Improving the environmental situation and obtaining green cement composites with new properties for various operating conditions is possible through secondary resources. This article is devoted to the criteria for evaluating the environmental impact of clinker-free cement. The methodological approach to selecting a functional unit for the comparative assessment of the ecological footprint of clinker-free cement is justified. The following are the findings from research on the characteristics of concrete that affect its endurance in harsh settings like transit building sites and livestock ranches. The usage of clinker-free and green cement in transportation and industrial construction will increase as a result of these findings, which will also help to develop an ecological approach to component selection for clinker-free cement and inform design choices in construction.
The issues of environmental protection through the development of technologies with low carbon dioxide emissions, using secondary resources, are becoming global. Cement and building materials production is an industry that can significantly contribute to the integrated processing of secondary resources. Cement composites account for the main share in the production of materials. Involving secondary resources in their production allows for improving the environmental situation and obtaining composites with new or improved properties.
Clinker-free cement, primarily represented by alkali-activated cement, consists of inorganic powder and an alkaline activator of hardening. Water solutions of calcined soda, sodium sulfate, sodium hydroxide, liquid glass, and similar substances can be used as alkaline activators.
Current studies on clinker-free cement focus on the theoretical and practical justification for obtaining new compositions based on multicomponent mineral raw materials from secondary resources for durable cement matrices. These studies aim to increase binder reactivity, reduce water demand, regulate phase and structure formation processes, and correlate these with processes determining internal corrosion of the matrix. This leads to increased physical and mechanical properties, which determine matrix durability. However, high strength alone is insufficient to ensure matrix durability; other properties determining material durability in required operating conditions must also be considered.
Examples of using alkali-activated slag concrete in challenging operating conditions, such as concrete for railway sleepers and livestock farm floor structures, highlight the environmental impact of these cement. Assessing the ecological effect of binders is crucial when developing their compositions and selecting components. The technology of clinker-free cement should address saving Portland cement clinker, recycling industrial wastes, and obtaining concrete with new and improved properties.
More publicly available data are now required for the quantitative evaluation of clinker-free cement’s environmental impact. There are several reasons for this dearth of information, including the lack of proof of effective use in difficult circumstances and the scarcity of knowledge regarding the industrial production of new cement. Additionally, independent assessments of environmental indicators are rare due to commercial restrictions. Manufacturers of clinker-free cements face barriers such as regulatory restrictions, slow adaptation of standards, and reluctance to use less studied materials, despite their technical and environmental advantages over Ordinary Portland Cement (OPC). Therefore, the construction material and technology choice should be based on technical and economic comparisons and their ecological impact.
Existing studies on assessing the environmental impact of cement are based on process-based life cycle assessments (LCA). The ISO14067 standard was developed for the quantitative evaluation of the carbon footprint (CF) of products, based on greenhouse gas emissions normalized to carbon dioxide equivalent (eCO2) and LCA methodology. The results of CF quantification are expressed in the mass of eCO2 per functional unit.
Published results on cement CF assessment vary significantly. Environmental advantages in these studies are attributed to various binders: clinker-free cement, low-clinker cement, and OPC. These varying conclusions are often due to differences in production technology (e.g., use of alternative fuels) or the need to transport components using high CF transport. These factors significantly alter the CF of products.
According to ISO14067, product CF is assessed to compare a product’s environmental impact on the climate and inform strategic or design decisions. Comparative results on the CF of different cement types may not be valid if various methods are used for product evaluations, which can impede the comparability of results.
Most studies on cement CF use a functional unit based on mass measurement units (kg or tons). However, researchers have shown that other characteristics, such as compressive strength, are also important. Accounting for compressive strength in a functional unit can significantly impact LCA study results. Cement with less clinker will always show less environmental impact using mass as a functional unit, although it may have much lower strength or service life. Therefore, the actual environmental performance of cement may be questionable, as most LCA studies of cement production use a mass-based functional unit.
To evaluate and compare the environmental characteristics of cement, it is crucial to consider its main properties, such as compressive strength and concrete durability. This approach will support the development of clinker-free and green cement, focusing on properties rather than composition. Revising the functional unit based on mass measurement units is necessary for meaningful cement and concrete comparisons, considering properties like compressive strength, service life, and thermal conductivity.
The authors propose that when choosing a functional unit for the quantitative evaluation of concrete’s carbon footprint, consideration should be given to the characteristics of the concrete that are necessary for particular operating environments. The authors propose that when choosing a functional unit for the quantitative evaluation of concrete’s carbon footprint, consideration should be given to the characteristics of the concrete that are necessary for particular operating environments. Based on feasibility studies and environmental impact assessments, comparative assessments should employ an identical methodology to justify the choice of cement type (Portland cement, clinker-free cement, etc.).
Current construction design standards provide for selecting cement and concrete based on feasibility studies. However, regulatory documentation should also include comparative environmental impact assessments of concrete. Such assessments can benefit projects using clinker-free and green cement in severe operating conditions.
This paper discusses the need to consider all concrete properties that determine its durability to assess the environmental impact of clinker-free and green cement. Selecting a functional unit for quantifying the carbon footprint of Portland cement and clinker-free cement should consider all concrete properties required for specific operating conditions. High strength alone is insufficient to ensure durability; other properties must also be considered.
Concretes based on clinker-free binders that have demonstrated required durability in real construction projects, such as flooring structures of livestock complexes and prestressed reinforced concrete sub-rail structures, justify the choice of a functional unit.
Laboratory tests show that concrete based on OPC had the least resistance, with bending strength reduced by half after 150 days in aggressive media. CEM III 22.5 and super sulfated slag binder had better resistance coefficients. The highest resistance (K = 0.90) was observed in the supersulfated slag binder composed of 80% ground granulated blast furnace slag, 20% phosphogypsum, and cement kiln dust as an alkaline activator (10% of the slag and phosphogypsum mass). The strength characteristics of OPC-based samples continued to decline until destruction, while those of supersulfated slag binders stabilized over time, indicating the attenuation of the corrosion process. This example shows that excluding clinker can improve concrete’s physical and mechanical properties and increase its service life in specific conditions. Thus, all four characteristics of concrete durability (compressive strength, flexural tensile strength, frost resistance, and corrosion resistance) should be part of the functional unit, leading to a decreased carbon footprint of clinker-free cement concrete used in livestock complex flooring structures.
Concrete based on alkali-activated slag showed compressive strength of 70 MPa, frost resistance of F600, and water resistance of 2.2 MPa, using granulated blast furnace slag with a basicity modulus of 0.8, and 78 MPa, F700, and 2.5 MPa, respectively, using slag with a basicity modulus of 0.9. These characteristics were comparable to concrete based on CEM 52.5, with values of 60 MPa, F600, and 2.1 MPa, respectively. These results indicate that a generalized functional unit, including compressive strength, frost resistance, and water resistance, is necessary for the comparative carbon footprint quantification of cement for specific concrete applications…LEARN MORE
Green Cement is in every way better than Portland ™
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