Main Hydration Products Research Articles

Shock Wave–Induced Dynamic Mechanical Behavior of Calcium Silicate Aluminate Hydrate at the Molecular Scale

Calcium silicate aluminate hydrate (C-A-S-H) is the main hydration product of cement mixed with industrial wastes. The purpose of this study is to understand the dynamic mechanical behavior and structural transformations of molecular-scale C-A-S-H induced by shock waves. Three C-A-S-H models with Al/Si ratios of 0.0, 0.1, and 0.2 are constructed and reactive molecular dynamics simulations are used to perform shock compressions with different shock velocities from 0.1 km/s to 3.6 km/s. The distributions of particle velocity, pressure, and density along the shock direction are calculated using the binning analysis method, allowing Hugoniot pressure-specific volume curves to be derived. The results reveal that shock waves may induce elastic, elastic-plastic, or shock Hugoniot responses in molecular-scale C-A-S-H, depending on the Al/Si ratio and the shock velocity. Below the Hugoniot elastic limit (HEL), higher Al/Si ratios cause the elastic wave to propagate farther due to the cross-linking effect of aluminate units. Above the HEL, higher Al/Si ratios give rise to a distinct two-wave structure characteristic comprising a plastic front and an elastic precursor. This characteristic becomes less pronounced as the shock velocity increases. Analysis of the molecular structural transformations of C-A-S-H revealed that the main atomic deformation behavior below the HEL involves a reduction of interatomic distances; above the HEL the main response is a densification of water molecules followed by a general collapse of the layered structure as the shock velocity increases.

Optimization design and characterization of slag cementitious composites containing carbide slag and desulfurized gypsum based on response surface methodology

Since many independent factors can affect the property of geopolymer, it is of great significance to seek optimization technologies to maximize the recovery and utilization of solid waste resources. In this work, a cementitious material was prepared using ground granulated blast furnace slag (GGBS), carbide slag (CS) and desulfurized gypsum (DG). Utilizing the Box-Behnken design under the response surface method, the content of DG and CS, along with the water-binder ratio, were selected as impact factors. Regression models were established to investigate their impact on fluidity, setting time, and compressive strength. In addition, the changes in hydration products, microstructure and pore characteristics of hardened paste were explored through microscopic tests. The results show that the multivariate correlation coefficients of each model are greater than 0.99, the coefficient of variation is less than 10%, and the signal-to-noise ratio is greater than 4, which indicates that the fitting accuracy of established models is extremely high. Microstructural testing shows that the main hydration products of cementitious material are ettringite (AFt), calcium hydroxide and calcium-aluminosilicate (C-A-S-H) gel. CS provided an alkaline environment for GGBS dissolution to promote C-A-S-H gel formation, while DG provide SO42− for AFt formation. Under optimal state, the C-A-S-H gel and AFt crystals in matrix are gradually formed and promoted by each other, making paste structure more compact, which improves mechanical property. This work serves as a valuable reference for the optimal design of cementitious composites under multiple factors and expands the scope of solid waste utilization.

The Wetting Behavior of Water Droplets on Silane and Silane/GO-Modified Ettringite Surfaces: Insights into Molecular Dynamics Simulations

The use of rapid-hardening cementitious materials for the emergency repair of critical infrastructure in coastal environments is becoming increasingly widespread, and concrete surface hydrophobic protection treatment is equally necessary to improve the durability of both new and old concrete. Among them, silane-based hydrophobic materials play an important role in concrete hydrophobic protection. Graphene oxide (GO)-modified silane materials can significantly improve the hydrophobic performance of coatings, but the hydrophobic mechanism of coatings modifying the sulfoaluminate cement’s main hydration product ettringite (AFt) has not yet been explored. In this study, molecular dynamics simulations were conducted to investigate the wetting properties of water droplets on the surface of AFt, isobutyltriethoxy silane (IBTS)-modified AFt, and IBTS/GO-modified AFt. It was found that the AFt substrate had good hydrophilicity, and the droplets could wet the interface through Ca-O ionic bonds and H-bonds. The IBTS coating initially impeded droplet wetting, but the adsorption stability of IBTS on the AFt substrate surface was poor under droplet action, leading to droplet penetration and dispersion of the IBTS coating on the AFt surface. However, the IBTS/GO coating significantly restricted droplet wetting due to the stable adsorption of GO on the AFt surface and the strong stability of hydrogen bonds between IBTS and GO. In conclusion, selecting a suitable bridging material between AFt and silane is crucial for improving the hydrophobic stability of silane coatings on sulfoaluminate cement materials.

In situ monitoring of the hydration of calcium silicate minerals in cement with a remote fiber-optic Raman probe

This study utilized a novel in situ fiber-optic Raman probe to continuously monitor the hydration progress of tricalcium silicate (C3S) and dicalcium silicate (C2S) without the need for sampling, from early hydration stage to later stages, and from fresh to hardened states of paste samples. By virtue of the remarkable ability of this technique in characterizing either dry or wet and crystalline or amorphous samples, the hydration processes of C3S and C2S pastes with different water-to-solid (w/s) ratios could be monitored from the start of the hydration reaction. The main hydration products, calcium silicate hydrate (C–S–H) and portlandite/calcium hydroxide (CH), have been successfully identified and continuously monitored for variations in their respective amounts in situ. The effect of w/s ratio on the hydration processes of C3S and C2S pastes was also considered. Meanwhile, the x-ray diffraction (XRD) and thermogravimetric analysis (TGA) results showed a great correlation with the in situ Raman test results about hydration products, which demonstrated the reliability of this technology. Moreover, the signal-to-noise ratio (SNR) of this Raman probe is significantly superior to existing technologies for in situ fiber-optic Raman spectroscopy. This remote fiber-optic Raman probe enables the use of Raman spectroscopy in future construction projects for on-site monitoring and evaluation of health conditions and performance of concrete structures.

The characteristics of alkali-activated slag-fly ash incorporating the high volume wood bottom ash: Mechanical properties and microstructures

The main objective of this study was to evaluate the mechanical properties and microstructure of alkali-activated material (AAM) incorporating the high volume of wood bottom ash (WBA) for the production of paste samples (AAWP). WBA was used to replace 0 %, 30 %, 50 %, and 70 % of the mass of a blend of ground granulated blast furnace slag (GGBFS) and class-F fly ash (FA) with a mass ratio of GGBFS/FA of 1:1. These paste mixtures were activated by an alkaline solution of sodium hydroxide (NaOH) 10 M and sodium silicate (Na2SiO3), with an alkali concentration Na2O of 4 % and varied silica modulus (Ms) ratios of 0.5, 0.75, and 1.0. A series of tests were performed following the relevant standards, including slump flow, setting time, compressive strength, and ultrasonic pulse velocity (UPV) to evaluate the mechanical properties of paste samples, while the microstructure of hardened paste was examined by X-ray diffraction (XRD), scanning electronic microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). The compressive strength of AAWP ranged from 14.6 to 50.0 MPa at 56 days of curing age. The results revealed that using 30 wt% WBA significantly improved compressive strength and microstructure compared to the reference mixture. Meanwhile, the AAWP with 50 wt% WBA replacement performed the compressive strength of approximately 30 MPa, and the replacement by 70 wt% WBA exhibited a significant reduction in strength. Moreover, increasing the Ms ratio slightly increased the compressive strength and qualities of the paste samples in all levels of WBA replacement. The C-(A)-S-H/Calcite gel and the Ht-like phase were the main hydration products of the paste samples.

Effect of blended inorganic salts containing negative hydration ions on hydration and properties of alkali-activated slag cement

Water glass (WG) is generally considered to be the most effective activator to prepare alkali-activated slag (AAS) cement in terms of strength and durability. However, the rapid setting and hardening of WG activated slag results in rapid loss of fluidity of AAS concrete mixture, which limits its engineering application. In the paper, the effect of blended inorganic salts containing negative hydration ions on the fluidity, setting time and mechanical strength of AAS cement was studied. The hydration process and hydration products were used to explore the action mechanism. Ba(NO3)2 greatly delayed the hydration of AAS cement. The four inorganic salts (KCl, KNO3, KBr and NaCl) blended with a small amount of Ba(NO3)2 can improve both the initial fluidity and fluidity retention, and a wide setting time range can be obtained to meet engineering requirements. The compressive strength decreased with the increase of inorganic salts. The incorporation of inorganic salt did not change the composition of the main hydration products. Considering the fluidity required by construction, mechanical properties and the durability of structure, it is recommended to add 4%–5% KBr or KNO3 blended with no more than 0.2% Ba(NO3)2 into AAS cement.

Influence of H2O/MgCl2 molar ratio on strength properties of the magnesium oxychloride cement solidified soft clay and its associated mechanisms

The solidifying soft soils with eco-friendly magnesium oxychloride cement (MOC) have gained much attention due to increasing environmental protection concerns. In this paper, a parametric study has been conducted to investigate the influence of H2O/MgCl2 molar ratio on the mechanical properties of MOC-solidified soft clay at different MgO/MgCl2 molar ratios and curing times by performing unconfined compressive strength (UCS) tests. The microstructure and pH were studied to the inherent mechanisms by scanning electron microscopy (SEM), X-ray diffraction (XRD), and acid-base tests. The results indicate that the influence of the H2O/MgCl2 molar ratio on the mechanical properties of solidified soft clay is dependent on MgO/MgCl2 molar ratio. The optimal H2O/MgCl2 molar ratio was found as 15–20 when MgO/MgCl2 molar ratio was 3:1 – 5:1, while it was 29 – 41 when MgO/MgCl2 molar ratios were 6:1 and 7:1. The main hydration products of MOC-solidified soft clay with MgO/MgCl2 molar ratio of 3:1 – 4:1 were 5 Mg(OH)2·MgCl2·8H2O (phase 5) and 3 Mg(OH)2·MgCl2·8H2O (phase 3), whereas phase 5 and Mg(OH)2 were mainly produced when MgO/MgCl2 molar ratio was 5:1–7:1. The UCS increases and then exhibits a decreasing trend with the curing time due to the gradual transformation of phase 5 into phase 3 and Mg(OH)2. The influence of curing time is dependent on H2O/MgCl2 molar ratio. The pH value first increases and then decreases with the H2O/MgCl2 and MgO/MgCl2 molar ratios, while it decreases with the curing time. The decreasing pH value results in the instability of the hydration products and reduced UCS of MOC-solidified soft clay.

Very high early strength calcium aluminate based binary and ternary cementitious systems: properties, hydration and microstructure

Calcium aluminate cement (CAC) is a cement type that has superior properties such as rapid strength gain, high resistance to high temperatures and harmful chemicals. However, the result of the using of CACs in the production of structural elements occur strength decreases at later ages as a result of a series of chemical reactions called ‘conversion reactions’ seen in these cements. In this study, the hydration kinetics and the crystalline and amorphous structures formed as a result of hydration were investigated in CAC containing different amounts and types of main oxides-based binary and ternary systems. Considering the results obtained, the main hydration product seen in these specimens was ettringite. Unlike many studies in the literature, metastable structures which cause conversion reactions, such as CAH10, C2AH8, have not been observed. Instead of conversion of the phases, ettringite needles were became thin and elongate which causes the paste structure porous and thus causing expansion and strength reduction at the later stages of hydration in some mixtures produce high amounts of ettringite. On the other hand, it is understood that the formation of strätlingite was limited strength decreases in systems where high silica fume is used.

Effects of additives on the mechanical properties, rheology, and printing properties of Pcc-based 3DPMs

A study was performed on printing concrete made with Portland cement clinker (Pcc) (the base material), quartz sand (the aggregate), a water reducer, and the additives hydroxypropyl methyl cellulose ether (HMC), redispersible latex powder (RLP), lithium carbonate (LC) and triethanolamine (TEA) were used to adjust the material properties. A clinker-based 3D printing material exhibiting excellent rheology, extrudability, buildability, and mechanical properties was developed. Admixture incorporation decreased the spread and slump of the Pcc while improving the rheological properties (G', G'', |η*|, and the torque). The addition of HMC and appropriate quantities of RLP and LC increased the slump and expansion of the cement paste, but the addition of TEA had adverse effects on the slump and expansion of the slurry paste. The admixture decreased the setting time of the Pcc slurry, and the effect decreased in the order TEA, LC, RLP, and HMC. The admixture also degraded the mechanical properties of the slurry. The use of a D-2 mix design consisting of 0.25% HMC, 0.20% RLP, 0.08% LC, and 0.010% TEA resulted in the maximum extrusion length of the printed sample, 90 mm, and the maximum number of printing layers, 32. SEM images showed that the main hydration products were calcium silicate hydrate (C–S–H) and calcium hydroxide (CH). The admixture mainly affected the early performance of the samples and had little influence on the late performance. This result was consistent with those obtained from hydration tests on Pcc. A reaction model for the addition of an admixture to a Pcc slurry was proposed.

Static and dynamic mechanical properties of magnesium phosphate cement modified by metakaolin after high-temperature treatment

Magnesium phosphate cement (MPC) is widely used in fields of construction and fire-retardant coatings due to its excellent properties. The hydration properties of MPCs at high temperatures are the points of interests. In this work metakaolin was used to improve workability and mechanical properties of MPC, and static and dynamic mechanical properties and hydration products of the MPC after high temperature treatment were investigated. The results showed that the incorporation of metakaolin in MPC allows extending and importantly tuning the setting time of MPC. Notably, 40% replacement of dead burnt magnesia with metakaolin in MPC could extend the setting time of MPC to about 24 min. While the fluidity of MPC significantly decreased with increasing metakaolin content. Typically, increasing the temperature leads the deterioration of mechanical properties of the MPC. However, static and dynamic strength enhancement was also observed at 600℃. The main hydration products of MPC with metakaolin are struvite (MgNH4PO4·6H2O), unreacted MgO, aluminum phosphate (APH) and possibly amorphous substance containing aluminum. Moreover, the impact resistance of MPC at high temperatures were significantly improved with incorporation of metakaolin.

Solidification/stabilisation behaviours of Zn2+ in magnesium potassium phosphate cement: Experiments and density functional theory study

The solidification/stabilisation behaviours of Zn2+ in magnesium potassium phosphate cement (MKPC) have not been thoroughly investigated. Herein, a series of experiments and a detailed density functional theory (DFT) study were conducted to investigate the solidification/stabilisation behaviours of Zn2+ in MKPC. The results showed that the compressive strength of MKPC reduced with the addition of Zn2+ because the formation of MgKPO4·6H2O (the main hydration product in MKPC) was delayed with the addition of Zn2+, as discovered by the crystal characteristics, and because Zn2+ exhibited a lower binding energy in MgKPO4·6H2O compared to Mg2+, as revealed by DFT results. Additonally, Zn2+ had little influence on the structure of MgKPO4·6H2O, and Zn2+ existed in MKPC as the formation of Zn2(OH)PO4, which was decomposed in the range of around 190–350 °C. Moreover, there were a lot of well-crystallised tabular hydration products before the addition of Zn2+, but the matrix was comprised of irregular prism crystals after adding Zn2+. Furthermore, the leaching toxicity of Zn2+ of MKPC was much smaller than the requirements of Chinese and European standards.

Test research on the effect of waste ceramic polishing powder on the compressive strength and chloride penetration resistance of seawater concrete

Waste ceramic polishing powder (CPP) is a by-product created during the grinding and polishing process of the ceramic industry, which adversely affects the environment. In this research, it was used as auxiliary material to partially replace cement during the casting of the test specimens. The effect of cement substitution by 0%, 5%, 10%, 20%, 30%, 40% and 50% of the CPP with seawater and freshwater mixing on the compressive strength and resistance to chloride penetration of the concrete is compared. Moreover, the microstructure development and hydration products of both pastes are determined by different methods. Experimental results show that the compressive strength and resistance to chloride penetration of concrete samples, with the CPP and seawater mixing, is superior to that of the freshwater specimen, with the CPP mixing at the same curing time and the same CPP content. The compressive strength of both types of concrete tends to decrease with increasing content of CPP replacing cement. The compressive strength of concrete meets design requirements when the rate of cement replacement is up to 30% of CPP content when mixed with seawater, but the compressive strength of concrete meets design requirements when the rate of substitution cement reaches a maximum of 10 wt% CPP content mixed with freshwater. In contrast, the resistance to chloride penetration of both types of concrete mixed with CPP is better than that of the specimen without CPP and with the increase of cement replacement rate with CPP, the chloride resistance of concrete shows a rising trend. Under the same CPP substitution and the same curing time, the resistance of chloride penetration of concrete with freshwater mixing is lower than that of concrete mixed with seawater. In addition, the main hydration products in freshwater and seawater pastes with that CPP mixing were CH, ettringite and CSH. In particular, the component of the CPP promoted the formation of Friedel’s salt in concrete mixed with seawater. Seawater increased CH content at an early age (7 days) and decreased later (28 days). At a later age, most of the chlorides in seawater with that CPP component were immobilized by hydrocalumite, which microstructure became denser and compacted structure of concrete.

Hydration evolution of calcium sulfoaluminate cement modified with styrene-butadiene copolymer: Effect of various temperatures and relative humidity

The behavior of styrene-butadiene copolymer (SB) modified calcium sulfoaluminate (CSA) cement hydrated under different temperatures and relative humidity conditions was studied. X-ray diffraction (XRD) and thermogravimetry (TG) were used to investigate cement hydration development in different temperatures (5 °C, 20 °C, and 40 °C) and relative humidity (low, middle, and high) conditions at different ages (28 days, 1 year and 2 years), as well as the micro-morphology of hydration products was analyzed by scanning electron microscope (SEM). Meanwhile, a control group test was set up in a natural environment. The results showed that the hydration products were susceptible to environmental temperature and humidity. With the temperature rising, the hydration degree of CSA cement was promoted, and the content of AH3, monosulfate, and hemicarbonate increased, but the ettringite content decreased. With environmental humidity rising, the hydration degree and content of the main hydration products (ettringite and AH3) increased, while the content of hemicarbonate increased among 30% RH ∼ 60% RH and then decreased among 60% RH ∼ 90% RH. The presence of SB restrained the formation of CAH10, monosulfate, and strätlingite, but increased the content of ettringite and AH3. A hydration model under different environmental conditions was proposed.

Effects of Mud Content on the Setting Time and Mechanical Properties of Alkali-Activated Slag Mortar.

High mud content in the sand has a negative impact on cement mortar but there is little research on Alkali-activated slag (AAS) mortar. In order to explore the impacts of mud content in the sand on the performance of AAS mortar, this paper used sand that contains silt, clay, and a mixture of silt and clay; tested the setting time of AAS with different mud contents of 0%, 2%, 4%, 6%, 8%, and 10%; and measured the unconfined compressive strength and beam flexural strength of 3 d, 7 d, and 28 d AAS mortar specimens. The microstructure of AAS mortar with different kinds of mud was observed by scanning electron microscope (SEM), the elemental composition of the hydration product was tested by energy dispersive spectroscopy (EDS), and the AAS interaction mechanism with different kinds of mud was analyzed. The main conclusions are: the higher the mud content in the sand, the shorter the initial setting time and the longer the final setting time of AAS, mainly because the mud in the sand affects the hydration process; mud content above 4% causes a rapid decrease in the compressive and flexural strengths of AAS mortar, mainly because the mud affects the hydration process and hinders the bonding of the hydration product with the sand. When there is no mud in the sand, the main hydration product of AAS is dense calcium-alumina-silicate-hydrate (C-A-S-H) gel. When the sand contains silt, the hydration product of AAS is loose C-A-S-H gel. When the sand contains clay, the hydration products of AAS contain C-A-S-H gel and a small amount of sodium-aluminum-silicate-hydrate (N-A-S-H), and needle-like crystals. Loose gel and crystals have a negative effect on the AAS mortar strength.

Characterization and performance evaluation of geopolymer prepared with thermal-mechanical activated aluminum sulfate residue

In this study, geopolymer prepared from thermal-mechanical activated aluminum sulfate residue (TMASR) and alkali activator was studied. This work aims to investigate the effects of different design factors on the workability, compressive strength, and efflorescence of TMASR-based geopolymer. The reaction products and structures of the geopolymer binders made from TMASR were tested by FTIR, XRD, and SEM. The results showed that the type, dosage, silicate modulus of the activator, and the water to binder ratio can significantly affect the fresh and hardened properties of TMASR-based geopolymer. A mixture with optimal compressive strength, workability, and efflorescence characteristics can be obtained by using Na2SiO3 solid content of 30%, the water to binder ratios of 0.6–0.65, and the modules of sodium silicate of 1.2–1.6. The main hydration products of TMASR-based geopolymer were amorphous geopolymeric materials. The efflorescence product compositions in TMASR-based geopolymer were Na2SO4, Na2SO4·10H2O, Na2CO3, and Na2CO3·nH2O. The results obtained in this study can promote the utilization of waste acidic aluminum sulfate residue for the production of sustainable construction materials.

The role of calcium aluminate cement in developing an efficient ultra-high performance concrete resistant to explosive spalling under high temperatures

Conventional ordinary Portland cement (OPC)-based UHPC is vulnerable to explosive spalling under high temperatures. This study aims to classify the role of calcium aluminate cement (CAC) as the substitution for OPC in UHPC under high temperatures and finally develop an efficient UHPC without explosive spalling. It was found that CAC-based UHPC (UHPC-CAC) and OPC-based UHPC (UHPC-OPC) reached their peak strength both at 250 °C, but the peak strength (153.8 MPa) of UHPC-CAC was higher than that (137.5 MPa) of UHPC-OPC. Explosive spalling was found in UHPC-OPC after reaching 500 °C, while no spalling was observed in UHPC-CAC even at 1000 °C. The effectiveness of CAC in reducing the mechanical degradation and preventing the spalling of UHPC was attributed to three potential mechanisms: (1) CAC had less physically bound water to cause the vapor pressure in UHPC; (2) The main hydration product (i.e., calcium aluminosilicate hydrates) decomposed to a lesser extent, compared to the hydration product (i.e., calcium silicate hydrates) of OPC, as proved by X-ray diffraction (XRD) analysis, Thermogravimetric analysis (TGA), and Fourier-transform infrared (FTIR) analysis; (3) there exists pores coarsening in UHPC-CAC, as evidenced by micro-XCT, which could release the water pressure in UHPC and thus prevent the spalling at elevated temperatures.

Study of the Hydration Mechanism of Portland Cement with Raman Spectroscopy Applying CO2 Laser Radiation

This work presents the results by irradiating fresh Portland cement pastes with CO2 laser, at powers of 1.6, 2.0, and 2.4 W, at different water-to-cement (w/c) ratios 0.4, 0.45, and 0.5. Raman spectra show the evolution and accelerated growth of the main hydration products through the intensity changes of the Raman signal. The Raman shifts reveal that the C-S-H, CH, AFt, and CaCO3 bands are detected in a shorter time, which means that the setting times are also reduced. The detected band of calcium carbonate, which is due to the incorporation of limestone during the grinding process, shows that it is responsible largely for the acceleration in the reactions during the hydration of the cement. The Raman signals of the hydration products of nonirradiated cement pastes present a delay in their evolution with respect to the irradiated pastes. The curves obtained from the Raman spectra can be used to model the mechanism of hydration as well as to understand the setting process.

Investigation of the performance of cement mortar incorporating lithium slag as a super-fine aggregate

As a by-product of lithium salt mining, the emission of lithium slag increases yearly due to increased demand. Therefore, the utilization of lithium slag faces a huge challenge. In this study, a new approach to using lithium slag as a super-fine aggregate in cement systems was proposed. The use of lithium slag as a super-fine aggregate replacing 0%, 30%, 50%, 70%, and 100% of the standard sand was tested. The main hydration products of cement–lithium slag paste were calcium silicate hydrate gel, calcium hydroxide, unhydrated particles, and a small amount of ettringite. Lithium slag as a super-fine aggregate could significantly reduce the dead load of structures, enhance flexural and compressive strength and the peak stress of mortar, and no more than 50% lithium slag could significantly enhance the permeability of mortar. The study revealed that the replacement rate of lithium slag as a super-fine aggregate could reach 50%, which is five times more than the amount used as supplementary cementitious material. Therefore, the study brings an innovation in the use of lithium slag in cement systems and improves the performance of cement mortar.

Research Progress and Discussion on Modified Cement-Based Borehole Sealing Materials for Mining.

As the concept of green mining develops, organic sealing materials are losing popularity in mining, yet the development of inorganic sealing materials for mining has become a research focus. The most common inorganic sealing materials are Portland cement (PC) and sulfate aluminate cement (SAC), but they fail to meet the performance requirements for sealing gas boreholes in complex coal seams due to their limitations. Thus, their performance needs to be modified. This study aims to explore and grasp the current development of inorganic modified cement-based materials from the perspective of improving the performance of cement-based materials of PC and SAC. First, the characteristics of the main hydration products of PC and SAC as well as the effects of these characteristics on their properties were analyzed. Next, the effects of additives such as admixtures, coagulant regulators, and nanomaterials on their properties including hydration properties, coagulation time, and strength were analyzed. Finally, the modification methods and mechanisms were discussed. It is proposed that the optimization of modification effects by various additives is of great practical significance for the development and application of modified PC and SAC in sealing gas boreholes in engineering practice.

Study on anti-corrosion performance of composite modified magnesium ammonium phosphate cement-based coatings

Corrosion of metals not only fails the overall stability of a building but causes significant economic losses. Spraying anti-corrosion coatings is the simplest and most effective method of corrosion protection. Magnesium phosphate cement-based coatings are attractive due to their fast-setting speed, high strength and durability. This paper aims to improve the corrosion protection properties of magnesium ammonium phosphate cement-based coatings. Zinc oxide and aluminum tripolyphosphate were used as additives at 3% and 4% by mass of magnesium oxide. Meanwhile, metakaolin and aluminum tripolyphosphate at 15% by mass of magnesium oxide was added as admixtures for compound modification. In addition, the electrode potential and current density, impedance spectra, passivation films and phase composition of the materials were investigated using LPR, EIS, SEM and XRD/TG-DTG measurements. Comparing the anodic slope Ba of the polarization curve shows that the Zinc oxide mixed metakaolin specimens(Zn-CSA) have the highest Ba value, indicating that the coating prevents rusting by inhibiting the anodic electrochemical reaction. The EIS impedance spectroscopy results show that sulfate aluminate cement as a compound modifier of the admixture can effectively improve the corrosion protection of the coating. The addition of ATP is effective in inhibiting the transfer process of the coating in the charge. Furthermore, the addition of Zn is to improve the corrosion resistance of the coating by enhancing the shielding properties of the coating. SEM results show that the Zn-CSA surface is very dense, with a lamellar distribution of crystals consisting of tiny crystals closely packed at the bottom and a lamellar distribution at the top. This effectively prevents the erosion of the substrate by corrosive media. The XRD/TG-DTG results show that the composite modified coating consists mainly of incomplete MgO, the main hydration product MAP, Mg2SiO4 and MgCaSiO4. Moreover, Zn-CSA showed the lowest porosity before and after immersion in the coating porosity test. In the salt spray test, the composite-modified coating showed good corrosion resistance, with no bulging, flaking or rusting of the coating surface after 1440 h of salt spray time. This study has important implications for improving corrosion resistance and reducing corrosion costs.