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The structural parameters, electronic structures, and mechanical and thermodynamic properties of TaSi2 under different pressures have been completely explored by a combination of density functional theory and quasi-harmonic Debye model. Results show that our computed structural parameters and elastic constants are in consistency with available experimental findings and previous theoretical calculations. The electronic structures of TaSi2 under different pressures including band structures and density of states are reported. It turns out that TaSi2 should be metallic. The elastic constants Cij , bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio ν, B/G, Debye temperature θ, and wave velocities under pressures are also evaluated successfully. The calculated Cij obeys the Born–Huang stability criterion, which demonstrates that TaSi2 is mechanically stable under different pressures. More interestingly, the three-dimensional surface constructions and projections of E and B under different pressures are also systematically evaluated. With the increase of applied pressure, TaSi2 exhibits subtle anisotropy under zero pressure, and the anisotropy strengthened. Finally, the dependence of the thermodynamic properties on pressure/temperature is obtained and analyzed for the first time.

The consolidation properties of soil-bentonite (SB) backfills containing 20% of the weight of sodium-hexametaphosphate-modified calcium bentonite (SHMP-20CaB) and prepared with 0 mM to 1000 mM calcium chloride (CaCl2) solution were evaluated. The results indicated that both consolidation stress and CaCl2 concentration had significant effects on the consolidation behaviors of the SHMP-20CaB backfill. In general, an increase in consolidation stress resulted in a decrease in the void ratio (e) and in the coefficient of volume change (mv), alongside an increase in the coefficient of consolidation (cv). The increased CaCl2 concentration yielded a dropped void ratio, and a nonlinear decreased compression index (Cc) and rebound index (Cs), respectively, from 0.18 to 0.13 and from 0.022 to 0.010, and a nonlinear increase cv. A threshold CaCl2 concentration of 100 mM was observed at the inflection points of the Cc, Cs, and cv. In contrast, the mv was insensitive to the CaCl2 solutions. The deterioration in e, Cc, and Cs and the increase in cv were the result of a compressed diffuse double layer of the bentonite by the CaCl2 solution, which thus exerted certain negative effects on the consolidation behaviors of the SHMP-20CaB backfill.

Considering the long-term development of digital construction, a cost-effective and environmental printing material was designed with blast furnace slag as main cementitious material and sodium desulfurization ash as activator. However, weak alkaline environment lead to the insufficient 3D printability (e.g. yield stress, viscosity). Ethylene/vinyl acetate copolymer (EVA) was used to make up this defect, and it was found that there was a synergistic effect between EVA and sodium desulfurization ash (NS), which is beneficial to the improvement of the printing performance. The synergistic effect of EVA and NS was investigated in terms of fresh, hardened and microstructure properties. Experimental results show that under varying resting times and shear rates, the addition of 0.6−1.6% (i.e.by mass of binder) EVA could increase the yield stress and apparent viscosity of HVGS. Moreover, it was also found that the addition of EVA could help improve the polymerization degree of printing materials and increase the compressive strength of 28d by about 22%. To verify the practical value of the printing material, an industrial product was printed, and the maximum number of continuous printing layers can be up to 30 layers.

Due to the shortage of natural materials, using steel slag (SS) as replacement for natural sand to manufacture mortar has attracted worldwide attention and becomes a promising technology. This study aims at employing SS as fine aggregate for natural sand substitute in cement mortar synthesis. The measurement of expansion value generated by fine SS aggregate was performed by autoclave test. On the basis of further tests, the optimum content of SS fine aggregate was 25%. The autoclave experiment results indicate that the mortar bar was seriously damaged with higher dosages of SS fine aggregate. The X-ray diffraction (XRD) technique was offered to identify the mineralogical phases of the autoclaved SS. Additionally, this work investigated the printability of 3D printing mortar by assessing its fluidity, slump and mechanical strength. The printing mortar mixed with 25% SS was used in the printing of an actual 3D structure, demonstrating its feasibility to be used in 3D printing field. The microstructure and elements distribution were characterized by scanning electron microscopy (SEM) and the energy dispersive spectroscopy (EDS) techniques. The results showed that it is feasible to incorporate SS in 3D printing mortar, which contributes to the improvement of working properties and the enhancement of mechanical strength. This study provides a novel 3D printing SS mortar with good economic and potentially great environmental benefits.

This study illustrates the significant influences of rice husk ash (RHA) addition on the mechanical properties, freezing resistance and microstructure of alkali-activated slag (AAS) material. The results indicate that the incorporation of rice husk ash enhanced the compressive strength, and reduced the mass loss percentage and compressive strength loss percentage during freeze-thaw cycles, improving the freezing resistance of hardened AAS pastes evidently. The primary reasons for this optimization are the synergistic functions from the potential filling effect of RHA particles and gels enrichment in nature and content of AAS samples. The former refined the capillary pores definitely and the later was responsible for the development of compressive strength. However, the excessive contents (more than 20%) of rice husk ash did make a side effect on the development of freezing resistance and microstructure of AAS samples, which was likely related to the structure of rice husk ash itself. The dosage of rice husk ash used in AAS should be within 20% when considering the achievement of better comprehensive properties.

In this work, the effects of slag addition on the geopolymerization process and sulfate resistance of alkali-activated cement were studied. The substitution of metakaolin by slag increased the reactivity of precursors, contributing to a higher reaction rate and accelerating geopolymerization process. The mechanical properties and sulfate resistance were significantly improved with the incorporation of slag. The results show that the transformation of gel phases and development of pore structures were the vital reasons for improvement of sulfate resistance. The quantity of C-A-S-H generation increased with the slag content and consequently to a more compact microstructure. The refinement of pore structures came from the higher space-filling capacity of C-A-S-H phase and the filling effect of slag particles. The optimum replacement level of metakaolin was 30 wt%, in terms of sulfate resistance development and the potential damage of ettringite. This work provides a reference for the utilization of granulated blast furnace slag in metakaolin based geopolymer, which is of great value in urging geopolymer towards practical application in harsh environment.

In the present study, unprocessed phosphogypsum (PG), a byproduct generated by the phosphorus fertilizer industry, is mixed with conventional oil-well cement (CM) and ground-granulated blast-furnace slag (GGBFS or SG), along with other activators and admixtures (such as silica fume (SF), retarder (USZ), and fluid loss control additive (BXF200-L)), to form a PGS slurry for oil well cementing. The mix proportion was optimized step-by-step according to the key properties of hardened PGS slurry, such as compressive strength, linear expansion, porosity, and permeability. The results indicate that the optimized PGS slurry (PGS-optimal slurry), made with the neat PGS:SF:USZ:BXF200-L (by weight) = 100:6:0.4:2, w/c = 0.44, where the neat PGS is consisting of a ratio of PG:SG:CM = 50:20:30 (by weight), had met major technical requirements for oil well cementing operation. Advantageous over the hardened CM slurry, the hardened PGS-optimal slurry generates significant expansion during hydration, thus providing the hardened slurry with excellent shrinkage compensation capability. The hardened PGS-optimal slurry has lower porosity, especially lower amount of harmful pores (>100 nm), than the hardened CM slurry. Consequently, the hardened PGS-optimal slurry also displays much lower permeability.

The air-cooled ferronickel slag is already selected as a raw material (aggregate) in concrete manufacturing, while the using as supplementary cementitious materials is still limited because of the high magnesium content. The objective of this study focuses on the practicality of air-cooled high-magnesium ferronickel slag (HMNS) blended Portland cement pastes, providing experimentally criterion for air-cooled HMNS's application. The different fineness on compressive strength and soundness of mixtures were investigated comprehensively. To be compared with the actual expansion of the HMNS blended Portland cement pastes, the mixtures containing MgO expansive agent addition (on the basis of the MgO content in the HMNS blended mixtures) were especially produced for autoclave expansion test. An optimum strength in practical application was obtained when the dosage of HMNS and its particle size were 20% and less than 50 μm respectively. The expansions of all mixtures were not only quite small (scattered around 0.09%) by traditional autoclave test, but the HMNS blended mixtures also exhibited the lower expansion when autoclave time is 6 h and 12 h. However, the expansive values of MgO expansive agent blended mixtures express more expansion than that of the HMNS blended mixtures in all autoclave times. This phenomenon was attributed to the form of magnesium in HMNS, where the primary phase of magnesium was clinoenstatite (MgSiO3) or forsterite (Mg2SiO4) and those phases showed inactive in this system by XRD, TGA and BSEM-EDS analyses. Therefore, HMNS used as supplementary cementitious material could not bring volume expansion, and this conclusion may present a great benefit to the recycling of HMNS in the field of construction materials.

In this study, the effects of key design parameters, such as SiO2/Na2O mole module (Module), concentration of solute in alkaline solution (Concentration), liquid-to-fly ash mass ratio (L/F), and curing temperature on the geopolymerization process, set time, and compressive strength of high calcium fly ash geopolymer mixes were investigated. The geopolymerization process of these mixes was monitored using a semi-isothermal calorimeter at testing temperatures of 23 °C and 50 °C for 24 h. The results showed two major exothermic peaks generated during the fly ash geopolymerization processes. The first peak, the dissolution peak, appeared within the first hour after the fly ash was in contact with a liquid activator, and it did not vary very much with mix design parameters, while the second peak, the polymerization peak, varied largely in its amount and emerging time with mix design parameters of the geopolymers. As Module increased, the set time was accelerated but the total heat generated from geopolymerization and the compressive strength of the geopolymer were reduced. As Concentration increased, the set time for mixes with 1.0 and 1.5 Module prolonged but it was shortened for the mixes with 2.0 Module, while the total heat of geopolymerization and strength of these mixes were increased. Elevated curing temperature decreased the polymerization peak time, increased the total heat of geopolymerization, and improved the strength of the geopolymers. Additionally, the close relationships between the calorimetric characterization and setting time/compressive strength were obtained. To achieve optimal strength and setting behavior, it is recommended that a geopolymer mix made with high calcium fly ash shall be designed to have an activator with Modules ≤ 1.5, Concentrations of 20–25%, and L/F ≤ 0.40, and elevated curing (e.g., at 50 °C) is preferred.

The synthesis of polyaniline (PANI) with H4Nb6O17 (HNbO) to form PANI/HNbO lamellar nanocomposite by in situ polymerization using aniline (ANI) intercalation compound ANI/HNbO as the intermediate has been investigated. The properties of the samples were characterized by means of XRD, SEM, TEM, FT-IR, UV–vis spectroscopy, and TG-DTA. The in situ polymerization of ANI packed in a regular orientation in a mono- and bilayers (i.e., pseudo-bilayers) structure within the HNbO interlayers led to PANI/HNbO nanocomposite powder using (NH4)2S2O8 as the catalyst with PANI monolayer packing orientation within the HNbO interlayers. PANI/HNbO nanocomposite showed improved thermal stability compared with original PANI by TG analysis. The PANI/HNbO nanocomposite was studied by cyclic voltammetry (CV), which indicated the good redox activity and electrochemical-cycling stability in acidic solution. The interaction between PANI and nanosheets greatly affected the electrochemical behavior of PANI/HNbO nanocomposite. Two couples of redox peaks corresponded to two oxidation process of PANI in acid conditions. The PANI/HNbO nanocomposite exhibited much higher photocatalytic activities for the degradation of methylene blue (MB) in aqueous solution under visible light irradiation than HNbO itself. POLYM. COMPOS., 34:834–841, 2013. © 2013 Society of Plastics Engineers

The calcining process was recorded by differential scanning calorimetry and thermogravimetry (DSC-TG). The dehydroxylation (activating process) was partitioned into two steps by calculating and comparing the O—H bond lengths between inner hydroxyl group and surface hydroxyl group, as well as the ionic bond of Al—OH and position of —OH. X-ray diffraction (XRD) and compressive strength measurement show that the activity of calcined materials increases with the increasing of temperature in dehydroxylation region but decreases abruptly in the “spinel” region. The suggested temperature for activating kaolinite is 900 °C.

To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences of polypropylene (PP) fiber on the mechanical properties and volume stability were investigated. The results show that compressive strength of the geopolymer containing 33.3%(mass fraction) fly ash by steam curing at 80 °C for 6 d is improved by 35.5%. The 3-day compressive strength, flexural strength and impacting energy of geopolymers containing 0.05%PP fiber increase by 67.8%, 36.1% and 6.25%, while the shrinkage and modulus of compressibility decrease by 38.6% and 31.3%, respectively. The results of scanning electron microscopy (SEM) and the appearances of crack growths confirm that PP fiber can offer a bridging effect over the harmful pores and defects and change the expanding ways of cracks, resulting in a great improvement of strength and toughness.

Abstract The fragile damage of cement sheath, induced by perforation and stimulation treatments, can bring formation fluid to cross flow and increase the damage rate of casing. The fragile damage can be avoided by using fiber-toughening agents. With ordinary fiber-toughening agents, the toughness of set cement is increased, but the Young's modulus is barely decreased and the elasticity is hardly improved. In fact, as the Young's modulus is decreased, the spread rate of stress wave produced by perforation in cement sheath is decreased. Because the spread rate of stress wave in cement sheath is decreased, the fragile damage of cement sheath is decreased. Therefore, a novel fiber-toughening agent, named PJ, was developed. It consisted of carboxylated nitrile rubber particles named J at 5.5% by weight of cement (BWOC) and a polypropylene fiber named P (0.2%BWOC). Its effects on the mechanical properties, the engineering properties and the microstructure of set cement and the compatibility with other admixtures were evaluated. Experimental results showed that both the elasticity and the toughness of set cement with PJ were increased markedly.The comprehensive engineering properties of the slurry with PJ (5.7% BWOC), drag reducer USZ (0.2% BWOC), filtrate loss additive F17B (1.2% BWOC) and expanding agent F17A (3% BWOC) met technical requirements of cementing operation. Good quality cement sheath with PJ was observed by the CBL /VDT logs (cement bond log/variable density log). Introduction Cementing is a process that slurry is placed into annulus between casing and cement sheath to isolate producible formation horizons and support casing[1]. Although cement is one of the most important cementing materials, set cement has inherent frangibility. During the development of an oil well, cement sheath is exposed to high energy convergence of perforating charge which brings 3000 to 4000MPa impact pressure[2]. Cement sheath will crack if the radial tensile stress exceeds its limit. The cracks in cement sheath may extend with further well stimulations, even lead to the total failure of the isolation and bring formation fluid to cross flow. During the production of an oil well, casing may expand radially and axially because of high pressure and high temperature resulting from hydraulic fracturing treatments, high drawdown pressures and steam injection. The expansion stress brings cement sheath to crack, or brings the bond interface between the external surface of casing and cement sheath to fail. The bond interface is named the second interface. If cement sheath fractures or bond interface fails, the damage rate of casing will be increased because of severe corrosion on casing, and the output of the oil well will be reduced remarkably. Additionally, the toughness of cement sheath needs to be improved further in the ever increasing number of intricate wells, such as horizontal wells, inclined wells and thermal production wells. A usual measure to improve the toughness of cement sheath is using fiber-toughening agent. However, many overseas and Chinese researches show that, the toughness of the set cement with ordinary fiber-toughening agent is increased, but the Young's modulus is barely decreased and the elasticity is hardly improved [3∼8]. In fact, as the Young's modulus is decreased, the spread rate of stress wave produced by perforation in cement sheath is decreased. Because the spread rate of stress wave in cement sheath is decreased, the fragile damage of cement sheath is decreased. Therefore, it is necessary to develop a novel agent that is able to improve both the elasticity and the toughnessof set cement, while doesn't affect the engineering properties of slurry. The influences of J, P, and PJ on the mechanical properties of set cement were studied. The effect of PJ on the engineering properties of slurries, and the compatibility of PJ with cement and other admixtures were investigated. The function mechanism of PJ was discussed. The field performance of the slurry with PJ was evaluated by CBL /VDT logs. Experimental Program Materials Used: Class G oil-well cement was used in the study. Rubber particles J and fiber P were used as the agents. The properties of J and P are shown in Table 1. Filtrate loss additive F17B and expanding agent F17A were used to evaluate the compatibility of admixtures. Drag reducer USZ (0.2% BWOC) was added into all samples (except neat slurry) to improve the fluidity of slurries.