Viscosity Modifying Agent Research Articles

Detailed study on flexural strength of polypropylene fiber reinforced self-compacting concrete

Self-Compacting Concrete (SCC) is a standout amongst “the most progressive advancements” in developing the industry. This solid can stream and fill the most confined spots of the structural work without vibration. The Self-Consolidating Concrete is a superior solid which is progressively predict the strength. To improve the quality of SCC, polypropylene is included. Polypropylene Fiber is moderately another developing material, which is utilized in SCC to expand the flexural and elasticity of cement. For proper work capacity, Super Plasticizer (SP) and Viscosity Modifying Agent (VMA) are added to lessen isolation of the total. Self-Compacting Concrete has indistinguishable quality, with the utilization of VMA and Super Plasticizer. The expense of SCC is a lot higher than the Conventional Concrete [1]. The expense of materials for SCC is most prominent around 10–15%, when contrasted with materials for conventional Concrete. Be that as it may, it is affordable like, reserve funds in the rate of work, rate of flow and rate to fix work and so forth. In this examination 0.3%, 0.6%, 0.9% and 1.2% of polypropylene fiber by the heaviness of bond are included cement to upgrade the assets of SCC. Polypropylene fiber with a fiber length of 6–12 mm breadth of 14 µm and an angle proportion of 0.3, 0.6, 0.9, and 1.2 is utilized. In this test work, M20 evaluation of cement is taken to decide the Flexural quality, split rigidity of SCC with the ideal level of Super plasticizer, polypropylene fiber and VMA.

Improvement of viscosity-modifying agents on air-void system of vibrated concrete

The influence of viscosity-modifying agent (VMA) on air-void system of self-compacting concrete has attracted considerable attention in recent years. But for conventional concrete with a sharp loss of air content due to vibration operation, the role of VMA on air-void system remains unclear. This paper aims to validate and clarify the positive effects of VMA on air bubbles stability and air voids homogeneity in vibrated concrete. Three typical VMAs with variable dosages were incorporated to prepare twenty air-entrained fresh mixtures. Rheological properties of mortar matrix portion of fresh concrete, surface tension of aqueous solution and time-dependent air content were evaluated for every mix. The air-void system in hardened concrete was inspected at three casting depths of prism specimen. Results showed that the surface tension of VMA solution played a key role in the stabilization effect on air bubbles, which strongly varied with VMA molecules. A higher plastic viscosity induced by the higher VMA dosage was favorable for maintaining the homogeneous distribution of entrained small air bubbles and reducing the formation of large voids in vibrated concrete. Therefore, a proper incorporation of VMA can improve the freeze-thaw resistance of vibrated concrete with lower spacing factor and smaller chord length.

Optimisation of Mix Proportioning of Self-Compacting Concrete using Heuristic Search

The quality of concrete construction mainly depends on the factors like concrete constituents, degree of supervision, method of curing, etc. Hitherto, one of the most influencing factors is the mix design or proportioning that contributes major parts directly to the quality of finished product. Unlike conventional concrete the mix proportion of Self-Compacting Concrete or Self-Consolidating Concrete (SCC) is complex since it incorporates special concrete chemicals such as Viscosity Modifying Agent (VMA), Air Entraining Agent (AEA), and so on, that tends to alter the workability and other properties of concrete and moreover it has no standard procedures and is generally carried out by trial and error method. This research seeks to develop a rational methodology for optimal mix proportion strategy for SCC based on the standard tests on SCC such as V-funnel and J-ring test conducted in the concrete laboratory in controlled environment as per EFNARC 2005 standard guidelines. The test results are incorporated for computer simulation and using a Heuristic Search Algorithms, the optimum mix proportioning of SCC for different admixtures are obtained.

The effect of a polyacrylic acid viscosity modifying agent on the mechanical, thermal and transport properties of hemp and rapeseed straw concrete

In recent decades sustainability, carbon footprint and pollution have become significant issues on a global scale. It is widely recognised that the carbon footprint of the construction industry can be reduced which has led to sustainable materials being used more and more widely to meet emissions targets. Two of these materials are hemp concrete and rapeseed-straw concrete which are bio-composites made of a bio-aggregate, water and a lime binder, in this investigation Vicat prompt natural cement (PNC). The addition of a viscosity modifying agent (VMA) is studied for its effect on the mechanical, thermal and transport properties. It was found that the use of a VMA was very effective at countering the two biggest weaknesses of bio-based building materials as it reduced the capillarity absorption of the concrete significantly and also greatly increased the compressive strength and modulus of elasticity of the material.

Influence of Sporasarcina pasteurii cells on rheological properties of cement paste

Nowadays with the developments in the concrete materials technology, researches started to focus on highly flowable mixes with improved rheological properties. These highly flowable mixes generally require use of viscosity modifying agents (VMAs) to reduce bleeding and segregation. VMAs are water-soluble polymers that can be produced from acrylic polymers and polysaccharide-based biopolymers obtained from cellulose, starch or bacterial fermentation. Through the literature, nopal mucilage, brown algae and bacterial cell walls were proposed as alternatives to these bio-based admixtures. However, these alternatives also require extra processing which results again with a higher unit cost. This paper summarizes the rheological properties of a cement paste including bacterial cells. The main goal of this study was to investigate the influence of Sporasarcina pasteurii (S. pasteurii) cells on viscosity and yield stress of cement-based materials. The bacterial cells were directly incorporated to the mix water and influence of cells on viscosity and yield strength was evaluated by rheological tests. In addition, the influence of bacteria dosage, water to cement ratio (w/c), use of superplasticizers and fly ash on performance of biological VMA were investigated. Our results showed that the apparent viscosity and yield stress of the cement-paste mix were increased with the addition of the microorganisms. Moreover, the provided biological VMA was found to be compatible with the use of fly ash and superplasticizers depending on the w/c of cement paste.

Measuring the thixotropy of conventional concrete: The influence of viscosity modifying agent, superplasticiser and water

The study sets out to evaluate the thixotropy of conventional concrete containing rheology modifiers using various methods of rotational rheometry. Five mixes were examined: the control, two mixes with viscosity modifying agent (VMA) and superplasticiser (SP) respectively, a mix with combined viscosity modifying agent and superplasticiser (VMA + SP) and the last mix with an increase in water content. These mixes were formulated to achieve concrete with varying rheological properties. Tests were carried out to examine the evolution of rheology parameters (static yield stress, dynamic yield stress and plastic viscosity), thixotropy index, shear thinning and thickening, flocculation properties, torque decay pattern (with a subsequent drop in apparent viscosity), and hysteresis loop. Results show that conventional concrete known to be a shear thinning and thixotropic material, can possess anti-thixotropic (rheopexy) and shear thickening properties depending on the condition pre-history, resting time, shearing rate and inclusion of rheology modifiers. These factors also influence the magnitude of the thixotropy but not necessarily the evolution of thixotropy. Inclusion of VMA in conventional concrete had only slight influence (both increasing and decreasing depending on the method of measurement) on its thixotropic behaviour while the inclusion of SP, VMA + SP and increased water considerably influenced concrete’s thixotropic behaviour in a similar pattern. However, each rheology modifiers had its unique influence. VMA significantly improves the evolution of concrete’s viscosity; inclusion of SP tends to result in a rheopectic concrete; addition of VMA + SP and pre-shearing of concrete may result in an unstable thixotropy, while SP can initially dominate the thixotropic behaviour of concrete containing both VMA and SP, VMA’s influence may later surpass that of SP; more water in concrete tends to result in a lesser rate of thixotropic structure breakdown.

Cellulose nanofibrils extracted from fique fibers as bio-based cement additive

Bio-based additives are currently of special interest in the construction industry. The use of biopolymers increases every year owing to the industry's goal to provide non-toxic and emission-free construction products. Therefore, the addition of bio-based nanofibers to cement paste was studied. The bio-based nanofibers were isolated from fique fibers as cellulose nanofibrils (CNF) through mechanical and chemical treatments. The CNF acted as viscosity-modifying agent for the cement paste, thereby increasing its yield point exponentially with small additions. Moreover, the CNF increased the hydration degree and storage modulus of the cement paste, which were measured through a dynamic thermo-mechanical analysis (DMA) at high temperatures. Furthermore, the CNF-modified cement paste presented less microcracking under stress and at high temperatures. Thus, a synergetic interaction occurred between the cement paste and the bio-based nanofibers isolated from fique fibers.

Combination of superplasticizers with hydroxypropyl guar, effect on cement-paste properties

Abstract Viscosity-modifying agent (VMA) are used in several applications of concrete, such as underwater concrete, Self-Compacting Concrete (SCC) or Self-Levelling Underlayments (SLU) in order to improve the washout resistance and the stability. The study focuses on the modifications of cement pastes properties implied when a VMA (hydroxypropyl guars or HPG) and a superplasticizer are introduced together. For reaching this objective, two chemically different polycarboxylate-based superplasticizers (PCE) and two HPGs exhibiting different molar substitution ratios (MSHP), were studied. A method, combining total organic carbon and size exclusion chromatography, was developed in order to quantify the adsorption of the both admixtures. The adsorption of HPGs appears being significantly lowered by the presence of PCE, while only the adsorption of the less charged PCE is slightly affected by the HPG. As consequence, strong modifications of the rheological properties of cement pastes were noticed when HPG and PCE are combined. The desorption of HPG leads to higher yield stress and residual viscosity than with PCE alone.

Fresh and hardened properties of self-compacting concrete using silicon carbide waste as a viscosity-modifying agent

The aim of this paper was to evaluate the preparation of self-compacting concrete (SCC) with silicon carbide waste (SCW) as an alternative of the viscosity-modifying agent. Fresh properties like flowability, viscosity, filling and passing abilities as well as segregation resistance were measured while hardened properties such as strength, drying shrinkage, water absorption and chloride permeability were determined. The mechanisms responsible for the performance variations were explored by X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and nitrogen adsorption analyses. Results show that SCW improves the viscosity, filling and passing abilities, segregation resistance and flowability retention of SCC at proper replacement ratios although superplasticizer demand is increased. Besides, strength, drying shrinkage, water absorption and chloride permeability are closely related to SCW amount. Specifically, drying shrinkage, initial absorption and chloride permeability decreases as SCW increases and SCW improves strengths and final absorption at ratio no less than 15%. It is proved that SCW has porous structure with high water absorption, mainly accounting for its viscosity regulating performance. Water absorption and chloride impermeability improvement of SCC can be explained by the microstructure densification. Drying shrinkage is reduced due to the high water absorption and timely releasing ability of SCW. And the combined effects of internal curing, reinforcing filling and further hydration promotion of SCW boost the strength development of SCC. These results favor the reutilization of SCW and the sustainable development of cement and concrete industries.

3D printable concrete: Mixture design and test methods

The current study deals with a yield stress based mixture design approach for 3D printable concretes. The mixtures were evaluated based on buildability, extrudability, robustness and tests for structural build-up. For the print parameters (such as pump type, nozzle size and extrusion velocity) used in the study, it was found that both extrudability and buildability could be achieved only when the material yield stress was within a range of 1.5–2.5 kPa. Below this range, the material lacked enough strength to achieve shape stability, while above this range, the extrudabilty of the material was difficult. The robustness of the mixtures was quantified in terms of a variability factor defined in terms of the variation in yield stress with small changes in the superplasticizer dosage. Inclusion of 10% of silica fume, 0.1% of viscosity modifying agent (VMA) and 0.1–0.3% addition of nanoclay resulted in decreasing the variability factor, hence improving the robustness. The structural changes due to thixotropy and cement hydration increased the yield stress with time. This structural build-up was assessed by measuring the yield stress with increasing rest duration. The mixture with silica fume showed the maximum structural build-up while the mixture with VMA showed the least. Heat curves from semi-adiabatic calorimetry and penetration curves were also used to assess the structural build-up. They showed a similar trend to that of the yield stress vs time plots.

Utilization of Olive Waste Ash and Sea Sand Powder in Self-compacting Concrete

The main difference between self-compacting concrete (SCC) and other types of concretes is its aptitude for self-leveling. SCC can be achieved by using viscosity-modifying agents, superplasticizers, fillers or increasing the amount of fine aggregate. This research investigated the effects of two different fillers namely olive waste ash (OW) and sea sand powder (SS) of different proportions on some mechanical properties of SCC. Besides compressive strengths and volume variations during hydration, porosity has been evaluated by using X-ray computed tomography method. Moreover, mixes with limestone powder (LS) were prepared for better comparison. Findings showed that although there is not considerable difference in compressive strength and porosity using SS instead of LS, considering volumetric shrinkage is of the utmost importance. Also, OW increases the viscosity of SCC in fresh state but dramatically reduces compressive strengths and considerably increases the volumetric changes. Furthermore, porosity is noticeable in comparison with LS mixes.

Fundamental Fresh State Properties of Self-Consolidating Concrete: A Meta-Analysis of Mix Designs

The study reported in this paper is the first meta-analysis aimed at obtaining statistical models for the fresh state behavior of self-consolidating concrete (SCC) mixes which effectively reproduce the complex relationships between mix design and fresh state performance. A database compiled with data from more than 120 different sources was analyzed. This study proves that SCC fresh state performance is determined by three fundamental, uncorrelated properties: flow time, flow spread, and resistance to segregation, which constitute a robust mathematical framework for the optimization of SCC mixes. The models obtained for these fundamental properties have proved consistent and reproduce very well the general trends and interactions implicit in SCC mix design recommendations, which in effect constitute the mathematical validation of recommendations well sanctioned by practice. It has been proved that, if no supplementary cementitious materials (SCMs) are used, there is a remarkably narrow margin in which the three fundamental properties of fresh SCC mixes can be simultaneously optimized. The most stable mixes were found to be associated with sand-to-coarse aggregate ratios of at least 1.1. The flowability of SCC mixes in terms of both flow times and flow spread can be optimized when the following conditions concur: w/c ratio of 0.45, SCMs content below 100 kg/m3, and sand content not lower than 750 kg/m3. Furthermore, it was also proved that, in general, it is best to keep the dosages of superplasticizers (HRWRs) and viscosity-modifying agents (VMAs) below 1.7% and 0.7%, respectively, subject of course to variation across the different types of products available.

Feasibility of using cellulose filaments as a viscosity modifying agent in self-consolidating concrete

Nanomodification of concrete represents one of the phenomenal leaps in concrete technology providing innovative tools for engineering cement composites with improved performance. In self-consolidating concrete (SCC), for instance, designing flowable–yet stable and robust–SCC mixtures requires an optimum balance between flowability and stability. This is conventionally achieved by optimizing the dosage of high range water reducing admixtures (HRWRA) indispensable for flowability, while increasing the binder content or introducing viscosity modifying agents (VMA) necessary for stability. This study shows how cellulose filaments (CF)–a new type of nanocellulose materials–can be used as a novel tool for rheology modification and strength enhancement in SCC. CF were incorporated at concentrations ranging from 0.05 to 0.30% per weight of binder in cement pastes and SCC. Rheological and mechanical properties of CF systems were compared to those of plain systems and systems incorporating a commercially available VMA of welan gum type. Results showed that CF serve as a VMA due to the buildup of flexible nanoscale CF networks. As such, a geometry-based percolation model showed that at a concentration of 0.12 wt.%, a network of percolating CF was formed. Beyond this CF content, the yield stress, the plastic viscosity, as well as the HRWRA demand exhibited a substantial increase. CF networks increased mixture viscosity–essential for stability–at low shear rates. On the other hand, at high shear rates, CF networks led to lower apparent viscosity essential for improving pumpability; owing to the streamlining of the flexible nanocellulose fibrils in the direction of flow, thereby imparting a shear thinning behavior. Furthermore, CF imparted improvement in mechanical performance of 12–26% in compression, splitting-tension, and flexure. Research outcomes are expected to contribute towards offering an alternative VMA with strength improvement potential while contributing towards the implementation of sustainable materials for concrete technology.

EFFECT OF VISCOSITY MODIFYING AGENTS ON DEWATERING UNDER PRESSURE AND THE PERFORMANCES OF MORTAR AND CONCRETE

This study emphasizes the effect of viscosity modifying agents (VMAs) on bleeding and dewatering of fresh mortars under high pressure. A detailed experimental dewatering device was designed and the analysis was carried out in order to evaluate the influence of two types of VMA on dewatering of freshly mixed mortars under high pressure. Additionally, the influence of the VMAs on mortar flow and air content of concrete was investigated. Two different types of VMA, which are a surfactant type and a starch ether type with various dosages were used in the tested mortar and concrete sample having the same water to binder ratio. Experimental results showed that by using dosages of surfactant type VMA equal to or higher than 3%, the pressurized dewatering of the mortars was significantly reduced. The use of starch in mortar mixtures was ineffective to reduce dewatering of mortars under high pressure. At same water to binder ratio, the addition of surfactant type VMA slightly increased the mortar flow and the v-funnel flow time due to enhancement of the air content in mixtures whereas starch ether decreased the mortar flow and increased the v-funnel time. The results of this study indicate that the surfactant type VMA is useful to control the dewatering of concrete under high pressure.

Influential Mechanisms and Potential Applications of Nano-Silicas in Cement Composites

Nanosilicas have been known as super-pozzolanic materials and compared to silica fume, these materials have higher purity of silica and finer particles. However, in contrast to silica fume, nanosilicas are produced by various methods, leading to different morphologies and agglomeration statuses in their initial form. On the other hand, due to several mechanisms such as the bridging effect of calcium ions between particles, double layer compression at a high ionic concentration, and dehydration of silica surfaces, nanosilica particles are destabilized in the pore solution environment of cement mixtures. Thus, the behavior of these materials is different from that of silica fume. In this research, considering the recent studies, a comprehensive investigation has been carried out on the influence of nanosilicas on the mechanical, durability and microstructural characteristics of cement composites. This study investigates the mechanisms that influence the performance of nanosilica in cement-based materials. Based on these mechanisms, several applications have been suggested and discussed. Some of these applications include viscosity-modifying agent in self-compacting concrete, enhancing the cohesion of cement composites, increasing the adhesion capacity of repair mortars and shotcrete to the substrate surface, accelerating the cement hydration, developing low-alkali cements and fast early-strength cements.

Mix design factors of self-consolidating cement paste affecting the magnitude of variations in rheological properties induced by the addition time of PCE-superplasticizer

Robustness, which is defined as the capacity of a mixture to tolerate changes and variations in materials and procedures that are inevitable with production at any significant scale, is a key property to expand the use of self-consolidating concrete (SCC). Typically for robustness studies, the most investigated parameter is a variation in the water content. This paper evaluates the effect of the adding time of superplastizer (SP), which was either incorporated in the mixing water or delayed for 2.5 min, on the rheological properties of cement pastes with SCC consistency. Two different SCC mix design concepts, the powder-type (mixture 1) and VMA-type (mixture 2), were selected for this research. The results show that the selected powder-type mix design is more robust than the VMA-type to a change in addition time of SP. In the next step, different mix design parameters have been evaluated by varying the binder combination, the type of PCE-SP and the addition of viscosity-modifying agent (VMA) to determine which particular parameters cause the largest difference in rheological behavior due to a change in adding time of SP. The results have revealed that the limestone filler appears to have the most beneficial effect on the robustness of the cement pastes.

An investigation of the effects of limestone powder and Viscosity Modifying Agent in durability related parameters of self-consolidating concrete (SCC)

This work aims to analyse and compare a number of durability related parameters including diffusivity, absorption and electrical resistivity in conventional concrete (CC) and self-consolidating concrete (SCC). Three different types of SCC were mix-designed containing different additions such as limestone powder (LSP), Viscosity Modifying Agent (VMA) and hybrid type. Two water to cement ratios were selected for this study. Eight different concrete mixes including 6 SCC and 2 CC were then fabricated and the specimens were water cured at 22°C. Results showed a better performance of SCC with powder addition while compared to CC mixtures, although a weaker performance of SCC-VMA types in comparison with CC was found. Hybrid types of SCC showed weaker performance in chloride diffusivity and porosity, although better results have been shown in resistivity. Correlation between the different durability-related parameters was studied and strong regression were extracted. Finally, the results found were correlated with the maximum paste thickness (MPT) concept which seems to demonstrate the durability parameters of SCC is linked not only with the quality of the cement paste but rather with the distance among embedded aggregate particles.

Comparative study on flexural behaviour of RCC beam and SCC ternary beams with mineral admixtures

Self compacting concrete (SCC) has an ideal fluid character at the fresh state and becomes solid once it sets/hardens completely when poured on the desired shape of the mould. The increase of workability and the control of segregation were taken care by super plasticizer (SP) and viscosity modifying agent (VMA) dosages. In this paper an attempt was made to study the flexural behaviour of ternary SCC beams. Cement was replaced with two different combinations viz metakaolin (mk)+ground granulated blast furnace slag (ggbs) and silica fume+ggbs. The experimental results of these ternary beams were compared with Conventional Vibrated Concrete (CVC) & SCC control concrete (SCC 0). Fresh properties of SCC like slump flow, spread were studied in accordance with EFNARC guidelines. Flexural strength of concrete was tested at the age of 28days. Load-deflection characteristics were studied at mid span of the beam (L/2). From the results it was observed that SCC ternary blended beams have higher flexural strength and better ductile performance compared to CVC and SCC0 beams.

Three-Dimensional Electrical Impedance Tomography to Monitor Unsaturated Moisture Ingress in Cement-Based Materials

The development of tools to monitor unsaturated moisture flow in cement-based material is of great importance, as most degradation processes in cement-based materials take place in the presence of moisture. In this paper, the feasibility of electrical impedance tomography (EIT) to monitor three-dimensional (3D) moisture flow in mortar containing fine aggregates is investigated. In the experiments, EIT measurements are taken during moisture ingress in mortar, using electrodes attached on the outer surface of specimens. For EIT, the so-called difference imaging scheme is adopted to reconstruct the change of the 3D electrical conductivity distribution within a specimen caused by the ingress of water into mortar. To study the ability of EIT to detect differences in the rate of ingress, the experiment is performed using plain water and with water containing a viscosity-modifying agent yielding a slower flow rate. To corroborate EIT, X-ray computed tomography (CT) and simulations of unsaturated moisture flow are carried out. While X-ray CT shows contrast with respect to background only in highly saturated regions, EIT shows the conductivity change also in the regions of low degree of saturation. The results of EIT compare well with simulations of unsaturated moisture flow. Moreover, the EIT reconstructions show a clear difference between the cases of water without and with the viscosity-modifying agent and demonstrate the ability of EIT to distinguish between different flow rates.

Influence of Mineral Admixture on Stress Strain Behaviour of Self Compacting Concrete under Elevated Temperature

Background: The aim of the research is to study the effect of elevated temperature on different grades of Self Compacting Concrete (SCC), which is having excellent deformability and segregation resistance. Methodology: SCC specimens were cast using Silicafume (SF), Flyash (FA) and Metakaolin (MK) as mineral admixture, Master Glenium SKY as Superplasticizer (SP) and Glenium Stream as Viscosity Modifying Agent (VMA). After heating the specimens to 900oC, samples were allowed to cool naturally in case of air cooling and water was sprayed on the specimens in case of water cooling. Compressive strength and Stress Strain behaviour of specimens were found. Findings: Compressive strength of SCC specimens with SF, FA and MK were found to decrease by 53.57%, 65.25% and 72.95% respectively for air cooling. In case of specimens cooled by water, the decrease in strength was found to be 78.67%, 81.19% and 83.01% respectively for specimens with SF, FA and MK. The higher powder content of SCC makes the permeability of concrete as low, thus makes SCC more susceptible to spalling under high temperature. The percentage reduction in compressive strength of M50 grade specimens with MK was found to be 72.95% and 83.01% for the specimens cooled by air and water respectively. Higher strength loss was observed for higher grade of SCC. It was found from the experimental investigations that, higher strain values were observed for the specimens cooled by water as compared to specimens cooled by air and reference specimen. Application: Fire safety design of structural elements.