Phosphoaluminate Cement Research Articles

Effects of slag on mechanical and microstructural properties of iron-rich phosphoaluminate cement subjected to high temperature oil well environment

Iron-rich phosphoaluminate cement (shortened as PAC) exhibits excellent high temperature resistance characteristic, enabling it to withstand the ultrahigh temperatures required for the in situ combustion (ISC) of heavy oil. The addition of slag could influence its high temperature resistance by altering its hydration products. Hence the thickening time, physical properties, phase components and microstructure of PAC with slag that were subjected to different high temperature environment (315, 550 and 800 °C) were investigated deeply in this paper. The experimental analysis results revealed that PAC had better high temperature resistance than CAC with and without slag. The addition of slag improved effectively the high temperature resistance of PAC. The influencing mechanism of slag were as follows. C2ASH8 formed at 50 °C inhibited the conversion of C(A,P)H10 to C3AH6. C2AS3H, C3AS2H2 and C3(Fe,Al)S3 formed at 315 °C alleviated the rapid release of the compound water. The phase Ca5(PO4)3OH and C2AS was stable in the range of 550–800 °C. In addition, the capillary pore structure of PAC was optimized. Therefore, PAC with slag had the potential to be used for high temperature oil well cementing.

Chloride binding behavior and mechanism of phosphoaluminate cement clinker and its hydration products

As one of potential materials for extending the lifetime of reinforced concrete serving in chloride-rich environments, phosphoaluminate cement (PAC) offers excellent chloride binding capacity and superior resistance to chloride penetration. The chloride binding behavior as well as binding routes and mechanisms of the clinker and its hydration products had not been clarified so far. This study revealed that the clinker would preferentially form Friedel's salts through a dissolution-precipitation route in NaCl solutions, thereby binding chloride. This dissolution-precipitation process led to an accumulation of Al3+ in solutions, which negatively affected the subsequent hydration reactivity of the clinker. In the hydration products, the calcium hydroaluminates, mainly as C2(A,P)H8 with minor C(A,P)H10, could bind chloride rapidly via an ion exchange mechanism. Through the ion-exchange route, the chemical binding of calcium hydroaluminates to chloride could be completed in less than 1 hour. In contrast, the unhydrated clinker exhibited a slow chloride binding behavior until 72 hours. All these would provide theoretical guidance for using PAC cementitious materials in reinforced concrete to enhance resistance to chloride attack.

Physical and chemical chloride binding characteristics of the hydration products for phosphoaluminate cement

Phosphoaluminate cement (PAC) has the potential to prepare the anti-corrosive coatings for rebar due to with high compactness and resistance to chloride. Whereas, the reports of the binding type, its ratio and binding capacity of PAC for chloride ions are not found up to now. Thus, the chloride binding performance of PAC hydration products, as well as the binding isotherms and kinetic models, were investigated in this work. The experimental results showed that the binding capacity of the fully hydrated sample reached 21.03 mg/g in 0.56 mol/L NaCl solution. Up to 80 % of this total was non-water-soluble chloride, dominated by the chemical binding of calcium hydroaluminates (i.e., C(A,P)H10 and C2(A,P)H8). The water-soluble chloride at 20 ℃ accounted for only 20 % and was mainly adsorbed physically by Al(OH)3 and Fe(OH)3 gels. The whole chloride binding process of hydration products was well described using Freundlich isotherm and Elovich kinetic models. Its non-water-soluble bound chloride was more suitable for D-R isotherm and Elovich kinetic models, while the water-soluble bound chloride was more applicable to Freundlich isotherm and PSO kinetic models. These data will offer theoretical support for the rational use of PAC in constructions exposed to high chloride environments, such as the ocean.

Feasibility of using iron-rich phosphoaluminate cement to prepare anti-corrosive coatings for rebars

The anti-corrosive coating has been taken as an effective measure to keep rebars from corrosion. In this study, the iron-rich phosphoaluminate cement (IR-PAC) based anti-corrosive coating for rebar was prepared. The Cl- diffusion coefficient, strength against abrasion, and impact ductility of IR-PAC mortar were tested, with ordinary Portland cement (OPC) and sulphoaluminate cement (SAC) mortar as controls. The experimental results demonstrated that the chloride ion diffusion coefficient of IR-PAC was the lowest at any age. Compared with OPC and SAC, the strength against abrasion of IR-PAC at 90 d increased by 19.19 % and 14.32 %, respectively. The impact ductility of IR-PAC at 28 d increased by 28.21 % and 17.37 %, respectively. IR-PAC had good resistance to Cl- penetration, excellent strength against abrasion and impact ductility, which assisted the coating in blocking Cl- intrusion and resisting damage. The optimum SCMs based coating for rebar is as follows: 10.08 % Fly ash (FA), 0.1 % nano-silica (NS), and 0.65 % superplasticizer (SP). The coatings prepared with this formulation were used for electrochemical experiments. The rebars coated with IR- PAC had good corrosion resistance, which proved it is feasible to use IR-PAC to prepare anti-corrosive coatings for rebars.

Hydration characteristics of iron-rich phosphoaluminate cement: effect of accelerating admixtures on the setting time and compressive strength

Hydration characteristics of iron-rich phosphoaluminate cement: effect of accelerating admixtures on the setting time and compressive strength

Influence of PZT volume fraction, composite thickness and cement matrix on the performance of d15 shear mode 1–3 connectivity cement-based piezoelectric composites

In this work, we investigated the influence of PZT volume fraction, composite thickness and cement matrix on the performance of 1–3 connectivity cement-based piezoelectric composites working in d15 shear mode. Results revealed that the piezoelectric strain coefficient d15 and the relative dielectric coefficient εr decrease with the decrease of the PZT volume fraction and increase with the increase of the composite thickness. The piezoelectric strain coefficient d15 of the composite specimens with Phosphoaluminate cement (PALC) matrix is the largest, followed by Sulfoaluminate cement (SAC) matrix and Portland cement (PC) matrix. The relative dielectric coefficient εr of the composite specimens with PC matrix is the largest, followed by PALC matrix and SAC matrix. The piezoelectric voltage factor g15 increases with the decrease of the PZT volume fraction and decreases with the increase of the composite thickness. The piezoelectric voltage factor g15 of the composite specimens with PC matrix is the smallest, and the values of specimens with SAC matrix and PALC matrix are very close.

Variation of durability and physical performance of barium-calcium phosphoaluminate cement exposed to high temperature

The influences of high temperature on the performance of cement cannot be ignored, but there was little research on the high-temperature resistance of barium-calcium phosphoaluminate cement (PABC) based on the phosphoaluminate cement (PAC) with the excellent mechanical properties. In this paper, the durability and physical performance of PABC after exposure to elevated temperatures were discussed through the analysis of XRD, SEM-EDS and pore structure. The experimental results indicated that the resistance to chloride ions penetration and sulfate attack decreased to varying degrees at elevated temperatures ranging from 100 °C to 300 °C. Besides, high temperatures ranging from 800 °C to 1200 °C worsened the performance of cement including compressive strength, mass loss ratio and water absorption ratio, but a rise in performance can be observed at 1400 °C due to the generation of a new phase and changes of pore structure. The changing rules presented on these performance were consistent as the temperatures elevated, which demonstrated the unique characteristics of PABC confronted with high temperatures.

Chloride binding and transport characteristic of phosphoaluminate cement-based marine sand coating subjected to marine environment

Marine sand with more or less aggressive Cl− has received considerable attention because of the depletion of river sand resources; however, it should be treated to avoid harmful effects on reinforced concrete. Phosphoaluminate cement (PAC)-based coating is a promising method to treat marine sand, and it can potentially solidify Cl−. In the experiment, the characteristics of Cl− binding and transport of PAC-based coating material were thoroughly investigated. The results indicated that the characteristic of prohibiting Cl− transport by PAC was more effective than using Portland cement in terms of erosion depth and free surface Cl− concentration. The PAC-based coating material can bind large amounts of Cl− efficiently by chemical bonding and improve the electrochemical performance of steel bar. In concrete, Cl− can be bonded by PAC-based marine sand coating. Further, PAC-based marine sand coating can prohibit the transport of Cl−, and significantly improve the resistance to chloride penetration of concrete.

Early hydration properties and performance evolution of phosphoaluminate cement concrete

As a novel cementitious material, phosphoaluminate cement (PAC) has the characteristics of early strength and high strength. The early hydration properties of PAC were investigated, and the influence of curing age on concrete strength, anti-permeability, surface ventilation and micro structure was analyzed. Moreover, the inherent correlation between hydration mechanism and process of PAC was explored deeply by different test methods. The research results indicate that the curing age has significant effects on the performance development and micro structure of the concrete. The variation of concrete strength with curing age can be expressed by a Boltzmann function. Besides, the changes of relative permeability coefficient of anti-water permeability and chloride diffusion coefficient with curing age meet an exponential function. There exists a good linear relationship between natural logarithm of permeability pressure of concrete surface and time. The early hydration process of PAC is consisted of four stages, i.e., dissolution, induction, acceleration and deceleration.

Variation of resistance to chloride penetration of iron-rich phosphoaluminate cement with admixture materials subjected to NaCl environment

Iron-rich phosphoaluminate cement (iron-rich PAC) is one new type of special cement with good mechanical property and durability, which is promising to prepare inorganic coating materials and protect marine engineering. In this paper, the variation of resistance to chloride penetration of the mortars for iron-rich PAC with admixture materials (AMs), including limestone powder, gypsum and silica fume, was investigated carefully. Experimental results showed that the addition of AMs could improve significantly the resistance to chloride penetration of the mortars of iron-rich PAC. This was contributed to the decrease of porosity and reduction of pore size of the mortars of iron-rich PAC with the addition of AMs. Their appropriate addition content was 6% of limestone powder, 2% of gypsum and 4% of silica fume, respectively. Also, some new hydration products of calcium carbonaluminate hydrate (C4ACH11) and stratlingite (C2ASH8) were formed, which could optimize the ITZ area between AMs and hardened paste in the iron-rich PAC mortars.

Effect of SCMs on the freeze-thaw performance of iron-rich phosphoaluminate cement

Due to the low durability of ordinary Portland cement (OPC), the deterioration of OPC-based materials is very severe in marine structures exposed to cold weather. In contrast, iron-rich phosphoaluminate cement (iron-rich PAC) has good durability and is promising for applications in marine construction. In this context, in the present study, the freeze-thaw (F-T) performance of iron-rich PAC mortar was evaluated and compared with those of OPC and sulphoaluminate cement (SAC) mortars. In addition, the influences of supplementary cementitious materials (SCMs), such as fly ash (FA), limestone powder (LP) and gypsum (GP), on the F-T behaviour of the blended iron-rich PAC mortar were carefully investigated by testing the compressive and flexural strengths, analysing the pore structure using mercury intrusion porosimeter (MIP), and examining the microstructure using XRD and SEM-EDS analysis. The experimental results elucidated that the F-T performance of the iron-rich PAC mortar was far better than those of the OPC mortar and the SAC mortar. In the SCM blended iron-rich PAC systems, the most favourable modification results were obtained with replacement by LP at the optimum dosage of 3–9% (wt%). In this replacement range, the F-T resistances of the LP blended iron-rich PAC systems were better than that of the reference PAC (without SCMs). Further, the F-T performances of the FA and LP blended iron-rich PAC systems were superior to those of the OPC and SAC systems.

Variation in the sulfate attack resistance of iron rich-phosphoaluminate cement with mineral admixtures subjected to a Na2SO4 solution

Phosphoaluminate cement (PAC) has excellent resistance to sulfate attack due to its unique hydration product and dense hardened matrix. Mineral admixtures (MAs) are also known to enhance the performance of conventional cementitious systems. Thus, in this study, the effects of three kinds of admixtures (limestone powder, fly ash and gypsum) on the performance of iron rich-phosphoaluminate cement (IR-PAC) against sulfate attack were analysed using XRD, MIP, DSC and MTS to examine any synergistic effects resulting from their combination. The results indicated that excessive limestone powder incorporation (more than 9%) was detrimental to the IR-PAC performance. The addition of fly ash resulted in fluctuation of the flexural strength of the mortar due to the reduction in cement content and the micro-aggregate action of fly ash particles. The resistance coefficient of the IR-PAC mortars (against sulfate attack) with fly ash replacement of 9% (by weight) at 90 d could reach 1.13–1.16, and at a 12% replacement, the value could even reach 1.12. The addition of gypsum could transform etched components in IR-PAC mortar into ettringite in the early stage of cement hydration. As a result, the IR-PAC could maintain the stability of its own components under external sulfate erosion. However, excessive gypsum at the expense of cement would cause a decrease in the strength of the mortar and result in a slight reduction in the sulfate attack resistance coefficient.

Effect of BaO on mechanical and hydration characteristic of C8A6P as predominant mineral in phosphoaluminate cement

Phosphoaluminate cement clinker (PAC) was one type of cementitious material due to its high durability and mechanical performance. As the predominant mineral phase in PAC, the high-temperature formation and property of calcium phosphoaluminate mineral (C8A6P) were related closely with hydration and mechanical characteristic for PAC. Thus, the influence of BaO on the performance of C8A6P mineral phase was investigated carefully in this paper. It was found that BaO of 17.5–20% content could endow C8A6P mineral with predominant mechanical performance. This was due to the fact that C8A6P mineral was activated by BaO. Excessive BaO would lead to the formation of new unexpected phase BaO·Al2O3. The limited solid solubility of BaO in C8A6P mineral was 20%. The addition of BaO changed the ratio of hydration products of C2(A,P)H8 and C(A,P)H10 for C8A6P mineral.

Effect of BaO on mineral structure and hydration behavior of phosphoaluminate cement

Phosphoaluminate cement (PAC) clinker was one new type of special cement, which exhibits good mechanical properties and durability. In this paper, the effect of BaO on the mineral structure and hydration behavior of PAC clinker were investigated. The experimental results showed that the mineral structure of PAC clinker was modified by the addition of barium oxide (BaO). The optimal content of BaO in PAC clinker was 10.5 mol% (the substitution mole ratio of BaO for CaO, calcium oxide). Compared with reference specimen, the rate of strength growth of hardened paste for PAC clinker with 10.5% BaO cured for 1, 3, 7 and 28 days was 50.8, 21.0, 27.0 and 49.9%, respectively. The possible reason was that the addition of BaO could activate crystal structure of calcium phosphoalumniate (8CaO·6Al2O3·P2O5, C8A6P, C8A6P) and improve its hydration activity, which has been proven by the XRD and hydration heat analysis. The addition of BaO also affected the ratio of hydration products of PAC clinker, which were illustrated by XRD and DSC analysis. The MIP analysis showed that the addition of BaO could optimize the pore structure of hardened paste for PAC clinker, which was accordance with the discussion of compressive strength of hardened paste for PAC clinker. In conclusion, the addition of BaO dramatically improved the compressive strength of hardened paste for PAC clinker and changed remarkably its ratio of hydration products.

Effect of BaO on the calcination and hydration characteristic of CA

Phosphoaluminate cement (PAC) clinker had good mechanical properties at early and long-term period. In comparison, the compressive strength of PAC clinker modified by BaO was more prominent. As primary mineral phase for PAC clinker, CA’s mineralogical structure and hydration characteristics were intimately related to the compressive strength of hardened cement paste. In this study, the effects of BaO content on the calcination, mineralogical structure and hydration characteristics of CA were investigated. Experimental results showed that the appropriate calcination temperature of CA was 1400 °C. No more than 11% (the substitution ratio of BaO for CaO) addition of BaO can promote the conversion of C12A7 to CA and increase the formation ratio of CA. Appropriate content of 7 mol% BaO could endow the hardened paste with excellent compressive strength. In CA mineral phase the high limit addition of BaO was 15 mol%. The addition of BaO decreased and even restrained the formation of C2AH8 and C3AH6 of CA hydration products and also improved the content of CAH10. The addition of BaO dramatically decreased the hydration velocity and cumulative heat of CA mineral.

Amphoteric ion polymer as fluid loss additive for phosphoaluminate cement in the presence of sodium hexametaphosphate

The fluid loss of modified aluminate phosphate cement system with excellent CO2 resistant ability cannot meet the demand of cementing engineering and the conventional fluid loss additive lose effectiveness in this cement system. The aim of this paper is to reveal the failure mechanisms of the conventional fluid loss additive and develop one kind of amphoteric ion polymer to control the fluid loss. Results showed that massive of sodium hexametaphosphate exists in cement system limits the hydration and expansive degree of hydrophilic group of fluid loss additive and succeeds in the competition with fluid loss additive for adsorbing on the surface of cement particle. Using 2-acrylamido-2-methyl propane sulfonic acid, acrylamide, diallyl dimethyl ammonium chloride, and itaconic acid, a new fluid loss additive which has excellent ability to control fluid loss is synthesized by free radical aqueous solution copolymerization. The reducing fluid loss function of this kind of fluid loss additive is achieved by the cationic groups adsorbing on the surface of cement particle and anionic groups absorbing water to achieve hydration expansion to plug the flow passages between the cement particles. However, the dosage of this kind of fluid loss additive is limited by the negative retarding effect.

Constituent phases and mechanical properties of iron oxide-additioned phosphoaluminate cement

Iron oxide was added to phosphoaluminate clinker and its effects on cement constituents were determined using XRD, DSC, SEM-EDS and conduction calorimetry analysis. The variations in compressive strength were also studied. The results showed that in moderate amounts, iron oxide acts as a mineraliser during clinker sintering, furthering the conversion of CA1-Y(PY) to LHss at a lower temperature than normally required for that reaction. The main constituents of iron oxide-rich phosphoaluminate clinker included LHss, CA1-Y(PY), CP1-Z(AZ) and ferrite. The EDS findings showed that the composition of the ferrite phase was nonuniform. The conclusion drawn was that by modifying the dose of Fe2O3) , the composition of phosphoaluminate cement can be controlled to produce clinker and cement compliant with different mechanical strength requirements. The conduction calorimetry findings were consistent with those results.

Treatment of toxic metal aqueous solutions: Encapsulation in a phosphate-calcium aluminate matrix

Polyphosphate-modified calcium aluminate cement matrices were prepared by using aqueous solutions polluted with toxic metals as mixing water to obtain waste-containing solid blocks with improved management and disposal. Synthetically contaminated waters containing either Pb or Cu or Zn were incorporated into phosphoaluminate cement mortars and the effects of the metal's presence on setting time and mechanical performance were assessed. Sorption and leaching tests were also executed and both retention and release patterns were investigated. For all three metals, high uptake capacities as well as percentages of retention larger than 99.9% were measured. Both Pb and Cu were seen to be largely compatible with this cementitious matrix, rendering the obtained blocks suitable for landfilling or for building purposes. However, Zn spoilt the compressive strength values because of its reaction with hydrogen phosphate anions, hindering the development of the binding matrix.

Preparation and performance of a lignosulfonate–AMPS–itaconic acid graft copolymer as retarder for modified phosphoaluminate cement

In this article, a new type of graft copolymer retarder as modified phosphoaluminate cement (MPC) has been discussed. Graft copolymerization of 2-acrylamido-2-methyl propane sulfonic acid (AMPS) and itaconic acid (IA) onto sodium lignosulfonate (LS) was performed using potassium persulfate as an initiator by free radical aqueous solution copolymerization. The optimal LS/AMPS/IA copolymer (OLSAI) was obtained under the optimum reaction conditions: mass ratio of LS/(AMPS+IA)=1:1, temperature=60°C, mole ratio of AMPS/IA=9:1, initiator concentration=1%, pH value=5. The synthesized copolymer OLSAI was characterized by FTIR analysis. The experimental results demonstrate that the OLSAI has excellent retarding ability, dispersing power, thermal-resistant and pressure-tolerant properties, and little negative impact on the compressive strength of MPC. The graft copolymer OLSAI is expected to be an excellent retarder for MPC.

Influence of Nano-Clay on the Performance of phosphoaluminate cement

The influence of nano-clay on the physical and mechanical properties of the phosphoaluminate cement (PALC) was studied in the paper. The experimental results showed that nano-clay changed the water requirement of normal consistency and the setting time of phosphoaluminate cement. However its soundness was not affected by adding nano-clay. With 3% nano-clay added by weight of cement, PALC has an optimum compressive strength.