Development and application of novel high‐efficiency composite ultrafine cement grouts for roadway in fractured surrounding rocks

The fractured surrounding rocks of roadways pose major challenges to safe mining.Grouting has often been used to reinforce the surrounding rocks to mitigate the safety risks associated with fractured rocks.The aim of this study is to develop highly efficient composite ultrafine cement(CUC)grouts to reinforce the roadway in fractured surrounding rocks.The materials used are ultrafine cement(UC),ultrafine fly ash(UF),ultrafine slag(US),and additives(superplasticizer[SUP],aluminate ultrafine expansion agent[AUA],gypsum,and retarder).The fluidity,bleeding,shrinkage,setting time,chemical composition,microstructure,degree of hydration,and mechanical property of grouting materials were evaluated in this study.Also,a suitable and effective CUC grout mixture was used to reinforce the roadway in the fractured surrounding rock.The results have shown that the addition of UF and US reduces the plastic viscosity of CUC,and the best fluidity can be obtained by adding 40%UF and 10%US.Since UC and UF particles are small,the pozzolanic effect of UF promotes the hydration reaction,which is conductive to the stability of CUC grouts.In addition,fine particles of UC,UF,and US can effectively fill the pores,while the volumetric expansion of AUA and gypsum decreases the pores and thus affects the microstructure of the solidified grout.The compressive test results have shown that the addition of specific amounts of UF and US can ameliorate the mechanical properties of CUC grouts.Finally,the CUC22‐8 grout was used to reinforce the No.20322 belt roadway.The results of numerical simulation and field monitoring have indicated that grouting can efficaciously reinforce the surrounding rock of the roadway.In this research,high‐performance CUC grouts were developed for surrounding rock reinforcement of underground engineering by utilizing UC and some additives.

Using Flowable Composite as Gingival Retraction Cord in Prosthodontics Dentistry: Two Case Reports: A Dental Technique

One of the most challenging factors affecting impression quality and good marginal fit is the gingival retraction method, which aims to separate the gingiva from the tooth to expose the finishing line of the prepared tooth. Bleeding and contamination from the crevicular fluid may compete for space with the impression material within the sulcus, leading to indistinct preparations and a lack of detail at the margin. In addition, such procedures might damage the PDL and cause permanent recession. Flowable composite cable, as opposed to traditional retraction cords, offers the proper marginal seal and visibility during the impression record because of its lower viscosity, improved adaptability, and elastic properties. The aim of this report is to present a brand-new, innovative method for controlling gingival hemorrhage in addition to the gingival retraction in restorative and prosthodontic treatment by utilizing a flowable composite during the final impression record procedure. In these case reports, the flowable composite cord technique is used instead of traditional gingival cords to modify and refine the gingival tissue before taking the traditional final impression or digital scan. Two cases were done for patients undergoing fixed prosthodontics and veneer treatment within a 2-year follow-up period. In addition, the flowable composite cord was used as temporary restoration before the final prosthetic cementation or under the provisional crowns. As a result, clean and healthy gingival tissues render cementation of the final prosthesis quicker and easier to perform. The patients in both cases claimed that their prosthodontic treatments, which involved the application of a flowable composite cord to temporarily retraction the gingiva, had produced good outcomes at the yearlong follow-up. In conclusion, the flowable composite cord technique is found to be a useful tool to improve the quality of impressions in fixed prosthodontics by providing excellent access for impression material to record fine details of the finish line of the prepared tooth structure, and to alter the inflamed tissue into a healthy tissue.

Multiphysics processes in the interfacial transition zone of fiber-reinforced cementitious composites under induced curing pressure and implications for mine backfill materials: A critical review

The mesoscale fiber-matrix interfacial transition zone(FM-ITZ) under induced curing pressure plays a key role in the effectiveness of fiber reinforcement and the engineering application of fiber-reinforced cementitious composites(FRCCs). This critical review establishes the link among induced curing pressure(i.e., external loading condition), multiphysics processes(i.e., internal governing mechanism), and interface behavior(i.e., material behavior) for FRCC materials through analysis of the state-of-the-art research findings on the FM-ITZ of FRCC materials. The following results are obtained. For the mechanical process, the induced curing pressure changes the stress state and enhances multicracking behavior, which can strengthen the FM-ITZ. For the hydraulic process, the strengthened seepage of the FM-ITZ under induced curing pressure weakens the effective stress and exaggerates the deficiency in water retention capacity between the bulk matrix and the FMITZ. For the thermal process, the induced curing pressure causes a steep temperature gradient in the FM-ITZ and thus influences the temperature evolution and thermally-induced microcracks in the FM-ITZ. For the chemical process, the induced curing pressure enhances hydration kinetics and results in the formation of additional hydration products in the FM-ITZ. Moreover, recommendations are proposed on the basis of findings from this review to facilitate the implementation of fiber reinforcement in cemented paste backfill technology.

Effect of Polyaniline/manganese Dioxide Composite on the Thermoelectric Effect of Cement-based Materials

To enhance the thermoelectric effect of cement-based materials,conductive polyaniline(PANI)modified MnO_(2)powder was synthesized and used as a thermoelectric component in the cement composites.The nanostructured PANI was deposited on the surface of the nanorod-shapedα-MnO_(2)particle and the weight ratio of PANI to MnO_(2)was 22.3:77.7 in the composite.The synthesized PANI/MnO_(2)composite was nanostructured according to the SEM image.The test results of the thermoelectric properties proved that the PANI/MnO_(2)composite was effective as the Seebeck coefficient and electrical conductivity values of the cement composites with PANI/MnO_(2)inside were 3-4 orders of magnitude higher than those of pure cement paste and the thermal conductivity values of these cement samples were similar.The obtained maximum figure of merit(ZT)value(2.75×10^(-3))was much larger than that of conductive materials reinforced cement-based composites.The thermoelectric effect of cement composites is mainly enhanced by the increased Seebeck coefficient and electrical conductivity in this work.

Long-term Properties of Aeolian Sand-magnesium Oxychloride Cement Composites and Its Engineering Application

In order to prepare a new material with long-term stable performance,low cost,easy construction,and ecological environmental protection,the influence of aeolian sand on the compressive and flexural strength as well as micro morphology and phase composition of magnesium oxychloride cement(MOC)was studied.The experimental results indicate that,with the increase of content of doping sand,the compressive strength and flexural strength of MOC decrease significantly.However,when the quality ratio of aeolian sand and light burned magnesia powder is 1:8,the performance meets the actual engineering needs.Namely,the compressive strength of MOC is not less than 18 MPa,and flexural strength is not less than 4 MPa.Meanwhile,within 12 months of age,the compressive strength and flexural strength are stable.There is no obvious change in phase composition,and its main phase is still 5·1·8 phase.Microscopic appearance changes from needle-like to gel-like shape.Based on engineering applications,it is found that when the novel sand-fixing material is used in the field for one year,its macroscopic feature is not damaged,compressive strength and flexural strength are also more stable,phase composition negligibly changes,and micro morphology has also been turned into be gellike shape.These further confirm the long-term stability and weather resistance of MOC doping aeolian sand,providing theoretical and technical support for the widely application of MOC in the field of sand fixation in the future.

Influence of Bayer Red Mud on the Operational and Mechanical Characteristics of Composite Cement Mortar

The aim of this study is to enhance the value and utilization of red mud generated in the Bayer process by preparing composite cement mortars.The effects of two different types of Bayer red mud with varying physical and chemical characteristics on the fluidity,mechanical strength,mineral composition,and microstructure of the composite cement mortar were systematically evaluated.The results showed that the optimal addition of red mud A was 10 wt%,while it was 20 wt% for red mud B.The mechanical properties of the composite cement mortar met the standards for P·O42.5 cement.Furthermore,the composite mortar with the addition of red mud B showed higher flexural and compressive strengths compared to the composite mortar with red mud A.This improvement is attributed to the smaller particle size of red mud B,which filled the micro-pores and increased the compactness of the cement stone,as well as its higher content of Na_(2)O,K_(2)O,and other free alkalis,which resulted in more obvious alkali activation,accelerating the hydration of the active minerals in the slurry.

Fracture Properties of Cement Composites Reinforced with Steel Polypropylene Hybrid Fibres

Polypropylene fibres and three sizes of steel fibres reinforced concrete are discussed. The total fibres content ranges from 0 4%-0 95% by volume of concrete. A four point bending test is adopted on the notched prisms with the size of 100?mm×100?mm×500?mm to investigate the effect of hybrid fibres on crack arresting. The research results show that there is a positive synergy effect between large steel fibres and polypropylene fibres on the load bearing capacity in the small displacement range. But this synergy effect disappears in the large displacement range. The large and strong steel fibre is better than soft polypropylene fibre and small steel fibre in the aspect of energy absorption capacity in the large displacement range. The static usage limitation for the hybrid fibres concrete with “wide peak' or “multi peaks' load CMOD pattern should be carefully selected. The ultimate load bearing capacity and the crack width or CMOD at this load level should be jointly considered.

Preparation of Super Composite Cement with a Lower Clinker Content and a Larger Amount of Industrial Wastes

The effects of the grinding mode,fineness,gypsum kinds and dosage,mix proportions on properties of the composite cements consisting of slag,fly ash,limestone and a lower content clinker were investigated,respectively.The results show that when the proportions among slag,fly ash and limestone are appropriate,the grinding technology and system are reasonable,the optimized gypsums and additives are effective,the 52.5R grade cement (52.5R grade cement means a higher strength than 52.5 at early age) can be prepared by clinker dosage of 50% in weight,the 42.5R or 42.5,32.5 grade composite cement containing 40% and 30% clinker also may be made, respectively.Moreover,the high performance concrete prepared from the above composite cements was studied experimentally.

Dynamic properties of composite cemented clay

In this work, the dynamic properties of composite cemented clay under a wide range of strains were studied considering the effect of different mixing ratio and the change of confining pressures through dynamic triaxial test. A simple and practical method to estimate the dynamic elastic modulus and damping ratio is proposed in this paper and a related empirical normalized formula is also presented. The results provide useful guidelines for preliminary estimation of cement requirements to improve the dynamic properties of clays.

Synthesis of Chitosan-Hydroxyapatite Composites and Its Effect on the Properties of Bioglass Bone Cement

Chitosan-hydroxyapatite （CS-HA） composite powders were synthesized via in situ co-precipitation method, through the reaction of Ca（NO3）2 and H3PO4 in the simulated body fluid （SBF） containing appropri- ate amount of chitosan. The thermal evolution, microstructure and morphology were studied by TG-DTA （thermogravimetry-differential thermal analysis）, XRD （X-ray diffraction）, FTIR （Fourier transform infrared spectroscopy） and TEM （transmission electron microscopy）. The in vitro bioactivity test showed that the obtained CS-HA composites had higher capability of inducing calcium ions deposition. Effects of CS-HA com- posites on the bioactivity and compressive strength of bioglass bone cement were investigated. The results indicated that the bioactivity of bioglass bone cement could be improved further when CS-HA composite pow- ders were added into the cement, and appropriate amount of CS-HA additive was favorable for compressive strength improvement of bioglass bone cement.

Microstructure of a Planting Material Consisting of Nutrition-Expansive Perlitic-Cement Composites

An ecotypic revetment material consisting of nutrition-expansive perlitic-cement composites is introduced. This planting material can combine vegetation recovery with slope protection. The XRD, SEM and image analysis techniques were used to study its composition and microstructure. Its strength was measured by an electro-hydraulic servo-controlled testing machine. The results show the unconfined compressive strength is about 393.6 kPa, and the average elastic modulus is about 47.0 MPa. The quartz, felspar, chlorite and calcite are the main non-clay minerals in the planting material. Its particles are mainly spherical,and the range of the equivalent diameter is 1.83 to 15.96 μm. The results also show the planting material contains a large amount of micro non-capillary and capillary pores, and has a microstructure characteristic of honeycomb and coralline. CSH gel produced by hydration of cement increases the strength and water stability of the particles. The anisotropy and slight orientation of the particles increase the void cross-section area,providing an explanation of the high permeability for the planting material.The better porosity of the planting material is apt tokeep moisture and nutriment, provides oxygen for plant root breathing, and aids to exhaust the carbon dioxide by means of exchanging with atmosphere, hence it can facilitate vegetation.

Development of Clinical Cement of Nanoapatite and Polyamide Composite

A new type of inorganic organic biomimetic bone cement consisting of nano hydroxyapatite and polyamide 66 composite was investigated. This cement can be handled as paste and easily shaped into any contour. Nanoapatite and polyamide composite cement has a reasonable setting time, excellent washout resistance, high mechanical strength and bioactivity, and it is easily handled and shaped, which can be developed as a clinical cement. It can be predicted that nanoapatite/polymer composite cement would be a new trend of biomedical material, showing a promising prospect.

Beneficial use of stainless steel EAF slag as composite cement admixture and its heavy metals leaching risk analysis

This study analyzes the feasibility of using stainless steel electric arc furnace （EAF） slag as composite cement admixture and the risk of leaching-out of heavy metals. The results show that the stainless steel EAF slag, mainly made up of Ca2 SiO4, Ca3 Mg （ SiO4 ） 2, some Cr-containing minerals and in small particle size, is easily ground and has cementitious activity. EAF slag, when used as cement admixture, can be added with a maximum percentage of 32%. It can meet the strength requirements of the standard P · C 32.5 cement. When the mixing percentage is decreased to 25 % , the strength of the cement can be increased to that of P · C 42.5 cement. Other main quality indexes of composite cement, such as the setting time and stability, also satisfy standard requirements. The results also show that most of the heavy metals in the stainless steel EAF slag exist in a stable speciation. The concentration of heavy metals that leach out from the stainless steel EAF slag and the composite cement products is far lower than the standard limit of hazardous wastes. The main heavy metal, chromium, exists as less hazardous trivalent chromium. Therefore, the risk of heavy metals leaching out from the stainless steel EAF slag is low. The internal exposure index （IRa） and the external exposure index （Iγ） of the stainless steel EAF slag are both lower than 1.0, satisfying the standard requirements of the state for the radionuclides of building materials. Therefore, stainless steel EAF slag can be safely used as admixture to produce composite cement.

Test on Sensor Effect of Cement Matrix Piezoelectric Composite

A novel cement matrix smart piezoelectric composite and its application as sensing element are presented.A cement matrix smart piezoelectric composite piece encapsulated in a cement mortar formed a practical sensor, and it was tested on material test system with cyclic loading.According to the theoretical analysis, the function of the cement matrix piezoelectric sensor output voltage was expressed in terms of the magnitude of the input cyclic loading amplitude and frequency.The curve fitting of gain function that is defined as sensor′s gain factor under different frequencies of input loading was carried out. From the results of curve fitting, it is found that the cement matrix smart piezoelectric composite has a simple relationship between input loading and output voltage.Therefore the cement matrix piezoelectric composite sensor is suitable to be applied in structural health monitoring.

DEVELOPING A NEW GENERATION OF HIGH PERFORMANCE COMPOSITE CEMENT

This paper proposed a new generation of high performance composite cement which is designed according to the optimization of composition and structure of cement paste and is manufactured by blending the differ ent components with special composite techniques. Each of these components has its different special property, and should be compatible with each other and match each other, and the properties of them are complementary mutually. At present, such kind of high performance composite cement can be manufactured with high reactivity cement clinker, ground granulated blast - furnace slag, high grade fly ash, silica fume etc..

Electrical Resistance and Microstructure of Latex Modified Carbon Fiber Reinforced Cement Composites

The electrical resistance,flexural strength,and microstructure of carbon fiber reinforced cement composites（CFRC） were improved greatly by adding water-redispersible latex powder.The electrical resistance of CFRC was investigated by two-probe method.The input range of CFRC based strain sensors was therefore increased,whereas electrical resistance was increased and remained in the perfect range of CFRC sensors.The analysis of scanning electron microscopy indicated that elastic latex bridges and a latex layer existed among the interspaces of the adjacent cement hydration products which were responsible for the enhancement of the flexural strength and electrical resistance.The formation mechanism of the elastic latex bridges was also discussed in detail.The continuous moving of two opposite interfaces of the latex solution-air along the interspaces of the adjacent hydrated crystals or colloids was attributed to the formation of the elastic latex bridges.

STUDY ON THE ELECTRICAL PROPERTIES OF CARBON FIBER-CEMENT COMPOSITE(CFCC)

The relationship between the resistivity of Carbon Fiber-Cement Composite (CFCC) and the content of fiber has been discussed in this paper. The results show if the weight percentage of carbon fiber increases from 0.4% to 1.2%, the resistivity of CFCC changes over the range (10M Omega . cm similar to 100 Omega . cm), and the percolation threshold is about 0.8w%. The conduction mechanism and percolation phenomenon of the composite can be explained by the tunneling model.

The Smart Behavior of Cement-based Composite Containing Carbon Fibers under Three-point-bending Load

The influences of the fiber volume fraction on the electrical conductivity and the fraction change of electrical resistance under three-point-bending test were discussed.It is found that the relationship beween the electrical conductivity of composites and the fiber volume fraction can be explained by the percolation theory and the change of electrical resistance of specimens reflects to the process of loading.The sensitivity and the response of the change of electrical resistance to the load for specimens with different fiber volume fractions are quite different.which provide an important guide for the manufacture of conductive and intrinsically smart carbon fiber composite.

Development of the nano-composite cement:Application in regulating grouting in complex ground conditions

Improvement of the fluidity and setting time of grouting materials has been recognized as an effective approach of seepage prevention in foundation works, and it is quite common to be used for handling severe leakages in complex ground conditions, such as loose, broken and fully fissured stratum. For the purposed of better meeting the engineering requirements, experimental studies were conducted in this study with focus on the nanocomposite grouting materials and the related controlled grouting technology. As compared with the commonly used silicate-sulpho-aluminate composite cement, which is characterized by relatively poor rheological property, quick setting time and low strength, the most suitable nano-material with proper reactants were selected intentionally to improve the mentioned attributes of composite cement. Due to the setting time and strength of the targeted cement slurry behaving with poor performance of harmonization to engineering construction problems, hydration synergistic effect of these composites were investigated in our experiments. Results showed that the properties of grouting materials, including initial fluidity, setting time, ideal right-angle thickening, and early strength and late strength were sufficient to produce an expected grouting application. It is therefore advocated that the refined grouting material could provide a better solution to fix grouting problems in complex ground cementing operations.

Improvement of Water Sensitivity of Macro-defect-free Cement Based Composites with Cross Coupling Agent

The enhancement of interface bonding between cement and polymerand the structural reticula- tion of the water-soluble polymer areproposed to minimize the shortening of the mechanical properties ofmacro-de- fect-free(MDF)cement based composites at high relativehumidity. The MDF composites incorporated with vari- ouscross-coupling agents studied experimentally. The results show thatthe MDF composites modified with small amounts of cross-couplingagent had raised mechanical properties, but it is more important thatthe modified MDF composites had a significant increase in waterresistance compared to the original one.