Mechanical and Morphological Properties of Highly Dispersed Carbon Nanotubes Reinforced Cement Based Materials

Stable homogeneous suspensions of multi-walled carbon nanotubes （MWCNTs） were prepared using gum arabic （GA） as dispersant and were incorporated to Portland cement paste. The dispersion was examined by ultraviolet visible spectroscopy （UV-vis）, and the concentration measurement shows that the optimum concentration of GA is 0.45 g · L^-1. The dispersibility of the surface-modified MWCNTs in aqueous solution and cement matrix were investigated by transmission electron microscopy （TEM） and energy dispersive spectroscopy （EDS）, and the mechanical properties of the composites were investigated. The results show that the addition of the treated nanotubes can improve both the flexural strength and the compressive strength of the Portland cement composite significantly. The flexural strength of the composite increases up to 43.38% with the MWCNT concentration of 0.08% （by weight of cement）. The porosity and pore size distribution of the composites were measured by mercury intrusion porosimetry （MIP）, and the results indicate that the cement paste doped with MWCNTs obtained lower porosity and concentrated pore size distribution. The morphological structure was analyzed by field emission scanning electron microscopy （FESEM） and EDS. It is shown that MWCNTs act as bridges and networks across cracks and voids, which transfer the load in case of tension, and the interface bond strength between the nanotubes and matrix is very strong.

Preparation and Properties of Paraffin/PMMA Shape-stabilized Phase Change Material for Building Thermal Energy Storage

The composite phase change material(PCM) consisting of phase change paraffin(PCP) and polymethyl methacrylate(PMMA) was prepared as a novel type of shape-stabilized PCM for building energy conservation through the method of bulk polymerization. The chemical structure, morphology, phase change temperature and enthalpy, and mechanical properties of the composite PCM were studied to evaluate the encapsulation effect of PMMA on PCP and determine the optimal composition proportion. FTIR and SEM results revealed that PCP was physically immobilized in the PMMA so that its leakage from the composite was prevented. Based on the thermo-physical and mechanical properties investigations, the optimal mass fraction of PCP in the composite was determined as 70%. The phase change temperature of the composite was close to that of PCP, and its latent heat was equivalent to the calculated value according to the mass fraction of PCP in the composite. For estimating the usability in practical engineering, thermal stability, reliability and temperature regulation performance of the composite were also researched by TG analysis, thermal cycling treatments and heating-cooling test. The results indicated that PCP/PMMA composite PCM behaved good thermal stability depending on the PMMA protection and its latent heat degraded little after 500 thermal cycling. Temperature regulation performance of the composite before and after thermal cycling was both noticeable due to its latent heat absorption and release in the temperature variation processes. The PCP/PMMA phase change plate was fabricated and applied as thermal insulator in miniature concrete box to estimate its temperature regulation effect under the simulated environmental condition. It can be concluded that this kind of PCP/PMMA shape-stabilized PCM with the advantages of no leakage, suitable phase change temperature and enthalpy, good thermal stability and reliability, and effective temperature regulation performance have much potential for thermal energy storage in building energy conservation.

Detection of Chlorides in Pore Water of Cement Based Materials by Potentiometric Sensors

Free chloride ions dissolved in pore water of cement based materials initiate the corrosion of steel rebars used for reinforcement of concrete and thus pose serious constant danger to the safety of reinforced concrete structures.The in-situ monitoring of the content of chlorides in pore water with second order Ag/AgCl electrodes is an elegant approach which, however,suffers from poor stability of Ag/AgCl electrodes in highly alkaline environment like pore water.In this work the electrochemical stability of plain and stabilized electrodeposited Ag/AgCl sensors in extreme alkaline conditions are presented. The electrochemical processes were elucidated which govern the potentiometric response of Ag/AgCl sensors and determine their performance.The results have shown suitable stability and reproducibility of stabilized Ag/AgCl sensors over five months, which was sufficient for laboratory testing of chloride ingress into cement based materials.The embedded calibrated sensor elements were used to monitor the chloride uptake into cylindrical mortar specimen dipped into simulated pore water containing about 3 wt% of chloride ions.The velocity of diffusing front and the diffusion coefficient of chloride ions in pore water of cylindrical mortar sample were estimated from concentration-time profiles determined by chloride sensors positioned at defined positions in the sample wall.

Utilization of Basalt Saw Mud as a Spherical Porous Functional Aggregate for the Preparation of Ordinary Structure Concrete

To promote the production and application of artificial aggregates,save natural sand resources and protect the ecological environment,we evaluated the feasibility of using spherical porous functional aggregates(SPFAs) formed by basalt saw mud under autoclave curing in ordinary structural concrete.In our work,two types of prewetted functional aggregates were taken as replacements for natural aggregates with different volume substitution rates(0%,5%,10%,15%,20%,25%,and 30%) in the preparation of ordinary structural concrete with water-to-binder ratios(W/B) of 0.48 and 0.33.The effects of the functional aggregate properties and content,W/B,and curing age on the fluidity,density,mechanical properties and autogenous shrinkage of ordinary concrete were analyzed.The experimental results showed that the density of concrete declined at a rate of not more than 5%,and the 28 d compressive strength could reach 31.0-68.2 MPa.Low W/B,long curing age and high-quality functional aggregates were conducive to enhancing the mechanical properties of SPFAs concrete.Through the rolling effects,SPFAs can optimize the particle gradation of aggregate systems and improve the fluidity of concrete,and the water stored inside SPFAs provides an internal curing effect,which prolongs the cement hydration process and considerably reduces the autogenous shrinkage of concrete.SPFAs exhibits high strength and high density,as well as being more cost-effective and ecological,and is expected to be widely employed in ordinary structural concrete.

Characterization and Thermal Conductivity of Modified Graphite/Fatty Acid Eutectic/PMMA Form-Stable Phase Change Material

We prepared and characterized a form-stable composite phase change material （PCM） with higher thermal conductivity. Capric acid（CA）-myristic acid（MA） eutectic as core, poly-methyl methacrylate （PMMA） as supportive matrix and modified graphite （MG） powders serving as the thermal conductance improver were blended by bulk- polymerization method. The composite PCMs with different MG mass fraction （2%, 5%, 7%, 10% and 15%） were characterized by FT-IR, SEM, DSC technique and mechanical tests. Thermal conductivities of the composites were measured by transient hot-wire method. The results indicate that MG powders have been successfully inserted into the CA-MA/PMMA matrix without any chemical reaction with each other. The MG/CA-MA/PMMA composites maintain good thermal storage performance while the thermal conductivity has been enhanced significantly. The composite PCM added with 15 wt% MG powders increases approximately as 195.9% in thermal conductivity. Moreover, the thermal conductivity improvement of the composite PCMs is also verified by the melting-freezing experiment, which is profitable for the heat transfer efficiency in latent heat thermal energy storage system.

Synthesis and Characteristics of Mesoporous Silica Aerogels with One-step Solvent Exchange/Surface Modification

The synthesis procedures and physical properties of the ambient dried hydrophobic silica aerogels by using different contents of ethanol （EtOH）/trimethylchlorosilane （TMCS）/n-Hexane as surface modification agent were investigated. One-step solvent exchange and surface modification were simultaneously progressed by immersing silica hydrogels in EtOH/TMCS/n-Hexane solution. It is found that microstructures as well as properties of silica aerogels like porosity, specific density and specific surface area are affected by the contents of surface modification agent in the sol from the results of SEM, TEM morphology, FT-IR chemical structure, BET surface area and BJH pore size analyses. The volume of TMCS is of 10% and 20% of hydrogels, and the final product is hydrophilic xerogels. When TMCS＇s percent （v/v） is elevated to 75 %-100%, hydrophobic silica aerogels with good performance are synthesized, the porosities of aerogels are in the range of 93.5%-95.8% and the average pore size diameter is less than 20 nm.

Properties of Alkali-activated Yellow River Sediment-slag Composite Material

In order to consume the Yellow River sediment as much as possible and improve the longterm stability of the Yellow River, Yellow River sediment was utilized as the main raw material to produce a composite material. Ca(OH)_2 was used as alkali-activator to activate the active SiO_2 and Al_2O_3 compositions in Yellow River sediment. 10 wt% slag was added into the mixture to further improve the strength of the composites. The effect of activity rate of the Yellow River sediment and dosage of Ca(OH) _2 on the compressive strength of the Yellow River sediment-slag composite material at different curing ages was researched. XRD, SEM/EDS, light microscope and FTIR were used to further explore the products and the microstructure of the composite material. Results showed that the active ratio of sediment had a great influence on the compressive strength of specimen. In addition, the compressive strength of specimen increased with the increase of Ca(OH)_2dosage and curing age. When the dosage of Ca(OH)_2 was more than 5 wt% as well as the curing age reached 90 days, the compressive strength of the composite material could meet the engineering requirement. In the alkali-activated process, the main product was hydrated calcium silicate(C-S-H) gel, which filled up the gaps among the sediment particles and decreased the porosity of the specimen. Moreover, the CaCO_3 produced by the carbonization of the C-S-H gel and excess Ca(OH)_2 also played a role on the strength.

Preparation and Properties of Alkali Activated Foam Cement Reinforced with Polypropylene Fibers

A new form of foam cement was produced by mixing alkali-activated slag,clay,a small amount of polypropylene fibers with prepared foam during stirring.The preparation of the material is quite different from the normal one,which is produced just at room temperature and without baking.The fabrication of this energy-saving and low-price material can be favorable for lowering carbon emission by using recycled industrial wastes.Thermal conductivity of 0.116 W/（m·k）,compressive strength of 3.30 MPa,flexural strength of 0.8 MPa and density of 453 kg/m3 can be achieved after 28 days aging.The hydration product is C-S-H with less Ca（OH）2,calcium aluminum and zeolite,which was characterized by X-ray diffraction（XRD） measurement.This prospective foam cement may be expected to be an excellent economical energy-saving building material.

Structural Characteristics and Photocatalytic Activity of Ambient Pressure Dried SiO2/TiO2 Aerogel Composites by One-step Solvent Exchange/Surface Modification

An ambient pressure synthesis of SiO2/TiO2 binary aerogel was prepared through the low-cost precursors of titanium tetrachloride（TiCl4） and sodium silicate（Na2O·nSiO2）.After gelation,solvent exchange and surface modification were performed simultaneously and the modified gel was finally dried under ambient pressure.Microstructural analyses by transmission electron microscope（TEM） indicate that fabricated SiO2/TiO2 aerogel composite shows similar sponge-like nanostructure as silica aerogel,and the Brunauer-EmmettTeller（BET） analysis shows that the specific surface area of the composite reaches 605 m^2/g,and the average pore size is 9.7 nm.Such binary aerogel exhibits significant photocatalytic performance in this paper for treating model pollutant of methyl orange（MO）,and the decolorizing efficiency of MO is detected as 84.9%after 210 mins exposure to UV light irradiation.Degraded gel suspends in the water so as to separate from solution for reuse,and after 4 times recycling,70%degradation efficiency can be easily reached when composite catalyzed system is exposed for 210 mins under UV irradiation.

Research on Preparation and Influencing Fctors of High Calcium High Sulfate Ash to Autoclaved Aerated Concrete

In this paper, a high calcium high sulfate ash as the main material, adding fly ash, lime, cement, gypsum and some modifiers to prepare autoclaved aerated concrete. The products complies with the technical requirements of GB/T11968-2006. This paper also studies the influence of the physical methods and water ratio on autoclaved aerated concrete by high calcium high sulfate ash aerated concrete. The best ratio of water and Grinding time were found in practice study.

SYNTHESES OF STYRENE-METHYL METHACRYLATE BLOCK COPOLYMER BY POLYAZOAMIDE AS INITIATOR

Polyazoamide（PAA） was used as initiator to prepare block copolymer P（MMA-b-St） byfree radical polymerization. The fraction of block copolymer was about 50%. The structureof the block-copolymer was characterized by IR and the results of;H-NMR and GPCshowed that the content of the block and the molecular weight （M;） of the prepolymerand block copolymer could be controlled by varying the mol ratio of styrene/PAA andMMA/prepolymer. DSC and TEM results revealed that the block copolymer has twoseparated glass transition temperatures and phase separation within the domain structure.

A comparative study of drying techniques on the morphology of porous silica gels synthesized via sol-gel process

The effect of drying techniques on the microstructure,morphology and pore structure of porous silica gels was studied in the paper.The gels were prepared by using sol-gel process and different drying routes:freeze-drying (FD),low pressure drying (LPD),high temperature drying (HTD) and chemical modification & ambient drying (CMD) techniques.Observation under pore distribution and structural properties showed that CMD technique leads to homogenous mesoporous silica material with specific surface area of 745 m2/g,and the average pore size around 20 nm,while LPD and HTD result in loosely packed particles with non-isotropic aggregation pattern.The specific surface areas of LPD and HTD samples are 419 and 513 m2/g respectively,and the pore size distribution of the samples are observed distributing widely in range of 10-100 nm.Freeze drying method is a new but prospective way to prepare mesoporous silica.The specific area of FD sample is around 500 m2/g.By the comparison for the properties of the gels,this paper wants to induce a further interest in finding a proper method to synthesize the porous silica gels for low price use.

Synthesis and Characterization of Multi-walled Carbon Nanotube Doped Silica Aerogels

Multi-walled carbon nanotube doped silica aerogels（MWCNT-SAs） were synthesized from a wet gel of well-dispersed MWCNT by one-step solvent exchange/surface modification and ambient pressure drying（APD）. Waterglass was employed as a precursor to prepare wet gel. The content of MWCNT varied from 0 to 15% volume by wet gel. The surface group, thermal stability and microstructure of pure silica aerogel and MWCNT-SAs were investigated by FTIR, DTA, and TEM. Experimental results show that MWCNT-SAs are hydrophobic when the temperature is below 400 ℃, MWCNT-SAs exhibit a mesoporous network structure, and they achieve the largest scale with least shrinkage and lowest density when doped with 5 vol% MWCNT.

STUDY OF THE STRESS INTENSITY FACTOR OF PREFORMED V SHAPE FRACTURE TIP

In order to make the fracture cross-section of rock smooth in controlled cutting-blast, generally, two V-shape-notches on the inner wall of a shot hole are notched in symmetry along the design direction. A V-shape notch approximately be considered as V-shape-fracture under certain condition. This paper gave the complex stress function of preformed V-shape-fracture under a blasting load. The stress field and displacement field at the tip of a preformed V-shape-fracture were derived with Westergaard's method, hence its stressintensity factor was obtained. To verify the derived results, blasting tests were made with concrete samples of 400mm×400mm×300mm, and all having, in the center, a drilled hole of 25mm in diameter and 200mm in height. The test result showed that the formulas derived are correct and effective.

CHARGE-TRANSFER AND ENERGY-TRANSFER IN THE PHOTO-INDUCED COPOLYMERIZATION OF 2-VINYLNAPHTHALENE WITH MALEIC ANHYDRIDE

The initiation mechanism of the copolymerization of 2-vinylnaphthalene with maleic anhydride was studied under irradiation of 365 nm. The excited complex was formed from (1) the local excitation of 2-vinylnaphthalene followed by the charge-transfer interaction with maleic anhydride and (2) the excitation of the ground state charge-transfer complex, and then it collapsed to 1,4-tetramethylene biradical for initiation. A1: 1 alternating copolymer was formed in different monomer feeds. Addition of benzophenone could greatly enhance the rate of copolymerization through energy-transfer mechanism.

Behaviors of Rural Structures during Destructive Earthquakes

This article deals with the results of the research on the behaviors of the rural buildings made up of local materials during earthquakes. This article reveals the mechanical properties of masonry detected based on experimental research results on wall samples made of local materials such as mud bricks, clay and straw mixture, rubble stones and limestones cut in standard sizes. In addition, the constructive measures prepared for the earthquake resistance of rural structures and the application techniques of these buildings in common construction are also generalized in this article.

The Research of Formations Intended to the Prevention of Lateral Strain of Columns

In this paper, the research for the constructive formations preventing the buckling of the columns is being covered. Especially, the behavior of the constructive support elements which are used during the design of the industry building＇s columns is analyzed. The preparation of constructive formations which is intended to the prevention of changing shape and the proposals aimed at the use of widespread construction practices are being covered.

A State-of-the-Art Review of Electrochemical Chloride Extraction for Concrete Structures

Electrochemical chloride extraction is a promising technique for the rehabilitation of concrete structures under chloride induced corrosion. This study consists of an extensive literature review of this treatment including application cases. It is found that the rate of chlorides removed is affected by the total charge passed, whereas increasing charge in a range between 1500 to 2000 Ah/m2 increases the amount of chlorides removed and this can be more effective by increasing current density instead of duration of treatment. Bound chlorides are extracted during treatment and, water works better than Ca(OH)2 as an electrolyte, possibly due to modifications on the concrete pore structure. Moreover, ECE is not efficient in repassivate structures but is efficient in its purpose of removing chlorides if treatment setup is well planned, which justifies the need for better international standards on the topic.

桥面用丁苯乳液改性水泥砂浆的力学性能

用德国标准和规范研究了丁苯乳液D6 2 3对桥面用水泥砂浆力学性能的改性效果 .丁苯乳液D6 2 3对砂浆有良好的减水作用 ,对提高抗折强度和粘结抗拉强度也有显著作用 ,并可大幅度降低压折比、提高折弹比 .综合抗压强度、抗折强度、抗拉粘结强度和弹性模量等力学性能 ,桥面用改性砂浆的聚合物D6 2 3掺量范围为 1 0 .0 %～ 1 7.5 % .

掺矿渣粉和减水剂的HEMC水泥砂浆力学性能

研究了掺矿渣粉和高效减水剂的羟乙基甲基纤维素改性水泥砂浆的力学性能 (包括抗压强度、抗折强度、弹性模量、粘结抗拉强度 )及其与新拌砂浆体积密度和硬化砂浆孔隙率的关系 .掺加减水剂、矿渣粉和羟乙基甲基纤维素后 ,砂浆的抗压强度与新拌砂浆体积密度和硬化砂浆孔隙率密切相关 ,抗折强度与之部分相关 ,粘结抗拉强度则与之无关 .减水剂和矿渣粉可增加砂浆的密实度 ,减小孔隙率 ,从而使砂浆的抗压强度、抗折强度、粘结抗拉强度和弹性模量得到提高 ;羟乙基甲基纤维素虽可保持砂浆的粘结抗拉强度稳定 ,但却使抗压强度和弹性模量降低 .减水剂、矿渣粉和羟乙基甲基纤维素的共同作用 ,既增加了砂浆的粘结抗拉强度 ,又使砂浆有足够的抗压强度、抗折强度和弹性模量 .当羟乙基甲基纤维素掺量被控制在一定范围内时 。