Magnesium Potassium Phosphate Cement Research Articles

Mechanical properties of micro-steel fibre reinforced magnesium potassium phosphate cement composite

This paper presents the mechanical properties of micro-steel fibre (MSF) reinforced magnesium potassium phosphate cement (MPPC) composites with multi-composite retarder. The compressive strength, flexural strength, flexural toughness and flexural ductility of the MSF reinforced MPPC composite (MSFRMC) were experimentally explored. The variables of the experiment included sand-cement mass ratio, water-cement mass ratio, curing time and fibre volume fraction. In addition, the effect of different types of cement on the mechanical properties of MSF reinforced composites was investigated. It was found that with the increase of water content in the MPPC paste, the average compressive strength, flexural strength and flexural toughness of MSFRMC decreased significantly and the ductility of MSFRMC increased slightly. With the increase of MPPC content in the paste, the flexural toughness of MSFRMC increased significantly and the flexural ductility of MSFRMC increased moderately. With the increase of the addition of MSF, the compressive strength, flexural strength, flexural toughness and flexural ductility of MSFRMC improved significantly. The compressive strength, flexural strength, flexural toughness and flexural ductility of MSFRMC were high at the early stage of curing, especially during the first 3 days. The addition of MSF in MPPC composite improved the compressive strength, flexural toughness and flexural ductility significantly more than the addition of MSF in sulphoaluminate cement and ordinary Portland cement composites.

Experimental research on seawater erosion resistance of magnesium potassium phosphate cement pastes

This paper aims to study the resistance of magnesium potassium phosphate cement (MKPC) paste to seawater erosion. MKPC paste specimens were prepared and their compressive strength, mass change, hydration temperature and water absorption were measured. The phase composition and microstructure were also analyzed. The results show that the initial hydration age of the reference sample M1 under natural curing condition has a significant effect on its compressive strength development in seawater. The residual ratios of the compressive strengths of M1(3d) and M1(28d), hydrated for 3 and 28 days, respectively, under natural curing condition, are 76.6% and 91.1% at 360-day seawater immersion age, respectively. This also indicates that early-age M1 has poor resistance to seawater erosion. Adding some limestone (LS) powders and silica fume (SF) can significantly improve the strength of early-age MKPC paste. The 3-day compressive strength of M2 with LS and SF is about 50% higher than that of M1. After immersion for 360 days in seawater, the residual ratios of the compressive strength of M2(3d) and M2(28d) are both close to 93%. This implies that initial hydration age of M2 under natural curing condition has almost no effect on its compressive strength development in seawater. Compared with M1, M2 has higher resistance to seawater erosion, which is attributed to the higher hydration degree and more compact structure of M2. This paper might be useful for preparing MKPC-based materials that can meet the requirements of marine concrete.

Influence of fly ash and metakaolin on the microstructure and compressive strength of magnesium potassium phosphate cement paste

The influences of fly ash and metakaolin added as substitutions (by up to 50 wt%) of magnesium potassium phosphate cement (MKPC) on the microstructures and compressive strengths of the MKPC pastes were investigated. The results indicate that the aluminosilicate fractions of both fly ash and metakaolin are involved in the acid-base reaction of MKPC system, leading to a preferential formation of irregular crystalline struvite-K incorporated with Al and Si elements and/or amorphous aluminosilicate phosphate products. Metakaolin is more reactive than fly ash in the MKPC system. For the same addition dosage, the MKPC pastes containing metakaolin exhibit higher compressive strengths than the pastes containing fly ash. This is attributed to the formation of more highly reinforced microstructures and denser interfaces between the metakaolin particle and hydration products (e.g. struvite-K) in the MKPC paste containing metakaolin. Addition of 30 wt% metakaolin increases the compressive strengths of MKPC pastes at all test ages.

Effect of calcium aluminate cement on water resistance and high-temperature resistance of magnesium-potassium phosphate cement

The effects of calcium aluminate cement (CAC) on strength, water resistance and high-temperature resistance of magnesium-potassium phosphate cement (MKPC) was investigated. The CAC substituted with 20, 30 and 40 wt% of MgO in MKPC. It resulted in higher compressive strength and better water resistance. This improvement is originated from K-struvite crystals coated by the amorphous and hydrous phases from the CAC. Improved high-temperature resistance of CAC-MKPC was observed as well. Spinel MgAl2O4 formed in CAC-modified MKPC after the sintering.

Influence of the w/c ratio on the hydration process of a magnesium phosphate cement and on its retardation by boric acid

Magnesium potassium phosphate cements (MKPCs) are prepared using calcined magnesia (MgO) and an acidic solution of potassium dihydrogen phosphate (KH2PO4). Their fast setting and high heat of hydration can be problematic when large volumes of materials are produced. Boric acid (B(OH)3) is thus commonly added as a set retarder. This work investigates MKPC hydration in paste (water-to-cement ratio w/c = 1) and its retardation by B(OH)3. The precipitation of K-struvite (MgKPO4·6H2O) is preceded by that of phosphorösslerite (MgHPO4·7H2O) and Mg2KH(PO4)2·15H2O. Cattiite (Mg3(PO4)2·22H2O), an end-product in diluted suspension (w/c = 100), is not observed. B(OH)3 slows down the formation of hydrates in two ways: (i) by stabilizing in solution the cations that outbalance the negative charges of the polyborates formed at pH above 6, and (ii) through the precipitation of an amorphous mineral containing borate and orthophosphate. The first process occurs both in diluted suspensions and pastes, the second is specific to pastes.

Investigation on early hydration features of magnesium potassium phosphate cementitious material with the electrodeless resistivity method

An electrodeless resistivity method is applied to trace the early hydration behavior of magnesium potassium phosphate cement (MKPC). The relationship between setting times (including initial and final setting time) and the characteristic points of the electrodeless resistance is studied, aiming to establish a rapid testing method which could predict the setting time of MKPC. Moreover, a linear relationship between the standard compressive strength at 28 days and the resistivity at 24 h of MKPC is also established, and demonstrates that the resistivity and the standard compressive strength have a compact corresponding relationship. Therefore, the standard compressive strength of magnesium potassium phosphate cement could be predicted by electrodeless resistivity parameters.

Reaction mechanism of magnesium potassium phosphate cement with high magnesium-to-phosphate ratio

Understanding reaction mechanisms of magnesium potassium phosphate (MKP) cement is of significant importance, as it is closely related to the optimum design of MKP cement-based materials. In this study, reaction mechanisms of MKP cements with a high magnesium-to-phosphate (Mg/PO4) molar ratio of 8 were investigated at two different water-to-solid (w/s) ratios of 0.5 and 5. The experimental findings show that the use of this high Mg/PO4 molar ratio suppresses the formation of potassium-free magnesium phosphate hydrates. K-struvite is mainly formed with probably more phosphate than the theoretical value. Moreover, the w/s ratio plays a crucial role on governing the reaction path of MKP cements. The lower w/s ratio (w/s = 0.5) leads to higher potassium concentration and pH value, thus suppressing the formation of intermediate product, Mg2KH(PO4)2·15H2O, which is formed at the higher w/s = 5. However, it causes the formation of minor amount of brucite at 28 d, which coexists with K-struvite in the paste.

Properties of fly ash blended magnesium potassium phosphate mortars: Effect of the ratio between fly ash and magnesia

The ratio between fly ash (FA) and magnesia is an important factor for the optimum design of FA blended magnesium potassium phosphate cements (MKPCs). In this study, a high CaO content FA (CaO = 12.5 wt%) was used to partially replace magnesia at 0 wt%, 30 wt%, 50 wt%, 70 wt%, and 90 wt%, respectively. The experimental results showed that a FA replacement of 50 wt% led to the highest compressive strengths. A FA replacement of 70 wt% is considered as upper limit, as the presence of more FA caused significantly lower strength. In the plain and the FA blended MKPCs, K-struvite (MgKPO4⋅6H2O) was the main hydrate. At very high FA contents, additional calcium potassium hydrogen phosphate (CaK3H(PO4)2) was observed as well as the destabilization of K-struvite to cattiite (Mg3(PO4)2⋅22H2O), which could be one of the main factors responsible for the lower strength of high FA blended MKPC mortars stored under water.

Effect of Borax on Properties of Potassium Magnesium Phosphate Cement

The effects of borax on the setting time, compressive strength, bond strength, drying shrinkage and pH value were investigated for potassium magnesium phosphate cement (MKPC). The results show that with the increase of borax dosage, the setting time is gradually extended, both compressive strength and bond strength are greatly decreased, the drying shrinkage rate is increased. Especially high dosage of borax, the extension of setting time is more obvious. Compared with that without borax, when the dosage of borax is 12.5%, setting time can be prolonged by 214.8%.The influence of borax dosage on the time-dependent effect of compressive strength shows that when the dosage of borax is 2.5%~5.0%, compressive strength increases rapidly from 4h to 1d, and increases relatively slowly from 1d to 3d. When borax dosage is less than 2.5% or higher than 5%, the law of time-dependent effect of compressive strength is the opposite. Compared to borax prior to magnesia addition, the pH value of the system is larger and the time of inflection point is advanced when borax and magnesia are mixed together at the same time. The increase of borax dosage can reduce the pH value of the system, and decrease the rising rate of pH value, at the same time the required time when the final pH value is relatively stable is longer.

A study on bone cement containing magnesium potassium phosphate for bone repair

A novel type of bone cement, magnesium potassium phosphate cement (MKPC), was fabricated by mixing 5% phosphoric acid with magnesia, potassium dihydrogen phosphate, sucrose, hydroxyapatite, and sod...

Preparation of Magnesium Phosphate Cement and Application in Concrete Repair

Potassium magnesium phosphate cement (MKPC) was prepared by using magnesium oxide (MgO) and potassium dihydrogen phosphate (KH2PO4, KDP). The effects of different calcination temperature, water-cement ratio and ratio on the operation of magnesium phosphate cement were studied. The effects of different water - cement ratio and ratio on the bonding strength of potassium magnesium phosphate cement and the application of potassium phosphate and magnesium cement in concrete repair and reinforcement were determined by experiments such as bending resistance, splitting, compression and bearing capacity. The experimental results show that the calcination temperature is 1100 °C, the calcination time is 1h, the settling time of magnesium oxide is 39min, and the compressive strength of one day reaches 53MPa. The water - cement ratio with the best bonding strength is 0.2, the mass ratio is 2:1.To meet the rapid repair of the construction requirements, is expected to be applied to the actual repair works.

Preparation of Magnesium Phosphate Cement and Application in Concrete Repair

Potassium magnesium phosphate cement (MKPC) was prepared by using magnesium oxide (MgO) and potassium dihydrogen phosphate (KH2PO4, KDP). The effects of different calcination temperature, water-cement ratio and ratio on the operation of magnesium phosphate cement were studied. The effects of different water - cement ratio and ratio on the bonding strength of potassium magnesium phosphate cement and the application of potassium phosphate and magnesium cement in concrete repair and reinforcement were determined by experiments such as bending resistance, splitting, compression and bearing capacity. The experimental results show that the calcination temperature is 1100 °C, the calcination time is 1h, the settling time of magnesium oxide is 39min, and the compressive strength of one day reaches 53MPa. The water - cement ratio with the best bonding strength is 0.2, the mass ratio is 2:1.To meet the rapid repair of the construction requirements, is expected to be applied to the actual repair works.

Polyamorphism and frustrated crystallization in the acid–base reaction of magnesium potassium phosphate cements

The kinetics of MgO dissolution explain the amorphous–amorphous transformation and frustrated crystallization of reaction products in Mg-phosphate cements.

Influence of steel slag powders on the properties of MKPC paste

This paper aimed to study the influence of steel slag powders on performance of magnesium potassium phosphate cement (MKPC) paste. We prepared MKPC pastes containing different contents of steel slag powders. Then their fluidity, initial setting time, compressive strength, strength residual ratio under water curing condition, shrinkage deformation and hydration temperature were measured. Furthermore, we analyzed the phase composition and micro-morphology of hardened MKPC pastes by XRD, TG-DTG, BET and SEM-EDS. The results were as follows. Adding some steel slag powders to MKPC can significantly improve the early compressive strength of hardened MKPC paste and slightly improve its late compressive strength. This should be attributed to the improvement of particle size distribution, filling and active effect of steel slag powders on MKPC paste. Compared with the 5-h, 1-day and 60-day compressive strengths of hardened MKPC paste without steel slag powders, those of hardened MKPC paste containing 20% steel slag powders were improved by 5%, 30% and 8%, respectively, and its 60-day compressive strength residual ratio under water curing condition was over 90%. In addition, adding some steel slag powders to MKPC can significantly decrease the shrinkage deformation of hardened MKPC paste, which should be attributed to improvement of pore structure and more compact structure of hardened MKPC paste. The shrinkage deformation of hardened MKPC paste containing 20% steel slag powders mainly occurred during the first 28 days of hydration. Its 28-day and 60-day shrinkage ratios were 1.7 × 10−4 and 2.34 × 10−4, respectively, and its 60-day shrinkage ratio was about 60% of that of the specimen without steel slag powders (3.97 × 10−4).

The effects of admixtures of inorganic hydrates on the hydration hardening of magnesium potassium phosphate cement

Admixtures of Na2B4O7·10H2O (NB), Ca(NO3)2·4H2O (CN) and Na2SO4·10H2O (NS) are studied to discover how they affect the work performance, hydration-induced increases in temperature and mechanical performance of magnesium potassium phosphate cements (MKPCs). Analytical methods such as X-ray diffraction spectroscopy, eight-channel microcalorimetry and thermogravimetric-differential scanning calorimetry are used to investigate the underlying mechanisms of these changes. Incorporation of a single retarder (NB) results in short MKPC hardening times and low early strengths. Admixture with 1·5% or more NB and CN effectively lengthens the hardening time of MKPC, but greatly decreases its fluidity. Incorporation of NB, CN and NS in the ratios 1·5%:1·5%:5% results in an initial hardening time of 37·02 min and the appearance of two temperature peaks in the hydration temperature curve. The resulting cement mix has fluidity of 115 mm and strength of 52·56 MPa after 12 h of hydration. Reaction between NB and CN creates a calcium borate film that envelopes magnesium oxide particles, preventing dissolution of magnesium oxide and generation of the hydrated product MgKPO4·6H2O (MKP), thus slowing down the hydration process. Incorporation of an appropriate quantity of NS endows fluidity of MKPC that can reach 125 mm, owing to crystal waters released during solvation and changes in phase.

Influence of lead on stabilization/solidification by ordinary Portland cement and magnesium phosphate cement

Inorganic binder-based stabilization/solidification (S/S) of Pb-contaminated soil is a commonly used remediation approach. This paper investigates the influences of soluble Pb species on the hydration process of two types of inorganic binders: ordinary Portland cement (OPC) and magnesium potassium phosphate cement (MKPC). The environmental leachability, compressive strength, and setting time of the cement products are assessed as the primary performance indicators. The mechanisms of Pb involved in the hydration process are analyzed through X-ray diffraction (XRD), hydration heat evolution, and thermogravimetric analyses. Results show that the presence of Pb imposes adverse impact on the compressive strength (decreased by 30.4%) and the final setting time (prolonged by 334.7%) of OPC, but it exerts much less influence on those of MKPC. The reduced strength and delayed setting are attributed to the retarded hydration reaction rate of OPC during the induction period. These results suggest that the OPC-based S/S of soluble Pb mainly depends on physical encapsulation by calcium-silicate-hydrate (CSH) gels. In contrast, in case of MKPC-based S/S process, chemical stabilization with residual phosphate (pyromorphite and lead phosphate precipitation) and physical fixation of cementitious struvite-K are the major mechanisms. Therefore, MKPC is a more efficient and chemically stable inorganic binder for the Pb S/S process.

Shear Strength and Microstructure of a Soil Treated by Magnesium Potassium Phosphate Cement (MKPC)

Shear Strength and Microstructure of a Soil Treated by Magnesium Potassium Phosphate Cement (MKPC)

Effect of seawater for mixing on properties of potassium magnesium phosphate cement paste

This paper aims to study the effect of seawater mixing on the properties of potassium magnesium phosphate cement (MKPC) paste. Fresh water and seawater were used to prepare MKPC pastes, respectively. Then, the compressive strength, residual ratio of compressive strength, hydration temperature, phase composition and microstructure of the MKPCs prepared with seawater and fresh water were compared. Results showed that the MKPC pastes prepared with seawater had higher fluidity, longer initial setting time and lower compressive strength than those prepared with fresh water. Adding silica fume and limestone powders to MKPC pastes prepared with seawater can accelerate the early-stage hydration and make the pastes more compact, leading to significantly less loss of compressive strength. Thus, adding some mineral admixtures into MKPC paste prepared with seawater could lessen the negative effect of seawater for mixing on the properties of hardened body. This study might provide useful information for application of seawater in mixing MKPC for marine construction.

Response to the discussion by Hongyan Ma and Ying Li of the paper “Characterization of magnesium potassium phosphate cement blended with fly ash and ground granulated blast furnace slag”

We recently reported the first comprehensive investigation of magnesium potassium phosphate cements (MKPCs) blended with supplementary cementitious materials (pulverized fuel ash and granulated blast furnace slag) for the encapsulation of radioactive wastes [Gardner et al., Cem. Concr. Res. 74 (2015) 78–87]. Using a combination of characterization techniques, we demonstrated the important role of the reaction of the supplementary cementitious materials in contributing to the development of the microstructure and strength of MKPC composites. Here, we clarify aspects of our experimental design, and elaborate on the interpretation of our data, following discussion by Ma and Li.

Discussion of the paper “Characterisation of magnesium potassium phosphate cement blended with fly ash and ground granulated blast furnace slag” by L.J. Gardner et al.

A recently published paper authored by Gardner et al. [Characterisation of magnesium potassium phosphate cement blended with fly ash and ground granulated blast furnace slag, Cem. Concr. Res. 74 (2015) 78–87] is discussed. This work is of great significance in understanding the reaction mechanism of magnesium potassium phosphate cement blended with supplementary cementitious materials. However, several points in this work need to be further discussed, as shown in this discussion, including the mix proportion, paste morphology, mechanism of the synergy between MKPC and fly ash/ground granulated blast furnace slag.