Viscosity Modifying Admixture Research Articles

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.

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.

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.

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.

Rheology of cement–sodium silicate grout containing bentonite and cellulose ether at high temperatures

Cement–sodium silicate grout (CSG) is widely used to control water inrush disasters, and its apparent viscosity considerably impacts its water-plugging effect. However, traditional grouting materials and methods are inappropriate for high-temperature environments as high temperatures can affect the grout's viscosity. To thicken grout and increase its apparent viscosity, viscosity-modifying admixtures can be used. In this work, two types of bentonite (calcium bentonite (Ca-B) and sodium bentonite (Na-B)) and hydroxyethyl methyl cellulose (HEMC) were used to modify CSG and laboratory tests were performed to evaluate the fluidity, gelation time and rheology. The results showed that both bentonites and the HEMC decreased fluidity and prolonged the gelation time. HEMC, Ca-B and Na-B decreased the fluidity by 46.8–60.4%, 12.5–31.5% and 17.7–39.1%, respectively, at different temperatures. HEMC, Ca-B and Na-B increased the gelation time by 23.8–50.1%, 23.3–71.4% and 20%–57.1%, respectively. Bentonite can partially resist high temperatures and improve the apparent viscosity of grout owing to its water-absorption capacity. Conversely, HEMC has a negative effect on apparent viscosity, which is attributed to the formation of a complex microstructure resulting from intermolecular cross-linking between the cement particles and HEMC, preventing the connection of sodium silicate.

Effect of competitive adsorption between specialty admixtures and superplasticizer on structural build-up and hardened property of mortar phase of ultra-high-performance concrete

This study aims to enhance structural build-up of ultra-high-performance concrete (UHPC) without influencing the initial flowability, which is critical in repair applications (e.g., use of UHPC in thin bonded overlays for bridge deck rehabilitation). Specialty admixtures, such as a viscosity-modifying admixture (VMA), have been used to enhance the structural build-up at rest. However, the use of specialty admixtures can increase superplasticizer (SP) demand to maintain proper flowability; the synergistic effect of these admixtures on structural build-up is not well understood as the coupled admixture content can reverse the net effect on yield stress, viscosity, and thixotropy. In this study, VMAs including welan gum (WG), diutan gum (DG), and cellulose ether (CE) were used. Styrene-butadiene rubber (SBR) and acrylic ester (AE) latex polymers (LPs) that can enhance structural build-up and bond strength were also incorporated. The competitive adsorption between these specialty admixtures and SP and its effect on structural build-up, early-age hydration, compressive and pull-off strengths, porosity and entrapped air content of UHPC mortar (i.e., without fiber) were systematically investigated. Test results indicated that the incorporation of anionic WG and DG that exhibited high competitive adsorption with SP led to a 275%–450% enhancement in structural build-up despite the 55%–135% increase of SP demand. Such increase was limited to 130% when using CE, SBR, or AE that cannot effectively adsorb onto cement particles in the presence of SP. This was because the high competitive adsorption between specialty admixtures and SP strengthened the particle flocculation and promoted the cement hydration in the first hour; the latter resulted in 20%–40% enhancement in non-reversible component of structural build-up. Furthermore, the use of LP at low and moderate dosages secured high bond strength to normal strength mortar despite 8%–33% decrease in compressive strength given the increased capillary porosity. The use of VMAs increased the entrapped air and resulting 5%–15% lower compressive strength, while the bond strength was not influenced.

Lateral pressure of nano-engineered SCC combining nanoclays, nanosilica and viscosity modifying admixtures

Self-compacting concrete (SCC) is an energy efficient building technology widely used for multiple constructive applications. However, the large flowability of fresh SCC produces an increase of the lateral pressure exerted on the formwork regarding to conventional concretes. One solution to reduce the maximum lateral pressure (Pmax) is to modulate the fresh performance of SCC by the addition of rheology modifiers. Among them, nanocomponents highlight due to their larger efficiency derived from their tiny particle size. In this study, the efficiency of nano-engineered SCC (NE-SCC) combining small amounts of nanocomponents, as nanoclays and nanosilica, with viscosity modifying admixtures (VMAs) to decrease Pmax is explored. Lateral pressure exerted by NE-SCC on cylindrical columns subjected to self-weight and to air pressure was assessed using wall and capillary pressure sensors over time. It was found that the incorporation of attapulgite and bentonite nanoclays combined with VMAs could reduce Pmax. This reduction was measured with wall and capillary pressure sensors on self-weight column and air pressure column laboratory tests, and good correlation between them over time was obtained. A predictive model of the maximum lateral Pressure (Pmax) and its evolution over time (PL) was proposed, related to SCC paste thixotropy (Athix,p), casting height (H) and SCC pressure decay coefficient (Cd).

Determination of optimum VMA utilization dosage in cementitious systems: In terms of rheological and flowability properties

In mixtures such as self-compacting concrete (SCC) and 3D printing concrete (3DPC) having a high amount of binder, utilization dosage of water-reducing admixture (WRA) is increased to provide the rheological requirements. In such a case, in addition to the increase in cost, the presence of a high dosage of WRA in the system can cause segregation in the SCC mixture and a decrease in the buildability capacity of the 3DPC mixture. However, the addition of viscosity-modifying admixture (VMA) to the mixture together with the WRA reduces the risk of bleeding and segregation in SCC mixtures and increases shape stability and buildability in 3DPCs. Nevertheless, it was emphasized that these properties were seriously affected by the VMA dosage. It was aimed to determine the optimum VMA utilization dosage by examining the effect of dosages of VMA on the rheological properties and flow performance of paste mixtures in this study. Paste mixtures containing 4 different dosages of VMA (0%, 0.2%, 0.4% and 0.6%) were prepared. In all mixtures, the w/c and the WRA dosage were 0.35 and 0.2%, respectively. The rheological properties of the mixtures were evaluated by measuring the dynamic yield stress (DYS), final viscosity value and structural build-up (Athix) parameters. In addition, flowability of mixtures was also examined. DYS value of all mixtures decreased with the increase in VMA utilization dosage. The highest viscosity and Athix values were measured in the mixture containing 0.4% VMA. However, the lowest DYS, viscosity and Athix values were determined in the 0.6% VMA-containing mixture. Flowability of the mixtures generally increased with the increase of VMA utilization dosage. The optimum VMA usage dosage was chosen to be 0.4% in terms of rheological properties.

Effects of viscosity modifying admixture and nanoclay on fresh and rheo-viscoelastic properties and printability characteristics of cementitious composites

This study explores the effects of a viscosity modifying admixture (VMA) and attapulgite nanoclay (ANC) on rheological and viscoelastic properties as well as printability characteristics of mortar mixtures used for 3D printing. A total of sixteen mortar mixtures with varying dosages of VMA and ANC are prepared using a factorial design of experiments. Rheological properties of each mixture including static yield stress, plastic viscosity, and dynamic yield stress are evaluated through rotational rheometry tests such as ramp test and stress growth test. Then, the viscoelastic properties such as storage modulus, loss modulus and linear viscoelastic range are determined using oscillatory rheology tests. A thermogravimetric analysis (TGA) is conducted to assess the effects of VMA and ANC on hydration characteristics of mortar mixtures. A statistical analysis is performed to further evaluate the individual and joint effects of VMA and ANC on key performance parameters. An unsupervised clustering algorithm is used to group the mixtures into three clusters based on the obtained rheological and viscoelastic properties. A direct printing test using a screw type 3D concrete printing is conducted to assess the printability and buildability of the mortar mixtures selected from each cluster. Results indicate that the ANC can more effectively alter both rheological and viscoelastic properties of mortar composites for 3D printing compared with VMA. However, the combined use of VMA and ANC in printable mortar mixtures leads to a high static yield stress and storage modulus and the resulted mixture exhibits good buildability without any plastic collapse.

Mass Concrete Mixtures Optimized for Temperature Control and High Workability

Mass concrete is prone to thermal cracking, deleterious chemical reactions, and ultimate strength reduction caused by a high temperature rise. Defining mass concrete has been difficult since many factors affect the thermal behavior and the distress formation. Mass concrete is usually reinforced and may have geometric constraints that require concretes with high workability, as with self-consolidating concrete. For high workability and strength, high amounts of cementitious material are used for stability and low water–cementitious material ratios. Such amounts generally cause high water and paste contents that lead to cracking because of moisture loss and thermal contraction. In this study, a practical and useful definition of mass concrete was explored. Concretes with low cementitious material contents and high workability were investigated. To minimize the total cementitious material and paste contents, optimum aggregate gradations were considered. To achieve and maintain high workability during construction, a combination of admixtures was used that included high-range water reducing, workability-retaining, and viscosity-modifying admixtures. Laboratory testing of concretes with reduced cementitious material contents including high amounts of the supplementary cementitious materials and a combination of admixtures showed that concretes with a decreased temperature rise, high workability, and adequate strength can be obtained.

The net-zero and sustainability potential of SCC development, production and flowability in concrete structures

Abstract Climate action around the world has shifted to the potential of global warming contribution from the design and construction of infrastructures, especially those in demand for concrete. Concrete production and use have been identified as contributing to >5% of the world’s greenhouse gas (GHG) emissions. The main aim of this research work is to critically study the net-zero and sustainability potentials that the world can leverage on from the development, production and flowability of self-compacting concrete (SCC). Conventional concrete is made of >50% of ordinary cement, which contributes to >7% of the world’s GHG emissions. But in 1988, a fluidized concrete that compacts under its self-weight, known as SCC, was formed and developed to overcome the need for durability, skill and manpower that were dwindling in Japan at the time. This concrete created a pathway for cement to be replaced partially or totally by certain pozzolanic materials that function as viscosity-modifying admixture, high-water reducing agent or microencapsulated phase-change materials in the concrete mix. However, research findings have shown that for these materials to alter the flowability of SCC, there has to be reduced yield stress and moderate viscosity for allowable internal friction based on the Bingham model, and this has to be achieved under the same water–cement ratio. Fortunately, the implication of the use of these admixtures as replacements for cement is that there is a reduced demand for cement production and use in cleaner concrete production and, as such, a reduced CO2 emission associated with this process.

Comparison between Random forest and M5P to predict the compressive strength of concrete modified with solid wastes.

The efficacy of two machine learning algorithms to predict the concrete compressive strength is investigated in this research. For this objective, a vast amount of experimental data from numerous academic research articles was statically evaluated and modelled. In all, 265 observations were considered in this investigation 70% of the data was used for training, while the remaining 30% was used for testing. The data used in this paper was divided randomly. Cement, ground granulated blast furnace slag, limestone powder, fly ash, rice husk ash, fine aggregate, coarse aggregate, silica fume, superplasticizer, water, viscosity modifying admixture, and coarse aggregate were among the 11 input parameters employed in the study. The concrete compressive strength was taken as the output parameter of the model. To assess the models’ prediction abilities, correlation coefficient (CC), the mean absolute error (MAE) and root mean square error (RMSE) values were employed. From the results it was concluded that RF-based model outperforms the M5P Model. The CC, RMSE and MAE values for RF are 0.9867, 3.7887 and 2.9244 for training and 0.8668, 9.1723 and 5.8552 for testing stage respectively.

Effect of Cellulose Ether and Starch Ether on Hydration of Cement Processes and Fresh-State Properties of Cement Mortars.

The production of factory-made mortars is a multicomponent system. Viscosity-modifying admixtures (VMAs) are an inherent ingredient of these materials. The correct choice of the amount and type of these admixtures is important from the practical and scientific points of view. In this article, the use of cellulose ether (CE) and starch ether (SE) in cement pastes and mortars is studied. This research focuses on the hydration process and fresh-state properties of mortars because this subject determines the correct choice of the amount and type of admixture used, and the results determine the application and properties of hardened mortars. Polymers were added in the range from 0.056% to 0.22% in relation to the dry ingredients of the mortar. The research showed that cellulose ether had the greatest impact on the consistency, air content, bulk density, and water retention of ordinary dry-mix mortars. On the other hand, starch ether affected the hydration process, delaying the setting and hardening processes much more than cellulose ether. The action of these admixtures rose with the increase in the amount of polymer used in different ways (depending on the type of ether).