7TH INTL. SYMP. ON SUSTAINABLE CEMENT PRODUCTION

This paper presents that the CO₂ footprint of cement can be reduced significantly by blending Portland cement clinker with thermally activated (calcined) clays (CCs). Investigations on pure meta phases obtained via calcination of kaolin, montmorillonite, illite and muscovite reveal that they increase water demand and decrease workability of the cement. The effect depends on fineness and internal porosity of the calcined clay and the chemical composition of the native clay, with illite and kaolin behaving much less favorably than montmorillonite or muscovite. A comparison of three industrial calcined samples of mixed layer clays originating from natural clay deposits in Germany, India and China confirmed the increased water demand of composite cements holding up to 40 wt. % of these calcined clays. The increase in water demand correlates well with the amorphous part and the content of meta kaolin in the calcined mixed layer clay. For one sample holding ~ 50 % meta kaolin, an increase in superplasticizer dosage of ~ 400 % as compared to neat OPC was recorded. Whereas, a high content of meta kaolin proved to be favorable with respect to early strength development as a result of its high pozzolanic reactivity. It can be concluded that calcined clays offer the potential of significant CO₂ reduction in cement manufacture, however this comes at the price of higher admixture dosages for superplasticizers. Still, a substantial savings in CO₂ emission can be realized, and the cement industry can progress into an era of more eco-friendly binders.

Conservation and reuse of natural resources in the construction industry are becoming crucial to maintain sustainable and environmentally friendly construction. The use of recycled aggregates (RA) and treated wastewater (TWW) in concrete has been widely studied in the literature over the past years. It has already been shown that replacing 20% to 30% of natural aggregates with RA and replacing TWW with tap water have negligible effects on the mechanical and durability properties of concrete [1-4]. However, only a limited number of studies were conducted to study the combined effect of using RA and TWW combined in concrete. In a study conducted by Tenjhay et al. [5], it was concluded that the use of RA and TWW combined in concrete is possible after additional research is conducted to study the durability. Therefore, the main aim of this study was to evaluate the mechanical properties and durability characteristics of concrete developed using 20% recycled aggregate and secondary treated wastewater subjected to different exposure conditions of tap water, treated wastewater, and salt water. Overall, the results showed that the use of 20% RA and TWW is only substantial on mechanical properties when concrete is exposed to either TWW or SW. The durability results on the other hand showed that all the mixes were considered durable in terms of chloride ion penetration (RCPT & resistivity results), however, additional tests are necessary to precisely study the impact of different variables on concrete durability.

Municipal solid waste incineration (MSWI) is a widely implemented waste management option. Although MSWI reduces waste volume by 90%, it generates considerable incinerator residues, namely, bottom ash and fly ash – the latter posing a greater challenge on account of containing leachable heavy metals, chlorides, and organic contaminant. On the other hand, the bulk of the fly ash’s composition makes it a rich mineral source for silica and lime, and potentially well suited as a raw meal in cement production. This paper presents a study on the feasibility of making green cement using three of the incinerator by-products: incinerator heat, residue ashes and carbon dioxide. The green cement can be synthesized exclusively with incinerator residues at incinerator heat temperature of 1000°C. The cement paste is then activated by carbon dioxide to produce strength. Municipal solid waste incineration can be turned into a green cement production. Paste compacts prepared from this material displayed a high CO2 reactivity, achieving an average compressive strength of 53 MPa and an average CO2 uptake of 6.7 wt. % after only 2 hours of carbonation activation at 1.5 bar. QXRD and QEMSCAN results identified the reactive phases to be chloro-ellestadite (Ca10(SiO4)3(SO4)3Cl2) and γ-C2S, which, upon CO2 activation, formed a binding matrix comprised of gypsum, calcium-carbonate precipitates, and a Ca-Si intermix. Leaching tests deem this cement non-hazardous as the monitored heavy metal concentrations in the leachate were well below regulatory limits. Concrete specimens prepared from the cement displayed comparable performance to Portland cement concrete, while additionally demonstrating a viable approach for waste utilization, carbon emission reduction, and natural resource preservation.

In recent years, the “greening” of cement and concrete has taken on a different path with a sharper focus on reducing carbon footprint while enabling companies and countries to benefit from carbon credits. It is only in 2012 that the first academic paper on the use of biochar – the solid by-product of pyrolysis or gasification – was published. In the following 9 years, biochar concrete has taken an upward trajectory in terms of academic research and commercial consideration. Two of the key reasons accounting for this popularity are that biochar is potentially a carbon negative material from the life-cycle accounting perspective [1], and that biochar is a widely available material that has primarily been used in agriculture (for soil enhancement) and for water purification.
This talk aims to demystify the near-decade long development of this young field of research, and summarize the key milestones in the growth path of this sustainable construction material. The different technical ideas and scientific technique used to achieve these milestones will be elaborated. For example, it was found that coating polypropylene fibers with biochar, and deploying these fibers to reinforce mortar, decreases water sorptivity of the mortar by about 44%, and water penetration by about 62%. Correspondingly, it increases 7-day and 28-day compressive strength by about 11% and 4.3% respectively [2]. When biochar was deployed evenly in the mortar mix without any fibers, biochar reduces water penetration by about 58.8% and increases 7-day compressive strength by about 13.8% [3]. Methods used for these studies include ASTM C1585-04 (Standard Test Method for Measurement of Rate of Absorption of Water by Hydraulic-Cement Concretes) and different characterization methods, such as Fourier Transform Infrared analysis for studying the surface chemical species found on biochar, and Brunauer-Emmett-Teller method for measuring pore size distribution of mortar samples containing different quantities of biochar.
These efforts have created several important areas of research, including the potential of using biochar as a mean of enhancing accelerated carbonation curing of concrete; that is, using biochar to increase the total amount of CO₂ that can be removed from the atmosphere through the process of carbonation of the calcium hydroxide and calcium silicate hydrate found in curing mortar mixture [4]. Latest evidence for the effectiveness of specially made biochar in improving electromagnetic wave (GHz) shielding of mortar tiles and application of biochar concrete under extreme environmental conditions (for example, using biochar to reduce the infusion of sulfate and chloride ions into mortar submerged in aqueous medium [5], and for increasing the “crack-resistance” of concrete operating under high temperature [6]) will also be presented.
This talk will end by boldly charting the future directions of biochar concrete and how it can continue to stay abreast and relevant, by addressing some of the most challenging sustainability-related problems facing the construction industry the world over.

SIPS is the flagship event of FLOGEN STARS OUTREACH, a not-for-profit, non-political and all-inclusive science organization. SIPS as well as FLOGEN STARS OUTREACH takes no sides in political, scientific or technological debates. We equally welcome, without reservations, all spectrum of ideas, theories, technologies and related debates. Statements and opinions expressed are those of individuals and/or groups only and do not necessary reflect the opinions of FLOGEN, its sponsors or supporters.

FLOGEN Stars OUTREACH | Home | Contact Us | Privacy Policy | Cancellations/Refund Policy
© Copyright of FLOGEN Stars Outreach Organization: The content of this page including all texts and photos are copyright of FLOGEN Stars Outreach and none can be used in their original or in any modified or combined form in any publication, web site or in any other medium whatsoever without prior written permission from FLOGEN Stars Outreach.