Investigation of Phosphate Cement-based Binder with Super High Early Strength for Repair of Concrete

Magnesium phosphate cement- based binder ( MPB ) for repair of concrete was prepared by proportionally mixing over burned MgO powder ( M) with NHH2 PO4 powder ( P) and set modifying admixtures . It is characteristic by excellent properties such as rapid setting, high strength and high bond strength to old concrete .. The study is focused on the key factors influencing the setting time and strength of MPB, the bond property of MPB to old concrete and the kinetic feature of the hydration of MPB,     

Early Hydration and Setting Process of Fly Ash-blended Cement Paste under Different Curing Temperatures

A specially developed ultrasonic measurement apparatus (UMA) was used to in situ monitor the setting process of fly ash blended cement paste.Combined with the results of Vicat Needle tests,isothermal calorimetric measurement,XRD analysis,SEM morphology and compressive test,the influence of curing temperature (20,40,60,and 90 ℃) and fly ash content (0,10%,20% and 30%) on the setting and hydration process of fly ash blended cement paste was analyzed.The results show that setting and hardening process of fly ash blended cement paste at elevated temperature can be clearly identified into three stages including dormant stage,acceleration stage and deceleration stage.The increasing of curing temperature greatly accelerates the setting and hardening process.However,the content of fly ash does not have significant effect on the setting in condition of 90 ℃.Besides,the initial and final setting time of cement paste is correspondent with the time of duration of dormant stage and the time of UPV value is 1 500 m/s (T1500),respectively.Thus,the UMA can be used to determine the initial and final setting time of cementitious material under different curing temperatures.The compressive test results indicate that the paste with 20% fly ash presents higher compressive strength than the plain paste at curing temperatures of 90 ℃.Therefore,appropriate amount of fly ash is beneficial for concrete in the high temperature curing conditions.     

Effects of Calcination Temperature of Boron-Containing Magnesium Oxide Raw Materials on Properties of Magnesium Phosphate Cement as a Biomaterial

A new magnesium phosphate bone cement(MPBC) was prepared as a byproduct of boroncontaining magnesium oxide(B-MgO) after extracting Li_2CO_3 from salt lakes. We analyzed the elementary composition of the B-MgO raw materials and the effects of calcination temperature on the performance of MPBC. The phase composition and microstructure of the B-MgO raw materials and the hydration products(KMg PO_4·6H_2O) of MPBC were analyzed by X-ray diffraction and scanning electron microscopy. The results showed that ionic impurities and the levels of toxic elements were sufficiently low in B-MgO raw materials to meet the medical requirements for Mg O(Chinese Pharmacopeia, 2010 Edition) and for hydroxyapatite surgical implants(GB23101.1-2008). The temperature of B-Mg O calcination had a marked influence on the hydration and hardening of MPBC pastes. Increasing calcination temperature prolonged the time required for the MPBC slurry to set, significantly decreased the hydration temperature, and prolonged the time required to reach the highest hydration temperature. However, the compressive strength of hardened MPBC did not increase with higher calcination temperatures. In the 900-1 000 ℃ temperature range, the hardened MPBC had a higher compressive strength. Imaging analysis suggested that the setting time and the highest hydration temperature of MPBC pastes were dependent on the size and crystal morphology of the B-Mg O materials. The production and microstructure compactness of KMgPO_4·6H_2O, the main hydration product, determined the compressive strength.     

Effect of Different Kinds of Zinc (Ⅱ) on Early Hydration of Calcium Aluminate Cement

The early hydration of calcium aluminate cement (CAC) with different kinds of zinc (II),such as ZnSO_4g7H_2O,ZnO,Zn(NO_3)_2·6H_2O and ZnCl_2,was analyzed.Changes in consistency,setting time,hydration heat flow,hydration heat amount,ion concentration in solution,and hydration products were found upon the addition of different Zn~(2+).The water consumption of standard consistency of CAC is decreased with different Zn~(2+).Zn~(2+) can delay the initial hydration of CAC.The induction period of cement with Zn~(2+) is longer than that of CAC,especially the reaction time of the acceleration period is extended.Zn~(2+) can promote hydration hydrate of CAC at 24 h.The characteristic diffraction peaks of CA and CA_2 in CAC with different Zn~(2+) are significantly reduced.It can inhibit the formation of CAH_(10 )and promote the formation C_3AH_6 and AH_3 in hydration products at 24 h.     

Hydration mechanism of silica fume-sulphoaluminate cement

Setting time and strength of sulphoaluminate rapid hardening cement （SAC） incorporated in the presence and absence of silica fume （SF） were determined. Combined with the techniques of＂ isothermal calorimeter, XRD and FSEM, the hydration kinetics of the two systems and the effect mechanism of SF on SAC were investigated. The experimental results showed that SF was proved to be beneficial for SAC system, in terms of setting time and late strength gain. Evidence of accelerator effect of silica fume was found during the first 8 hours of hydration. The formation of AFt was accelerated and the microstructure of the hydration products grew denser with incorporation of SF. SF was proved to play the role of dispersion and setting control at early age and had a greater contribution to later strength due to the increment of crystal nucleation point and the pozzolanic activity. Therefore, SF can be used to not only control the hydration kinetics of SAC, but also develop the late strength and improve the microstructure.     

Effect of Triisopropanolamine on the Compressive Strength and Early Hydration of Cement at Low Temperature

Triisopropanolamine (TIPA) was used as an early strength component to study its effects on mortar strength,cement paste setting time and early hydration characteristic of cement.And the early strength mechanism of TIPA at low temperature of 5 ℃ was also discussed.The results showed that,at 5 ℃,the incorporation of TIPA promoted the condensation of cement paste,shortened the initial and final setting time,and accelerated the strength development of specimens at all ages,among which the strength after 3 d increased significantly.The 1,3,7,and 28 d compressive strength ratios of the mortars mixed with 1% TIPA could reach 196%,179%,160% and 110% respectively,and the mortar strength after 3 d exceeded that of the contrast sample cured at 20 ℃.Under low temperature condition,TIPA could promote the hydration reaction of cement,shorten the induction period and advance the acceleration period.Furthermore,the maximum heat release rate and cumulative heat release quantity would be all increased,and the cumulative heat release of the cement mixed with TIPA hydrated for 12 h and 7 d increased 73% and 38% respectively.TIPA could shorten the nucleation and crystal growth (NG) stage and increase its hydration degree significantly,so it promoted cement hydration reaction.Additionally,the hydration reaction rates in phase boundary reaction (I) phase and diffusion reaction (D) phase were increased,and the duration of I process was prolonged,thereby the development of specimen strength would be accelerated.TIPA did not obviously change the types of hydration products,but increased the content of Ca(OH)_2 in the samples and the degree of cement hydration.After hydration to 7 d,large amounts of hydration products,whose surface was smooth,were formed and bonded into sheets,and the structural density of samples improved significantly.     

Hydration swelling characteristics of needle-punched geosynthetic clay liners

A series of confined swell tests were conducted on a needle-punched geosynthetic clay liner (GCL) with tap water as the hydration medium. The effects of the static confining stress on the swelling characteristics of GCLs and the hydration time under different confining stresses were explored. Increasing the static confining stress led to: shorter hydration time; smaller final GCL height; less final GCL bulk void ratio; smaller final bentonite moisture content. The confined swell pressure determined for the tested GCL was 82.2 kPa, and the relationships between confining stress, final bulk void ratio (or final GCL height, final bentonite moisture content) were attained through the analyses of the confined swell test results in this study.     

Hydration Behavior and Cementitious Properties of Calcium Carbonate-aluminate Minerals Composite

The purpose of this research is to investigate the hydration behavior and cementitious properties of the mixture of calcium carbonate and aluminate, and to explore whether it can be adopted as a new low-carbon cementitious material. The composite system of calcium carbonate and aluminate minerals is studied by measuring the component of hydration products, the hydration heat, setting time and compressive strength.The results prove that the composite system has certain cementitious properties and...     

Hyperbolic method to analyze the electrical resistivity curve of Portland cements with superplasticizer

Electrical measurement was employed to investigate the early hydration characteristics of cement pastes with different dosages of superplasticizer in the same W/C ratio. The hyperbolic method was applied to analyze the electrical resistivity development. The peak point （Ph） on the hyperbolic curve could be easily read. The time （th） to reach the point Ph had strong relations with the setting time. th was delayed with the increment of the dosage of superplasticizer. The time th was used to plot the relationship between the initial setting time and final setting time. The hyperbolic equation was established to predict the ultimate resistivity. The retardation effect of the superplasticizer was confirmed in the same W/C ratio by setting time and isothermal heat evolution.     

Effects of Ag on microstructure and mechanical properties of 2519 aluminum alloy

The effects of Ag on the microstructure and mechanical properties of 2519 aluminum alloy were investigated by means of tensile test, micro-hardness test, transmission electron microscope and scanning electron microscope. The results show that the addition of 0.3 % （mass fraction） Ag accelerates 2519 aluminum alloy＇s age-hardening, increases its peak hardness and reduces 4 h of peak aged time at 180 ℃. The addition of 0. 3% （mass fraction） Ag increses the tensile strength at room temperature and elevated temperature. This increment at room temperature and 200 ℃ is 24 MPa and 78 MPa, respectively. In contrast, the elongation of 2519 aluminum alloy is decreased with Ag addition. The increase of tensile strength of 2519 aluminum alloy with Ag addition is attributed to the high volume fraction of Ω phase.     

Effect of Glutinous Rice Flour on Mechanical Properties and Microstructure of Cement-based Materials

The mechanism of glutinous rice flour, a kind of natural admixture, on the hydration process,setting time, and microstructure of the Portland cement was investigated. The experimental results show that the glutinous rice flour has an obvious setting retarding effect on cement pastes. The optimal dosage of the glutinous rice flour is 3wt%. In this case, the initial and final setting time of the paste are delayed by 140 and185 min, respectively. The flexural and compressive strengths of the harden...     

Magnesia Modification of Alkali-Activated Slag Fly Ash Cement

A new type of magnesia modification alkali-activated cement was prepared, the strength, setting time, shrinkage ratio and cracking behavior, as well as the composition and structure of the hydration product were investigated. The results indicate that the setting time of this cement is similar to that of the ordinary commercial cements; its strength reaches the standard of 42.5 degree cement, its cracking resistance has been remarkably improved because of the micro-aggregate effect of fly ash and shrinkage compensating of magnesia.     

Effect of Different Ways of STPP Retarder Addition on Properties of Recycled Gypsum

We analyzed the influence of sodium polyphosphate(STPP) on the performances of recycled gypsum(RG). This analysis was performed with two different ways of STPP addition: One was that the STPP was added into Plaster of Paris(POP), then recycled plaster(R-SP) was obtained after a series of processes and the other was that the STPP was directly put into recycled plaster(R-PS). The conclusions confirmed that STPP increased the water demand and delayed the hydration of R-PS. With regard to its hardened performance, STPP provided hardened recycled gypsum with a loose structure which led to the lower strength and higher water absorption than recycled plaster(R-P) without STPP. On the contrary, the water requirement and the setting time were decreased and shortened by STPP in R-SP, respectively. A dense structure was also possessed by R-SP which contributed to the high strength and low water absorption. The analysis shows that STPP is selectively chemisorbed on the(111) face of R-PS crystals, it inhibits the growth in c axis direction, resulting in the extending of setting time and the transformation of morphology, making the hardened R-PS crystals coarsened, which results in high W/P and low strength. Whereas the low W/P is made by both the rod-like crystals of low length-radius possessed by R-SP and the relatively high ζ-potential absolute value caused by –(PO_3Ca) on the surface of R-SP, leading to the complete development of crystals and their close overlapping, thus bringing about the increase of strength.     

Activation of anhydrate phosphogypsum by K<Subscript>2</Subscript>SO<Subscript>4</Subscript> and hemihydrate gypsum

Lime pretreated phosphogypsum(PG) was calcined at 500 ℃ to produce anhydrate gypsum cement. Due to the slow hydration of anhydrate gypsum, additives, K2SO4 and hemihydrate gypsum were selected to accelerate the hydration of anhydrate. The hydration characteristics, the resistance to hydrodynamic water, and the mineralogical studies were investigated. The experimental results suggest that activated by K2SO4 and hemihydrate, anhydrate PG hydrates much more rapidly than that in the presence of only K2SO4 or in the absence of additives. The binder has proper setting time, good strength development, and relatively better resistance to water. The hardened binder has hydrated products of rod or stick like shaped dihydrate gypsum crystals.     

Osteogenesis Capacity of a Novel BMP／a-TCP Bioactive Composite Bone Cement

To improve the osteogenesis ability of α-trkalcium phosphate (a-TCP ) bone cement, a novel BMP/ a- TCP composite bone cement was prepared. By measuring the setting time and compressive strength, the hydration characteristic of bone cemtwnt icts eralnated. Animal experiments including histological observation, radiographic investigation as well as digital image analyses reveal the difference of osteogenesis ability among BMP, a TCP bone cetnent and BMPI a-TCP composite bone cement, Results show that a-TCP bone cement possesses excellent hydration and setting properties as well as high mechanical property, Comparison experiments show that BMPI a-TCP composite bonc cement has a stronger osteogenesis obility. The gross observation of the implant site does not exhibit any inflammation or necrosis. Histohwcal analyses reveal that the material has good osteointegration with host bone, and new bone formntion is detected within the materials, which are degrading. Strong osteogenesis ability of the composite is due to not only the excellent osteoconductive potential but also the osteoinductive potential contributed by attire BMP releasing and the material degradation . Large skull defect could be well-healed ty filling BMPl a-TCP composite bone cement. This novel material proves itself to be an absorbable and bioaetive bonecement with an osteogenesi ability.     

Preparation of Anhydrate Phosphogypsum Binders

In this work,phosphogypsum(PG) with a small amount of lime was thermally pretreated at 450 ℃ to produce anhydrate gypsum for the purpose of searching new ways for utilization of waste PG. Additives,K2SO4 and one selected seed crystal(SC),were used as activator for anhydrate PG. The hydration characteristics of the anhydrate PG binders were investigated by determination of the setting time,the ratio of hydrated anhydrate PG,the compressive strength development,and the microstructure of the hardenite. The resistance to water was studied by measuring mass loss of binders exposed to hydrodynamic water. Results suggest that activated by K2SO4 and SC,anhydrate PG hydrates much more rapidly than that without additives. The anhydrate PG binder with K2SO4 and SC has proper setting time and good strength developments. SEM photos show that the set binders have hydrated products of rodlike and regularly shaped crystals. Those crystals connected closely,and the hardenite has a compact structure,which is beneficial to the obtainment of good properties.     

Effects of Coal Metakaolin on the Mechanical Properties and Microstructure of High-belite Sulphoaluminate Cement

The effects of coal metakaolin on the mechanical properties of high-belite sulphoaluminate cement under compressive loading were investigated. The composition and microstructure of hydration products at different hydration times were analyzed by X-ray diffraction and scanning electronic microscopy. The hydration process of blended cement was studied via electrochemical impedance spectroscopy. In particular,replacing a part of cement with CMK (10%, 20%, and 30%) was found to promote the hydration...     

Effect of Active Mineral on Load-Bearing Autoclaved Aerocrete

Influence of ultrafine active mineral (DK mineral) on mechanical property of fly ash based load-bearing aerocrete was analyzed. The result shows that the addition of DK mineral in a suitable amount can enhance obviously the compressive strength of aerocrete. According to the SEM-EDS and X-ray diffraction analyses, the crystal shapes of hydration products are well developed and interlocked for samples containing DK mineral. Its microstructure is denser than that of the samples without DK mineral. Having a good activation, the DK mineral makes both the type and the quantity of hydrated products be obviously superior to that of the contrast sample.     

Effect of calcium aluminate cement variety on the hydration of portland cement in blended system

Two kinds of CACs with different monocalcium aluminate（CA） contents were used in the PC/CAC（PAC） mixtures. Effects of CA and CACs on the properties of PAC were analyzed by setting times and the compressive strength tests, and also by means of calorimetry, XRD, DTA-TG and ESEM. The experimental results show that the compressive strength of the PAC mortars decreases with increasing content of CAC while it declines sharply with a higher content of CA in CAC. Compared with neat PC paste, the content of calcium hydroxide in hydrates of PAC paste decreases significantly, and the hydration time of PC is prominently prolonged. Additionally, the higher the content of CA in CAC, the more obviously the hydration of PC is delayed, confi rming that the CA phase in CAC plays an important role in the delay of PC hydration.     

Microstructure and Properties of Activated Slag Cement

Activation of the slag cement was performed using a composite activator. Experimental results show that the performance of the cement is remarkably improved. The fineness and specific surface area of the cement are increased by 23.7% and 1.4% , and 3d flexural strength and compressive strength are enhanced by 20.9% and 22.9%, respectitely. Microstructure and phase composition of the hydrates were analysed by X-ray diffraction( XRD ) and scanning electron microscopy( SEM ). The results indicate that Ca(OH)2 in the hydrates decrease obvioasly. The morphology of the other hydrates appears to be flocculent, with a dense structure. The improvements of the properties is related to the microstructural changes.