Rheological Properties Of Mortars Research Articles

Investigations on the rheological properties of cement mortar based on fine aggregate characteristic and its extended prediction model

The rheological property of mortar is significantly influenced by its contained fine aggregate morphology characteristic and capable predictive models are limited. This work aims to expand the film thickness theory by developing an index that integrally represents variations in grain shape, gradation, and mix proportions, and elucidates the impact and the mechanism of these multifactorial differences on rheological performance. The quantitative analysis of the aggregate gradation and particle shape differences were performed, which was used to assess the impact of these variations and different mix ratios on the rheological performance of mortars. A correlation between aggregate differences and film thickness was established using specific surface area and void ratio. The result shows that variations in aggregates are accurately assessed by image analysis and consistently reflected in specific surface area and void ratio metrics. Since variations in rheological performance are predominantly governed by differences in film thickness, the disparities among aggregates can be quantified in terms of their impact on rheological properties by considering specific surface area and void ratio, thus translating into variations of film thickness. The differences in rheological properties due to variations in grain shape, gradation, and mix proportions can be comprehensively represented and controlled through an expansion of the film thickness model.

Correlation between the automated slump test and the rheological properties of Portland cement mortars

The aim of this work was to conduct a rheological assessment of mortars based on the automated slump test. Using this test to monitor the transient and permanent regime of slump and its spread, the parameters were correlated with the rheological properties of the mortars. Based on dimensionless slump/spread, yield stress and viscosity, empirical models were developed for obtaining rheological parameters, which provided correlations with good coefficients of determination (R2 > 0.85). Through analysis of the slump behaviour of the mortars, a correlation between the viscosity and the maximum slump velocity was obtained (R2 = 0.90), showing that viscosity could be determined based on the slump velocity. Furthermore, based on a physical description of the slump test related to the Reynolds number, three distinct stages in the slump process were defined: the viscous phase (characterised by high viscosities), the intermediate phase (the coexistence of viscous and inertial effects) and the inertial phase (characterised by low viscosities and a higher sensitivity to lifting of the mould). The dynamic similarity of the analysed mortars (vertical Reynolds number/radial Reynolds approximately equal to one) indicated that the shear rate could be measured based on the vertical direction of the flow (slump).

Effect of Hydroxypropyl methyl cellulose (HPMC) on rheology and printability of the first printed layer of cement activated slag-based 3D printing concrete

Nowadays, Ground Granulated Blast Furnace Slag (GGBFS) is generally used to replace cement for reducing carbon emissions, but due to its low hydration activity and unstable working performance in the early stage, it is difficult to apply in 3D printed concrete (3DPC) as the main binder. In this study, a combination of ordinary Portland cement and calcium sulfoaluminate cement was used to activate GGBFS. In the presence of 0.2 wt% polycarboxylate superplasticizer (PCE), in order to achieve high-precision printing, hydroxypropyl methyl cellulose (HPMC) was used. The rheological properties of mortar were evaluated by the slugs-test and a rotational rheometer. The results show that the yield stress and thixotropy of slag cement-based 3D printing concrete are significantly increased, with addition of HPMC. The slugs-test shows its advantages in measuring rheological properties, such as superior repeatability of rheological data and a better association with 3D printing performance. Pumpability, extrudability, and buildability of the first printed layer of slag cement-based 3DPC were evaluated using pumping pressure, horizontal printing, and vertical printing. The results show that, with a 0.15 wt% HPMC, the 3D printing properties of the first layer are greatly improved, a stable and high-precision slag cement-based 3DPC can be developed, and the relationship between rheological properties and 3D printing performance can be established.

Systematic approach for printability evaluation and mechanical property optimization of spray-based 3D printed mortar

Systematic approach for evaluation and optimization of spray-based 3D (S-3D) mortar printing technology are explored. Effects of different fly ash (FA), silica fume (SF) and water-binder (W/B) ratios on the rheological properties of mortar are firstly evaluated by orthogonal tests. The mortar with excellent rheological properties is then adopted to assess the S-3D printability. The test results show that proper additions of FA, SF and W/B can prolong the printing window to 120–135 min as well as improve the printing accuracy. Single layer and accumulative thickness tests are innovatively used to quantify the morphological sustainability of S-3D printed mortar. The mechanical strengths of S-3D printed mortar are remarkably higher than those of the cast counterparts in view of maximum increase of 72.64% compressive, 45.83% flexural and 33.33% splitting strengths, respectively. The high spraying pressure of S-3D printing procedure avails small pore size, therefore the compactness of the internal microstructure of S-3D printed mortar. A special-configured convex nameplate “HEBUT” with size of 2200mm × 500mm × 30 mm (X × Z × Y directions) is successfully printed on a vertical platform, which proves the applicability and dexterity of S-3D printing technology in spatial context.

The Effect of Sand Type on the Rheological Properties of Self-Compacting Mortar

In order to understand the effect of sand type on the rheological properties of self-compacting mortar, four varieties of sand, namely, quartz sand (QS), river sand (RS), and two kinds of manufactured sand, marked as MS-A and MS-B, were studied. As part of this study, the sands’ particle shape parameters, such as their length:width ratio and roundness, were determined. Mortars containing the four varieties of sand were tested using the slump flow test and the V-funnel test in oven-dried (OD) and saturated surface-dried (SSD) conditions in order to identify the water absorption, shape-related differences, and specific gravity in their rheological performance. The changing trends of the slump flows and the V-funnel times of the different mortars in OD and SSD were similar. By eliminating the influence of water absorption on mortar rheology, shape–weight parameters, such as the ratio between the length:width ratio and specific gravity (LWS) and the product of roundness and specific gravity (ROS), were defined in order to quantify the compound effects of sand type on mortar rheology. The regression analysis showed an excellent linear correlation between slump flow and both LWS and ROS, and a very good linear correlation was also demonstrated between the V-funnel time and both LWS and ROS. Based on the particle shape–weight parameters, the rheological properties of mortars can be predicted. Based on the mortar rheological threshold theory, the self-compacting mortar (SCM) zone can be drawn. The predicted SCM zone overlaps considerably with the experimental SCM zone for MS-A.

Changes in Rheological Properties of Mortars with Steel Slags and Steel Fibers by Magnetic Field.

The effect of a magnetic field on the rheology of mortars with steel slags and fibers was evaluated in this study. The rheology of the mortar measured with and without a magnetic field was compared. The effect of steel fiber addition to normal and steel slag mortars, mix ratio and size of steel fibers, and magnetic field formation position on rheology were evaluated. Steel fiber addition increased the yield stress and viscosity of the normal and steel slag mortars. The increased rheology was almost restored because of the magnetic field applied to the normal mortars. However, the increased rheology of the steel slag mortars with steel fibers was restored only upon the application of the magnetic field, whose position was continuously changed by a power relay. It is deduced that the alignment of the steel fibers by the magnetic field contributes to the rheology reduction of the mortars. However, in the case of steel slag mortar, experimental results demonstrated that steel slag, which is a ferromagnetic material, receives constant force by the magnetic field, which increases the rheology. This is evidenced by the decrease in the rheology of steel slag mortars under a continuously changing magnetic field formation position by power relay.

Change in Fresh and Rheological Properties of Mortar and Concrete prepared using Red Mud- A Review

The construction industry produces 5-7% of all CO2 emissions and is the second-highest emitter of all industrial carbon dioxide. Reusing industrial waste and by-products in cementitious materials has found to enhance properties and reduce the carbon footprint. Red mud is one such byproduct generated in large quantities during the manufacturing of alumina. Red mud’s utilization in the construction industry can also address the challenge of increasing red mud reserves, posing a threat to the environment. The studies carried out by various authors suggest that red mud could successfully be incorporated in concrete and mortar. The extent of incorporation of red mud in the material can be decided based on the required application and properties. This paper presents a comprehensive review of red mud’s effect on the rheological and fresh properties of concrete and mortar which are crucial for their constructability.

Research on the influence of machine-made sand gradation and fineness modulus on the workability and rheological properties of mortar

The gradation and fineness modulus of machine-made sand are important factors affecting the performance of mortar. By studying the influence of different machine-made sand gradation and fineness modulus on the workability and rheological properties of mortar, the gradation and fineness of machine-made sand are explored. The relationship between modulus and mortar fluidity, yield stress and plastic viscosity. Research shows that with the increase of the cumulative screening rate and fineness modulus of machine-made sand with different gradations, the fluidity of the mortar increases and the workability of the mortar increases. The cumulative screening rate and fineness modulus of machine-made sand are negatively correlated with the yield stress and plastic viscosity of the mortar. The cumulative screening rate and fineness modulus of machine-made sand have a good correlation with the yield stress of the mortar, and the mechanism is 1.18-0.6mm Sand gradation is significantly negatively correlated with the yield stress of mortar, and the cumulative sieving rate and fineness modulus of machine-made sand have poor correlation with the plastic viscosity of mortar.

Influence of Tack Speed on The Rheological Properties of Mortar in Fresh State

In the present work, the squeeze flow techniques were used to investigate the influence of tack speed to the rheological properties of mortar in fresh sate, including yield stress and extensional viscosity.Tested samples were prepared under similar conditions of room temperature and atmospheric pressure. Compositions of mortars were tested at two different squeezing rates (20 and 200 mm/s) 15 min after mixing. Results indicate that mortar’s yield stress increases with the increasing of the pulling speed. This increase is evident at low tensile speeds. At high speed of tack, this increase is not obvious, especially in case of high squeeze speed of 200 mm/s. It can be concluded that the optima speed for removing the mortar and the upper surface is lower than 20 mm/s. The extensional viscosity of fresh mortars significantly decrease as the tack speed increases. Elongational viscosity values decreased as a result of gap increasing. The increase of the gap during tack experiment stimulates different units (grains getting far apart to each other) causing the observed decrease of the mortars' elongational viscosity

Value-added waste latex paints in masonry cement for plastering applications

Polymeric latexes are commonly used in cement-based plastering and rendering works. This paper assesses the effect of recycled polymers obtained from waste latex paints (WLPs) on flowability and mechanical properties of masonry cement (MC) mortars, including whether such performance would be similar to that induced by virgin polymers. Three MC classes prepared with different cement-to-limestone ratios are produced in compliance to relevant EN 413-1 and ASTM C91 specifications. The WLPs were not obtained from waste collection sites, rather produced to monitor constituents and properties prior to use. Test results showed that water retention and rheological properties of mortars containing virgin or recycled polymers are remarkably higher than unmodified mixtures. The mechanical properties of WLP-modified mortars including compression, flexure, and pull-off adhesion strength were pretty similar, or even higher than equivalent mixtures containing virgin polymers. This was attributed the presence of ultrafine pigment and extender particles that improve packing density and infer nucleation benefits for the growth of additional hydrates. The dry curing regime applied for virgin and recycled polymer-modified mortars is particularly advantageous in construction sites, as this reduces the hassle of moist curing normally required for unmodified plasters while securing higher resistance against sorptivity and shrinkage cracks.

Effect of non-ionic auxiliary dispersants on the rheological properties of mortars and concretes of low water-to-cement ratio

A high plastic viscosity can be very disadvantageous for the processing of concrete as it often entails a sticky and honey-like consistency. This is especially the case for concretes prepared at low water content and a large amount of fine supplementary cementitious materials (e.g. silica fume). Unfortunately, most of the common polycarboxylate (PCE) superplasticizers cannot effectively reduce the plastic viscosity of such highly particle loaded systems, even though they exhibit strong dispersing capability and can produce high spread flow or slump. In this study, it is demonstrated that non-ionic molecules like diethylene glycol or 2-methyl-2,4-pentane diol can reduce the plastic viscosity when admixed with a PCE superplasticizer. The effect of those auxiliary dispersants on the rheological parameters was investigated by spread flow, flow line and V-funnel tests using mortar and concrete prepared from Portland-limestone cements exhibiting low w/c ratios (0.26 and 0.35, respectively). Moreover, the impact of such non-ionic molecules on the strength development of mortar specimens was tested. Mechanistic investigations revealed that the co-dispersants increase the amount of the liquid phase and hence the thickness of the lubricating layer around the particles. As a result, interparticle friction is reduced and a less sticky material with a higher speed of flow is obtained.

Statistical methods for determining rheological parameters of mortars modified with multi-walled carbon nanotubes

This paper investigates the influence of composition in the presence of multi-walled carbon nanotubes (MWCNT) on the rheological properties of mortars over the time. A rheometer Viskomat NT was used to assess rheological parameters, yield stress and plastic viscosity. On the basis of rheological results, a statistical model of composition variability on the rheological parameters of mortars in the presence of MWCNT was determined by the multiple regression method. The significance of the influence of variable factors and their interactions on parameter of yield stress and plastic viscosity was presented by means of ANOVA. It was found that w/c ratio has the most significant influence on rheological properties mortar modified with MWCNT, for both yield stress and plastic viscosity. For the yield stress parameter, immediately after mixing the ingredients, apart from the largest influence of w/c ratio, the impact is also shown by: amount of superplasticizer (SP), a combination of w/c ratio and SP, amount of MWCNT.

Rheological properties of mortar containing recycled powders from construction and demolition wastes

Various types of recycled powders (RPs) can replace cement or fly ash in preparing concrete due to the acceptable impact on the mechanical properties. However, the workability of concrete containing RPs may decrease significantly that render their practical application. This paper investigated the rheological properties of mortar containing different RPs processed from the construction and demolition wastes, which were clay brick powder (CBP), mixed brick powder (MBP) and dust powder (DP). Firstly, the basic properties of RPs were studied for a better understanding the effect on the properties of mortar. Then, the rheological properties of mortar were examined with different RPs to determine the influence of different RPs and superplasticizer dosage, respectively. The experimental results showed that RPs had higher content of Al2O3 and alkali and lower content of SO3, and accordingly, the hydration heat of pastes with RPs were found higher than that of cement paste in the first 30 min. The yield stress, plastic viscosity and thixotropy increased significantly with the use of different RPs, among which mortar with DP were the maximum. Mortar with MBP showed better rheological behavior. Whereas, CBP presented the worst compatibility with SP.

Influence of the Variability of Calcareous Fly Ash Properties on Rheological Properties of Fresh Mortar with Its Addition

One of the main by-products of brown coal burning is calcareous fly ash (CFA). Apart from other applications, it is used as a main component of cement, or as an active mineral additive to concrete. The present study involves the impact of the raw and processed calcareous fly ash (CFA) on the changes of rheological properties of mortars. The said impact was determined by using the coefficient of variation (CV) given in percentage. CFA samples collected from various sources were subjected to testing. The samples were collected from two electrofilters of blocks with boilers of different combustion parameters and from the retention tanks of the CFA sales department (CFA T) in which CFAs from various boilers are mixed. It has been demonstrated that the degree of the impact of CFA addition on the rheological properties of mortars depends on the source of this addition and on bulk density. The present work demonstrates the negative impact of raw CFA on mortar workability, and hence it is questionable to support its use in concrete technology.

Physico-Mechanical Features of Portland Cement Mortars Replaced Partially with Aluminium Cement

The purpose of the research was to recognize the effect of the addition of aluminium cement on the properties of cement mortar made of Portland cement CEM I 42.5R. Alumina cement is a hydraulic binder. It is a finely ground organic material that when mixed with water binds as a result of reactions and hydration processes. After hydration, stable hydrate phases form and, as a consequence, the material strength parameter is obtained. The main constituent is calcium aluminate (CaO⋅Al2O3), in smaller amounts there are: calcium aluminate, dicalcium silicate and calcium aluminium silicate or gelenite. Hydraulic hardening of aluminium cement occurs mainly through calcium hydration but other chemicals may also take part in the hardening process. The specific chemical composition of aluminium cement and the fact that calcium hydroxide is not released during hydration allows the leaven to resist many aggressive factors. Therefore, in the literature, we can meet guidelines so that the w / c ratio is not greater than 0.40 for applications to structural elements. The article discusses the results of laboratory tests on the impact of replacing Portland cement with aluminium cement in the amount of 10%, 20%, 50%, 100% on the physical and mechanical properties of mortars. The rheological properties of mortars, i.e. consistency, setting time and parameters of hardened mortars were examined, among others compressive and bending strength, capillary rise and absorbability. Compressive strength and bending strength were tested after 1, 7 and 28 days on samples with dimensions 4 × 4 × 16 cm. Absorption and capillary rupture were tested 28 days after being formed on standard bar beams 4×4×16cm. The mortar was made with a constant coefficient w/c = 0.38.

RHEOLOGY OF MORTAR WITH PORTLAND-LIMESTONE CEMENT CEM II/A,B-LL IN RELATION TO PROPERTIES OF CEMENT

Abstract The paper presents the results of rheological research, conducted to examine how the properties and composition of cement affects the yield stress and plastic viscosity of Portland limestone cements. Portland limestone cements used in the research were obtained by mixing four Portland cements of various chemical and phase compositions with two limestones of different origin, in an amount of 6, 10, 20 and 30% of cement mass. The yield stress and plastic viscosity were determined using the Viskomat NT rheometer, after 5 and 60 minutes from combining the constituents. Obtained results indicate a significant effect of the C3A content in cement on the rheological properties of mortars, mainly yield stress. The specific surface area of the tested cements has a lesser effect on the rheological properties of mortars with Portland limestone cements.

Effect of Calcareous Fly-ash Processing Methods on Rheological Properties of Mortars

The paper presents the results of research into the influence of calcareous fly ash (CFA) processing methods on the rheological properties of mortars. The study consisted of a comparison of changes of the rheological properties (plastic viscosity and yield value) of the mortars during 90 minutes when CFA, unprocessed or processed by grinding, grain separation, or selective collection from the filter, was used as a substitute for a part of the cement. The results show that processing of CFA decreases its negative influence on the rheological properties; the efficient methods are separation or grinding, while the effect of selective collection is almost insignificant.

Variation of mechanical and rheological properties of mortar by replacement of natural sand with crushed sand

This work aims at studying the performance of crushed sand (CS), resulting from limestone quarries, when partially or completely replaces the natural sand (NS) in mortar. NS is replaced by different ratios with CS to make mortars with three w/c ratios. The tests consist of determining the superplasticizer requirement to have a plastic consistency of mortar according to the CS content. For a given workability, mechanical, and rheological properties of different mortars are tested. It is concluded that CS has a great effect on mortar properties. Its presence enhances the compressive strength, decreases the rheological parameters and reduces the dosage of superplasticizer which becomes very suitable even with low w/c ratio. Then for making mortar with low w/c ratio, it is interesting to use partial replacements of CS than using an excessive dosage of superplasticizer. The CS has a great potential to provide an alternative to NS and helps in maintaining the environmental balance.

Impact of metakaolin characteristics on the rheological properties of mortar in the fresh state

Abstract This study investigated the flow properties (slump, flow time, apparent viscosity at different shear rates) of cement/metakaolin-based mortars. The mix proportion that was used per weight was 3:1:0.5 (sand:binder:water), and the binder was composed of either 100% cement (OPC) or combinations of cement and metakaolins (MKi). Replacement rates of cement with MK were 12.5% and 25% per weight. Four metakaolins produced in two areas with two processes of calcination (fluidized bed and flash calcination) were employed. Their chemical and mineralogical compositions, physical properties, size distribution and morphology were fully characterized. Relationships between various MK properties and the flow properties of mortars were studied. Results show that metakaolins can produce significant differences in the flow of mortars, depending on their physical and chemical properties. In particular, the nature and content of impurities are key factors acting directly on the morphology of the distribution of the constituting particles and the water demand of MK. All these parameters control the rheological properties of the resulting cementitious suspensions. The mode of calcination is a second order factor influencing the shape of particles, since the flash process can smooth the surface of the smallest particles. More specifically, the high quartz content present in flash MK as rounded particles is minimally or not at all affected by the calcination process, and maintains flow properties more successfully than mortar incorporating cement only.

Influence of organic thickening admixtures on the rheological properties of mortars: Relationship with water-retention

In this study, we consider the influence of different types of polymer thickening admixtures on the rheological behavior of render mortars. The admixtures considered include cellulose–ethers with different molecular weights, a guar ether, and a starch ether. A thorough rheological investigation is performed, including the characterization of the steady state flow behavior and the microstructure at rest. The latter is examined through measuring linear viscoelastic properties using oscillatory rheology. First, it is shown that the fresh mortars behave generally as Hershel–Bulkley fluids with a non-trivial evolution of the rheological parameters with admixture content. The evolution of the viscoelastic properties with admixture content shows that the cellulose ethers and guar ethers decrease the gel-like response of the mortars, while starch ether increases their gel feature. This indicates that there should be a profound difference between the two types of admixtures regarding their organization within the pore solution and their interactions with the mineral particles. The rheological properties are discussed in relation to water retention. It is shown that the ratio between dissipation and elasticity (or cohesion) correlates well with water retention. The more the admixture introduces viscous dissipation (as compared to cohesion) into the system, the more it increases its water retention capacity. Water retention is also correlated with air-entrainment, indicating that the surfactant property of the admixture is a contributing factor.