Colloidal nanoSiO2 Research Articles

Mitigation mechanisms of alkali silica reaction through the incorporation of colloidal nanoSiO2 in accelerated mortar bar testing

Alkali Silica Reactivity (ASR) is a prominent issue concerning the durability of concrete structures. To mitigate this deleterious reaction, a widely accepted practice involves replacing significant cement portions with supplementary cementitious materials (SCMs). Given the scarcity of high-quality SCMs, nanoSiO2 exhibits considerable promise, given its minimal dosage requirement for ASR mitigation, whether applied independently or in conjunction with other SCMs. This research investigates the efficacy and underlying mechanisms of colloidal nanoSiO2 (CNS) in accelerated mortar bar tests according to the ASTM C1260 method. The experimental methodology incorporated two distinct forms of CNSes, CNS1 and CNS2, with average particle sizes of 14 and 67 nanometers, respectively. The outcomes are subsequently compared to the ASR performance of a sample containing silica fume (SF). The results demonstrate that the CNS size is pivotal in governing the pozzolanic reaction rate. The CNS2 and SF exhibited analogous pozzolanic reactions, displaying superior effectiveness in promoting pozzolanic activity compared to the CNS1. At a 4.75% cement replacement level, the CNS2 achieved a 78% reduction in mortar expansion over the control sample. The CNS1, when utilized at 4.75% and 7% cement replacement levels, yielded expansion reductions of 38% and 43%, respectively. It was found that the inclusion of the CNS can increase the porosity of mortar and contribute to silica dissolution from the reactive aggregates. Meanwhile, the addition of CNS improved the bulk resistivity of mortar by 200%-600% and flexural strength by 25%-62% based on the replacement levels and the CNS types. Moreover, improvements in calcium hydroxide consumption and alkali binding in the ASR gel were observed during the test, indicating the underlying mechanisms for expansion mitigation. These research outcomes can accelerate the CNS utilization to mitigate the ASR in practical field applications.

Optimizing mix proportions of blended cement composites through rheological and strength relations: A numerical modelling approach with curve fitting

The research presented is part of a larger project focusing on finding the optimum mix design for cement pastes using ternary blended binder containing cement, Calcium metasilicate (CMS), and colloidal nano-SiO2. Water absorption and sorptivity tests were also conducted to ascertain the porosity of the paste mixes. Compressive and flexural strength were used for the mechanical properties of different mixes, and rheology was conducted to find the flow characteristics of paste mixes. The numerical modeling employed involves regression analysis and curve fitting to find the significant factors affecting the properties of cement composites. The experimental data were subjected to analysis of variance (ANOVA) to determine the essential factors and their interactions. The results for strength parameters for high-volume replacement suggests that the optimum replacement levels for nano-SiO2 were 3% in both w/b ratios. The rheological parameter states that microfibres of CMS and nano-SiO2, increased the viscosity and decreasing the yield stress. The FESEM micrographs show the sequestration of CO2 and calcite formation due to high-volume CMS.

Effects of colloidal nanoSiO2 on the hydration and hardening properties of limestone calcined clay cement (LC3)

This research investigates the influence of colloidal nanosilica (CNS) on the hydration and hardening properties of Limestone Calcined Clay Cement (LC3). The sulfation degree for LC3 was first optimized based on the hydration heat, and the results suggested that gypsum increases the cumulative heat release during the hydration process of LC3, with a dosage of 2% by weight gypsum leading to the highest heat release. The effects of CNS on hydration reaction, fluidity, mechanical properties and microstructure of LC3 were then investigated. According to the results obtained from isothermal calorimetry and thermogravimetric analysis, CNS can considerably accelerate the reaction rate of the LC3 system. 3% and 5% by weight CNS can significantly improve the compressive strength of LC3 blends, especially at early ages of 3 and 7 days. The findings from this study lead to a better understanding of the modification effects of CNS on LC3 which subsequently provides an insight into regulation mechanism of CNS on LC3.

Experimental study on application performance of foamed concrete prepared based on a colloidal NanoSiO2-stabilized foam

In this study, colloidal nanoSiO2 (CNS) was added into the foaming agent at 0, 0.5, 1, 1.6, and 2 wt% of the binder mass to enhance the stability of foaming agent and prefabricated foam, further the stability of foamed slurry and hardened foamed concrete. First, the stability of CNS on foaming agent and prefabricated foam was investigated by examining surface tension, surface viscoelastic modulus E, foam parameters, surface shear viscosity, and morphology. Prefabricated foam containing CNS was then used to prepare foamed concrete with a dry density of 700 kg/m3. The rheological characteristics, volume change, setting time, hydration properties, and gas content for fresh foamed slurry and the pore characteristics, compressive strength, and thermal conductivity of hardened foamed concrete were characterized. The microstructural crystalline structures of the foamed slurry and hardened foamed concrete were also investigated. Results of this study indicated that nanoSiO2 nanoparticles in colloidal state improved the stability of foam, especially when the CNS dosage was ≥ 1 wt%, because CNS caused increases in the surface viscoelasticity modulus E of the foaming agent and the surface shear viscosity of the prefabricated foam. Moreover, foamed slurry with a shorter hydration induction period, more stable volume, a shorter initial setting time, and higher viscosity was obtained when the CNS dosage was ≥ 1 wt%. Hardened foamed concrete with higher early compressive strength and superior thermal insulation properties was correspondingly obtained when fresh slurry with higher stability was used. However, the effect of CNS will decrease on the compressive strength of the hardened foamed concrete after 14 days of hydration. Finally, mechanisms were proposed regarding the stabilization effects of CNS on the prefabricated foams, foamed slurry, and hardened foamed concrete.

Enhanced effect and mechanism of colloidal nano-SiO2 modified rubber concrete

With the addition of rubber particles, the intensity of concrete reduces, limiting the application of rubber concrete in engineering. To increase the strength and applicability of rubber concrete, a highly dispersible colloidal nano-SiO2 (CNS) is used as an admixture. This study analyzes the enhanced effects and mechanisms of CNS on rubber concrete. The microcracks measurement results indicated that the width of the microcracks in the CNS-modified rubber concrete ranges within 3–10 μm, whereas that in ordinary rubber concrete ranges within 35–45 μm. The gray value correction method of the energy dispersive spectrometer map quantified the element distribution of the rubber-cement interfacial transition zone (ITZ). The results show that, compared with rubber concrete, the length of the growth segment with element distribution in the CNS-modified rubber-cement ITZ decreased by more than 40%. Additionally, the highest relative enhancements (30.3%) in early rubber concrete compressive strength were achieved by adding CNS. These findings indicate that the enhancement mechanism of CNS to rubber concrete can be attributed to the interfacial microstructure modification caused by the surface effect of nano-SiO2 and filling effect of the nanoparticles in the ITZ.

Enhanced Effect and Mechanism of Colloidal Nano-Sio2 Modified Rubber Concrete

Enhanced Effect and Mechanism of Colloidal Nano-Sio2 Modified Rubber Concrete

Flow Mechanism and Strength Characteristics of Textile Reinforced Concrete Mixed with Colloidal Nano-SiO2

In order to develop textile reinforced concrete (TRC) with good flowability and strength, colloidal nano-SiO2 (CNS) is adopted to improve the performance of TRC. The flowability, compressive strength, flexural strength, and four-point bending tests of TRC matrix with CNS are carried out, and the changes of internal micromorphological characteristics of TRC matrix are analyzed by combining with scanning electron microscopy. The results show that the CNS has an inhibitory effect on the flowability of TRC matrix, and the greater the amount of admixture is, the smaller the slump expansion of TRC matrix is. The compressive strength and flexural strength of TRC matrix show a trend of increasing and then decreasing as the amount of CNS increases, and the compressive strength reaches the maximum at each age (7 d, 14 d, 28 d) when CNS and silica fume replace 5% cement by 1 : 4 equal mass. The flexural strength reaches the maximum at each age (7 d, 14 d, 28 d) when 5% cement is replaced by CNS and silica fume with 3 : 7 equal mass. The flexural strength increases with the increase of CNS admixture. It is found by electron microscope scanning that the incorporation of CNS consumes more Ca(OH)2, refines the Ca(OH)2 crystal size, and generates more C-S-H gels. These C-S-H gels are distributed in a net-like pattern inside the concrete, filling the internal pores, effectively densifying the interfacial transition zone between the cementitious material and the aggregates, and optimizing the internal structure.

Effects of colloidal nano-SiO2 on the immobilization of chloride ions in cement-fly ash system

This paper investigates effect of colloidal nano-SiO2 (CNS) on chloride immobilization of cement-fly ash (FA) system composed of 70% cement and 30% FA from 7 d to 90 d age. The mechanism was revealed in terms of migration resistance, chemical binding, and physical binding; and each aspect was determined with corresponding measurements, including microstructure of hydrates examined by XRD, EDS, TGA and NMR, and pore structure evaluated by MIP. Results reveal that the CNS dosage influenced immobilized chloride ratio (ICR). 0.5% CNS promoted the ICR, while more than 0.5% CNS decreased ICR. The promotion by 0.5% CNS was derived from the refined pore structure and the increased amount of C–S–H gel, which could enhance the migration resistance and physical binding; the decrease by more than 0.5% CNS was because of the reduced amount of chloroaluminates and the decreased Ca/Si ratio, leading to the decline in chemical binding and physical binding. Furthermore, curing age also affected ICR. 28-day ICR was higher than that at 7 d or 90 d. The increase of ICR from 7 d to 28 d was attributed to the refinement of pore structure and the increase in amount of chloroaluminates and C–S–H gel; reduction from 28 d to 90 d age was due to the negative effects including the decrease in content of chloroaluminates and the reduced Ca/Si ratio. The findings are expected to give new insight into the effect of nano-SiO2 on performance of cement-based materials.

Improvement of Microstructure and Barrier Properties of Silicate Coatings on Low Carbon Steel by Incorporating Colloidal Nano-SiO2

Improvement of Microstructure and Barrier Properties of Silicate Coatings on Low Carbon Steel by Incorporating Colloidal Nano-SiO2

Strength, elastic and microstructural properties of SCCs’ with colloidal nano silica addition

One of the concerns regarding the elastic behavior of self-compacting concretes (SCC) is their lower stiffness tendency compared to conventional concretes (CC). Because of mixture design methods applied, SCC mixtures, in general, contains higher amounts of fine materials. The use of high volume of fine materials causes a decrease in the amount of total aggregates which have an important role on the strength and elastic properties of concretes. This paper discusses the results of an experimental study which investigated the strength, elastic and microstructural properties of SCC mixtures modified with different particle sizes of colloidal nano-SiO2 (CNS). CNS samples, having 35, 17, and 5 nm average particle size, were used with the aim of reducing the total fine material (fly ash) content in SCC designs. With the help of CNS, the amount of fly ash in reference SCC mixture design was gradually reduced and replaced with aggregates. The mixtures which fulfill desired fresh SCC properties were subjected to compressive tests at 28th and 120th days. Moduli of elasticity of concrete specimens were also measured. Results have shown that, although the use of CNS in reduced-fly ash content mixtures could not compensate the strength decrement, the stiffness of SCC mixtures containing CNS together with fly ash has been strikingly improved even the increase in total aggregate content is not noteworthy. Microscopic investigations has indicated the development of a dense C-S-H gel and interfacial transition zone.

Enhancing the permeability and abrasion resistance of concrete using colloidal nano-SiO2 oxide and spraying nanosilicon practices

By protecting concrete from penetration of aggressive chemicals, low permeability is one of the most important contributory factors to the concrete’s durability. In this paper the effects of nano-SiO2 particles on concrete permeability are studied through employing the technique of spraying nanosilicon and treatment in the water-diluted nano-SiO2 oxide. To this end, some mechanical and microstructure properties of concrete are investigated. The results show that the compression strength and the resistance of specimens to water penetration are significantly increased, whether in the mixtures cured in the colloidal solution or those being sprayed with nano-SiO2. The minute dimensions of these particles allow them to penetrate up to a particular depth in a concrete panel. Hence, through improvement of concrete panel nanostructures, these particles participate in the completion of the hydration process, which in turn leads to a reduction in their permeability and development of a protective layer, and therefore the increase of bulk concrete panel durability. The experiment’s outcomes also develop thorough understanding of the effects of nano-SiO2 as an additive material after preparing the concrete and during the curing process.

Rheological and fresh properties of reduced fine content self-compacting concretes produced with different particle sizes of nano SiO2

In this study, colloidal nano SiO2 (CNS), which can be assumed as a multi-functional nano-technological material in cement-based systems, was utilized in an effort to reduce the total fine material content in self-compacting concrete (SCC) designs. The influence of CNS addition on flow properties and rheological parameters has been investigated. Three different average particle diameter of CNS which was used to modify the SCC mixtures are 35nm, 17nm and 5nm. CNSs were used at different amounts and total fly ash amount in the mix design was decreased step by step from 160kg/m3 down to 0kg/m3. The volumetric emptiness occurred by the reduction of fine materials was filled by aggregates. On fresh state, T500 slump flow time, slump flow diameter, V-funnel time, static penetration resistance, sieve segregation and visual stability index tests were performed. Moreover, rheological parameters such as static yield stress, dynamic yield stress and plastic viscosity were obtained by using a concrete rheometer. In this way, it was aimed to design SCC mixtures with reduced fine material content by benefiting of the viscosity modifying effect of CNSs with various sizes. Results have shown that the effectiveness of CNS, in an effort to reduce the fine material content in SCC design is very significant.

Synthesis of SiO<sub>2</sub>-PCE Core-Shell Nanoparticles and its Modification Effects on Cement Hydration

NanoSiO2 was widely used to modify the property of cementitious materials, however, for nanoparticles used in cement-based materials, key problem is the effective dispersion. The surface modification technology can be introduced to promote dispersion of nanoparticles in aqueous system, especially in cement pore solution, which possess high concentration of ions. In this study, at first, NanoSiO2-polycarboxylate superplasticizer (SiO2-PCE) core-shell nanoparticle was synthesized from silanized polycarboxylate superplasticizer and colloidal nanoSiO2 by the “grafting to” method, then SiO2-PCE was testified by UV-Vis, FTIR, and TGA. Additionally, stability of SiO2-PCE and its effect on cement hydration were investigated. Results shows: SiO2-PCE possess higher stability in saturated calcium hydroxide solution compared to nanoSiO2, and heat development of cement hydration can be regulated by shell structure of SiO2-PCE. The research implied a new approach for nanoSiO2 to optimize cement-based composites.

Synthesis of nanoSiO2@PCE core-shell nanoparticles and its effect on cement hydration at early age

NanoSiO2 has been widely used to improve properties of cement-based composites, but effective dispersion of nanoparticles in cementitious materials remains to be a challenge for their practical applications. This paper introduces a surface modification technique that can enhance dispersion of nanoparticles in aqueous system, especially in the pore solution of cement paste. First, a series of nanoSiO2-polycarboxylate superplasticizer core-shell nanoparticles (nanoSiO2@PCE) were synthesized from silanized polycarboxylate superplasticizer and colloidal nanoSiO2 by the “grafting to” method, the prepared nanoSiO2@PCE were characterized by DLS, FTIR, and TGA. Then the investigation on the interaction between nanoSiO2@PCE and cement shows that nanoSiO2@PCE exhibits higher stability in saturated calcium hydroxide solution than pristine nanoSiO2, and the heat development during cement hydration can be regulated by shell structure of nanoSiO2@PCE. The research provides a new route for nanoSiO2 to optimizing cement-based composites.

Effect of the Electrochemical Migration of Colloidal Nano-SiO2 on the Durability Performance of Hardened Cement Mortar

Effect of the Electrochemical Migration of Colloidal Nano-SiO2 on the Durability Performance of Hardened Cement Mortar

Effects of colloidal nanoBoehmite and nanoSiO2 on fly ash cement hydration

The influences of colloidal nanoBoehmite (CNB) and colloidal nanoSiO2 (CNS) on fly ash cement mortar hydration and microstructure development of fly ash cement pastes were investigated. The results revealed that fly ash cement hydration was accelerated by CNB and CNS at early age thus enhancing the early age strength of the materials. Although higher content of nanoparticles significantly hindered cement hydration, adding appropriate amount of CNB and CNS benefited the development of compressive strength both at early and later age.

Effects of the pozzolanic reactivity of nanoSiO2 on cement-based materials

The aim of this work is to understand the characteristics of the pozzolanic reactivity of nanoSiO2 from studies of its pozzolanic reaction kinetics, morphology and structure of the hydrates and the influences of these features on the properties of cement-based materials, so as to explore a more targeted way of using nanoSiO2 in cement or concrete. It revealed that the pozzolanic reaction of nanoSiO2 is of the first-order and the apparent reaction rate constant of nanoSiO2-4nm is about one order of magnitude bigger than that of silica fume, but the specific reaction rate constant is about one half to that of silica fume. A compacter gel structure and poorer crystallinity of the hydrates of nanoSiO2 to those of silica fume are found, as well. The rate of hydration of cement at very early ages is enhanced by nanoSiO2, but the rate slows down with aging due to the compact gel structure. To make the use of the high pozzolanic reactivity and ultrafine particle size of nanoSiO2, as well as its resulting compact gel structure, colloidal nanoSiO2 was applied onto the hardened cement mortar by brushing technique and a less permeable surface was resulted, which shows the potential of using nanoSiO2 as a surface treatment material for cement-based materials.

Characteristics of surface-treatment of nano-SiO2 on the transport properties of hardened cement pastes with different water-to-cement ratios

A reduced transport property of the superficial part of concrete structures is beneficial for enhancing their durability, due to the blocking of the migration of aggressive agents. In this study, influences of colloidal nano-SiO2 (CNS) with a mean particle size of 20nm and its precursor, tetraethoxysilane (TEOS), on the transport properties of hardened cement pastes with water-to-cement ratios of 0.26, 0.38, 0.60 and 1.0 by mass were investigated by measuring the water absorption ratio and water vapor transmission coefficient, after the samples were first soaked in treatment agents for 1h. Results showed that CNS and TEOS are capable of reducing the transport properties of hardened cement pastes by altering the pore structures. CNS reduces the threshold value and volume of the pores larger than about 0.1μm, while TEOS reduces the threshold value and volume of the pores smaller than 0.1μm, and TEOS also reduces the ratio of the ‘ink-bottle’ pore volume to the throat pore volume to a greater extent. A linear relationship between the volume of capillary pores smaller than 0.1/0.01μm and the transport property was found, which can be ascribed to the reduction of transport properties of hardened cement pastes after surface-treatment with CNS or TEOS.

Preliminary attempt of hardened mortar sealing by colloidal nanosilica migration

An innovative electrochemical treatment for the sealing of hardened mortar by nanosilica migration is proposed. The composition of the colloidal suspension and the electric field power were assessed as significant parameters of the transport efficiency. The interaction between the nano-SiO2 and the cement matrix was characterized by different techniques: electrical resistivity measurements, DTA–TGA, BS-SEM with EDX microanalysis coupled and MIP. Results showed that the transport of colloidal nano-SiO2 under the action of the electric field can be achieved. An active interaction with the solid phases of the mortar samples was confirmed from the decrease in the portlandite content of treated mortar and from the smaller C/S ratio found in the solid hydrated phases of the treated mortars. A significant decrease of capillary pores was also identified at the age of 28days after finishing the treatment. The sealing ability of migrated silica nanoparticles was enhanced with the ageing of the treated sample; smaller amount of micropores was measured with the treated mortar ageing.

Effects and mechanisms of surface treatment of hardened cement-based materials with colloidal nanoSiO2 and its precursor

A dense surface structure of cement-based material is important for its resistance to the impacts of environment. Effectiveness and mechanisms of colloidal nanoSiO2 (CNS) and its precursor, tetraethoxysilane (TEOS), on surface-treatment of the one-month-old cement mortar by brushing technique were studied in this work. It revealed that CNS decreases the water absorption ratio of mortar when cured at 50°C and/or in sealed condition, but its effect is negligible when samples are cured at 20°C. A greater reduction of water absorption ratio is found in TEOS-treated mortar at 20°C or 50°C and under sealed or unsealed condition. Pozzolanic reaction between CNS/TEOS and Ca(OH)2 was observed by XRD, IR and EDS techniques. In addition, filler effects as revealed by SEM/EDS techniques were ascribed to for the densification of the exposed hardened mortar. Pore size distribution analysis conducted on mercury intrusion porosimeter showed that TEOS is more effective than CNS in filling pores finer than 50nm, while CNS is found effective in filling capillary pores coarser than 50nm.