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Due to the shortage of natural materials, using steel slag (SS) as replacement for natural sand to manufacture mortar has attracted worldwide attention and becomes a promising technology. This study aims at employing SS as fine aggregate for natural sand substitute in cement mortar synthesis. The measurement of expansion value generated by fine SS aggregate was performed by autoclave test. On the basis of further tests, the optimum content of SS fine aggregate was 25%. The autoclave experiment results indicate that the mortar bar was seriously damaged with higher dosages of SS fine aggregate. The X-ray diffraction (XRD) technique was offered to identify the mineralogical phases of the autoclaved SS. Additionally, this work investigated the printability of 3D printing mortar by assessing its fluidity, slump and mechanical strength. The printing mortar mixed with 25% SS was used in the printing of an actual 3D structure, demonstrating its feasibility to be used in 3D printing field. The microstructure and elements distribution were characterized by scanning electron microscopy (SEM) and the energy dispersive spectroscopy (EDS) techniques. The results showed that it is feasible to incorporate SS in 3D printing mortar, which contributes to the improvement of working properties and the enhancement of mechanical strength. This study provides a novel 3D printing SS mortar with good economic and potentially great environmental benefits.

This study illustrates the significant influences of rice husk ash (RHA) addition on the mechanical properties, freezing resistance and microstructure of alkali-activated slag (AAS) material. The results indicate that the incorporation of rice husk ash enhanced the compressive strength, and reduced the mass loss percentage and compressive strength loss percentage during freeze-thaw cycles, improving the freezing resistance of hardened AAS pastes evidently. The primary reasons for this optimization are the synergistic functions from the potential filling effect of RHA particles and gels enrichment in nature and content of AAS samples. The former refined the capillary pores definitely and the later was responsible for the development of compressive strength. However, the excessive contents (more than 20%) of rice husk ash did make a side effect on the development of freezing resistance and microstructure of AAS samples, which was likely related to the structure of rice husk ash itself. The dosage of rice husk ash used in AAS should be within 20% when considering the achievement of better comprehensive properties.

The air-cooled ferronickel slag is already selected as a raw material (aggregate) in concrete manufacturing, while the using as supplementary cementitious materials is still limited because of the high magnesium content. The objective of this study focuses on the practicality of air-cooled high-magnesium ferronickel slag (HMNS) blended Portland cement pastes, providing experimentally criterion for air-cooled HMNS's application. The different fineness on compressive strength and soundness of mixtures were investigated comprehensively. To be compared with the actual expansion of the HMNS blended Portland cement pastes, the mixtures containing MgO expansive agent addition (on the basis of the MgO content in the HMNS blended mixtures) were especially produced for autoclave expansion test. An optimum strength in practical application was obtained when the dosage of HMNS and its particle size were 20% and less than 50 μm respectively. The expansions of all mixtures were not only quite small (scattered around 0.09%) by traditional autoclave test, but the HMNS blended mixtures also exhibited the lower expansion when autoclave time is 6 h and 12 h. However, the expansive values of MgO expansive agent blended mixtures express more expansion than that of the HMNS blended mixtures in all autoclave times. This phenomenon was attributed to the form of magnesium in HMNS, where the primary phase of magnesium was clinoenstatite (MgSiO3) or forsterite (Mg2SiO4) and those phases showed inactive in this system by XRD, TGA and BSEM-EDS analyses. Therefore, HMNS used as supplementary cementitious material could not bring volume expansion, and this conclusion may present a great benefit to the recycling of HMNS in the field of construction materials.

It is difficult to treat dredged sludge with high organic matter content by solidification. A new solidification of dredged sludge with high organic matter content was developed, using cement, fly ash, slag, and phosphogypsum as a solidifier and strong oxidant KMnO4and GH as additives, to improve the engineering performance of dredged sludge and make it as a roadbed material possible. The properties of the solidified samples were determined in terms of unconfined compressive strength, products of hydration, toxicity characteristics, water stability, freeze-thaw resistance, and volume stability. The microstructure and hydration products of the dredged sludge after solidification were evaluated by X-ray diffraction analysis, scanning electron microscopy, and thermogravimetry-differential scanning calorimetry analysis. Experimental results showed that the strength of the solidified samples has been significantly improved after treatment by strong oxidants. The effect of GH is better than that of KMnO4. Hydration products (ettringite) were well formed. After solidification by using the binders and strong oxidant GH, the samples had sufficient strength and good water stability performance, freeze-thaw resistance performance, and volume stability performance. The leach liquid of the dredged sludge solidified body meets the standard requirements. So, the dredged sludge after solidification can reach the requirement of the roadbed material.

In this study, the effects of key design parameters, such as SiO2/Na2O mole module (Module), concentration of solute in alkaline solution (Concentration), liquid-to-fly ash mass ratio (L/F), and curing temperature on the geopolymerization process, set time, and compressive strength of high calcium fly ash geopolymer mixes were investigated. The geopolymerization process of these mixes was monitored using a semi-isothermal calorimeter at testing temperatures of 23 °C and 50 °C for 24 h. The results showed two major exothermic peaks generated during the fly ash geopolymerization processes. The first peak, the dissolution peak, appeared within the first hour after the fly ash was in contact with a liquid activator, and it did not vary very much with mix design parameters, while the second peak, the polymerization peak, varied largely in its amount and emerging time with mix design parameters of the geopolymers. As Module increased, the set time was accelerated but the total heat generated from geopolymerization and the compressive strength of the geopolymer were reduced. As Concentration increased, the set time for mixes with 1.0 and 1.5 Module prolonged but it was shortened for the mixes with 2.0 Module, while the total heat of geopolymerization and strength of these mixes were increased. Elevated curing temperature decreased the polymerization peak time, increased the total heat of geopolymerization, and improved the strength of the geopolymers. Additionally, the close relationships between the calorimetric characterization and setting time/compressive strength were obtained. To achieve optimal strength and setting behavior, it is recommended that a geopolymer mix made with high calcium fly ash shall be designed to have an activator with Modules ≤ 1.5, Concentrations of 20–25%, and L/F ≤ 0.40, and elevated curing (e.g., at 50 °C) is preferred.