome reveals that the mechanical properties were increased when 30% silica fume was added to a higher dose of steel fibre to improve the microstructure of GUHPC. It is hypothesized that the brittleness of GUHPC was mitigated by adding 1.5% steel fibre reinforcement, which played a role in the decrease of contact explosion cratering and spalling. Removing the need for cement in GUHPC was a key factor in the review, indicating a promising potential for lowering carbon emissions. However, GUHPC research is still in its early stages, so more study is required before its full potential can be utilized. [ABSTRACT FROM AUTHOR]

• This paper presents a new material to be used as a partial substitute for cement in UHPC. • Slump flow diameter of fresh concrete decreased with the addition of FS and SF. • The addition of FS and SF at 20% contributed to achieve the highest compressive strengths of UHPC. • FS led to the improvement of transport properties of UHPC. • FS substantially improved the microstructure of the UHPC matrix. This paper presents a new material that can be used as a partial substitute for cement in the production of ultra high-performance concrete (UHPC). This material is an industrial waste product of ferrosilicon (FS) alloy, which is available as furnace slag. It is used as a partial substitute for cement after grinding until it reaches the stage of microparticles with a surface area of 12,850 (cm2/gm). UHPC mixtures are designed with cement replacement ratios of 5%, 10%, 15%, 20% and 25% by FS, and same proportions of silica fume (SF). Fresh concrete properties are assessed by applying tests of air content and workability. Mechanical properties are assessed by applying tests of compressive strength, split tensile strength, flexural strength and modulus of elasticity. Moreover, transport properties are assessed by chloride penetration resistance and initial sorptivity water permeability test. Microstructure analyses are carried out by SEM-EDX and XRD tests. Results show that the increase in cement replacement rates by SF and FS by 25% of cement mass reduces slump flow to 345 and 356 mm, respectively, whereas it is 385 for the control mixture. Inclusion up to 20% FS enhances compressive strength by 210.4 MPa compared with 178.6 for the control mix at 90 days. In addition, including up to 25% FS improves the transport properties of UHPC by increasing permeability resistance compared with the control mixture. [ABSTRACT FROM AUTHOR]

[Display omitted] • NCSA from agricultural waste, was used as cementitious material. • Replacement of 5% of NCSA with 20% of PLA improved the mechanical properties. • The highest compressive strength was 170.1 MPa at the age of 90 days. • A compressive strength was 143.8 at 90 days at 10% NCAS combined with 30% PLA. • 30% of PLA replacement achieves a compressive strength of 149.1MPa at 90 days. The demand for partial replacement and complementary products of cement to enhance the properties of concrete and reduce the environmental pollution from the cement industry is recently increasing. Nano cotton stalk ash (NCSA) and palm leaf ash (PLA) are agricultural residues resulting from the burning of cotton stalk and palm leaves used as biomass. This investigation aims to study the effect of using NCSA and PLA as partial replacements to cement in ultrahigh-performance concrete (UHPC). As partial replacements for cement mass, 0%, 2.5%, 5, 7.5% and 10% of NCSA and 10%, 20% and 30% of PLA were adopted to produce the UHPC. Sixteen mixtures were prepared to evaluate the new and mechanical properties of UHPC containing the NCSA and the PLA. In addition, NCSA and PLA morphologies were evaluated using a scanning electron microscope, and thermogravimetric analysis with differential thermal analysis and X-ray diffraction was applied to assess ash characteristics. Results of the microstructure tests showed that heat treatment of the ash improved its properties by removing carbon and unburned organic matter with a slight change in the mineral composition of the PLA. The increase in the cement replacement rates by ashes led to a decrease in the slump flow, whilst the largest slump flow reduction was recorded in the mix containing 30% of PLA and 10% of NCSA as a replacement of Portland cement by 14.5% mm compared with the reference mix. The application of replacement rates by 2.5% and 5% of NCSA and 20% of PLA by cement mass to produce UHPC respectively realised the highest compressive strengths of 161.7 and 170.1 MPa at 90 days. Moreover, the mixture containing 20% of PLA with 5% of NCSA achieved the highest values of splitting tensile strength, flexural strength and elastic modulus. [ABSTRACT FROM AUTHOR]

• As the HF content increased, the workability of the mixtures decreased. • Oven-dry unit weight of all mixtures is below 1300 kg/m3. • As the HF content increased, the thermal conductivity coefficient of the mixtures decreased. • The compressive strength of the mixtures is between 1.28 and 2.73 MPa. • HF reduced drying shrinkage by 1.3 times. • HF increased the compressive strength after high temperature. The objective of the current research is to find out what impacts hemp fibers (HF) lengths and percentages have on the fresh, physical, mechanical, sorptivity, dry shrinkage, and thermal properties of HF-reinforced alkali-activated composite (AAC) reinforced with ground blast furnace slag (GBFS). Two groups of AAC mixes with 10 and 20 mm HF lengths were produced. Each group contained different percentages of HF with varying fiber lengths added to mixes at 0.5 %, 1 %, 2 %, and 3.0 % by weight of cement, respectively. Flow diameters were measured to determine the fresh-state properties of the AACs. Water absorption and apparent porosity were determined as physical properties. The unit weights of AAC mixtures are between 1045–1672 kg/m3. Measurements were made on compression and flexural characteristics at 7 and 28 days. The 28-day compressive strengths of AAC mixtures vary between 1.28 and 2.73 MPa, and the bending strengths vary between 0.48 and 1.65 MPa. AAC was also tested for water absorption, drying shrinkage, thermal conductivity, fresh and dry unit weight and porosity. The resistance of high temperatures at 250, 500, and 750 °C was determined. There is a significant improvement in compressive and flexural strength and thermal conductivity when HF is added at a 20 mm length. This improvement was confirmed and emphasized through scanning electron microscopy (SEM). According to study results, high-temperature alkali cooking treatments up to 250 °C may improve the thermal stability of HF cellulose. The best HF mix, M2-2 %, increased the 28-day compressive strength by 28.8 % and produced the best results at temperatures as high as 750 °C. The compressive strength of the mixtures exposed to 750 °C was obtained as approximately 2 MPa. [ABSTRACT FROM AUTHOR]

Nano sesame stalk ash (NSSA) and rice straw ash (RSA) are by-products of bioenergy production. The aim of this paper was to investigate the effects of using NSSA with RSA on high-strength concrete (HSC) properties. The properties of NSSA and RSA were evaluated using scanning electron microscopy with energy dispersive X-ray spectroscopy, thermogravimetric analysis with differential thermal analysis and X-ray diffraction. Ordinary Portland cement ratios were replaced by different ratios of NSSA (0%, 2.5%, 5%, 7.5% and 10%) with RSA (10%, 20% and 30%) to prepare 16 concrete mixtures. The properties of HSC-containing NSSA and RSA were evaluated by slump test immediately after casting, compressive strength at 7, 14, and 28 days, furthermore indirect tensile strength, flexural strength, and modulus of elasticity were tested at 28-days. Microstructure tests showed that ash treatment improved HSC properties by removing carbon and unburned organic matter. The increase in ash replacement rate led to a decrease in workability. The mixtures containing (20% RSA and 2.5% NSSA) and (20% RSA and 5% NSSA) achieved the highest compressive strengths of 88.9 and 90.7 MPa, respectively. Furthermore the mixtures containing (20% RSA and 2.5% NSSA) achieved the highest splitting tensile strength, flexural strength, and elastic modulus values of 7.3, 10.7, and 38600 MPa, respectively. [ABSTRACT FROM AUTHOR]

• This study focused on the effect of replacing large quantities of U-POFA (up to 60%) on chloride penetration in HSGC cured by steam curing regimes. • These different temperatures (50°C, 65°C, and 80°C) and periods (6, 11, and 16 hours) of steam curing regimes were applied. • The HSGC large quantities of U-POFA (40% and 60%) have high performance when compared to the replacement rates (0% and 20%). Since diminishing the consumption of cement has many benefits, ongoing research on the incorporation of the industrial/agricultural wastes as an alternative or partial substitution for cement is of paramount significance. This study aims to examine the effect of steam curing regimes (SCRs) on the chloride resistance and microstructure of high-strength green concrete (HSGC). To this end, palm oil fuel ash, a type of waste from the palm oil industry, was treated so that ultrafine palm oil fuel ash (U-POFA) could be obtained. U-POFA was utilized as a partial substitute of the mass of cement at 0%, 20%, 40%, and 60% to produce HSGC. Varying steam curing temperatures (50 °C, 65 °C, and 80 °C) and varying periods (6, 11, and 16 h) were applied to the HSGC. Moreover, a steam curing cycle that did not exceed 24 h was applied. The tests performed on the HSGC samples included compressive strength (CS), rapid chloride permeability, and rapid chloride migration. The evaluation of the microstructure of the HSGC samples was undertaken via Mercury Intrusion Porosimetry (MIP) in addition to scanning electron microscopy with energy dispersive x-ray. The results showed that the application of SCRs with a high volume with UPOFA resulted in enhanced CS, chloride resistance, and microstructure properties of HSGC at an early age of 3 days and a later age of 360 days. Such enhancement in the concrete properties mainly depends on the cement replacement rates by U-POFA, temperature, and the steam curing period. It was, therefore, concluded that U-POFA played a key role in reducing the negative impact, which might have been caused by the utilization of varying SCRs. [ABSTRACT FROM AUTHOR]