Magnesium Phosphate Cement Research Articles

Effects of sodium dihydrogen phosphate on properties of magnesium phosphate cement

Magnesium phosphate cement (MPC) has attracted much attention in repair materials due to its excellent properties. However, the variability and harshness of the environment put increasing demands on the mechanical properties of materials. Modifying the crystal structures of hydration products is a simple and effective method for improving the mechanical properties. In this paper, the effects of sodium ions on the structures of the hydration products were first investigated at a high water-to-cement ratio, and then the setting time, the heat of hydration, flexural strength and compressive strength were systematically studied for cement at a low water-to-cement ratio. X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, pore structure determination, micromorphology analysis and energy spectrometry was used to investigate the effect of the SDP content on MPC. The results showed that adding SDP could change the crystal structure of the hydration products and cause the formation of more uniform struvite whiskers. The main hydration product is struvite, and sodium ions can promote the hydration reaction and increase the amount of hydration products. In addition, the sodium ions replace some of the potassium ions in struvite to form a more stable crystal structure, from potassium-containing magnesium phosphate to sodium-potassium coexisting struvite whiskers. This promotion can refine the crystal structure of the hydration product, thereby changing the pore structure and improving the mechanical properties of SDP-MPC. Typically, the 1 d flexural strength of MPC with 50 wt% SDP addition is up to 12.7 MPa, and the 1 d compressive strength is up to 78.1 MPa; MPC with 50 wt% SDP was found to have 65% higher flexural strength and 122% higher compressive strength compared to MPC without SDP addition, and the 28 d flexural strength and compressive strength also increased by 58% and 70%, respectively. The results show that incorporating sodium ions changes the crystal structure of struvite and can effectively improve the strength properties of magnesium phosphate cement.

Optimization of magnesium phosphate cement: Stabilization of a kaolinitic soil

Magnesium phosphate cement (MPC) can provide a resilient, sustainable, and low-CO2 emission alternative to conventional soil stabilization techniques. Changes in the mechanical properties of a kaolinitic, clay-textured soil were quantified after stabilization with 5, 12, and 20 % (w/w) MPC. The unconfined compressive strength (UCS) of the stabilized soils increased from 1.36 MPa when compacted without the stabilizer to 2.06 MPa with 5 % MPC, 3.51 MPa with 12 % MPC, and 3.47 MPa with 20 % MPC. Similarly, the elastic modulus of the compacted soils increased from 182.10 MPa in the unamended control soil to 266 MPa with 5 % MPC, 456 MPa with 12 % MPC, and 410 MPa with 20 % MPC. There were no significant differences observed in the UCS between 7- and 28-days curing time for samples stabilized with MPC (p < 0.05). The major MPC product, K-struvite, was present in the stabilized soil samples as determined by X-ray diffraction. Scanning electron micrographs of compressed MPC samples found hollow lens-shaped sections of pure struvite filled with aluminosilicates from the soil, and these structures appear to be the binding mechanism between the major soil minerals bind and the phosphate groups of K-struvite. Significant gain in the UCS of 12 % MPC stabilized soils to 8.12 MPa was observed with the addition of 1 % (w/w) 6.35 mm long dried jute fibers. Soils stabilized with 12 % MPC showed no significant change in strength after 3 cycles of capillary soaking with water and drying at 40 °C. Soil stabilization with MPC had similar strength to Portland cement stabilization.

Effect of borax on the hydration and setting of magnesium phosphate cements

• Borax effect on the hydration of magnesium phosphate cements was studied. • The setting was investigated with Gillmore tests, calorimetry, Raman and pH analyses. • Set cements were studied with XRD, SEM, mechanical tests and Solid State NMR. • Borax prolongs the setting time and reduces the heat released during setting. • Retarding action is due to the interaction between borates and Mg 2+ and NH 4 + . This work unravels for the first time the concentration dependent retarding effect of borax on tri-magnesium phosphate-based cements by studying the hydration and the phases formed in the set cements, exploiting multiple characterization techniques. In the presence of borax, the hydration was found to be slower and less exothermic, leading to the formation of struvite without newberyite, with no effect on cement’s strength. The observed boron species allowed us to ascribe the retardation to the complexation of NH 4 + and Mg 2+ by borate and polyborate anions.

Design and Experimental Evaluation of Composite Magnesium Phosphate Cement-Based Coating with High Cooling Effect

The application of surface heat reflective coatings is one of the effective measures to solve the temperature disease of concrete structures in sunlit environments. To achieve strong bonding, high durability, and good cooling characteristics, a novel inorganic reflective thermal insulation coating was prepared using magnesium phosphate cement (MPC) as the binder and reflective matrix, and titanium dioxide and glass beads as the reflective thermal insulation reinforcement functional additives. The optimum ratio of the new reflective thermal insulation coating was preferred through laboratory irradiation test, thermal conductivity test, and spectral reflectance test. The results show that MPC itself was a good reflection cooling material, and the surface and internal temperatures of concrete blocks were reduced by 7.6 °C and 6.6 °C, respectively, after using MPC as the cooling coating. When 2% titanium dioxide was added to MPC, the surface and internal temperatures were further reduced by 6.0 °C and 4.9 °C, respectively. On top of this, the surface and internal temperatures of the concrete were reduced by a further 3.9 °C and 2.2 °C when 8% glass beads were added. The bond strength of the MPCTG coating to the concrete matrix reached 2.1 MPa. Finally, the microscopic characteristics and the reflective thermal insulation mechanism of the MPCTG coating were investigated with the aid of SEM, thermo gravimetric analysis, and XRD analysis. The results show that the MPC in the MPCTG coating was well hydrated, and a large number of hydration products encapsulated the unreacted MgO particles, titanium dioxide, and glass beads, forming a dense whole with high reflection and low thermal conductivity, and the coating effectively prevented the entry of radiant heat. At the same time, the MPCTG coating was thermally stable below 70 °C. The magnesium phosphate cement-based reflective thermal insulation coating developed in this study has potential application prospects in concrete structure cooling coatings.

The mechanical and conductive properties of intelligent magnesium phosphate cement mortar

•Mechanical performance of MPM with conductive fibers is presented. •Conductive properties of MPM with conductive fibers is determined. •Self-sensing performance of MPM and the corresponding properties is investigated.

The Corrosion Resistance of Reinforced Magnesium Phosphate Cement Reactive Powder Concrete.

Magnesium phosphate cement-based reactive powder concrete (MPC-RPC) is a cement-based material with early strength, high strength and excellent durability. The slump flow and setting time of steel fibers reinforced MPC-RPC are investigated. Meanwhile, the flexural strength, the compressive strength, the ultrasonic velocity and the electrical resistivity of specimens cured for 3 h, 1 day, 3 days and 28 days are determined. Moreover, the corresponding corrosion resistance reinforced MPC-RPC exposing to NaCl freeze-thaw (F-T) cycles and dry-wet (D-W) alternations is researched. In this study, the steel fibers used are 0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5% and 3.0% by the volume of MPC-RPC. The corrosion of the inner reinforcement is reflected using the mass loss, electrical resistivity, ultrasonic velocity, and the AC impedance spectrum. Researching findings show that the steel fibers lead to decreasing the slump flow and setting time. The flexural strength, the compressive strength and ultrasonic velocity of MPC-RPC cured for 3 h are higher than 45% of the MPC-RPC cured for 28 days. Moreover, when the MPC-RPC is cured for 7 days, the flexural strength, the compressive strength and ultrasonic velocity of MPC-RPC are higher than 85% of the specimens cured for 28 days. The electrical resistance decreases in a quadratic function as the volume ratio of steel fibers increases. The corrosion resistance of the internal reinforcement can be improved by adding steel fibers at appropriate dosages. The reinforcement inner MPC-RPC corrodes more seriously under the NaCl D-W alternations than NaCl F-T cycles.

Water-resisting performances and mechanisms of magnesium phosphate cement mortars comprising with fly-ash and silica fume

Design of hydraulic structures using magnesium phosphate cement (MPC) composites is a still challenging issue because of the volume instability of MPC matrices in water environment. In this research, an attempt was taken to progress the water-resistance performance of MPC blended with fly ash (FA) and silica fume (SF). The FA was introduced as one third of magnesia in the mortar specimens, where SF dosages were 5%, 10% and 15% as the substitution of magnesia. Physico-mechanical and microstructural properties of mortar samples were examined considering the air and water curing systems. The analytical results bared that compressive strength (CS) and flexural strength (FS) of specimens composed with MPC + FA+5%SF were observed about 25% higher as compared to control. Both strength properties having the optimized content of SF (i.e. 5%) was reduced close by 3–4% in water system, whereas the pure MPC matrix exhibited around 20% less at 28 d. In addition, mass loss (ML) was found nearby 1.56% at 28 d. Moreover, SEM, EDS and XRD tests were detected that intermediate minerals namely Berlinite, Mullite, Lizardite and Enstatite were formed in the microstructures, and micro-cracks and micro-pores were significantly reduced. Consequently, compact microstructure was obtained that resulted the well water-resistant of proposed MPC mortar. The outcomes of this research might be a potential information for constructing the MPC-based water structures.

Early-age mechanical properties and hydration degrees of magnesium phosphate cement paste in freezing winter of cold regions

Magnesium phosphate cement (MPC) paste is a good patching material for concrete repair works. This study focused on early-age mechanical properties and hydration degrees of MPC paste in freezing winter of two types of cold regions, which are highland regions and high-latitude regions. MPC pastes with different mix proportions under different curing modes were experienced a series of experiments, including fluidity and setting time, compressive strength, pore structure characterization, thermogravimetric analysis, X-ray diffraction and electron microscopic scanning. Results showed that for winter applications, MPC pastes in simulated highland temperature conditions performed better than those in true high-latitude temperature conditions, illustrated by pore structure analyses and hydration products analyses. The best M/P ratios for highland applications and high-latitude applications were respectively 4 and 5, which respectively delivered 24 h strengths at about 50 MPa and 25 MPa. Even in severe cold winter, the setting of MPC paste depended on the hydration speed instead of the frozen action. Mixing water temperature was good for early-age hydration of MPC paste which cured for six hours in natural cold environment, however, the effect vanished at 24 h. Both the amounts of struvite and unhydrated phosphate, which could be quantitatively assessed by TG-DSC tests or qualitatively assessed by XRD test, were good indicators of the hydration degree of MPC paste in cold weather. These results provided valuable suggestions for winter applications of MPC paste in different types of cold regions.

Study on frost resistance of EPS concrete based on EPS beads wrapping modification

Expanded polystyrene (EPS) concrete is an ideal low carbon green building material, but the frost resistance is weak in natural environment, which hinders the popularization of EPS concrete. In this study, magnesium phosphate cement (MPC), ultra-high performance concrete (UHPC), and waterborne polyurethane (WPU) were used to wrap the surface of EPS beads and enhance its concrete performance. The frost resistance durability of four groups of EPS concrete was studied, the uniaxial compression tests of concrete after freezing and thawing were conducted, the results show that: the freeze thaw damage law of EPS concrete is different from ordinary concrete, the standard of freeze-thaw failure of EPS concrete is the sudden increase of dynamic elastic modulus but not continues decreasing, the mass of EPS concrete increases but not decreases; concrete with EPS beads wrapped by UHPC and WPU has good frost resistance, the frost resistance level has been increased by 100 levels and the service life increased by 60% than that of EPS beads unwrapped, the strength-degradation is much slower than that of concrete without wrapped; after freeze-thaw failure, the cracks and the interface transition zone (ITZ) gap of concrete with EPS beads wrapped is smaller than unwrapped, the macro phenomenon of freeze-thaw failure is explained from the micro level, based on macro and micro test results, the degradation mechanism of concrete with EPS wrapped and unwrapped under the action of freezing-thawing cycles are discussed. Beside, the stress-strain curves of EPS concrete after freeze-thaw attenuation were studied, the attenuation of concrete with EPS beads wrapped with WPU and UHPC is not serious as the concrete with EPS unwrapped, the proposed stress-strain model is in good agreement with the experimental results, which can provide a reference for evaluating the mechanical properties of EPS concrete after freeze-thaw. Finally, it is suggested to use linear segment and curve segment to describe the attenuation trend of relative dynamic elastic modulus, the fitted model is in good agreement with the experimental results, it can provides a reference for the study of freeze-thaw mechanical properties and the prediction of freeze-thaw cycle of this kind of concrete.

Effects of Electrochemical Chloride Extraction on the Properties of Chloride-Contaminated Reinforced Concrete by Using Magnesium Phosphate Cement Bonding Carbon Fiber Reinforced Plastics as Anode

Effects of Electrochemical Chloride Extraction on the Properties of Chloride-Contaminated Reinforced Concrete by Using Magnesium Phosphate Cement Bonding Carbon Fiber Reinforced Plastics as Anode

Experimental Research on Magnesium Phosphate Cements Modified by Fly Ash and Metakaolin

To increase performance and save costs when utilizing magnesium phosphate cements (MPC) to repair a damaged building structure or a cement pavement, MPC is typically combined with fly ash (FA) and metakaolin (MK). The influence of FA and MK on the workability, rheological characteristics, flexural strength, compressive strength, and drying shrinkage of MPC was investigated in this research. MPC samples with different percentages of FA and MK by weight replacement were prepared. The results indicate that an appropriate dosage of MK and FA could decrease MPC fluidity and delay the setting time. MPC’s yield stress and plastic viscosity were increased when MK was added. FA has a negative influence on flexural and compressive strength as compared to control MPC and the compressive strength of MPC with MK increases and then decreases. The drying shrinkage of MPC containing MK and FA is superior to control mixture. MPC with 10% FA and 10% MK has the best-modified performance in terms of the comprehensive performance of MPC at all test ages.

Investigating the Hybrid Effect of Micro-steel Fibres and Polypropylene Fibre-Reinforced Magnesium Phosphate Cement Mortar

To overcome the drawbacks caused by the intrinsic brittleness of cementitious materials, various types of fibres were incorporated as reinforcements. Extensive research on Ordinary Portland cement indicated that compared with the use of a single type of fibres, the mixed-use of multiple fibres can significantly improve both strength and toughness of the cementitious composites, which is referred to as the hybrid effect. However, such hybrid effect in multiple fibre-reinforced magnesium phosphate cement-based composite (HFRMC) still lack quantitative understanding. Therefore, this study conducted a series of experiments, including slump flow tests, compression tests, four-point bending tests and microstructure analysis, to investigate the hybrid effect of micro-steel fibres (MSF) and polypropylene (PP) fibres in HFRMC. Two types of mixed designs of HFRMC were conducted: 1. total fibres fraction (including both PP fibres and MSF) was fixed to be 1.6%; 2. PP fibres fraction was fixed to be 1.6% with different addition of MSF. Our results indicated that the slump flow of magnesium phosphate cement mortar varied around 7.6–8.8% with the hybrid use of MSF and PP fibres, while the flexural strength and toughness increased around 13.7–23.1% and 1.6–45.9%, respectively.

Investigation of sodium alginate as a candidate retarder of magnesium phosphate cement: Hydration properties and its retarding mechanism

This work investigated the effect of sodium alginate on the hydration properties of magnesium potassium phosphate cement (MKPC) suspension with a high w/c ratio, and explored its retarding mechanism. At w/c = 10, hydration of MKPC presented a mult-step process, specifically, KMg2H(PO4)2•15H2O and possibly MgHPO4·7H2O first precipitate, then decomposed to struvite-k. As sodium alginate was added, Na2HPO4•12H2O and KMg2H(PO4)2•15H2O precipitated at the initial stage, and then destabilized afterwards. Sodium alginate could delay dissolution of KMg2H(PO4)2•15H2O as well as precipitation of struvite-k. Moreover, sodium alginate tends to transform to alginic acid at low pH, and left a large number of Na+ ions, leading to precipitation of Na2HPO4•12H2O. The alginic acid is difficult to dissolve at low pH, which limited its effect on extending the setting time of MKPC further.

A novel iron phosphate cement derived from copper smelting slag and its early age hydration mechanism

Copper slag (CS), a by-product of copper smelting, is normally stockpiled, leading to wastes of resource and space as well as environment pollution. It has not been massively reutilized as a supplementary cementitious material in Portland cement due to its low reactivity. In the present study, CS is for the first time utilized as the base component to prepare an iron phosphate cement (IPC) by reacting with ammonium dihydrogen phosphate (ADP) at room temperature. The influence of the raw materials mass ratio (CS/ADP) on the microstructure and performance of IPC pastes are investigated. It is found that the compressive strength of IPC pastes at all ages is not a monotonic function of CS/ADP, and the paste with CS/ADP of 2.0 gives the highest strengths, i.e., 26.8, 38.9 and 47.5 MPa at 1, 3 and 28 d, respectively. The crystalline phases including FeH2P3O10·H2O and FePO4 are formed as the main reaction products to bind the unreacted CS particles. The early age hydration of IPC is found to be a multi-stage process, involving the initial dissolution of ADP and iron-containing phases of CS, the formation of FeH2P3O10·H2O, the initial generation of FePO4, and the attainment of the hydration reaction equilibrium. Unlike the magnesium phosphate cement, a redox reaction of Fe(Ⅱ) into Fe(Ⅲ) occurs due to the suitable range of pH and oxidation-reduction potential of the IPC system during the hydration reaction.

Workability and Mechanical Properties of Tensile Strain–Hardening PVA Fiber-Reinforced Magnesium Phosphate Cement Composites

Workability and Mechanical Properties of Tensile Strain–Hardening PVA Fiber-Reinforced Magnesium Phosphate Cement Composites

Hydration products and microstructural properties analysis of magnesium phosphate cement comprising with industrial residues

Cavities, micro-cracks and micro-pores are formed in the microstructures of magnesium phosphate cement (MPC) due to the rapid hydration process. For increasing the structural solidity, formation of secondary minerals is necessary through filling the micro-cracks and micro-pores. In addition, existence of optimum level of intermediate crystals increases the microstructural density as well as strength performance of MPC compounds. To attain the high-quality microstructures of MPC for water stability, present study added four different pozzolanic properties based industrial by products namely fly ash (FA), silica fume (SF), bauxite (BX) and phosphogypsum (PG) were introduced by means of their optimum dosages. The 1d aged SEM micrographs with high magnifications shown that free particles of magnesia and phosphate salts reacted with the used all supplementary cementitious materials and formed huge secondary crystals. In addition, presence of intermediate crystals was detected by EDS and X-ray diffraction tests in the powder specimens at 1d age, which are Enstatite, Mullite, Lizardite, Berlinite, kaolinite, kyanite, CSH and ettringite. It has been noted from crystallinity analytical results that MPC specimens comprising with BX and PG including FA exposed the higher intermediate crystal amounts around 34.3% and 41.6% at 1d; 49% and 47.6% at 28d, respectively. In the similar way, amorphous contents were significantly reduced with the passages of hydration ages. Furthermore, all the nominated blends with SCMs unveiled the well heat resistance and lost structural water at higher temperature as compared to control mix. The outcomes of present research might be applicable to design MPC matrices for higher strength and water structures.

Designing Magnesium Phosphate Cement for Stabilization/Solidification of Zn-Rich Electroplating Sludge.

Electroplating sludge is a hazardous waste due to its high potential to leach toxic elements into the natural environment. To alleviate this issue, we tailored magnesium phosphate cement (MPC) as a low-carbon material for stabilization/solidification (S/S) of Zn-rich electroplating sludge. The interaction between MPC and ZnO was investigated to clarify the precipitate chemistry, microstructure transition, and chemical environment of Zn species in the MPC-treated Zn sludge system. Comprehensive characterization (by X-ray diffraction (XRD), 31P nuclear magnetic resonance (NMR), and extended X-ray absorption fine structure spectroscopy (EXAFS)) and thermodynamic modeling results revealed that the incorporated ZnO preferentially reacted with phosphate to form Zn3(PO4)2·2H2O/Zn3(PO4)2·4H2O, changing the orthophosphate environment in the MPC system. Stronger chemical bonding between Zn and phosphate in comparison to the bonding between Mg and phosphate also resulted in the formation of amorphous Zn3(PO4)2·2H2O/Zn3(PO4)2·4H2O. Zn3(PO4)2·4H2O precipitate appears to predominate at high {K+}{H+}{HPO42-} values, and the formation of Zn3(PO4)2·2H2O/Zn3(PO4)2·4H2O competed for the Mg sites in the MPC system, leading to the inhibition of formation of Mg-phosphate precipitates. Overall, this work uncovers the precipitate chemistry and microstructure transition of Zn species in the MPC system, providing new insights into the sustainable S/S of Zn-contaminated wastes by adopting MPC.

Effects of the absorber, thickness and surface roughness on the electromagnetic wave absorption characteristics of magnesium phosphate cement

Magnesium phosphate cement (MPC) functionalized with excellent electromagnetic wave absorption performance, bonding capacity, fast hardening and early strength can meet the requirements for rapid electromagnetic radiation protection of military and civil building structures. Hollow glass microsphere (HGM) is added uniformly to improve the impedance matching of MPC to free space, so that the electromagnetic wave is able to be maximally introduced into MPC and effectively absorbed by carbon nanotubes (CNT) through high dielectric loss effect. Influences of HGM contents, thickness and surface roughness of specimens on the electromagnetic wave absorption performance of MPC are systematically investigated. Test results demonstrate that the electromagnetic absorption performance of MPC is significantly enhanced by the additions of HGM and CNT. The peak reflection loss and the bandwidth below −10 dB first increase and then decrease with increasing HGM content. Increasing the thickness of the MPC improves the electromagnetic reflection loss. The electromagnetic absorption properties of MPC are improved further by cutting notches. MPC blended with 50 vol% HGM and 1 wt% CNT (by MgO) with 5 mm deep notches spaced 18 mm apart has excellent electromagnetic absorption capacity as featured by a peak reflection loss of –33.5 dB and a bandwidth of 7.03 GHz below −10 dB. In the perspective of structural strengths, the modified MPC is able to repair damaged concrete of pre-fractured concrete. It achieves the dual features of absorbing electromagnetic waves and repairing existing concrete structures.

Effect of titanium slag on the properties of magnesium phosphate cement

Titanium slag is industrial solid waste, and its efficient utilization has important practical significance for reducing the environmental impact and promoting resource utilization. In the magnesium phosphate cement (MPC) application process, its high hydration heat and setting rate are always difficult problems to solve, adding fillers is the main method to improve the performance of MPC. Therefore, this paper mainly studies the influence of titanium slag on the working performance, hydration temperature and mechanical properties of MPC. X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were also used to analyze the hydration products and microscopic morphology of the samples. The results show that titanium slag can effectively improve the working performance of the MPC slurry and reduce the heat of hydration. When the content of titanium slag is 50%, the fluidity of MPC samples with M/P of 2:1 and 3:1 is significantly higher than that of the original group, the setting time is increased by 115.4% and 100%, respectively, and the hydration temperature is reduced by 21.9% and 17%, respectively. The compressive strength of MPC decreases with increasing titanium slag content, and when M/P is 3:1, the early strength is increased. XRD and TG analysis showed that adding titanium slag reduced K-struvite formation in the MPC sample. SEM and EDS analysis indicate that large amounts of titanium slag will change the shape and size of the hydrated product, and the structure will become loose. When the titanium slag content is 30%, the sample with M/P = 3:1 has a dense structure and high strength. A certain amount of titanium slag is beneficial for prolonging the setting time of MPC, and a lower hydration exotherm and higher fluidity will also increase with titanium slag addition.

Fractal Analysis on Pore Structure and Modeling of Hydration of Magnesium Phosphate Cement Paste

Magnesium phosphate cement (MPC) paste is hardened by the acid–base reaction between magnesium oxide and phosphate. This work collects and evaluates the thermodynamic data at 25 °C and a pressure of 0.1 MPa and establishes the hydration reaction model of MPC pastes. The influence of the magnesium–phosphorus molar (M/P) ratio and water-to-binder (W/B) ratio on the hydration product is explored by the thermodynamic simulation. Following this, the initial and ultimate states of the hydration state of MPC pastes are visualized, and the porosity of different pastes as well as fractal analysis are presented. The result shows that a small M/P ratio is beneficial for the formation of main hydration products. The boric acid acts as a retarder, has a significant effect on lowering the pH of the paste, and slows down the formation of hydration products. After the porosity comparison, it can be concluded that the decreasing of M/P and W/B ratios helps reduce porosity. In addition, the fractal dimension Df of MPC pastes is positively proportional to the porosity, and small M/P ratios as well as small W/B ratios are beneficial for reducing the Df of MKPC pastes.