Belite-rich Cement Research Articles

Physicochemical properties of CO2-cured belite-rich cement with electric arc furnace reduction slag as a partial replacement

This study investigates the physicochemical properties of CO2-cured belite-rich cement with electric arc furnace (EAF) reduction slag as a partial replacement at varying weight percentages (0–20%). The results revealed that water-cured specimens (WRS) showed significant increases in the numbers of gel and medium capillary pores, while carbonation-cured specimens (CRS) demonstrated increases in the numbers of large capillary and macro pores. Moreover, up to 10% replacement of the slag led to a decrease in the compressive strength, accompanied by increased CO2 absorption and reduced alkalinity. When the EAF reduction slag content increased from 15% to 20%, CRS exhibited a trend reversal in the compressive strength, marked by an increase in the pH, approaching compressive strength comparable to those of WRS. This signified that higher percentages of EAF reduction slag are advantageous for enhancing CO2 sequestration due to the potential reactivity of magnesium oxide in EAF reduction slag with CO2.

Effect of low-heat cement Portland cement on alkali-silica reaction of aggregates with different alkali-reactivities

This study investigated the impact of cement clinker percentages on the alkali-silica reaction (ASR) mechanisms of aggregates with varying alkali-silica reactivity. Experimental findings indicated that the low-heat Portland cement (LHC) mitigated the development of the ASR process in soda-lime glass aggregate (SLGA) concrete. The ASR in ordinary Portland cement (OPC) mainly initiated within the SLGA, leading to crack propagation through the matrix. The in-situ X-ray micro-computed tomography test indicated that LHC altered the manifestation of ASR in concrete containing SLGA, leading to different destructive forms. Specifically, ASR between the LHC and SLGA primarily occurred at the periphery of the SLGA. The in-situ quantity analysis results illustrated that the LHC mitigated the ASR-induced cracks in the SLGA concrete. For the less alkali-reactive natural aggregate, the effect of LHC cement on ASR was diminished. ASR still only occurred within the natural aggregate concrete, distributing in highly alkali-reactive phases inside the aggregates. The chemical analysis results supposed that the differing ASR pathways could be attributed to the interaction between the calcium content in the LHC and the spatial distribution of alkali-reactive phases within the aggregates. These findings help interpret the mechanism of the slower ASR process in the belite-rich cement concrete.

Carbonation curing of belite-rich cement: The role of fly ash and strengthening mechanism

Belite-rich cement (BRC) has gained increased attention in recent years due to its low energy consumption and high long-term performance. However, the carbonation behavior of the binder formed by its combination with fly ash (FA) has been scarcely revealed. This study investigated the influence of carbonation curing and FA replacement level on the carbon capture and mechanical properties of BRC. The carbon uptake, phase composition, microstructure, and micromorphology of BRC-FA composites after carbonation curing were characterized through quantitative XRD, TG, FT-IR, MIP, and SEM-EDS. The results indicated that carbonation curing significantly increased the compressive strength by up to 81.6% of BRC compared to standard curing due to the high reactivity of belite phase with CO2, whilst the hydration products of BRC gradually disappeared, and calcite and amorphous silica became the main phase accompanied with pore refinement behavior. Moderate addition of FA increased the degree of carbonation and compressive strength of BRC-FA composites, however excessive addition (45%) of FA results in adverse effect. Additionally, FA accelerated the phase recombination but coarsened the pore structure. The rapidly formed calcium carbonate crystals stacked and squeezed together, its blend with amorphous silica gel, and the pore structure rapidly densified explain the carbonation strength growth of BRC-FA composites.

Assessment of the physicochemical properties of alkali-activated slag blended with belite-rich cement subjected to carbonation attack

The present study investigated the physicochemical transformation of alkali-activated slag (AAS) under CO2 exposure. The belite-rich cement (BRC) used as an additive up to 30 wt% of GGBFS and Ca(OH)2 was used for alkali activation. The threshold ratio of lime/slag and BRC/binder was 4.5% and 20%, respectively, for the improvement in strength and the physicochemical properties. The residual strength after CO2 exposure was higher for an AAS mix prepared with 30% BRC/binder and a 6% lime/slag ratio. Due to the additive (BRC) in AAS, the unreacted β-C2S and portlandite act as a buffer during CO2 exposure. The additional supply of Ca2+ ions provided via Ca(OH)2 contributed to promoting the reactivity of AAS. The decrease in critical pore diameter by 51.6% as the prepared AAS with the higher BRC/binder ratio was exposed to CO2 increased the solid-phase assemblage per unit volume, which also contributed to the physicochemical properties.

Cesium immobilization of high pH and low pH belite-rich cement under varying temperature

Low-pH cement is being studied in radioactive waste repositories. The belite-rich cement (BRC) recently gained attention due to its higher CO2 sequestration and low pH attainment under carbonation exposure. Therefore, this study evaluated the effects of pH and temperature on cesium immobilization of BRC. High pH (12.6) and low pH (9.9) BRC were produced via air curing and carbonation treatment, respectively. The high and low pH BRC samples were placed in a leaching environment at 25 °C and 45 °C for 90 days. An inverse correlation between pH and cesium mobilization of BRC was observed. The high pH BRC achieved the lowest effective diffusion coefficient (4.05E-09 cm2/s), whereas the highest value (2.64E-07 cm2/s) was achieved in case of low pH BRC. The physicochemical and morphological properties unveiled the decrease in Si/Ca ratio of gel, precipitation of Ca2+ ions in calcite formation, and increment in pore structure connectivity (pore size > 100 nm) in low pH BRC. However, the high pH BRC demonstrated the high Si/Ca ratio in C-S-H gel, hydroxide phases and higher disconnected pores. Thermodynamic modeling revealed the presence of significant carbonated phases beyond 15% CO2 uptake. The findings contributed to the BRC’s feasibility in developing nuclear waste storage facility.

Influence of hygiene tissue paper used as an additive on the physicochemical and mechanical properties of CO2-cured belite-rich cement paste

The present study investigated the fresh, hardened, and physicochemical properties of CO2-cured belite-rich cement (BRC) paste incorporating hygiene tissue paper (HTP) as an additive. HTP was added at 0.5% and 1.0% by wt. of BRC paste. The BRC paste was prepared at a water-to-cement ratio of 0.4 and cured under water and carbonation. The results demonstrated that upon carbonation, the incorporation of HTP at 1.0% increases the CO2 uptake and compressive strength of specimens by 18.60% and 22.29%, respectively. A pore structure analysis shows a decrease in the threshold pore size diameter with an increase in the HTP content for CO2-cured samples. An SEM analysis revealed precipitation and impregnation of calcites in and around the HTP microfiber particles. The incorporation of HTP under water curing on the other hand did not significantly influence the strength or the physicochemical properties. It was observed that HTP contributes to improving the properties of CO2-cured BRC paste in two ways; the porous structure of HTP provides pathways for the deep permeation of CO2 into the matrix, and the surface of HTP offers an additional area for calcite precipitation.

Role of fiber dosages and lengths on the mechanical strength, shrinkage, and pore structure of CO2-cured amorphous metallic-fiber-reinforced belite-rich cement composites

The impact of varying dosages and lengths of amorphous metallic fiber (AMF) on the mechanical strength, shrinkage, and pore structure of fiber-reinforced cementitious composites cured in water and in a carbonation chamber were assessed. This study evaluated fourteen mortar mixes, i.e., seven mixes for traditional water curing and seven for CO2-curing (60% relative humidity, 20 °C, and 10% CO2 concentration). The outcomes reveal that the compressive and flexural strength are significantly augmented for the mixes reinforced with AMFs as compared to the control mix (fiber-free mix), and this behavior is more pronounced with increased dosages and lengths of the AMF. Furthermore, compared to the control mix, significant mitigation in the development and magnitude of shrinkage was recorded with increased dosages and lengths of the AMF. The porosity and voids were all increased in the samples with AMF as compared to the control mix. The carbonation-cured specimens exhibited significantly higher mechanical strength, fewer voids, and higher shrinkage than those cured in water. Based on the experimental findings, it is recommended to use 0.50% volume of AMF and a length of 20 mm to produce fiber-reinforced cement composites, as this combination provides outstanding performance among all mixes tested here.

Understanding the CO2 utilisation potential of various cementitious materials through review and analytical modelling

Carbon dioxide sequestration in cement-based materials has emerged as a promising avenue for utilising captured carbon dioxide (CO2) and reducing the carbon dioxide footprint of the concrete industry. This article presents a comprehensive review of various studies conducted in this domain with a particular emphasis on factors affecting the carbon dioxide uptake potential of various concrete types and the effect of carbonation on the critical properties of concretes. Studies conducted on the micro-mechanical analysis of carbon sequestered concrete show that carbonation significantly improved the microhardness of the concrete samples, thereby increasing the strength and reducing the cement intake requirement. Further, keeping two parameters, namely water/solid (w/s) ratio and carbonation reaction time, in focus, the carbon dioxide uptake capacity in concrete slurry waste (CSW) was evaluated using non-linear regression analysis. It was observed that CSW paste had a maximum carbon dioxide uptake with an intermediate w/s ratio of 0.2 due to carbon dioxide reaction hindrances during diffusion at a higher w/s ratio and lack of hydration at a lower w/s ratio. On the contrary, for belite-rich cement, a higher w/s ratio led to higher carbon dioxide uptake owing to belite phase consumption leading to increased calcite production. Additionally, comparing the maximum carbon dioxide uptake capacity of CSW at a particular condition with various other cement-based materials, it was observed that belite-rich cement had the ability to sequester the maximum amount of carbon dioxide compared to the other cement-based materials considered in this study.

Effects of curing regime, cement type, and water-to-cement ratio on the physicochemical, mechanical, and hydraulic properties of pervious mortar

This study investigated the influence of curing regime, type of cement, and water-to-cement ratio (W/C) on the physicochemical, mechanical, and hydraulic properties of pervious mortar. The carbonation degree of mortar produced using ordinary Portland cement (OPC) and belite-rich cement (BRC) increases with an increase in the W/C ratio. Mortar produced using calcium sulfoaluminate (CSA) cement was completely carbonated within the first three days. A greater degree of carbonation was observed for BRC mortar compared to that of OPC mortar at 28 days. The hydraulic properties of pervious mortar were dominated by the curing regime. Specimens subjected to carbonation curing displayed more open voids and higher permeability. Further, both OPC and BRC mortars displayed higher compressive and flexural strength levels when subjected to carbonation curing. However, mortar produced using CSA displayed significantly lower compressive strength than those of OPC and BRC.

Eco-friendly belite cement elaborated from shell and glass powder

The purpose of this study is to use inorganic wastes to completely replace traditional raw materials for the production of belite rich clinkers, waste glass as a source of SiO2 oxide and shells as a source of calcium carbonate CaCO3 to synthesize belite-rich cement. After grinding, the raw materials were blended to synthesize the dicalcium silicate phase (Ca2SiO4) in a heat treatment up to 1000 °C. The clinkers produced were rich in elaborated Ca2SiO4, mixed with gypsum and shell powder as a source of calcium carbonate to form belitic cements. The cements were prepared and hydrated with different proportions of belitic clinker (56, 62 and 72%).The specimens were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The results of the XRD and FTIR analyses demonstrate that hydration of the three cements over time leads to the formation of crystallized C-S-H compounds, which increase in abundance after 90 days upon the increase of the C2S percentage. We have attempted here to provide an update on the development of high-belite cements with low CO2 emissions.

Flexural behavior, porosity, and water absorption of CO2-cured amorphous metallic-fiber-reinforced belite-rich cement composites

The present study aims to scrutinize the flexural behavior and engineering properties of beams reinforced with amorphous metallic fiber (AMF) at varying dosages (0%, 0.25%, 0.50%, and 0.75% AMF according to the volume of mortar) and lengths (5 mm, 10 mm, 15 mm, and 20 mm). A total of fourteen mortar mixes, i.e., seven mixes for water curing (immersed in fresh tap water) and seven mixes for carbonation curing (60% relative humidity, 20 °C, and 10% CO2 concentration) were considered. The load–deflection behavior, flexural strength, pore structures, voids, and water absorption of the beams were investigated. The outcomes were justified with the mix containing 0.5% steel fiber (SF) and a length of approximately 20 mm. The results reveal that the load–deflection behavior and flexural strength were dramatically augmented for the beams with AMF as compared to the control beam (fiber-free beam), and the difference was more pronounced with an increase in both the dosage and the length of the AMF. Greater flexural strength with a lower deflection at failure was registered for the beam with AMF compared to that with SF. The voids and water absorption increased with an increase in the dosage and length of the AMF compared to the control specimen. It was also revealed that the carbonation-cured beams exhibited lower load–deflection behavior and lower flexural strength than those cured in water due to the substantially increased number of voids and greater water absorption driven by the better-connected pores. This study demonstrates that 0.50% AMF with a length of 20 mm can be used in cement-based materials due to the outstanding performance among all mixes.

Microstructural evolution of belite-rich cement mortar subjected to water, carbonation, and hybrid curing regime

The present study investigates the influence of various curing schemes on the strength and microstructural evolution of belite-rich cement (BRC) mortar. The sets of BRC mortar were subjected to different carbonation and/or water curing for 28 days. The mineralogical changes in BRC depend upon the w/c ratio of the mix and CO2 concentration at the initial days of curing. Ettringite, portlandite, and unreacted belite were the hydrated phases at a 0.3 w/c ratio. Regardless of curing type, rapid mineralogical changes at higher w/c ratios through different polymorphs of CaCO3 and de-calcified silica gel were observed. The carbonation curing was efficient for higher strength development at all the w/c ratios (0.3–0.7). However, hybrid curing was more efficient than water curing at higher w/c ratios (0.6 and 0.7) in improving the compressive strength.

Effect of belite-rich cement replacement on the properties enhancement of eco-friendly ultra-high performance concrete containing limestone powder and slag

Cement-slag-limestone (CSL) powder concrete is a new type of ternary concrete. Thus far, CSL powder application in ultra-high performance concrete (UHPC) remains relatively limited. Furthermore, the effects of different types of cements, including belite-rich Portland cement (BRC), on CSL concrete have not been investigated. Therefore, in this study, a new CSL-UHPC was designed, where the sustainability of CSL-UHPC was systematically improved by using BRC to replace the ordinary Portland cement (OPC) in CLS cementitious materials and realize a UHPC with a low heat of hydration, low autogenous shrinkage, low CO2 emissions, and high strength. According to the experimental data, the heat released by the hydration reaction during the early stages of BRC concrete was less than that released in the early stages of OPC concrete. The cumulative heat release from hydration and the maximum heat release rate were minimal, approximately 171.8 J/g and 1.41 mW/g of the binder, respectively, for 100% BRC replacement. Moreover, the autogenous shrinkage generation in the early stages was effectively reduced; notably, the reductions autogenous shrinkage were particularly pronounced (approximately 39.5–36.7%) for 66% and 100% BRC replacement. After 56 days of curing, the compressive strength of the BRC-infused concrete was similar to or higher than that of OPC concrete. In addition, the CO2 emissions and the CO2 emissions per unit strength decreased by 2.6–7.8% and 7.0%, respectively, as the percentage of BRC replacement increased. Thus, CSL-UHPC combined with BRC is more effective than OPC in terms of promoting a sustainable concrete industry.

Effect of Mg-doping on the hydration reactivity of polycrystalline dicalcium silicate: A study explored by DFT simulation

Dicalcium silicate is widely used in belite-rich cement due to its lower Ca/Si ratio, energy consumption and CO2 emissions than tricalcium silicate, and its hydration reactivity plays an important role in the strength development of the cement. This work provides an atomic-scale understanding of the electronic structure on the hydration reactivity of C2S polycrystals and elucidates the effect of Mg-doping on their reactivity and intrinsic mechanisms. The results show that the hydration reactivity is more closely related to electrophilic attack due to the absolute numerical dominance of electrophilic active sites and the presence of steric hindrance. The hydration reactivity of α′L-C2S is mainly achieved by electrophilic attack, γ-C2S mainly by nucleophilic attack, and β-C2S by both electrophilic and nucleophilic attack. Among these three polymorphs, the order of hydration reactivity is β-C2S > α′L-C2S > γ-C2S. Mg-doping can change the crystal and electronic structure used to characterize the chemical reactivity of C2S, and the higher the hydration reactivity of intrinsic minerals, the greater the effect of Mg doping. Mg-doping causes irregular distortions in the overall structure and local coordination of α′L- and β- C2S, which coincide with the structural activation caused by impurities. The hydration hysteresis of Mg-doped α′L- and β- C2S is caused by the sharp decrease in the number of reaction sites and a more localization of the effective charge density. In contrast, the LDOS in Mg-doped γ-C2S shows slight change in both aspects, resulting small effect on its hydration activity. These insights should pave an effective way to regulate the hydration reactivity of cementitious materials by selecting suitable foreign ions.

Dimensional stability of belite-rich cement subject to early carbonation curing

This study investigated the dimensional stability and physicochemical changes of belite-rich cement (BRC) subjected to carbonation curing with four distinct water-to-cement ratios. Shrinkage of carbonation and water-cured BRC was measured to assess the dimensional stability. The carbonation-cured BRC exhibited more shrinkage than the normal-cured specimen. The mass loss of the BRC paste subjected to normal curing was greater than that of the carbonation-cured BRC paste. The mechanism involved in the dimensional stability and mass loss of carbonation- and normal-cured specimens was investigated by physicochemical analysis. The large amounts of calcite were observed in carbonation curing, but negligible in normal cured specimen. Furthermore, carbonation of Ca(OH)2 and decalcification of C–S–H released water from gel in pores during carbonation curing. These reactions were exothermic in nature and led to the evaporation of some free water. This mechanism accelerated the consumption of water and increased the shrinkage of the carbonation-cured cement paste.

Limestone calcined clay binders based on a Belite-rich cement

Portland-based Limestone Calcined Clay Cements, LC3, are receiving considerable attention because the CO2 footprint can be reduced up to 40 %. Here, we report a related family: Belite-rich-LC3. These blends are expected to have very good durability performances. Selected properties for two members are reported including calorimetric data and mechanical strength developments. The phase evolutions are studied by Rietveld analysis backed by the thermal behaviour. Their microstructures are studied by mercury intrusion porosimetry. The hydration rates of these blends have been boosted by C-S-H seeding which led to an increase of mechanical strengths. At 28 days, seeded mortars with cement replacement degrees of 30 and 45 wt% displayed 74 and 61 MPa of compressive strengths, respectively. Moreover, overall porosities and pore entry threshold values decreased in the admixture-containing binders.

Resistance of carbonation-cured belite-rich cement mortar to adverse environments: Magnesium sulfate and sulfuric acid exposure

The present study investigates the potential of carbonation-cured belite-rich cement (BRC) to resist magnesium sulfate (MgSO4) and sulfuric acid (H2SO4) environments. BRC mortar was submerged in 5% and 10% MgSO4 and H2SO4 solutions. The gains of the compressive strength and mass under MgSO4 environment significantly depend upon the buffer (unreacted belite phase) left in the specimen after 28 days of curing. The lowest buffer level, found after 28 days of carbonation curing, stemmed from the higher reactivity of the belite phase as opposed to water curing followed by carbonation curing. Furthermore, degradations in the strength and mass were found in the H2SO4 environment. The presence of the calcium carbonate phase in carbonation-cured BRC mortar increased the acid resistance. An XRD analysis showed sulfate-based mineral phases in the external and core areas of a carbonation-cured BRC mortar cube, representing the higher diffusion efficiency of acid ions than magnesium ions in BRC.

Effect of carbonation curing on physicochemical properties of mineral admixture blended belite-rich cement

The present study investigates the effect of CO2 curing on carbonation degree, CO2 uptake, mechanical and physicochemical properties of mineral admixtures blended with belite-rich cement (BRC). Pulverized coal combustion (PCC) ash, circulating fluidized bed combustion (CFBC) ash, and blast furnace slag (SG) were utilized as mineral admixtures. The results revealed that the PCC ash blended with BRC attained the highest compressive strength under CO2 curing. CFBC ash was comparable to PCC ash in terms of the ability to improve the mechanical and physicochemical properties. TG analysis revealed that CFBC ash blended BRC was excellent for promoting carbonation and CO2 uptake. TG, MIP, XRD, and 29Si NMR results showed that the SG was the least reactive mineral admixture with BRC under CO2 curing and negatively affects the strength attainment outcome, carbonation degree, and CO2 uptake. 29Si NMR confirmed the potential of PCC ash and CFBC ash in enhancing the reactivity of BRC under CO2 curing than the SG. Therefore, it is concluded that the blending of PCC ash and CFBC ash is beneficial in promoting the CO2 sequestration characteristics and compressive strength of BRC.

Effect of Alkali Salts on the Hydration Process of Belite Clinker.

Belite-rich cement is a low carbon footprint binder. However, its use is accompanied by a low initial rate of hydration. This can be partially eliminated by grinding to a high specific surface or through the addition of admixtures (mineralizators or activators). The influence of alkaline activators CaSO4, Na2SO4 and Na2CO3 (in the amount of 5 wt.% related to the clinker weight) on the hydration course, as well as the quantity of hydration products in belite-rich cements, were investigated in this paper. Belite-rich clinker was laboratory-synthetized and ground together with activators to prepare various belite-rich cements. Next, the hydration kinetics and the hydrated phase assemblage were investigated using isothermal calorimetry, X-ray powder diffraction and thermogravimetric and differential thermal analyses. The use of selected admixtures allowed us to obtain belite-rich cements with higher hydraulic activity in the initial period.

Effect of carbonation curing on the mechanical properties of belite-rich cement mortar exposed to elevated temperatures

The present study aims to investigate the residual properties of carbonation-cured belite-rich cement mortar exposed to a high temperature. The mortar was carbonation-cured with a 10% CO2 concentration for 28 days and was then exposed to elevated temperatures of 300 °C, 600 °C, 900 °C and 1200 °C. The findings revealed that the heat resistance of a cement mortar relative to that of standard water-cured sample was enhanced by carbonation curing. Moreover, it was noted that in comparison to Portland cement mortar, the residual mechanical performance was improved for the carbonation-cured belite-rich cement mortar sample. A physicochemical analysis revealed that the formation of thermally stable calcium carbonate due to carbonation curing was the primary cause of the enhanced residual properties. Furthermore, for samples exposed to 1200 °C, it was observed that the carbonation reaction products became thermally stable alite and belite phases.