Analysis of the Fractal Growth Characteristics and Nucleation Mechanism of Phosphogypsum-based Materials

HOU Jiaojiao, NI Xiaoyang＊, LUO Xin

(1. Faculty of Engineering, China University of Geosciences, Wuhan 430074, China; 2. College of Chinese Language and Literature, Wuhan University, Wuhan 430072, China)

Abstract: Phosphogypsum-based materials (PBM) were synthesized with varied phase compositions of phosphogypsum, portland cement and fly ash. Effects of fractal growth characteristics on physicochemical properties, pore structure, compressive strength, as well as the hydration behaviour and mineralogical conversion of mortars were examined by a multitechnological approach, including mercury intrusion porosimetry, rietved phase analysis, thremal analysis, calorimetry and Fourier transforminfrared spectroscopy analysis. Expermental results indicate that the specimens cured with mosite resulted in higher strength and lower porosity compared with those cured in the drying chamber. In addition, a more complicated course of the aluminate and silicate reactions during the hydration process has been published, with the hydration products mainly consisting of calcium silicate hydrate (C-S-H), portlandite, ettringite, hemicarbonate, monocarboaluminate, calcite, quartz, a mixed AFm passed with carbonate, and hydroxide. After all, the nucleation process is a reaction that can be defined as a solid, liquid and gaseous phases that goes through the four stages of materialization mixing and modification, i e, hydration of low calcium content, secondary hydration, high calcium condensation and geoplymensation, respectively. The rupture, recombination, polymerization reactions of Si-O, Ca-O, Al-O bonds contribute to the nucleation mechanism that serves as the formation of C-S-H in hydration products.

Key words: phosphogypsum; pozzolanic addition; quantification analysis; microhydration characteristic;nucleation mechanism

1 Introduction

The large-scale utilization of phosphogypsum(PG), a by-product generated from the phosphorus fertilizer industry[1](phosphoric acid production), solves the waste disposal and pollution problems that cause severe pollution of the soil, water, and atmosphere.Efforts have been made to use virgin and calcined PG as the retarders in Portland cement[2](PC), but the hydration kinetics of PC are negatively affected compared to natural gypsum due to impurities[3].Therefore, the raw PG with a processing method such as calcining,lime water washing or neutralization through studies is strongly recommended[4-6]. To improve the performance of PG production, alkali-activated cements such as granulated slag, fly ash and zeolitic waste have been added to make PG-based cementitious binders, which have become a viable ecological alternative to traditional cementitious materials.

PG is widely used in ordinary Portland cement[2],oilwell cement[5], calcium sulfoaluminate cement[7],magnesium phosphate cement[8], alkali-activated fly ash[9], supersulfated cement[10], and cemented paste backfill[11]. Calcium sulfoaluminate (CSA) cement[7],which was developed by the China Building Materials Academy in the 1970s, was advertised as a sustainable alternative to PC. Belite sulfoaluminate (BSA) cement[10,12], which is based on CSA cement, is made from clinker containing 40%-70% of C2S and 20%-50%of C4A3S. In this work, PG is used as a substitute for natural gypsum in the production of BSA cement and an excess of PG is added to the raw materials, which not only for the sulfur emissions, but also means that the anhydrite phase remains in the clinkers produced.

Calorimetric studies on PG efficiency as a source of alkali-activated cements[13,14]have shown, its interpretation cannot automatically be applied to these cements due to hydration processes.

For this reason and based on prior comments, the aim of this research was to analyze the influence of the phase composition on PBM, synthesized from amalgamatious of PC and waste materials (FA and PG), in terminology of hydration and hardening under different curing conditions via the technological properties, microsturcture, mineralogical properties and calorimetric to investigate the fractal growth characteristics and the mechanism of nucleation.

2 Experimental

2.1 Sample preparation

The PG was taken from the Dayukou Mine, Hubei, China; it consisted mainly of CaO (34.31%) and SO3(47.30%). The X-ray diffraction spectra (Fig.3)of this material showed that it is dominated by gypsum (CAS, 91.51%). The particle size distribution of the NPG (Fig.1), which was characterized with a laser particle size analyzer (BT-9300HT), is dominated by the 1-100 µm fraction. The values ofD50,D95,Davwere 41.35, 86.83 and 49.94 µm, respectively.

Portland cement (PC, 42.5) and high-calcium fly ash (FA) were manufactured by the Huaxin Co., Ltd and the Ezhou Power Plant Group, respectively. The mineralogical composition of these materials is shown in Table 1, determined by XRD analyzes (Fig.3). PC is mainly composed of alite (C3S, 66.12%), belite (C2S,8.81%), calclum aluminate (C3A, 7.23%) and ferrite(C4AF, 14.31%), and FA contains quartz (S, 12.54%),mullite (M, 20.35%) and amorphous (66.92%).

Table 1 lists the chemical and mineralogical composition of three solid wastes that comprise the NPG.Fig.2 shows the composition diagram of the model of CaO-Al2O3-SiO2to indicate compositions of NPG, PC and FA. Fig.3 shows the XRD patterns of threshold materials that were subjected to a Rietveld refinement for the quantitative evaluation of the component minerals.

Fig.1 Particle size distribution of the NPG

Fig.2 Modified CaO-Al2O3-SiO2 composition diagram

2.2 Test methods

The mean particle size and particle size distribution for the PG were quantified using a laser particle size analyzer (BT-9300HT).

The compressive strength of the PBM after 3, 7,28, 56, 90 and 180 days of curing age was determined by the hydraulic servomotor HY400X125 according to GB/T 17671-1999.

A micromeritics-9310 MIP device was used for MIP testing. The volume and size of the intrudable pores in porous PBM are primarily determined by themaximum pressure applied by MIP. The pressurization took place in low and high pressure parts corresponding to the maximum and minimum applied pressure of 100 MPa and 0.2 MPa.

Table 1 Chemical and mineralogical composition of raw materials

Fig.3 XRD patterns of PG-phosphogypsum, PC-portland cement and FA-fly ash

Three raw materials in different fractions were measured with the X-Pert PRO DY2198 XRD, which is supposed to determine the chemical composition and the crystal phases of all pastes at different curing ages on a Bruker (model D8 Advance A25).

An isothermal calorimetrics study was performed in an eight channel thermal activity monitor (TAM) air calorimer to estimate the heat release from hydration reactions of the C-1, C-2, W-1, W-2 samples. The heat flow was recorded for 90 days under different curing conditions.

Thermogravimetric (TG) and microquotient thermogravimetry (DTG) measurement for hydration reactions of the C-1, C-2, W-1, W-2 samples: 7 d was carried out in a Mettler TGA/DSC 250 analyzer.

Fig.4 X-rays patterns of hydrated PC at different hydration time

Fourier transform infrared spectroscopy (FTIR)was performed using a Spectrum 400 MIR-NIR spectrometer. The spectra of the pastes for C-1, C-2, W-1 and W-2 samples after 28 days were recorded for wavenumbers in the range between 1 800 and 400 cm-1.

2.3 Sample characterization

2.3.1 Evolution of the phase composition

In the microstructure characterization of PBM,minerals and hydration products are the two main phases[15]that are intensively investigated. In Fig.4 and Fig.5, a selection of the X-rays patterns between 5° and 65°(2θ) for hydrated PC and FA at the curing age of 3, 7,28, and 90 days is plotted. The following phases of PC were readily diagnosed as clinker components (C3S-34°,C4AF-29°, C2S-46°, C3A-23° and amorphous-9°) and hydration product (C-S-H-18°), and the phases of FA were reconstructed: S-26°, Al4SiO8-34°, M-41°, Al2O3-47° and amorphous-51°. They are all crystalline with typical crystal sizes in the range from about 10 nm to as much as 50 µm and the hump in the diffractograms from approximately 8° to 55° (2θ) is predominatly caused by the the existence of phosphogypsum.

2.3.2 Reaction of the medium properties

Due to the ‘‘dissolution-crystallisation” process[16],the properties of the reaction medium during or after the reaction may differ from those in the initial stage.Therefore, a further step in understanding the intricate equilibria that regulate the establishment of PBM and the role of the various C-S-H phases has been taken by dividing the Ca/Al and Ca/Si ratios in MIX A, MIX B and MIX C systems in which ettringite, monosulphate,portlandite, C4AF phases are the main hydration products and C-S-H, C3S, C3A and C2S can be present in smaller quantities for 3 to 7 days (Fig.6).

Fig.5 X-rays patterns of hydrated FA at different hydration time

Fig.6 Reaction medium properties of hydration products in different mixtures at moist curing

In MIX A, porlandite is the main crystalline phase that occurs in PC hydrares[4,17], which are formed as a by-product from the reaction of C2S and C3S with water. In addition, during the early hydration between the aluminate clinker phases (C3A and C4AF) and gypsum,a large amount of ettringite forms in the shape of large prismatic and extremely stable crystals.

In MIX B, the proportions of portlandite and ettringite were lower than in MIX A, while some raw phosphogypsum materials were not yet hydrated, as the high content of Ca2+icons in phosphogypsum has a retarding effect that is not conductive to early coagulation.

In MIX C, FA which encompasses more S and Al-4SiO8components, can react chemically with portlandite and other substances under moist conditions and form corresponding gelling substances as C-S-H[18].

The hydration kinetics of C3A and C4AF do not change significantly between the different samples.However, compared to FA, NPG material has a drastically different performance, C3S and C2S progress to the formation of C-S-H and if enough Ca2+is available,a higher quantity of C-S-H is formed (MIX B)(Fig.6).

3 Model

3.1 Pre-existing approaches and models

Fig.7 shows the stages of acceleration of nucleation and growth of C-S-H on the pitted or smooth surface of alites[19]and the process of building simulation boxes of C3S with water[20]. The results propose that the precipitation of portlandite with increased CH formation reduces the calcium hydroxide concentration and increases the undersaturation with respect to C3S and consequently contributes to increasing the frequency of hydration reactions, with C-S-H being rapidly isolated.The findings, which cater as a benchmark for the C3S box, were implemented to calculate the water at which recommended water to solids fractions are between 0.36 and 0.6[8].

3.2 An advanced approach and model

Fig.8 shows the prevalence of PBM as a function of time, which is given by isothermal calorimetry measurement. In accordance with the study, PBM is a three-phase composite material where hydration is the consequence of the co-hydration of multiple minerals.The nucleation process is a reaction that can mainly be described as a solid, liquid and gaseous phases that has passed through four stages, as demonstrated in Fig.8.

I: Physical and chemical mixing and modification treatment. Phosphogypsum, portland cement and fly ash are pulverized in a certain proportion (Table 2) to form a slurry and dissolved to provide a good hydration environment.

II: Modification and hydration with low calcium content. The hydration of three materials produces a plasma like [SiO4]4-, Ca2+, [AlO4]5-, [CaSiO4]2-and OH-that breaks any chemical bond, reploymerizes to form new hydrates that are on the surface particles adhere to the solid, gradually forming an irregular surface layer and pore structure. This phase manifests itself mainly that the ions of [SiO4]4-, dissolved by C3S and C2S, reacted with calcium aluminate to form AFt, and then combinated with Al2O3and SiO2, dissolved by FA,produced C-S-H gels. The growth of C-S-H, the product of hydration in this phase, occurs mainly on the surface of the mineral mud particle.

III: Secondary hydration. The hydration products react with free ions to gradually form C-S-H and irregular crystals that bridge each other to form a layer and network structure and then combine to form a new silicate framework[21]. Part of the crystals and unreacted particles are filled into the framework and pore structure, which form a certain strength of materials.This phase manifests itself mainly in the fact that the vitreous structure of C3A in the PC is stimulated to depolymerize by the Ca(OH)2in the hydration solution.Since the C-S-H growth is intertwined at different nucleation sites on the surface of the slurry mineral particles, the inter-gel pores are formed between the products of hydration.

IV: High calcium condensation and geoplymencation. As hydration progresses, the insufficiently reacted plasma of Ca2+, [AlO4]5-, [CaSiO4]2-and OH-in the slurry and segment of the C-S-H repolymerize to form C-A-S-H. Eventually, PBM is slowly solidified and formed with new mineral crystals (Fig.6) and C-S-H.

Fig.7 Stages of the nucleation and growth of C-S-H and process to build simulation boxes of C3S

Fig.8 Rate of PBM as a function of time given by isothermal calorimetry measurement

Table 2 Details of mix proportions of phosphogypsum-based materials

4 Results

4.1 Mixture proportions

In this study, phosphogypsum-based materials(PBM) and mortar specimens were fabricated, which were prepared according the mixing proportions in Table 2. Four types of PG were employed in the experiments: raw materials (N-PG), dried phosphogypsum(D-PG), crushed phosphogypsum (C-PG), combusted phosphogypsum (B-PG), washed phosphogypsum (WPG). 70.7 mm × 70.7 mm × 70.7 mm cubes were made with a water to solids ratio of 0.55 and cut into two systems. System No.1 was transferred to a hardness box with a mass of 95% and a temperature of 20 ℃. System No.2 was processed in a mass of 5% and a temperature of 60 ℃. Fig.9 presents the weight variation tendency of the components about PBM’s specimens. The compressive strength of the PBM was quantification determined after 3, 7, 28, 56, 90 and 180 days of curing age.

Fig.9 Weight variation tendency of the components about PBM’s specimens

4.2 Compressive strength

Table 3 presents the compressive strength of PBM with different proportions on the substrates of the mixture proportions (Table 2) after 3, 7, 28, 56, 90 and 180 days of curing. This study illustrated that PBM cured under different curing conditions had different technical properties. PBM’s system No.2 cured under mosit curing conditions was found to achieve higher compressive strength than those cured under dry chamber conditions for all treatments and inclusion ratios. At 28 days, PBM has already evolved a certain strength,which is still comparatively low, as hydration is suppressed when the content of soluble phosphogypsum gradually decreases. In system No.1, the compressive strength of C-1 (83.4 MPa) and W-1 (90.5 MPa) were higher than the other three compositions, as the similar results of System No.2 of C-2 (85.7 MPa) and W-2 (92.1 MPa).

Fig.10 provides the observations of the non-linear adaptation computation of the compressive strength ration to curing age. As shown in equation (y=A1*exp(-x/t1)+y0), the compressive strength ratio from 3 days to 28 days was broadly higher than from 28 days to 180 days due to the further hydration of FA, resulting in a faster pozzolanic reaction[22,23]. This is probably because a considerable amount of calcium carbonate is formed after carbonization, which not only causes the volumn expansion but also leads to external strength.Combined with the observations from the compressive strength test, it can be commented that the early robustness of PBM with higher dissolved phosphogypsum was poor. Besides, the phosphogypsum affects the alkalinity of the solution, which is also detrimental to the development of ettringite, which leads to a lower early strength. Morevoer, at later stage, the C-S-H and C-A-H gels[23-24]are gradually carbonized, and converted into a gel with a high extent of polymerization, which generates the new capillary pores.

Table 3 Compressive strength of PBM with different ratios

Fig.10 Compressive strength ratio to curing age of PBM with different proportions

4.3 Characteristics of the pore structure

The pore structure of PBM generally has three characteristic parameters: pore volume, pore size and specific surface area. Fig.11 presents the four details from SEM images depicting microstructure of C-1,W-1,C-2 and W-2 materials. Fig.12 shows the comparison of cumulative pore volume and the cumulative area of PBM in two samples clusters by experiments.With increasing age, the pore volume of all specimens decreased. In order to characterize the deviations in the pore size distribution, the quantified pores, which were essentially concentrated at 3 nm-5 µm, were classified into 3 nm≤d＜ 50 nm (non-hazardous pores),50 nm≤d＜5 μm (less detrimental pores) and 5 μm≤d(harmful pores), while the peak occurs at 3 nm≤d＜50 nm, and the connected holes were most at 50 nm≤d＜5 μm. It depicts that the integration of phosphogypsum does not enhance the early pore structure of the slurry, but in the middle and later stages it consumes the pozzolanic activity of FA and PC, which is generated in the slurry of phosphogypsum, and formes a considerable amount of C-S-H gels filling the pores between the polymer pastes, thereby reducing the porosity and refining the pore size.

Fig.11 SEM images of (a) C-1, (b) W-1, (c) C-2 and (d) W-2 after 28 days

Fig.12 Comparison of cumulative pore volume and cumulative area of PBM on MIP results(a) System No.1; (b) System No.2

Table 4 Mineral composition of structural details in relation to curing conditions/%

Fig.13 Evolution of the phase assemblages during the reaction of System No.1 and No.2 in relation to curing conditions

Based on the comparison results defined in Fig.12,it indicates that the PBM has a weaker product in the preliminary stage of hydration with a large pore volume in the system and a looser structure. As the soluble ions continued to dissolve, disperse and combine, the crystallinity of the hydrated product increased and the internal pores were progressively filled with hydration products and reduced to micropores. Unhydrated phosphogypsum particles evenly filled the pores, optimizing the pore structure of the materials and increasing the density of the slurry, presumably reducing the porosity,further densifying the polymer and drastically increasing the compressive strength. Overall, it corroborates that the reduction in pore volume leads to an increase in compressive strength, as illuminated in Table 3 and Fig.10.

4.4 Mechanical properties of hybrid C-S-H/C-A-S-H gels

Table 4 shows the results of XRD evaluation of the mineral composition of structural details under the dry chamber and moist curing conditions.Mortars cured moist illustrated higher contents of C-S-H (CaSiO3·CaCO3·CaSO4·15H2O) and C-A-S-H(Ca6Al2(SO4)3(OH)12·26H2O), which means that the internal reactions generated by the water in the mortar mass proceeded more slowly, resulting in a higher pozzolanity in the blends and an improvement in mechanical behaviour. The reduction in C3S, C2S and C4AF values is correlated to better mechanical behaviour, as this is the primary strength-promoting phase during PBM hydration.

At the commencement of the reaction, C3A and C4AF are the first to hydrate, and calcium sulfate dihydrate reacts with CaO and Al2O3to form needle-shaped AFt crystals that were connected to other minerals and built up a framework that was conductive to strength development. With higher subsequent hydration C3S and C2S, a substantial amount of Ca(OH)2and low density C-S-H gels is produced, while segment of Ca(OH)2crystallizes out and fills the crystal structure of low density C-S-H gel and phosphogypsum particles. Eventually, the low density C-S-H gels proceed to hydrate to form high density C-S-H and/or C-A-S-H.

Morever, as can be seen in Table 4 in the mineralogical phase of the mortar, not only the curing conditions are influential. The different treatments of PG listed in Table 2 also resulted in a variation in the mineralogical phases of each mortar. This was a higher compressive strength in mortars C-2 and W-2 for both curing conditions. The determinant correlating with the Ca(OH)2obtained at 90 days (Fig.10), since it was higher in these mortars than in those who have been using PG with the other treatments.

Fig.13 shows the evolution of the phase assemblages for PBM, which were examined during the reaction of System No.1 and No.2 with regard to the curing conditions. The main hydrates are C-S-H and Afm phases, while the portlandite content is lower in conjunction with pozzolanic FA, so that the activity of PC and FA reduces the Ca/Si ratio and enhances the Ca/Al ratio of the C-S-H (Fig.6). Anhydrite and bassanite were not recognized, while merwinite progressively disappears after a longer curing time. When the molarity of the Ca(OH)2activator is increased, the C-A-S-H development and the C-S-H phase are promoted[24].The stability of the monosulfate phase converted from ettrigite should be further investigated. CaSO4·2H2O in System No.1 and No.2 was secondary gypsum, which can adversely affect strength.

5 Discussion

5.1 Effect of solidifying on the mechanical properties

5.1.1 Thermal analysis study

Fig.15 displays a compendium of the thermal analysis traces for the pastes with higher compressive strength pastes of C-1, C-2, W-1 and W-2 after 90 days of hydration, which were separated into two groups based on the curing conditions. In the presence of CH (hydrated by secondary gypsum), the main phases detected by XRD (Fig.14) and TGA are CS-H, ettringite, AFm phases (mainly hemicarbonate,monocarbonate and a mixed AFm containing carbonate and hydroxide[22,25]) and portlandite. From a thermodynamic point of view, only monocarbonate is stable, and ettringite is also found to be somewhat more stable, as can be seen from the TGA data, since the formation of mono- and hemicarbonate prevents monosulfate formation. Furthermore, small amounts of calcium carbonate can be seen in the thermal traces, weight losses close to 700 ℃, which mainly results from the PC employed(Fig.13).

In accordance with the progress of the hydration reactions, the free water levels decline with the hydration time at each temperature. As shown in Fig.14, the samples of C-2 and W-2 with higher FA and PC have little more bound water than C-1 and W-1, which is due to the faster pozzolanic reaction due to an inhomogeneous algorithm with higher Ca/Si ratio of C-S-H,as observed in Fig.6. Therefore, the coarsening of the C-S-H gel with moist curing for C-2 and W-2 is considerably more important than that of C-1 and W-1 with dry chamber curing, which also clarifies that C-2 and W-2 showed better mechanical strength performances(Fig.10) with relatively higher percentages of bound water.

Fig.14 Selected region of the Rietveld plots of X-rays patterns for C-1, C-2, W-1 and W-2

Table 5 Full spectrum fitting parameters of the Rietveld plots for Fig.12

Fig.15 Thermal analysis traces for C-1, C-2, W-1 and W-2 at 90 days of hydration

5.1.2 Calorimetric study

The calorimetric investigation of the heat flow and the cumulative heat up to 7 days for the hydration of C-1,W-1,C-2,W-2 is exemplified in Fig.16. The heat release during the initial phase, in the span from 0 to 500 min, is generally attributed to the dissolution of PG and PC, the initial precipitation of hydrates. The first peak in C-1 and W-1 is due to C3S hydration at a higher hydration time owing to the aluminate hydration contribution. For C-2 and W-2, the first peak has two contributions, C3S hydration and pozzolanic response of FA to yield ettringite. After this period, it can be determined that the addition of phosphogypsum is excessive for the hydration from 3 to 7 days if the heat flow decreses aftewards, as the excessive calcium sulfate impedes the conversion of AFt to AFm from the strength results (Fig.4). The cumulative heat advancement of four samples after 7 days was 220(C-1),320(W-1), 230(C-2) and 330(W-2) J/g, which is the rise in reactivity for dry chamber curing and moist curing,as diagnosed by calorimetry from 20 to 60 ℃. The heat flow during this time is mainly related to the depletion of calcium sulfate and the formation of ettringite[26].

5.1.3 Fourier transform infrared spectroscopy (FTIR)

Fig.16 Calorimetric study of heat flow and cumulative heat up to 7 days for C-1,W-1,C-2,W-2 hydration

The spectra of hydrated pastes for C-1, C-2,W-1 and W-2 with different curing conditions at the age 28 days are shown in Fig.17, which indicates the occurrence of bands that are frequently the hydration products ascribed to cementitious materials. A band at 1 625 cm-1referring to the O-H stretching in calcium hydroxide, and the bands at at 1 420 and 1 280 cm-1correspond to the stretching and bending of the O-H bond in the H2O molecule. Bands that signify the existence of amorphous or low crystalline carbonate are diagnosed in the scope of 1 000 cm-1(asymmetric stretching of the C-O bonds of the CO32-group), which can be associtated with the presence of hemi- and monocarboaluminate phases.

Fig.17 Transmittance curves of hydrated pastes for C-1, C-2, W-1 and W-2 at 28 days

Shoulder bands at 820 and 618 cm-1are attributed to the vibration of Al-O-Si bonds and the asymmetric elongation of [AlO4]5-groups associated with the presence of aluminates and aluminosilicates (C-A-H and C-A-S-H). The shift at 750 and 464 cm-1indicates the asymmetric tension of the Si-O bonds of the [SiO4]4-clusters of C2S and the symmetrical stretching of the Si-O-Si bonds in the C-S-H gel, respectively.

Overall, the FTIR results reveal that the main phases were ettringite, portlandite and calcite, as well as C-S-H and carbonate phases with low crystallinity.

5.2 Mechanism of nucleation on the conversion rules of C-S-H/C-A-S-H phase

The mechanism of microscopic nucleation is listed that PG ionizes to generate ions of [SiO4]4-and OH-, combined with covalent bonds of Si-O-Si and Al-O-Si broken in PC, and with the acid radical ions such as [SiO4]4-and [AlO4]5-that have been ionizated in FA. Due to the excessive CH generated by Ca2+and OH-, [SiO4]4-reacts with Ca2+to continuously generate C-S-H, whereby [SiO4]4-and [AlO4]5-accelerate the polymerization to form a stable hexahedral framework structure of - Si-O-Al-O-Ca-O- and finally produces phosphogypsum-based materials.

The main chemical reaction is shown in Eqs.(1)-(3):

6 Conclusions

The phosphogypsum-based material (PBM) with a variety of target compositions was successfully synthesized from PG, FA and PC. Phosphogypsum with a high Ca content can be used both as a setting regulator at early ages and as a pozzolanic addition after 7 days of hardening in hydration of PBM.

The curing conditions and treatments of PG significantly affected the compressive strength and pore structure, whereby curing the specimens in mosite resulted in a higher strength and well-known porosity than those cured in dry chamber.

Based on the results of the quantitativein-situXRD analysis and calorimetric data, it illustrates a more complicated course of the aluminate and silicate reactions than those previously published during the hydration process, with the hydration products mainly consisting of C-S-H, portlandite, ettringite, hemicarbonate, monocarboaluminate, calcite, quartz, and a mixed AFm that encompasses carbonate and hydroxide.

PBM is a three-phase composite material, the hydration of which is the consequence of the co-hydration of multiple minerals. The nucleation procedure is a reaction that can mainly be defined as a solid, liquid and gaseous phases that goes through four stages.