Time Of Cement Paste Research Articles

Study of Different Composition of Gypsum as Retarder in Ordinary Portland Cement

Mortar is another construction medium made of cement, which is mixed with sands and water, and lime is applied to increase the product's longevity. The gypsum renders workability to make mortar or concrete by keeping the cement in plastic state at early age of hydration. The gypsum is called the retarding agent of cement because the gypsum which is mainly used for regulating the setting time of cement. To get the optimal setting time for optimum compressive strength, gypsum in the cement needs to be control. Cement setting time when it hydrates and renders cement paste when combined with water. The objective of this research is to analyze the effect of different amount in Ordinary Portland Cement (OPC). Vicat apparatus was used to analyze the initial setting time of cement paste. Gypsum and clinker were used in production of mortar with the size 50 mm x 50 mm x 50 mm. This research deals with observation of the cement setting time to point out some differences that would effect to strength of mortar. The results reveal that control gypsum with 4% of gypsum has the highest strength as compared to 0% of gypsum and 8% of gypsum. The setting time of cement paste are discussed with respect to their influence on the strength of mortar.

Influence of the Chemical Composition of Bauxite on Mineral Formation and Properties of Sulfoaluminate-Ferrite Cement

The influence of the chemical composition of bauxite on the mineral formation and structure of sulfoaluminate-ferrite clinker (SAFC), and physical and mechanical properties of cement based on it is studied. Ferrous bauxite, marble crushing screenings and neutralized fluorine-anhydrite were used for the synthesis of SAFC. The compositions of raw mixes of low-and high-alkaline SAFC are calculated with modular characteristics: Mf (ferritic modulus) = 0.35 and 0.7, Мs (sulfate modulus) = 0.167 and 0.5, respectively. Clinker synthesis from a raw mix containing ferrous bauxite with a quality coefficient of 1.7 must be carried out at a temperature of 1250 °C, which is reduced to 1200 °C for burning a raw mix based on bauxite with a quality coefficient of 2.2. Intensive decomposition of anhydrite occurs with the release of sulfur dioxide into the atmosphere at a temperature of 1300 °C, so it is not recommended to burn SAFC at this temperature. The mineral composition of the obtained SAFC is represented by sulfoaluminate, calcium sulfoferrite and free anhydrite. There is no C2S as a separate phase in clinkers, since in the process of their synthesis belite dissolves in 3С(A,F)·СŜ, mainly in the aluminoferrite phase. The use of bauxite with a quality coefficient of 2.2 in the SAFC raw mix increases the cement activity up to 54.2 MPa. Increasing its specific surface from 350 to 460 m2/kg significantly reduces the setting time of cement paste and increases the strength of sulfoaluminate-ferrite cement both in the early (up to 43.4 MPa) and late hardening periods (up to 67.3 MPa).

Properties of the Cement Paste Mixed with Various Types of Aluminum Sulfate Based Liquid Alkali-Free Accelerator

In this paper, the effects of various components in alkali-free accelerator on the setting of cement paste were studied, and the morphology of the hydrates during hydration was investigated with SEM. The experimental results show that the aluminum sulfate, diethanolamine and hydrofluoric acid can effectively shorten the setting time of cement paste, while excessive dosage has minimal impacts on the setting time. The diethanolamine and hydrofluoric acid can not only shorten the setting time but also can improve the stability of the accelerator. It was evidenced by the SEM that the aluminum sulfate accelerates cement coagulation by quickly forming a large amount of ettringite in the cement paste. The results in this study suggest that the shortest setting can be achieved when the dosage of aluminum sulfate, diethanolamine and hydrofluoric acid in a liquid alkali-free accelerator is 57 %, 5 % and 5.7 % , respectively.

IMPACT OF MULTI-WALLED CARBON NANOTUBES ON WOOD SAWDUST EXTRACT CEMENT MORTAR

It is well known that organic waste materials deteriorate the performance of concrete. The impregnation of organic aggregates and their application in combination with other chemical admixtures and mineral additives are used in order to improve the concrete properties in case of their modification by organic components. The current research is focused on the evaluation of impact of multi-walled carbon nanotubes (MWCNT) on the properties of cement systems prepared based on wood sawdust extract (WSE). The setting time, density, consistency, flexural and compressive strength, water absorption tests were undertaken. The retardation effect of (WSE) on the initial and final setting time of cement paste was observed. The additional modification of cement paste with WSE by MWCNT in the dosage of 0.005% by weight of cement (bwoc) did not show the significant changes in initial and final setting time. The application of MWCNT in the dosage of 0.005% bwoc contributed to the increase of early strength of cement mortar prepared with WSE.

Time Evolution of Rheology of Cement Pastes Affected by Mixture Design and Mixing Procedure

Robustness is defined as the capacity of cement-based materials to retain fresh properties when subjected to either small variations in the constituent elements or small changes in the mixing procedure. Compared to normal concrete, self-consolidating concrete (SCC) may show less tolerance to those changes. Most robustness studies focus on initial rheological properties or workability, but concentrate less on the evolution of these properties within the first hour(s). This paper presents the results of an investigation aimed at evaluating the change of yield stress and plastic viscosity with time of cement pastes with SCC consistency, which is mainly affected by variations in the water content and the adding time of the superplasticizer. A change in water content also influences the initial rheological properties, and these differences are amplified over time. The difference due to the different adding time of the superplasticizer is, however, reduced or even reversed over time.

Influence of silicons of different structures on the hydration of compositional cements

The object of research is cement, which contains in its composition silica of various structures. The increase in the production of composite cements leads to the need to search for new active mineral additives. At the moment, the choice of mineral additives is made without taking into account the state in which the silicate component is located, therefore, it is necessary to develop certain criteria for the targeted selection of possible materials. This will reduce the cost of labor and financial resources to conduct relevant research. As it is known, silicates can be in a crystalline, amorphous and glassy state; therefore, the reactivity of various additives, even with the same chemical composition, can also differ significantly. It is proposed to study the effect of silica structure on hydration processes and properties of cements. The effect of silica in a different phase state (crystalline, amorphous, and glassy) on the hardening processes and physico-mechanical properties of composite cements has been investigated. It is established that the crystallinity degree of silica significantly affects the normal density of cement paste. Thus, the introduction of crystalline silica increases the normal thickness by 0.1–1.1 %, amorphous by 12.3–136.1 %, glassy by 11.2–56.2 %, compared with non-additive cement. The setting time of cement paste varies slightly. In the early stages of hardening, the rate of drop in strength is highest with the introduction of amorphous silica. For example, when enter 10 wt. % of crystalline silica shows a slight increase in the strength of the samples, compared with 8.2 % non-additive cement. The same amount of amorphous silica additive reduces strength by 33 %, glassy silica – by 19.2 %. This trend continues with increasing content of additives. The obtained research results allow to conclude that it is most appropriate to use in the production of composite cements mineral additives containing in their composition silica phases in a crystalline and glassy state.

Applicability of Ultrasonic Measurement on the Monitoring of the Setting of Cement Pastes: Effect of Water Content and Mineral Additions

Abstract Until now, standardized methods developed for the detection of initial and final setting time of cement paste were destructive and non-continuous. The well-established ultrasonic pulse transmission velocity (UPV) method can be correlated to the setting process of cement-based materials by the measurement of P-waves. However, S-waves seem to be better indicators of the setting of cement-based materials, because they are more sensitive to the solid matrix connectivity and less dependent to the air content. A new methodology, based on the combined monitoring of P-waves and S-waves, has already been developed to determine the setting times of mortar and concrete. The purpose of this study is to extend this methodology to cement pastes. Ordinary portland cement pastes with three water/cement ratio between 0.3 and 0.5 have been investigated. In addition, a portland cement, blast-furnace slag and limestone filler blended cement paste with a 0.4 water/cement ratio is studied in order to validate all observations. This study shows that the dynamic elastic properties can be linked to the initial and final setting times of cement paste. The early age evolution of the elastic properties depends on the air content and the binder nature. The combined monitoring of P-waves and S-waves provide accurate indicators of the setting process.

Evaluation of initial setting time due to superplasticizers

This paper shows how polycarboxylate based superplasticizer affects the initial setting time of cement paste. Three superplasticizers are used in this study with different properties and aiming to determine the delay in initial setting time due to superplasticizer. Initial setting time is calculated as per IS: 4031-PART 5-1988 with different SP dosages (0.5%, 0.75%, 1.0% and 1.5% of weight of cement). Superplasticizer is an admixture which reduces the water-cement ratio or increase the workability at the same water content. This paper deals with the evaluation of initial setting time due to superplasticizers.

Calorimetric study on the influence of redispersible E/VC/VL terpolymer on the early hydration of Portland cement

The effects of redispersible ethylene–vinyl chloride–vinyl laurate terpolymer (E/VC/VL) on the early hydration evolution of Portland cement were quantitatively investigated by isothermal calorimetry, setting time testing, thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction analysis and environmental scanning electron microscope analysis. The results show that the E/VC/VL definitely affects the early hydration process of cement paste, increases the initial exothermic peak value, decreases the heat evolution rate of the acceleration period and the second hydration exothermic peak, but increases the heat evolution rate during the deceleration period. And the E/VC/VL has little effects on the length of these different hydration periods. The E/VC/VL decreases hydration heat and hydration degree within 72 h, and the bigger the E/VC/VL dosage is, the less hydration heat and hydration degree are. The E/VC/VL retards the formation of hydrates, decreases the content of Ca(OH)2 and CSH gels, affects the morphology evolution of hydrates and declines the crystalline degree and crystal size of Ca(OH)2. Besides, the E/VC/VL retards the formation of AFt and inhibits the conversion of AFt to AFm, accordingly keeping AFt content higher at later hydration time. In addition, no new phases are formed in cement paste with the E/VC/VL. The retardation of E/VC/VL is also evidenced by the setting time of cement pastes. But with hydration time prolonging, the retardation of E/VC/VL on cement hydration gradually weakens.

Effect of competitive adsorption between polycarboxylate superplasticiser and sodium tripolyphosphate on cement paste fluidity

Sodium tripolyphosphate is a common retarder used to delay the hydration and prolong the setting time of cement paste. It is also sometimes employed to enhance superplasticiser dispersity to improve the fluidity and workability of cement and concrete, but the reason for this effect is unclear. The work discussed in this paper investigated the early hydration process of cement paste and the adsorption of sodium tripolyphosphate and polycarboxylate superplasticiser (PCS). The results show that there is competitive adsorption between PCS and sodium tripolyphosphate, sodium tripolyphosphate inhibits PCS from adsorbing onto the surface of cement particles, and PCS also reduces the adsorption of sodium tripolyphosphate. When both of these are reduced, there is a significant increase in the thickness of the adsorption layer and the zeta potential, which is shown to be the main reason for the improvement in fluidity. This indicates that some salts can be used to adjust the adsorption process of PCS in order to improve the fluidity and workability of cement paste and fresh concrete.

Properties of High Performance Concrete Containing Waste Glass Micro-Filler

The article discusses possibilities for use fine ground glass obtained from fluorescent lamp utilisation as micro filler in High Performance Concrete (HPC). Investigated mix compositions are based on silica fume (SF) and SF combination with glass powder. Testing results indicates that replacing silica fume by additionally ground fluorescent glass (up to 50%) slightly increasing consumption of water and delaying setting time of cement paste. All HPC mixes with glass powder showing decreased early-age strength and considerable strength gain after long-term hardening. It is concluded, that the best way of glass application in HPC is use fine ground glass powder together with silica fume as complex admixture.

Continuous tracking of the relationship between resistivity and pore structure of cement pastes

The electrical resistivity changes with time of cement pastes with water to cement ratio of 0.23, 0.35 and 0.53 were in situ continuously monitored by using a non-contact resistivity apparatus. To aid in understanding the evolution of effective resistivity, a hydration model CEMHYD3D was then utilized to simulate the early age formation of microstructure. Based on the effective media theory, the relationship between the change of relative resistivity and the evolution of total porosity, tortuosity factor and constrictivity is established. The results show that a lower water to cement ratio shows a smaller porosity and constrictivity as well as a higher tortuosity factor. Moreover, according to the experimental and simulated results, it is found that the evolution of resistivity is not only controlled by capillary pores but also C–S–H phases. Before arriving fully de-percolation time of capillary pores, the reduction of pores connectivity shows a higher influence on the paste resistivity than the decrease of capillary porosity. After that, the resistivity change of cement paste is mainly determined by the volume fraction of C–S–H.

Effect of Fly Ash and nanoCaCO<sub>3</sub> on the Setting Time of Cement Paste

This paper presents an experimental study to evaluate the effects of fly ash and nanoCaCO3 on setting time of cement paste. The test group included the contents of fly ash was 30%, 40%, 50%, 60% and content of nanoCaCO3 was 2.5%, 5%, 10%, 20%. Results indicate that setting time was increased with the incorporation of fly ash, shortened with the incorporation of nanoCaCO3. The incorporation of 5% nanoCaCO3 by mass of cementitious materials reduced initial and final setting times by 60 and 70 min, respectively. In comparison to the referenced paste with 40% fly ash. The best fly ash content appear to be 40% when nanoCaCO3 was added.

Effect of Structure of Polycarboxylate Superplasticizer on Hydration of Cement in Early Period

Effect of polycarboxylate superplasticizer (PCs) with different bond between side chain and truck chain on hydration of cement in early period was studied. The performance of PCs in concrete was investigated by setting time, TGA and SEM. PC-based superplasticizer with ester bonding between side chain and truck chain. Although they had the proximate structure parameters in density of side chain and absorption group (carboxyl groups), the setting time of cement paste was significantly different when different PCs were employed in the preparation of cement. Decomposing of this bond in alkali environment may lead to a shorter setting time. On the other hand, same difference in hydration production was observed in early period hydration of cement paste when two different PCs was incorporated, which indicated that the different bond structure in PCs affected the hydration of cement in a different manner. The result of SEM indicated that the morphological phase of hydrated product was different when PC was applied, this may be related with the different result in the TG and TGA

Stabilisation of medical waste ash in mortar mixtures

This study investigates the stabilisation of medical waste ash (MWA) in mortar mixtures. Three MWA dosages were considered in the study: 5%, 10% and 15%. The other experimental parameters investigated in the study were: aggregate type and curing regime. The properties explored in the study include: setting time, workability, compressive and flexural strength and leaching of heavy metals. The mortar mixture proportions were 1∶3∶0·7 by weight for cement, sand and water, respectively. The results of the study have shown that MWA can be stabilised in mortar mixtures without significant leaching of heavy metals. The setting time of cement paste decreased with the increase in MWA content. The workability of mortar increased when the MWA level was increased. The compressive strength of mortar increased with the increase in the MWA content as a partial replacement of silica sand under moist and autoclaving curing conditions. However, the flexural strength of mortar decreased as the content of MWA increased as a partial replacement of silica sand under moist and autoclaving curing. The amount of heavy metals leached from mortar specimens after 28 days’ immersion in water were very small and insignificant (maximum percentage 0·58%) compared with the original heavy metals present in the MWA powder.

Experimental study on the setting time of cement paste mixed with accelerating admixtures based on C3A

Setting time is a very important factor in terms of affecting the quality of tunnel lining and inclined slope strengthening. However, the quality criterion of the accelerating admixture (AA) used to improve setting time is not well established. In this study, methods of measuring the setting time of cement pastes with mixed AAs were evaluated using the Gillmore and Vicat needle test methods. It was found that for both test methods, regardless of initial and final setting, the setting time when the admixture was simultaneously added was faster than the post-addition method. For the Gillmore needle test method, two types of measurement methods were evaluated and it was observed that the setting time with cement type varied even when the same AA was used. Accordingly, manufacturing companies should develop AAs that are less influenced by cement type. For the Vicat needle test method, six types of measurement methods were evaluated and the following conclusions were obtained: (a) the temperature of materials should be controlled exactly and (b) to evaluate the performance of AA, an admixture usage of 5% (ratio of cement weight) was recommended.

The influence of alkalis on rheological properties of fresh cement pastes

The following paper presents the results of the research carried out to investigate the influence of alkalis built in clinker phases and introduced from the outside together with make-up water, on the rheological properties of pastes in Portland cement at an early stage of hydration (less than 1 hour). The estimation of the alkaline influence of rheological properties of fresh clinker and cement pastes was performed referring to the obtained consistency curves and stress change characteristics in time and at constant shear rate. It was found that clinker reactivity exerts an influence on the consistency of the cement paste prepared using this very same clinker. The effect of gypsum as a controller of setting depends on the clinker reactivity. The more reactive the clinker is, the smaller is the influence of alkalis introduced into make-up water, on consistency and consistency changes in the time of cement pastes.

Dielectric study on the hydration process of cement paste

The results obtained from the dielectric measurements on the hydration process of cement paste are summarized as follows. 1. In the high frequency loss measurement, the tanδ of Ca3SiO5 showed a large value in the beginning and then decreased gradually with the curing age. It seems to be due to the decrease of the ions which contributes to the electric conductivity by the micelle formation and the fixation of ions with the progress of the hydration. 2. In Ca2SiO4, the tanδ increases with the increase in the curing age and then decreases gradually after passing through the broad peak. Compared with the electric conductivity curve at low frequency, it is considered that not only the loss (σ term) due to the electric conductivity but also the loss (e″ term) due to the dielectric polarization of the quasi-structural group such as the ionic micelle formation and the ion adsorbed layer contribute to the high frequency loss of Ca2SiO4. 3. In cement paste, the tanδ appears to be the sum of the tanδ of Ca2SiO4 and Ca3SiO5. In this case, the setting time of cement paste comes about on the tanδ curve. 4. The results obtained by the electric conductivity measurements seem to support the above conclusion. 5. The results obtained in the present study showed the similar tendency to those obtained in the previous nuclear magnetic resonance study.