Cement Suspensions Research Articles

Investigation of the effect of electromagnetic activation of concentrated cement suspension on the properties of cement stone and concrete

Problem statement. The strength of cement stone has a significant impact on the properties of concrete. Therefore, much attention is paid to the formation of the structure and properties of cement stone. Improvement of the properties is achieved by activating the hardening of the cement paste in various ways. One of such methods is the processing of cement paste in electromagnetic field mixing with water or cement suspension of low concentration. When processing concentrated cement suspension in an alternating electromagnetic field, there is the intensification of dissolution, dispergation, hydration of the cement components and the formation of a cohesively dispersed structure of cement stone. The given paper gives research results of the impact of the processing concentrated cement suspension containing lime in an alternating electromagnetic field on hardening and strength processes of cement stone. The purpose of the article is to study the joint influence of alternating electromagnetic field and Са(ОН)2 on the properties of cement stone. Conclusion. The impact of the alternating electromagnetic field on the concentrated cement suspension, containing Са(ОН)2 as the result of synergetic effect enables to intensify hardening process and increasing the physical and mechanical properties of cement stone.

The Influence of Bleeding of Cement Suspensions on Their Rheological Properties.

Flowable concretes tend to segregate. The risk of segregation is particularly high when the concrete is vibrated during the compaction process. A well-known segregation phenomenon is the so-called “bleeding”. This is a rise of water to the surface of the freshly poured concrete due to the difference in density between the mixing water and the concrete’s denser solid components (aggregates, cement and additives). This type of segregation occurs particularly within the paste. The focus of this paper is, therefore, on the sedimentation behavior at the microscale of concrete and especially on the influence of this process on rheological properties of the cement paste. In addition to common bleeding tests of cement suspensions using standing cylinders, rheometric measurements were performed on the suspensions during the bleeding process. A measuring procedure was developed for the rheometric measurements of the sedimenting cement suspensions. The rheological properties of the investigated cement suspensions were determined at four specific measuring times and at four specific measuring heights (i.e., positions) each. With this method it could be shown that the cement suspensions are not homogeneous over their height and that bleeding has a great influence on the rheological properties of cement suspension.

Onset and intensity of shear thickening in cementitious suspensions – A parametrical study

Understanding the intensity and onset of the shear thickening behaviour for cementitious suspensions is of prime importance in high shear processes like mixing and pumping of concrete in construction. In the present study, the onset and intensity of shear thickening of cementitious suspensions were investigated by a parametrical approach (water binder ratio (w/b), high range water reducer (HRWR) dosage, mineral admixture, shear rate) using an appropriate rheological protocol. Results show that, among the mineral admixtures, the suspension with ground granulated blast furnace slag (GGBS) features the highest shear thickening intensity and the earliest onset of shear thickening with respect to HRWR dosage. Moreover, this investigation shows that, among all the investigated parameters, the HRWR dosage influences the intensity and onset of shear thickening profoundly.

STABILIZATION OF CLAY POWDER WITH MINERAL WOOL FLY ASH

The aim of this article – to determine short term and long term strengthening of clay soil, by strengthening it with fly ash obtained during the production of mineral wool. This article introduces research which is used to determine the optimal ratio of fly ash in cement suspension for strengthening of clay soil. Samples which were investigated in this research work prepared by mixing Portland cement, mineral wool fly ash, clay powder, sand and water. All investigated samples compressive strength after 6 months exceeded 1.7 MPa. It is enough of such strength in geotechnics to conduct strengthening of soil and it is possible to argue that soil is strengthened.

Compositions of calcium aluminate cement containing gold and silver nanoparticles for biomaterial applications

Research has been developed in the biomedical engineering field to seek biomaterials that favor bone repair. Studies on orthopedics point out the advantages of using calcium aluminate cement (CAC) to repair bone defects. This is due to its similarity in chemical composition and thermal expansion coefficient of the bones, besides its high viscosity, low heat release, and biocompatibility. The aim of the present study was to investigate the influence of gold (AuNPs) and silver (AgNPs) nanoparticles on the properties of CAC since nanotechnology allows improving the properties and biomaterials, as well as enhancing bone modeling. The samples were prepared from suspensions of homogeneous calcium aluminate cement (CACH) with AuNPs or AgNPs and were evaluated for theoretical density, uniaxial cold crushing strength, flexural stress, microhardness, apparent porosity, pore size distribution, and bioactivity in simulated body fluid (SBF). The suspensions were also evaluated to check their viscosity, injectability, and setting time as functions of solid content. The addition of AuNPs increased the flexural stress, decreased porosity and pore diameter, and increased bioactivity. Injectable pastes were prepared with solid content of 76 wt%, indicating their application potential to bone defects as they are associated with many advantages, for instance, perfect adjustment to the geometry of the bone defect, lesser trauma to the patient, and lower risk of infections. The AuNPs and AgNPs showed influence on the mechanical properties of CACH. The combination of CACH + AuNPs improved its properties, resulting in higher flexural resistance and lower porosity and pore diameter, but AgNP addition showed the worst results in terms of mechanical properties.

Shifting factor—A new paradigm for studying the rheology of cementitious suspensions

AbstractOne of the main challenges when studying the rheology of cementitious systems is that cement particles are large and susceptible to gravity, in particular in dispersed systems. This implies that the range of volume fractions over which rheological properties of cement pastes can be measured is limited, as too high water content causes segregation and too low water content results in pastes that are too cohesive to measure. Consequently, the impact of the volume fraction of solids on yield stress is still not reliably established. A similar situation is encountered when studying cementitious systems with superplasticizers, whose impact is highly dependent on dosage. An important issue here is that admixture effects cannot be reliably established with respect to nonadmixed references as the latter ones can most often not be measured at the volume fractions for which admixed pastes do not segregate. The “Shifting factor” approach presented in this paper overcomes this long‐standing issue establishing exponential dependences of yield stress both with respect to volume fraction and admixture adsorption.

Early hydration and microstructure formation of Portland cement paste studied by oscillation rheology, isothermal calorimetry, 1H NMR relaxometry, conductance and SAXS

An open question in predicting the rheological properties of cement suspensions has been whether changes of rheology during hydration are merely a result of shifts in the electrostatic interaction patterns of the particles over time, or whether and to which extent steric bridging by hydration products occurs. The latter could explain phenomena such as thixotropy. In this context, parallel investigations using both rheological tests and isothermal calorimetry, 1H NMR relaxometry, conductance and small-angle X-ray scattering (SAXS) measurments were carried out. It could be shown that as early as approx. 2.5 h after water addition at approx. 30 °C, small amounts of Calcium Silicate Hydrate (C-S-H) form which may contribute to a bridging of the cement particles. This phase is followed by rapid C-S-H formation, leading to a non-linear increase in paste stiffness. This phase ends with percolation, i.e. the paste stiffness increases dramatically, simultaneously with the formation of gel pore like structures, which could be observed using NMR.

Insights in thixotropic concrete pumping by a Poiseuille flow extension

AbstractThixotropy is a reversible time-dependent phenomenon in fluids, in which an internal structure grows due to flocculation and breaks down under shear action. Numerous fluids are thixotropic,e.g.concretes and cementitious suspensions. Pumping of concrete is an important application. Since current approaches omit thixotropic effects, we aim to develop a simple theoretical model to evaluate or understand the significance of thixotropy on the concrete pumping behaviour. We therefore extended Poiseuille flow for thixotropic concretes and reformulated it in a dimensionless form to gain insights. After a validation, the results and significance are elaborated and concluded.Results showed that for increasing thixotropy and decreasing flow rates, the plug radius, wall shear rate and pumping pressure loss increase. Even though all thixotropy mechanisms may not be covered, a simple model is delivered to interpret or predict the effect of thixotropy on the pumping behaviour of cementitious suspensions. The dimensionless formulations via the Bingham numberBnand related discharge diagrams are sufficiently elegant for computational implementation and very insightful to distinguish a thixotropic flow regime. The model could be extended for more complicated thixotropies, irreversible time-dependent effects or even other pumping related phenomena.

ВЛИЯНИЕ НЕОРГАНИЧЕСКИХ ЭЛЕКТРОЛИТОВ НА УСКОРЕНИЕ СХВАТЫВАНИЯ ПОРТЛАНДЦЕМЕНТНЫХ СИСТЕМ

The study showed that in order to accelerate the hydration of inorganic binders it is necessary to use additives of such electrolytes that increase the concentration of calcium ions in the liquid phase of the cement suspension. Electrolytes (soda ash, sodium and potassium hydroxides), precipitating calcium ions in the liquid phase, promote their exit from the "shut-off" layer of hydration products. In this paper, we studied the additives – electrolytes – as regulators of the setting time of fine-grained and porous concrete. To increase the activity of the additive as a concrete mixtures setting time regulator, acidic varieties were used instead of main salts. The studied additives – electrolytes – draw practical interest, as their usage in production of foam concrete and fine-grained concrete lets accelerate hardening of products and speed up reuse of mould.

Non-adsorbing small molecules as auxiliary dispersants for polycarboxylate superplasticizers

The dispersing ability of polycarboxylate superplasticizers (PCEs) can be ascribed to the electrostatic and steric stabilization of cement suspensions. For this purpose, PCEs need to adsorb on the cement particle surface to become effective at all. In this study, it is demonstrated that at low water to cement ratios ≤ 0.30, even non-ionic molecules like diethylene glycol or 2-methyl-2,4-pentanediol which do not adsorb on cement, but remain dissolved in the interstitial pore solution, can greatly enhance cement dispersion when combined with PCEs such as conventional methacrylate ester based comb co-polymers. Their effect as co-dispersant is particularly pronounced for PCEs possessing a low side chain density and long side chain length. Relative to the co-dispersants it was found that especially non-polar small molecules like neopentyl glycol greatly enhance the paste fluidity. These molecules significantly reduce the surface tension of the pore solution and thus increase the wettability of cement. Based on results from spread flow tests, adsorption measurements and pendant drop tensiometry it is concluded that in cementitious systems formulated at low w/c ratios, non-adsorbing molecules with a molecular weight of ≤ 1000 g/mol induce repulsive depletion forces which prevent cement particles from agglomeration. This way, such small molecules act as auxiliary or co-dispersant when combined with PCEs.

Application foam agent to foam cement slurry for geothermal well drilling

One type of light weight cement is foam cement which can be used in cementing operations in weak zones with the possibility of small fractures and reducing the amount of light weigh cement suspension levels. The foam cement suspension can be used to solve lost circulation due to natural vertical fractures or cavernous formations. The purpose of this study was to determine the potential of foam cement slurry to solve the lost circulation in geothermal well. Making slurry cement uses class G cement at 200 mesh and 100 mesh size with the composition of cement. The cements put into the waring blender containing water stirit for 35 second, adding foam agent into cement slurry with variations in foam agent concentration of 0.03%, 0.06%, 0.09%, 0.12% and 0.15%. observations of foam cement above were carried out for 30 minutes to test the stability of bubbles in the mixture. The result this study showed different compressive strength values at variations the concentrations of foam agent. The strength value is strongly influenced by result of sample with 0.03% with Sika-aer concentration have a compressive strength value of 3745 psia, while sample with Sika-aer concentration of 0.15% have compressive strength value of 1701 psia. The value of compressive strength core foam cement can form a linear line according percentage foam agent concentrations. Foam agent between 0.03% - 0.15% with Sika-aer qualified the minimum requirements BHCT compressive strength according API-10B rules to reduce severity lost circulation in the well X-E2 in geothermal drilling well.

Development of Cement Compositions with a Finely Dispersed Additive for Consolidation of Soil by the Injection

Cement compositions prepared by mixing cement with a stabilized finely dispersed slag suspension, which allow improving the structural, physical and mechanical characteristics of the cement stone are considered. On the first day of hardening, the strength of modified specimens increased by 54%, at the grade age - by 43%, and the porosity decreased by 13.8 and 17.3%, respectively. The possibility of obtaining an injection solution for soil consolidation on the basis of Portland cement and a stabilized slag suspension with the concentration of a finely dispersed slag of 50 g/l is considered. Studies have shown that the injection solution under study has reduced viscosity and sedimentation, increased compressive strength. After 28 days of hardening, the strength was 14.2 MPa, which is higher than the recommended values ​​for consolidation of soil under the foundations (4-6 MPa), and at a concentrated load, for the base under the foundations of the columns (9-10 MPa). The data obtained allows considering an injection solution based on Portland cement and slag suspension for the use in the injection technology of soil consolidation.

The effect of electromagnetic treatment of concentrated cement slurry on the physical and mechanical properties

Problem statement.At the beginning of the week, in Ukraine the transfer is more significant in concrete consolidation. Especially important is the need to lower the supply of concrete and concrete, with the change in portability, without any loss of strength. The purpose of the article. For increased concrete and concrete strength, when changing the number of Portland cement, it is necessary to consolidate the various methods of the concrete concrete process. The most common are methods of heat exposure, as well as the use of various chemical additives. Electrophysical methods of influence are used to a lesser extent, namely intensification with the help of electric and electromagnetic fields. Purpose.To improve the quality and strength of concrete, while reducing the use of Portland cement, it is necessary to use various methods to intensify the concrete preparation process. Methodology. From the electrophysical methods of intensifying concrete preparation processes, the method of electromagnetic treatment of concentrated cement slurry, which was passed through an alternating electromagnetic field and was used to prepare the concrete mixture, is promising. Results. The performed tests showed that when an electromagnetic field is infused, a positive effect is induced to concentrate on a concentrated cement suspension in the process of structural adjustment and reduction of physical and mechanical power to concrete. It has been established that, as a result of processing, there is a greater variety, dispersion and better storage of cement and a form of cemented stone structure. Conclusion. Outlined above allows us to assert that electromagnetic processing of cement paste has a positive effect in the process of structure formation and the improvement of physico-mechanical properties of concrete based on the processed in the electromagnetic field of the cement paste.

Elucidating how particle packing controls rheology and strength development of dense cementitious suspensions

Although maximizing particle packing strategy is primarily applied to formulate high performance cementitious suspensions, this may induce constraints for the growth of hydration products, resulting in reduced microstructural evolution at later ages. This paper elucidates the effects of particle packing on rheology and strength development of dense suspensions containing ordinary portland cement (OPC) and supplementary cementitious materials (SCMs). The particle packing was altered through tuning water film thickness to examine its impact over transition of cementitious suspensions from concentrated state to the onset of flow state. This transition was characterized by determining the optimum water demand to achieve maximum solid concentration and minimum water demand to initiate flow. A series of virtual microstructural simulations were also performed to examine the effect of excess water on inter-particle spacing and formation of the connected solid network through formation of main cement hydrate (i.e., calcium-silicate-hydrate (C-S-H)). The results indicate that although transition of the cementitious suspension from concentrated state to the onset of flow state reduces particle packing and elevates separation between neighboring particles, these effects become less pronounced for the OPC-SCM systems than the plain OPC system. The synergistic effect between OPC and SCMs on strength development is controlled by water extent. An account of saturated surface area effect, rate of strength evolution slows down at concentrated state. The outcomes of this study can be applied to optimize the design of dense cementitious suspensions by exploiting optimal particle packing while enabling strength development by providing pore space for growth of hydration compounds.

Application of Poly-γ-Glutamic Acid Flocculant to Flocculation–Sedimentation Treatment of Ultrafine Cement Suspension

We examined the effect of poly-γ-glutamic acid flocculant (PGAF) on the removal of ultrafine cement (UFC) particles stabilized by a poly-carboxylate co-polymer, which is a superplasticizer (SP). The flocculation–sedimentation treatment with PGAF successfully removed the SP-stabilized cement particles through the gravitational settling of the formed flocs. The removal efficiency reduced with the increase in the ionic strength, probably because of the shrunk form of poly-γ-glutamic acid (γ-PGA) at high ionic strengths. Increasing the mixing intensity during rapid mixing improved the removal efficiency. A series of flocculation–sedimentation experiments provided a diagram showing the relationship between ionic strengths and the addition amount of PGAF. Our results suggest that PGAF is a good candidate for the purification of cement suspension by flocculation–sedimentation, and a better removal performance can be obtained at lower ionic strengths with intense rapid mixing. From the diagram of the control charts presented in this study, we can determine the optimal addition amount of PGAF for achieving the target removal rate for cement suspension under any ionic strength.

Improving the early strength of concrete: Effect of mechanochemical activation of the cementitious suspension and using of various superplasticizers

The novelty of the paper is to identify the scientific patterns of the influence of naphthalene formaldehyde and polycarboxylate superplasticizers during the activation process cementitious suspensions by the rotary pulsation apparatus (RPA), which have an energy density of 25 KW/m3 on the hydration mechanism and the structure of the cement stone. Cementitious suspensions obtained by mechanochemical activation in liquid state were prepared as novel compositions, on the basis of which concretes with high early strength are created. The strength characteristics of concrete mixes were researched by a series of tests (compressive strength, prism strength, flexural strength). In addition, the durability characteristics (frost resistance, sulfate resistance, water impermeability) were determined by standard techniques, confirm the creation of durable composites with high exploitation properties. Besides, the microstructural, morphological and thermal properties of such concrete at 28 days of curing were determined. For the first time, scientific data were obtained on the properties of cementitious suspension and concrete based on it, obtained by mechanochemical activation in an aqueous medium in the RPA with superplasticizers having different chemical bases. The results indicate that the mechanochemical activation of cementitious suspension by the RPA with the addition of Relamiks T-2 superplasticizer contributes to the improvement of the physicomechanical properties of concrete: the elastic modulus increases by 20%, flexural strength by 54%, prism strength by 67% compared to the control composition having the elastic modulus 33.57 GPa, flexural strength 5.41 MPa and prism strength 32.66 MPa.

Biocementation technology for construction of artificial oasis in sandy desert

Artificial oasis could be supported by the trapping and retaining rainfall water by impermeable layer of artificial material. In case of average annual rainfall in Arabian or Pakistani Deserts of 100 mm the watershed area must be at least 1000 ha to ensure rainfall water supply for consumption and irrigation in the artificial oasis of 100 ha area. Minimum cost for the sealing of 1000 ha of the sand slopes with 1 mm geosynthetic liner is about 112 mln Saudi Arabian Riyal, which could be not acceptable price for 100 ha of artificial oasis land. However, this cost could be diminished to 17 mln Saudi Arabian Riyal if to coat watershed slopes with 1 mm of biocemented sand crust using a low viscosity solution of biocement. Conventional cementation is cheaper but it cannot be used to make 1 mm sand crust because of a high viscosity of the cement suspension. The novel biotechnological method is based on the formation of the sand surface crust for water collection and transportation on the surrounding slopes. Most environmentally friendly biotechnology for this biocementation is aerobic biooxidation of cheap calcium formate or calcium acetate. Biocementation of the sand crust could be used to make a low-cost artificial desert oasis fed by rainfall.

Effects of fineness and substitution ratio of limestone powder on yield stress of cement suspensions

This paper aims at investigating the evolution of the yield stress of cement suspensions with the variation of its properties for an environmentally friendly alternative material of cement clinker, the limestone powder (LP). We first showed that the yield stress of cement suspensions varies significantly with different particle size distribution, LP substitution ratio and superplasticizer dosage. We then showed that for the cement suspensions without superplasticizer, the yield stress is dominated by the impacts of the median particle size and maximum packing fraction of the binary powder mixtures. However, for the cement suspensions with low dosage of superplasticizer, the yield stress of the LP substituted suspensions decreases with the increase of the substitution ratio. It is finally suggested that the impact of superplasticizer on the yield stress is conspicuous in the condition of similar median particle size and packing properties while can be neglected in the case of the significant change of the particle size of the powder mixtures.

Rheological characterization of low-calcium fly ash suspensions in alkaline silicate colloidal solutions for geopolymer concrete production

The rheological behavior of low-calcium fly ash suspensions in activating solutions of colloidal silica and alkali hydroxide is investigated. The study is aimed at relating the rheological behavior of alkali-silicate activated low-calcium fly ash (AAF) suspensions with Portland cement paste suspensions. The yield stress and the viscosity of the AAF suspensions increase with the alkalinity of the colloidal solution, which is due to changes in the surface charges on fly ash particles with the change in the ionic medium. Increasing the alkalinity results in a less negative zeta potential of fly ash in the alkaline solution of colloidal silica and an increase in the yield srtess of the AAF suspension. The thixotropic behavior in AAF suspensions is associated with structure breakdown to a finely dispersed suspension of particles produced by shearing. Energy measurements indicate a very slow change in the internal particle structure with age at room temperature. A comparison of AAF suspensions is presented with suspensions of Portland cement in water, which are proportioned for similar physical flow characteristics and yield stress. AAF suspensions have a larger solid fraction than the cement suspensions in water of comparable yield stress. The zeta potential of cement particles in water is less negative when compared to fly ash in alkaline-silicate solutions. The AAF suspensions of comparable yield stress exhibit a significantly higher viscosity than the cement suspensions in water. Cement paste and AAF suspensions exhibit a rate dependent yield response. Cement paste suspensions exhibit a threshold strain rate for minimum yield stress. In AAF suspensions there is a continuous decrease in the yield stress at lower strain rates. The thixotropic behavior in cement paste is influenced by chemical ageing which produces a rapid recovery of yield stress. In comparison, there is very little ageing at room temperature in the AAF suspensions and a very slow recovery of yield stress after shearing.

Effects of starch-type polysaccharide on cement hydration and its mechanism

Polysaccharides are widely used as chemical admixtures to modify the early age properties of mortars and concrete and a new starch-based chemical admixture pre-dissolved in NaOH and water was used to reveal the mechanism. The result shows that the induction period can be extended obviously. The impacts of dissolved TRI on surface state of cement particles, C-S-H nucleation and growth process in ion reaction and in cement suspension were investigated. It can be reported that TRI molecular would also adsorb on the surface of generated C-S-H globules which inhibits transforming C-S-H globules to the soil-like C-S-H, C-S-H (around 50 nm) continues to nucleate, transform and grow to large particles after that dissolved TRI are completely consumed by the generated C-S-H gel which causes the prolonged induction period. In addition, it has been shown that polysaccharide with larger average molecular sizes result in longer cement hydration induction times.