Low Carbon Cement Research Articles

Effect of iron on the preparation of iron-rich calcium sulfoatablluminate cement using gypsum as the sole calcium oxide source and its incorporation into mineral phases

Iron-rich calcium sulfoaluminate (IR-CSA) cement is a low-carbon cement that contains small amount of aluminum. In this study, IR-CSA cement preparation method using gypsum as the source of calcium oxide was developed. The effects of iron on the decomposition of gypsum, formation of phases, microstructure of the clinker, and hydration of cement paste were investigated. The results indicated that the decomposition of gypsum and the formation of the target phase were first slightly promoted and then hindered when the iron content in the raw material increased. The presence of iron enhanced the growth of crystal grains and densification of the microstructure in the clinker. The early hydration behavior of IR-CSA cement mainly depended on the hydration of the iron-bearing ye’elimite and ferrous phases. Furthermore, the incorporation of iron into mineral phases was studied. The maximum incorporation content of Fe2O3 in ye’elimite and belite phase reached 19.36 wt%, expressed as C4A2.61F0.39S-, and 2.83 wt%, respectively. The chemical composition of the ferrous phase was similar to that of C4AF, and its mineral phases were C2F, C6AF2, C4AF, and C6A2F from the center to the edge. Finally, the feasibility of preparing IR-CSA cement using phosphogypsum as the sole calcium oxide source was evaluated for engineering applications. This unique preparation method reduces the use of aluminum in raw materials and thus promotes recycling of iron-containing or low-aluminum-containing industrial solid waste materials.

Influence of water repellent on the property of solid waste based sulfoaluminate cement paste and its application in lightweight porous concrete

• It is feasible to use water repellents reduce the water absorption of LPC based on SW-CSA cement. • The effect of water repellents on the properties of SW-CSA cement paste was presented. • Using calcium stearate as the water repellent doesn’t affect the hydration of SW-CSA cement. Solid waste-based calcium sulfoaluminate (SW-CSA) cement is a type of low carbon cement that uses solid waste as raw material. It is usually used to prepare lightweight porous concrete (LPC) due to its short setting time. However, high water absorption of LPC based on SW-CSA cement limits its extensive application. Water repellent can be mixed into binder material to reduce the water absorption of LPC, but it may affect the hydration properties of SW-CSA cement paste, which influences the performance of LPC correspondingly. Calcium stearate (CS), sodium oleate (SO) and sodium methyl siliconate (SMS) are three familiar commercial water repellents. To find the suitable internal mixing water repellent for LPC based on SW-CSA cement, the effects of three CS, SO and SMS on the water absorption, hydration, compressive strength, fluidity, and setting time of SW-CSA cement paste were explored. Besides, the properties of LPC with CS and SO added were also studied. The results indicated that using CS as the water repellent could reduce the 1 day water absorption of SW-CSA cement paste by 45.9% and the water absorption of LPC by 33.0%. It also reduced the setting time of SW-CSA cement paste and increased the final compressive strength of LPC, which was conducive to the preferred rapid setting and high compressive strength of LPC. The hydrophobicity of SW-CSA cement paste with SO was better than that of SW-CSA cement paste with CS. But using SO and SMS as the water repellent retarded the early hydration of SW-CSA cement and prolonged the setting time of SW-CSA cement and reduced the final compressive strength of SW-CSA cement paste. Therefore, SO and SMS can’t be used as the internal mixing water repellent of LPC based on SW-CSA cement, while CS is a promising internal mixing water repellent of SW-CSA cement to prepare LPC.

Effect of Low Temperatures on the Mechanical Performance of GFRC Modified by Low Carbon Cement

Glass fibre reinforced cement (GFRC) is a composite material with great ductility but it undergoes severe strength and ductility degradation with ageing. Calcium sulfoaluminate (CSA) cement is low carbon cement, and more importantly, it exhibits great potential to produce more ductile and durable GFRC. This study focuses on mechanical performance, e.g., compressive strength, stress‐strain curve, and freeze‐thaw resistance of CSA/GFRC as well as its microstructural characteristics under low temperatures. XRD was applied to investigate the hydration mechanism of CSA cement under −5°C, 0°C, and 5°C. It was found out that low‐temperature environments have very little effect on the type of hydration products, and the main hydration product of hydrated CSA cement cured under low temperatures is ettringite. Moreover, low‐curing temperatures have an adverse effect on the compressive strength developments of CSA/GFRC but the strength difference compared with that under 20°C reduces gradually with increasing curing ages. In terms of bending performance, both ultimate tensile strength and ultimate strain value indicate considerable degradation with ageing under low temperatures after 14 d. The ultimate strain value reduces to 0.34% at −5°C, 0.39% at 0°C, and 0.44% at 5°C compared with 0.51% for that cured at 20°C for 28 d. The tensile strength of samples cured at −5°C for 28 d is only 15.2 MPa, taking up only 40% of that under 20°C. CSA/GFRC also demonstrated great capability in the antifreeze‐thaw performance, and the corresponding strength remains 95.9%, 94.7%, 94.2%, and 94.3%, respectively, for that cured under 20°C, 5°C, 0°C, and −5°C after 50 freeze‐thaw cycles. Microstructural studies reveal that densification of the interfilamentary space with intermixtures of C‐A‐S‐H and ettringite is the main reason that causes the degradation of CSA/GFRC, which may result in loss on flexibility when forces are applied, therefore reducing the post‐peak toughness to some extent.

Comparative Analysis of the Oxyfuel and Calcium Looping Processes for Low-Carbon Cement Production

In this work, the performance of a cement plant with the integrated calcium-looping (CaL) system being developed in the H2020 CLEANKER project are simulated and benchmarked against alternative CO2 capture options, namely: (i) Tail-end CaL configuration (an end-of-pipe CaL option, with circulating fluidized bed reactors) (ii) Full Oxyfuel configuration (where both the pre-calciner and the rotary kiln are operated in oxy-combustion mode), and (iii) Partial Oxyfuel configuration (where only the pre-calciner is converted to oxy-combustion). Both CaL and oxyfuel options are integrated with a CO2 purification unit (CPU). The analysis performed shows that CaL systems provide greater CO2 reductions (both direct and indirect) than oxyfuel systems, but are subject to greater fuel consumption. The integrated CaL system shows better energy performance than the tail end CaL system (which is the most fuel consuming system) thanks to the presence of a single calciner. The full oxyfuel system shows the lowest SPECCA value among the systems studied but is penalized by the high electric energy demand. Finally, the partial oxyfuel system has lower electricity consumption than the full oxyfuel system, but it is the system with the highest CO2 emissions.

Toward a Tradable Low-Carbon Cement Standard: Policy Design Considerations for the United States

This paper outlines design considerations for an effective low-carbon cement standard in the United States, including how to set benchmarks and stringency, how to address leakage and competitiveness, and how to structure cost containment policies. A low-carbon cement standard offers several advantages as part of a broader climate change policy portfolio and can serve dual purposes: moving the market in the nearer term through existing technological opportunities while setting a clear regulatory roadmap to inspire long-term investment in deep emissions reductions. We envision that this publication will equip policymakers to consider such a standard as an element of relevant climate policy packages and help ensure that if it is included, it will be designed in a sensible manner based on our recommendations.

Techno-Economic and Off-Design Analysis of Two CO2 Purification Units for Low-Carbon Cement Plants with Oxy-Fuel Calcination

This paper presents the techno-economic assessment of the CO2 Purification Unit (CPU) included in cement plants based on CO2 capture via oxy-fuel calcination. Two configurations, targeting two different outlet CO2 specifications (‘moderate’ and ‘high’ purity), have been optimized in order to minimize the increase in the clinker production cost due to this process unit. Air infiltration rate is the parameter with the highest impact on the operational conditions (e.g. separation pressure) and on the incremental cost of clinker due to the CPU (up to 20% for the worst case considered). The work has been carried out within the framework of the CLEANKER project.

Pb-Zn Smelter Residue (LZSR) Stabilized Using Low-Carbon, Low-Cost Limestone–Calcined Clay Cement: Leachability, Chemical Speciation, Strength, and Microstructure

Abstract The low-carbon and low-cost cement known as limestone–calcined clay cement (LC3) is used in this study to investigate the immobilization potential of Pb-Zn smelter residue (LZSR). The perf...

Municipal Solid Waste Incineration Bottom Ash as Sole Precursor in the Alkali-Activated Binder Formulation

The concern about the large amount of weathered bottom ash (WBA) produced in waste-to-energy plants (WtE) has caused an increased search for alternatives to reduce their environmental impact. The present study aims to provide an added value through the WBA valorization from municipal solid waste incineration (MSWI) for its use as a sole precursor for developing alkali-activated binders (AABs). Alkali-activated weathered bottom ash binders (AA-WBA) were formulated with a liquid-to-solid ratio of 1.0 and using sodium silicate (80 wt.%) and NaOH (20 wt.%) at different concentrations (2, 4, 6, and 8M) as alkali-activator solutions. AA-WBA were cured at room temperature to extend their applicability. The effect of the alkali-activator solution molarity on the final properties of the AA-WBA was evaluated. The physicochemical characterization by XRD, FTIR, and SEM evidenced the presence of the typical phases (calcium silicate hydrate and gehlenite) of C-(A)-S-H gel. Leaching concentrations of As, Cu, and Mo exceed the acceptance in landfills for inert waste, while the leaching concentration of Sb exceeds the one for non-hazardous waste. The structure of the binders depends on the alkalinity of the activator, obtaining better results using NaOH 6M in terms of microstructure and compressive strength (6.7 MPa). The present study revealed that AA-WBA for non-structural purposes can be obtained. The AA-WBA formulation contributes to the WBA valorization and development of low-carbon cements; therefore, it is an encouraged alternative to ordinary Portland cement (OPC). Considering the amounts and costs of the WBA, sodium silicate, NaOH, and water, the total cost of the developed formulations is comprised in a range between 137.6 and 153.9 €/Tn.

Effect of CaSO4 batching in raw material on the iron-bearing mineral transition of ferric-rich sulfoaluminate cement

Ferric-rich calcium sulfoaluminate (FR-CSA) cement is a type of low-carbon cement. Common CSA needs to consume a large number of bauxite during the preparation process. In FR-CSA, Fe2O3 can act as an alternative for Al2O3 by shaping some iron-bearing minerals (Ca4Al2Fe2O10 (C4AF), Ca2Fe2O5 (C2F), and Ca4Al6−2xFe2xSO16 (C4A3-xFxS-)). In order to reduce the use of Al2O3 and optimize the iron-bearing mineral compositions in the FR-CSA clinker, this study investigated the effect of CaSO4 batching in raw material on the formation of C4AF and C4A3-xFxS- at 1250 °C. It was proved that CaSO4 plays an important role and the maximum incorporation amount of Fe2O3 could be 16.18 wt% in C4A3-xFxS-, thereof x in the subscripts being 0.33. With the CaSO4 contents in the targeted clinker increasing from 0 to 10 wt%, the effective utilization rates of both Al2O3 and Fe2O3 significantly increased. When the excess amount of CaSO4 was >10 wt%, the effective utilization rate of Fe2O3 increased but that of Al2O3 decreased. The findings in this research can contribute to the mineral optimization of FR-CSA cement clinker and the improvement of effective utilization of Al2O3 and Fe2O3. The production of high-performance FR-CSA cement becomes possible by the substitution of solid wastes containing relatively low Al2O3 content for bauxite.

Feasibility of Using Calcium Silicate Carbonation to Synthesize High-Performance and Low-Carbon Cements

Cement is the world’s most widely consumed man-made material and it contributes between 5% and 10% of the total annual anthropogenic CO2 emissions. Here, we report on a new method for producing cry...

Recycling of quarry dust for supplementary cementitious materials in low carbon cement

The main purpose of this study is to investigate the potential of using quarry dust as supplementary cementitious materials (SCMs) in alkali activated slag and Portland cement synthesis. The incorporation of quarry dust increased the early compressive strength of samples and led to a little detrimental impact on the compressive strength at 28 days curing. From the results of thermogravimetric (TG) and X-ray powder diffraction (XRD), there was nearly no change in the hydration phase assemble. Mercury intrusion porosimeter (MIP) indicated that the addition of quarry dust by 10–20% increased the porosity but decreased the average pore diameter after curing for 28 days. As a result, quarry dust shows great potential to be used as SCMs for low carbon cement preparation.

A Kinetic Study of the Pozzolanic Reaction of Fly Ash, CaO, and Na2O in the Preparation of Fly Ash Belite Cement.

Fly ash belite cement is a kind of low-carbon cement prepared by a two-step process involving hydrothermal synthesis and low-temperature calcination. Pozzolanic reaction pastes, as the precursors of fly ash belite cement prepared by hydrothermal synthesis, are affected mainly by reaction temperature, time, ratios of the mass of fly ash/lime (FA/CA), and the dosage of Na2O. The absorbance rate of CaO with reaction time was tested for all samples, and the reaction kinetic model and parameters of the granule-hydrothermal synthesis method were discussed. A kinetic model for the hydrothermal synthesis in the presence of Na2O was proposed based on the Kondo’s modified Jander equation and Arrhenius equation. The activation energy (Ea) of the process was determined to be 67.76 kJ/mol. In addition, with an increasing dosage of Na2O, the pre-exponential factor A of the Arrhenius equation increased. However, the hydrothermal reaction degree was accurately predicted using the kinetic model characterized by the absorption rate of CaO. The results indicated that Na2O, as an alkali activator, facilitated the diffusion of Ca2+ firstly, then partly dissolved the amorphous phase in the mixtures and, finally, accelerated the formation of poorly crystallized hydrates.

Decarbonising construction: Six things the industry could do

According to a new study by Arup, the University of Leeds and the international cities network, C40 Cities, a 44% reduction in emissions could be achieved in the procurement and construction process if the industry did six things: 1) used materials more efficiently; 2) used existing buildings better; 3) switched to lower-emission materials; 4) developed low-carbon cement; 5) recycled building materials and components; and 6) used low-emission construction machinery. Their thinking is explored here.

Sustainability assessment in Cuban cement sector- a methodological approach

The search of sustainability is a need for human activities in general. Particularly, cement sector as a significant contributor to climate change has to implement strategies to reduce its environmental impacts. But, effective strategies have to be complemented by adequate methodological techniques to assess, guide and certificate sustainability. Amongst all the techniques developed by the scientific community in recent years, life cycle techniques highlight as one of the most used one due to its integrated and holistic philosophy. In Cuba, a new cement based on a combination of calcined clay and limestone to reduce clinker to 50% (Low Carbon Cement, LC3) is been developed as part of an international collaboration project. The main goal of this research is to assess sustainability of cement sector in Cuba using life cycle techniques such as: Life cycle assessment (environmental-LCA), Social Life Cycle Assessment (S-LCA), Life Cycle Costing (LCC), Economic Life Cycle Assessment (EcLCA). As part of the assessment LC3 is compared with traditional produced cements in Cuba OPC and PPC. Results show that LC3 introduction allows increasing sustainability in cement sector by reducing carbon emissions, energy consumption, costs and reporting positive effects on society.

Ion Distribution at Steel/Concrete Interface in Steel Reinforced CSA Concrete by Newly Updated Image Analysis Technique

Calcium sulfoaluminate (CSA) cement is potential low-carbon cement; therefore investigation on ion exchange property at the steel/concrete interface is of great importance to understand the corrosion resistance and long-term durability properties of steel reinforced CSA concrete. Moreover, there is still a lack of standard procedure for quantitative imaging analysis in the study of cementitious materials so far. In this study, we developed an updated imaging analysis technique to investigate the atomic information in steel reinforced CSA concrete by using quantified elemental mappings. Microstructure of steel reinforced CSA concretes were characterized by SEM/EDX. The results indicated that there was less active ion distribution at the steel/concrete interface in CSA concrete than that for OPC concrete. Al/Ca ratio decreased over the interfacial zone gradually with ageing period of up to 1.5 years, but Al still dominated in the CSA concrete compared to the OPC concrete.

Development of a novel low carbon cementitious two stage layered fibrous concrete with superior impact strength

This study proposes a novel low carbon cementitious two stage layered fibrous concrete (LCCTSLFC) derived from clinker, flyash, calcined clay and steel fibres. In two stage fibre reinforced concrete (TSFRC), the volume of steel fibres together with coarse aggregates are pre-mixed and pre-placed into the mold. Henceforth, filling of voids in-between the aggregates is done by grouting that flows through gravity. The short and long steel fibres used throughout the thickness (layered), manufactured low carbon cement, X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis were considered here in. For the first time, this research develops the concept of impact resistance of LCCTSLFC under falling weight collision. For this purpose, short crimped fibres and long hooked end steel fibres were used in two stage layered concrete and tested as per ACI committee 544 guidelines. The results reveal that the proposed layered LCCTSLFC specimen shows superior impact strength compared to that of fully reinforced cross-section with equivalent dosages of fibre. This study emphasizes the potential to engineer a new layered LCCTSLFC with superior compressive and impact strength properties for the safety of civil and military infrastructure during terrorist attacks.

Effects of sodium sulfate on the hydration and properties of lime-based low carbon cementitious materials

To reduce the carbon footprint and energy consumption from the cement manufacturing industry, lime-based low carbon cementitious materials (LCM) has caught strong attention. LCM as a novel low-carbon cement shows impressive performance and promising prospects; however, its mechanical properties are inferior to those of ordinary Portland cement (OPC). In this study, different dosages of sulfate sodium was incorporated into LCM to investigate the effects of sodium sulfate on LCM performance. The properties and hydration of LCM with and without sulfate sodium were systemically investigated and analyzed. The results revealed that LCM blending with 2–3 wt% sodium sulfate showed the best mechanical performance. The compressive strength of LCM containing 3 wt% sodium sulfate was increased by 57.0% and 20.8% relative to the plain LCM at 3 d and 90 d, respectively. Microstructural characterization showed that a great amount of ettringite had formed at 3 d, which effectively improved the mechanical performance of LCM at early stage. Moreover, the addition of sodium sulfate effectively accelerated the hydration of the solid waste in LCM, and more hydrated lime was consumed in the hydration process. The ettringite became embedded in C(A)SH gel with increasing curing age, which resulted in a dense microstructure of hydrated paste with fewer coarse pores and an enhancement in the mechanical performance of LCM. Thus, the sodium sulfate effectively increased the strength of LCM at both early and later stage.

Properties of Cement Mortar Using Limestone Sludge Powder Modified with Recycled Acetic Acid

One of the various methods of manufacturing low-carbon cement is substituting limestone powder as a raw material or admixture. Limestone sludge powder (LSSP) has the same composition as that of limestone powder. The surface characteristics of LSSP powder modified with recycled acetic acid (RAA) and the characteristics of cement using this modified LSSP as a substitute were investigated in this study. The surface of LSSP modified with RAA was converted into calcium acetate and had a large grain size. When conventional LSSP was used as a substitute for cement, the initial strength increased owing to improved pore filling; however, the strength after 28 days of aging was lower than that of non-substituted cement. In the case of modified LSSP being replaced with cement at up to 10% of the cement weight, however, the calcium acetate on its surface increased the amount of hydration products in the cement, thereby increasing both the initial and the long-term strength.

Calcined clays for low carbon cement: Rheological behaviour in fresh Portland cement pastes

In this paper the rheological behavior of fresh Portland cement pastes mixed with different calcined clays was analyzed. For this purpose, two samples of Portland cement with different mineral composition (one with low C3A and high C3S content and another with low C3S and high C3A) were used combined with different replacement percentages of two calcined clays (two different metakaolin). Grounded α-quartz was used as control as well. Both mineral admixtures had different crystallinity and morphology: the α-quartz is fully crystalline while metakaolin is completely amorphous with a very small crystalline fraction giving very high pozzolanic properties in the vitreous state. All determinations were performed in the hydration latency period. The results show that the fresh Portland cement paste with low C3A(%) content and high C3S(%) content present great shear strength and the replacement with calcined clays affects the rheological behavior of the fresh pastes depending on the greater or lower pozzolanic reactivity of the mineral addition.

Low carbon cement manufacturing in India by co-processing of alternative fuel and raw materials

ABSTRACTCement production consumes 9.10% of the total industrial energy, thus making it the third largest consumer of energy. Each ton of cement generates approximately 0.7–0.93 ton of CO2 depending on the kiln technology used. The top 10 cement producing countries along with the European Union emits 1445 million tonnes of CO2 each year. Therefore, increased focus is given on different strategies of carbon mitigation. Co-processing is seen as one of the most prominent methodologies for making the cement manufacturing a low carbon process. The study shows low carbon manufacturing potential of cement plant in India based on the available literature and two case studies, considering economical and environmental sustainability. Co-processing leads to low carbon cement manufacturing process as traditional fuel and raw materials are saved and simultaneously waste going to the landfill gets reduced, thus making co-processing a holistic methodology for resource recovery.