CA Paste Research Articles

Effect of polymer dispersion characteristics and incorporation methodology on properties of cement asphalt mortar for high-speed rail slab track system

This study investigates the impact of polymer dispersion characteristics and incorporation methods on the polymer modified asphalt emulsion (PMAE) characteristics and, consequently, on the properties of Cement Asphalt Mortar (CAM) for high-speed rail tracks. The results showed that latex-form polymer dispersions with anionic charge and coagulation values below 1 % after 30 minutes provided stable mortars with shorter flow times. Mortar with PMAE produced through terminal blending (TB) method exhibited superior workability characteristics compared to those produced via soap pre-batch (S) and co-milling (C) methods. Differential Scanning Calorimetry (DSC) studies indicated improved polymer integrity in the CAM when produced with PMAE:TB. Mortar containing PMAE:C found to have the highest compressive strengths, with values of 1.49 MPa at 7 days and 2.32 MPa at 28 days, followed by PMAE:S, PMAE:TB, and the control asphalt emulsion (AE). Thermogravimetric Analysis (TGA) results on hydrated CA paste were consistent with the compressive strength trend, and Field Emission Scanning Electron Microscopy (FESEM) analysis revealed a more uniform polymer distribution in TB method. The study concludes that anionic polymer dispersions having low coagulation values introduced through terminal blending are most suitable for CAM production.

Enhancing sustainability in pavement Engineering: A-state-of-the-art review of cement asphalt emulsion mixtures

Cement asphalt emulsion mixture (CAEM) is an environmentally sustainable substitute for hot mix asphalt and can trigger a substantial economic benefit. This paper systematically reviews the interactions between the organic–inorganic composites and their influence on the performance of CAEM. First, the interactions between asphalt emulsion (AE) and cement are introduced. Next, the demulsification of AE and hydration of cement in the CAEM system are analyzed. Finally, the fresh properties of CA paste, the static and dynamic mechanical properties of CA mortar and its applications in ballastless slab tracks, and the road performance of CAEM and its applications in pavement construction are discussed. This review allows for a better understanding of the interaction of the organic–inorganic composite and thus has a better strategy to regulate the performance of CAEM and promote its practical application.

Calcium-doped zinc oxide nanocrystals as an innovative intracanal medicament: a pilot study.

This study investigated the cytotoxicity, radiopacity, pH, and dentinal tubule penetration of a paste of 1.0% calcium-doped zinc oxide nanocrystals (ZnO:1.0Ca) combined with propylene glycol (PRG) or polyethylene glycol and propylene glycol (PEG-PRG). The pastes were prepared by mixing calcium hydroxide [Ca(OH)2] or ZnO:1.0Ca with PRG or a PEG-PRG mixture. The pH was evaluated after 24 and 96 hours of storage in deionized water. Digital radiographs were acquired for radiopacity analysis and bubble counting of each material. The materials were labeled with 0.1% fluorescein and applied to root canals, and images of their dentinal tubule penetration were obtained using confocal laser scanning microscopy. RAW264.7 macrophages were placed in different dilutions of culture media previously exposed to the materials for 24 and 96 hours and tested for cell viability using the MTT assay. Analysis of variance and the Tukey test (α = 0.05) were performed. ZnO:1.0Ca materials showed lower viability at 1:1 and 1:2 dilutions than Ca(OH)2 materials (p < 0.0001). Ca(OH)2 had higher pH values than ZnO:1.0Ca at 24 and 96 hours, regardless of the vehicle (p < 0.05). ZnO:1.0Ca pastes showed higher radiopacity than Ca(OH)2 pastes (p < 0.01). No between-material differences were found in bubble counting (p = 0.0902). The ZnO:1.0Ca pastes had a greater penetration depth than Ca(OH)2 in the apical third (p < 0.0001). ZnO:1.0Ca medicaments presented higher penetrability, cell viability, and radiopacity than Ca(OH)2. Higher values of cell viability and pH were present in Ca(OH)2 than in ZnO:1.0Ca.

Factors influencing the performance of cement emulsified asphalt mortar – A review

Cement emulsified asphalt mortar (CEAM) is an essential component in the ballastless slab track system. It is a semi-rigid composite material consisting mainly of hardened cement paste and demulsification asphalt, possessing the advantages of both ordinary Portland cement and asphalt. Its primary functions include: supporting structures, adjusting the slab track's geometry during construction, and dissipating/reducing orbital vibration. In this review, the preparation technology of CEAM was introduced at first. Subsequently, the hardening mechanism between asphalt emulsion and cement in CEAM was summarized. Meanwhile, the influence of asphalt emulsion type and dosage, sand to cement ratio (S/C), water to cement ratio (W/C), common auxiliary additives, and temperature on the properties of CEAM were compared and analyzed. This current review concludes that the most significant influence on CEAM performance is the mass ratio of asphalt to cement. With the increase of asphalt content, hardened cement asphalt paste (CA paste) would show two different overall mechanical properties. Besides, the effects of the S/C ratio and W/C ratio on high strength CEAM are not the same as that of low strength CEAM. Future research is recommended: to develop sustainable CEAM without prejudice to the performance; and to further analyze the interaction mechanism between emulsified asphalt and cement materials from the microscopic perspective.

Comparative study of hydration of monocalcium aluminate and quaternary phase and the amorphous AH3 phase in their hydrates

Monocalcium aluminate (CaAl2O4, CA) and quaternary (Q) phase (Ca20Al26Mg3Si3O68) are the two principal hydraulic phases in calcium aluminate cement. Their strength development has been reported. However, little information about the difference of their hydration and hydrates composition is available. For this reason, the hydration process of CA and Q phase was investigated and compared. Results of conductometry indicate that the rate of Q phase hydrates precipitation is much slower than that CA latter. Hydrates identification demonstrates that the most prominent difference between the hydrates for these two compounds is the amorphous AH3 content. The quantity of amorphous AH3 (A=Al2O3, H=H2O) in Q phase hydrates is evidently less than that of CA, as confirmed by FTIR, TG and BSE. Even-distributed amorphous AH3 fills in the crystalline skeleton of calcium aluminate hydrates (C–A–H) enhancing the compactness of CA paste. Hence, CA exhibits a higher 72-day compressive strength than Q phase.

The rheological properties and mechanisms of cement asphalt emulsion paste with different charge types of emulsion

Cement asphalt emulsion (CA) composites are very promising materials suitable for many applications. The rheological properties of CA paste, which can reflect the workability of CA paste and the stability and demulsifying behavior of asphalt emulsion, have attracted much attention. However, the rheological properties of CA paste with different charge types of emulsion (i.e. cationic and anionic) as well as the influencing mechanisms are not clearly understood. In this paper, the rheological properties of CA paste with cationic and anionic emulsion were studied, and the potential influencing factors were analyzed, i.e. pH value, emulsifier, and the adsorption behavior between asphalt droplets and solid particles. Results indicate that the apparent viscosity of CA paste at high shear rate is mainly related to emulsifier type. However, emulsifier type and pH value are not the primary factors of the yield stress of CA paste. The yield stress of CA paste is closely related to emulsion charge types. CA paste with cationic emulsion has a higher yield stress than CA paste with anionic emulsion. This is because that the cationic asphalt droplets has a much stronger adsorbing ability on solid particles surface compared with anionic asphalt droplets.

Factors influencing the structure build-up of fresh cement asphalt emulsion paste

Fresh cement asphalt emulsion mortar (CA mortar) is required to be highly flowable for grouting when it is employed in slab track structure. Segregation and bleeding easily occur after placement. In essence, it is because fresh CA paste has a low rate of structure build-up. However, limited information is reported about the thixotropy of CA paste. A thixotropy model based on structure parameter, which is deduced from constant shear rate test, is proposed to study the structure build-up of CA paste. In the model, the initial structure parameter and the rate of structure build-up are used to describe the evolution law of the structure parameter with resting time, which can be employed to quantitatively evaluate the structure build-up process of CA paste. The thixotropy model is used to study the influence of every constituent on the structural build-up process of CA paste. Results show that asphalt emulsion and superplasticizer dosage are two main factors influencing the structure build-up of CA paste, but water-to-cement ratio and viscosity-modified agent dosage have little effect on the structure build-up of CA paste.

Viscosity prediction of fresh cement asphalt emulsion pastes

Cement asphalt emulsion (CA) composite materials are becoming promising building materials in recent years. Assessing their rheological behavior is crucial for the success of a particular application. Fresh CA pastes with different asphalt emulsion to cement mass ratios (AE/C) have significantly different compositions, and design of their rheological properties is not an easy task. The minimum apparent viscosity of CA pastes with different AE/C is predicted by a viscosity prediction model. The model parameters include maximum particle packing density (ϕ m) and an adjusting factor b. A predictive model of CA composite particles is proposed, in which the maximum particle packing density of CA pastes can be determined by the maximum particle packing density of cement paste, the maximum particle packing density of asphalt emulsion, and the volume fraction of asphalt in asphalt-cement system. The predictive model requires different adjusting factor b for CA pastes with anionic and cationic asphalt emulsion when the predicted ϕ m is used for viscosity prediction. The proposed viscosity prediction equations do offer a simple and reliable method for the viscosity prediction of CA pastes with a wide AE/C range, and can be used to design the rheological properties of CA pastes.

Investigation on the Mixing Stability of Asphalt Emulsion with Cement through Viscosity

AbstractCement asphalt emulsion (CA) mortar is a key material in the nonballast slab track. Its properties are largely dependent on the compatibility between asphalt emulsion and cement. The mixing stability of asphalt emulsion with cement is investigated by analyzing the viscosity of CA paste. Viscosity and the critical particle volume fraction of CA paste are proposed as indexes in evaluating the mixing stability of asphalt emulsion with cement, and factors influencing the mixing stability of asphalt emulsion are studied. Mixing stability is dependent on mixing method, superplasticizer, and emulsion type. The premixing cement method, superplasticizer, and good asphalt emulsion can increase the critical particle volume fraction of CA paste, which is helpful in achieving a low water–to–cement mass ratio (W/C). Anionic emulsion has much better mixing stability with cement than does cationic emulsion. The critical particle volume fraction of CA pastes with anionic emulsion increases stably with the mass rat...

Factors Influencing the Rheology of Fresh Cement Asphalt Emulsion Paste

AbstractCement asphalt emulsion paste (CA paste) is known to be a low-yield stress suspension suitable for many applications in which high flowability is desired. The factors that lead to the low yield stress of CA paste are still unknown, however. The effect of the components in CA paste on the rheology of fresh CA paste is studied to reveal the primary factors that lead to the low yield stress. The effect of emulsifier and superplasticizer on cement paste, the effect of asphalt emulsion, and viscosity modifying agents on CA paste are studied. Results indicate that emulsifier can reduce the yield stress and apparent viscosity of cement paste, but the effect of emulsifier is small compared to the effect of the superplasticizer. The low yield stress of CA pastes is primarily because of the combined effect of superplasticizer and asphalt emulsion. Both CA paste without superplasticizer and cement paste have high yield stress. Viscosity modifying agents can significantly increase yield stress of CA paste wit...

The thixotropic behavior of fresh cement asphalt emulsion paste

The workability of grouting cement asphalt emulsion (CA) mortar is governed by the intrinsic thixotropic behavior of CA paste, but limited information is reported about the thixotropic behavior of CA paste. A new thixotropy method of constant shear rate test is proposed to study the thixotropic behavior of CA paste with different asphalt emulsion to cement ratios (AE/C). In the model, the initial structure parameter and the structure rebuilding rate are used to quantitatively describe the structure rebuilding process, the characteristic time of de-flocculation is used to evaluate the de-flocculation process, and the equilibrium shear stress is used to study the irreversible change of CA paste in the thixotropy test. Results show that CA pastes have significantly different thixotropic behavior compared to cement paste. The initial structure parameter and structure rebuilding rate of CA pastes are much smaller than cement paste, and the structure rebuilding rate decreases significantly with AE/C. The characteristic time of de-flocculation of cement paste changes little at different resting time, however, it increases significantly at the first 5min resting time and then keep stable for CA pastes. The equilibrium shear stress of cement paste does not change in 20min, but it increases with time for CA pastes due to the demulsification of asphalt emulsion.

Study of hydration potential and kinetics of the ferrite phase in iron-rich CAC

With the presence of CA,11Cement notation is used in this paper: C, CaO; A, Al2O3; F, Fe2O3; H, H2O; $, SO3; c, CO2. the hydration kinetics of ferrite phase is influenced and decreased dramatically. Heat flow measurements, QXRD data, and heat flow calculations show concordantly that hydration of ferrite in mix with CA is retarded until the onset of CA hydration and that less ferrite is dissolved. Analysis of the liquid phase of CA paste and CAC-like cement paste displayed significant higher concentrations of Al3+ and Ca2+ compared with pure ferrite paste. Thus, the composition of the liquid phase is set by initial dissolution of CA. We assume that an instant dissolution of the ferrite phase is blocked when solubility equilibrium is dominated by CA. Dissolution of ferrite is only possible after massive precipitation of hydrates and reduction of Ca2+ and Al3+ concentration in the liquid phase.

Rheology of fresh cement asphalt emulsion pastes

The rheology of fresh CA pastes of different asphalt emulsion to cement mass ratio (AE/C) with different particle volume fraction was studied. A modified Herschel–Bulkley model was proposed to fit the flow curve of CA pastes and calculate the yield stress and special viscosity (minimum apparent viscosity) of CA pastes. According to the fitted viscosities and yield stresses, a viscosity model was employed to establish the relationship between viscosity and particle volume fraction of CA pastes, and a yield stress model was employed to study the relationship between yield stress and particle volume fraction of CA pastes. Based on the two relations, maximum particle packing density of CA pastes was calculated and the relation between yield stress and viscosity was established to study the rheology of grouting CA pastes. Results indicate CA pastes with different AE/C have significant different relation of viscosity with particle volume fraction and relation of yield stress with particle volume fraction. In the condition of the same viscosity, the yield stress of CA pastes decreases quickly with the increasing AE/C from 0 to 0.4, and then increases slightly with AE/C from 0.4 to 1.0. The yield stress of CA pastes is very low and should be improved for grouting. These works can well reveal the rheology of CA pastes.

Demulsification process of asphalt emulsion in fresh cement-asphalt emulsion paste

The demulsification process of asphalt emulsion in fresh cement asphalt emulsion (CA) paste was investigated by measuring the viscosity and the particle size distribution of CA paste. The morphology evolution of asphalt droplets was also observed by optical microscope. Superplasticizer was used to adjust different demulsifying speed of asphalt emulsion in CA paste. Results indicate that the viscosity development of CA paste can reflect the demulsification process of asphalt emulsion in CA paste. The demulsification process of asphalt emulsion in CA paste has two main stages under the continual induction effect of cement hydration. Asphalt droplets in CA paste are firstly coalesced to big droplets, and then recover their adhesive force. In the first stage, the viscosity of CA paste increases little with the changing particle size distribution. However, the viscosity of CA paste increases sharply in the second stage.

Factors influencing rheological properties of fresh cement asphalt emulsion paste

As a grouting material, the flow ability and uniformity of fresh cement asphalt emulsion mortar (hereinafter abbreviated as CA mortar) are governed by its rheological properties. The rheological properties of fresh cement asphalt paste were investigated, in which influencing factors, such as type of asphalt emulsion, superplasticizer dosage, and water to cement ratio, were discussed. Results indicate that CA paste with plain asphalt emulsion has too low yield stress to resist segregation, while it has good yield stress when employing asphalt emulsion modified by viscosity modifying agent. Superplasticizer can reduce the initial yield stress and plastic viscosity, however, its water-reducing effect is not obvious for the water-reducing effect of emulsifier in asphalt emulsion. The stability of asphalt emulsion affects the growth rate of plastic viscosity of CA paste, and superplasticizer dosage affects the growth rate of yield stress, which both affects the retention ability of good fluidity. Therefore, a well stable asphalt emulsion modified with viscosity modifying agent, and high superplasticizer dosage (1% recommended in here) are preferred to produce CA mortar.

Performance Evaluation of an Eco-Binder Made with Slag and CFBC Fly Ash

AbstractPerformance of the engineering properties of paste manufactured with an eco-binder was evaluated. The eco-binder without cement, SCA, was made with slag (S) and fly ash (CA) that had been created by circulating fluidized bed combustion (CFBC). Experimental results show that the pure slag paste hardly sets and the pure CA paste gives very little strength. But when slag and CA are mixed together, the SCA paste not only has proper setting times but also has sufficient strength. The compressive and tensile strength of SCA paste can reach 80 MPa and 4.6 MPa, respectively, at 28 days and higher at longer ages. In addition, the early expansion of the SCA paste compensates for its later shrinkage so that the ultimate drying shrinkage of SCA paste is lower than that of ordinary portland cement paste. The hydration products of the SCA paste detected by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray (EDX) are ettringite, calcium silicate hydrate (C-S-H), and calcium ...

Study on the rheological properties of fresh cement asphalt paste

The rheological properties of fresh cement asphalt paste (CA paste) were investigated, in which influencing factors such as type of asphalt emulsion, temperature, and time were discussed. CA pastes with two types of asphalt emulsions and varied asphalt contents were prepared at 0, 20 and 40 °C. The initial yield stress and its development over shelf time were tested to characterize the rheological properties of the pastes. The measurement of semi-adiabatic temperature development during hydration and optical microscopic observation were carried out to determine the hydration kinetics and microstructure evolution of the pastes. Results indicate that the initial flowability and flowability retention over shelf time of the pastes visibly improve because of the plasticizing effect of the asphalt emulsion and its retardation effect on cement hydration. The anionic asphalt emulsion is more effective than the cationic type because the former exhibits favorable adsorption onto the surface of cement grains. The temperature sensitivity of the rheological properties of the CA paste depends on the type and content of asphalt emulsion. The effects of time and temperature on rheological behavior were integrated into the effect of cement hydration degree. A generalized model linking yield stress and relative hydration degree α′ was established. Experimental results show that yield stress increases in a roughly linear fashion with 1/(1− α′) for all tested CA pastes.

Extrusion behavior of mono-calcium aluminate (CaAl2O4) paste

The present work describes the extrusion behavior of mono calcium aluminate (CaAl2O4; CA) paste in order to develop a new inorganic binder for extrusion. Hydration imparted significant flowability and rigidity to the CA paste. CA paste was successfully extruded using a piston-cylindrical die with low extrusion force, under optimum curing period. Furthermore, even without the addition of the organic binder, a small amount of CA acted as a suitable inorganic binder for extrusion. These good extrusion behaviors such as good flowability and rigidity of these samples were probably caused by much free space filled with water and the lubricating effect between the particles.