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The paper analyses the effect of waste sludge from paper industry (paper sludge) on physical and mechanical properties of clay bricks, their microstructure and resistance to freezing and thawing. Paper sludge is not hazardous industrial waste mainly consisting of cellulose and calcite. Clay bodies were made from the mix containing from 5% to 20% of paper sludge and fired at 900 °C and 1000 °C temperatures. Open pore structure in the clay body is developed as a result of burnt cellulose fibres and calcite decarbonization. Physical and mechanical properties of clay bodies change depending on the content of added PS: shrinkage, density and compressive strength reduce, water absorption and effective porosity increase. It is recommended to add 5% of paper sludge to the clay body and fire it at 900 °C temperature, or alternatively add 5–15% of paper sludge and fire the clay body at 1000 °C temperature. In terms of resistance to freezing and thawing, such products are regarded as frost resistant in moderately aggressive environment, i.e. in structures protected from direct environmental effects. [ABSTRACT FROM AUTHOR]

Highlights: [•] In TPC cement (APS/FA) predominates carboaluminate phase. [•] In OPC cement is formed ettringite as main phase. [•] Different morphologies and crystal sizes founding both cements. [•] The formation of non-expansive ettringite inside the pores is identified. [•] The TPC and OPC pastes can be catalogued as resistant to sulphate ions. [ABSTRACT FROM AUTHOR]

Abstract: Kaolin, one of the materials of major importance for the ceramic and paper industry, is also used in the construction industry as a raw material for the production of white cement clinker and, in the form of metakaolin, as an artificial pozzolanic additive for concrete. Metakaolin is a vital component of high-performance and architectural concrete; however, its application in regular concrete is very limited due to relatively high production costs. This report evaluates the performance of a low-cost metakaolin-based additive called thermally activated kaolin (TAK), in cement. Due to its pozzolanic properties and the densification of cement matrix, the application of TAK provides a 15% improvement of the compressive strength. It was shown that TAK of optimal quality can be manufactured by the thermal treatment of raw kaolin with 74% of kaolinite at 750°C without the intermediate beneficiation stage. The application of a developed approach can significantly reduce production expenditures and make the application of such an additive feasible even in regular-grade cement and concrete. [Copyright &y& Elsevier]

The objective of this paper is to investigate the microstructure of high-viscosity modified asphalt binder (HVA) containing high-content polymers and its effect on fatigue performance, as well as the applicability of different analytical methods and failure criteria of linear amplitude sweep (LAS) test to HVA. In this paper, two types of HVAs with different polymer contents, a commercial HVA, a conventional polymer-modified asphalt binder, and a base asphalt binder were first prepared or selected. Fluorescence microscopy tests, time sweep tests, and LAS fatigue tests were then performed on these binders. Finally, the fatigue properties of the different binders were analyzed in depth using different analytical methods and failure criteria. The results show that the polymers in HVA crosslink with each other to form a strong cross-linking structure, and the phase inversion of the polymers renders them into a continuous phase, which significantly improves the fatigue damage resistance of the HVA; moreover, the evolutions of stress with shear strain for the fatigue process of HVAs is related to the polymer network. Besides, the two-dimensional damage characteristic curve (DCC) cannot accurately reflect the evolution of the fatigue performance of HVA, and this paper suggests the use of a three-dimensional DCC curve with strain information. Furthermore, the 35% reduction in C 0 in the dissipative energy method is not a suitable failure criterion, a more accurate fatigue performance ranking can be obtained by using the yield stress as the failure criterion. Although the fatigue resistance of HVA after yield stress is theoretically considered using the pseudo-strain energy approach, HVA does not show a peak of stored pseudo-strain energy even when the strain is increased to 60% in the LAS test. Therefore, the maximum strain value (30%) in the standard LAS test is not sufficient in characterizing high-polymer HVAs because there is not enough fatigue accumulation of HVAs in this range, consequently, the maximum shear strain parameter in the LAS experiment needs to be reconsidered. • Polymer morphology and its crosslinking networks in HVA with high-content polymers were analyzed. • The fatigue properties of HVAs based on LAS test and different analytical methods are compared. • The fatigue crack length and its evolution of HVA are characterized. • The deficiencies of the LAS test to evaluate the fatigue resistance of HVA and suggestions for modifications are presented. [ABSTRACT FROM AUTHOR]

Modified bitumen is a critical material to ensure the durability of asphalt pavements. Traditional polymer-modified bitumen (PMB) has been widely researched and applied in the past two to three decades. Recently, a high-content SBS (Styrene-Butadiene-Styrene) polymer-modified bitumen (HSBSMB) with a higher SBS content of up to 7–9% by weight has started attracting interest from researchers. There are, however, still few specifications or technical guidelines for HSBSMB. To gain a better understanding of HSBSMB, the composition and structure of typical polymer SBS and base bitumen, the micromorphology and micromechanics of HSBSMB, its rheological and aging characteristics, as well as its asphalt mixture and field pavement performance were reviewed comprehensively in this paper. The content covered in this paper is primarily derived from 210 pertinent papers published between 1990 and 2023 in two databases, Web of Science and Google Scholar. It appears from our review that HSBSMB has a stronger internal polymer network than conventional SBSMB and thus exhibits better resistance to rutting, fatigue, and cracking as well as better aging resistance. Furthermore, findings from both laboratory scale and field pavement scale indicate that HSBSMB not only offers higher performance and durability but also leads to reduced pavement structural layer thicknesses in ensuring performance. However, many issues and challenges still remain before HSBSMB will become a viable option for large-scale application in road infrastructure, aspects such as the mechanism of its internal structural changes, the optimization of methods for evaluating its rheological properties, the life cycle assessment of its long-term benefits, as well as the storage stability and workability of HSBSMB. It is hoped that this review will contribute to a better understanding of HSBSMB and promote its application. • The chemical properties of SBS polymer and base bitumen as well as their interactions were comprehensively summarized. • The mechanisms of SBS in bitumen and polymer phase inversion were discussed under different microscopy techniques. • The current standard rheological evaluation methods may need to be improved for high-content SBS polymer-modified bitumen. • High-content SBS polymer-modified bitumen exhibits better resistance to rutting, fatigue, cracking, and aging. [ABSTRACT FROM AUTHOR]

• SAXS is an advantageous technique for analyzing the microstructure of asphalt. • The primary factor responsible for microstructural changes is the aggregation of micelles. • The microstructure of recycled asphalt is mainly affected by the mass ratio of old and new asphalt. The microstructure of asphalt plays a crucial role in determining its overall performance. However, the lack of comprehensive research on parameterizing the microstructure of asphalt has hindered the establishment of a clear relationship between microstructure and macroscopic performance. To address this gap, this paper conducted a study involving small-angle X-ray scattering (SAXS) experiments to investigate the changes in the microstructure of asphalt during aging and regeneration processes. The SAXS experimental results were then subjected to fitting using the Unified function, enabling us to derive key microstructural parameters. The SAXS data profiles obtained from virgin, aged, and recycled asphalt samples exhibit a remarkable degree of similarity, suggesting that their microstructural features are highly comparable. Additionally, the scattering characteristics observed in the SAXS data point to the presence of secondary structure scatterers within the asphalt samples. The presence of secondary structure scatterers suggests that the asphalt samples consist of microstructural entities, such as micelles or aggregates, which form the basis for the scattering patterns observed. During the aging of asphalt, the size of micelles and the heterogeneity of their sizes undergo a progressive increase. Simultaneously, the surface activity of these micelles gradually diminishes. However, a notable reduction in micelle size and size heterogeneity is achieved when regenerating aged asphalt using virgin asphalt. Furthermore, the surface activity of micelles is improved through the regeneration process. On the contrary, the rejuvenator used in this study did not exhibit a significant restorative effect on the microstructure of aged asphalt. Rheological analysis indicates that the observed viscoelastic changes in asphalt during aging and regeneration align with microstructural variations, but the effect of the rejuvenators on viscoelasticity do not correlate directly with their impact on microstructure. The differences between rejuvenators in improving the properties of aged asphalt cannot be solely inferred from their effect on microstructure. The findings in this paper contribute significantly to our understanding of asphalt microstructure and its evolution during aging and regeneration processes. [ABSTRACT FROM AUTHOR]

• LSS used as a NS substitute in FA/GGBS-based mortar increases compressive strength. • GO-modified mortars show superior viscosity recovery to NC-modified ones. • LSS mortars offer higher strength and lower drying shrinkage than NS mortars. • Formwork-free conditions increase drying shrinkage in 3D printed mortars. • High temperature & humidity reduce drying shrinkage in printed GO/NC modified mortar. The environmental impact of concrete 3D printing (C3DP) has become a concern due to its large cement consumption and over-exploitation of natural resources. This study investigates the viability of using geopolymer mixtures in C3DP prepared with fly ash (FA)/ground granulated blast furnace slag (GGBS) and underutilised aggregate as substitutes for ordinary Portland cement (OPC) and natural aggregate, respectively. This paper focuses on the rheological, mechanical, and shrinkage properties of FA/GGBS-based geopolymer mortar with lead smelter slag (LSS) as natural sand (NS) substitute and the impact of adding nanoclay (NC) and graphene oxide (GO), as thixotropy agents, on the yield stress development and viscosity recovery properties of the mixtures. The effect of various outdoor environmental conditions of 24 °C -50 %RH, 35 °C -90 %RH and 35 °C -50 %RH on pore water evaporation and 28-day drying shrinkage of 3D printable geopolymer mortar was studied, considering the effect of NS, LSS, NC and GO in free-formed and control conditions. LSS GO-modified mortars exhibited superior viscosity recovery capacity and yield stress evolution compared to their NC-modified counterparts. Moreover, using LSS instead of NS resulted in increased 28-day compressive strength under various environmental conditions, and LSS mortars exhibited lower drying shrinkage in both conventional casting and free-formed conditions. The findings of this paper will serve as a benchmark for further studies on the effect of different curing techniques (internal or external) on the hardened state dimensional stability of 3D printed products using alkali-activated binder systems to improve the structural integrity by controlling the water evaporation and drying shrinkage development. [ABSTRACT FROM AUTHOR]

• Evaluate the nano silica (NS) types, dispersion methods and fabrication methods of utilizing NS in cementitious composites. • A small content of NS can significantly enhance the mechanical properties and durability of cementitious composites. • NS can also improve the multifunctional properties of cementitious composites. • The modification mechanism of NS on cementitious composites is nano-core effect. • NS has a potential to develop the low carbon cementitious composites. To reduce the life-cycle carbon emissions of cementitious composites, potential pathways are to use more low-carbon raw materials, enhance the composites' performance and further extend the service life of their structures. Nano silica (NS), dividing into powder and colloid, and colloidal NS is less harmful to human than that of powdery NS. NS holds nanomaterial characteristics, pozzolanic activity, and more reactive compared with traditional supplementary cementitious materials (SCMs). Therefore, a small content of NS can significantly improve in the mechanical properties, durability, and multifunctionalities, expected to achieve carbon emission reduction of cementitious composites. This paper provides a comprehensive review on the fabrication (NS, mix proportion, and fabrication method), microstructures (hydration products and microstructures), and properties (early performance, mechanical properties, durability, volume stability and functional properties), and applications of cementitious composites modified with NS. The paper also concludes with an outline of some future risks, challenges, and future development of cementitious composites modified with NS. [ABSTRACT FROM AUTHOR]

• The optimal calcination temperature of MFPSA is 800 °C and the dosage is 4%. • MFPSA can increase the 28d flexural strength of fiber cement by 11.5%. • MFPSA can increase the compressive of fiber cement strength by 5.7%. • MFPSA decreases the 28d capillary water absorption of fiber concrete by 31.9%. • MFPSA promotes hydration and introduces hydrophobic groups. The modified Fenton paper sludge ash (MFPSA) was employed to replace cement in different proportions to prepare fiber cement products. The mechanical and hydrophobic properties of the MFPSA/fiber cement and concrete were studied. When the calcination temperature is 800 °C and the dosage is 4%, the MFPSA increases 28d flexural strength of fiber cement by 11.5%, compressive strength by 5.7%, and decreases water absorption by 2.6%. The MFPSA also decreases the 28d capillary water absorption of fiber concrete by 31.9%. The XRD, SEM/EDS, FTIR were employed to reveal how the MFPSA affects the hydration mechanism, and microstructure of MFPSA/fiber cement products. [ABSTRACT FROM AUTHOR]

• This current research paper is focused on the toughness and impact resistance of hybrid fiber reinforced self-compacting concrete. • Compressive strength made this suitable for structural elements. • Using SEM images, the SCC's failure mechanisms were assessed and fibre-aggregate interface was evaluated. • In digital image processing, the cross sections inspected and fiber segregation coefficient values were evaluated. This research paper presents the results of extensive experimental investigations and analytical results on the fresh and hardened properties of self-compacting concrete reinforced with hybrid hooked end fiber (HF) and crimped steel fiber (CF) in different fiber volume fractions. In this present investigation, the mixes were reinforced with different fiber combinations of hooked end fiber (0.25, 0.5 and 0.75%) and crimped fiber (0.25 and 0.5%). The fresh state properties of the mixes were characterized by using slump flow diameter, T 50cm , and V-funnel test. The hardened properties of self-compacting concrete (SCC) mixes were assessed by using compressive strength, flexural strength and impact resistance test. Regression analysis was carried out in order to correlate the fresh and hardened state on the extensively large volume of collected experimental data. The results reported that adding hybrid hooked end-crimped steel fiber significantly improves the compressive strength, flexural strength and impact resistance. Addition of hooked end steel fiber led to improve the compressive strength when compared to crimped end fiber. Moreover, increasing the crimped fiber content decreased the effect of hooked end steel fiber in flexural strength improvement. [ABSTRACT FROM AUTHOR]

Unmodified thermal-activated recycled cement (RC) paste has unfavorable properties like fast setting. This paper intends to modify RC by adding phosphogypsum (PG) and ground-granulated-blast-furnace-slag (GGBS). A comprehensive experimental program combining isothermal calorimetry, mechanical tests, TG, XRD, MIP, 29Si NMR and SEM of modified RC (PG-GGBS-modified-recycled-cement) pastes was conducted. The results show that GGBS and PG not only effectively modified the setting time but also contributed to a more compact skeleton. The final setting time was extended from 12 mins to 84 mins. The 28d and 90d compressive strength reached 29.8 and 36.9 MPa, increaseing by 21.1 % and 39.9 %, respectively. It is shown that PG acted as a sulfate excitation to the active Al 2 O 3 in the GGBS and RC to generate AFt. Rehydrated C-S-H gel could both wrap and protect the CaSO 4 ·2 H 2 O crystals and crystalline contact points, and effectively filled the pores of the hardened paste, thus promoting the generation of C(-A)-S-H and Ca 5 (SiO 4) 2 (OH) 2. The rehydration of modified RC was associated with a remarkable amount of AFt and AFm intergrowing with the reformed C-S-H gel and generating a compact network skeleton. • Modification of recycled cement with phosphogypsum and GGBS was investigated. • GGBS and PG not only effectively modified the setting time but also contributed to a more compact skeleton. • Rehydrated C-S-H gel could effectively fill the pores, thus promoting the generation of C(-A)-S-H and Ca 5 (SiO 4) 2 (OH) 2. • The final setting time of recycled cement was extended from 12 mins to 84 mins. • The 28d and 90d compressive strength reached 29.8 and 36.9 MPa, increased by 21.1 % and 39.9 %. [ABSTRACT FROM AUTHOR]

The porous hydrophilic nature of cement-based material is susceptible to water and corrosive media, severely reducing the durability. In this paper, methyl siloxane-based hydrophobic powder was prepared, and its effect on the physicochemical and anti-corrosion properties of mortar with different water-cement ratios were investigated. The results show that the addition of hydrophobic powder significantly improved the hydrophobic properties of mortars. Especially for the mortars with w/c ratios of 0.2 and 0.4, it showed superhydrophobicity with a water contact angle up to 156.5 ° and 152.3 ° respectively. Lower w/c ratio mortar has a denser microstructure, which reduces the water absorption rate of the mortar, and the hydrophobic powder enhances the hydrophobic effect of low w/c ratio mortar more significantly. The methyl siloxane groups in the hydrophobic powders will bind to the C-S-H gel in the mortar through Si-O bonding, preventing the C-S-H gel connections from forming a continuous network structure. This increased the pore volume and reduced the compressive strength by 14.6%-22.7%, but the total hydration degree was increased, and significant corrosion protection of the steel rebar was demonstrated. [Display omitted] • Super hydrophobicity of mortar was achieved by modification of hydrophobic powder. • Hydrophobic mortar with lower w/c ratio exhibits better anti-corrosion performance. • Methylsiloxane groups combine with C-S-H gel by Si-O enhancing hydrophobic properties of mortar. [ABSTRACT FROM AUTHOR]

The mechanical properties and durability of concrete are significantly affected by early frozen, during the early curing phase, concrete has a relatively low initial strength, and its hydration reaction rate is impeded by the early frost stage, leading to internal water freezing and subsequent expansive stress. The freezing and expansion deformations induce crack formation in the concrete structure. Even if positive-temperature curing is implemented for a specific period, some deformations remain irreparable, significantly compromising the mechanical properties and durability of concrete. Research on early frozen concrete mainly focus on water-cement ratio, freezing temperature, curing age, and additive dosage, which have different effects on the mechanical properties, durability, and microstructure of concrete. This paper systematically summarizes and analyzes the effects of early freezing on the mechanical properties and durability of concrete subjected to early frozen at home and abroad, and predicts and analyzes its future research directions and trends in this field. • Influences of early frost on the mechanical properties, durability, and microstructure of concrete are reviewed. • Effects of different admixtures and dosages on early frozen concrete are discussed. • The directions for further research on the effect of early frost on concrete are proposed. [ABSTRACT FROM AUTHOR]

Supersulfated cement (SSC) incorporates a significant amount of ground granulated blast-furnace slag (GGBS) and phosphogypsum (PG), which contributes to low carbon emissions and offers for extensive application. This paper investigated the evolution characteristics of performance and microstructure of SSC and Portland slag cement (PSC) pastes under Na 2 SO 4 solution attack and Na 2 SO 4 -HCl solution compound attack, including visual appearance, compressive strength, hydration products, pore structure and morphology. The results show that SSC group demonstrates superior resistance to Na 2 SO 4 solution compared to PSC group, which is reflected in no change in visual appearance over immersion time, a continuous increase in strength and stable hydration products. The pore volume (＜50 nm) of SSC increased after 270 days of erosion, while PSC experienced a sharp increase in pore volume (＞50 nm), which is also reflected in the compressive strength, with PSC (52 MPa) significantly lower than SSC (67 MPa). Na 2 SO 4 -HCl solutions significantly deteriorate both SSC and PSC groups. The strength of SSC remained 45 MPa from 28 to 180 days, decreasing rapidly thereafter, while PSC strength decreased rapidly after 90 days. Compound solution reduced alkalinity, resulting in the decalcification of C-S-H gel and ettringite decomposition. After 90 days of erosion in compound solution, the total pore volume of both SSC and PSC increased from 0.15 to 0.17 mL/g, while the pore volume (＜50 nm) of SSC was higher than that of PSC. Additionally, the strength and strength retention rate of SSC group were higher than PSC after 28 days of erosion. Therefore, SSC exhibits superior resistance to compound chemical attacks compared to PSC, especially for long term attack. • Supersulfated cement (SSC) exhibits better resistance to sulfate solutions compared to Portland slag cement. • Formed ettringite with high content and more stable in SO 4 2− ions environment elevates the properties of SSC. • The resistance to compound chemical attack of SSC is superior than Portland slag cement, especially for long term attack. [ABSTRACT FROM AUTHOR]

Ultrafine cement is widely used in micro-fracture grouting due to its very small particle size, and the expansion agent can improve the dry shrinkage and cracking phenomenon of ultrafine cement grouting materials, and at the same time produce self-stress to enhance the sealing effect, but at present, there are fewer researches on the hydration synergistic effect of ultrafine cement and expansion agent. For this reason, this paper explored the effects of two commonly used expansion agents, U-type and MgO-type, on the mechanical properties, hydration heat, hydration products and microscopic morphology of ultrafine cement materials. The results demonstrated that the expansion performance of MgO-type expansion agent (MEA) was better than that of U-type expansion agent (UEA); At the same time, the MgO-type expansion agent delays the exothermic cement hydration and inhibits the transformation of hydration products, and the stress concentration generated by its delayed expansion effect leads to brittle damage of the material. UEA participates in cement hydration and produces swelling crystals, and at this time, the specimen was mainly cemented in the form of particles, and the pre-generated internal expansion stress densifies the pore structure of ultrafine cement, which enhanced the mechanical strength of the specimen. • The effects of MgO and U-type expansion agent on the expansion and mechanical properties of superfine cement were analyzed. • The effects of U-type and MgO type expansion agent on the microstructure of ultrafine cement grouting materials were analyzed. • The relationship between hydration coordination and properties of superfine cement and expander was revealed. [ABSTRACT FROM AUTHOR]

This paper presents the effect of incorporating wollastonite microfibers and cellulose nanofibers on mechanical properties and microstructure of ultra-high-performance mortar (UHPM). Cellulose nanofibers of 0.005%, 0.015%, and 0.030% are combined with 4.8% wollastonite microfiber by weight of binder, which consists of 10% silica fume and 90% cement. Compressive and flexural strengths of the UHPM specimens are measured at 7 days. The microstructure is characterized in terms of SEM/EDX, XRD, FTIR, and nanoindentation. The results show the effectiveness of the fiber hybridization in enhancing the compressive and flexural strength of ultra-high-performance mortar with the improvement in flexural toughness and fracture energy by as much as 10% than control mortar. Moreover, hybrid fiber-reinforcement based on the microstructural analysis provided more synergic effect and uniform distribution of the fibers, thus developing an efficient micro crack bridging mechanism as well as resulting in enhanced toughening properties and an increased load carrying capacity. Additionally, the combination of wollastonite microfibers and cellulose nanofibers promoted the hydration reaction products and contributed a denser matrix between the fibers and cement matrix, resulting in an increase of the microstructure and interface area between the fibers and cement matrix. Nano indentation analysis also confirmed the increase of UHD C-S-H from 65% to 84% and lower percentage of anhydrous phase in ultra-high-performance matrix after combining wollastonite microfibers and cellulose nanofibers. • The hybridization of cellulose nano fiber with wollastonite microfiber increased the compressive strength of unreinforced mortar. • The greatest advantage in hybrid-reinforcement systems in ultra-high-performance mortar is the improvement in flexural toughness. • Hybrid reinforcement systems develop an efficient crack bridging mechanism as well as resulting in enhanced toughening properties and an increased load carry capacity. • The addition of wollastonite promoted a higher UHD C-S-H compared to the control specimen and other hybrid reinforced mortars. • Cellulose Nano Fibers enhance cement hydration due to the high specific surface area, in addition to the promotion of adhesion with cement paste and bonding properties when combined with wollastonite. [ABSTRACT FROM AUTHOR]

This paper proposes an innovative preparation measure for magnesium oxide (MgO)-based foamed concrete. Carbon dioxide (CO 2) foam has been introduced into the sample as a substitute for air foam, resulting in a novel formulation referred to as MgO carbon sequestration foamed concrete (MCFC). This innovation facilitates the setting and hardening of MgO-based foamed concrete under ambient conditions. Basic mechanical properties were tested at three different ages. At the age of 28 days, the resultant MCFC has demonstrated mechanical performance comparable to conventional Portland cement-based foamed concrete including unconfined compressive strength and stain-stress behavior. Through SEM NMR and X-ray CT, the MCFC sample exhibited an increasingly compact matrix and an evolving distribution of pore structure as time progressed. Furthermore, a comprehensive life cycle assessment has revealed that MCFC has the potential to reduce carbon emissions by up to 50% when compared to conventional cement-based foamed concrete. The results imply that MCFC presents itself as a viable alternative to conventional PC-based foamed concrete, offering equivalent mechanical performance while delivering superior environmental advantages for engineering applications. ● MCFC using MgO, soil and CO 2 foam is proposed to realize the sequestration of CO 2 and the reduction in carbon emissions. ● MgO and CO 2 react to generate carbonated phases, and CO 2 is consumed to realize its solidification. ● MCFC can consume and sequester CO 2 and avoid environmental pollution, portraying great social and economic benefits. [ABSTRACT FROM AUTHOR]

Soilcrete is produced by adding a curing agent, such as cement, to the soil and mixing it thoroughly to form a solid, stable substance, but usually with poor early strength. To improve the early strength and stability of soilcrete, in this paper, solid waste materials such as mineral powder, and natural gypsum powder were added proportionately to replace parts of cement (called composite curing agent). The unconfined compressive strength (UCS), and dry-wet cycle strength of soilcrete were tested to evaluate the optimum mix design. The scanning electron microscope (SEM) and XRD test were applied for investigating the mechanism of early strength of solid waste-based soilcrete. The results show that the optimal mix ratio of cement and mineral powder is 4:6, the 7-day UCS is 1.61 MPa, and the 28-day UCS is 3.37 MPa. The composite curing agent mixed with gypsum powder and water glass has a good curing effect on silt and clay respectively, and the 28-day strength of the clay specimen can reach 3.97. During the dry-wet cycle test, the strength of the soilcrete increases first and then decreases with the number of cycles. The SEM results show that the soilcrete particles were denser, had more hydration products, and the soil particle morphology changed from loose to aggregated, accompanied by a decrease in pores. The study provides a cheaper and high-performance composite curing agent based on solid waste materials for soilcerte than conventional cement, which can promote the application in such field. • An early-strength, low-cost solicrete was proposed using solid waste materials, namely mineral powder and natural gypsum. • The UCS (Unconfined Compressive Strength), dry-wet cycle strength, and soil types of soilcrete were tested systematically. • The mechanism of the new solid waste material on soilcrete was revealed through SEM, XRD, and hydration analysis. [ABSTRACT FROM AUTHOR]

Superabsorbent polymers (SAPs) have emerged as promising additives to regulate cement hydration via their intrinsic water absorption/desorption characteristics. This paper aims to investigate the influence of SAPs with different functional groups on the development of cement hydration and growth of calcium hydroxide (CH). The current experiment firstly uncovered the active control mechanism of CH in cement paste by SAPs, especially for the nucleation site and crystallization orientation. Specifically, the pores left behind SAPs after water release usually processed higher w/c ratio, Ca2+ concentration and smaller crystallization pressure, which jointly triggered the in-situ nucleation and crystallization of CH along (0 0 1). However, the hydration degree of cement paste was reduced by 0.1∼4.4% with addition of SAPs, especially in the early stage, which was attributed to that less free water can be used for cement hydration due to the strong water absorption property of SAPs. These insights provide a valuable foundation for deploying SAPs in an active control strategy for CH growth position and crystal form in cement-based materials. • The nucleation site and crystallization orientation of CH can be controlled by SAPs. • Higher w/c ratio, Ca2+ concentration triggers the formation of CH around SAPs. • The addition of SAPs reduced the hydration degree of cement paste by 0.1 ∼ 4.4%. • The addition of SAPs primarily affects hydration during the early stage. [ABSTRACT FROM AUTHOR]

Highlights • This paper investigate the effect of Poly AMPS grade SAPs on the properties of cement paste material for the first time. • In addition, this paper compares the effect of Poly AMPS grade SAPs and Commercial ones on the hydration process of cement based materials too. Abstract Preparation and characterization of superabsorbent polymers (SAPs) of poly (2-acrylamido-2 methyl propane sulfonic acid) with different ratios of cross-linker/monomer (0.0043, 0.0086, 0.014, and 0.028) and swelling capacity on Portland cement properties and its hydration were investigated. The comparison between poly (AMPS) and commercial samples (agriculture and hygienic grade of SAP) was studied too. Synthetic and commercial grade SAPs were studied with FTIR (Fourier transform infrared spectroscopy), swelling (in distilled water and saline solution (0.9% NaCl, with pH 7)) and AUL (absorbency under load) were measured completely. As a result, poly (AMPS) with 0.03 g of cross-linker has the highest swelling capacity (425.52 g/g and 66.18 g/g in distilled water and saline solution respectively) and poly (AMPS) with 0.06 g of cross-linker shows the highest AUL (13.2 g/g) among the synthetic and commercial samples. The hydrations of cement paste were investigated by means of XRD (X-ray diffraction) and FTIR spectroscopy in combination with thermo analytical method (TGA/DTG) (Thermo gravimetric Analysis). To determine the crystal size and porosity, SEM-EDX (Scanning electron microscope-Energy-dispersive X-ray spectroscopy) was used and also, rheology was used to determine the workability and efficiency of cement paste. As it is concluded, the hydration of cement paste with agricultural SAP is better than the others. TGA shows that the intensity at 7 day hydration time is the most. The cement paste contains poly (AMPS) based SAP with higher amount of cross-linker (0.2 g) and low swelling content has the best workability. And the cement paste contains poly (AMPS) with low amount of cross-linker (0.03 g) and highest swelling had the lowest porosity and the best distribution. From viewpoint of workability A4 is the best and from viewpoint of swelling and microstructure of cement A1 is the best. [ABSTRACT FROM AUTHOR]

Highlights • UCS of CCSAGP depends on granite powder content, cement content, and curing time. • Inclusion of 10–20% granite powder remarkably increases UCS of CCSAGP. • Grain gradation effect and chemical cementation effect are analyzed. • Field investigations on the integrity of deep mixing columns is performed. Abstract The harmless treatment and even the effective reuse of wasted rock powders have become immediate tasks for multiple stone fabricating plants. However, there are poor techniques at present used to dispose of wasted rock powders properly and scientifically. In this paper, the concept of cemented coastal silt admixed granite powder (CCSAGP) was developed to address the recycling of granite powder as well as to improve the strength of cemented coastal silt. The granite powder, as an admixture, was first admixed into the cemented coastal silt, and the development of strength in CCSAGP specimens was assessed experimentally. This paper focuses on the roles of granite powder content, cement content, type of cement, and curing time in the development of strength in CCSAGP specimens. The results obtained show that the unconfined compressive strength of the CCSAGP specimens increases generally with an increase in granite powder content, cement content, and curing time. The inclusion of 10%-20% granite powder into the cemented coastal silt is clearly conducive to the development of strength in CCSAGP specimens, but the development of strength depends upon a number of factors. The role of the type of cement in the strength development of CCSAGP specimens is related to the growth in cementitious products, which demonstrates significant time-dependence. Moreover, scanning electron microscopy (SEM) experiments demonstrate that the microstructural evolution of the CCSAGP specimens exhibits three main effects, namely, a grain gradation effect, a cementation effect and a skeleton effect. Field investigations suggest that the field strength of deep mixing columns with admixing 10%, 15% and 20% granite powder is well enhanced when compared with columns without admixing granite powder. [ABSTRACT FROM AUTHOR]

Highlights • CNTs and CNFs are both the nano-structured fibrous materials with excellent properties. • The dispersion of CNTs/CNFs is the decisive factor affecting the performance of composites. • The incorporation of CNTs and CNFs affects the variety performance of cement-based materials. • CNTs/CNFs-modified cement-based composites have broad application prospects. Abstract CNTs and CNFs are drawing widespread attention due to the unique structure and excellent properties, such as the mechanical property and the electrical property. It will significantly improve the cement-based composites' properties when adding CNTs/CNFs into composites. This paper briefly introduces the CNTs'/CNFs' basic properties and dispersion methods, and elucidates the properties of cement-based composites recombining CNTs/CNFs, including the mechanical property, the deformation property, the durability property, the thermal conductivities and electrical conductivities. This paper also summarizes the problems existing in present research, and gives some proposes for future study. [ABSTRACT FROM AUTHOR]

Highlights • Compressive strength at high temperatures of fibre concretes studied. • Influence of the high temperatures on the physical and chemical changes of the concrete studied. • Behavior of the new Dramix 5D steel fibre concretes in fire studied. • Model for compression strength at high temperatures of fibre concrete proposed. Abstract The high temperatures of fires affect the physical and chemical properties of the concrete and thus influence its mechanical properties. This paper presents the results of an experimental investigation on the compressive strength at high temperatures of high-strength fibre concretes. The influence of the high temperatures on the physical and chemical changes of the concrete was also analysed by Thermo Gravimetric Analysis/Differential Thermal Analysis (TGA/DTA), X-Ray Diffraction (XRD) and Scanning Electron Microscopy with Energy Dispersive Spectrometry (SEM/EDS). Five concrete compositions with different steel fibre contents and types have been tested: one without steel fibres (reference composition), two with Dramix 3D steel fibres and two with Dramix 5D steel fibres (45 and 75 kg/m3). This new type of steel fibres, the Dramix 5D, presents a double curvature at its ends, allowing a more efficient anchorage in the cementitious matrix. The behaviour at high temperatures of concretes made with these 5D fibres has been compared with the one of concretes made with the Dramix 3D steel fibres. Therefore, the impact of the high temperatures on the compressive strength and morphology of the high-strength fibre concretes made with the Dramix 3D and 5D steel fibres has been evaluated. The paper proposes also models for the compressive strength at high temperatures of the studied high strength fibre concretes. [ABSTRACT FROM AUTHOR]

Highlights • Self-consolidating concretes (SCCs) incorporating volcanic materials in a sodium sulfate environment. • It intends to use volcanic materials as a cement replacement of binary and ternary concrete mixtures. • SCCs incorporating volcanic materials would allow to obtain ternary SCCs that meet the qualification criteria for sulfate resistance. Abstract This paper examines the performance of self-consolidating concrete incorporating volcanic materials in a sodium sulfate environment. The volcanic materials used as a cement replacement of binary and ternary concrete mixtures in this research were Tolima, Puracé and Boyacá. The results were compared to those of standard SCC. The physical properties (density, absorption and porosity) and sorptivity of water were determined. The degree of sulfate attack was evaluated using dimensional variation, visual examination and compressive strength change of SCC specimens immersed in two exposure media (reference medium and sodium sulfate solution (5% Na 2 SO 4)) for different ages exposure. The microstructure was studied using Scanning Electron Microscope (SEM) coupled to EDS and X-ray Diffraction (XRD) analysis. This paper shows that the use of inert (Tolima) and pozzolanic (Puracé and Boyacá) volcanic materials results in SCCs with good sodium sulfate resistance. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the discovery of the most severe form of corrosion induced degradation of steel – delamination. The causes and effects of preferred corrosion of steel are quantitatively determined through a comprehensive experimental program and detailed analysis of steel microstructure. A large number of simulated corrosion tests are conducted by immersing steel in acidic solutions to acquire new understanding of the corrosion process of continuously cast steel. Three microstructural characteristics that affect the corrosion resistance of steel are quantified: grain size, phase composition and distribution of impurities. The results and their analyses presented in the paper indicate that preferred corrosion occurs at locations of steel where the grain size is larger; there is less cementite and more impurities. The analysis of causes and effects of the preferred corrosion provides insight into the prevention of preferred corrosion from the steel making process through to the delamination of steel in structures. This information could be used to predict, mitigate or avoid catastrophic failures of structures made of steel, potentially saving lives and resources, whilst advancing the knowledge in corrosion science of steel and improving the manufacturing process of steel. [ABSTRACT FROM AUTHOR]

Highlights • The paper presents the in situ compression test-XCT scan of foamed concrete. • The meso-scale modelling is directly reconstructed from XCT images. • Failure mechanism of foamed concrete is elucidated by XCT scan and the meso-scale modelling. • The meso-scale simulation shows a good agreement with the observation from XCT scan. • The paper provides a comprehensive framework to understand the behaviour of foamed concrete. Abstract Foamed concrete has been widely used in infrastructure construction and poses new challenges to design and modelling. This paper investigates the behaviour of foamed concrete with the help of X-ray Computed Tomography (XCT), which is capable of characterising the microstructure of foamed concrete. An in situ compressive test-XCT scan is carried out to observe the failure mechanism of foamed concrete by XCT when subjected to compression load. A meso-scale simulation based on XCT images is conducted to simulate the behaviour of foamed concrete. An algorithm that directly reconstructs the meso-scale model from XCT images is developed. The experimental and numerical results show that foamed concrete exhibits a significant change in mechanical behaviour; it is less brittle compared to the response of dense samples. However, the reduction in the level of brittleness is accompanied by a significant decrease in compressive strength. Failure development inside samples is successfully captured by the XCT scan and the meso-scale modelling. The topology of foamed structures, in particular the chain of interconnected pores, influences the failure mechanism of foamed concrete. The combination of XCT scan and meso-scale modelling provides a comprehensive framework to understand the mechanical behaviour of foamed concrete. [ABSTRACT FROM AUTHOR]

Highlights • This paper reviews techniques and analyses performed on microstructure of the asphalt binder and mixture using Scanning Electron Microscopy (SEM) and Environmental Scanning Electron Microscopy (ESEM). • The principle and techniques of SEM and ESEM, different sample preparation methods, used instrument techniques for different binder and mixture types, limitation of instrument and their effects on network structure, deformation mechanism, dispersion, phase and formation of fibril structures are discussed in this paper. Abstract This paper reviews techniques and analyses performed on microstructure of the asphalt binder and mixture using Scanning Electron Microscopy (SEM) and Environmental Scanning Electron Microscopy (ESEM). An extensive insight on the SEM and ESEM principle and techniques, different sample preparation methods and instrument techniques for capturing the micromorphology of the binder and mixture have been presented. The difference between SEM and ESEM in terms of challenges and limitation regarding the analysis of bitumen has been explained. In depth discussions on the surface properties, fracture morphology, network structure, dispersion, phase morphology, structural and strength mechanism, adhesion, deform mechanism and the formation of fibril structures of asphalt binder and mixture have been provided. Recommendations and useful techniques are outlined for future research to obtain any correlation between the microstructure and physical/rheological properties of the asphalt binder/mixture. [ABSTRACT FROM AUTHOR]

This paper aims to study the resistance of magnesium potassium phosphate cement (MKPC) paste to seawater erosion. MKPC paste specimens were prepared and their compressive strength, mass change, hydration temperature and water absorption were measured. The phase composition and microstructure were also analyzed. The results show that the initial hydration age of the reference sample M1 under natural curing condition has a significant effect on its compressive strength development in seawater. The residual ratios of the compressive strengths of M1(3d) and M1(28d), hydrated for 3 and 28 days, respectively, under natural curing condition, are 76.6% and 91.1% at 360-day seawater immersion age, respectively. This also indicates that early-age M1 has poor resistance to seawater erosion. Adding some limestone (LS) powders and silica fume (SF) can significantly improve the strength of early-age MKPC paste. The 3-day compressive strength of M2 with LS and SF is about 50% higher than that of M1. After immersion for 360 days in seawater, the residual ratios of the compressive strength of M2(3d) and M2(28d) are both close to 93%. This implies that initial hydration age of M2 under natural curing condition has almost no effect on its compressive strength development in seawater. Compared with M1, M2 has higher resistance to seawater erosion, which is attributed to the higher hydration degree and more compact structure of M2. This paper might be useful for preparing MKPC-based materials that can meet the requirements of marine concrete. [ABSTRACT FROM AUTHOR]

Long-term durability of concrete has been of interest for researchers in past decades, and throughout their numerous research endeavors, they have tried to improve durability with the application of different methods. One technique is the integration of a new material into the concrete. One material that has attracted great attention of researchers is nano-SiO 2 (NS). Its considerable performance in the enhancement of durability properties of concrete and mortar provides reasonable specifications satisfaction for scholars. In this paper, important durability characteristics of concrete, including the chloride ion penetration, electrical resistivity, water penetration, water absorption, the pore size distribution, the carbonation, the sulfate resistance, frost resistance, shrinkage, and thermal properties were explored. Additionally, the effects on the microstructure of concrete and mortar in the previous studies were discussed. Mechanical properties, such as compressive strength, flexural strength, tensile strength, and abrasion resistivity were also investigated in the past and most recent papers. [ABSTRACT FROM AUTHOR]

Research on quantification of the size and porosity of the interface between the reinforcing steel and concrete is limited in the current published literature. This paper presents a reliable and accurate method for quantification of steel-concrete interface using the technique of Backscattered Electron (BSE) imaging. Details of sample preparation procedure designed to minimize the damage to the steel-concrete interface due to grinding and polishing are presented. A new thresholding method to separate porous band at the interface from steel and cement pastes is proposed. It is found that there is a relatively wide porous band with large pores and voids near the steel-concrete interface. It is also found that the size of porous band around the steel bar is not uniform, and that the water to cement ratio can significantly affect the size and distribution of porous band at the interface. Quantification of steel-concrete interface as proposed in this paper is of importance in crack prediction of corrosion-affected reinforced concrete structures. [ABSTRACT FROM AUTHOR]

Bamboo structures are susceptible to natural weathering when exposed to outdoor conditions, making it imperative to comprehend the aging resistance of bamboo. In this paper, the study of Moso bamboo exposed to outdoor environment for one year illustrates the discoloration, expansion, mass loss and density reduction of the specimens. The changes of relative crystallinity (CrI) of bamboo were measured by using X-ray diffraction (XRD), the microstructural changes of bamboo were observed by scanning electron microscopy (SEM), and the computed tomography (CT) scanning technology was used to analyze the internal structure of the damaged specimens. Meanwhile, the damage and differences in the mechanical properties of bamboo internodes and nodes were evaluated by the tests of compression parallel to the grain, compression perpendicular to the grain and compressive elastic modulus parallel to the grain, taking into account the bamboo height. The results showed that natural weathering reduces cellulose crystallinity and has a detrimental effect on the cellular structure of bamboo, resulting in a weakening of the interfacial bonding between the vascular bundles and the parenchyma. Consequently, this leads to a decrease in the mechanical properties of bamboo. Compared to the internode specimens, the compressive strength perpendicular to the grain and compressive elastic modulus parallel to the grain are higher in the bamboo node specimens. However, the compressive strength parallel to the grain will be significantly reduced due to the complex fiber structure inside the bamboo nodes. In light of the experimental findings, a constitutive model is proposed to describe the relationship between uniaxial compressive stress and strain in Moso bamboo, both before and after weathering. The numerical results obtained from this model demonstrate a strong correlation with the experimental findings, thereby establishing a solid foundation for conducting finite element analysis on Moso bamboo structures. • The cellulose crystallinity and microstructural changes of weathered bamboo were analyzed. • Comparative studies were conducted to investigate the mechanical properties of weathered bamboo. • An axial compressive stress-strain constitutive model of weathered bamboo was proposed. [ABSTRACT FROM AUTHOR]

Incorporation of fibers can significantly enhance the mechanical properties, and crack resistance of geopolymer concrete (GPC). However, the alkaline environment in GPC can adversely affect the performance of fibers. To address this issue, this paper focuses on the surface modification of basalt fibers using a silane coupling agent (SCA) to enhance their compatibility with the geopolymer matrix. Macroscopic tests are conducted to analyze the workability, compressive strength, and flexural strength of geopolymer concrete, as well as the three-dimensional condition of its damaged surface. At the microscopic level, the fiber/matrix interface is investigated using scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) to reveal the enhancement mechanism of the modified basalt fibers (MBF). The experimental results demonstrate that the MBF significantly improves the flexural of GPC and has stronger impact on the degree of flexural deflection of the fracture surface compared to unmodified basalt fibers (BF). Physical aspects of SCA film: increases the roughness of the surface of basalt fiber, improves the mechanical occlusion at the interface between the fiber and the matrix and the transfer of concrete matrix stress. Chemical aspects: reduces the ground polymer matrix -OH ions on the fiber surface erosion, to ensure the stability of the SiO 4 tetrahedral network structure of the basalt fiber surface, increases the fiber and matrix interface at the densification, improves the chemical adhesion. In summary, the MBF effectively enhances the mechanical properties of GPC by optimizing the interfacial bond, enhancing cohesion, and improving the microstructure. These findings provide valuable insights into the potential application of SCA-modified basalt fibers as a promising reinforcement in GPC for sustainable construction and infrastructure projects. • The mechanism of silane coupling agent modified fiber-reinforced geopolymer concrete was investigated. • Both physical adhesion and chemical bonding aspects were studied experimentally. • The action mechanism of modified basalt fibers was elucidated through microscopic characterizations. [ABSTRACT FROM AUTHOR]

This paper covers the result of physico-mechanical, microstructural, optimization, and environmental impacts of alkali-activated paste (AAP) produced from recycled waste concrete (RWC) powder and metakaolin (MK). The experimental findings revealed that RWC powder up to 40 % effectively reduced setting time. The specimens with M s ratios of 1.25 and 2.00 had similar setting periods, while the mixes activated with 0.50 had greater setting time variance. The compressive strength significantly increased with an increase in RWC powder, and the mix formulated with 40 % RWC powder and M s ratio of 2.00 showed maximum strength of 79.1 MPa at 28 days. However, further inclusion of RWC powder beyond 40 % constantly decreased the strength. A statistically significant model to predict compressive strength was obtained by response surface methodology study, and the obtained optimum mix design (RWC=36.33 % and M s :1.89) was experimentally validated with an absolute error of 0.17 %. The microstructural analysis indicated that N-A-S-H type gels were the major reaction products, and the inclusion of RWC powder led to the generation of C-(A)-S-H type gels along with N-A-S-H type gels. Furthermore, an increase in the RWC powder ratio increased the crystallinity index values of AAP samples, as shown by X-ray diffraction results. Life cycle assessment (LCA) analysis was performed for all AAP mixes, including the optimum mix. LCA results indicated that the addition of RWC powder consistently reduced the CO 2 emission, cumulative energy demand, and cost of the resulting AAP mixes; however, these parameters slightly increased with an increase in M s ratio of alkaline solution. [Display omitted] • Investigation on AAP containing recycled waste concrete (RWC) and metakaolin (MK). • Compressive strength of paste mixes enhanced up to 40 % RWC powder substitution. • A statistically significant RSM model was obtained to predict compressive strength. • CO 2 emission and energy demand decreased with an increase in RWC powder ratio. • RWC powder can be used to produce economical and green building materials. [ABSTRACT FROM AUTHOR]

In the process of service, the coating is vulnerable to ultraviolet radiation, which leads to aging failure. The metakaolin base geopolymer coating studied in this paper has excellent mechanical and anti-corrosion properties through the previous mix ratio study. However, the UV aging resistance of the coating is unknown. In response to this issue, the present study devised UV aging experiments for metakaolin based geopolymer coatings. Employing UV irradiation in conjunction with EIS tests, the aging resistance of the geopolymer coatings was assessed through electrochemical fitting and analyses such as SEM. The study delves into the structural evolution of metakaolin based geopolymer coatings under UV aging conditions. After 500 h of ultraviolet irradiation, the resistance of the geopolymer coating is enhanced, its water diffusion coefficient is reduced, two orders of magnitude increase the resistance of the coating, and the protection performance of the geopolymer coating is enhanced. In the control group, the waterproof performance of epoxy resin decreased significantly, the impedance decreased, and the resistance decreased by three orders of magnitude. SEM results show that the post-curing of the coating under UV irradiation continuously generates NASH gels, and the coating microstructure is dense. The results show that geopolymer has strong aging resistance. • This experiment investigates the mechanism of UV ageing resistance of metakaolin base geopolymer coatings. • Comparison with epoxy resin coatings concludes that the geopolymer coatings have very good UV aging resistance. • The system of evaluating the water resistance and porosity of the coatings by capacitance method based on Fick's law of diffusion is applicable to the geopolymer coatings. • UV irradiation induces a post-curing reaction of the geopolymer coatings. [ABSTRACT FROM AUTHOR]

In order to enhance the application of epoxy mortar in pavement repair engineering, an epoxy-based repair material with short molding time, easy fabrication, high early strength and good durability was developed. In the past, the fillers of epoxy mortar were mainly fly ash and silica fume. In this paper used loess (LS) and river sand (RS) which were lower cost and more readily available, mixed with epoxy resin to make a new epoxy mortar system. The influence of epoxy resin mass fraction (20%,25%,30%), filler type (LS, RS), and LS-to-RS ratio (2:1,1:1,1:2) on the mechanical properties and durability of the epoxy mortar were investigated. It was observed that the early compressive strength of the specimens increased significantly with the increase of the proportion of epoxy resin in the mixture, reaching 49.2 MPa after 2 h of curing. Moreover, when the mass fraction of epoxy resin increased from 20% to 30%, the flexural strength increased by more than 20% after curing for 2 h. Additionally, compared to single filler, mortar containing both LS and RS exhibited superior durability. Unlike the specimens of the all-river sand group L0, which showed a 40% to 60% decrease in mechanical properties in sulfate and chloride saline solutions, almost no loss of strength occurred in the L1R1 group. This phenomenon can be explained by the findings from SEM and MIP tests that the L1R1 group has a more compact pore structure compared to the L0 group. [Display omitted] • Epoxy resin with loess and river sand to form a new pavement emergency repair material system. • Under the curing effect of epoxy resin, the compressive strength of epoxy mortar can reach 49.2 MPa for 2 h. • Epoxy mortar had excellent durability in water and saline solutions. [ABSTRACT FROM AUTHOR]

This study delves into the influence of various nanomaterials on the mechanical performance and durability of sludge-based geopolymer. In terms of overall strength, it was evident that nanosilica (NS), when introduced at the same doping level, exhibited the most significant enhancement in mechanical properties, surpassing nano-calcium carbonate (NCC) and graphene nanoparticles (GNPs). For instance, the addition of 2% NS resulted in a remarkable increase of up to 108.2% in compressive strength and 69.9% in flexural strength. Furthermore, the early reaction rate of sludge-based geopolymers was positively affected by the incorporation of NS, NCC, and GNPs. After 28 days, thermogravimetric analysis demonstrated that the mass loss for the reference sample and geopolymers enhanced with NS, NCC, and GNPs was approximately 15.06%, 14.78%, 14.85%, and 14.95%, respectively. Regarding durability, the sludge-based geopolymers displayed enhanced resistance to sulfate erosion and freeze-thaw cycles. This improvement was attributed to the ability of nanomaterials to fill pores and promote hydration reactions, resulting in a denser matrix. This paper delves into the influence of nanomaterials on the gel microstructure and gel micromechanical properties, shedding light on the mechanisms responsible for the enhanced mechanical and durability properties. It also presents a comparative analysis of results at different doping levels, offering a promising solution for waste treatment and carbon emission reduction, while making a compelling case for practical engineering applications. • First study of mechanical and durability properties of nanomodified sludge-based geopolymers. • Nanomodified sludge-based geopolymers can be used for practical engineering applications. • The mechanical properties of nanomodified sludge-based geopolymers depend on factors such as gel strength, pore filling and chemical bonding. [ABSTRACT FROM AUTHOR]

Fly ash is known as a common geopolymer precursor. However, it is important to search for suitable alternatives as the availability of fly ash will reduce with the move to more renewable energies. This paper evaluates the feasibility of using waste clay brick powder (WCBP) as a partial alternative for fly ash in geopolymer mortars with ground granulated blast furnace slag (GGBFS), under ambient and heat curing conditions. The physical, mechanical, and mineralogical properties of geopolymer mortar with 10 to 40% WCBP were investigated. Microstructural properties of WCBP and geopolymer mortars were investigated using X-ray fluorescence (XRF), X-ray diffraction (XRD), tescan integrated mineral analyzer (TIMA), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Reductions of the flow of fresh mortar were observed with the increase of WCBP. The highest 28 days compressive strengths were obtained in the mortars containing 40% WCBP, both at ambient and heat curing conditions. Microstructural analysis highlighted compact structure and reduced porosity, which are attributed to the role of WCBP in enhancing fly ash-GGBFS mortar properties by promoting geopolymer gel formation. • Characterization of Waste Clay Brick Powder (WCBP) showed its potential use as a geopolymer precursor. • The effect of WCBP on the mechanical and mineralogical properties of fly ash-GGBFS-WCBP geopolymer mortar was investigated. • High strength and a compact microstructure development could be achieved by using up to 40% WCBP. [ABSTRACT FROM AUTHOR]

Agriculture waste generation is increasing daily, and agricultural waste management has become one of the most challenging issues for many countries. To contribute towards a sustainable waste management system, this experimental study evaluates the impact of using agricultural waste materials in concrete. Concrete that does not harm the environment and has improved engineering properties can be produced using agricultural waste ash such as green gram pod ash. Green concrete has been examined for its mechanical, durability and microstructure properties when partially replaced with Portland cement by green gram pod ash (GGPA). Conducting various tests using concrete containing different weight proportions of green gram pod ash in a mix at 2%, 4%, 6%, 8%, and 10%, respectively. This paper examines the mechanical, durability and morphological characteristics of green gram pod ash blended with cement concrete. It has been shown that concrete containing 8% green gram pod ash enhances the properties of GGPA concrete. It was observed that the addition of 8% green gram pod ash enhances the compressive strength. Split tensile strength, flexure strength, modulus of elasticity and impact strength of concrete by 4.26%, 4.07%, 35.19%, 16% and 10.3% at 28 days of curing. It was concluded that green gram pod ash was shown to satisfy engineering application design requirements and significantly reduce concrete production costs and environmental pollution. The cement replacement with 8% of GGPA is optimum for achieving better concrete properties. • Evaluations of the impacts of using Green Gram Pod Ash (GGPA) in cement and cementitious material production were conducted. • Incorporation of Green Gram Pod Ash (GGPA) in concrete improves the strength and ductility performance of concrete. • Substitution level of GGPA in concrete should be limited to 8% (by weight) • GGPA concrete samples containing 8% green gram pod ash displayed maximum static modulus of elasticity and higher impact energy. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) surpasses normal strength concrete in engineering properties such as durability under extreme conditions, strength, and ductility characteristics. However, the dense structure, impermeable nature, and lack of capillary pores in ultra-high-performance concrete may diminish its resistance to spalling when subjected to intense heating conditions, unlike normal and high-strength concrete. The behavior of UHPC under such conditions has not been extensively researched, especially in the context of engineering properties and spalling behavior. Existing knowledge is primarily inferred from normal and high-strength concrete behavior under high temperatures, but this approach has sparked contention due to differing phenomena at play. Given ultra-high-performance concrete's distinct composition and excellent mechanical features, the principles applied to normal and high-strength concrete may not sufficiently explain its complex behavior during thermal exposure, particularly regarding spalling and engineering properties. Furthermore, enhancing its fire resistance becomes increasingly crucial as UHPC gains popularity in new and existing structures. To bridge this knowledge gap, this review paper presents various facets of UHPC during intense heat exposure, emphasizing engineering properties, fire-induced spalling, its factors, underlying mechanisms, microstructural analysis, performance, and preventative and remedial strategies. Future research recommendations are also offered to improve UHPC's performance under elevated temperatures, potentially leveraging current knowledge in the field. • Adding fibers can mitigate spalling in UHPC. • Dense microstructure of UHPC helps lower spalling. • Intense heat can cause explosive spalling, if not treated well. [ABSTRACT FROM AUTHOR]

This paper developed a cost-effective and highly carbonatable industrial-grade γ-C 2 S binder sintered from limestone and sandstone, aiming to advance the industrialization of γ-C 2 S binder in construction fields. The carbonation behavior of the industrial-grade γ-C 2 S binder, including the evolution of carbonation kinetics, compressive strength, phase composition, and microstructure with carbonation duration was studied. Results showed that a temperature of 1400 °C and limestone-to-sandstone mass ratio of 2.1 can be regarded as the optimal sintering regime, which can secure a relatively complete self-pulverization of industrial-grade γ-C 2 S binder. The industrial-grade γ-C 2 S binder had a milder carbonation reaction, which can reduce the evaporation of water and lead to 48% greater compressive strength, compared to that sintered from analytically pure reagents. During carbonation, the proportion of γ-C 2 S phase significantly decreased, while the proportions of CaCO 3 and silica gel notably increased in the first 1 h, followed with a slight change in proportions of those phases with the carbonation further extending to 24 h. Similarly, the degree of carbonation rapidly increased to 36.3% in the first 1 h, followed with a slight increase to 43.7% at 24 h. The carbonation of industrial-grade γ-C 2 S, accompanied with the precipitation of CaCO 3 on γ-C 2 S phase surface and the bond of silica gel among CaCO 3 grains, contributed to the formation of nacre-bionic interlocking brick-mud microstructure. This led to the rapid enhancement of compressive strength with carbonation of industrial-grade γ-C 2 S. • Industrial-grade γ-C2S binder from limestone and sandstone was sintered. • Industrial-grade γ-C2S showed a greater compressive strength after carbonation. • Limestone-to-sandstone mass ratio of 2.1 sintered at 1400 °C was the optimal regime. • Nacre-bionic interlocking brick-mud microstructure was formed during carbonation. [ABSTRACT FROM AUTHOR]

Geopolymer concrete has been increasingly used in industry. However, if the geopolymer concrete is blended using a single percussor its performance is often very limited by the properties of the percussor. Thus, it is preferable to use multiple percussors to produce geopolymer concrete. In this paper an experimental study is reported on the residual micro- and macro-mechanical properties of the steel-fibre reinforced geopolymer concrete blended by using combined percussors of ground granulated blast-furnace slag, fly ash, and salic fume. The experimental work included the examination of the effects of exposure temperature, the volume fractions of coarse aggregate and steel fibre on the compressive strength, elastic modulus, peak strain, toughness, and stress-strain constitutive relationship of the mixed geopolymer concrete, and the characterisation of the micro-structure of the materials after they were exposed to various elevated temperatures by using X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, and mercury intrusion porosimetry techniques. The experimental results showed that the residual compressive strength and residual elastic modulus decrease with the increase of exposure temperature regardless of the mix designs. The residual compressive strength of the geopolymer concrete is higher than that of the geopolymer mortar when they both are not reinforced with steel fibre. However, when they are reinforced with steel fibre the residual compressive strength of the geopolymer concrete is lower than that of the geopolymer mortar. Based on the experimentally obtained results, a temperature-dependent uniaxial stress–strain empirical equation is also proposed for the purpose of practical use. • Residual mechanical properties of GPM/GPC after exposed to elevated temperatures are reported. • Micro-structure and phase change of GPM and GPC after exposed to elevated temperatures are examined. • The effect of coarse aggregate on the residual mechanical properties of GPM and GPC is presented. • The effect of steel fibre on the residual mechanical properties of GPM and GPC is presented. • Residual stress-strain constitutive equations of GPM and GPC with and without steel fibre are proposed. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the influence of introducing calcium sulfate whiskers (CSW) and basalt fiber (BF) on the gas permeability coefficients of concrete. Employing the Cembureau method, the research quantifies gas permeability while utilizing Nuclear Magnetic Resonance (NMR) to precisely measure pore structure parameters. The results highlight that the incorporation of CSW leads to a substantial reduction in gas permeability, exhibiting a remarkable 57.6% decrease when utilized at a dosage of 3.0 kg/m³ compared to the standard concrete. In contrast, the introduction of BF at the same dosage does not yield a commensurate reduction in permeability. Notably, the combined application of CSW and BF at 3.0 kg/m³ each yields the most effective mitigation of gas permeability. Furthermore, the judicious addition of either CSW or BF demonstrates the capacity to diminish the overall porosity of concrete, alongside a reduction in the proportion of harmful pores (R 100 , featuring diameters larger than 100 nm). Optimal outcomes manifest when both CSW and BF are introduced at the 3.0 kg/m³ dosage, effectively minimizing R 100 and the gas permeability coefficient. It is interesting to find that in comparison to the correlation observed between the total porosity and gas permeability of concrete, the relationship between the proportion of R 100 and gas permeability emerges as more statistically significant (R 2 approximately 0.800), especially for CSW concrete. This can reveal the interconnection between the concrete's pore structure and its gas permeability characteristics more appropriately. • Optimal gas impermeability achieved with 3.0 kg/m3 of CSW and BF in concrete. • Optimal CSW and BF dosage mitigates total porosity and reduces harmful pores (R100). • Gas permeability coefficient has a strong correlation with R 100 proportion. [ABSTRACT FROM AUTHOR]

In the mudslide prone areas of western China, concrete piers were severely damaged by washing.In our previous research, the anti-abrasive UHPC prepared with saturated prewet high titanium heavy slag sand (ST-UHPC) is proposed to prevent such damage. And we studied the effect of grinding and erosion on the performance of ST-UHPC before, but the mechanism has not been studied in depth In order to study the microstructure evolution of ST-UHPC cement by the grinding and erosion, we use XRD, SEM, 27Al NMR, 29Si NMR test methods in this paper. By this way, we studied the effects of shock and salt erosion on hydration products composition, migration and transformation of Al-containing hydration products, hydration degree of cement and C-A-S-H gel microstructure. The results showed that the impact of bedload damaged the microstructure of UHPC. Then the damage of UHPC microstructure accelerates the transport of aggressive ions. Next, SO 4 2- erodes from the site of damage and produces expansive erosion products such as gypsum and calcareous vanadite. The erosion of SO 4 2- and Mg2+ resulted in the dealuminization and decalcification of C-A-S-H gel in UHPC cement and mechanical properties degradation. Thus, the expansion damage of UHPC and the impact damage of UHPC structure are aggravated. So the microstructure damage of UHPC was further aggravated. Under the action of impact, the water impacting material forms various chemical bonds with the C-A-S-H substrate. The chemical bonds results in the evolution of C-A-S-H microstructure. In conclusion, the structure of C-A-S-H substrate deteriorates obviously under the coupling effect of scouring and erosion. And the impact resistance of C-A-S-H substrate decreases significantly. • The anti-abrasive UHPC prepared with saturated prewet high titanium heavy slag sand was proposed. • XRD, SEM, 27Al NMR, 29Si NMR were used to study the microstructure evolution of ST-UHPC. • The microstructure evolution of UHPC was studied by molecular dynamics simulation. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) made of limestone calcined clay cement (LC3) exhibits excellent mechanical properties as well as good environmental friendliness. This paper studied the improving effect of nano-SiO 2 on the mechanical properties and microstructure of LC3-UHPC. The experimental results show that the addition of nano-SiO 2 demonstrates obvious advantages. The mechanical properties of LC3-UHPC are enhanced, and the frictional bond performance between steel fiber and cementitious matrix is also improved. The fiber/matrix bond strength is increased. A constitutive model describing the single fiber pullout behavior is established, and the values of related parameters are suggested. Besides, nano-SiO 2 also refined the cementitious microstructure of UHPC and made the matrix denser. Based on the comprehensive analysis of mechanical properties and microstructural characteristics, the optimal content of LC3 and nano-SiO 2 were proposed. [Display omitted] • The performance of LC3-UHPC was improved by using nano-SiO 2. • The microstructure of UHPC using nano-SiO 2 was optimized. • The fiber/matrix bonding behavior of LC3-UHPC was improved. • Comprehensive evaluation of the influence of nano-SiO 2 was conducted. [ABSTRACT FROM AUTHOR]

The hydration of cement-based materials, especially at early ages, directly affects the development of matrix strength and the later durability. In this paper, in order to explore the hydration behavior and microstructure of cement-based composites modified by low melting point Field's Metal Particles (FMP), inverted cone method, standard Vicatometer method, isothermal calorimetry, and compressive strength test, TGA, SEM, and XRD are used to investigate the fresh properties, heat of hydration, matrix strength, hydration products and transition zone between FMP and cement matrix. The results show that the incorporation of FMP can improve the fluidity of cementitious composites by 31.6%, due to the hydrophilicity of FMP. Meanwhile, due to the small heat capacity and large thermal conductivity of low-melting FMP, the heat stored in FMP is naturally released and used to promote hydration reaction when the hydration rate slows down. Additionally, FMP does not affect the types of hydration products in cement-based composites, but the total amount of hydration products increased at 7 d, especially calcium hydroxide (CH). Unexpectedly, FMP can reduce the compressive strength of the hardened paste, due to the large particle size of FMP than cement particles and the presence of directionally growing CH crystals in the interface transition zone between FMP and cement matrix. • Field's Metal (FMP) can promote the hydration and the generation of products at early age. • FMP can improve the fluidity of cement pastes. • Directional growth of calcium hydroxide is the main reason for strength reduction in cement pastes with FMP. [ABSTRACT FROM AUTHOR]

Producing limestone calcined clay cement (LC3) can reduce cement use and CO 2 emissions, but the availability and quality of clay and limestone pose challenges. This paper explores substituting these materials with seashell powder and engineering spoils for their high CaCO 3 content and cohesive clay. This study introduces the concept of shell powder-calcined slag cement (SCSC) and compares its properties with traditional limestone powder-calcined slag cement (LCSC). Results indicated that the 3d compressive strength of seashell powder calcined slag cement reached 29.19 MPa at 15% supplementary cementitious materials (SCM) dosage, which was 4.7% higher than that of limestone powder calcined slag cement at 27.87 MPa, and the 7d strength was 12.1% higher, which was attributed to the fact that calcium carbonate in seashell powder existed in a more active form. The addition of shell powder enhances the formation of calcium-rich compounds, leading to an optimized mineral phase composition in the ternary cement. Importantly, shell powder's impact on the heat of hydration, pore structure, and mechanical properties matches or surpasses that of limestone powder. Therefore, shell powder proves to be a viable substitute for limestone in ternary cement preparation. • Innovatively substituted limestone with seashell powder in ternary cement. • Created an eco-friendly, cost-effective new ternary cement material. • Seashell powder enhanced ternary cement's early mechanical properties. • Applied NMR first-time for pore structure study in ternary cement. • Seashell powder's role in stabilizing AFt in cement system confirmed. [ABSTRACT FROM AUTHOR]

Transforming phosphogypsum (PG) into β-hemihydrate gypsum plasters is one of the most effective and high-value-added pathways to consume and utilize PG. However, the relationship between the evolution of organic impurities and the properties of gypsum plaster is still unclear. In this paper, the composition and evolution of organic impurities, including pure organic matter (PO) by flotation and polyacrylamide (PA), were characterized, and their influence on the dehydrate behavior of PG and water requirement for normal consistency, setting time, mechanical strength, microstructure, and appearance of gypsum plasters at the calcination temperature of 150 °C and 200 °C were explored. The results showed that at 150 °C, PA and PO could increase the water requirement for normal and setting time of gypsum plaster and reduce the mechanical strength due to the reduced wettability and bonding strength causing by their intact structure and covering on HPG surface. At 200 °C, decomposed products of PO containing P-O-P and OH- groups could interact with Ca2+ and inhibit the dissolution of hemihydrate gypsum, resulting in coarsened crystals, thereby reducing the compressive strength. PA could partially decompose into the micro-molecular polymer and cover on the hydration products, leading to an increased densification compared to 150 °C. Besides, organic impurities could cause blackening, spots, and mildew on the gypsum plaster surface. • Relationship between evolution of organic impurities and properties of HPG was studied. • Organic impurities at different calcination temperatures plays a different role on properties of HPG. • Organic impurities delayed the setting and reduced the mechanical strength. [ABSTRACT FROM AUTHOR]

• CA is a commercial product in a powder form and up to 80 wt% of CA content is cement. • CA has little effects on fresh properties and mechanical strength of CA-cementitious composites. • Self-healing in wet/dry cycle has better efficiency than in water immersion or air exposure. • Mechanical recovery of specimens cured in freeze–thaw cycles is lower that by wet/dry cycle. • CA addition improves the resistance of sorptivity, permeability, and chlorides penetration. • The application of CA is a cost-effective method in crack self-healing of concrete. Crystalline admixture (CA) has garnered attention as a promising self-healing agent for cementitious composites. This paper aims to provide a compressive review on the effects of CA on the self-healing behaviours and durability properties of cementitious composites. CA is in powder form, consisting of Portland cement and special chemicals as self-healing stimulants. Since the powder-form CA was directly mixed with the cementitious mixture, CA addition has no significant impact on the properties of fresh concrete but enhances the compressive strength of CA-cementitious composites. Furthermore, self-healing is activated by moisture, resulting in the production of calcium-based self-healing products. In terms of crack closure efficacy, CA-cementitious specimens cured under wet/dry cycle demonstrated a higher crack closure ratio than those cured under water immersion or air exposure. Specimens cured in chloride solution exhibited the best healing recovery. However, reduced mechanical recoveries are observed in specimens exposed to freeze–thaw cycles and those in chloride solution, while better mechanical recoveries are found in specimens exposed to wet/dry cycles. Overall, CA can reduce the sorptivity, permeability, chloride penetration, and the depth of sodium ions penetration, offering favourable protection for cementitious composites. Although some durability properties of CA-cementitious composites have been explored, further studies are required to investigate potential effects on shrinkage, ingress of aggressive ions, carbonation, and alkali-silica reaction (ASR). The application of CA in cementitious composites could be considered as a cost-effective approach for inducing self-healing capability, given its affordable and straightforward construction process. [ABSTRACT FROM AUTHOR]

• The effects of polypropylene fiber, basalt fiber and rubber particles on the compressive strength of CCAB are analyzed. • The interaction of basalt fiber, polypropylene fiber and rubber particles on the strength of CCAB was studied. • The mechanism of the influence of the composite content of fiber and rubber particles on the physical properties of CCAB was elucidated. • The optimum content of basalt fiber, polypropylene fiber and rubber particles was determined. In this paper, the influence of basalt fiber, polypropylene fiber and rubber particles on the strength of cemented coarse aggregate backfill (CCAB) was deeply studied. Moreover, based on the engineering example, the optimal content of basalt fiber, polypropylene fiber and rubber particles is determined. The findings indicate that when utilizing mixed fiber and rubber particles to enhance the mechanical properties of CCAB, the reasonable content ranges for basalt fibers (BF), polypropylene fibers (PF), and rubber particles (RP) are 0.2 % to 0.6 %, 0.2 % to 0.4 %, and 5 % to 15 %, respectively. Among these additives, BF exerts the most significant influence on CCAB strength, followed by PF, while RP has the least impact. When BF content reaches 0.4 %, the addition of PF leads to a reduction in the compressive strength of CCAB. Fibers primarily enhance the macroscopic strength of CCAB by load dispersion and load sharing, while increased rubber particle content effectively fills void structures within CCAB, thereby improving its macroscopic strength. Based on engineering examples and fuzzy mathematics comprehensive evaluation model, the optimum content of the three types of admixtures is 0.4 % basalt fiber, 0.6 % polypropylene fiber and 5 % rubber particle. [ABSTRACT FROM AUTHOR]

• The mechanical, acoustic and microstructural characteristics of water glass cured sandy soils were analysed. • Mathematical models between mechanics, acoustics and curing time of the cemented body were developed. • The relationship between gel crystal structure and the macroscopic phenomenon was studied. • The factors influencing strength evolution and the formation mechanism were discussed. Water glass, which can be cured by rapid dehydration, is an ideal environmentally friendly material for engineering grouting solidification and ecological environment restoration. The curing efficiency of water glass at room temperature was low, the curing mechanism and strength characteristics at high temperature were not clear, and the engineering applicability and optimal curing methods were to be explored. In this paper, 10 curing paths were designed within 100 °C. The mechanical and acoustic characteristics of water glass-cured sandy soils were tested by uniaxial compressive tests and acoustic emission (AE). The relationship between strength, wave velocity and curing age was established based on the "logistics" model. The characteristic parameter "Q" value was proposed based on the AE characteristic value. Combined with the results of scanning electron microscopy (SEM), the solidification evolution process was revealed in terms of gel structure, crystal morphology and pore space. The process of water glass curing sandy soil was divided into a "strength rising period" and a "strength deterioration period". The enhancement and weakening effects of high temperature on the gel layer were stronger than those at room temperature. The longer the room temperature curing time is, the weaker the effect of high temperature on the specimen. After high-temperature curing, the maximum strength of the specimens increased by 107.85 %, and the strength growth rate and strength deterioration rate increased by 586.34 % and 3738.79 %, respectively. The conversion rate of the gel under high temperature conditions determined the strength of the specimen. The rate of strength deterioration of the specimen was determined by the hardening effect of the undehydrated gel and the excessive dehydration effect of the rigid gel. [ABSTRACT FROM AUTHOR]