Effect of the Retarder on Initial Hydration and Mechanical Properties of the"one-step"Alkaliactivated Composite Cementitious Materials

This paper studied the effects of different retarders on the performance of the"one-step"alkali-activated composite cementitious material(ACCM)which is composed of ground granulated blast slag(GGBS)and fly ash(FA),and analyzed its mechanical properties,hydration mechanism,and retardation mechanism.The effects of retarders on the hydration products,mechanical properties,and hydration kinetics of ACCM were investigated using XRD,SEM,FTIR,EDS,and thermoactive microcalorimetry.The results showed that Na_(2)B_(4)O_(7)·10H_(2)O(B)delayed the exotherm during the alkali activation process and could effectively delay the setting time of ACCM,but the mechanical properties were slightly decreased.The setting time of ACCM increased with the increase in SG content,but the mechanical properties of ACCM decreased with the increase in SG content.C1_(2)H_(22)O_(11)(CHO)could effectively delay the hydration reaction of ACCM and weakly enhanced the compressive strength.H_(3)PO_(4)(HP)at a concentration of 0.05 mol/L had a certain effect on ACCM retardation,but HP at a concentration of 0.07 and 0.09 mol/L had an effect of promoting the setting and hardening time of ACCM.

Synergistic Flame Retardant Effect of Ammonium Polyphosphate and Aluminum Hydroxide on Polyurethane

The flame-retardant properties of polyurethane(PU)containing ammonium polyphosphate(APP)and aluminum hydroxide(ATH)were investigated.Moreover,the flame retardant performance was investigated through thermogravimetric analysis,limiting oxygen index(LOI),vertical combustion(UL 94),and cone calorimeter.When 15 wt%APP and 5 wt%ATH were added together,the PU/15%APP/5%ATH sample shows better thermal stability and flame-retardant properties.When 15 wt%APP and 5 wt%ATH were added together,the LOI value of the PU/15%APP/5%ATH sample was 30.5%,and UL 94 V-0 rating was attained.Compared with PU,the peak heat release rate(PHRR),total heat release(THR),and average effective heat combustion(av-EHC)of the PU/15%APP/5%ATH sample decreased by 43.1%,21.0%,and 29.4%,respectively.In addition,the flame-retardant mechanism was investigated through cone calorimeter.The APP/ATH addition simultaneously exerted condensed phase and gas phase flame retardant effects.APP and ATH have synergistic flame retardant properties.

Application of diffusive transport model for better insight into retardation mechanisms involved in ion-imprinted membrane transport

Heavy metal removal from water is a great concern for environmentalists and engineers. Ion-imprinted membranes are among the state of the art technologies for selective adsorption of heavy metals from aqueous environment. Dialysis permeation of nickel ions through Ni(II)-imprinted membranes has been thermodynamically studied in our prior work. In current study, the diffusive transport model was developed and then applied for better insight into the retardation mechanisms involved in the ion-imprinted membrane transport. The Sips isotherm model was coupled with the transport model to obtain the governing equation. Chemisorption and physical interactions(bulk diffusion and pore-clogging) were the most probable retardation mechanisms according to the modeling results. Relative retardation factor(η) was also defined as; transport-rate controlled by chemical adsorption to that controlled by physical interactions. With the help of the retardation factor, it was understood that the membrane behavior gradually changes from chemisorption to facilitated transport during permeation time. Effect of important operating parameters such as time, temperature and concentration on transport behavior was also investigated. Results indicated that chemisorption rate is rather higher at lower concentrations, early permeation times and reduced temperatures. In addition, η tabulated greater values for Ni(II) compared to Co(II) due to the imprinting effect.

Experimental study on retarding mortar and its application in prestressed concrete

Based on a large number of orthogonal tests and theoretical analyses, the retarding mortar which meets the requirements of retard-bonded prestressed concrete was prepared. Initial setting time of the retarding mortar may vary from several hours to 15 d at 5 ℃-35 ℃ due to quantities and average curing temperature. And its 28 d compressive strength is above 35 MPa. Thus the influence of quantities on setting time and 28 d compressive strength, and the relationship between setting time and average curing temperature were investigated. The optimum quantities were obtained by studying the interaction of admixtures, and the retarding mechanism was discussed. Based on 52 retard-bonded prestressed strands by manual work from 24 retard-bonded prestressed concrete T-beams, static friction drag, change factor κ and friction factor μ were obtained from the test when retard-bonded prestressed strands were tensioned. Application of the retarding mortar will be vast in practical concrete projects.

Effects of processing parameters and addition of flame-retardant into moulding sand on the microstructure and fluidity of sand-cast magnesium alloy Mg-10Gd-3Y-0.5Zr

In this study, the effects of processing parameters（such as pouring temperature and mould pre-heating temperature） and flame-retardant content on the microstructure and fluidity of sand-cast magnesium（Mg） alloy Mg-10Gd-3Y-0.5Zr（GW103K） were systematically investigated. It was found that the increase of pouring temperature leads to coarsened microstructure and decreased fluidity of sand-cast GW103 K alloy. Increase of mould pre-heating temperature incurs coarsening of as-cast microstructure and increase of fluidity. The addition of flame-retardant into moulding sand has a negligible influence on the microstructure of sand-cast GW103 K alloy. With the increase in flame-retardant content,fluidity of the alloy initially increases and then decreases. The optimized process parameters and flameretardant addition were obtained to be pouring temperature of 750？C, mould temperature of 110？C, and flame-retardant addition of 1%. The fire retardant mechanism of moulding sand was determined.

The effect of metal ions with different valences on the retardation of soil–bentonite barrier materials and its mechanism

In this paper, with K＋, Ca2＋ and Fe3＋ as the objects of study, retardation of soil-bentonite （SB） barrier materials for metal ions with different valences is investigated, and the adsorption mechanism, migration patterns and permeation behavior are explored so as to provide a theoretical basis for their application. The results show that the adsorption process for metal ions with different valences by SB barrier materials is fast, and the higher the valence, the greater the adsorption capacity. The fitting of the adsorption process conforms to pseudo-second-order adsorption kinetics and Langmuir-Freundlich adsorption equation, which explains that chemical adsorption is the dominating state and that the SB surface has certain heterogeneity. The permeability coefficient of K＋, Ca2＋ and Fe3＋ in SB each has a maximum and the higher the valence, the sooner the maximum appears. Also the higher the valence, the more obvious the effect on SB retardation performance; and the sooner the ion breaks through the barrier wall completely, that is, the wall＇s retardation performance for higher valent ions may decline.

Synergistic effects of zeolitic imidazolate frameworks(ZIFs)with different transition metals on intumescent flame-retarded polypropylene composites:A comparative study

The use of intumescent flame retardants(IFRs)is considered an environmentally friendly and cost-effective strategy to suppress potential fire hazards from synthetic polymers.However,some conventional IFRs are neither efficient in developing a thermally stable char layer nor reducing the release of toxic byproducts during polymer combustion.In this work,we aim to discuss the effects of zeolitic imidazolate frameworks(ZIFs)on synergistically improving the flame retardancy behaviors in polypropylene(PP)composites,including thermal degradation(evolved gas analysis),free radical reactions in the gaseous phase(in-situ chemiluminescent image analysis),and carbonaceous structure in the condensed phase(micro-morphology and composition analysis).It is found that the transition metals in ZIFs can catalytically accelerate the crosslinking reaction at a lower initial temperature and decrease the amount of hydrocarbon volatiles in the gaseous phase.Once ignited,the embedded ZIFs can firstly bridge adjacent phosphorus chains in the polymer matrix to expand crosslinking degrees and then they are anchored in the developed N-doped phospho-carbonaceous networks after pyrolysis.As a result,more compact char residue structures are observed in the condensed phase for ZIF-reinforced composites.For example,by replacing 2 wt%of IFR with ZIF-67,the peak heat release rate,peak smoke production rate,and peak CO production rate are reduced by 69%,80%,and 72%,respectively,when compared to the conventional composite.These results indicate an excellent solution to resolve inherent fire hazards associated with IFRs in polymers and achieve necessary efficiency for industrial applications.It also provides a new strategy for determining flammability characteristics and combustion mechanisms of polymer composites using in-situ chemiluminescence analysis.

Recent Progress in Two-dimensional Nanomaterials Following Graphene for Improving Fire Safety of Polymer(Nano)composites

The high fire safety of polymer nanocomposites is being pursued by research institutions around the world.In addition to intrinsic flame retardancy strategy,the additive-type flame retardants have attracted increasing attention due to low commercial cost and easy fabrication craft.However,traditional additive-type flame retardants usually need high addition amount to achieve a desirable effect which causes many side-effects on the overall performance of polymer materials,such as deteriorated mechanical property and processability.At present two-dimensional(2D)nanomaterials have also been applied to reduce the fire hazards of polymer(nano)composites with the coupling of barrier function and catalysis as well as carbonization effect.Even though most research work mainly focus on graphene-based flame retardants,more emerging two-dimensional nanomaterials are taking away research attention,due to their complementary and unique properties,mainly including hexagonal boron nitride(h-BN),molybdenum disulfide(MoS2),metal organic frameworks(MOF),carbon nitride(CN),titanium carbide(MXene)and black phosphorene(BP).In this review,except for graphene,the flame retardant mechanism involving different layered nanomaterials are also reviewed.Meanwhile,the functionalization method and flame retardancy effect of different layered nanomaterials are emphatically discussed for offering an effective reference to solve the fire hazards of polymer materials.Moreover,this work objectively evaluates the practical significance of polymer/layered nanomaterials composites for industrial application.