Development of Supplementary Cementitious Materials by Mechanochemical Activation Using Raw Materials from Hungary

The availability of industrially used supplementary cementitious materials (SCMs, e.g., fly ash) decreases due to the rise in renewable energy sources and recycling technologies. Therefore, it is essential to find alternative SCMs (e.g., waste glass and clay brick powder) that are locally available. Accordingly, in this paper, the mechanochemical activation of clay brick waste (CBW) with abrasive glass powder (GP) and its pozzolanic reactivity are investigated. The mixtures of CBW and GP in mass ratios of 100:0, 75:25, 50:50, and 25:75 were mechanochemically activated for 15, 30, 45, and 60 min. The physical, chemical, and structural changes of the mixtures were examined by X-ray diffractometry, Fourier-transform infrared spectroscopy, scanning electron microscopy, and specific surface area measurements. The pozzolanic reactivity was characterized by the active silica content and the 28-day compressive strength of the binders (a mixture of ordinary Portland cement and activated material). The addition of GP favorably reduced the agglomeration and increased the active silica content of the activated mixtures (e.g., by 7–37% m/m at 15 min of mechanochemical activation). The 60 min of mechanochemical activation and the addition of 50% m/m of GP can increase the compressive strength by approximately 8%. Economically, the addition of 50% m/m of GP was found to be favorable, where only 30 min of mechanochemical activation resulted in a considerable increase in strength compared to that of the ordinary Portland cement.

• The pozzolanic activity of natural clays was improved by mechanochemical activation (MCA) in a planetary ball mill. • Strength activity index (SAI) and Frattini test confirmed the increased pozzolanic reactivity after MCA. • XRD and SEM-EDX investigations confirmed the ability of the MCA-clays to act as pozzolans. • Mechanochemical activation can be considered a feasible and alternative method to enhance the pozzolanicity of poorly reactive clays. Replacement of cement with supplementary cementitious materials (SCMs) is a proven method to reduce clinker in cement and contribute to decreased CO 2 emissions. Natural clays are commonly occurring materials that do not possess pozzolanic activity in their original state. Mechanochemical activation (MCA) can be an alternative and sustainable method to enhance their reactivity. In this study, the pozzolanic reactivity of three natural clays, originating from Sweden, was analyzed after the application of MCA in a planetary ball mill. Strength activity index (SAI), Frattini test, and conductivity test were used to evaluate the pozzolanic reactivity. All processed clays by MCA have achieved a SAI greater than 100%, while the Frattini test indicated an improved pozzolanic activity of samples containing a higher amount of clay minerals. The obtained results show that MCA could improve the pozzolanic reactivity, but the effect depends on the mineralogical composition and particle size of the clays.

Mechanochemical and thermal activation of kaolin for manufacturing geopolymer mortars – Comparative study

The effects of silica fume and diatomaceous earth on the mechanochemical activation and pozzolanic activity of kaolin

Decarbonizing cement production

Some of the industrial solid waste materials, despite having sizeable quantities of silica and alumina, do not meet the requirements of a supplementary cementitious material (SCM) as per ASTM C618. Conversely, these materials may well be classified as alternative supplementary cementitious materials (ASCM) in accordance with ASTM C1709. Even though they have the potential of enhancing the properties of concrete and promoting sustainability, these materials are often underutilized in construction. In an asphalt batching drum plant, large quantities of waste silica-rich ASCM (SR-ASCM) are collected during the crushing and heating of limestone aggregates. Hence, the primary aim of this study was to find the feasibility of using SR-ASCM as a partial replacement of ordinary Portland cement (OPC) for developing structurally viable and durable concrete towards a sustainable future. The raw SR-ASCM obtained from the plant was characterized to determine its mineralogical and morphological properties. Subsequently, the engineering properties and durability of concrete synthesized by partially replacing OPC with SR-ASCM were thoroughly investigated. Based on the characterization results, SR-ASCM failed to qualify as an SCM; however, due to its sizable pozzolanic activity, it could be classified as an ASCM. Concrete with 15% OPC replacement achieved a compressive strength of 51.9MPa after 90days, comparable to the control mix (51.0MPa). There was remarkable resistance to chloride penetration in SR-ASCM-based concrete when the curing was extended from 7 to 90days, with a 36% reduction in the chloride migration coefficient. These outcomes show that the mechanical properties and durability of SR-ASCM concrete were either equal to or better than those of conventional concrete. This was probably due to the SR-ASCM's pozzolanic reactivity and physical influence on the microstructure. A substantial reduction in CO2 emissions in the range of 14 to 33% was achieved across different replacement levels of OPC by SR-ASCM. Promoting the integration of such materials in concrete will have significant socio-economic and environmental advantages.

This research investigated the physicochemical properties and pozzolanic reactivity of mechanochemically and thermally treated clay, marl, and obsidian as supplementary cementitious materials (SCMs). The results suggest that the mechanochemical treatment of clay and marl resulted in delamination, dehydroxylation, and amorphisation of the mineral components (including calcite); while for obsidian, the main effect was particle size reduction. Among all samples prepared, the mechanochemically treated obsidian exhibited the best performance as a SCM and achieved marginally higher strength performance at 20% cement replacement compared with the CEM I cement mortar (with on SCM). The thermally activated clay and marl exhibited highest pozzolanic reactivity than the mechanochemically treated counterparts owning to the formation of free lime from calcination of calcite. However, the mechanochemically treated clay and marl were still able to achieve over 80% of the strength activity index and performed much better than the untreated materials. These results indicate that mechanochemical treatment can effectively improve the pozzolanic reactivity of clay minerals that contain calcite up to 68% without directly emitting process CO2 to the environment (calcination of carbonates), which can be an alternative activation route to the high-temperature calcination-treatment method.

Reducing the environmental footprint of cement is an absolute necessity to meet the commitments of COP26 and to limit global warming to + 1.5°C compared to the pre-industrial level. In this context, particular interest has developed in recent years in the use of calcined clays as supplementary cementitious materials (SCMs). Due to their high reactivity, large reserves and homogeneous distribution on the earth's surface, calcined clays represent a viable alternative to conventional SCMs. Clay minerals are highly variable and numerous, each with their own characteristics. As a result, not all of them have potential for use as SCMs. The present paper investigated the use of palygorskite (a clay that has been relatively poorly studied) as an SCM. Two commercial palygorskites of different grades were selected and their calcination was studied by X-ray diffraction and pozzolanic activity tests. Blended cements incorporating 20% of each calcined palygorskite were prepared and the mechanical performance and resistivity of the mortars measured. The results show that the optimum calcination temperature is 800°C (allowing complete amorphization of the clay fraction and the highest pozzolanic reactivity) for both clays. Mortars made with 80% ordinary Portland cement (OPC) blended with 20% of 800°C calcined palygorskite allowed a significant increase in compressive strength and electrical resistivity compared to the reference (100% OPC). The clay sample with palygorskite as the dominant mineral exhibited the greatest pozzolanic reactivity and mechanical performance in cementitious systems, confirming that palygorskite is a clay mineral with a significant potential for a use as a SCM. The second sample with smaller palygorskite content also allowed a significant increase in mechanical performance. This demonstrated that it is not necessary to use high-purity samples and enhances the value of this type of material.

Contribution to low-carbon cement studies: Effects of silica fume, fly ash, sugarcane bagasse ash and acai stone ash incorporation in quaternary blended limestone-calcined clay cement concretes

Basic oxygen furnace slag (BOFS) is one of the major by-products of the steelmaking industry. Its limited utilization as a construction material is primarily attributed to its chemical properties, which hinder its stability and hydraulic activity due to its high free lime (f-CaO) content. This paper explores the performance of supplementary cementitious material (SCM) synthesized with ground granulated blast furnace slag (GGBFS), freshly produced BOFS (f-BOFS), and stockpiled BOFS (s-BOFS). A total of 10 mixtures with ordinary Portland cement (OPC) replacement percentages were assessed, maintaining a total replacement of 50% OPC, incorporating 15%, 25%, and 35% of each material by weight. The laboratory experimental program encompassed material characterization, fresh and hardened properties, pozzolanic activity, and durability assessment, with comparative studies conducted for each evaluation item. Test results indicate that f- or s-BOFS, when used with GGBFS, can be a viable alternative SCM with the potential for hydraulic activities and pozzolanic reaction. The newly synthesized SCMs demonstrated improved strength development in mortar mixtures. The mixture containing [15% f-BOFS + 35% GGBFS] achieved a 28-day compressive strength of 20.6 MPa, while the [25% BOFS + 25% GGBFS] blend reached a compressive strength of 19.7 MPa. These mixtures meet Grade 80 criteria as per ASTM C989/C989M Standard Specification for Slag Cement for Use in Concrete and Mortars. A performance-based ranking system was developed by integrating results from flowability, air content, strength activity index, drying shrinkage, alkali–silica reaction, and sulfate attack. The novelty of this work lies in assessing BOFS–GGBFS blends as SCMs using this multi-criteria approach to identify the most sustainable and technically viable mixtures. Moreover, the study highlights the influence of storage-induced weathering by directly comparing the reactivity and performance of f- and s-BOFSs in ternary blends, providing new insights into optimizing the utilization of slag. Notably, regardless of f- and s-BOFSs, proportions of [15% BOFS + 35% GGBFS] demonstrated superior strength development and achieved an excellent overall ranking. These findings confirm the potential of such slag blends as suitable SCMs for mortar and concrete applications, thereby advancing the sustainability and efficiency of cementitious materials.

Investigating the environmental and economic impacts of using supplementary cementitious materials (SCMs) using the life cycle approach

Enhanced pozzolanic reactivity in hydrogen-form zeolites as supplementary cementitious materials

Thermally and mechanically treated Greek palygorskite clay as a pozzolanic material

An effective method to make cement and concrete more sustainable is to blend them with the proper supplementary cementitious materials (SCMs). This study evaluates a pair of schist‐type materials with slightly different phase compositions, as a partial replacement for ordinary Portland cement (OPC). Materials received from several mines in ground powder form were studied by X‐ray diffraction, thermogravimetric analysis (TGA), and scanning electron microscopy. According to the TGA results, the activation procedures for the candidate SCMs were determined. The as‐received powders were heat treated in three different decomposition regimes (30%, 50%, and 80% of the total weight losses during thermal decomposition). These regimes corresponded to the activation level of the potential SCMs due to the de‐hydroxylation of the clay‐type minerals within them. Pozzolanic reactivity (pozzolanicity) of untreated as well as treated powders were estimated via electrical conductivity measurements in saturated calcium hydroxide solution. Blended cement pastes with 30 wt.% of OPC substituted with calcined clay‐type materials have developed mechanical properties equal to those of pure cement (100 wt.% OPC) paste after 28 days of hydration time. Two blended cement pastes prepared with candidate SCMs were compared to 100% OPC and OPC composite paste with metakaolin, which is regarded in the literature as a standard.

The need to reduce environmental impact inevitably leads to research on new, more sustainable construction materials. In recent times, the use of the main slags from the steel industry has been vigorously investigated; however, the use of other industrial by-products should also be considered. This study aims to analyze the viability of the use of value-added silicomanganese slag (siderurgical aggregates from ferroalloy industries) in two ways. On the one hand, the potential of ground silicomanganese siderurgical aggregates as a binder or supplementary cementitious material (SCM) due to their high content of silica and alumina. On the other hand, the use of silicomanganese siderurgical aggregates for the manufacture of concrete. The hydraulicity of the ground material has been determined by designing mortars with 20 % replacement of cement and comparing the mechanical performance with Portland cement and fly ash at different ages. Its application as a granulometric skeleton of concrete has been analyzed by comparing the physical-mechanical performance and docility in the fresh state with a conventional limestone aggregate concrete. The results obtained guarantee the pozzolanicity of the material, obtaining resistances similar to Portland cement mortar at 90 days. Furthermore, the material as an aggregate meets the geometric, mechanical and leaching requirements imposed by current regulations, although its use with almost total replacement leads to mechanical losses of 25–30 %. For this reason, its use is only recommended in small replacement proportions or in concrete for non-structural use.