Viscosity Modifying Admixture Research Articles

Synergistic effects of superplasticizers and biopolymer-based viscosity-modifying admixtures on the rheology of cement-based systems

The study investigated the synergistic effects of combining superplasticizers with biopolymer-derived viscosity-modifying admixtures (VMAs) to enhance the performance of cement-based systems. Superplasticizers, including polycarboxylate ethers (PCE) and polynaphthalene sulfonates (PNS), were combined with VMAs derived from anionic (welan, tragacanth, and almond gums, and giant kelp extract) and non-ionic (guar and locust bean gums) biopolymers. Performance analysis methods included: (1) assessment of elasticity and structural build-up, (2) evaluation of viscosity, yield stress, and stability, and (3) analysis of hydration kinetics and development of compressive strength. Anionic biopolymers, such as welan gum and giant kelp extract, formed strong elastic flocculated networks, while tragacanth and almond gums led to networks with rapid rigidification. These biopolymer-based mixtures exhibited high stability against forced bleeding due to their superior viscoplastic properties. Among non-ionic biopolymers, guar gum systems resulted in higher visco-elastoplastic properties compared to locust bean gum systems. The hydration process and compressive strength development were significantly influenced by the type of VMA and dosage, as well as the type of superplasticizer used.

Effects of cement paste viscosity on the properties of lightweight expanded polystyrene concrete

Lightweight expanded polystyrene concrete (EPS-C) offers several advantages, including low density, sound resistance, and good thermal insulation. These characteristics are contributed by the use of expanded polystyrene (EPS) with a closed cellular structure, which is non-absorbent, hydrophobic, and low-density (around 6.9 kg/m³). Since EPS is much lighter than cement paste, the viscosity of the paste plays an important role indirectly affecting segregation and the properties of EPS-C mixtures. This paper presents the experimental results of the viscosity and its influence of cement paste on both the segregation of the concrete mixture and thecompressive strength of EPS-C. The research revealed that a viscosity of cement paste below 50 mPa.s resultsin segregation of the concrete mixture. As the viscosity increases, the degree of segregation decreases. However, when the viscosity exceeds 180 mPa.s, using a viscosity-modifying admixture becomes a good solution to prevent segregation in EPS-C mixtures. Therefore, the optimal viscosity range for the binder paste to ensure the concrete mixture does not segregate is between 50 and 180 mPa.s.

Improved Low-field NMR porosity characterization of cementitious materials containing water-soluble organic admixtures

Water-soluble organic admixtures (WSOAs) are widely used in cementitious materials, and may affect the porosity, but their effects on low-field nuclear magnetic resonance (LF-NMR) measurement are often overlooked. Using viscosity modifying admixture (VMA) as an example, this study demonstrates the presence of WSOAs would lead to an overestimation of porosity and a leftward shift of pore size distribution using LF-NMR. This is attributed to the formation of hydrogen bonds between polymer and water molecules, and the decreased distance between nuclear spins, respectively. A strategy is proposed to improve the accuracy of the porosity characterization by eliminating the additional effects of WSOAs in LF-NMR testing. The results show that the addition of small molecular mass non-ionic VMAs replacing mixing water (within a 20 % replacing rate) does not alter the porosity of the paste. This method can be extended to characterize the porosity of various porous materials containing WSOAs.

Influence of polycarboxylate superplasticizer and polyacrylamide on mirror effect of fair-faced concrete

This work successfully prepared fair-faced concrete with mirror effect. The gray value standard deviation, porosity, crack rate and glossiness of the concrete surface were used to characterize the apparent quality of fair-faced concrete. The effect of polycarboxylate superplasticizer and polyacrylamide viscosity-modifying admixture on mirror effect of fair-faced concrete was investigated. The changes of hydration products and microstructure of fair-faced concrete were monitored by the measurements of X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM) and mercury intrusion porosity (MIP), and the potential mechanism was analyzed. The results indicate that the polyacrylamide reduces the number and size of Ca(OH)2 and change the morphology of Ca(OH)2 crystals from large-size parallel stacking state to small-size edge corrosion structure. The polyacrylamide can refine the pore size of concrete, the most probable pore size at the optimum dosage is 13.73 nm, which is much lower than that at other dosages. The usage of the polycarboxylate superplasticizer will introduce air, which has adverse effect on the concrete surface. But polycarboxylate superplasticizer can also improve the flowability of concrete and make bubbles easy to discharge. The combined action of polycarboxylate superplasticizer and polyacrylamide contributes the fair-faced concrete for better mirror effect.

Influence of Admixture Source on Fresh Properties of Self-Consolidating Concrete.

The study presented herein was intended to (1) compare the optimum (minimum) dosage requirements of four different sources of polycarboxylate-based high-range water-reducing admixtures (HRWRAs) and viscosity-modifying admixtures (VMAs) in attaining slump flows of 508 mm, 635 mm, and 711 mm, and a visual stability index (VSI) of 0 (highly stable concrete) or 1 (stable concrete), and (2) assess the flowability/viscosity, stability, passing ability, and filling ability of the resulting self-consolidating concretes. The test results showed that the optimum dosage requirements to obtain a uniform slump flow and visual stability index varied among the four selected admixture sources. The required dosage amount for HRWRAs was highest for the polycarboxylate-ester (PCE) type and lowest for the polycarboxylate-acid (PCA) type. Acceptable flowability plastic viscosity dynamic and static stability, passing ability, and filling ability of self-consolidating concrete can be achieved with the proper dosing of the four studied admixture sources.

3D Printing of Fiber-Reinforced Calcined Clay-Limestone-Based Cementitious Materials: From Mixture Design to Printability Evaluation

Sustainability and limitations in embedded reinforcement are the main obstacles in digital fabrication with concrete. This study proposed a 3D printable fiber-reinforced calcined clay-limestone-based cementitious material (FR-LC3). The binder systems incorporating calcined clay (CC) and limestone filler (LF) were optimized by determining the flow characteristics and water retention ability of the paste. The effect of fiber volume on the key fresh and mechanical properties of the fiber-reinforced mortars made with the optimized binder was evaluated. A combination of offline assessments and inline printing were employed to investigate the printability of the FR-LC3 with various binder systems and viscosity-modifying admixture (VMA) dosages. The results revealed that the binary system with 20% CC and the ternary system containing 30% CC and 15% LF were highly advantageous, with enhanced packing density, robustness, and water retention ability. Incorporating 2% 6-mm steel fiber contributed to the highest 28-day compressive and flexural strengths and toughness without significantly compromising the fluidity. Finally, the developed FR-LC3 mixtures were successfully printed using an extrusion-based 3D printer. The LF addition in the ternary system decreased the maximum buildable height of a single-wall printed object while reducing the SP/VMA ratio significantly increased the height due to enhanced yield stress and thixotropy.

A comprehensive review on fresh and rheological properties of 3D printable cementitious composites

The undeniable potential of 3D printing technology to revolutionize global manufacturing processes has led to the emergence of advanced, digitalized, and fully automated construction techniques. Despite the growing interest in this technology, a significant challenge still exists in the development of cement-based printing material due to the complex interaction of various fresh and rheological property parameters. This review comprehensively explores fundamental fresh properties (flowability, buildability, extrudability, pumpability and open time) and rheological properties (static yield stress, dynamic yield stress, plastic viscosity) essential for the formulation of 3D printable cementitious composites, with and without fibres. The results obtained from different rheometers for successful 3D printed mixes are also summarized, highlighting variation in recorded values. Moreover, the review thoroughly investigates factors affecting both fresh and rheological properties, such as the type of supplementary cementitious materials, fibre type and dosage, superplasticizer, and viscosity-modifying admixture. It also identifies the clear impact of these parameters and further recommends the optimal range of some properties, such as a flowability value between 160 and 200 mm, to achieve desirable 3D printability of cementitious composites. Overall, this review offers valuable insights for developing new mix compositions suitable for 3D printing and serves as a useful tool in establishing guidelines for 3D printable cementitious composite materials, which are currently lacking but crucial for research, development, and application in this field.

A Comprehensive Review of Plant-Based Biopolymers as Viscosity-Modifying Admixtures in Cement-Based Materials

As the construction industry is facing the challenge of meeting the ever-increasing demand for environmentally friendly and durable concrete, the role of viscosity-modifying admixtures (VMAs) has become increasingly essential to improve the rheological properties, stability, and mechanical properties of concrete. Additionally, natural polymers are ever evolving, offering multiple opportunities for innovative applications and sustainable solutions. This comprehensive review delves into the historical context and classifications of VMAs, accentuating their impact in enhancing the rheological properties, stability, and mechanical properties of concrete. Emphasis is placed on the environmental impact of synthetic VMAs, promoting the exploration of sustainable alternatives derived from plant-based biopolymers. Indeed, biopolymers, such as cellulose, starch, alginate, pectin, and carrageenan are considered in this paper, focusing on understanding their efficacy in improving concrete properties while enhancing the environmental sustainability within the concrete.

A chloride diffusion model for cementitious material with pore-solution viscosity enhancement

A promising approach to retard chloride attack has been proposed by increasing the pore solution viscosity in contrast to the traditional methods, but the dependence of chloride diffusion coefficient on viscosity has not been included in the current transport models. This paper presents a model for the diffusion of chloride in cementitious materials based on the viscosity-enhancing behavior of pore solution using viscosity modifying admixtures (VMAs). The parameters affecting the diffusion of chloride in the viscosity-enhancing solution are proposed to be the VMA molecular shape factor and VMA volume fraction based on the Maxwell approximation of spherical inclusions in the effective medium approximation theory. VMA shape factor is modeled with VMA molecular mass as a key variable. VMA volume fraction is calculated as a function of water-cement ratio, hydration age, initial VMA volume fraction, and VMA leaching residual fraction. This chloride diffusion model is developed and validated, which is based on the modification of Fick's second law and takes into account the pore solution viscosity-enhancing behavior and VMA-induced pore coarsening. This model differs from traditional models based on ion transport paths and provides a new reference for concrete durability design in terms of the intrinsic properties of the pore solution.

Polycarboxylate Superplasticizers Used in Concrete: A review

Modern concrete frequently uses a variety of chemical admixtures, like setting time-retarding admixtures, viscosity-modifying admixtures (VMA), and superplasticizers (SPs). These chemical admixtures greatly impact cement components like film-forming capacity, flowability, and film drying time. Currently, the market provides a broad variety of chemically distinct polycarboxylate (PCE) products; of these IPEG and HPEG PCEs have a wide market share due to their cost-effectiveness. New PCE types such as GPEG and EPEG PCEs are currently being introduced, which will expand the family of vinyl ether (VPEG) SPs. In summary, this study examines the chemistry, functionality, the interaction between the chemical structure of PCEs and their behavior with concrete and/or cement-based materials (CBM). The performance of concrete and/or CBM is significantly influenced by the chemical structure of PCE, along with their main chain, anchoring group, side chain, molecular weight, and structure. In conclusion, more precise quantitative micro-analytical methodologies and modelling tools are required to get a comprehensive grasp of the variables influencing the microstructure of concrete and to apply PCE SPs to create more durable concrete.

Effect of Silica Fume Utilization on Structural Build-Up, Mechanical and Dimensional Stability Performance of Fiber-Reinforced 3D Printable Concrete.

It is known that 3D printable concrete mixtures can be costly because they contain high dosages of binder and that the drying-shrinkage performance may be adversely affected. Mineral additives and fibers are generally used to control these negative aspects. In this study, the use of silica fume, a natural viscosity modifying admixture, was investigated to improve the rheological and thixotropic behavior of 3D printable concrete mixtures reinforced with polypropylene fiber (FR-3DPC). The effect of increasing the silica fume utilization ratio in FR-3DPC on the compressive strength (CS), flexural strength (FS), and drying-shrinkage (DS) performance of the mixtures was also examined. A total of five FR-3DPC mixtures were produced using silica fume at the rate of 3, 6, 9, and 12% of the cement weight, in addition to the control mixture without silica fume. As a result of the tests, the dynamic yield stress value decreased with the addition of 3% silica fume to the control mixture. However, it was found that the dynamic yield stress and apparent viscosity values of the mixtures increased with the addition of 6, 9, and 12% silica fume. With the increase in the use of silica fume, the CS values of the mixtures were generally affected positively, while the FS and DS behavior were affected negatively.

XGB-Northern Goshawk Optimization: Predicting the Compressive Strength of Self-Compacting Concrete

The contributions of this study, which include enhanced predictive precision and the integration of supplementary admixtures, may be effectively used in real-world scenarios to optimize self-compacting concrete (SCC) mixes for particular applications. This technology exhibits the capacity to improve construction productivity, minimize material wastage, and foster the development of resilient and environmentally friendly infrastructures. This research examined radial basis function (RBF) network and extreme gradient boosting (XGB-based models for predicting the compressive strength (Cs) of SCC. A dataset was generated through the collection of experimental samples, which encompassed supplementary admixtures in addition to the conventional constituents of concrete comprised of lime powders, fly ash, granulated blast furnace slag, silica fume, steel slag powder, super-plasticizer, and viscosity-modifying admixtures. In the present study, two optimization algorithms named the northern Goshawk optimization algorithm (NGOA), and Henry gas solubility optimization (HGSO) were linked with RBF and XGB models (abbreviated as XGBNG, XGBHG, RBFNG, and RBFHG). The results indicate that each of the four models exhibits a notable degree of precision in their prediction methodologies for Cs. A considered comprehensive metric named OBJ showed that the XGBNG simulation received the slightest value at 0.8062, followed by XGBHG at 1.657, then RBFNG at 2.4891, and last RBFHG by 3.9131.

Mitigating chloride attack in cementitious materials without compromising other properties via the use of viscosity modifying admixture

To mitigate the harmful chemicals ingression into cementitious materials, traditional methods often aim to densify the pore structure, posing challenges for concrete dead-load or crack control. This paper proposes a facile method to mitigate chloride attack via increasing the pore solution viscosity in cementitious material without changing the matrix density or compromising other properties. The results indicate that the addition of viscosity modifying admixtures (VMAs) to the mortar, as an equivalent mass replacement of mixing water, can mitigate chloride ingress. Although it reduces the early age hydration heat, the mechanical strength at full age (3 d–28 d) and the porosity at 28 d remain unchanged when using an effective VMA (PEG1000). In addition, the matrix resistance to leaching is improved as well. These results may be attributed to the enhanced pore solution viscosity and the coexistence of VMA and C–S–H with decreased interlayer distance and shortened mean chain length. After 28 d of exposure, the most effective experimental group (PEG1000) showed approximately a 28 % decrease in chloride diffusion coefficient compared to the control group. This paper may inspire new technology to mitigate ions diffusion and promote its practical application.

Avaliação da trabalhabilidade de pastas cimentícias autonivelantes através da variação do teor dos aditivos superplastificante e modificador de viscosidade

Abstract To meet the self-leveling pastes’ performance requirements, its flowability is linked to the absence of segregation or exudation, which makes a high cohesion between the components mandatory. Therefore, the ideal dosage for these materials is an essential topic to provide such specific properties. To evaluate the composition effect on fresh state, a method was proposed to quantify self-leveling pastes’ uniformity through the analysis of the spread pastes’ diameter and borders. Thus, different dosages were tested varying some input contents. The uniformity was quantified with the development of indexes such as Perimeter Ratio (PR) and Input Relation (IR). It was concluded that lower spread diameters incurred in higher uniformity index. Furthermore, it was observed that to achieve an ideal dosage for pastes, there is a tendency of direct correlation between the uniformity index and the water/powder ratio (w/p) and superplasticizer (SP) content and an inverse one between it and viscosity modifying admixture (VMA).

New biopolymers as viscosity-modifying admixtures to improve the rheological properties of cement-based materials

The performance of various new biopolymers as viscosity-modifying admixtures (VMAs), including tragacanth, almond, and locust bean gums and giant kelp extract, in addition to two commercial biopolymer-VMAs, welan and guar gums in cement-based materials was evaluated. The effect of the preparation/addition method, type, and dosage of the investigated biopolymers on rheology, hydration kinetics, stability, and compressive strength of various cement paste mixtures was evaluated. The pre-dispersion and pre-dispersion/pre-hydration techniques showed greater influence on the rheology of the investigated mixtures compared to dry addition. Moreover, the investigated biopolymers led to a shear-thinning response with higher viscoplastic properties than the reference. The structural build-up of the mixtures was mainly influenced by the type and dosage of the biopolymers, observing higher performances in mixtures containing guar gum, giant kelp extract, and welan gum. The use of the investigated biopolymers enhanced the stability of the paste mixtures, while negatively influenced the early-age strength development.

Synergetic effect of viscosity modifying admixtures and polycarboxylate ether superplasticizer on key characteristics of thixotropic UHPC for bonded bridge deck overlay rehabilitation

Thin bonded ultra-high-performance concrete (UHPC) overlay is an advanced technology for bridge deck rehabilitation. UHPC should be tailored to secure adequate flowablility and high thixotropy to facilitate mixing and placement with a low risk of sagging of the material on sloped bridge deck surfaces. The synergetic effect between nanoclay (NC) and polycarboxylate ether (PCE) superplasticizer or cellulose-based viscosity modifying admixture (VMA) and PCE on the rheological properties (yield stress, plastic viscosity, and thixotropy), cement hydration, autogenous shrinkage, compressive strength, and porosity was systematically investigated. The bond strength between conventional concrete (CC) representing existing bridge deck concrete and thixotropic UHPC and the flexural performance of UHPC-CC composite beams were determined. Test results indicate that the incorporation of 1% cellulose-based VMA combined with 0.4% PCE can increase thixotropy from 12 to 60 Pa/min when the initial fluidity of the mortar phase of the UHPC was maintained at 200 mm. Such increase was limited to 19 Pa/min in mixtures prepared with 1% NC and 1.55% PCE. The thixotropic UHPC containing NC and cellulose-based VMA provided tensile bond strength higher than 3 MPa. The combination of NC and PCE improved the flexural toughness and strength by up to 45% and 30%, respectively, for composite beam specimens. It also led to slightly higher compressive strength associated with greater cement hydration and decreased porosity. The combined use of cellulose-based VMA and PCE led to 15% and 40% greater flexural strength and toughness, respectively, despite the 10% lower compressive strength due to a 30% increase in the volume of pores with diameters larger than 5 µm.

Printability and shape fidelity evaluation of self-reinforced engineered cementitious composites

Incorporating fibers into Engineered Cementitious Composites (ECC) renders it a promising self-reinforced candidate for additive manufacturing, which can effectively address the challenges of reinforcement and automation. Considering this research challenge the current study aimed at designing 3D printable ECC mixes. The problems involved in the printability of ECC such as poor extrudability, buildability and shape retention, were addressed by utilizing the methylcellulose (MC) as a viscosity-modifying admixture. The results indicated that adding 1 % MC improved the fiber dispersion coefficient by 28 % and increased static yield stress in a range of 4 % to 237 % and plastic viscosity in the range of 247 % to 950 % in four different ECC mixes. Accordingly, the dimensional conformity of 3D printed filaments was considerably improved, and all designed ECC mixes meet the extrudability and buildability requirements.

Viscoelastic properties of fresh cement paste: measuring procedures and influencing parameters

Fresh cement pastes behave as viscoelastic materials below the flow onset. The measurements of viscoelastic properties of fresh cement paste provide valuable insight into the dispersion of solid particles as well as the hydration kinetics at early age and its influence on the structural evolution and solidification behavior at quasi-static conditions. Monitoring the development of viscoelastic properties of fresh cement paste using dynamic oscillatory shear measurements can also elucidate the working mechanisms of chemical admixtures. These properties are efficient indicators to guide mixture proportion design and are necessary to understand the rheology and stability of concrete. In this paper, the most common techniques, including dynamic oscillatory measurements, used to assess the viscoelastic properties of fresh cement paste are presented and discussed. The measurement challenges and their effects on the accuracy of the obtained properties are highlighted. On the other hand, the effects of high-range water-reducer, viscosity-modifying admixture, and supplementary cementitious materials are discussed. Furthermore, the use of viscoelastic measurements to assess yield stress and structural build-up of cement paste is presented.

Extrusion and structural build-up of 3D printing cement pastes with fly ash, nanoclays and VMAs

3D printing technology (3DP) has provided new design and structural opportunities for cement-based systems (CBS) in architectural construction. However, there are still some issues related to extrudability and buildability of CBS, which can be overcome by using components for CBS rheology control. In this study, three types of nanoclays, a bentonite (BEN), a sepiolite (SEP) and an attapulgite (ATT), and two viscosity modifying admixtures (VMAs), a poly-acrylamide (VMA1) and a methylcellulose ether (VMA2), were added to a reference cement-fly ash 3D printing paste to evaluate their impact on CBS rheological properties and their implications in extrusion and buildability for 3DP. A polycarboxylate-ether based high range water-reducing admixture (HRWRA) was used to reach a target stiff consistency. Four laboratory tests were used to assess paste rheology, extrusion and structural build-up. Proper and deficient material extrusion limits were defined considering cohesion and initial yield stress. It was found that the combination of VMA2 and SEP increased cohesion, enhancing extrusion and avoiding water drainage and frictional behavior of pastes, producing properly extrudable paste. SEP by itself also improved structural build-up. Besides, samples with NC and VMAs required larger amounts of HRWRA, delaying cement setting and compressive strength gain.

Abrasion resistance and mechanical strength of underwater repair concrete curing under hydrostatic pressure

Damages of hydraulic concrete structures caused by erosion are a significant repair problem. Modern concrete enables performing the repair works without using the so-called dry dock. The repairs are often carried out at great depth. A special container, which could simulate placing and curing concrete under hydrostatic pressure, was used to study the concreting depth’s influence on the concrete’s future abrasion resistance. Two compositions of the underwater repair concrete were tested. The maximum grains size was 8 and 16 mm. Also, a viscosity-modifying admixture was used. The designed composites met the standard requirements in maintaining consistency in time and limiting the wash-out losses. The concrete specimens, taken for testing the abrasive resistance and compressive strength, were initially cured in the container for 28 days under pressure from 0 to 0.5 MPa. The pressure range corresponds to curing the concrete at a depth of up to 50 m. The abrasion tests were conducted using Böhme’s disk. The results show that the hydrostatic pressure does not negatively affect the strength and abrasion resistance of the underwater concrete. The abrasion resistance is not directly related to compressive strength. It has been observed that the higher is hydrostatic pressure, the higher is abrasion resistance of the concrete’s top layer compared to the bottom layer. The hydrostatic pressure acting when placing and curing the concrete mix causes releasing the bigger air voids. Therefore, the specimens taken from the top layer are less porous, which was confirmed by testing the apparent density.