利用固体激发剂生产^#525碱矿渣水泥

本文阐述了碱矿渣水泥的应用前景及国内碱矿渣水泥研究中存在的问题，介绍了利用固体激发剂生产碱矿渣水泥的研究结果，找出了在试验条件下利用固体激发剂生产碱矿渣水泥的最佳参数，测试了所得碱矿渣水泥性能，初步探索了碱矿渣水泥性能优异的原因。碱矿渣水泥生产能耗低、生产成本低、性能优良，有可能成为一种有发展前途的新型水泥。     

The theoretical maximum achievable dispersion of nanoinclusions in cement paste

A major challenge of successfully incorporating nanometric inclusions (nanoinclusions) within cement paste is achieving a uniform distribution of the nanoinclusions. Cement particles have a larger diameter than the average spacing between nanoinclusions when the nanoinclusions are fully dispersed, which means that the presence of cement particles in the fresh paste degrades the maximum achievable dispersion of the nanoinclusions in the hardened paste. To determine the significance of this effect, a novel method for dispersion quantification was implemented to calculate the theoretical maximum achievable dispersion of nanoinclusions in fresh cement paste. Three-dimensional simulations were performed for cement pastes with common values of water to cement ratio, nanoinclusion to cement ratio, and cement fineness. The results show that for cementitious nanocomposites simulated in this study, degradation of the maximum theoretical achievable dispersion of nanoinclusions due to the presence of cement particles is negligible as long as the cement particles are not agglomerated.     

高贝利特硫铝酸盐水泥活化研究进展

基于我国提出的“双碳”战略目标,水泥行业应针对其高碳排放问题制定脱碳计划,因此,低碳水泥的研发和应用迫在眉睫。高贝利特硫铝酸盐水泥是一种在节能减排的同时能够资源化利用含铝工业废弃物的新型低碳水泥,未来也将会是一种具有高强度的低成本水泥。因此,高贝利特硫铝酸盐水泥的研发促进了水泥行业的绿色化发展。然而,水泥矿物组成中高活性无水硫铝酸钙含量较低,导致水泥石早期强度较低。对水泥早期活性进行研究可提升水泥强度,进而扩大其应用范围。本文通过简述高贝利特硫铝酸盐水泥的组成、特点和研究现状,从水泥主要矿物硅酸二钙、无水硫铝酸钙的活化和水泥矿物组成设计优化三个方面总结了影响高贝利特硫铝酸盐水泥活性的因素,旨在为高性能水泥的研制提供理论指导。     

用正交试验法确定复合水泥配方

用正交试验法研究了以沸石和石灰石生产复合水泥的原料选择及最佳掺量，借助XRD和SEM等测试手段，对水泥水化产物和微观结构进行了分析。结果表明：正交试验法可以较好地应用于复合水泥配方的制定，为水泥企业生产不同称号的复合水泥提供可靠的理论依据。     

水泥净浆结粒评价方法比较与研究

试验比较了2种测量净浆结粒的方法——水筛法和针入法,并利用计算机软件引入Boltsmann模型,对试验结果进行了S拟合。拟合曲线分析结果表明,水筛法适用于测量结粒量小的水泥,针入法适用于测量结粒量大的水泥。     

高掺量粉煤灰水泥胶凝材料的水化性能研究

用ＴＭＳ－ＧＣ,ＸＲＤ,ＤＴＡ,ＳＥＭ等方法研究了高掺量粉灰水泥胶凝材料的水化性能;分析了粉煤灰掺量、激发剂等对高掺量粉煤灰水泥胶凝材料水化性能的影响,并与硅酸盐水泥的水化性能进行了对比。结果认为：高掺量粉煤灰水泥的水化速度低于不掺灰的硅酸水泥的水化速度,但后期增长较快;激发剂能加快高掺量粉煤灰水泥的水化速度。     

聚苯乙烯微球改性水泥耐Na2CO3腐蚀的研究

硅酸盐水泥硬化成水泥石之后,在碳酸盐环境下,水泥中的组成成分氢氧化钙会与碳酸盐发生碳化作用从而引起其结构发生破坏,为改善水泥的抗Na2CO3腐蚀性能,在水泥中加入聚苯乙烯（PS）微球,研究水泥石腐蚀前后质量变化和PS微球与水泥作用的机理,以及采用电子扫描显微镜（SEM）分析改性水泥的微观结构形态。     

关于水泥与超塑化剂相适应性的几个问题

从水泥化学角度讨论了预拌混凝土的经与超塑化剂相适应性的几个问题。超塑化剂主要是大量吸附在水泥颗粒表面的水化产物上而不是吸附在未水化水泥颗粒表面。水泥与超塑化剂相适应性不好主要是水泥化产物吸附大量的超塑化剂所致。凡是加速水泥初期水化的因素，特别是使水泥凝结加速的因素如Ｃ，Ａ含量过高、ＳＯ３掺量过少、碱含量高以及掺入内比表面积大的火山灰质混合材等均使水泥与超塑化剂的相适应性变差。据此，提出了生产与超塑     

Phase distribution and microstructural changes of self-compacting cement paste at elevated temperature

Self-compacting concrete, as a new smart building material with various advanced properties, has been used for a wide range of structures and infrastructures. However little investigation have been reported on the properties of Self-compacting when it is exposed to elevated temperatures. Previous experiments on fire test have shown the differences between high performance concrete and traditional concrete at elevated temperature. This difference is largely depending on the microstructural properties of concrete matrix, i.e. the cement paste, especially on the porosity, pore size distribution and the connectivity of pores in cement pastes.In this contribution, the investigations are focused on the cement paste. The phase distribution and microstructural changes of self-compacting cement paste at elevated temperatures are examined by mercury intrusion porosimetry and scanning electron microscopy. The chemical decomposition of self-compacting cement paste at different temperatures is determined by thermogravimetric analysis. The experimental results of self-compacting cement paste are compared with those of high performance cement paste and traditional cement paste. It was found that self-compacting cement paste shows a higher change of the total porosity in comparison with high performance cement paste. When the temperature is higher than 700 °C, a dramatic loss of mass was observed in the self-compacting cement paste samples with addition of limestone filler. This implies that the SCC made by this type of self-compacting cement paste will probably show larger damage once exposed to fire. Investigation has shown that 0.5 kg/m³ of Polypropylene fibers in the self-compacting cement paste can avoid the damage efficiently.     

Stress relaxation of foamed high-alumina cement paste

A series of stress relaxation tests on foamed high-alumina cement pastes with different relative densities under various temperatures and imposed fixed strains were conducted to study the effects of relative density and imposed strain on the stress relaxation rates of foamed high-alumina cement pastes. At the same time, the activation energy for stress relaxation of foamed high-alumina cement paste was determined from experimental results. Experimental results on the stress relaxation rates of foamed high-alumina cement pastes are also compared to a theoretical expression obtained from a cell-edge relaxation-bending model. Consequently, the microstructural coefficients included in the theoretical expression for describing the stress relaxation rates of foamed high-alumina cement pastes are found. Furthermore, the stress relaxation rates of foamed high-alumina cement pastes can be predicted from the theoretical expression once their relative density and the imposed strain are known.     

水泥粒径分布对水泥石孔结构与强度的影响

通过计算不同粒径分布水泥样品的堆积密度和测定水泥石强度和孔结构,探讨水泥粒径分布对水泥石强度和结构的影响。研究表明：适当的水泥粒径分布可以使水泥具有最佳的堆积密度,并使水泥水化物的生成量与水泥浆初始孔隙量相匹配,从而得到孔隙率较小的密实而均匀的水泥石,使水泥石的性能提高。     

美国水泥市场及水泥工业概况

美国2018年水泥总产量约为8850万吨,国内水泥消耗量约70%销往预拌混凝土生产商。外资水泥厂约占美国水泥厂的80%。水泥总产量的50%集中在德克萨斯州、加利福尼亚州、密苏里州、弗罗里达州和阿拉巴马州。美国现有水泥厂大部分比较老旧,规模普遍偏小,替代燃料的使用较广。水泥成品主要以火车散装方式出厂。     

Mechanical response and crack propagation of oil well cement under dynamic and static loads

The dynamic mechanical properties and fracture mechanism of three types of oil well cement with different formulations were investigated using a Φ50?mm split Hopkinson pressure bar (SHPB) and quasi-static mechanical tests were conducted with a hydraulic universal testing machine. The stress-strain diagram, time-stress diagram, total energy absorption diagram, and the dynamic growth factor (DIF) under different strain rates were obtained. The crack propagation process of the oil well cement under dynamic loading is evaluated using high-speed photography to determine the fracture mechanism. The test results show that the strength of the cement increases under a dynamic impact. The compressive strength of the pure cement increases from 37?MPa to 184.80?MPa under static loading. However, the peak stress of the cement stone strengthened with cellulose fiber is lower under a dynamic load than a static load. Under dynamic loading, the absorption energy is higher for the pure cement stone than for the cement stone reinforced with whiskers and cellulose. Furthermore, the crack initiation, crack propagation, and fracture characteristics of the oil well cement are different under dynamic and static loads. Under a static load, the rupture of the cement is the result of the propagation of the tensile cracks. Under dynamic loading, there are fewer micro cracks on the cement surface and a composite fracture results from tensile and shear cracks.     

The pozzolanic reactivity of monodispersed nanosilica hydrosols and their influence on the hydration characteristics of Portland cement

This study reveals that the nanosilica hydrosols with higher specific surface areas had faster pozzolanic reactivity, especially at early ages; moreover, the results are indicative of the accelerating influence of nanosilicas and silica fume on the hydration of cement. Faster initial and final setting times observed for cement pastes containing nanosilicas are consequence of these mechanisms. However, less hydration degree of cement compared to the plain paste was observed at age of 7 days and after. This can be attributed to the entrapment of some of mix water in the aggregates of nanosilicas formed in cement paste environment, making less water available for the progress of cement hydration. The same mechanism is believed to be responsible for the reduction of flowability of cement pastes.     

Alternative blended cement with ceramic residues: Corrosion resistance investigation on reinforced mortar

Blended cements are largely used for concrete: they are usually considered cements with a low environmental impact, as they require less clinker than ordinary Portland cement (OPC). Different constituents can be used as supplementary clinker component usually leading to cement with high resistance to outdoor environment. Polishing residue (PR), coming from porcelain stoneware tiles production, can be successfully used as new constituent for blended cement, however its action for enhancing the durability of cement matrix must be assessed. With this purpose, electrochemical tests (half cell potential, impressed voltage and linear polarization techniques) have been carried out on steel reinforced mortar samples, prepared using a 25% PR based cement and 100% OPC as binder and exposed to a 3.5% NaCl solution. The corrosion resistance results and microstructure analysis highlight better durability performances for PR based cement than those exhibited by OPC, mainly for curing time > 28 days.     

Grindability of some additions and its significance in the production of mixed cements

Grinding tests were conducted in a laboratory steel ball mill, to investigate the grind-ability of some natural and artificial materials as “additions” for incorporation in Portland cement. Strength tests were performed on mixed cements composed of 71% Portland cement clinker, 25% addition and 4% gypsum. In one series of experiments, the components of the mixed cement were separately ground and in another one they were simultaneously ground. It was found from surface production curves and from compressive strength data that when materials which are harder to grind than clinker such as sand are interground with clinker, the resulting cement develops higher early strength than a corresponding cement in which the pozzolanic addition is softer than clinker. For materials which are softer to grind than clinker, separate grinding of the cement components is better than combined grinding, particularly for the development of early strength.     

利用窑灰生产高效土壤稳定水泥的研究

研究了用纯窑灰、掺ＣａＳｏ４－ＣａＦ２复合矿经剂的窑灰煅烧熟料与适量石膏混合配制的窑灰水泥稳定土的力学性能,并探讨了煅烧温度和石膏掺量对窑灰水泥稳定土强度的影响。结果表明,窑灰水泥对土壤的稳定效果显著优于普通水泥。用于稳定土的水泥其技术指标与普通水泥有很大差异,可允许水泥中含有一定数量的ｆ－ＣａＯ,ＳＯ和碱含量。     

Comparative evaluation of cement-matrix composites with distributed versus networked exfoliated graphite

Cement with distributed exfoliated graphite (isotropic) is made by incorporating exfoliated graphite in the wet cement mix; cement with networked exfoliated graphite (anisotropic) is made by compressing a dry mixture of exfoliated graphite and cement particles, followed by curing with water. The graphite layers in the latter are preferentially oriented in the plane perpendicular to the compression direction; the in-plane electrical resistivity is much lower than the out-of-plane resistivity and the loss tangent, storage modulus and loss modulus are much higher for out-of-plane flexure than in-plane flexure. The latter gives higher density, lower electrical resistivity, higher compressive strength and superior vibration damping than the former. Compared to plain cement, it gives higher density and higher compressive strength. In contrast, cement with distributed exfoliated graphite gives lower density and lower compressive strength than plain cement, though it gives lower resistivity and superior damping. Distributed exfoliated graphite is detrimental when silica fume is present. The high damping of cement with networked exfoliated graphite is attributed to the effective sandwiching of the network ligaments by the cement matrix (constrained-layer damping); the high density and compressive strength are attributed to the low porosity caused by the compression of the exfoliated graphite during composite fabrication.     

Gradients of microstructure and diffusion properties in cement paste caused by drying

This paper demonstrates that the microstructure of hydrated cement paste varies with distance from an exposed, drying face. Supporting measurements of cement hydration, adsorption capacity, porosity and diffusion rate are reported for an ordinary Portland cement and an ordinary Portland/pulverised fuel ash blended cement at ages of 28 and 163 days. Possible causes of the microstructural gradients are discussed in relation to the effects of

• 1.a) moisture condition upon cement hydration and pore structure changes and
• 2.b) carbon dioxide upon cement hydrates and porosity.

The practical implications of microstructural gradients are discussed with particular reference to the region immediately below the exposed surface.