Alternative Supplementary Cementitious Materials Research Articles

Proportioning of Oil Shale Ash for Sustainable 3D Printable Mortars

To achieve optimal strength and printability, mortars used in 3D printing typically contain high proportions of cement and other fine-grained powders. Consequently, the majority of mixtures used in 3D printing have high carbon footprint. Hence, there arises a critical need to study alternative supplementary cementitious materials aimed at reducing the environmental impact of mortars used in 3D printing. The use of oil shale ash as a partial substitute for cement not only addresses this issue but also presents an opportunity to repurpose waste from power plants in the Baltic states, where oil shale is intensively utilized.In this study, the influence on mechanical properties and durability of cement-based mortars was evaluated by substituting cement with oil shale ash in varying quantities. Specifically, 0% to 40% of cement mass was replaced with oil shale ash. Life cycle assessment (LCA) was performed for each mixture. By analyzing the material properties alongside the environmental impact for each mixture, the optimal percentage of substitute was determined.For the determination of the mechanical properties of each mixture, compressive and flexural strength tests were conducted on 3D printed samples in various directions, as well as on cast samples. To assess the durability of each mixture, freeze-thaw tests were performed on both 3D printed and cast samples.From the obtained results, we developed an algorithm that chooses the optimal mixture proportioning. Depending on material performance requirements set in the beginning, this algorithm gives the exact proportions of oil-shale ash and cement for the mixture, by taking into account both desired material properties and carbon dioxide emissions. As a result, an environmentally friendly cement-based mixture is obtained without losing the desired properties. By using this algorithm, it is possible to create a mortar with properties comparable to concrete with strength class C30/37 while reducing carbon emissions by 15% to 30%.

Pozzolanic Reactivity of High-Alkali Supplementary Cementitious Materials and Its Impact on Mitigation of Alkali-Silica Reaction

The growing scarcity of conventional supplementary cementitious materials (SCMs) such as Class F, Class C fly ashes, and slag has necessitated exploring alternative SCMs previously considered suboptimal. In particular, high-alkali SCMs are often avoided because of the potential concern that their alkali content could release into the concrete pore solution, thus exacerbating the potential for alkali-silica reaction (ASR). However, preliminary research indicates that not all high-alkali SCMs are deleterious, and some can effectively suppress the ASR expansive reaction when used in sufficient dosage levels. This study evaluates the feasibility of using high-alkali SCMs, such as high-alkali natural pozzolans and reclaimed fly ashes, focusing on their pozzolanic reactivity and the correlation between the reactivity and their ASR mitigation performance. The pozzolanic reactivity of the SCMs was evaluated by the R3 test per ASTM C1897 and strength activity index test per ASTM C311. Thermogravimetric analysis was used to determine the calcium hydroxide consumption by the SCMs. ASR mitigation performance of SCMs was evaluated in accordance with American Association of State Highway and Transportation Officials (AASHTO) T380 miniature concrete prism test. Additionally, pore solution expression and analysis of paste specimens were conducted to determine the correlation between the total alkali and the released alkali levels into the pore solution. Based on the results of this study, all SCMs indicated high pozzolanic reactivity; however, individual performance varied by test method. Ultimately, the high-alkali SCMs, particularly natural pozzolans, did not appear to release any significant levels of alkalis into the pore solution readily and, therefore, show potential for ASR mitigation when used in sufficient dosage levels.

Utilization of Recycled Brick Powder as Supplementary Cementitious Materials-A Comprehensive Review.

Over the past two decades, extensive research has been conducted to explore alternative supplementary cementitious materials (SCMs) in order to address the environmental concerns associated with the cement industry. Bricks, which are frequently preferred in the construction sector, generate a lot of waste during the production and demolition of existing buildings, requiring environmentally sustainable recycling practices. Therefore, many studies have been carried out in recent years on the use of brick waste as supplementary cementitious materials (SCMs) in cement mortar and concrete production. This critical review evaluates the impact of waste brick powder (WBP) on the mechanical and durability properties of mortar and concrete when used as a partial replacement for cement. It was observed that the properties of WBP-blended cement mortar or concrete depend on several factors, including WBP particle size, replacement ratio, pozzolanic activity, and mineralogical structure. The findings indicate that WBP with a particle size range of 100 µm to 25 µm, with a maximum cement replacement level of 10-20%, exhibits a positive impact on the compressive strength of both mortars and concretes. However, it is crucial to emphasize that a minimum curing duration of 28 days is imperative to facilitate the development of a pozzolanic reaction. This temporal requirement plays a vital role in realizing the optimal benefits of utilizing waste brick powder as a supplementary cementitious material in mortars and concretes.

Reactivity of Calcined Clays as SCM-A Review.

Calcined mixed clays are one of the most promising alternative supplementary cementitious materials. However, their standardized use is difficult due to the wide range of compositions of the raw materials. The reactivity potential of different clays can hardly be estimated on the basis of simple characteristics so far. This review aims to identify and compile the factors that determine reactivity. At first, an overview of the methods to evaluate reactivity is presented in order to provide a definition of this term. Subsequently, the reactivity-determining factors are compiled and subdivided into the characteristics of the raw material (chemical and mineralogical composition), the parameters of calcination (furnace type, temperature, grain size, retention time, and cooling), and the characteristics of the calcined material (physical properties and amorphous phase). Interrelations are discussed qualitatively. In the second step, a quantitative literature analysis was conducted to quantify correlations between the different factors and reactivity. However, since the characterization methods in the literature are very different, the data can hardly be analyzed quantitatively. Consequently, this paper points out what information is needed to conduct profound, comparable studies to evaluate the reactivity potential of clays.

Avaliação mecânica e cinética de hidratação de pastas de cimento com fíler dolomítico

Abstract The scarcity of high-purity limestone subjects the cement industry to consider alternative supplementary cementitious materials for cement production. This research aimed to investigate the mechanical properties and the hydration kinetics of cement pastes in the presence of high levels and different fineness of dolomite, especially the formation of thaumasite. A dolomite filler with 20% magnesium oxide, with average diameters of 10 µm, 6 µm and 4 µm was used as a partial replacement for Portland cement at 0%, 15% and 35% in cement pastes cured at 5 ºC and 20 ºC. The results of compressive strength showed similarities in all pastes analyzed, but the fineness of the dolomite showed a significant difference between the strengths obtained. The isothermal calorimetry indicated that the presence of dolomite had a nucleation and dilution effect. The thermogravimetry revealed that dependent of the substitution levels, the pastes with dolomite presented significant differences in the amount of ettringite and carbonate phases. The mineralogical analysis detected the presence of thaumasite only at the temperature of 20 ºC, which this mineral can also form at higher temperatures than those reported in the literature. Finally, we conclude positively about the possibility of using dolomite in cementitious matrices at levels up to 35%, regardless of fineness and curing temperature.

Hydration characteristic and strengthening mechanism of municipal solid waste incineration fly ash cementitious composites modified by nano SiO2

As a by-product from the incineration of municipal solid waste (MSW), the incineration fly ash (MSWIFA) possesses potential hydration reaction activity and could be as an alternative supplementary cementitious material (SCM). In this study, 85 wt% cement and 15 wt% MSWIFA were blended to prepare the MSWIFA cement-based composites. Nano SiO2 (NS) was added at varying dosages to strengthen the performance of the composite materials. The fresh and mechanical properties of the nano SiO2-modified MSWIFA cement-based composite (NMCC) were examined to determine the optimal NS dosage. Moreover, the hydration behavior, phase composition, pore structure, and microstructure morphology of the NMCC were examined to dissect the hydration characteristic of NMCC and the strengthening mechanism of NS. The results showed that NS significantly accelerated the hydration process of the NMCC, reflected by a higher hydration degree, the formation of more C-(A)-S-H gels formed, and superior mechanical properties. MSWIFA bestowed the NMCC with a high alkali content, which was beneficial to accelerating the hydration process. However, a low silicon content in MSWIFA failed to provide sufficient [SiO4]4- to react with Ca(OH)2 to produce C-(A)-S-H gels. This problem was effectively addressed by the addition of an optimal dosage of NS, which was rich in silicon element, so as to compensate for the decline in MSWIFA performance caused by insufficient Si elements in the composite. The NMCC sample, which consisted of 15 wt% MSWIFA and 1.0 wt% NS, exhibited the highest percentage (53 %) of harmless pores after 28 days. Additionally, its compressive strength reached 96.78 % (42.9 MPa) of the pure cement control indicating superior mechanical properties a compact microstructure. The utilization of NS as a viable material holds great potential in augmenting the application of MSWIFA as a SCM within the construction and building industry.

A Locally Available Natural Pozzolan as a Supplementary Cementitious Material in Portland Cement Concrete

For several decades, class F fly ash has been an attractive supplementary cementitious material, at least in part, due to its ability to reduce Portland cement consumption and mitigate alkali-silica reactions in concrete. However, fly ash availability is becoming uncertain as the energy industry decommissions coal burning power plants as it transitions to renewable energy production. This situation creates a need to identify viable and sustainable alternative supplementary cementitious materials. There are several types of supplementary cementitious materials, such as natural pozzolans, metakaolin, or ground granulated blast-furnace slag, which appear to be potential alternatives to fly ash in concrete. In this research, a locally available natural pozzolan (pumicite) was selected to replace fly ash in concrete. After conducting alkali-silica reaction tests on mortar mixtures, rheological and strength properties, shrinkage, resistance to freezing and thawing, and chloride ion permeability of concrete mixtures containing different amounts of fly ash and natural pozzolan were evaluated. The results showed that pumicite was more effective than fly ash at mitigating the alkali-silica reaction, and a pumicite content of 20% was necessary to mitigate the alkali-silica reaction. Ternary mixtures containing both pumicite and fly ash were the most effective cementitious materials combinations for mitigating the alkali-silica reaction expansion. Additionally, pumicite provided acceptable compressive strength and modulus of rupture values (greater than 4.0 MPa) that exceeded the flexural strengths provided by established mixtures containing only fly ash. Shrinkage and durability factor values for all mixtures were less than 710 μstrain and greater than 75, which are generally considered acceptable. Additionally, all mixtures with acceptable alkali-silica reaction expansions had very low chloride permeability. These results indicate that pumicite can be a reliable alternative for fly ash.

A study on the strength and durability characteristics of fiber-reinforced recycled aggregate concrete modified with supplementary cementitious material

Recycled aggregate (RA) made from waste concrete is an environmentally friendly alternative to natural aggregate (NA) for concrete manufacturing. However, compared to NA concrete, concrete produced with recycled aggregates has poor characteristics. Supplementary cementitious materials (SCMs) can be used to enhance the poor properties of recycled aggregate concrete (RAC). Silica fume and fly ash are commonly used SCMs in the World, but their high usage led to a shortage of silica fume and fly ash. Still, the deficiency of these materials in large parts of the world is a challenge that requires exploring alternative feedstock materials for the construction industry in the coming years. Wheat straw ash (WSA) is an agricultural waste product that could be used as an alternative SCM due to its pozzolanic behavior to enhance the properties of RAC. In addition, concrete is brittle and needs reinforcement, for which polypropylene fibers (PPFs) can be used. The current research examines the mechanical characteristics of fiber-reinforced RAC, including compressive strength, splitting tensile strength, and ductility performance. Durability indicators, such as chloride diffusion, chloride penetration, acid resistance, and water absorption test, were also assessed. The results showed that concrete samples with 10% WSA, 50% RA and 1.5% PPFs had the highest compressive and splitting tensile strength, 60.2 MPa and 7.25 MPa, respectively, representing increases of 24.75% and 30.65%, as compared to plain samples at 56 days. In these samples, water absorption was reduced by 13% due to the finer WSA particles resulting in the lowest reduction in strength and mass recorded when exposing concrete samples to acidic media. The statistical analysis also validated that irrespective of WSA and PPFs, the concrete with 0% RA had the highest performance in strength and durability behavior. The study showed that WSA and PPFs might be employed in tandem to offset the poor behavior of RA, enhance the bond between fibers and concrete, and improve the mechanical strength and durability performance of RAC, thus demonstrating its suitability as a sustainable and economical construction material.

Limestone-Calcined Clay (LC2) as a supplementary cementitious material for concrete

In this work, limestone-calcined clay (LC2) is studied as an alternative supplementary cementitious material (SCM), combining two widely available resources – calcinated kaolinitic clay and limestone, to partially substitute portland clinker. The primary goal is to assess the potential of LC2 to produce moderate to high strength concretes with design compressive strengths of 20 to 50 MPa. For this purpose, 27 mixes with LC2 were prepared with a range of binder contents and water-binder ratios, and the performance was benchmarked against those of mixes having fly ash (PFA). In addition to the quantification of strength and concrete resistivity, life cycle assessment was performed for the concretes considering a typical situation in India. The efficiency of concretes made with LC2, PFA and ordinary portland cement (OPC) was analyzed using the energy intensity index (eics) and apathy index (A-index) as sustainability indicators. This framework establishes the sustainability potential of the LC2 with insights on the influence of strength on the indicators. It is concluded that the LC2 concretes with 45% replacement level, w/b≤0.45 and binder content lower than 400 kg/m3 possess the highest sustainability potential, among the concretes studied here.

Capability of R3 test to evaluate pozzolanicity of ground raw and calcined sugarcane bagasse ashes

Sugarcane bagasse ash (SCBA) is a by-product of sugar and ethanol production and is largely disposed in landfills. Although the SCBA feasibility as pozzolanic material has been widely explored, traditional screening reactivity tests have shown inappropriate to evaluate alternative supplementary cementitious materials (SCM). The R3 test is a novel method to assess the reactivity of SCMs in a simplified system without Portland cement. This work aims to investigate the capability of the R3 test methods to measure the reactivity of ground raw (SCBA) and calcined (SCBA600) sugarcane bagasse ashes benchmarked against 2,7, 28, and 90-days compressive strength of mortars using SCM as cement replacement. Besides SCBA specimens, two traditional SCMs, silica fume (SF) and metakaolin (MK), were also evaluated. As expected, the R3 test obtained the same order regarding the reactivity of the studied SCMs for the three methods, from the highest to the lowest MK > SF > SCBA600 > SCBA. Regarding the R3 heat release evolution, raw and calcined sugarcane bagasse ashes had a very analogous trend and slow reaction of hydration. In R3 bound water results, a more prominent distinction was verified between SCBA and SCBA600. Moderate to poor correlations are observed between the R3 CH consumption and the portlandite content of cementitious pastes. The benchmark test confirmed the slow reaction of the studied ashes, presenting a significant increase in compressive strength only after 28 days. R3 test results correlate well (R2 ≥ 0.85) with the relative compressive strength of mortars at 7 days. Only a moderate relationship exists between the R3 tests and the relative strength at 28 days, decreasing at 90 days. This contribution indicates that the R3 test methods are sensible to evaluate the early age pozzolanic reactivity of SCBA and SCBA600.

Mitigating calcium oxychloride formation in cementitious paste using alternative supplementary cementitious materials

Supplementary cementitious materials (SCMs) are known to reduce calcium oxychloride (CAOXY) contents in cementitious pastes. However, when availability or cost precludes the use of traditional SCMs, such as fly ash, mitigation could be provided through alternative materials. Fly ash (FA), rice husk ash (RHA), bottom ash (BA), limestone filler (LS), nepheline syenite filler (NS), sandstone filler (SS), and silica flour (SFL) were evaluated for CAOXY mitigation in cementitious paste using low-temperature differential scanning calorimetry, reactivity testing, thermogravimetric analysis, and compressive strength testing. The order of CAOXY mitigation from least to most effective is SS, LS, SFL, NS, BA, FA, and RHA.

Supplementary Cementitious Materials in Building Blocks—Diagnosing Opportunities in Sub-Saharan Africa

Sustainable building should at least be affordable and carbon neutral. Sub-Saharan Africa (SSA) is a region struggling with housing affordability. Residential buildings are often constructed using block-based materials. These are increasingly produced using ordinary Portland cement (PC), which has a high carbon footprint. Using alternative Supplementary Cementitious Materials (SCMs) for block production might reduce the footprint and price. The purpose is to assess the level of information for SCM use in blocks in SSA and to use this information for Diagnosing the improvement potential as part of an Opportunity Study. Results from the scoping review show that aggregated information on SCMs and the quantities available is limited. Diagnosing the theoretical improvement potential in using cassava peel ash, rice husk ash, corn cob ash, volcanic ash and calcined clays, indicates that SCMs could represent a yearly value of approximately USD 400 million, which could be transferred from buying cement to local production. The use of SCMs could save 1.7 million tonnes of CO2 per year and create some 50,000 jobs. About 5% of the PC used for block production could be substituted, indicating that, in addition to using SCMs, other solutions are needed to secure production of sustainable blocks.

3D Construction Printing Standing for Sustainability and Circularity: Material-Level Opportunities

Three-dimensional Cementitious materials Printing (3DCP) is a cutting-edge technology for the construction industry. Three-dimensional printed buildings have shown that a well-developed automated technology can foster valuable benefits, such as a freeform architectural design without formworks and reduced human intervention. However, scalability, commercialization and sustainability of the 3DPC technology remain critical issues. The current work presents the ecological fragility, challenges and opportunities inherent in decreasing the 3DCP environmental footprint at a material level (cementitious materials and aggregates). The very demanding performance of printable mixtures, namely in a fresh state, requires high dosages of cement and supplementary cementitious materials (SCM). Besides the heavy carbon footprint of cement production, the standard SCM availability might be an issue, especially in the longer term. One exciting option to decrease the embodied CO2 of 3DCP is, for example, to incorporate alternative and locally available SCM as partial cement replacements. Those alternative SCM can be wastes or by-products from industries or agriculture, with no added value. Moreover, the partial replacement of natural aggregate can also bring advantages for natural resource preservation. This work has highlighted the enormous potential of 3DCP to contribute to reducing the dependence on Portland cement and to manage the current colossal wastes and by-products with no added value, shifting to a Circular Economy. Though LCA analysis, mixture design revealed a critical parameter in the environmental impact of 3DCP elements or buildings. Even though cement significantly affects the LCA of 3DCP, it is crucial to achieving adequate fresh properties and rheology. From the literature survey, mixtures formulated with alternative SCM (wastes or by-products) are still restricted to rice husk ash, Municipal Solid Waste ashes and recycled powder from construction and demolition wastes. Natural aggregate replacement research has been focused on recycled fine sand, mine tailing, copper tailing, iron tailing, ornamental stone waste, recycled glass, crumb rubber, rubber powder and granules, recycled PET bottles and steel slag. However, flowability loss and mechanical strength decrease are still critical. Research efforts are needed to find low-carbon cement replacements and mix-design optimization, leading to a more sustainable and circular 3DCP while ensuring the final product performance.

Optimum pretreatment of corn stover ash as an alternative supplementary cementitious material

As sustainable construction practices become more popular, researchers are looking into using readily available and inexpensive agricultural waste materials as a supplementary cementitious material. This study investigates the impact of various pretreatment methods on the chemical composition, crystal structure, morphology, and cost of producing pretreated corn stover ash collected from four different sources in the U.S. This study also evaluates the performance of mortars and pastes containing treated corn stover ash through tests such as compressive strength, flow measurement, calorimetry, and thermal analysis. In addition, thermodynamic modeling is used to predict the phase composition, chemical composition of the pore solution, pH, and electrical resistivity of pastes made with selected pretreated corn stover ashes. The results suggest that acid pretreatment is the most effective and economical method for improving the quality of corn stover ash and that it removes a significant amount of alkalis from the raw material. The simulation of the reaction between cement and the pretreated corn stover ash was confirmed by the experimental results, indicating a marked enhancement in the pozzolanic activity and chemical and physical characteristics of the system.

A Review on Emerging Cementitious Materials, Reactivity Evaluation and Treatment Methods

Alternative to traditional concrete, sustainable concrete reduces cement content, waste management issues, and CO2 emissions. To achieve sustainable concrete, waste materials can be used as supplementary cementitious materials (SCMs) to partially replace cement. Fly ash, ground-granulated blast furnace slag, and silica fume have been heavily studied as SCMs. However, due to the retirement of coal-fired power plants and switching to renewable energy, existing SCMs are losing their dominance. With SCMs becoming more widely accepted as partial cement substitutes, there is fear that the current supply will not meet future demand. As a result, researchers have been looking for alternative SCMs. The circular economy can be achieved by reusing non-hazardous construction and demolition materials, timber, and metal/steel production waste as SCMs. This article discusses emerging SCMs, reactivity evaluation methods, their limitations, and treatment methods that may improve reactivity. Emerging SCMs can replace existing SCMs in quantity, but their supply to cement factories and low reactivity due to stable crystallinity hinders their use. Among treatment methods, particle size reduction effectively enhances reactivity; however, very fine SCM may increase the overall water demand due to the large surface area. Decades-old reactivity evaluation methods have relatively weak correlations and thus misreport the reactivity of SCMs. Newer R3 models, such as calorimetry and bound water, give the best correlations (R ≥ 0.85) for 28-day relative strength and better performance. Additionally, more concrete testing with emerging SCMs under different durability and environmental protection conditions is required and life cycle assessments are needed to determine their regional environmental impact.

Investigation of different paper mill ashes as potential supplementary cementitious materials

Integrating supplementary cementitious materials (SCMs) in cement-based construction materials is a key strategy for reducing environmental burdens and the greenhouse gas emissions related to cement production. Supplies of commonly applied SCMs such as fly ash and blast furnace slag are becoming limited, and therefore the search for alternative SCMs is of high significance. The present research investigates the viability of four paper mill ashes collected at different stages from the same incineration process as SCMs at different cement substitution rates (5–30 wt%). The ashes were first classified depending on their mineralogical and chemical composition, and their contribution to strength development of the prepared mortars is examined. Furthermore, the effects of the ashes on the hydration kinetics and the fresh and hardened properties of the prepared mortars were studied. The obtained results showed that a high level of SCM replacement accelerates the early hydration reactions and decreases the setting time. In addition, the incorporation of paper mill ashes increased the bound water depending on the ash type and resulted in strength development of the mortars at low replacement percentages (5–10 wt%). This study shows that the ashes belonging to type C medium acid based on bio ash classification could be incorporated as SCMs at a maximum level of 10 wt%, while those corresponding to type C low acid could be used up to 20–30 wt%. • Four paper mill ashes were characterized and classified based on the chemical and mineralogical composition then used as SCM. • Paper mill ashes corresponding to type C low acid based on bioash classification could be used as SCMs up to 20–30 wt%. • The addition rate of paper mill ashes controls the fresh properties and strength development of the mortars.

The efficiency of recycled glass powder in mitigating the alkali-silica reaction induced by recycled glass aggregate in cementitious mortars

With the potential for a decline in fly ash (FA) production over time, due to the phasing down of coal fired power plants, alternative supplementary cementitious materials need to be identified. The efficiency of pulverised glass powder (PGP) was studied for its reactivity and its capacity for inhibiting alkali-silica reaction (ASR) that results from utilisation of recycled glass as a fine aggregate (sand) replacement. Characterisations of pastes containing PGP reveal that PGP may possess latent hydraulic properties, resulting in a more than 75% strength activity index, together with better strength gain than FA-blended pastes. PGP also offered increased heat of hydration compared to FA, from a combination of the dilution effect, filler effect and early-age reactions of PGP. A comparable efficiency of PGP and FA in ASR expansion mitigation was confirmed with mortar bar expansions of less than 0.10% at cement replacement levels of at least 10%. Both PGP and FA provided alkali dilution and reduced the mass transport in hydrated cement paste from the refinement of larger pores to below 60 nm. The FA mix consumed calcium hydroxide and, thus, performed marginally better than the PGP mix in mitigating ASR. This pozzolanic reactivity is not evident for PGP, whereas in the literature glass powders are often regarded as pozzolanic. Microscopic images confirm that PGP and FA significantly limit the occurrence of ASR gels without altering its composition. It was concluded that PGP is a comparable ASR inhibitor to FA, despite the underlying differences in their mechanisms. The result of this research support the utilisation of recycled glass both as an aggregate, and as an ASR-inhibiting SCM in cementitious systems.

Report of RILEM TC 267-TRM phase 3: validation of the R3 reactivity test across a wide range of materials

RILEM TC 267 TRM– “Tests for Reactivity of Supplementary Cementitious Materials” recommends the Rapid Reliable Relevant (R3) test as a method for determining the chemical reactivity of supplementary cementitious materials (SCMs) in Portland cement blends. In this paper, the R3 test was applied to 52 materials from a wide range of conventional and alternative SCMs with the aim to validate such test. An excellent correlation was found between the cumulative heat release and the bound water determined following the R3 test method. Comparison of the R3 test results to mortar compressive strength development showed that all conventional SCMs (e.g. blast furnace slag and fly ashes) followed the same trend, with the notable exception of very reactive calcined kaolinitic clays. It is discussed, through an in-depth statistical regression analysis of the R3 reactivity test results and the 28 days relative compressive strengths, how reactivity threshold values for classification of the chemical reactivity of SCMs could be proposed based on the R3 test results.

Circular concrete: validating new technologies in the lab and on-site

The growing importance of a circular economy also holds possibilities for concrete. Some of the principles of circularity, like the re-use of "waste" as secondary raw material and the optimisation of the design with regards to lifespan, environmental impact and re-use, can be applied. Several technological innovations in this domain are in an advanced stage of development. However, the transition from research to full commercial applications is held back, mostly due to the absence of documented experience and the lack of a technical framework (prescriptions). In order to accelerate the adoption of new technologies, the Belgian Building Research Institute (BBRI) started the project "Circular.Concrete". In this paper, the results are presented of validation tests regarding 1) smart crushing technology, 2) the carbonation of recycled aggregates, 3) concrete using only recycled aggregates and 4) the use of alternative binders and supplementary cementitious materials.

Suitability of Blending Rice Husk Ash and Calcined Clay for the Production of Self-Compacting Concrete: A Review.

One principal approach to achieve self-compacting properties is the increased amount of finer constituents of the mixture. This, in turn, increases cement consumption leading to higher greenhouse gas emissions. Pozzolanic materials, like rice husk ash or calcined highly kaolinitic clays, have gained increased attention as supplementary cementitious materials in self-compacting concrete production. These materials could be viable alternative supplementary cementitious materials for sub-Saharan Africa which already lacks fly ash, slag and silica fume. This current effort reviews the impact of rice husk ash and calcined clays for the production of self-compacting concrete. Special focus is on their impact on rheological, mechanical and durability properties of self-compacting concrete. Rice husk ash and, in particular, calcined highly kaolinitic clays are introduced as technical and cost-effective supplementary materials for use in self-compacting. The review disclosed a lack of knowledge when it comes to the use of low-kaolinitic calcined clays as sole SCM or together with rice husk ash, which could be a very promising combination for e.g., several countries in Africa. Further studies are needed on the rheological properties, shrinkage, creep, and durability of self-compacting concrete produced with other calcined common clays and their blend with rice husk ash.