Effect of Hydrated Calcium Aluminate Cement on the Chloride Immobilization of Portland Cement Paste

To improve the efficiency and stability of chloride immobilization of portland cement paste,hydrated calcium aluminate cement(HCAC)prepared by wet grinding of CAC was added into portland cement paste as an additive.The immobilized chloride ratio(ICR)was evaluated,and the mechanism of chloride immobilization was researched by XRD,DTG,NMR,and MIP tests.The analysis results demonstrated that HCAC could improve the chloride immobilization capacity of portland cement paste.The mechanism was attributed to the following aspects:chemical binding capacity was enhanced via producing more Kuzel’s salt;physical adsorption capacity was reduced by decreasing the C-S-H gel;migration resistance was enhanced through refining the pore structure.

Chloride Corrosion of Reinforced Calcium Aluminate Cement Mortar

This paper describes a study on the corrosion behavior of steel reinforcement in CAC mortars via electrochemical methods including corrosion potential,electrochemical impedance,and linear polarization evaluation.Results indicate that there is a non-linear relationship between the corrosion degree of steel reinforcement in CAC mortar and the concentration of NaCl solution.The electrochemical parameters of specimens immersed in 3%NaCl solution suddenly drop at 40 days,earlier than 60 days of the reference.And the charge transfer resistivity of the specimen has decreased by 11 orders of magnitude at 40 days,showing an evident corrosion on steel reinforcement.However,it is interesting to notice that the corrosion is delayed by high external chloride concentration.The specimens immersed in 9%and 15%NaCl solutions remain in a relatively stable state within 120 days with slight pitting.The great corrosion protection of CAC concrete to embedded steel bars enables its wide application in marine.

Effect of Curing Temperature on Intermediate Temperature Properties of Calcium Aluminate Cement Bonded Corundum Castables

In order to study the effect of the curing temperature on the intermediate temperature properties of calcium aluminate cement bonded corundum castables,the prepared castables were cured at 5,10,25,40 and 50℃,respectively,dried at 110℃ for 24 h and heat treated at 800 and 1100 ℃,respectively.Then the apparent porosity,the cold modulus of rupture and the cold crushing strength were measured.The phase composition of castable matrix specimens treated under the same conditions and the influence of the curing temperature on the intermediate temperature strength of the castables were also analyzed.The results show that with the increase of the curing temperature,the hydration degree of calcium aluminate cement increases,which promotes the uniform distribution of hydration products with AI203 after decomposition,thus enhancing the intermediate temperature strength of castables.

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 ZnSO4g7H2O,ZnO,Zn(NO3)2·6H2O and ZnCl2,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 CA2 in CAC with different Zn^2+ are significantly reduced.It can inhibit the formation of CAH10 and promote the formation C3AH6 and AH3 in hydration products at 24 h.

Effect of ZnO Precursor on Properties of Calcium Aluminate Cement Bonded Corundum Castables

Calcium aluminate cement(CAC)bonded corundum based castables were prepared using tabular corundum and activated alumina as the starting materials,CAC as the binder,zinc hydroxide(Zn(OH)_(2))and basic zinc carbonate(BZC)as the ZnO precursors.The effects of the two ZnO precursors on the phase composition and the microstructure of the CAC bonded corundum based castable matrix specimens were analyzed,and the reasons affecting the hot performance of the castables were studied.The results show that Zn(OH)_(2) with a smaller particle size(d_(50)=1.26μm)is prone to agglomerate during sample preparation and generates ZnAl_(2)O_(4) spinel grains after firing,hindering the growth of CA_(6),thus decreasing the mechanical strength of the castables.BZC with a larger particle size(d_(50)=2.91μm),which shows a sound dispersity,in-situ generates nano-sized ZnO after firing,and ZnO or Zn^(2+)diffuses into calcium aluminates,promoting the sintering of CA_(2) and CA_(6),thereby enhancing the hot properties of the CAC-bonded corundum based castables.

Effect of Calcium Aluminate Cement Addition on Properties of Al_(2)O_(3)-SiO_(2) Based Gunning Mixes

Al_(2)O_(3)-SiO_(2) based gunning mixes were prepared with electric porcelain waste,silica fume,bauxite,quartz powder,and calcium aluminate cement(CAC)of different additions as raw materials firing at different temperatures to research the effect of the CAC addition on their phase change and properties.The results show that:from theoretical analysis of the phase diagram,with the CAC addition increasing from 8%to 14%,anorthite increases from 40.0%to 77.7%,by mass.With the rising CAC addition,the permanent linear change on heating of specimens increases;for the specimens dried at 110℃or hot-treated at 1000℃,the bulk density and the mechanical properties increase,and the apparent porosity decreases;and for those hottreated at 1300℃,the bulk density and the mechanical properties firstly increase,and then decrease,while the apparent porosity shows an opposite trend.Taking into account the phases at high temperatures and the properties,the optimal CAC addition of Al_(2)O_(3)-SiO_(2) based gunning mixes is 12%.

Fluoride Ion Adsorption Effect and Adsorption Mechanism of Self-Supported Adsorbent Materials Based on Desulfurization Gypsum-Aluminate Cement

The adsorption method has the advantages of low cost,high efficiency,and environmental friendliness in treating fluorinated wastewater,and the adsorbent material is the key.This study combines the inherent anion-exchange adsorption properties of layered double hydroxides(LDHs).Self-supported porous adsorbent materials loaded with AFm and AFt were prepared from a composite cementitious system consisting of calcium aluminate cement(CAC)and flue gas desulfurization gypsum(FGDG)by chemical foaming technique.The mineral composition of the adsorbent material was characterized by X-ray diffraction(XRD)and Scanning electron microscopy(SEM).Through the static adsorption experiment,the adsorption effect of the mineral composition of the adsorbent on fluoride ions was deeply analyzed,and the adsorption mechanism was revealed.XRD and SEM showed that the main hydration phases of the composite cementitious system consisting of CAC and FGDG are AFm,AFt,AH_(3),and CaSO_(4)·2H_(2)O.FGDG accelerates the hydration process of CAC and inhibits the transformation of AFt to AFm.The AFt content increased,and the AFm content decreased or even disappeared as the amount of FGDG increased.Static adsorption experiment results showed that AFm and AFt in adsorbent materials could significantly enhance the adsorption of fluoride ions.The adsorption of F^(−)in aqueous solution by PAG tends more towards monolayer adsorption with a theoretical maximum capacity of 108.70 mg/g and is similar to the measured value of 112.77 mg/g.

Rheological and mechanical properties of aluminosilicious cementitious materials as refractory castable binders

Metakaolin(MK)is an important refractory raw material,which has been used as a cementitious material.In order to improve the bonding strength of MK,the composite cementitious materials were prepared by MK mixed with hydrat-able alumina(HA)and microsilica(MS),respectively.The silane coupling agent(SCA)was introduced as a modifying agent.The rheological properties of MK-based composite cementitious slurries were investigated.The mechanical properties of corundum castables bonded with the composite cementitious materials and calcium aluminate cement(CAC)were comparatively studied.The results show that SCA improves the rheological properties of MK-based composite cementitious materials.The slurry of MK–MS mixture flows in a plastic manner,while the slurry of MK–HA mixture presents pseudoplastic flow.The addition of SCA reduces the yield stress value of the MK–HA slurry.The bonding strength of castables bonded with MK-based composite cementitious materials is lower than that of CAC bonding castables.The room temperature strength of MK–MS composite bonding castable remains the highest after being treated either at 1100 or 1550°C,and its high temperature modulus of rupture is higher than that of CAC bonding castables with microsilica added.