Torque Viscosity Research Articles

Prediction of Plastic Shrinkage Cracking of Supplementary Cementitious Material-Modified Shotcrete Using Rheological and Mechanical Indicators.

Plastic shrinkage cracking is a complex and multifaceted process that occurs in the period between placement and the final setting. During this period, the mixture is viscoplastic in nature and therefore possesses rheological properties. The investigation of the relationship between rheological behavior and its propensity to undergo cracking during the plastic phase presents an intriguing subject of study. However, many factors influence plastic cracking, and the corresponding interaction of its effects is complex in nature. This study aimed to evaluate the impact of rheological and physicomechanical properties on the occurrence of plastic cracking in high-performance shotcrete containing various supplementary cementitious materials. To achieve this, plastic cracking was evaluated employing the ASTM C 1579 standard and a smart crack viewer FCV-30, and the rheological parameters were controlled using an ICAR rheometer. In addition, a study was conducted to assess the strength development and fresh properties. Further, a relationship was established via statistical evaluation, and the best predicting models were selected. According to the study results, it can be concluded that high-yield stress and low plastic viscosity for colloidal silica mixtures are indicators of plastic cracking resistance owing to improved fresh microstructure and accelerated hydration reaction. However, earlier strength development and the presence of a water-reducing admixture allowed mixtures containing silica fume to achieve crack reduction. A higher indicator of yield stress is an indicator of the capillary pressure development of these mixtures. In addition, a series containing ultrafine fly ash (having high flow resistance and torque viscosity) exhibited a risk of early capillary pressure build-up and a decrease in strength characteristics, which could be stabilized with the addition of colloidal silica. Consequently, the mixture containing both silica fume and colloidal silica exhibited the best performance. Thus, the results indicated that rheological characteristics, compressive strength, and water-reducer content can be used to control the plastic shrinkage cracking of shotcrete.

Influence of Colloidal Silica and Silica Fume on the Rheology and Mechanical Properties of High-Performance Shotcrete

Wet-mix shotcrete technology is widely used worldwide. One possible approach to developing this technology is the use of various admixtures to improve its pumpability and shootability. However, the commonly used slump test is insufficient to evaluate the capabilities of fresh shotcrete, because they do not assess the influence of multiple factors on its workability and placement properties. The purpose of this paper is to investigate and determine the effect of colloidal silica with a particle size of 10 nm (with 2%, 3%, and 4% replacement) on high-performance shotcrete from a rheological and mechanical perspective. In addition, to compare these indicators, silica fume is used with a 4% and 7% mixing rate. Rheological parameters such as torque viscosity and flow resistance of fresh concrete were evaluated using an ICAR rheometer, and the measured values were correlated with pumpability and shootability. The results of the study demonstrate that torque viscosity decreases and flow resistance increases with the increase in the percentage of colloidal silica. Similarly, silica fume increases flow resistance and reduces torque viscosity. These findings demonstrate the possibility of obtaining high-performance shotcrete with improved pumpability and shootability by employing more colloidal silica and silica fume. It was also established that these supplementary cement materials improve the strength and durability of shotcrete.

Rheological Behavior of High-Performance Shotcrete Mixtures Containing Colloidal Silica and Silica Fume Using the Bingham Model.

There have been numerous studies on shotcrete based on strength and durability. However, few studies have been conducted on rheological characteristics, which are very important parameters for evaluating the pumpability and shootability of shotcrete. In those studies, silica fume has been generally used as a mineral admixture to simultaneously enhance the strength, durability, pumpability, and shootability of shotcrete. Silica fume is well-known to significantly increase the viscosity of a mixture and to prevent material sliding at the receiving surface when used in shotcrete mixtures. However, the use of silica fume in shotcrete increases the possibility of plastic shrinkage cracking owing to its very high fineness, and further, silica fume increases the cost of manufacturing the shotcrete mixture because of its cost and handling. Colloidal silica is a new material in which nano-silica is dispersed in water, and it could solve the above-mentioned problems. The purpose of this research is to develop high-performance shotcrete with appropriate levels of strength and workability as well as use colloidal silica for normal structures without a tunnel structure. Thereafter, the workability of shotcrete with colloidal silica (2, 3, and 4%) was evaluated with a particle size of 10 nm and silica fume replacement (4 and 7%) of cement. In this study, an air-entraining agent for producing high-performance shotcrete was also used. The rheological properties of fresh shotcrete mixtures were estimated using an ICAR rheometer and the measured rheological parameters such as flow resistance and torque viscosity were correlated with the workability and shootability. More appropriate results will be focusing on the Bingham model properties such that the main focus here is to compare all data using the Bingham model and its performance. The pumpability, shootability, and build-up thickness characteristics were also evaluated for the performance of the shotcrete. This research mainly focuses on the Bingham model for absolute value because it creates an exact linear line in a graphical analysis, which provides more appropriate results for measuring the shotcrete performance rather than ICAR rheometer relative data.

Rheological, mechanical properties, and statistical significance analysis of shotcrete with various natural fibers and mixing ratios

The rheological properties of concrete with natural fibers is studied herein. Natural fibers improve the concrete performance, moreover it covers the similarity between natural fibers and cement matrix. Natural fibers may decrease the pumpability of shotcrete as they reduce workability, which is a critical factor for shotcrete application in construction. The rheological analysis was conducted on 28 specimens, both with and without natural fibers, considering three natural fibers—kenaf, flax, and jute—three fiber lengths—5 mm, 10 mm, and 20 mm—and three mixing weights—0.5 kg, 1.0 kg, and 1.5 kg. The rheological properties of the specimens, such as flow resistance and torque viscosity, were measured using an ICAR rheometer, and correlated with pumpability and shootability. To adequately compare the recorded data, the rheological parameters were converted to Bingham model parameters. Furthermore, the compressive strength, flexural strength, and chloride penetration resistance of the specimens were determined to evaluate their durability. Slump and air content decreased based on the fiber weight and types compared with OPC. Moreover, rheological properties and mechanical properties of the fiber incorporated concrete are analyzed here. Finally, the statistical significance of the fibers was determined through an analysis of variance (ANOVA). Based on the results of the tests determined the optimal combination of fiber parameters that provides the best shotcrete performance.

Empirical models to predict rheological properties of fiber reinforced cementitious composites for 3D printing

3D printable construction materials need to be conveyed through a delivery system whilst possess certain flow resistance to ensure materials can sustain the weight of subsequent layers. To meet these requirements, material rheological properties should be optimized. In this study, factorial design was adopted to evaluate the influences of five variables (water-to-binder ratio, sand-to-binder ratio, fly ash-to-cement ratio, silica fume-to-cement ratio, and dosage of fiber) on material rheological properties (flow resistance, torque viscosity and thixotropy). Empirical models were established to predict rheological properties and were verified by experiment. Results imply that the increment of the dosage of fiber boosts all the rheological parameters, which are declined with the increment of water-to-binder ratio. Torque viscosity raises while flow resistance and thixotropy are decreased with the rise of fly ash-to-cement ratio. Conversely, the influence of silica fume-to-cement ratio shows an opposite trend on rheological properties as compared to that of fly ash-to-cement ratio. Flow resistance and torque viscosity are improved whilst thixotropy is declined if sand-to-binder ratio increases. Different formulations were adopted in printing test for verification and demonstration purpose via a robotic arm printing system in the end.

Effects of mineral admixtures and steel fiber on rheology, strength, and chloride ion penetration resistance characteristics of wet-mix shotcrete mixtures containing crushed aggregates

This study presents the effects of various mineral admixtures such as silica fume, fly ash, ground granulated blast furnace slag (GGBFS), and metakaolin and steel fiber on the rheology, strength, and chloride ion penetration resistance characteristics wet-mix shotcrete (WMS) mixtures made with crushed aggregates. The mixtures tested in this study are mostly ternary mixtures blended with silica fume. Potential implications of measured rheological properties in relation to pumping and shooting performance of WMS mixtures were also analyzed. The results have shown that silica fume may be an effective admixture benefiting both pumpability and shootability of WMS. Fly ash was found to adversely affect the pumpability of WMS mixtures by markedly increasing the torque viscosity. GGBFS had non-significant effects on both pumpability and shootability, whereas it strongly improved the chloride ion penetration resistance and strength of WMS. It was also identified that no more than 5% metakaolin by mass of cement is necessary to enhance the pumpability, shootability, and chloride penetration resistance of WMS. Despite many expected advantages of using steel fibers in WMS, special attention should be paid to prevent excessive degradation of pumpability and chloride ion penetration resistance when a high dosage (>50kg/m3) of steel fibers is used.

Predicting Pumpability and Shootability of Crushed Aggregate Wet-Mix Shotcrete Based on Rheological Properties

This study aims to estimate the pumpability and shootability of wet-mix shotcrete (WMS) made with crushed aggregates and various admixtures such as silica fume, fly ash, ground granulated blast furnace slag (GGBFS), metakaolin, and steel fiber based on rheological properties. The IBB rheometer was employed as an apparatus to measure the rheological properties of freshly mixed shotcrete such as flow resistance and torque viscosity. Results have shown that the use of silica fume and metakaolin led to satisfactory pumpability, whereas mixtures with fly ash and steel fiber failed to meet the pumping criteria at normal pump pressure. The build-up thickness, an indicator to represent shotcrete shootability, was predicted to vary between 68 and 218 mm, demonstrating that the use of admixtures resulted in a wide spectrum of shootability. In particular, the use of metakaolin was found to substantially increase the predicted build-up thickness only with a small replacement. The findings of this study are expected to be used as an easy-to-use guideline for estimating pumpability and shootability of WMS when no compliance testing data is available.

Correlating rheological properties to the pumpability and shootability of wet-mix shotcrete mixtures

The pumpability and shootability of fresh wet-mix shotcrete (WMS) mixtures are important factors determining the quality of applied wet-mix shotcrete. Currently, one of the simplest and most accepted methods for estimating the performance of the pumping and shooting process is the slump test. It is well known that the slump test, however, has some limitations in its ability to reasonably evaluate pumping and shooting performance, since it exhibits large variations even among mixtures with the same slump. This paper presents efforts to provide a quantifiable means of estimating the pumping and shooting performance of WMS mixtures in relation to fresh materials’ rheological parameters such as flow resistance and torque viscosity, focusing on investigating the effects of various additives and admixtures. The findings of this study reveal that fairly good statistical correlations exist between torque viscosity and piston pump pressure, flow resistance and build-up thickness, and rebound rate and build-up thickness. By contrast, it was quite challenging to define clear relationships between flow resistance and piston pump pressure, torque viscosity and build-up thickness, and rebound rate and rheological parameters.

Effects of admixtures on the rheological properties of high-performance wet-mix shotcrete mixtures

This study investigates the effects of various admixtures on the rheological properties of high-performance wet-mix shotcrete (HPWMS) in an attempt to resolve practical issues faced in conventional wet-mix shotcrete processing. The admixtures used in this study were silica fume, air-entraining agent (AEA), superplasticizer, synthetic fiber, powdered polymer, and a viscosity agent. Representative rheological properties such as yield stress and plastic viscosity were measured using an IBB rheometer to evaluate the pumpability and shootability of HPWMS with varying admixture types and contents. The results demonstrated that the use of AEA tended to reduce both flow resistance and torque viscosity of HPWMS almost proportionally. A superplasticizer had a relatively greater impact on the flow resistance rather than torque viscosity. Also, it was observed that silica fume led to a remarkable increase in flow resistance while it slightly reduced torque viscosity. This behavior trend indicates that silica fume is quite effective in enhancing the rheological properties of HPWMS, particularly in terms of shootability and pumpability.

Sensitivity analysis of the transient torque viscosity measurement method

While a new type of oscillating-cup viscometer which uses a rotating magnetic field has been developed and tested, the uncertainty of such measurements has been considered to only a cursory level. This paper reports work in which the sensitivities of this new method’s output are studied for the measurement of mercury with a particular device. It is concluded from the analysis that while the new method requires dramatically shorter measurement times than previous methods, the resultant uncertainty seems to be nearly the same as the classical oscillating cup method. As such, since the results are just as precise as other oscillating-cup methods, the new method should be employed for its speed advantage, allowing the viscosity of materials as functions of temperature or pressure to be economically determined.

Low-volume wet-process sprayed concrete: pumping and spraying

This paper, which reports on part of a three-year research project into wet-process sprayed concrete for repair, examines the influence of rheology on the pumping and spraying of fine concretes. The performance of ten laboratory-designed fine concretes were examined using a rotational viscometer, the slump test, a build test and a vane shear strength test. Visual grading and a sorptivity test were used to quantify the degree of reinforcement encasement which is a crucial factor in long term performance. Taken together, these tests form a rheological audit of each concrete which can help guide the design of sprayable, but also durable concretes. The two-point apparatus was successful for determining the flow resistance and torque viscosity of fine aggregate concretes, including those with air entrainment. The vane shear strength test was successful in providing an instantaneous reading of the shear strength of the concretes and is compared with their slump. The concretes were pumped and sprayed through a piston pump to assess their suitability and to measure their adhesion to a substrate by build thickness. This value is a measure of sprayability and is converted into values of maximum shear and tensile stress which are then compared with the workability parameters in order to determine their inter-relationship. These relationships are also compared with those obtained from a separated study of mortars. On its own, the sorptivity test did not accurately assess the encapsulation of the reinforcement. However, when considered with a visual grading of the cores, a more reliable indication can be obtained of the potential durability of the finished concrete, as well as the degree of encapsulation of the reinforcement. We demonstrate the conflict in selecting mix proportions that satisfy requirements for both installation and product quality.

Design of bauxite-based low-cement pumpable castables: a rheological approach

The growing demand for pumping of refractory castables, as a high efficient placing technique, has stimulated the development of compositions with specific rheological properties. In this work, a new type of rheometer has been used to measure the rheological behaviour and to predict the pumpability of bauxite-based low-cement castables. This overcomes the shortages of traditional techniques based on either flow measurements or working with the matrix portion of castable. The parameters which strongly influence the rheological properties and pumpability of bauxite-based low-cement castable such as particle size distribution, ratios of coarse to matrix and water to matrix, water addition and time have been studied. It has been found that the optimal flow resistance and torque viscosity are two important properties to be taken into consideration while designing a castable.

Applicability and Significance of Rheometric Tests for Rheology of Fluid and Self-Leveling High-Strength Concrete

The emergence of new special concretes on construction sites has shown that concretes of the same slump may behave quite differently on the job. For these concretes, one cannot rely on the traditional workability tests for quality control and rheological characterization. It has been claimed that the flow behavior of fresh concrete closely approximates the Bingham model and that at least two parameters are therefore needed to describe its rheology. Thus, rheological measurements must be carried out at not fewer than two shear rates. This study examines the applicability of the Bingham model to fluid and self-leveling highstrength concrete (HSC). Results obtained from a rheometer are compared with results of the standard slump test. Fluid concrete mixtures were investigated that had a water/binder ratio ( w/ b) of 0.33 and slump values of 200 ± 20 mm and incorporated proportions of limestone filler, silica fume, and ground silica as partial replacement (by volume) of cement. In addition, self-leveling concrete mixtures (torque viscosity ≤ 1 Nm at 15 min) having a w/ b ratio of 0.25 and 15 percent replacement of cement by various fillers were examined. The possibility of characterizing the rheology of fluid and self-leveling HSC on the basis of only two tests carried out at two different shear rates was addressed. An effort was made to define which is more relevant in a rheometer flow curve: the ascending part, the descending part, the maximum stress requirement, the flow resistance, the torque viscosity, or combinations of these factors. The possibility of measuring the rapid stiffening behavior of fresh HSC with time and the effect of ultrafine particles on the rheology using rheometric tests were also investigated.

Functionalization of polyethylenes and their use in reactive blending

AbstractThe grafting of maleic anhydride (MAn) to low density polyethylenes (PEs) dissolved in 1,2‐dichlorobenzene (DCB) has been studied. Grafting was successful at temperatures of about 160°C both in air without initiator and under nitrogen with the radical initiator 2,5‐di(t‐butylperoxy)‐2,5‐dimethyl‐3‐hexyne (LPO). The presence of succinic anhydride grafts was shown by FTIR spectroscopy of the product; 1H‐NMR spectroscopy indicates that the grafts consist of single succinic anhydride units. The graft content was determined by nonaqueous titration, and the extent of crosslinking inferred from the melt flow rates (MFR) of the products. The effects of concentration of initiator, MAn, and PE on the graft content were determined; the influence of PE structure, reaction time, and temperature was also studied. Melt blending of the grafted PE with polystyrene containing oxazoline functional groups (OPS) was investigated using a Rheomix mixer. The interpolymer reaction which occurs during blending was studied by means of FTIR, and the morphology of the blends by scanning electron microscopy (SEM). Information was also gained from the change in torque viscosity during the blending process.