Carbonation of Portland Cement Studied by Diffuse Reflection Fourier Transform Infrared Spectroscopy

Carbonation is a natural ageing process for cement. This study focuses on how the carbonation rate varies with selected hydration times and atmospheric conditions during the early stages of reacting dried cement paste. Diffuse reflection Fourier transform infrared spectroscopy is shown to be a suitable technique to monitor the formation of carbonates in cement. Combined with a previously developed freeze drying technique, carbonation can be studied at specific hydration stages. In ambient air both calcium hydroxide and calcium silicate hydrate (C–S–H) in cement are carbonated. Increased hydration time enhances the carbon dioxide uptake, which indicates that the calcium in the hydration products reacts more easily than the calcium in the clinker phase. In a humid CO2 atmosphere, the carbonation process is so pronounced that it decomposes C–S–H into calcium carbonate and silica. In a moist N2 atmosphere no carbonation occurs, but the sulfate chemistry of the cement seems to be affected due to the formation of ettringite

Managing Choice Uncertainties in Life-Cycle Assessment as a Decision-Support Tool for Building Design: A Case Study on Building Framework

To establish a circular economy in society, it is crucial to incorporate life-cycle studies, such as life-cycle assessment (LCA), in the design process of products in order to mitigate the well-recognized problem of the design paradox. The aim of the study was to provide means in a structured way to highlight choice uncertainty present in LCA when used as decision support, as well as to mitigate subjective interpretations of the numerical results leading to arbitrary decisions. The study focused on choices available when defining the goal and scope of a life-cycle assessment. The suggested approach is intended to be used in the early design phases of complex products with high levels of uncertainty in the product life-cycle. To demonstrate and evaluate the approach, a life-cycle assessment was conducted of two design options for a specific building. In the case study two types of building frameworks were compared from an environmental perspective by calculating the global warming potential, eutrophication potential, acidification potential, stratospheric ozone depletion potential and photochemical oxidants creation potential. In the study, a procedure named the Decision Choices Procedure (DCP) was developed to improve LCA as an effective tool for decision support concerning design alternatives when less information is available. The advantages and drawbacks of the proposed approach are discussed to spur further improvements in the use of LCA as a decision-support tool

Life Cycle Assessment of an Office Building Based on Site-Specific Data

Life cycle assessment (LCA) is an established method to assess the various environmental impacts associated with all the stages of a building. The goal of this project was to calculate the environmental releases for a whole office building and investigate the contribution in terms of environmental impact for different parts of the building, as well as the impact from different stages of the life cycle. The construction process was followed up during production and the contractors provided real-time data on the input required in terms of building products, transport, machinery, energy use, etc. The results are presented for five environmental impact categories and, as expected, materials that constitute the main mass of the building and the energy used during operation contribute the largest share of environmental impact. It is usually difficult to evaluate the environmental impact of the materials in technical installations due to the lack of data. However, in this study, the data were provided by the contractors directly involved in the construction and can, therefore, be considered highly reliable. The results show that materials for installations have a significant environmental impact for four of the environmental impact categories studied, which is a noteworthy finding

Monitoring Early Hydration of Cement by Ex Situ and In Situ ATR-FTIR – a Comparative Study

Diffuse Reflection Fourier Transform Infrared (DR-FTIR) spectroscopy has previously proven to provide time-resolved insights into early cement hydration spanning ~30 s to ~36 h after completing the mixing. Here, a previously validated ex situ freeze-dry procedure to stop hydration at preset times is complemented by an in situ Attenuated Total Reflectance (ATR) infrared spectroscopy method. The qualitative overall agreement between ex situ freeze-drying and in situ monitoring is demonstrated. Moreover, water conversion during hydration comes out clearly in the time-resolved ATR-FTIR spectra. This information is absent in DR-FTIR where buildups of crystal water and hydroxides are observed, while quenching of the hydration process requires removal of free water prior to acquiring the spectra. The ability of the IR technique to monitor the initial rate of hydration as a function of time is validated by comparing to calorimetry. The two approaches are understood to be complementary in that the former monitors alite grain surface hydration, while the latter reflects bulk hydration. IR is complementary to the calorimetry in cases of surface processes in conjunction with low enthalpy changes, that is, initial C–S–H formation and additive related surface chemistry

Insights into Early Hydration of Portland Limestone Cement from Infrared Spectroscopy and Isothermal Calorimetry

Isothermal calorimetry and diffuse reflectance infrared DR–FTIR spectroscopy are combined to correlate evolutions of spectroscopic signatures with rates of chemical reactions as reflected in the rate of heat emitted during the first 38 h of cement hydration. Portland limestone cement mortar is employed and the analysis is repeated for two different mixing procedures. Intensive blender mixing with quartz sand is found to cause activation of the cement resulting in a faster hydration process. At early stages of hydration, two types of C–S–H are formed. The spectral intensity of the earlier C–S–H is found to saturate, while that of the later form continues to acquire intensity throughout the 38 h of the experiment. Evidences are presented which support the interpretation that the two forms differ mainly in morphology and water content. Simultaneously with the saturation of the early C–S–H, a transient species is observed with DR–FTIR. This species correlates with the observed thermogram fine-structure

The influence of secondary effects on global warming and cost optimization of insulation in the building envelope

The relative environmental impact from the building construction phase is increasing compared to the operation phase for new buildings. Therefore, it is important to consider the complete environmental life cycle of energy improvement measures. Many advanced optimization methods have been developed in recent years to assess building life cycle impact. However, these previous studies have not fully addressed the secondary effects, in other words, indirect effects outside the actual design option. This may lead to conclusions of optimization studies based on misleading calculation results. The main purpose this study was to highlight the relevance of including secondary effects in optimization of building design with respect to global warming potential and cost. This was done by conducting a parameter study of the building envelope insulation thickness with regard to global warming potential and life cycle costs, while considering secondary effects induced by the different design options. Findings from this study show that secondary effects influence the system boundary, algorithm architecture, results and the final conclusions of optimal building design. Omitting secondary effects can thus lead to incorrect decision on optimal solutions with regard to global warming potential and life cycle cost. Therefore, it is therefore important to take them into consideration when performing optimization studies of building design options

Approach to manage parameter and choice uncertainty in life cycle optimisation of building design : Case study of optimal insulation thickness

In order to mitigate global warming, it is important to decrease the climate impact from the building stock, which accounts for 39% of the GHG emissions in Europe. An extensive portion of these emissions are generated from the heating of buildings, but emissions also occur from the production of building materials. It is therefore important to find building design solutions that consider both production and operation and maintenance in order to minimise the climate impact of a building during its entire lifetime. At the same time, the production of buildings has to be cost-efficient. In the design of buildings, both climate impact and cost must be evaluated in order to make well-supported decisions. The overall aim of this study was to develop a procedure to facilitate using life cycle studies as decision support for building design. The presented approach will provide a structured means to manage choice and parameter uncertainty when life cycle studies are used as decision support in order to optimise building design. There are many uncertainties in the design phase of buildings, and the approach is demonstrated here in a case study of insulation thickness in the building envelope. The results can be used to support decisions on where to effectively make improvements when subjective choices and parameter uncertainties are considered in the study. The suggested approach will lessen the problem of false certainty in the conclusions drawn, and at the same time provide strong decision support

Managing choice uncertainties in life-cycle assessment as a decision-support tool for building design : A case study on building framework

To establish a circular economy in society, it is crucial to incorporate life-cycle studies, such as life-cycle assessment (LCA), in the design process of products in order to mitigate the well-recognized problem of the design paradox. The aim of the study was to provide means in a structured way to highlight choice uncertainty present in LCA when used as decision support, as well as to mitigate subjective interpretations of the numerical results leading to arbitrary decisions. The study focused on choices available when defining the goal and scope of a life-cycle assessment. The suggested approach is intended to be used in the early design phases of complex products with high levels of uncertainty in the product life-cycle. To demonstrate and evaluate the approach, a life-cycle assessment was conducted of two design options for a specific building. In the case study two types of building frameworks were compared from an environmental perspective by calculating the global warming potential, eutrophication potential, acidification potential, stratospheric ozone depletion potential and photochemical oxidants creation potential. In the study, a procedure named the Decision Choices Procedure (DCP) was developed to improve LCA as an effective tool for decision support concerning design alternatives when less information is available. The advantages and drawbacks of the proposed approach are discussed to spur further improvements in the use of LCA as a decision-support tool

The importance of including secondary effects when defining the system boundary with life cycle perspective : Case study for design of an external wall

Life cycle assessment and life cycle cost analysis are suitable tools in trying to minimize environmental impact and cost. To get reliable results it is crucial to set up correct system boundaries for the investigation, but it is often difficult to understand a complex products system because of the cascade effects of consequences that can be induced even by small changes. In this paper the effects and consequences evaluation (ECE) method is introduced to systematically identify and organize the effects and consequences for a design change of parts of a complex system. The method is applied in a case study of external wall insulation for a new building to investigate the importance of correct system boundaries. Using the methodical approach in identifying all significant consequences showed that unexpected unit processes can be important when deciding on the relevant system boundary. We also conclude that such processes can have a significant impact on the final results by calculating the change in global warming potential and life cycle cost for the processes affected by the design option