Comparison between two ultrasonic methods in their ability to monitor the setting process of cement pastes

This paper presents the comparison between ultrasonic wave transmission (USWT) method and ultrasonic wave reflection (USWR) method in their ability to monitor the setting process of cement pastes. The velocity of ultrasonic longitudinal waves and shear wave reflection coefficient were measured simultaneously on cement pastes with different hydration kinetics. Even though both methods are able to reliably monitor the hydration process and formation of structure of an arbitrary cement paste, they monitor the setting process in different ways. The relationship between the velocity of longitudinal waves and shear wave reflection coefficient can be simplified into three characteristic phases and the end of the first phase can be used to define the beginning of the setting process of cement paste.     

Effect of various superplasticizers on the rheological properties of Portland cement pastes

In the present work, the influence of the addition of some superplasticizers employed for maximising the solid loading of Portland cement pastes has been investigated. Cement pastes were prepared from deionized water and a commercial manufactured ordinary Portland cement 32.5 R (produced by Buzzi Unicem). Cement and water were mixed with a vane stirrer according to ASTM Standard C305. The water/cement ratio was kept fixed at 0.32. Three commercial superplasticizing agents produced by Ruredil were used: they are based on a melamine resin (Fluiment 33 M), on a modified lignosulphonate (Concretan 200 L), and on a modified polyacrylate (Ergomix 1000). Rheological tests were carried out at 25 °C by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-Osc., measuring device MV2P with serrated surfaces. The tests were performed under both continuous and oscillatory flow conditions. Ergomix 1000 presents a different behaviour as that of the other two superplasticizers studied, because it shows a marked shear-thickening behaviour above a critical deflocculant concentration and slight elastic effects particularly at high dosages as well.     

Effects of air voids on ultrasonic wave propagation in early age cement pastes

The objective of this paper is to investigate effects of air voids on ultrasonic wave propagation in fresh cement pastes, and relate ultrasonic wave parameters to cement setting times. First, Biot's theory was used to analyze wave propagation in poroelastic media containing air bubbles. Then, in the experimental study, both the compressional (P) and shear (S) waves were monitored in cement pastes with different water/cement ratios (w/c = 0.4 and 0.5) and various air void content (0.1%–5.3% by cement paste volume). Experimental results indicated that existence of air bubbles in cement paste significantly decreases the P wave velocity, but has little effect on the shear wave propagation. Further analysis shows that the shear wave velocity corresponding to the Vicat initial setting times is a relatively constant value for the investigated air content range. This study shows the potential of using shear waves to monitor setting and hardening process of cement.     

Steady and transient flow behaviour of fresh cement pastes

Fresh cement pastes behave as non-Newtonian viscous fluids. During steady flow, their apparent viscosity depends on the applied strain rate. During transient flow, the apparent viscosity is a function of time. In this work, a thixotropic model is presented. Its four parameters are identified experimentally for a tested cement paste using coaxial viscometer test. Viscometer flow simulations are then carried out. The model proves to be able to predict the trends of the fresh behaviour of cement pastes in various flow situations.     

Effect of some water‐soluble melamine formaldehyde‐free polycondensates on the rheological properties of cement pastes

Water‐soluble melamine formaldehyde‐free polycondensate products were prepared. The chemical structure of these polymers was confirmed with different spectroscopic techniques. The effects of these polymers on the rheological properties of the cement pastes were investigated. The rheological parameters (shear stress, yield stress, and plastic viscosity) were calculated with the Bingham model. The minislump of superplasticized cement pastes at different interval times (5, 30, 60, 90, and 120 min) was determined. The results showed that the new superplasticizers increased the fluidity and minislump of the cement pastes and reduced the minislump loss of the cement pastes not only at early ages (30 min) but also at later early ages (120 min). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2212–2218, 2005     

Influence of time addition of superplasticizers on the rheological properties of fresh cement pastes

It is well known that the fluidity and the fluidity loss of fresh cement pastes are affected by the kind and the time of addition of organic admixtures. The influence of the time addition of two chemical admixtures, namely, melamine formaldehyde sulfonate (MFS) and naphthalene formaldehyde sulfonate (NFS), on the rheological properties of ordinary Portland and sulfate-resisting cement pastes through the first 120 min of hydration was investigated. The admixture addition was delayed by 0, 5, 10, 15, 20, and 25 min. Shear stress and apparent viscosity of the cement pastes were determined at different shear rates (3-146 s⁻¹) and hydration times of 30, 60, 90, and 120 min. The concentration of Ca²⁺ and the combined water content of the cement pastes were determined after 120 min. Yield stress and plastic viscosity values were also determined by using the Bingham model. The results show that an increase in the addition time of the admixture reduces the shear stress, the yield stress, and the plastic viscosity of the cement pastes at the early ages (15 min) as well as at later early ages (120 min). The optimum delaying time of admixture addition is found to be 10-15 min. This time does not depend on the cement and superplasticizer type.     

Hardened Portland cement pastes,modelisation of the micro-structure and evolution laws of mechanical properties I- Basic results

This paper is the first of a series of three. For Portland cement pastes, it presents a model of the micro-structure and the associated compressive strength law which will be the base of the two following papers.Model and strength law involve that the most important parameter influencing the strength is the capillary porosity. They allow to foresee the characteristic properties of the pastes of the first and of the second group. At last they give informations about the structure of the gel.     

Effect of temperature on dynamic rheological properties of uncured rubber materials in both the linear and the nonlinear viscoelastic domains

Investigating how rubber materials are affected by strain and strain rate (or frequency) in the room‐to‐curing temperature range allows to fully characterize them not only with respect to their processing behavior but also in view of their likely performances after vulcanization. Using a closed cavity dynamic rheometer, the adequate test protocols and data treatment, three gum elastomers, and three carbon black filled compounds were investigated in the 60–180°C range. The article describes the test protocol and the associated data treatment that were developed to document the effects of strain and temperature in both the linear and the nonlinear domains. Complex modulus G* and third relative torque harmonic variations with strain amplitude and temperature are reported and discussed in details. A set of relatively simple mathematical equations are demonstrated to offer the possibility to summarize large quantities of experimental data through a limited number of parameters whose physical meaning can be explained with respect to known aspects of polymer and rubber sciences. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Structural effect of prepared and commercial superplasticizers on performance of cement pastes

The sodium salt of melamine‐phenol formaldehyde sulfonate (MPhFS), melamine formaldehyde sulfonate (MFS), and phenol formaldehyde sulfonate (PhFS) were prepared according to a four‐step reaction procedure. The four steps of the reaction are hydroxymethylation, sulfonation, low pH condensation, and high pH rearrangement. Fourier transform IR and differential scanning calorimetry spectra were used to determine the structure of the synthesized resins. The effects of MFS, PhFS, MPhFS, and commercial superplasticizers on the rheological properties of cement pastes were investigated using a rotating coaxial viscometer. It was found that the prepared resins enhanced the rheological properties of cement pastes more than commercial ones. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 482–487, 2003     

阿利特—硫铝酸盐水泥与硅酸盐水泥复合性能的研究

研究了阿利特－硫铝酸盐水泥与硅酸盐水泥复合所制备的水泥的性能。结果表明,复合后水泥的强度性能优于单一品种水泥的性能;凝结时间则由复合体中占比例较多的一种水泥所控制。     

In situ measurement of elastic properties of cement by an ultrasonic resonant sensor

The ultrasonic sensor is composed of a resonator excited by a piezoelectric element. It is in the shape of a solid metallic cylinder with a fine cylindrical tip. The tip is dived into the cement to be tested, where it generates propagating and standing waves. The frequency of resonance of the system gives us information on the elastic properties of the paste. The sensor is mostly sensitive to the shear modulus G′ of the medium. With the described sensor, the range 10⁶<G′<10⁷ Pa is tested. Other ranges can be selected by changing the size of the cylinder or the tip.     

Properties of plain and latex modified Portland cement pastes and concretes with and without superplasticizer

This paper deals with the effects of latex concentration on the workability and strength characteristics of Portland cement pastes with and without superplasticizer. Durability assessments are made by immersing these pastes in 5% Na₂SO₄ and 2.5% NaCl solutions. From the results obtained, it is found that the superplasticizer and superplasticizer-latex combinations may improve the workability of the Portland cement pastes. The Portland cement pastes with superplasticizer have much higher strengths than the latex modified Portland cement pastes with and without superplasticizer. In general, curing in lime-saturated water adversely affect the strength of the pastes containing latex from about 28 days onwards. In the durability test, the resistance of latex modified Portland cement pastes with and without superplasticizer to NaCl is decreased. Degradation mechanism depends on the characteristics of the corrosive medium as well as the resistance of the material itself to the resulting chemical action. The character of strain-stress data of latex modified concretes becomes more prominent as the latex concentration increases. These data are anomalous when compared with the data normally observed for concretes without admixture. The proposed equations are found adequate to describe the stress-strain behaviour of latex modified concretes in compression. These equations can also be applied in calculating the initial modulus of elasticity and proportional limit in the case of polymer modified concretes, which exhibit non-linear behaviour at high stress.     

硫铝酸盐水泥与硅酸盐水泥复配性能研究

基于硫铝酸盐水泥、硅酸盐水泥各自的特点,研究了二者复配后的标准稠度用水量、凝结时间、水化热效应、胶砂强度、膨胀性、水化产物的物相及微观形貌。结果表明,复配水泥的标准稠度用水量因复配比例不同而变化,凝结时间相对于占主导地位的单组分水泥明显缩短;复配水泥的早期水化速率得到提高,1d、7d的水化放热量均低于占主导地位的单组分水泥;28d抗压、抗折强度低于任何单组分水泥;膨胀性的大小取决于两种水泥的复配比例;硫铝酸盐水泥与硅酸盐水泥的复配使二者的水化相互促进,随着硫铝酸盐水泥掺量的增加,Ca(OH)2相的衍射峰减弱,AFt相的衍射峰增强;纯硅酸盐水泥水化后的微观形貌是致密的,而与硫铝酸盐水泥复配后则出现微观裂纹。     

Monitoring the setting behavior of cementitious materials using one-sided ultrasonic measurements

Cementitious materials are transformed from a fluid to a solid state due to a chemical reaction known as hydration. These cementitious materials exhibit a continuous change in the mechanical properties with time; there is a steady increase in the stiffness after setting. An ultrasonic test setup and the data analysis procedure, which provide for continuous monitoring of the hydrating cementitious materials from a very early age, have recently been developed. The test procedure for obtaining the ultrasonic test data from cementitious material at different stages of hydration and the theoretical analysis, which allows interpreting the ultrasonic response in terms of the changes in the acoustic shear impedance of the hydrating cementitious material, are presented in this paper. Experimental test results obtained from mortar mixtures of known composition are presented. It is shown that the initial and final setting times correspond approximately with the occurrence of distinctive features in the ultrasonic response.     

Possibilities of using the ultrasonic wave transmission method to estimate initial setting time of cement paste

In this paper, the applicability of the ultrasonic wave transmission method to estimate the initial setting time of an arbitrary cement paste is discussed. Ultrasonic pulse velocity measurements were fully automated and measured continuously. The Vicat Needle Test was used in order to determine the initial setting time of cement pastes. Different cement pastes were prepared in order to check the influence of the water/cement ratio, type of cement, curing temperature, cement fineness, and some clinker compositions, on the relationship between the initial setting time and ultrasonic pulse velocity. It was found that the initial setting time of an arbitrary cement paste can be estimated very accurately by the time the first inflection point appears on the ultrasonic pulse velocity curve. Moreover, it can be estimated quite accurately by the time the ultrasonic pulse velocity reaches a fixed value, close to the value of the ultrasonic pulse velocity in water.     

Numerical and analytical effective elastic properties of degraded cement pastes

Cement pastes are heterogeneous materials composed of hydrates, anhydrous products and pores of various shapes. They are generally characterized by a high particle concentration and phase contrasts, in particular in the case of degraded materials which exhibit important porosity. This paper compares the performance of several classical effective medium approximation schemes (Mori–Tanaka, Zheng-Du, self-consistent) through their ability to estimate the mechanical parameters of cement paste samples obtained numerically. For this purpose, finite element simulations are performed on 3D structures to compute for each sample accurate values of these mechanical properties. For these simulations, the cement paste is considered as a matrix of C–S–H in which are embedded inclusions of anhydrous, hydration products, and pores. In order to evaluate the importance of the particle shape, two types of samples are generated, one with only spherical inclusions and the other containing both spherical and prismatic particles. Simulations with three perpendicular loading directions and both uniform and mixed boundary conditions are performed in order to verify that the dispersion in the computed elastic moduli is low, or equivalently that the generated structures are close to representative volume elements (RVEs). It is shown that the considered effective medium approximation schemes, except the self-consistent one, provide relatively good estimations of the overall mechanical parameters when compared to simulation results, including when both particle volume fraction and phase contrast are high. The analytical methods taking into account the particle shapes also give estimates close to the corresponding numerical simulations, the latter confirming the influence of the particle form.     

Sorption kinetics of superabsorbent polymers (SAPs) in fresh Portland cement-based pastes visualized and quantified by neutron radiography and correlated to the progress of cement hydration

Water sorption of two superabsorbent polymers in cement-based pastes has been characterized by neutron radiography. Cement pastes with W/C of 0.25 and 0.50 and one additionally containing silica fume (W/C = 0.42) were investigated. The SAPs differed in their inherent sorption kinetics in extracted cement pore solution (SAP 1: self-releasing; SAP 2: retentive).Desorption from SAP 1 started very early after paste preparation. Hence, its individual non-retentiveness governs its behavior only.SAP 2 released water into all matrices, but its kinetics were different. In the paste with the highest W/C, some moderate water release was recorded from the beginning. In the other two pastes, SAP 2 retained its stored liquid during the dormant period, i.e., up to the percolation threshold. Intense desorption then set in and continued throughout the acceleration period.These findings explain the pronouncedly higher efficiency of SAP 2 as internal curing admixture as compared to SAP 1.     

The effect of microencapsulated phase change materials on the rheology of geopolymer and Portland cement mortars

The effect of microencapsulated phase-change materials (MPCM) on the rheological properties of pre-set geopolymer and Portland cement mortars was examined. Microcapsules with hydrophilic and hydrophobic shells were compared. The shear rate dependency of the viscosities fitted well to a double Carreau model. The zero shear viscosities are higher for geopolymer mortar, illustrating poorer workability. The time evolution of the viscosities was explored at shear rates of 1 and 10 s⁻¹. New empirical equations were developed to quantify the time-dependent viscosity changes. The highest shear rate disrupted the buildup of the mortar structures much more than the lower shear rate. Microcapsules with a hydrophobic shell affect the rheological properties much less than the microcapsules with a hydrophilic shell, due to the higher water adsorption onto the hydrophilic microcapsules. Shear forces was found to break down the initial structures within geopolymer mortars more easily than for Portland cement mortars, while the geopolymer reaction products are able to withstand shear forces better than Portland cement hydration products. Initially, the viscosity of geopolymer mortars increases relatively slowly during due to formation of geopolymer precursors; at longer times, there is a steeper viscosity rise caused by the development of a 3D-geopolymer network. Disruption of agglomerates causes the viscosities of portland cement mortars to decrease during the first few minutes, after which the hydration process (increasing viscosities) competes with shear-induced disruption of the structures (decreasing viscosities), resulting in a complex viscosity behavior.     

Assessment of morphological,thermal, and viscoelastic properties of epoxy vinyl ester coating composites: Role of glass flake and mixing method

In this work, glass flake (GF)/epoxy vinyl ester resin composites were fabricated with various compositions and mixing methods. The effect of GF on thermal and mechanical behavior of these composites was investigated using different techniques such as differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and thermogravimetric analysis (TGA). The results showed that the presence of GF in epoxy vinyl ester formulation could obviously affect the cure temperature, reaction enthalpy value, and degradation temperature. DMTA results also exhibited that the tan δ peak area decreased and storage modulus increased with increasing GF content and this effect seemed to be different depending on the initial epoxy vinyl ester compositions. The scanning electron microscopy (SEM) images showed that mixing method had a strong effect on the surface morphology, size, and distribution of glass flake. The effect of mixing method on properties of produced composite was also studied.     

Influence of the inorganic phase concentration and geometry on the viscoelastic properties of latex coatings through the glass-transition

The mechanical properties of artists’ acrylic (latex) paint films containing different volume fractions of TiO₂, CaCO₃ and kaolin were measured in uni-axial tension over a broad range of temperatures and crosshead speeds. Young’s modulus results in the glassy region were first compared with several micromechanics theories for particle-filled composites containing elastic phases. It was found that the Mori-Tanaka theory slightly under-predicted the modulus enhancement, while the Lielens approach provided the most accurate results. A nonlinear viscoelastic material model involving a Prony series and the neo-Hookean hyperelastic function was used to represent the tensile data up to relatively small strains of a few percent. From the experimental data, the material model was calibrated and the required parameters were determined. The derived parameters were then used to re-construct relaxation modulus plots, which were compared with the approximations given by Clements and Mas for the viscoelastic Mori-Tanaka theory in the time-domain. It was found that the experimentally observed modulus enhancement was much stronger than the predicted values in the rubbery region. Mechanisms such as constrained polymer at the inorganic particle interface, and the possible formation of a percolation network are discussed.