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Alkali-activated materials (AAMs) are a kind of hardened slurry produced by an alkali activation reaction between a silicate precursor and an alkali activator that is treated as an environmentally friendly cementitious material that can be used in place of ordinary Portland cement (OPC). However, some studies point out that the AAMs with a single precursor had some defects. To realize the high value-added utilization of phosphorus slag (PS), this paper mixed PS with granulated blast furnace slag (GBFS) to prepare alkali-activated composite cementitious materials. The workability, mechanical properties, and hydration of alkali-activated phosphorus slag—granulated blast furnace slag (AAPG) were characterized using fluidity, setting time, compressive strength, flexural strength, hydration heat, XRD, FTIR, TG-DSC, and SEM + EDS. The results show that GBFS can improve the fluidity of AAPG, but the slurry will flash set after exceeding 20% GBFS content. GBFS can rapidly hydrate to generate C-S–H to improve its early strength, but the later stage results in larger pores due to the uneven distribution of matrix products. The hydration generation products of AAPG are C-S–H and C-(N)-A-S–H dominated by the Q 2 unit, with some hydrotalcite by-products generated.

Recently, industrial waste has grown drastically, causing several countries to investigate its usage. Recycling industrial waste in concrete is an efficient way to achieve sustainability while decreasing the environmental impact. This strategy not only improves the characteristics of concrete but also reduces building expenses. The current study focuses on using powdered burnt clay (surkhi), air-cooled blast-furnace slag (ACBFS), and ground granulated blast-furnace slag (GGBFS) as partial replacements for fine and coarse aggregates, as well as ordinary Portland cement. The research examines M40 grade concrete with a water-to-cement ratio of 0.36, utilizing three different percentages of cement and coarse aggregate replacements with GGBFS and ACBFS: 20%, 30%, and 40%. Additionally, fine aggregate is replaced with surkhi in three percentages: 10%, 20%, and 30%. Compressive and splitting tensile strength tests are conducted on different curing days for all mixes. The strength of the cube specimens ranges from 51.87 N/mm² to 69.71 N/mm². The optimum compressive strength of the concrete mix is observed to be 69.71 N/mm², achieved with 20% GGBFS and 10% silica fume, and the sample containing 20% ACBFS and 10% silica fume has the maximum splitting tensile strength.

Slag compositions are significant for the viscosity of blast furnace slag. An improved Urbain model (IUM) was proposed by introducing R5 ((X(CaO) + X(MgO) + 2X(TiO2))/(2X(SiO2) + 3X(Al2O3))) and N (X(MgO)/3X(Al2O3)) as the model parameters. By comparing IUM with other models, the model parameters of R5 and N are more reasonable and suitable for TiO2-bearing blast furnace slag, and IUM for predicting viscosity has a higher precision, and its relative error is only 10%. The viscosity isolines of the CaO–SiO2–15%Al2O3–MgO–2.5% TiO2 system were plotted, and the results show that the viscosity center of the slag is between Rw2 (w(CaO)/w(SiO2)) = 0.77–1.39 and Nw (w(MgO)/w(Al2O3)) = 0–1.37, the value of the viscosity center is 0.3 Pa·s, the viscosity increases gradually from the center to the outside, and the viscosity of the slag gradually decreases with the increase in Nw and Rw2. Furthermore, FTIR (Fourier Transform Infrared Spectroscopy) analysis was carried out in order to understand the mechanism between the slag structure and viscosity. With the increase in Nw and Rw2, the peak values of the symmetrical stretching vibration of non-bridging oxygen in the Si–O tetrahedral structure of slag decrease, and the slag structures depolymerize, which leads to the decrease in the viscosity of the slag.

Expansive clays undergo swelling when subjected to water. This can cause damage, especially to light weight structures, water conveyance canals, lined reservoirs, highways, and airport runways unless appropriate measures are taken. In this study, granulated blast furnace slag (GBFS) and GBFS-cement (GBFSC) were utilized to overcome or to limit the expansion of an artificially prepared expansive soil sample (sample A). GBFS and GBFSC were added to sample A in proportions of 5–25% by weight. The effects of these stabilizers on grain size distribution, Atterberg limits, swelling percentage and rate of swell of soil samples were determined. GBFS and GBFSC were shown to successfully decreasing the total amount of swell while increasing the rate of swell.

Ferronickel slag and ground granulated blast-furnace slag (GGBFS) are solid waste by-products from the metallurgical industry. When incorporated into concrete, they help promote resource utilization, reduce hydration heat, and lower both solid waste emissions and the carbon footprint. To facilitate the application of ferronickel slag–GGBFS concrete in 3D printing, this study examines how aggregate size and nozzle diameter affect its performance. The investigation involves in situ printing, rheological characterization, mechanical testing, and scanning electron microscopy (SEM) analysis. Results indicate that excessively large average aggregate size negatively impacts the smooth extrusion of concrete strips, resulting in a cross-sectional width that exceeds the preset dimension. Excessively small average aggregate size results in insufficient yield stress, leading to a narrow cross-section of the extruded strip that fails to meet printing specifications. The extrusion performance is closely related to both the average aggregate size and nozzle diameter, which can significantly influence the normal extrusion stability and print quality of 3D printed concrete strips. The thixotropic performance improves with an increase in the aggregate size. Both compressive and flexural strengths improve with increasing aggregate size but decrease with an increase in the printing nozzle size. Anisotropy in mechanical behavior decreases progressively as both parameters mentioned increase. By examining the cracks and pores at the interlayer interface, this study elucidates the influence mechanism of aggregate size as well as printing nozzle parameters on the mechanical properties of 3D printed ferronickel slag–GGBFS concrete. This study also recommends the following ranges. When the maximum aggregate size exceeds 50% of the nozzle diameter, smooth extrusion is not achievable. If it falls between 30% and 50%, extrusion is possible but shaping remains unstable. When it is below 30%, both stable extrusion and good shaping can be achieved.

The casting and testing specimens for determining the mechanical properties of concrete is a time-consuming activity. This study employed supervised machine learning techniques, bagging, AdaBoost, gene expression programming, and decision tree to estimate the compressive strength of concrete containing supplementary cementitious materials (fly ash and blast furnace slag). The performance of the models was compared and assessed using the coefficient of determination (R2), mean absolute error, mean square error, and root mean square error. The performance of the model was further validated using the k-fold cross-validation approach. Compared to the other employed approaches, the bagging model was more effective in predicting results, with an R2 value of 0.92. A sensitivity analysis was also prepared to determine the level of contribution of each parameter utilized to run the models. The use of machine learning (ML) techniques to predict the mechanical properties of concrete will be beneficial to the field of civil engineering because it will save time, effort, and resources. The proposed techniques are efficient to forecast the strength properties of concrete containing supplementary cementitious materials (SCM) and pave the way towards the intelligent design of concrete elements and structures.

The fresh and rheological properties of alkali mortars activated by blast furnace slag (BFS) were investigated. Consistency tests, squeeze flow, dropping ball, mass density in the hardened state, incorporated air, and water retention were performed. Mortars were produced with the ratio 1:2:0.45 (binder:sand:water), using not only ordinary Portland cement for control but also BFS, varying the sodium content of the activated alkali mortars from 2.5 to 15%. The results obtained permitted understanding that mortars containing 2.5 to 7.5% sodium present a rheological behavior similar to cementitious mortars by the Bingham model. In turn, the activated alkali mortars containing 10 to 15% sodium showed a very significant change in the properties of dynamic viscosity, which is associated with a change in the type of model, starting to behave similar to the Herschel–Bulkley model. Evaluating the properties of incorporated air and water retention, it appears that mortars containing 12.5% and 15% sodium do not have compatible properties, which is related to the occupation of sodium ions in the interstices of the material. Thus, it is concluded that the techniques used were consistent in the rheological characterization of activated alkali mortars.

After ordinary Portland cement (OPC) concrete, geopolymer concrete (GPC) is the most advanced form of concrete. GPC has many advantages including improved strength and durability properties. High early age strength and ambient curing of GPC helps to reduce the construction time. Factors such as binder materials, alkali-activated solution, and curing methods control GPC’s strength properties. Moreover, when industrial byproducts such as fly ash and ground granulated blast-furnace slag (GGBS) are added to GPC, this leads to advantages such as reduced carbon dioxide emission, ability to reuse of waste materials, thus saving valuable lands from getting converted into dump yards, cost reduction, and so on. Moreover, the energy required for the extraction of raw materials is also reduced. In this paper, GPC’s strength and durability characteristics, its mix design procedure, its effect of fibers on mechanical properties, and its structural performance are comprehensively reviewed. Moreover, the development of high-strength GPC using fly ash with sodium hydroxide as an alkaline solution under oven curing condition is highlighted. To develop GPC from different binder materials, trial and error methods are proposed. Rangan’s mix design procedure is used for fly ash-based GPC. Moreover, the inclusion of fibers, it was found, improves the ductile nature of GPC. Suggestions and scope for future GPC-related research are also included.Graphic abstract

For sustainable development in the construction industry, blast furnace slag has been used as a substitute for cement in concrete. In contrast, steel-making slag, the second largest by-product in the steel industry, is mostly used as a filler material in embankment construction. This is because steel-making slag has relatively low hydraulicity and a problem with volumetric expansion. However, as the quenching process of slag has improved recently and the steel making process is specifically separated, the properties of steel-making slag has also improved. In this context, there is a need to find a method for recycling steel-making slag as a more highly valued material, such as its potential use as an admixture in concrete. Therefore, in order to confirm the possibility of using electric arc furnace (EAF) oxidizing slag as a binder, a comparative assessment of the mechanical properties of concrete containing electric arc furnace oxidizing slag, steel-making slag, and granulated blast furnace (GBF) slag was performed. The initial and final setting, shrinkage, compressive and split-cylinder tensile strength of the slag concretes were measured. It was found that replacing cement with EAF oxidizing slag delayed the hydration reaction at early ages, with no significant problems in setting time, shrinkage or strength development found.

The challenges of handling user-hostile alkaline solutions in the conventional alkali-activated binders (AAB) have initiated the development of “just add water” or one-part solid-based AAB systems. This paper aims to present a preliminary investigation on the development of one-part ambient-cured alkali-activated binders produced by synthesising high-calcium fly ash (HCFA) and ground granulated blast furnace slag (GGBS) using sodium metasilicate anhydrous. Three test series were conducted in this study to investigate the effects of GGBS/binder, activator/binder and water/binder ratios on the fresh and hardened properties of the one-part synthesis AAB system. It was found that the SiO2/Al2O3 molar ratio plays an important role in the attainment of compressive strength and limits the amounts of solid activators effective in contributing to the alkali-activation reaction process. The optimum SiO2/Al2O3 molar ratio was found between 3.20 and 3.30. The test results revealed that the optimum proportion between HCFA and GGBS was discovered at a GGBS/binder ratio of 0.50. The optimum activator/binder ratio was between 0.08 and 0.12, and it is recommended that the water/binder ratio should not exceed 0.50. This study demonstrated the potential of the one-part synthesis method in the production of alkali-activated binder for practical structural applications.