Cement Suspensions Research Articles

Use of Cement Suspension as an Alternative Matrix Material for Textile-Reinforced Concrete.

Textile-reinforced concrete (TRC) is a material consisting of high-performance concrete (HPC) and tensile reinforcement comprised of carbon roving with epoxy resin matrix. However, the problem of low epoxy resin resistance at higher temperatures persists. In this work, an alternative to the epoxy resin matrix, a non-combustible cement suspension (cement milk) which has proven stability at elevated temperatures, was evaluated. In the first part of the work, microscopic research was carried out to determine the distribution of particle sizes in the cement suspension. Subsequently, five series of plate samples differing in the type of cement and the method of textile reinforcement saturation were designed and prepared. Mechanical experiments (four-point bending tests) were carried out to verify the properties of each sample type. It was found that the highest efficiency of carbon roving saturation was achieved by using finer ground cement (CEM 52.5) and the pressure saturation method. Moreover, this solution also exhibited the best results in the four-point bending test. Finally, the use of CEM 52.5 in the cement matrix appears to be a feasible variant for TRC constructions that could overcome problems with its low temperature resistance.

Calculation of Dynamic Viscosity in Concentrated Cementitious Suspensions: Probabilistic Approximation and Bayesian Analysis.

We present a new focus for the Krieger–Dougherty equation from a probabilistic point of view. This equation allows the calculation of dynamic viscosity in suspensions of various types, like cement paste and self-compacting mortar/concrete. The physical meaning of the parameters that intervene in the equation (maximum packing fraction of particles and intrinsic viscosity), together with the random nature associated with these systems, make the application of the Bayesian analysis desirable. This analysis permits the transformation of parametric-deterministic models into parametric-probabilistic models, which improves and enriches their results. The initial limitations of the Bayesian methods, due to their complexity, have been overcome by numerical methods (Markov Chain Monte Carlo and Gibbs Sampling) and the development of specific software (OpenBUGS). Here we use it to compute the probability density functions that intervene in the Krieger–Dougherty equation applied to the calculation of viscosity in several cement pastes, self-compacting mortars, and self-compacting concretes. The dynamic viscosity calculations made with the Bayesian distributions are significantly better than those made with the theoretical values.

Performance of Microfine Cement Grouted Sands Under Quick Loading Conditions

An experimental investigation was conducted to evaluate the influence of factors pertinent to the suspension and the sand on the effectiveness of microfine cement grouts under quick loading conditions, that is, conditions, where the grouted soil mass is loaded at a rate which is much faster than the rate of pore water pressure dissipation and total stress behavior may be of interest. Unconfined compression and unconsolidated-undrained triaxial compression tests were conducted on grouted sand specimens obtained by injecting suspensions of 12 cements with three water to cement (W/C) ratios into four sands with different grain sizes. A Mohr–Coulomb type linear failure criterion describes satisfactorily the shear strength behavior of cement grouted sands in total stress terms. The values of the activated shear strength parameters generally increase with increasing axial deformation during loading. Grouting with suspensions having W/C = 1 yields unconfined compression strength of grouted sands up to 9 MPa, adds cohesion to the sands reaching 1.7 MPa, increases by 6–14 times the initial modulus of elasticity, reduces by 5–10 times the failure deformation and may increase up to 20% the angle of internal friction of the sands. The stress–strain–strength behavior of sands grouted with suspensions having W/C = 1 is similar to that of cement suspension sediments with the same W/C ratio, whereas the behavior of sands grouted with suspensions having W/C = 3 is similar to that of the clean sands.

Effect of ozone treatment on softwood soda lignin-based water reducer performance for concrete

A lignin-based water reducer for concrete was prepared from softwood soda lignin. The soda lignin and the lignin-polyethylene glycol (PEG) derivative were modified with ozone to improve their performance as water reducers. The performance of ozone-treated soda lignin was superior than untreated soda lignin and commercial lignosulfonate-type water reducers in the mortar flow test. The soda lignin treated with a high ozone charge showed better performance than lignin treated with a low ozone charge. The ozone treatment improved the performance of the lignin-PEG derivative water reducer as well. The lignin-PEG derivative water reducer with a longer PEG chain length showed better performance than that of the shorter PEG chain. The zeta potential of cement suspension with the ozone-treated soda lignin showed a higher negative value than the untreated soda lignin. The data of zeta potential analysis suggested that the electrostatic repulsion force of cement particles with the ozone-treated lignin would be larger than the untreated lignin.

СВЕТЯЩИЕСЯ ДЕКОРАТИВНЫЕ БЕТОНЫ С ИСПОЛЬЗОВАНИЕМ ОТХОДОВ КАМНЕДРОБЛЕНИЯ ГОРНЫХ ПОРОД

TLuminous products are obtained from architectural and decorative concrete using photoluminescent pigment, formed in various positions and any configuration that does not lose their architectural expressiveness over a long period of operation. The use of products with a glow effect provides increased safety at night and is an additional means of signaling on dangerous and worst-lit sections of roads, parking lots, bicycle paths. Optimally selected materials and the method of surface treatment of products provide decorativeness of small architectural forms in the daytime. The compositions of architectural and decorative concrete are designed and the influence of the quantitative content of photoluminescent pigment on the main physico-mechanical characteristics is evaluated. The rheological properties of cement suspensions and architectural and decorative concrete based on them are studied, and the decorativeness and luminescence of products with photoluminescent pigment are evaluated according to the methods developed by the authors. The resulting recommended composition of glowing architectural and decorative concrete with using white Portland cement СEM I 52.5 N, fractionated marble crushing waste, modifier of polycarboxylate type and photoluminescent pigment, allows to obtain the products with a glow effect, high architectural, decorative and physico-mechanical characteristics.

Generation and stability of cement soap films.

Foaming a cementitious suspension is a complex process that involves many multiscale chemical, physical and dynamical mechanisms. As a first step, we investigate here experimentally the possibility of withdrawing a single liquid soap film from a suspension of cement. We then determine the film lifetime and if particles are entrained or not. We vary the cement concentration, grain size, rheological properties and withdrawing velocity. We observed that the rheology of the cement paste, characterized through its yield stress, plays a key role in the film formation. We show that an optimum exists, as a low yield stress promotes film creation but is detrimental to the film stability. Another key result is that the rheology alone is not enough to describe film formation: the particle size in the suspension is also crucial, with large particles promoting film creation. Finally, we found that the withdrawing velocity also affects the ability to create films and the possibility to drag particles in them. Experiments performed with a silica suspension for comparison confirm these findings.

Prediction of cement suspension groutability based on sand hydraulic conductivity

The experimental investigation reported herein aims toward the development of groutability prediction models based on the hydraulic conductivity of sand and other parameters affecting the groutability of cement suspensions. For the purposes of the present study, suspensions of three different cement types, each at four different gradations, having water to cement (W/C) ratios of 1, 2 and 3, by weight, were injected into dry and dense sand columns with a height of 36.5 cm. The tested cements cover the range from ordinary to microfine materials having nominal maximum grain sizes of 100, 40, 20 and 10 μm. Six uniform, clean sands with different grain sizes were used alone or mixed in various proportions to obtain 48 additional sands, with different gradations, for grouting. Suspension groutability is improved by increasing cement fineness and suspension W/C ratio or by decreasing apparent viscosity and is controlled by the hydraulic conductivity and the gradation of the sand. The groutability and filtration limits defined in the present study, are based on sand hydraulic conductivity and suspension apparent viscosity and depend on cement fineness and sand gradation. The best model developed by performing Binary Logistic Regression analyses of the injection test results is regarded as an efficient tool for the prediction of groutability of cement suspensions in sands with different gradations, as it exhibits a coefficient of multiple determination equal to 0.914 and estimates successfully the outcome of the injection tests available from this study and collected from other studies at a rate equal to 89% and 70.5%, respectively.

Characterization data of reference industrial polycarboxylate superplasticizers used within Priority Program DFG SPP 2005 "Opus Fluidum Futurum - Rheology of reactive, multiscale, multiphase construction materials".

Two industrial polycarboxylate superplasticizer samples have been selected to be used within the Priority Program 2005 of the German Research Foundation (DFG SPP 2005). The PCE polymers were characterized via Size Exclusion Chromatography (SEC) to determine their molar masses (Mw, Mn), the polydispersity index (PDI) and the conversion rate which indicates the incorporation of the macromonomer into the polymer. The anionic charge amount of the PCE samples was assessed via charge titration employing a cationic polymer. Furthermore, the cement dispersing properties of the PCE polymers were captured via 'mini slump' tests so as to assess their ability to fluidize CEM I 42.5 R and CEM III/A 42.5 N samples, respectively. Also, interaction between the PCEs and the surface of the cements was investigated via adsorption and zeta potential measurements of aqueous cement suspensions. The results shall be used for the ongoing research within the Priority Program.

Architectural and decorative concrete with photoluminescent pigment

The authors received glowing products from architectural and decorative concrete with the use of photoluminescent pigment, formed in various positions and any configuration that does not lose their architectural expressiveness over a long period of operation. The use of products with a glow effect provides increased safety at night and is an additional means of signaling on dangerous and worst-lit sections of roads, parking lots, bicycle paths. Optimally selected materials and the method of surface treatment of products provide decorativeness of small architectural forms in the daytime. The compositions of architectural and decorative concrete were designed and the influence of the quantitative content of photoluminescent pigment on the main physico-mechanical characteristics was evaluated. The rheological properties of cement suspensions and architectural and decorative concrete based on them are studied, and the decorativeness and luminescence of products with photoluminescent pigment are evaluated according to the methods developed by the authors. The resulting recommended composition of glowing architectural and decorative concrete with using white Portland cement (CEM I 52.5 N), fractionated marble crushing waste 0.2-0.5; 0.5-1.0; 1.5-2.0; 3.0-7.0; 5.0-10.0; 10.0-20.0, modifier of polycarboxylate type and photoluminescent pigment, allows to obtain the products with a glow effect, high architectural, decorative and physico-mechanical characteristics that correspond to the operating conditions.

Determination of the plastic viscosity of superplasticized cement pastes through capillary viscometers

Determining correctly the rheological parameters of the cement paste is a matter of capital importance when designing a self-compacting concrete (SCC). For this, it is necessary to resort to rheometers, which are expensive and, therefore, not available in all laboratories. However, the measurement of plastic viscosity can also be carried out using capillary viscometers, simple and cheap instruments whose foundation lies in the time it takes for a volume of suspension to flow through the hole in a capillary. It is common practice to use the Marsh funnel in the construction industry but not the Cannon–Fenske viscometer, more used in other industries such as chemistry. Besides, most of the models associated with the Marsh funnel have been developed for drilling muds, although there are some exclusive for cementitious suspensions. However, the rheological nature of both materials is very similar, so it seems appropriate to check how these models behave in cement pastes designed for SCC. Consequently, the rheological behavior of 39 cement pastes of different composition was studied (varying the nature of cementitious materials and the superplasticizer admixture, with various water–cementitious materials ratios) to check the performance of said devices and models using the plastic viscosity measured with a rotational rheometer as a reference. The results indicate that the Cannon–Fenske viscometer offers a better approximation to the reference plastic viscosities than the Marsh funnel. As for the comparison between models for the Marsh funnel, the results obtained are disparate, so it would be convenient to expand the experimental research to adjust the parameters of the models that offer a good approach.

Preshearing is an in situ setting modification method for inorganic bone cements

AbstractThe flow behaviour and injectability of calcium phosphate cements are outcomes of the complex interplay between time‐dependent processes of dissolution, nucleation and crystal growth. Their dependence on shear strains, frequencies and rates has been revealed by rheological investigation of the setting processes of a brushite cement under torsional flow. Various oscillatory torsional strain amplitudes and frequencies were seen to promote dissolution or delay crystal intergrowth compared to quiescently set cement samples. Oscillatory torsional strain amplitudes higher than the linear viscoelastic strain limit resulted in a pronounced lag in crystal intergrowth. Dissolution was enhanced and setting was promoted with increasing frequency and strain amplitude within the linear viscoelastic strain range. Changing the preshearing mode to steady torsion increased energy spent to microstructural deformation, counteracting the beneficial vibratory effect on cement setting kinetics, and produced a net retardation by the disruption of the crystal network structure. Such deformation history can be created in the cement suspension prior to injection during clinical practice by precise adjustment of the preshearing modes and parameters to enable the orthopaedic surgeon tailor the setting time, flow behaviour and injectability of calcium phosphate cements in situ without altering the cement chemistry, hence bioactivity.

Modeling SAOS Yield Stress of Cement Suspensions: Microstructure-Based Computational Approach.

Two static yield stress models, one known as YODEL and the newly proposed BreakPro, based on inter-particle bond breaking probability, were employed to comparatively simulate the yield stress of cement suspensions, induced by oscillatory rheological tests with small amplitude oscillatory shear (SAOS). This yield stress occurs at a critical strain in the order of 0.01%, and is commonly attributed to the limit of the linear viscoelastic domain, where attractive forces bridge the cement particles and form a flocculated particle network. YODEL is based on van der Waals (vdW) interaction forces to describe the yield stress for flow onset at a critical strain of a few percent, developed for simple non-reactive particulate suspensions. However, due to the high pH and reactivity of cementitious suspensions, their particle interaction forces are much higher than vdW. Therefore, until now, the YODEL adaptations to cementitious suspensions did not explicitly consider the microstructural-based salient feature of the original model, but used it as an implicit fitting parameter to scale the average attractive force. In this paper, the force is inversely estimated using the full power of the two microstructural-based models, presenting a new mathematical tool for investigating the fragility of the rigid percolated structure of cement suspensions. The model parameters were calibrated on measured yield stresses obtained by SAOS measurements in a high-sensitivity rheometer. The estimated forces were found to be 5.57 (BreakPro) and 1.43 (YODEL) times higher than typical van der Waals forces. The YODEL percolation threshold of 21% turned out to be significantly lower than the one found by the BreakPro model (37%). This indicated that BreakPro modeling assumptions are better suited for the description of yield stress at SAOS critical strain than the YODEL model.

Optimization of Superplasticizer Dosage for Cementitious Suspension Involved in High Shear Applications

Optimization of Superplasticizer Dosage for Cementitious Suspension Involved in High Shear Applications

Effect of Pre-Shear on Agglomeration and Rheological Parameters of Cement Paste.

Cementitious pastes are multiphase suspensions that are rheologically characterized by viscosity and yield stress. They tend to flocculate during rest due to attractive interparticle forces, and desagglomerate when shear is induced. The shear history, e.g., mixing energy and time, determines the apparent state of flocculation and accordingly the particle size distribution of the cement in the suspension, which itself affects suspension’s plastic viscosity and yield stress. Thus, it is crucial to understand the effect of the mixing procedure of cementitious suspensions before starting rheological measurements. However, the measurement of the in-situ particle agglomeration status is difficult, due to rapidly changing particle network structuration. The focused beam reflectance measurement (FBRM) technique offers an opportunity for the in-situ investigation of the chord length distribution. This enables to detect the state of flocculation of the particles during shear. Cementitious pastes differing in their solid fraction and superplasticizer content were analyzed after various pre-shear histories, i.e., mixing times. Yield stress and viscosity were measured in a parallel-plate-rheometer and related to in-situ measurements of the chord length distribution with the FBRM-probe to characterize the agglomeration status. With increasing mixing time agglomerates were increasingly broken up in dependence of pre-shear: After 300 s of pre-shear the agglomerate sizes decreased by 10 µm to 15 µm compared to a 30 s pre-shear. At the same time dynamic yield stress and viscosity decreased up to 30% until a state of equilibrium was almost reached. The investigations show a correlation between mean chord length and the corresponding rheological parameters affected by the duration of pre-shear.

Plasma-generated silicon oxide coatings of carbon fibres for improved bonding to mineral-based impregnation materials and concrete matrices

To improve its bonding behaviour with cementitious materials, the surface of carbon fibre (CF) yarn was modified by depositing a SiOx-coating using a plasma-enhanced, chemical vapour deposition (PECVD) process with hexamethyldisiloxane (HMDSO) as precursor material. After applying the SiOx coating, the fibre was impregnated with a fine-grained cement suspension to process mineral-impregnated carbon fibres (MCF). After advanced hydration, the MCF were investigated in respect of their flexural strength as well as their porosity. Moreover, the MCF were implemented in a fine-grained concrete matrix and assessed with respect to their pull-out behaviour.It was found that the plasma generated SiOx coating led to a significant increase in maximum pull-out force, indicating better bonding between the modified carbon fibre yarns and the concrete matrix. This is attributed to a more pronounced pozzolanic reaction induced by the SiOx-films, promoting the local formation of calcium silicate hydrate (CSH) directly on the multifilament yarns, as supported by thermal gravimetric and microscopic analysis. However, it was also found that the deposition of the SiOx-films onto the CF resulted in more porosity in the impregnated cementitious matrix's structure, as proven by mercury intrusion porosity measurements. The higher porosity induced in turn a decrease in flexural strength for the MCF with high SiOx deposition.It can be concluded that the deposition of a SiOx film onto the CF surfaces via plasma treatment is an innovative, promising approach toward enhancing the interactions between fibre and the cementitious matrix, but the process and material parameters need to be well balanced with regard to the microstructure and mechanical properties of the MCF.

Influence of Ultrafine Addition Obtained from Pre-Hydrated Cement on Cement Paste

This article focuses to influence of a pre-hydrated cement suspensions on hardening cement paste properties investigation. The pre-hydration was occurred by 2-th, 4-th 6-th hours during forced mixing. Changes of particle dispersion caused by hydration were determined. It is shown that by hydrolysis increase particles dispersion and subsequently increases quantity of new hydrate formations. Influence of the pre-hydrated cement suspensions on hardening cement paste properties is determined. It is shown that application pre-hydrated addition leads to increasing a cement paste water demand by 12, 17 and 14% for duration of hydration by 2, 4 and 6 hours consequently and to decreasing setting time. It caused by generating supplementary new formations of crystalline hydrate with subsequently increasing rate cement paste structuration. Rate of hardening was increased with increasing duration of the pre-hydration for 10% pre-hydrated cement addition. Obtained results may recommended the addition of pre-hydrated cement in form of cement suspension as cement gel for concrete nanomodification

Influence of particle dispersion on the viscosity change in highly-concentrated cement suspensions: An experimental correlation

Fresh concrete is a concentrated suspension of Portland cement and aggregates. Cement-based materials show a fluid-to-solid transition incorporating water, which allows us to cast and place a structure in field. Ease of construction requires a lower viscosity of cement-based materials, and it could be achieved by cement particle dispersion in water. In this study, a laser backscattering measurement identifies the cement dispersion in in situ samples, and their size distribution are parametrized using the occurrence rate of a Poisson process. The cement dispersion is unaffected by external shearing intensity while the concentration (or water-to-cement ratio) or the use of dispersant alters its degree. Finally, associating the dispersion measurement with the microstructural state determined by their viscosity curves makes it clear how the cement viscosity decreases.

Effect of Different Shear Rates on Particle Microstructure of Cementitious Materials in a Wide Gap Vane-in-cup Rheometer.

Rheological properties of cementitious suspensions are affected not only by their mixture composition but also by process-related factors such as shear history. To enable a model-based description, investigations were carried out on the effect of shear history (shear rate variation over time) on the cement paste agglomeration state. Therefore, a Focused Beam Reflectance Measurement (FBRM) system and a wide gap rheometer were coupled to study the relation between shear history and in-situ chord length distribution simultaneously, indicating particle agglomeration. Hence, the effect of average shear rates (resulting from the applied shear profile), as well as shear rate distribution within the gap (local shear rates) on the particle agglomeration state have been investigated. The rheological properties of cement paste were evaluated with the Reiner–Riwlin approach. Furthermore, the agglomeration state of the particles was compared for different average shear rates and local shear rates at various positions of the FBRM probe. The results show that the median chord length increases in all positions when the average shear rate is decreased, indicating increasing particle agglomeration. Moreover, due to variable local shear rates at different FBRM probe positions, different agglomeration states are observed, resulting from two factors, shear rate dependent particle agglomeration and shear-induced particle migration.

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.