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Alkali-activated slag (AAS) presents a promising alternative to ordinary Portland cement due to its cost effectiveness, environmental friendliness, and satisfactory durability characteristics. In this paper, cow dung waste was recycled as a renewable natural cellulose fiber, modified with alkali, and then added to AAS mortar. The physico-chemical characteristics of raw and modified cow dung fibers were determined through Fourier transform infrared (FTIR), X-ray diffraction (XRD), and Scanning electron microscope (SEM). Investigations were conducted on the dispersion of cow dung fibers in the AAS matrix, as well as the flowability, strength, and autogenous shrinkage of AAS mortar with varying cow dung fiber contents. The results indicated that modified fiber has higher crystallinity and surface roughness. The ultrasonic method showed superior effectiveness compared to pre-mixing and after-mixing methods. Compared with raw cow dung fibers, modified fibers led to an increase of 11.3% and 36.3% of the 28 d flexural strength and compressive strength of the AAS mortar, respectively. The modified cow dung fibers had a more significant inhibition on autogenous shrinkage, and the addition of 2 wt% cow dung fibers reduced the 7 d autogenous shrinkage of the AAS paste by 52.8% due to the "internal curing effect." This study provides an alternative value-added recycling option for cow dung fibers as a potential environmentally friendly and sustainable reinforcing raw material for cementitious materials, which can be used to develop low autogenous shrinkage green composites. [ABSTRACT FROM AUTHOR]

The proper disposal of steel slag has always been a great challenge for the metallurgical industry in China and around the world. In this work, the steel slag aggregate (SSA) was surface pretreated (PSSA) and applied into asphalt mixture. The adhesive behavior between the bitumen and five different types of aggregates (i.e., limestone, diorite, diabase, SSA, PSSA) were evaluated based on the contact angle and binder bond strength tests. The pavement performance of three asphalt mixtures which contain normal aggregate, SSA and PSSA respectively, was analyzed by Marshall stability test, wheel-tracking rutting test, low-temperature bending creep test and water sensitivity test. The results showed that surface modification can improve the surface properties of SSA, reduce its contact angle with bitumen, and eventually lead to the improvement of adhesion between them. In addition to the satisfied low-temperature properties, PSSA was found to significantly improve the anti-rutting property and reduce the water sensitivity of asphalt mixture. This work is expected to promote an alternative application for recycling of SSA in pavement engineering. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation on the positive potential of steel slag (SS) to mitigate the autogenous shrinkage of alkali-activated slag (AAS) while maintaining a reasonably high strength. Changes of the physicochemical properties of AAS with the addition of SS were examined in terms of hydration heat, autogenous shrinkage, chemical shrinkage, internal relative humidity (RH) and mechanical behaviors. The microstructure of AAS-SS systems was characterized using X-ray diffraction, thermogravimetric analysis and nitrogen adsorption techniques. The shrinkage mechanism and quantification approach of the AAS-SS systems were discussed, in addition to a sustainability assessment. The results indicate that the 7-day autogenous shrinkage of AAS paste was decreased by 16 %, 35 % and 42 % when SS was incorporated by 15 %, 30 % and 45 % respectively, owing to the obviously slower hydration and higher internal RH at the early age. Meanwhile, the inclusion of SS substantially mitigates the chemical shrinkage and reduces the pores below 50 nm, thereby significantly decreasing the capillary pressure associated with smaller water-filled pore sizes. Substitutions of blast furnace slag by up to 45 % SS enable to reduce CO 2 emissions by 18.4 kg/m3 and decrease autogenous shrinkage by 42 % without obvious compromise in the loss of elastic modulus and compressive strength. • The steel slag shows a great potential to mitigate the autogenous shrinkage of AAS. • Adding 45 % steel slag has a minor impact on the elastic modulus of AAS. • Inactive C 2 S and RO phases decelerate the volume deformation of AAS-SS. • Under given capillary pressure the autogenous shrinkage of AAS is lower with SS addition. • The use of SS leads to considerable reductions in CO 2 emissions and materials cost. [ABSTRACT FROM AUTHOR]

The utilization of steel slag (SS) in the field of concrete remains limited due to its poor soundness. This work studies the long-term volume stability and strength development (up to 1 year) of engineered cementitious composites (ECC) containing high-volume SS. The result shows that the compressive, splitting-tensile and flexural strength of ECC containing SS begins to decline after 90 d, while the decline in the corresponding matrix is much higher. Especially, the matrix with 60 wt% SS loses its integrity by 360 d. The expansion of SS reduces the fracture toughness of the matrix, leading to an increase in toughness and ductility, while changing the cracking pattern of the ECC. Additionally, the introduction of ground granulated blast furnace slag (GGBFS) results in a decrease in volume expansion and strength loss of ECC caused by expansion of SS. Randomly distributed PVA fibers restrict volume expansion of ECC containing SS, while trapped air pores introduced with PVA fibers act as relievers, dispersing expansive stress. Combined introduction of GGBFS and PVA fibers leads to a 49.8 % reduction in expansive strain and a 126 % increase in compressive strength of ECC compared with the matrix with high-volume SS. [ABSTRACT FROM AUTHOR]

• The introduction of steel slag improves the flowability and fiber dispersion of ECC. • ECC containing high volume steel slag is not suitable for structural application. • The synergy of steel slag and GGBFS benefits achieving of strain-hardening behavior of ECC. • The material sustainability indicators (MSI) were proposed to assess material greenness of ECC. Engineered cementitious composites (ECC) achieve exceptional ductility and durability, but the heavy reliance on cement has notable environmental impacts. In this work, the steel slag (SS) and ground granulated blast furnace slag (GGBFS) are introduced into ECC by largely substituting cement. The impact of SS and GGBFS content on ECC's mechanical performance is analyzed at macro and micro scales in terms of fiber dispersion, mechanical properties, cracking patterns, cement hydration, and microstructure. The results demonstrate that SS can enhance fiber dispersion due to the low water demand and the strong electronic double layer formed on the surface of SS particles. While ECC with a high volume of SS alone (60 wt% SS) lacks the necessary strength for structural applications, the combination of GGBFS and SS exhibits favorable hydration properties and can effectively refine the pore structure. Thus, ECC with GGBFS and SS attains ideal toughness. ASTM C 1018 based toughness indices reveal that the I max of ECC with 30 wt% GGBFS and 30 wt% SS is 2.30 times that of OPC based ECC. A sustainability analysis demonstrates that substituting 30 wt% SS and 30 wt% GGBFS for cement leads to a 33% reduction in energy consumption and a 53% decrease in CO 2 emissions of ECC. [ABSTRACT FROM AUTHOR]

• The effects of SAP introduction on different properties of AAS are studied. • Different dosages and mixing ways (dry mixing and wet mixing) are considered. • SAP addition can improve the strength and impermeability of AAS mortar. • The frost resistance becomes better when more SAP is introduced regardless of the mixing way. Internal curing by superabsorbent polymer (SAP) has been applied in alkali-activated slag (AAS) systems by a few previous studies with the purpose to mitigate the autogenous shrinkage. However, the effects of SAP on other properties of AAS have been rarely studied. In this paper, the workability, strength, permeability, and frost resistance of AAS mortar with synthesized SAP are investigated besides the autogenous shrinkage. Two SAP introducing ways (dry mixing and wet mixing) are considered. It is found that the flowability of AAS mortar decreases with the increase of SAP dosage regardless of the introducing way. The strength and permeability increase with the SAP dosage when it is below a certain amount depending on the mixing way. The autogenous shrinkage can be mitigated significantly by the incorporation of SAP and the mitigating effect is more pronounced by wet mixing. The frost resistance becomes better when more SAP is introduced in either way. The mechanisms behind these phenomena are explained based on the characterization results on the reaction kinetics, reaction products and pore structure of the mixtures with SAP. [ABSTRACT FROM AUTHOR]

• Cementitious composites with ferronickel slag (FNS) were prepared. • The chloride penetration resistance was increased due to the inclusion of FNS. • The hydrotalcite of FNS cement pastes enhanced the chloride binding which can be described by the Langmuir isotherm. • The FNS facilitated the formation of amorphous C-S-H phases in cementitious systems. Sufficient utilizations of ferronickel slag (FNS), an industrial waste discharged from nickel smelting and stainless-steel production process, are essential under the background of sustainability development. In this work, the replacement of ordinary Portland cement by FNS and its influence on chloride penetration are systematically investigated. A range of measurements including RCPT, corrosion current, natural diffusion, pore structure and X-ray diffraction was carried out. The results show that the concrete pore structure can be refined with an appropriate dosage (up to 30%) of FNS, whereby a higher resistance to reinforcement corrosion and a reduction of electrical conductivity are found. With the inclusion of FNS the chloride binding capacity of cement pastes is enhanced and the binding behavior can be expressed by the Langmuir isotherm. The addition of FNS leads to a higher amount of amorphous C-S-H phases. The formation of hydrotalcite-like phases and the higher C-S-H content account for the enhanced chloride binding of FNS pastes. [ABSTRACT FROM AUTHOR]

• Alkali-activated nickel slag cementitious materials (ANC) were studied. • The effect of three alkali-activators on the performance of ANC was investigated. • Water glass-ANC possessed best mechanical behavior due to the finest pore structure. Comparisons between three alkali-activators (NaOH, NaOH/Na 2 CO 3 , water glass) on the performance of alkali-activated nickel slag cementitious materials (ANC) were made. The properties of ANC, including setting time, mechanical properties, morphology of hydration products and pore structure were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and nitrogen adsorption test etc. The average pore size and total pore volume of water glass-activated system (NS6) are the smallest, and then the NaOH/Na 2 CO 3 -activated system (NN42), and the average pore size and total pore volume of NaOH-activated system (NH6) are the largest. Interfacial transition zone (ITZ) between aggregate and hardened cement paste (HCP) decreased from large to small is in the order of NS6 > NN42 > NH6. The microcracks of NS6 in HCP is most obvious, and then the NH6, and the microcracks of NN42 in HCP is least obvious. The pore structure and ITZ play dominated role on mechanical properties, and therefore the compressive and flexural strengths of alkali-activated nickel slag mortar are ranked from large to small in the order of NS6 > NN42 > NH6. [ABSTRACT FROM AUTHOR]

A comprehensive study from detailed microstructure analyses to mass transport investigations was implemented to explore chloride penetration of unsaturated alkali-activated slag (AAS) mortars accounting for chloride binding behaviors. Unsaturated chloride penetrations reflected from diffusion cases of instantaneous plane source and sorption cases of wetting-drying exposure were elaborated in relation to solid hydrates and pore structure features. It is found that the specimen with lower saturation has a slower chloride diffusion but a larger chloride penetration under wetting-drying cycles. Slag mortars with sodium hydroxide activation exhibit higher chloride binding capacity owing to more hydrotalcite-like phases and higher Ca/Si ratio of C-(N-)A-S-H gels in the outer product zones as compared to sodium silicate activated slag mortars, regardless of the saturation. Accelerations of the chloride penetration under the wetting-drying exposure are limited in saturated AAS specimens while for unsaturated AAS specimens more wetting-drying cycles result in the inner layers to be gradually diffusion-controlled. The chloride binding capacity of AAS specimens follows Langmuir's isotherm and clearly decreases with a lower saturation. It is advised to consider the electrical double layer effect within narrow pores when applying rapid chloride migration tests for AAS systems. [ABSTRACT FROM AUTHOR]