Investigation on the hydration and strength properties of …

Interestingly, the cumulative heat results of samples with 5–15% gypsum additive were similar after the early-stage hydration (72 h) (Table 2). This confirms that the reduced content of the clinker can be compensated by adding gypsum to maintain the same reaction degree of hydration or even slightly increase.

Experimental Study on the Properties and Hydration Mechanism of Gypsum

The results show that the hydration reaction between FGDG and OPC can be synergistic with each other, and C-A-H further generates AFt under the action of SO42−, and at the same time, it plays the role of alkali-salt joint excitation for FA–GGBS, generates a large amount of cementitious materials, fills up the pores of the gypsum crystal ...

Effects of different gypsum varieties on the hydration and …

The hydration process of RFSAC can be divided into three stages: the initial stage of hydration, the accelerated stage of hydration, and the stable stage of hydration. The influence of gypsum is mainly reflected in the last two stages, which are the change in the formation rate of hydration products and the change in morphology.

Dehydration Pathways of Gypsum and the Rehydration …

Some researchers have argued that gypsum undergoes a two-stage ... If the dehydration product CaSO 4 ·nH 2 O occurs upon the heating of gypsum, then the dehydration reaction of gypsum can be expressed as the ... This in situ anal. procedure allowed for precise monitoring of dehydration/hydration reactions over a range of PH2O values from 4 to ...

The Mechanism of the First Hydration

The hydration reaction of β-HH before and after the 1st reaction cycle can be divided into four steps, as shown from the heat development curve in Figure 2(a). The first peak represents two hydration steps; in the first step, the hemihydrate becomes humidified, and a water film will be generated around the particles.

Early hydration of C3A–gypsum pastes with Ca- and Na …

The early age phase development during the hydration of C3A-gypsum pastes with 1 and 4% Ca- or Na-lignosulfonate (CLS and NLS) was investigated using isothermal calorimetry, in-situ XRD ...

Hydration reactions and stages of clinker composed mainly …

In a recent study, Bullerjahn et al. [89] identified five stages for the hydration of pure C4A3$, which can be summarized as follows: stage I (initial period), stage II (dormant period), stage III ...

The role of sulfate ions in tricalcium aluminate hydration: New

It corresponds to the reaction between C3A and gypsum, yielding a pour crystalline AFm-phase that coats the C3A particles that are quickly masked by needle-like ettringite precipitates (Geng et al ...

Early hydration of Portland Cement Compounds

The addition of gypsum leads to a slower reaction rate. With 10 wt% gypsum added the reaction occurred after 2-3 hours and with 20 wt% gypsum it occurred after 10 hours.

Influence of HPMC on the capillary water absorption, pore

Capillary water absorption is an important parameter to evaluate the durability of cement mortars. For testing the capillary water absorption of cement mortars, drying is a necessary and crucial procedure. However, different standards have different requests on drying temperatures for doing the tests. Since the calcium aluminate cement-hemihydrate gypsum …

Study on early hydration of gypsum-based materials

In this study, the early hydration of gypsum-based materials (GM) pastes was investigated by isothermal calorimetry and oscillation rheology. The effects and underlying mechanisms of chemical admixtures including polycarboxylate (PC), citric acid (CA), hydroxypropyl methyl cellulose (HPMC) and starch ether (SE) on early hydration of GM pastes …

Dehydration Pathways of Gypsum and the Rehydration …

Their experimental results reveal that gypsum dehydration proceeds through only a single CaSO 4 ·2H 2 O → γ-CaSO 4 step when the ambient water vapor pressure is less than …

Improving the early-age properties of eco-binder with high …

Together with the TG-DSC results for 28 d-hydrated samples (Table 8), it can be seen that the Ref has lowest GGBS hydration degree and content of hydrates, while highest gypsum consumption; and sample with 1.5% NaAlO 2 has higher GGBS hydration degree than that with 2.5%, while the later one shows higher content of hydrates and gypsum consumption.

(PDF) The Mechanism of the First Hydration-Dehydration Cycle of Pure …

Therefore, after the 1st reaction cycle of β-HH, the compressive strength decreases due to a decrease in the hemihydrate crystal size, an increase in the surface area, and an increase in the ...

Fluidity and hydration evolution of cement-LS binder in the …

The amount of CH enhanced at the early stage (3 d) due to the enhanced hydration of cement clinker and decreased at a later time (28 d) because of enhanced pozzolanic reaction. Enhanced cement hydration and pozzolanic reaction of LS generated more hydration products in the matrix, resulting in denser microstructure as well as enhanced ...

The effect of calcined mayenite on the hydration of ordinary …

It was observed that the mineral composition of additives has influence on the OPC hydration mechanism: at the first stage (after 3 min) of hydration, the calcination temperature has negative influence on the formation of ettringite; at the second stage of hydration (3–21 min), the reaction of gypsum with the additive calcined at 900 °C as ...

The acceleration period and end time of …

The ending time of induction period and the reaching time of the second peak are shortened significantly. ... content of gypsum. The hydration heat evolution rate and total hydration heat emission ...

The Mechanism of the First Hydration

In the first stage, the hydration reaction will take place immediately after hemihydrate addition to water. The hydration time varies depending on the physical properties of the …

A quantitative study of the C3A hydration

The reaction of C 3 A in the presence of gypsum can be divided into three stages, as depicted in Fig. 1 by the rate of heat evolution as function of hydration time. Stage 1 corresponds to the reaction between C 3 A and gypsum and in calorimetric measurements, it results in an initial dissolution peak followed by a stage of low heat release. This stage …

Effects of various gypsum on early-age hydration behavior …

It can be seen that gypsum does not participate in the hydration reaction in the early-ages and reduces the content of hydration products, which obviously inhibits the reaction progress of MOCP. On the other hand, for gypsum-modified MOCP, the main reason for its strength reduction is the reduction in hydration product (5-phase).

Formation of α-Hemihydrate Inside of a Gypsum Crystal …

Gypsum crystal, reaction stopped after beginning of dehydration, OM. Gypsum crystal partly dehydrated, cleaved along cleavage plane, with observable dihydrate, α-hemihydrate and β-hemihydrate.

Hydration of C3A–gypsum systems | Request PDF

Hydration of C3A–gypsum systems with different gypsum additions was investigated in terms of the phase assemblage, kinetics and microstructural development.

Influence of free calcium sulfate levels on the early hydration …

All samples were equilibrated at 20 °C for a 12-h period prior to adding water and mixing. ... These findings suggest that anhydrite facilitates the hydration heat release during the second and third hydration stages of BSA clinkers more effectively than gypsum, which appears to delay the second stage while only promoting the third stage ...

The hydration kinetics of cement pastes with …

In the acceleration stage, the first exothermic peak is primarily C 3 S hydration and the appearance of the second peak may be due to that the C 3 A continues to react with the ettringite to form monosulphoaluminate (AFm) after the gypsum is consumed in the hydration reaction system .

High value-added utilization of desulfurized building gypsum …

Building gypsum would dissolve in a fairly short time to form a supersaturated solution of Ca 2+ and SO 4 2−, and the accumulated heat release was highest in the S1 group at this stage since it had the highest gypsum content. In the second stage, the formation of CaSO 4 ·2H 2 O crystal is inhibited by protein retarder, that is, hydration of ...

Dual role of gypsum: Set retarder and strength accelerator …

Gypsum plays a crucial role in cement. Though it is used in a small quantity, in the range of 2.5-3.0 percent in terms of SO3, gypsum's role in cement is significant, more predominantly at early ages.

Effect of calcium sulfoaluminate cement on the hydration …

C 4 A 3 S ‾ hydrated rapidly in the early stages. Meanwhile, the reaction of dihydrate gypsum and CH in the system further promoted the hydration of CSA cement, causing the C 4 A 3 S ‾ to quickly react and form AFt, which resulted in a shortened setting time for the cement paste [45]. Additionally, due to the rapid hydration of ...

Formation of α-Hemihydrate Inside of a Gypsum …

Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials in the world. During calcination, calcium sulfate subhydrates are formed and, for technical reasons, are mixed with water to form dihydrate again. Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were investigated. This dehydration …

Effect of gypsum on hydration properties, composition and …

The strength of the control group without gypsum decreases rapidly in the later stage. The hydration reaction of the non-gypsum samples is more complex. The decrease in compressive strength over time may be due to the increase in internal porosity caused by the conversion of CAH 10 to C 36. Eq. (5) shows the reaction.

Acceleration of cement hydration -A review of the working …

The overall hydration rate of cement can be divided into four stages: (1) initial reaction, (2) slow reaction period, (3) acceleration period, and (4) deceleration period [101, 102]. Understanding ...

(PDF) The Mechanism of the First Hydration-Dehydration …

Therefore, after the 1st reaction cycle of β-HH, the compressive strength decreases due to a decrease in the hemihydrate crystal size, an increase in the surface area, and an …