Formation Of Calcium Silicate Hydrate Research Articles

Pb2+ Leachability in the Cement-Based Solidified/Stabilized Contaminated Clay Under Saline and Alkaline Environments

ABSTRACT Harsh environments such as saline and alkaline environments will affect solidification/stabilization quality, especially considering the long-term service cycle. To investigate the environmental influence on the leaching behavior of solidified/stabilized soils, the Pb2+ leaching behaviors of cement-stabilized contaminated clay (CSC) and ternary binder (CSG)-stabilized contaminated clay (CSGSC) under the endo/exogenous saline and alkaline attacking environment were discussed. Note that, the ternary CSG binder, consisting of cement, silica fume (SF), and desulfurization gypsum powder (DGP) in a ratio of 1:0.25:0.19, underwent pre-screening based on its unconfined compressive strength (UCS). Scanning electron microscopy was employed to reveal the environment-resisting mechanism. The leaching concentration of Pb2+ in the leachate from CSGSC was lower than that from CSC in both saline and alkaline environments with a same incorporation ratio (15%) to dry soils, indicating CSG’s efficiency. Under the exogenous environment, the Pb2+ cumulative leaching mass from the stabilized clays in saline environment was more than that in deionized water, while that under the endogenous environment was opposite. Microstructure analysis indicated that the SF and DGP in CSG facilitated the formation of calcium silicate hydrate and ettringite, resulting in a denser structure that greatly enhances the physical encapsulation and chemical fixation of Pb2+ cation. At the end, the different mechanism under endo/exogenous attacking environments was attributed to the cation influence on clay minerals and the formation of new substance. These findings provide a guidance for the remediation of contaminated soil in harsh environments.

Improving the mechanical performance of concrete by graphene nanoplatelets (GNP) enrichment in the interfacial transition zone (ITZ)

The interfacial transition zone (ITZ) between the aggregates and cementitious paste is generally a weak spot in concrete. To address this deficiency, the graphene nanoplatelets (GNP) are adopted and a novel approach is proposed in this study. Initially, GNP with three different diameters of 2 μm, 4 μm and 7 μm are evaluated. The 2 μm GNP are selected for the best strength and microstructure improvement in cementitious composites. Subsequently, the concrete made of GNP-precoated aggregate is prepared. The SEM and EDS are used to evaluate the microstructure and elementary composition of its ITZ. This research demonstrates that GNP-precoated aggregate approach significantly improves the efficacy of GNP in concrete by enhancing the ITZ. GNP promote the formation of calcium silicate hydrate (C–S–H) while concurrently mitigating the production of calcium hydroxide (CH) in ITZ, leading to enhanced elemental distribution and compactness of ITZ, as well as a reduced ITZ thickness. The proposed method notably enhances the mechanical properties of concrete.

Mechanical and self-healing properties of cement paste containing incinerated sugarcane filter cake and Lysinibacillus sp. WH bacteria

Cement is the most widely used construction material due to its strength and affordability, but its production is energy intensive. Thus, the need to replace cement with widely available waste material such as incinerated black filter cake (IBFC) in order to reduce energy consumption and the associated CO2 emissions. However, because IBFC is a newly discovered cement replacement material, several parameters affecting the mechanical properties of IBFC-cement composite have not been thoroughly investigated yet. Thus, this work aims to investigate the impact of IBFC as a cement replacement and the addition of the calcifying bacterium Lysinibacillus sp. WH on the mechanical and self-healing properties of IBFC cement pastes. The properties of the IBFC-cement pastes were assessed by determining compressive strength, permeable void, water absorption, cement hydration product, and self-healing property. Increases in IBFC replacement reduced the durability of the cement pastes. The addition of the strain WH to IBFC cement pastes, resulting in biocement, increased the strength of the IBFC-cement composite. A 20% IBFC cement-replacement was determined to be the ideal ratio for producing biocement in this study, with a lower void percentage and water absorption value. Adding strain WH decreases pore sizes, densifies the matrix in ≤ 20% IBFC biocement, and enhances the formation of calcium silicate hydrate (C–S–H) and AFm ettringite phases. Biogenic CaCO3 and C–S–H significantly increase IBFC composite strength, especially at ≤ 20% IBFC replacement. Moreover, IBFC-cement composites with strain WH exhibit self-healing properties, with bacteria precipitating CaCO3 crystals to bridge cracks within two weeks. Overall, this work provides an approach to produce a "green/sustainable" cement using biologically enabled self-healing characteristics.

Preparation and accelerating mechanism of alkali-free liquid accelerator made with silicon residue containing fluorine

Fluorine-containing silicon residue (FSR) is a solid waste that is harmful to the environment. A new alkali-free liquid accelerator based on aluminium sulfate (LAFS) was prepared using FSR. The addition of LAFS to cement mortar shortened the setting times and significantly improved the early strength. With the addition of 8% LAFS, the initial and final setting times were 2.48 min and 11.83 min, respectively, and the 1-day compressive strength was 14.6 MPa, which was 200% of that of the mortar without LAFS. The mechanism of the action of LAFS was studied using isothermal calorimetry test, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and other analytical methods. The results showed that the LAFS rapidly generated a large amount of ettringite and promoted the formation of calcium silicate hydrate in the cement paste. A conceptual model of the early hydration process of cement paste with added LAFS was established based on the analytical results.

Evaluation of mechanical strength, gamma-ray shielding characteristics, and ITZ microstructural properties of heavyweight concrete using nano-silica (SiO2) and barite aggregates

This research assessed the mechanical performance, gamma-ray shielding, and interfacial transition zone (ITZ) microstructural properties of concrete mixes that incorporate barite coarse aggregates and nanosilica. To achieve this goal, several concrete mixes containing normal coarse aggregate (NC), barite aggregate (BC), and nano-silica/barite aggregates (NSBC) were fabricated. Several properties such as workability, mechanical strength, electrical resistivity (ER), ultrasonic pulse velocity (UPV), chloride migration (RCPT), and gamma shielding were comparatively assessed for these concrete mixtures. In addition, analytical characterizations viz., x-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electronic microscopy (SEM), and energy dispersive x-ray (EDX) were employed to study the ITZ microstructure at mortar/aggregate interface of concrete mixtures. The results showed that barite concrete incorporating nanosilica (NSBC) exhibited higher density and improved mechanical properties compared to both normal concrete (NC) and barite concrete (BC). Specifically, concrete mixture containing barite aggregate and 3% nanosilica (3NSBC) content exhibited improved impermeability and reduced concrete porosity. The gamma-ray shielding properties for 3NSBC were superior among all concrete mixtures. After 28 days, 3NSBC exhibits higher compressive strength (18.26% and 14.76%) and greater shielding capacity (12.82% and 6.66%) compared to NC and BC, respectively. The analytical characterizations results have demonstrated that nanosilica helps prevent the accumulation of calcium hydroxide in the ITZ by utilizing it to form calcium silicate hydrate. This leads to the development of a more compact and denser microstructure in the ITZ of nano-silica-based barite concrete (NSBC). Furthermore, it was revealed that, the incorporation of nanosilica exceeding 3% led to agglomeration, resulting in a weaker ITZ within the concrete leading to overall reduction in concrete properties.

Hydration kinetics and mechanism of C3S with cellulose nanocrystals

Tricalcium silicate (C3S) is the primary ingredient in ordinary Portland cement (OPC). Understanding the hydration kinetics of C3S with cellulose nanocrystals (CNC) is the key to unveiling the intrinsic mechanism of CNC affecting OPC hydration. This study investigates the hydration interactions between C3S and CNC through extensive testing. Findings indicate that CNC incorporation can initially slow the hydration reaction and postpone the early-stage hydration of C3S. However, past the initial period (3 days in this study), CNC presence enhances the hydration pace and aids the hydration process, leading to an increase in the formation of calcium silicate hydrate (C–S–H) and calcium hydroxide (CH) without creating new phases. Further, the presence of CNC promotes the homogenous hydration of C3S, ensuring a homogenous distribution of hydration products. It also reduces the Ca/Si ratio in the C–S–H, without altering the C–S–H morphology. A correlation is made between heat flow and the thickness of hydration products enveloping C3S particles, confirming that CNC can intensify the inward water diffusion rate through C3S particles for the same hydration product thickness. Critically, it is found that the effect of CNC on C3S hydration is dependent on the water/C3S ratio. A low or moderate water/C3S ratio can promote C3S hydration but a very high water/C3S ratio diminishes the beneficial effects of CNC on C3S hydration. Finally, the study proposes a explanation for CNC's influence over the hydration of C3S with varying water/C3S ratios.

Design and characterization of iron–calcium–aluminium–silicate–hydrate as low-temperature binder

This work aims to synthesize new cementitious materials (binders) using marble powder, rice husk ash, activated laterite and NaOH solution by applying low energy process. The binder was used to stabilize solid precursors (laterite and pozzolan). To achieve this objective, calcium–silicate–hydrate (CSH) was first synthesized at different temperatures (26, 50, 80 and 100 °C). The best physical–mechanical properties were chosen to produce iron–calcium–aluminium–silicate–hydrate [Fe–C(A)SH] at different concentrations of sodium hydroxide solution: 4, 5, 6 M. Finally, the formulated binder at 6 M of NaOH solution was used to stabilize laterite and pozzolans at the following proportions 20%, 30%, 40% and 50%. The samples were characterized after 28 days of curing at room temperature. FT-infrared spectroscopy, X-ray diffraction, and environmental scanning electron microscope ESEM-EDS permitted to confirm the formation of CSH, and Fe–C(A)SH. The mechanical test used to evaluate the performance showed that the incorporation of 10% iron-rich laterite into CSH increased the strength up to 42.93 MPa and the addition of Fe–C(A)SH in the laterite/pozzolans increased the compressive strength of the final product (15.34 and 15.8 MPa for laterite and pozzolan, respectively). The highest concentration (6 M) increases the alkalinity and reduces the efficiency of silicate polymerization affecting the final structural compound. From the results, low-energy Fe–C(A)SH-based cement and stabilized compounds appeared promising for the development of sustainable infrastructures.

Study on the mechanical properties and strength formation mechanism of high-volume graphite tailings concrete

Graphite tailings and coal gangue (CG) are solid wastes produced by mines. The large accumulation of surface materials poses great harm globally, and resource utilization is an urgent problem to be solved. In this paper, steel slag (SS), granulated blast furnace slag (GGBS), and fly ash (FA) are used as binder materials. Graphite tailings sand (GTS) is used as a fine aggregate. Using coal gangue and natural gravel as coarse aggregates, high-volume tailings aggregate concrete was prepared by the alkali excitation method. The strength formation mechanism of concrete was analyzed by combining scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetry-differential scanning calorimetry (TG-DSC). The results showed that with increasing tailings replacement rate, the strength of concrete containing natural gravel and coal gangue as coarse aggregates gradually decreased. The strength of coal gangue aggregate concrete is 10-15 MPa lower than that of natural gravel aggregate concrete. The uniaxial compressive failure of GTS concrete is divided into three stages: quasielasticity, stable expansion, and critical stress. A small amount of steel scoria (less than 30 %) can provide a good calcium ion (Ca2+) environment for the hydration reaction. The concrete hydration products are mainly calcium silicate hydrate (C-S-H) gel, sodium aluminosilicate hydrate (N-(A)-S-H) gel, ettringite (AFt), etc., and the formation of calcium silicate hydrate C-S-H gel and N-(A)-S-H gel can inhibit the cracks that proceed by shrinkage deformation and improve the durability of concrete. GTS concrete can reduce carbon emissions and solidify some of the harmful substances of raw materials.

A Study on the Microstructure and Mechanical Properties of Portland Cement Incorporating Aluminosilicate Waste.

The influence of aluminosilicate pozzolanic waste, specifically spent fluid catalytic cracking waste (FCCW) and metakaolin waste (MK) from the expanded glass industry, on the properties of hardened Portland cement paste were analysed. The study involved replacing part of cement with FCCW and MK and observing their impact on the hydration, microstructure, density, and compressive strength of hardened cement paste. Various analysis methods were employed, including X-ray diffraction (XRD), thermogravimetric analysis (TG), and scanning electron microscopy (SEM), to understand the changes in the structure of the hardened cement paste during hydration. The findings revealed that FCCW tends to accelerate the cement hydration process due to its high surface area and pozzolanic activity. Notably, the formation of portlandite crystals was observed on FCCW particle surfaces in a specific direction. These crystals appeared smaller and developed in different directions in compositions containing a composite binder with mixture of FCCW and MK in a ratio 1:1. This could be influenced by pozzolanic reactions activated by fine particles of MK and the formation of calcium silicate hydrates (C-S-H) and calcium alumino silicate hydrates (C-A-S-H) in the presence of portlandite. The XRD and TG results indicated that the specimens containing a composite binder exhibited the least amount of portlandite. The compressive strength of these specimens increased compared to the control specimens, although the amount of cement was 9% lower.

Unraveling the molecular freezing behavior of water on a calcium silicate hydrate matrix.

The hydration process of cement-based materials primarily results in the formation of calcium silicate hydrate (CSH), which is crucial in deciding how long concrete will last. This study utilizes molecular dynamics simulation technology to explore the freezing behavior of pure water solutions within various calcium silicate hydrate (CSH) matrices. The investigated matrices encompass four different Ca/Si ratios. According to the simulation, as ice crystals develop close to the surface of CSH, the CSH matrix strengthens its hydrogen and ionic interactions with water molecules, which effectively prevents water molecules from crystallizing and nucleating. Consequently, these molecules compose an unfrozen water film structure that bridges between ice crystals and the CSH matrix. The research also reveals an intriguing relationship between silica chain behavior on the Ca/Si ratio and the CSH surface. Surface flaws arise as a result of the silica chains of CSH breaking into shorter segments as the Ca/Si ratio increases. These surface defects manifest as grooves on the matrix's surface, effectively capturing and retaining specific water molecules. The CSH matrix's hydrogen bonds with water molecules are weakened as a result of this process, facilitating their participation in the crystallization process, and leading to a thinner unfrozen water film thickness with an increased Ca/Si ratio. This study contributes to a greater knowledge of the performance and dependability of cement-based products by offering molecular-level insights into the freezing actions of liquids in gel pores.

Development of CO2-integrated 3D printing concrete

3D printing concrete (3DPC) technology is a promising technique for construction due to its advantages such as no formwork is needed, fast production, automation, and high architectural freedom. However, the layer-by-layer extrusion method has stricter requirements on the rheological properties of concrete. One of challenges of this technology is how to improve the rheological properties of concrete to satisfy the conflicting requirements during pumping and after extrusion. This study proposed to use CO2 as accelerator and rheology modifier by injecting CO2 during secondary mixing to improve the rheological and mechanical properties of 3DPC. The influences of the secondary CO2 mixing on the properties of poured concrete and 3DPC were investigated. After using the secondary CO2 mixing, the setting time and workability of concrete were reduced, which contributed to the significantly improved buildability of 3DPC. This was because CO2 accelerated the hydration of tricalcium aluminate (C3A) and tricalcium silicate (C3S) during the secondary mixing. After that, they were continuously accelerated by the calcium carbonate formed during CO2 mixing. Also, the compressive strength of poured concrete was enhanced by the secondary CO2 mixing because it reduced the volume of larger pores (>200 nm) and promoted the formation of calcium silicate hydrates (C-S-H), which simultaneously slightly increased the drying shrinkage. In addition, after using the secondary CO2 mixing, the compressive strength and interlayer bond strength of 3DPC was enhanced.

Circular economy strategy for the valorization of fly ash as a substitute for cement in monoliths (resistance and reactivity evaluation)

AbstractFly ash is currently a problem in different companies, mainly in thermoelectric plants, which must follow a production and consumption model that involves reusing, renewing, and recycling, thus contributing to the circular economy. This work aims to evaluate the reactivity and compressive strength of different types of ashes in concrete monoliths. For this purpose, sugarcane bagasse (SCBA), bituminous coal (BC), and untreated hazardous waste (RUD) were evaluated as replacements for cement. Monoliths and mortars have been manufactured in different mixtures, taken to a curing room, and their compressive strength and reactivity have been determined at different times (up to 28 days for the monoliths and up to 90 for the mortars), mainly in order to check the formation of calcium silicate hydrate (CSH) gels. In the monolith tests, the best performances have been with SCBA and BC, which have been used for the manufacture of the mortars. On day 56, the behavior of the replacement of 30% fly ash (15% BC:15% SCBA) presents a type H mortar behavior, with better results than the control. By day 90, all replacements had the same resistance as M mortars and even higher resistances than the control. This demonstrates the feasibility of its use in the production of Portland cement for the manufacture of low‐performance inputs. This implies the possible reduction of impacts, both in waste disposal sites and in emissions caused by the construction industry, thus contributing to the circular economy.

Effect of various additives in activating early age properties of phosphorus furnace slag blended cement

Phosphorus furnace slag (PFS) is an industrial by-product of yellow phosphorus production which causes environmental and landfill problems. Researchers have recently shown increased interest in the environmental benefits of incorporating PFS into mortar and concrete mixes. However, the low early strength and extended setting time of PFS restrict its use as a supplementary cementitious material (SCM). Considering this, the effect of different additives, namely sodium sulfate (Na2SO4), calcium sulfate anhydrite, calcined alumina (CA), and calcium aluminate cement (CAC) at up to 5 %, on the setting time, soundness, and early strength (2d) of 25 % and 50 % phosphorus furnace slag blended cement (PFSC) paste and mortar have been investigated. It is observed that chemical activation of PFSC paste is more critical in reducing the setting time. The addition of 3 % Na2SO4 to PFSC mortar resulted in the most significant improvement in early strength, with a 20 % increase in 25 % PFSC and a 27 % increase in 50 % PFSC compared to the reference PFSC mortar. Additionally, the microstructure analysis revealed the additional formation of calcium silicate hydrate (CSH) and ettringite in the 3 % Na2SO4 added PFSC paste compared to the reference PFSC paste. It is established that the relationship between microstructural changes and the enhancement of early strength in PFSC mortar is due to the chemical activation of PFSC paste.

Electro-cementation of calcareous sand using colloidal silica (CS) nanoparticles and alumina powder

The research investigates the effectiveness of a ground improvement technique that involves the electro-cementation of an onshore calcareous sand containing 95.3% calcium carbonate through a series of laboratory experiments. Colloidal silica (CS) nanoparticles and alumina powder were introduced as pozzolanic materials in the sand, and a direct current (DC) was passed through the sand-silica-alumina mix inside an electrokinetic (EK) cell. The method resulted in the electro-cementation of the calcareous sand through the formation of calcium silicate hydrates (C–S–Hs) and calcium aluminate hydrates (C–A–Hs) as products of the pozzolanic reactions between Ca(OH)2, SiO2 and Al2O3 after electrolysis occurred. Iron-rich cements were also formed by the degradation of anodes. These newly formed compounds changed the nature of the treated soil from a granular material into a rock. Results show that the compressive strength of the resulting rock formation is significantly improved. The treatment can be considered as an artificial lithification process through which the nature of the treated soil was changed from a granular material into a rock formation. The electro-cementation achieved by the treatment was further assessed by spectroscopic analyses including FE-SEM, EDX and XRD, which confirmed the formation of cementing agents within the structure of the treated sand. Potential applications of the technique include caissons, highway construction projects, dune fixation and erosion control, in addition to liquefaction mitigation due to electrolysis of pore water and plugging the pores with cementitious materials.

Study on Early Hydration Mechanism of Double-Liquid Grouting Material Modified by Composite Early Strength Agent.

To achieve an adjustable setting time and significantly improved early strength of a new type of sulphoaluminate cement-based double-liquid grouting material (SACDL), the effects of calcium formate, sodium sulfate, lithium carbonate, and a composite early strength agent on the setting hardening and early hydration behavior of SACDL paste were studied by means of setting time, fluidity, compressive strength, and viscosity tests. The results showed that the adsorption and osmosis of calcium formate, the complex decomposition of sodium sulfate, the precipitation polarization of lithium carbonate and the synergistic action of the composite early strength agent could accelerate the early hydration rate of SACDL, shorten the coagulation time, and improve the early strength of SACDL. The composite effect of 0.8% calcium formate and 0.5% sodium sulfate is the most significant in promoting coagulation and early strength; the initial setting time and final setting time of the slurry were shortened to 5 min and 10 min, respectively; and the 3 h compressive strength was capable of reaching 16.7 MPa, 31% higher than that of the blank group. In addition, X-ray diffraction and SEM morphology observation were used to study the composition of the hydration products and the evolution of the microstructure, which revealed the early hydration mechanism of SACDL under the synergistic effect of the composite early strength agent: (1) The solubility of tricalcium aluminate (C3A) and dihydrate gypsum (CaSO4·2H2O) increased under the low content composite early strength agent condition, which increased the ettringite (AFt) formation rate. HCOO- was able to penetrate the hydration layers of tricalcium silicate (C3S) and dicalcium silicate (C2S), accelerating the dissolution of C3S and C2S and promoting the early hydration of SACDL. (2) Under the condition of a high dosage of the composite early strength agent, the further increase in Ca2+ concentration promoted the crystallization nodules and precipitation of CH and accelerated the formation of calcium silicate hydrate (C-S-H) gel. C-S-H was filled between a large number of rod-like AFt crystals, thus making the structure more dense.

Influence of Integration of Iron Ore Tailings on the Physio-mechanical and Microstructure Properties of Fly Ash–Based Coarse Aggregates

Abstract The goal of this experimental study is to produce fly ash (FA)-based coarse aggregates by adding iron ore tailings (IOT) to the FA-based precursor as an additional mix component. The involvement of different types of binders—influential factors of both pelletization and geopolymerization that govern the production of FA-based coarse aggregates—was experimentally designed by adopting Taguchi’s experimental design. An evaluation was conducted utilizing response indexes at three curing periods to study the accumulation of all the influencing factors in the production process as well as on the engineering features of IOT admixed FA-based coarse aggregates. Aggregate impact and crushing values, individual pellet strength (IPS), and specific gravity and water absorption values were measured. According to experimental findings, IOT addition considerably affects the engineering characteristics of FA-based coarse aggregates. The heat resistance of the produced aggregates was found to be improved by the presence of different sodium oxide dosages and blending ratios (IOT:FA) based on analysis through scanning electron microscopy and thermogravimetric differential thermal analysis. The role of IOT in associative formation of calcium silicate hydrate is demonstrated by increasing calcium hydroxide, which supports increasing IPS values of produced aggregates. From the 1st to the 200th day of curing age, Fourier-transform infrared spectroscopy studies between the best- and worst-performing mixes showed two things: first, the emergence of new peaks with time, and second, the observation of major bands shifting to lower and higher wavenumbers, which was found to be directly correlated to the performance of the aggregates.

Shear strength and durability against wetting and drying cycles of lime-stabilised laterite soil as subgrade

Laterite soil is commonly used as a fill or pavement material. However, it tends to lose its natural bonding and experiences large deformation when subjected to cyclic rainy (wet) and hot (dry) seasons. This leads to cracking and deflection of road pavement. It has long been known that lime stabilisation can improve the engineering properties of laterite soils. Unconfined Compressive Strength (UCS) tests at different curing periods (0, 3, 7, 14, and 28 days) were conducted with various percentages of lime (3%, 5%, 7%, and 9%). The durability of stabilised soil against wet and dry cycles was also evaluated. In addition, the variation of shear strength parameters during the Consolidated Undrained (CU) triaxial test under different confining pressures has been presented. Microstructural analyses showed an increased soil strength due to the formation of calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH).

On the chemo-mechanical evolution process of high-volume slag cement paste

This study investigated the evolution process of high-volume slag cement (HVSC) paste from a chemo-mechanical standpoint. HVSC specimens with a 70 w.t. % slag replacement rate were studied at various ages. Evolution of phase assemblage, microstructure development, and micromechanical properties were analyzed using TGA/XRD/MIP/SEM-EDS and nano-/micro-indentation techniques. A two-scale micromechanical model was built to predict the effective elastic modulus based on the nanoindentation results. Key findings include: 1) Between 7 and 28 days, the formation of calcium silicate hydrate (C-S-H) gel phase improves the effective elastic modulus by filling capillary pores; 2) From 28 to 90 days, the phase assemblage and microstructure remain stable, with a transition from low-density to high-density C-S-H; 3) Between 90 days and 2 years, slag rims produced by slag grains result in increased elastic modulus; 4) The two-scale micromechanical model, combined with nanoindentation data, accurately predicts the effective modulus of HVSC composites, although the unhydrated slag grains-hydrated cement matrix interface may cause an overestimation at an early age. With longer curing time, this interface disappears owing to the continuous hydration of large slag particles and therefore a good match is found between the modelling and experimental results.

Effects of Nano-SiO2 grafting on improving the interfacial and mechanical properties of concrete with rice straw fibers

As a green and clean product, plant fiber has become a hot spot in the research of concrete. However, the weak interfacial properties of plant fibers with cement matrix restricted the development of plant fiber reinforced concrete. This study intends to prepare rice straw fiber reinforced concrete (RSFRC) grafting by Nano-SiO2 on the surface of rice straw fibers. The interface properties of silica grafted on straw fibers with cement were evaluated by the pull-out test of a single fiber from the cementitious matrix. The mechanical properties and fatigue resistance of RSFRC were investigated and a two-parameter Weibull probability fatigue equation of RSFRC was established. The enhancement mechanism of ITZ was revealed by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) tests. Results show that straw fibers grafted with Nano-SiO2 can momentously improve the mechanical and fatigue properties of RSFRC. The compressive strength, flexural strength, and abrasion resistance of RSFRC were increased by 14.6%, 22.3%, and 87.1%, compared with ordinary RSFRC after 28 days of curing. The specimens with 3% Nano-SiO2 concentration and the addition of 2% rice straw fiber to the cement weight exhibited the best flexural fatigue performance. From the microstructure analysis, Nano-SiO2 can enhance the interfacial properties of straw fibers in cement matrix, decrease the presence of calcium hydroxide and facilitate the formation of calcium silicate hydrate(C-S-H) gel. Beyond that, this research has a positive environmental impact on lowering the carbon footprint in concrete from using agriculture-based waste materials to extend the service life of infrastructures.

Repurposing carbonate-based waste for producing an innovative binder: optimization and characterization.

This study reports the full recycling of dolomite waste (DW) in the fabrication of a novel cementitious material through a facile and eco-efficient method. The proposed technique includes mixing different alkali-activators (i.e., NaOH and Na2SiO3) with DW powder, followed by curing at room temperature. Based on the alkali-activator type, sodium oxide concentration, and curing time, the formulated mixtures yield a wide range of compressive strengths. When DW powder is mixed with different contents of NaOH (2.5, 5, and 7.5 wt.% Na2O), the resulting hardened materials exhibited modest compressive strengths (less than 11 MPa) due to the formation of the gaylussite Na2CO3·CaCO3·5H2O phase. Concerning the other chemical activator (Na2SiO3), a significant improvement in the compressive strengths of the resulted hardened materials was detected. This was ascribed to the formation of calcium silicate hydrate, with a high binding capacity, through the exchange reaction between Na2SiO3 and CaCO3 inside DW. The sample activated with Na2SiO3 (silica modulus of 1.5) equivalent to Na2O of 7.5 wt.% offered the highest 90-day compressive strength (34 MPa). At silica modulus lower or higher than 1.5, a noticeable decrease in the performance of the hardened materials was observed, which could be attributed to the alter in binding phase composition. Overall, the present work presented a new approach in utilizing the available and low cost carbonate-based wastes as main precursors in the family of promising alkali-activated materials.