非均匀吸放湿过程对建材导热系数的影响

在针对含湿建材导热系数的研究中，预测模型一般假设材料含湿均匀，试验测量多采用均匀增湿方案，但实际使用过程中，受室内外湿度及气象条件影响，造成吸放湿过程中湿组分非均匀分布，相同含湿量下吸放湿过程中的材料导热系数存在差异。通过对孔隙特征不同的加气混凝土(AAC)、发泡水泥(FC)、红砖(RB)材料进行增减湿试验，控制试件在试验环境中的放置时间获得质量含湿量不均匀的试件，选择瞬态导热系数测量方案，通过分析含湿多孔建材增/减湿全过程导热系数变化趋势，研究非均匀湿分布材料导热系数变化特性。结果表明：AAC、FC、RB加湿过程导热系数相较干燥状态下分别增长了279%、266%、106%。增减湿过程中，含湿量相同的AAC导热系数差值范围约为-20.2%~63.4%，FC差值范围约为14.5%~53.3%，RB差值范围约为-18.0%~37.4%。     

Heterogeneous Nature of Calcium Silicate Hydrate(C-S-H) Gel:A Molecular Dynamics Study

Structure and mechanical properties of Calcium silicate hydrate (C-S-H) at a molecular level act as "DNA" of cement-based construction materials.In order to understand loading resistance capability of C-S-H gel,research on molecular dynamics (MD) was carried out to simulate the uniaxial tension test on C-S-H model along x,y,and z directions.Due to the structure and dynamic differences of the layered structure,the C-S-H model demonstrates heterogeneous mechanical behavior.On an XY plane,the cohesive force can reach 4 GPa,which is mainly provided by the Ca-O and Si-O ionic-covalent bonds.The good plasticity of calcium silicate sheet is attributed to the silicate branch structure formation and the recovery role of interlayer calcium atoms.However,in z direction,C-S-H layers connected by the unstable H-bonds network,have the weakest tensile strength 2.2 GPa.This results in the brittle failure mode in z direction.The relatively low tensile strength and poor plasticity in z direction provides molecular insights into the tensile weakness of cement materials at macro-level.     

Effect of curing conditions on the hydration and performance of CFBC ash cementitious system

Circulating fluidized bed combustion （CFBC） ash can be used as supplementary cementitious material for concrete production for its high pozzolanic activity. We investigated the effect of curing conditions on the hydration and performance of CFBC ash-Portland cement system （30： 70, by mass） including hydration products, paste microstructure, linear expansion ratio, chemically combined water content and compressive strength. The results show that tobermorite rather than ettringite is generated under the condition of autoclaved curing. The expansion and mortar strength of the system cured in water is higher than those cured in air at a given age, and the strength and bulk volume may retract under the condition of air curing. In addition, autoclaved curing facilitates the increase of strength gain at early curing ages （the increase rate lowers down in the following ages） and the improvement of system volume stability. It is suggested that sufficient water is necessary for the curing of CFBC ash cementitious system, and autoclaved curing may be considered where volume stability is a primary concern.     

Strength and Microstructure of Mortar Containing Glass Powder and/or Glass Aggregate

The compressive strength of mortar containing glass powder(GP) and/or glass aggregate(GA) was tested, and its microstructure was also studied by thermogravimetric and differential thermal analysis(TG-DTA), scanning electron microscopy(SEM), energy dispersive spectroscopic analysis(EDX), and X-ray diffraction(XRD) techniques. The incorporation of GA would decrease the compressive strength of the mortar in the absence of GP. Incorporating both GA and GP could change the hydration environment, promote pozzolanic reaction of GP and improve the compressive strength. GP does not lead to but can effectively control ASR(Alkali Silica Reaction). GP and GA do not transform the type of hydrates, but have a great influence on the amounts of hydration products, and generate more calcium silicate hydrate(C-S-H gel) with lower Ca/Si ratio. GP and GA with good gradation will make the microstructure denser.     

Influence of Hydrothermal Synthesis Conditions on the Formation of Calcium Silicate Hydrates: from Amorphous to Crystalline Phases

Hydrothermal treatment has been widely applied in the synthesis of well crystalline calcium silicate hydrate(CSH), such as tobermorite and xonotlite. However, both morphology and crystallinity of CSH are greatly affected by the conditions of hydrothermal treatment including siliceous materials, temperature increase rate and isothermal periods. In this study, the influence of hydrothermal conditions on the growth of nano-crystalline CSH was investigated based on XRD analysis. Results showed that siliceous materials with amorphous nature(i e, nano silica powder) are beneficial to synthesize pure amorphous CSH, while the use of more crystallized siliceous materials(i e, diatomite and quartz powder) leads to producing crystalline CSH. Results also indicate that the formation of tobermorite and xonotlite is greatly affected by the temperature rise rate during hydrothermal treatment.     

Influence of Polycarboxylic-type Admixture on the Strength of Autoclaved Aerated Concrete

The influence of polycarboxylic-type admixture on the strength of autoclaved aerated concrete(AAC) was investigated. The flexural strength and compressive strength of AAC with polycarboxylic admixture(PA) were tested. The microstructure of AAC reinforced by PA was analyzed using scanning electron microscopic(SEM) methods. The crystal structure analysis of AAC with PA was also carried out using X-ray diffraction(XRD). The results showed that the compressive strength and flexural strength of AAC were increased by 43.9% and 42.8%, respectively, when 1.5wt% of PA was mixed. In addition, the dosage of admixture influenced the reinforcing effect. Admixture affected pore structure and surface characteristic of the products in autoclaved curing process and improved the formation of high crystallite tobermorite which led to the enhancement of the compressive and flexural strength of AAC.     

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.     

矿渣基改性材料干化城市污泥的效果及微观分析

通过不同掺入量和养护龄期下矿渣基改性剂对城市污泥含水率的影响,采用X射线衍射、扫描电镜和热重分析方法表征矿渣基改性材料和干化污泥的水化产物和微观结构,探讨矿渣基改性材料对污泥干化的效果及机理.结果 表明:随着矿渣基改性剂掺量的增加和养护龄期的延长,污泥含水率大幅减少;在相同条件下,矿渣基改性剂对污泥的干化效果明显好于生...     

Thermal conductivity measurements on xonotlite-type calcium silicate by the transient hot-strip method

The experimental results of the thermal conductivities of xonotlite-type calcium silicate insulation materials were presented at different temperatures and pressures.Two appropriative surroundings,i.e.an elevated temperature surrounding from ambient temperature to 1450 K and a vacuum surrounding from atmosphere pressure to 10-3 Pa,were designed for the transient hot-strip (THS) method.The thermal conduetivities of xonotlite-type calcium silicate with four densities from ambient temperature to 1000 K and 0.045 Pa to atmospheric pressure were measured.The results show that the thermal conductivity of xunotlite-type calcium silicate decreases apparently with the fall of density,and decreases apparently with the drop of pressure,and reaches the least value at about 100 Pa.The thermal conductivity of xonotlite-type calcium silicate increases almost linearly with T3,and increases more abundantly with low density than with high density.The thermal conductivity measurement uncertainty is estimated to be approximately 3% at ambient temperature,and 6% at 800 K.     

钢渣-杂填土基层材料配合比优化试验研究

以杂填土、钢渣、矿渣微粉为原料,采用土体固化技术混拌制备钢渣-杂填土基层材料。开展钢渣、混凝土破碎料、素土等主料对基层材料强度的耦合影响试验,构建回归模型,得到主料最优掺入比例,试验验证表明,回归模型预测值误差小于2%;以钢渣、混凝土破碎料、水泥、固化剂为因素开展正交试验,得到的最优结果与强度耦合影响试验基本一致,从而确定钢渣-杂填土最优配合比。最优配合比试件试验结果表明：钢渣-杂填土强度随龄期增长显著提升,30 d高温水浴膨胀率仅为1.03%。X射线衍射分析（XRD）及扫描电子显微镜（SEM）测试表明：矿渣微粉中SiO₂与钢渣中f-CaO反应生成水化硅酸钙（C-S-H）凝胶,同时发现土壤固化剂对土体的改性可有效抑制钢渣膨胀;C-S-H凝胶填充于混凝土破碎料、钢渣、土颗粒间,增加了钢渣-杂填土基层材料密实度,使其强度得以提高。     

轻质自保温陶粒蒸压加气混凝土试验研究

目前蒸压加气混凝土砌块存在自身强度低、自保温性能差、易开裂等现象。本文通过对陶粒蒸压加气混凝土原材料优化设计、生产工艺参数调整、以及陶粒对加气混凝土浆体混合料和易性影响,结合陶粒蒸压加气混凝土的增强作用机理和减缩作用机理分析,利用正交设计试验方法,研制出立方体抗压强度8.8 MPa、干燥收缩值0.156 mm/m、导热系数0.127 W/(m.k)的陶粒增强蒸压加气混凝土。     

Hydration products of cement-silica fume-quartz powder mixture under different curing regimes

Composition, morphology, and structure of hydration products in hardened pastes of three kinds of blended cement(cement-silica fume, cement-quartz powder and cement-silica fume-quartz powder) hydrated under different curing regimes(standard curing, 90 ℃ steam curing, 200 ℃ and 250 ℃ autoclave curing) were investigated by X-ray diffraction and field emission scanning electron microscope equipped with EDAX system. Results showed that the main hydration products in three kinds of hardened pastes under standard curing condition are all C-S-H gels, CH, and AFt. Under 90 ℃ steam curing condition, the main hydration products of cement-silica fume and cement-silica fume-quartz powder are C-S-H gels, whereas those of cement-quartz powder are C-S-H and CH. Under 200 or 250 ℃ autoclave curing condition, no obvious crystallized CH phase is found in hardened pastes of three kinds of blended cement, and C-S-H gels are transformed into one or more crystalline phases such as tobermorite, jennite, and xonotlite. The chemical composition and morphology of these crystalline phases depend on the composition of mixture and autoclave temperature.     

The early hydration and strength development of high-strength precast concrete with cement/metakaolin systems

To study the relationship between material composition, curing conditions and strength development, the study simulated high-strength precast concrete pile production, and a high-strength mortar up to 90 MPa was designed and a hot-water pool was built for concrete curing. The major point of the study was to achieve a high early strength by using cement/metakaolin systems without autoclave curing with high-pressure steam. By means of XRD and thermal analysis, the progress of the hydration of the cement pastes blended with metakaolin was characterized. The main results indicate that high strength can be obtained at early age by the use of metakaolin and thermal treatment (hot-water curing). The improvement in strength of mortars with metakaolin can be explained by an increase in the amount of C-S-H and C-S-A-H hydrated phases and a decrease in the amount of calcium hydration(CH). Further more, a decrease in Ca/Si ratio of the matrix was observed from the results of EDX analysis, which also leaded to an improvement of the compressive strength. These results are of great importance for the high-strength precast concrete manufacturing industry.     

温度和含湿量对建筑材料导热系数的影响

导热系数是建筑材料最重要的热湿物性参数之一,温度和含湿量均能够对其产生影响。当温度和含湿量中的一个因素被确定后,一元线性函数通常被用来描述另一个因素对导热系数的影响。然而,实际情况下二者对导热系数的影响是同时存在的。采用防护热板法对聚苯乙烯泡沫（EPS）、岩棉、混凝土、胶粘剂和抹面胶等5种典型建筑材料在不同温度和含湿量下的导热系数进行测试。结果表明,对上述材料而言,二元线性函数可以用来描述温度和含湿量对导热系数的影响,且温度和含湿量之间的交互作用可以被忽略。对于EPS和岩棉等弱吸湿弱毛细材料而言,可以将二元线性函数简化为仅与温度相关的一元线性函数。     

镁渣等工业废渣应用现状的研究及前景分析

镁渣矿物属于介稳的高温型结构,结构中存在活性的阳离子,所以,镁渣本身具有很高的水化活性,水化后生成水化硅酸钙凝胶,镁渣作为破胶凝材料是可行的,镁渣中的[SiO4]4-更易丢失,链断裂,形成类似于有机-无机杂化物的结构,在镁渣中掺入一定的硅酸盐水泥或磨细硅酸盐水泥熟料和磨细矿渣,以提高镁渣胶凝材料的耐久性,镁渣作为砂浆的胶结材料是非常理想的,镁渣不但可以提高砂浆的和易性,而且还可以提高砂浆的强度和耐久性,镁渣中掺入一定量的轻骨料,可制作轻质保温墙体材料或制成屋面材料。     

Mechanical properties and microstructure of sulfur aluminate cement composites reinforced by multi-walled carbon nanotubes

The effect of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties and microstructure of sulfur aluminate cement (SAC) composites was investigated. The dispersed MWCNTs were added into SAC in various weight contents.The results of mechanical properties of the MWCNTs/SAC composites indicated that the addition of 0.08 wt% MWCNTs can improve the SAC compressive strength, flexural strength, and bend-press ratio by 15.54%, 52.38%, and 31.30% at maximum, respectively. The degree of SAC hydration and porosity and pore size distribution of the matrix were measured by X-ray diffraction (XRD), thermal analysis (TG/DTG), and mercury intrusion porosimetry (MIP). Results show that the addition of MWCNTs in SAC composites can promote the hydration of SAC and the formation of C-S-H gel, reduce the porosity and refine the pore size distribution of the matrix. The microstructure was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is found that the MWCNTs have been dispersed homogeneously between the hydration products of SAC paste and act as bridges and networks between cracks and voids, which prevents the development of the cracks and transfers the load.     

采用发泡聚苯乙烯保温砂浆芯材的夹芯叠合板受弯性能

为了提升装配式建筑预制夹芯保温叠合板（CSICPs）的工业化生产效率,从材料密度、吸水率、导热系数、抗压强度、抗折强度、压折比及软化系数等指标出发,借助正交试验设计方法,采用极差及方差分析,确定适用于夹芯保温叠合板的发泡聚苯乙烯保温砂浆（ETIM）的最佳配比. 在此基础上,针对2块ETIM夹芯保温叠合板、1块发泡聚苯乙烯（EPS）板夹芯保温叠合板及1块普通钢筋桁架叠合板进行受弯性能对比试验,分别从承载能力、荷载-挠度曲线、荷载-钢筋应变曲线及抗滑移性能方面展开分析. 结果表明：夹芯保温叠合板与普通钢筋桁架叠合板的受弯破坏过程类似,均经历弹性阶段、弹塑性阶段及破坏阶段;预制底板构造形式及芯材对夹芯叠合板的受弯性能有较大影响;采用ETIM芯材的夹芯保温叠合板的受弯性能优于采用EPS板的夹芯保温叠合板;钢筋桁架的配置对提升夹芯保温叠合板的受弯及抗滑移性能有较为显著的作用.     

Early hydration of composite cement with thermal activated coal gangue

Composite cement samples were prepared by mixing clinker, gypsum with burnt coal gangues which was calcined at various temperatures. The mechanical strength and Ca(OH)₂ content in the cement paste were tested, and the paste composition and microstructure were analyzed by thermogravimetry-differential thermal analysis (TG-DSC), X-ray diffraction(XRD), scanning electronic microscopy (SEM) and pore structure analysis. Results demonstrate that the thermal activated coal gangue could accelerate the early hydration of cement clinker obviously, which promotes the gangue hydration itself. The early hydrated products of the cement are C-S-H gel, Ca(OH)₂ and AFt. The cement with 30% (in mass) the gangue exhibits higher mechanical strength, and among all the cement samples the one with the gangue burnt at 700 °C displays the highest hydration rate, mechanical strength, the most gel pores and the lowest total porosity.     

Strength of limestone-based non-calcined cement and its properties

A new type of cement was prepared with ground limestone powder, blastfurnace slag, steel slag and gypsum without calcination. The fraction of ground limestone powder in the cement was as high as 40 wt%–60 wt% without Portland clinker. All of its physical properties can meet the requirements of masonry cement standards. The impact of limestone content on physical properties of the cement and determined its impact on law was investigated. The steel slag can excit the aquation activity of this cement effectively, and the influence of its quantity on the strength of the materials was studied, which shows that the optimum quantity of mixing is 10%. By way of changing the different content of the lime stone by quartzy sample, the law of the compression strength and the PH value was determined, confirming that the lime stone can promote the early aquation of the slag and improve the early strength. The main hydration product of this cement is calcium aluminate hydrate, ettringite and calcium silicate hydrate, as indicated by XRD and SEM analysis.     

石棉代用纤维的研究

本文总结了石棉代用纤维的研究工作.通过在压蒸硅酸钙中掺加玻璃纤维(Wolmix、Cem—Fil耐碱玻璃纤维);矿棉(Inorphil);硅酸铝纤维(Fiberfrax);碳纤维(Sigrafil);有机纤维(Kevlar、Dolan、and Crystalline Cellulose)和纤维矿(Attapulgite、Halloysite、Wollastonite and Asbestos)制成的复合材料性能研究,找到碳纤维和Cem—Fil玻璃纤维是石棉可能的代用纤维,在力学性能上碳纤维更好些,甚至超过原石棉纤维.