Low-carbon Binder Research Articles

Performance assessment and cost-benefit analysis of low-carbon binders containing calcined sediments from Chorfa II dam as new building materials

Recently, considerable attention has been given to the valorization of dredged sediments around the world, which are considered waste. The reuse of dredged sediments has significantly contributed to Sustainable Development Goals. However, the efficiency and cost assessments of calcined sediments as a partial replacement for cement are not well understood. In this present investigation, the use of calcined sediments from dams as a green construction material on the properties of eco-pastes and mortars formulation is explored. Properties measurements, microscopic observation, eco-strength efficiency, and cost assessments were performed on fresh, hardened mortars in order to valorize calcined sediments in the cement industry. The best findings for the compressive and tensile strengths of mortars containing calcined sediments were obtained after 180 days, which was compared to the control mortar. Furthermore, microscopic analyses showed that an increase in the substitution rates of calcined sediment resulted in the increasing germination of calcium aluminate silicate hydrate gel (C-A-S-H) and calcium silicate hydrate gel (C-S-H). The control mortar showed an efficiency of 0.0902 MPa/kgCO2 eq for 28 days while the eco-strength efficiency of mortars containing 5%, 15%, and 25% of calcined sediments presented an efficiency of 0.0920 MPa/kgCO2 eq, 0.0922 MPa/kgCO2 eq, and 0.0997 MPa/kgCO2 eq, which represents an increase of 1.9%, 2.21% and 10.51%, respectively. However, the replacement of cement with calcined sediments up to a rate of 25% decreases embodied carbon. In conclusion, the cost of treatment of one (1) ton of sediments is lower than cement, which represents a reduction from 81.96% to 86%.

Adhesion evaluation and interface characterization of 3D printed concrete for automatic repair

3D concrete printing can be used for automatic repair, aiming at increasing efficiency and reducing the use of manpower, as compared to conventional manual repair. Ensuring strong adhesion of the 3D printed materials and characterizing the interface is crucial for the success of this approach. To this end, we first evaluated the adhesion performance of 3D printed concrete based on a low-carbon binder, i.e., calcium sulfoaluminate (CSA) cement. CSA cement pastes with different re-dispersible polymer powder substitution rates were used as coating before 3D printing. We used two approaches, X-ray computed tomography (CT) and scanning electron microscopy (SEM), to characterize the interface region. Results indicate that the yield stress of the 3D printing material and the coating material plays an important role in the adhesion in both the fresh and hardened state. Moreover, the limited adhesion at the overlay interface can be due to the limited contact at the centimeter and micro scale, as reflected by CT and SEM, respectively. Applying a coating can fill the air voids at the interface, while the placement of a coating may not improve the bond strength and can even have a negative impact due to the limited liquid medium at the interface.

Shear wave velocities to monitor curing evolution of soils treated with alkali activated binders

The use of alkali activated binders for soil improvement has been significantly increased in the past decade indicating a significant interest in the use of alternative low carbon binders. The optimisation and preliminary characterisation of the mixtures is usually addressed with destructive tests to evaluate strength such as unconfined compression strength tests. Although important and necessary, these tests require a significant number of specimens, especially when monitoring the strength evolution with time due to curing. Seismic wave velocity measurements, in particular S wave velocities, allow a fast evaluation of the elastic shear stiffness with time avoiding specimens’ failure. This is even more important in soils stabilised with alkali activated binders, since its strength and stiffness evolution with time is generally very long, keeping increasing far beyond the 28 days mark usually assumed in soils improved with Portland cement. In this paper, the evolution of the elastic stiffness with time for different soils treated with alkali activated binders is presented. The compilation of the results for different soils and mixtures, allowed a clear definition of the typical trend and range.

Stabilization of iron ore tailing with low-carbon lime/carbide slag-activated ground granulated blast-furnace slag and coal fly ash

The massive accumulation of iron ore tailing (IOT) results in land resource wastage and increases the possibility of environmental pollution. In this study, the feasibility of using low-carbon alkali-activated ground granulated blast-furnace slag (lime/Carbide slag (CS)-GGBS) and coal fly ash (CFA) instead of portland cement (PC) for solidifying IOT was investigated. The effects of different binders on strength development and durability of cured IOT were analyzed through unconfined compressive strength (UCS), water stability, and dry-wet cycles tests. Furthermore, the microstructure characteristics of cured IOT were conducted by using scanning electron microscope (SEM) method, X-ray diffraction (XRD) analysis, and thermogravimetric analysis (TGA). The results showed that, using the low-carbon material lime/CS-GGBS to replace about 70% of PC (i.e., PC:lime/CS:GGBS=1:1:1) with 9% binder content, the strength and durability of cured IOT were significantly improved compared with using pure PC. The 28d-UCS of cured IOT was 4.86 MPa, which was twice higher than that with pure PC. The 7d-UCS of cured IOT was 8.22 MPa after 12 dry-wet cycles, which was 2.8 times higher than that with pure PC. Moreover, the water stability coefficient of 27 + 1d-cured IOT was 90%. The micro-analysis showed that, the amount of hydration products (i.e., CSH, CAH and ettringite) in IOT cured with low-carbon materials increased significantly, and the structure became denser, resulting in the increase of strength. This study develops a low-carbon binder instead of pure PC to solidify IOT, and the results can provide a theoretical basis and scientific guidance for the comprehensive utilization of IOT as a filler solid waste.

Performance assessment and cost analysis of slag/metakaolin based rubberized semi-lightweight geopolymers with perlite aggregate: Sustainable reuse of waste tires

Low-carbon binders or industrial waste can reduce or even eliminate the demand for Portland cement and other natural resources, which reduces environmental pollution in accordance with the principles of sustainable development. The assessment of the mechanical, durability and microstructural properties of slag/metakaolin based rubberized semi-lightweight geopolymer composites (LWGC) with perlite aggregate (PA) is the main objective of this study. Waste tires aggregates (WTA) was produced from discarded waste tires, another environmental pollutant, and used in LWGC mixtures as substitution for the fine perlite aggregate by 0%, 20%, 45%, and 60% replacement. Metakaolin (MK) and ground granulated blast furnace slag (GBFS) were used as precursors in the synthesis of LWGC. Sodium hydroxide and sodium silicate solution was used as activators. Eight mixtures were created; four of them had 100% GBFS, while the other four contained 90% GBFS slag and 10% MK. All eight mixtures were then cured for 5 h at 60 °C and 100 °C. The effects of curing temperature, WTA, and MK on the compressive, flexural strength, physical properties, and sorptivity of the LWGC were examined as well as flowability. The performance of the blends at high temperatures, freeze thaw cycles and sulfate attack was also evaluated. Microstructure analyses of the mixtures were also done using SEM. CO2 emissions and costs of the mixtures were also evaluated. The results showed that inclusion of WTA instead of PA and MK instead of GBFS decreased the flow diameter. Thermal conductivity and dry density of the mixtures also decreased considerably with the addition of WTA. The findings showed that 10%MK incorporated mixture with 60%WTA produced a compressive strength of 25.10 MPa at curing temperatures of 100 °C. The results indicated compressive strength of MK incorporated mixture with 60%WTA increased by 48.10% and 31.20% at heat curing of 60 °C and 100 °C, respectively. The mixture WT60MK0 cured at 100 °C exhibited the best high temperature resistance and the same mixture also presented the best F-T performance regardless of curing temperature. The mixture WT40MK0 cured at 60 °C and the mixture WT60MK10 cured at 100 °C performed the best sulfate resistance.

Effect of dry ice as admixture on engineering properties of alkali-activated slag: setting time, strength, and sustainability

Alkali-activated slag (AAS) is a low-carbon binder with the potential to replace cement-based materials. In this study, AAS was prepared by using dry ice as an admixture. The effects of dry ice on the actual engineering properties, such as the initial and final setting times and compressive strength of the AAS, were studied. In addition, the microstructure of the AAS was analyzed with X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The results of these experiments revealed that the added dry ice increased the setting time of the AAS. The initial and final setting times of the AAS with 2.5 ∼ 7.5% dry ice were prolonged by 59 ∼ 122 and 118 ∼ 173 min, respectively. Furthermore, the addition of dry ice to the AAS improved its mechanical properties. At 28 days, the compressive strengths of the AAS supplemented with dry ice were 4.7 ∼ 11.6% higher than that of the control group.

Role of magnesium acetate in hydration and carbonation of magnesium oxide-based cements

MgO-based cements have the potential for low carbon binders especially when MgO is sourced from non‑carbonate minerals. Understanding the reaction kinetics and products formed are the keys to pave the way for these binders as construction materials. In this study, the influence of acetate on hydration and subsequent carbonation of reactive MgO is investigated. MgO hydrated in Mg-acetate solution of various concentrations (0 to 0.5 M) and CO2 cured afterward was characterized at different reaction times. Magnesium acetate in addition to enhancing the hydration kinetics modifies the morphology and crystallinity of the precipitated brucite. Acetate also influences the carbonate phases formed when samples are cured with CO2. Giorgiosite, a lesser-known hydrated magnesium carbonate, was formed in the presence of acetate, while the control specimens prepared with neat water produced nesquehonite. The findings reported here give insights into the use of organic additives in improving the reaction kinetics of MgO and the possibility to tune the formation pathways of different magnesium carbonates.

Freeze-thaw resistance performance of alkaline residue-blast slag based low carbon binder material: Supplementary study

The freeze–thaw resistance performance of mortar is crucial for its engineering applications. This study provides supplementary research on the freeze–thaw resistance of AR-CCS activated GGBS-FA cementitious system. Cyclic freeze–thaw experiments were conducted considering factors such as mix proportion as well as curing methods. The results show that after 50 rapid freeze–thaw cycles, the strength loss and mass loss of this system fluctuated between approximately 16–24% and 2.0–4.5%, respectively. Microscopic analysis indicates that excessively high temperatures and curing time can lead to temperature-cracks, deteriorating its freeze–thaw resistance. The addition of FA will decrease the system's strength and degrade pore structure, resulting in decreased freeze–thaw resistance. However, FA promotes the formation of tobermorite and C-A-S-H in the system, reducing the sensitivity of strength loss to temperature. Through statistical analysis, established a predictive equation for freeze–thaw resistance based on compressive strength and Cl-electric flux, with a strong correlation, having R2 ranging from 0.989 to 0.994. Overall, while this cementitious system may have slightly lower freeze–thaw resistance compared to traditional Portland cement with similar strength, but still meets engineering application requirements. It shows a significant engineering application potential in products without steel reinforcement like pavement bricks.

Durability parameters of three low-carbon concretes (low clinker, alkali-activated slag and supersulfated cement)

The general transfer properties (water porosity, mercury intrusion porosimetry, water permeability, capillary absorption, gas permeability and resistivity) and chloride penetration resistance (natural chloride diffusion test and rapid chloride permeability test) of three low-carbon concretes C25/30 (low clinker (LCK) concrete, alkali-activated slag with sodium carbonate (Na2CO3-AAS) concrete and supersulfated cement (SSC) concrete) were evaluated and compared, in order to identify the strengths and weaknesses of each technology. The results show that the LCK concrete is characterized by “excellent” transfer properties (low water porosity, gas permeability, water permeability and capillary absorption) but high viscosity in the fresh state and very high chloride permeability. AAS and SSC concretes have similar transfer properties, comparable to classical concretes C25/30, and are extremely resistant to chloride penetration. Finally, the use of traditional protocols for durability tests applied to alternative low-carbon binders is questioned and metrology adaptations are proposed.

The role of admixed CaO in a sulphoaluminate cement system under winter environments

Sulfoaluminate cement (CSA) is a low-carbon binder and can be regarded as an ideal cementitious material for winter construction and repair projects. However, the admixed CaO on the performance of CSA and its mechanism is still unclear, as well as the investigations and applications of CSA in negative temperature environments are very limited. Therefore, the impact of CaO on the setting time, compressive strength, cooling curve, and microscopic properties of CSA composite are systematically investigated. The experimental results reveal that the admixed CaO can significantly improve the compressive strength of CSA composite at negative temperatures (e.g., −5 °C, −10 °C, and −20 °C), and the admixed 2% CaO is the most effective in enhancing the compressive strength of CSA paste. At the beginning of hydration, CaO-modified CSA paste shows a significant exothermic peak, thus the freezing process of the liquid phase is retarded and the CSA can sustain hydration at −20 °C. Remarkably, the admixed 2% CaO can reduce the freezing point of the liquid phase of CSA paste to −7.2 °C, accordingly, decreasing the amount of freezable water and the risk of frost damage.

Effects of sucrose on fresh-state and setting properties of air lime

The use of sustainable additives such as sucrose for improving the properties of lime-based materials can contribute to a wider use of such low-carbon binders with applications in both civil engineering and conservation of the built heritage. Various sucrose-modified lime pastes were prepared, and their microstructure, fresh and hardened properties, and carbonation rate were assessed with an array of analytical techniques. It was found that sucrose acts as a water-reducing agent with relevant effects on both, fresh and hardened properties of pastes while allowing carbonation to occur homogeneously across the whole sample without the formation of carbonation rims. Such effects were enhanced when sucrose was added to the mixture after the slaking as pastes show higher mechanical strength and carbonate at a slower rate. When sucrose was added before the slaking, pastes show high elasticity, low mechanical strength, and carbonate faster due to their fine microstructure.

Early metakaolin reactions in pozzolanic R3-test: calorimetry baseline correction of initial temperature jump due to ex-situ mixing

The increasing concerns regarding global warming and the scarcity of raw materials in the construction industry have led to a growing need for alternative low-carbon binders to partially replace ordinary Portland cement. To assess the suitability of pozzolans as supplementary cementitious materials (SCMs), the R3-test has been introduced and successfully validated for a wide range of materials. This test provides an opportunity to analyze the reactivity classification and study the reaction mechanisms and kinetics of novel SCMs in a well-controlled environment. In this study, the focus lies on evaluating the early reactions of lime paste samples through isothermal calorimetry tests conducted at 40 °C. However, conventional mixing methods present experimental challenges. In-situ mixing fails to achieve proper paste homogenization, while ex-situ mixing results in a temperature difference at the start of testing due to the elevated testing condition of 40 °C. To address these concerns, a novel calorimetric methodology is proposed for early detection of reactivity responses. The main concept involves establishing a baseline correction for the temperature difference caused by ex-situ mixing, which is calibrated using an inert sample. This correction allows for the extraction of the heat generated by the early reactions. Combined with the Tian time correction, this methodology enables the evaluation of early reactions in lime paste samples measured with isothermal calorimetry at 40 °C within the first 100 min after mixing. The effectiveness of this methodology was demonstrated by evaluating the early reactions and the impact of potassium sulfate on three different types of metakaolin.

Surface treatment of inorganic modifier for improving carbonation resistance of geopolymers

Geopolymer (GP) is a low-carbon binder with the potential to replace Portland cement in reinforced concrete, however, the risk of corrosion to reinforced steel bars due to its low carbonation resistance must be addressed. This study proposed the use of an inorganic surface modifier, sodium aluminate solution (AN), to improve the carbonation resistance of GP. The effects of AN surface treatment on carbonation depths were investigated for GP mortars using fly ash (FA), ground granulated blast furnace slag (BFS), or their blend as active fillers. Rational AN surface treatment conditions and microstructural changes of treated GPs were also discussed. The obtained results show that AN surface treatment can significantly reduce carbonation rates of FA/BFS blend-based GP, and largely delay the onset of neutralization of heat-cured GP through the reduction of cracks and the formation of Na-gmelinite and gismondine, which refine the surface layer of GP. The surface modification using 40 wt%-AN solution reduced carbonation rate coefficient by about 70% for the FA/BFS blend-based GP cured at 80 ℃, and by above 30% for that cured at 20℃. The larger the FA blending ratio or the smaller the liquid-active filler ratio, the greater the improvement in carbonation resistance of FA/BFS blend-based GPs, caused by the AN surface modification. For the ambient-cured GP, repeated surface treatment is preferred, while for the heat-cured GP, once treatment is enough, and seal curing after the AN surface treatment is recommended regardless of the curing method.

Comparative study on the electric resistance of mortars made of low carbon binders

Against the background of the high CO2 emissions generated in the production of Portland cement (OPC), research is being carried out worldwide into alternative binders that can be produced with lower energy consumption. These have a lower clinker-cement factor or contain no Portland cement at all. To enable these binders to be used on a large scale, also in reinforced concrete structures, their performance in terms of durability must be ensured. The specific electric resistance is a parameter for characterizing different binders. At a young age, the hydration progress and the formation of the pore structure can be observed based on the specific electric resistance. In connection with the electrical conductivity of the pore solution, statements about the pore structure and the resistance to the penetration of corrosion-promoting substances are possible. Finally, the electric resistance is an influencing factor for estimating possible corrosion rates after depassivation of the steel reinforcement. In this study, a wide range of mortars produced with different alternative binders were characterized in terms of their resistivity as a function of age and water content. From the group of clinker substitutes (SCMs), calcined clays and modified steel slag were investigated. The other binders included in the investigation program are produced entirely without Portland cement: In addition to a calcium sulfoaluminate (CS̅A) cement and the C-S-H binder Celitement®, alkali-activated materials (AAMs) in the form of geopolymers and alkali-activated slags were also investigated. The results show a wide range of specific electric resistances in a naturally water-saturated state of the mortar specimens between 5.5Ωm for an alkali-activated metakaolin and 971Ωm for the Celitement®. Clinker replacements with calcined clays metakaolin, or metaillite result in increased specific electric resistances. In addition, the different binders show a very different influence on the dependence of the resistivity on the water content.

Improving the performance of alkali-activated slag mortar with electro/chemically treated carbon fiber textile

Alkali-activated slag is a widely used low-carbon binder. Incorporation of textile can mitigate the brittle weakness of alkali-activated composites. The bonding between fibers and matrix is critical for the performance of textile reinforced mortar. This paper is focused on the effect of different treatment methods on the bonding properties of carbon fiber in alkali-activated slag. The interfacial shear strength of fiber bundles in matrix was determined by the pull-out test. The flexural strength of the reinforced mortar was evaluated by a repeated bending. A scanning electron microscopy test was performed to characterize the interfacial properties of the fiber bundles. The results show that the interfacial shear strength of carbon fibers in matrix is improved by the electroplating with calcium silica slurry (CSS), impregnation in different solutions, and plasma treatments. An electroplating in CSS has the best improvement in the bonding strength with an increase by 620%. The CSS treatment increases the maximum flexural strength of CFT reinforced mortar with 22.5% and 30% at 7 and 28 d respectively, and it significantly inhibits the crack growth under the cyclic loading. This effect becomes more significant after a longer curing age. The electroplating treatment eliminates the cracks in the interface of fiber yarns. Slag reacts with the plated portlandite to strengthen the bonding between mortar and fiber bundles, so it has a better inhibiting effect on the crack growth after a longer curing.

Development of a low-carbon binder based on raw, ground, and carbonated waste paper fly ash

The formulation of an eco-binder only makes sense if the technical and environmental suitability of new waste material have been assessed. This study focuses on the recovery of three sets of waste paper fly ash (WPFA): raw, ground, and carbonated, as the main component of an eco-binder. The effect of the partial replacement of ordinary Portland cement (OPC) with WPFAs is studied from a mechanical and environmental point of view. The results show that raw WPFA contributes to the development of compressive strength, especially for low substitution rates (10 and 20%). Grinding results in improved compressive strength, fineness, and stability (at high substitution rates), and also accelerated setting kinetics. Natural carbonation is an effective and low-cost solution that has been proposed to treat WPFA before incorporation into the cementitious matrix. The carbonation contributes to delaying the setting and improving the stability of the matrix. Furthermore, the process of carbonation has been observed to have a beneficial impact on the stabilization of barium through the reduction of its leaching potential, which can contribute to the environmental sustainability of the eco-binder. In conclusion, the replacement of OPC with 20% of carbonated WPFA can save significant amounts of greenhouse gas emissions (27.29%).

Investigation on the effects of desulfurization gypsum on the engineering properties of ternary geopolymers: Improving the utilization of industrial wastes

Geopolymer as a low-carbon binder can effectively reduce carbon emissions and improve industrial waste utilization. To optimize the performance of GGBS-FA binary geopolymer, a ternary geopolymer was designed by the addition of desulfurization gypsum (DG). The engineering properties of GGBS-FA-DG ternary geopolymers were investigated by laboratory tests. Moreover, microstructure tests were performed to reveal the improvement mechanism of the engineering properties of the ternary geopolymers. Results show that the compressive strength of ternary geopolymer with 60% GGBS was higher than that with 70% GGBS. With the increase in addition amount of DG, the strength first increased and then decreased, and the optimal DG content was 6%. However, the strength of ternary geopolymers with 50% GGBS was barely improved and remained the lowest. Initial and final setting times were prolonged with the increase in DG content, and the initial setting time reached 34 min for the optimal ternary geopolymers (i.e., 60% GGBS, 6% DG). Drying shrinkage was reduced by 15.8% as the DG content increased to 8%. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results revealed that gel products and needle-like ettringite (AFt) crystals were generated in the ternary geopolymers. AFt can fill the pores and further improve the strength based on the gel strength. AFt wrapped on the surface of early-formed aluminosilicate can prevent it from further polycondensation into three-dimensional network gels, thus retarding the setting at the early curing stage. In addition, the beneficial expansion of AFt can inhibit the drying shrinkage for the ternary geopolymers with the optimal DG content.

Evaluation of the thermo-physical, mechanical, and fire resistance performances of limestone calcined clay cement (LC3)-based lightweight rendering mortars

Limestone-calcined clay cement (LC3) is one of the potential green or low-carbon binders for replacing ordinary Portland cement (OPC), leading to sustainable infrastructure development. Improving the thermal properties of the building's rendering mortar is an effective solution to reduce the building's energy consumption. In this study, LC3 has been prepared by replacing 60 wt% of OPC with a blend of limestone (LS) powder and metakaolin (MK) with LS: MK of 1:2 (wt%). Three mixtures of LC3-based lightweight mortars were prepared in which the binder was combined with three types of expanded/exfoliated insulant lightweight aggregates (LWAs), including expanded perlite (EP), expanded clay (EC), and exfoliated vermiculite (EVM), with aggregate volume contents of 75%. Compressive strength, in-direct tensile strength, bulk density, thermal conductivity, thermal diffusivity, specific heat, volume of permeable voids, and capillary water absorption, have been assessed. The effect of fire on the compressive strength and microstructure has been studied to explore the thermal stability of the prepared mortars. The newly developed LC3-mortars possessed densities below the specified limit for lightweight rendering mortars (i.e., ≤1300 kg/m3) accompanied with good thermal insulation performance. The mortar incorporating EP showed the lowest thermal conductivity (≈0.2 W/m.K), the highest thermal mass (≈2.3 MJ/m3. K) and the lowest compressive strength (≈6.76 MPa). The EVM mortar showed the highest strength retention efficiency; a residual strength of about 79.4% was obtained after standard fire exposure for an hour. The integration of LWAs into the LC3 binder matrix is helpful in improving the structural integrity upon fire exposure. The simultaneous improvement of thermal and mechanical properties in addition to fire resistance with the potential to reduce carbon footprint summarize the major innovation presented in this study.

Composite alkali-activated materials with waste tire rubber designed for additive manufacturing: an eco-sustainable and energy saving approach

There is an increasing trend in research projects and case studies to demonstrate the potential of Additive Manufacturing (AM) with concrete, better known as 3D concrete printing. Like ordinary construction, the latest upgrades on this topic are strongly focused towards improving eco-sustainability in terms of low-carbon materials. Low-carbon binders’ alternative to Portland cement and the utilisation of selected waste materials in place to virgin aggregates has high potential in fulfilling the sustainable development goals. In this paper, an experimental study was performed by incorporating ground waste tire rubber aggregates of different size gradation (0–1 mm and 1–3 mm) and replacement levels (50 v/v% and 100 v/v%) in a “greener” alkali-activated mix designed for 3D printing applications. First, the experimental program involved the optimization of mix design rheology and printing parameters to successfully integrate rubber aggregates into the printable alkali-activated mixtures. Then, a comprehensive characterization, including static mechanical testing, dynamic thermo-mechanical analysis, thermal conductivity testing, and acoustic insulation measurements was conducted. Comparison with identical Portland-based rubberized formulations designed for AM revealed better mechanical isotropy, flexural strength, thermo-mechanical behaviour, heat insulation, and high-frequency acoustic insulation for alkali-activated composites. The influence of rubber aggregate size on the fresh and hardened state behaviour of the mixes was also studied and discussed. Keeping the losses in mechanical strength restrained, the rubberized composites designed in this study have demonstrated significant thermal and acoustic insulation properties that are desired for energy-saving applications in buildings. The research verified the practicability of using waste aggregates in low-carbon binders for sustainable lightweight and thermo-acoustically effective applications, establishing an attractive starting point to address future research on material optimization for practical purposes.

Synthesis and application of calcium silicate hydrate (C-S-H) nanoparticles for early strength enhancement by eco-friendly low carbon binders

Abstract C-S-H–PCE nanocomposites are known to perform as highly effective seeding materials in Portland cement. Here the effectiveness of a C-S-H–PCE nanocomposite admixture on early strength development of eco-friendly cements (clinker blended with up to 35% fly ash or calcined clay) was investigated. First, C-S-H–PCE nano-composites were synthesized from Ca(NO3)2/Na2SiO3 via a co-precipitation method and their particle size distribution was analyzed. Differently structured PCE comb polymers based on IPEG chemistry were used in the synthesis. Nanofoils of ∼50 nm length were identified as most promising seeding material. Furthermore, addition of such C-S-H–PCE nanofoils was found to substantially increase mortar strength at early ages, particularly after 6–24 h of curing. Isothermal heat flow calorimetry and in-situ XRD measurements indicate that silicate hydration in cement is significantly accelerated. Most remarkably, C-S-H–PCE also was confirmed to speed up the pozzolanic reaction of fly ash and calcined clay and to stimulate the formation of hemicarbo aluminate (Hc), especially in calcined clay cement. Thus, C-S-H–PCE can foster the more widespread use of eco-friendly CEM II/III cements.