Matrix‐Based Encapsulation of Construction Chemicals Using High‐Shear Agglomeration

Encapsulation of dry superplasticizers in matrix‐based encapsulation systems was investigated. As basic material, commercially available fly ash was granulated by high‐shear agglomeration. Due to a high variability of factors affecting the encapsulation process and later release of admixtures, the design‐of‐experiments method was applied to reduce the quantity of experiments. Statistical evaluation indicates that the particle characteristics of the agglomerates were mostly influenced by the binder viscosity during the investigations. The delayed admixture release was enhanced by high binder viscosity and low energy input during the agglomeration process due to a coating of the bigger superplasticizer particles by the smaller fly ash. These results will help to develop encapsulated construction chemicals with controlled admixture delivery for the future application in a wide range of different building materials.     

硅锰渣-固硫灰复合辅助性胶凝材料水化机理研究

早期水化活性过低是限制冶炼渣在胶凝材料体系中大掺量应用的重要因素之一。利用固硫灰(CFBA)中的硫酸盐激发硅锰渣(SM)水化活性,并研究硅锰渣-固硫灰复合辅助性胶凝材料的水化过程及活性发展。结果表明:随着固硫灰掺量增加,胶砂流动度大幅下降,但其早期和后期活性得到有效提升;当固硫灰掺量为10%(质量分数)时,复合辅助性胶凝材料3 d、7 d和28 d活性指数分别达到61%、71%和95%,均高于单独使用硅锰渣体系(3 d、7 d和28 d活性指数分别为50%、53%和81%)。固硫灰的掺入激发了水泥和辅助性胶凝材料的早期水化,延缓了水化过程中钙矾石转变为单硫型水化硫铝酸钙(AFm),使得胶凝材料早期水化形成更多钙矾石。     

热活化铅锌尾矿基碱激发胶凝材料的制备及性能

以铅锌尾矿为主要原料,添加由矿渣、钢渣、氟石膏混合而成的辅助胶凝材料,以水玻璃和氢氧化钠为碱激发剂制备铅锌尾矿基碱激发胶凝材料。通过正交试验,探讨了水玻璃模数、水玻璃掺量及尾矿与辅助胶凝材料质量比对胶凝材料抗压强度的影响,并得出最佳原料配比。通过800 ℃、1 000 ℃、1 200 ℃的热处理,制备热活化铅锌尾矿基碱激发胶凝材料,并测试其性能。采用X射线衍射谱、傅里叶红外光谱和扫描电子显微镜对热活化前后尾矿和胶凝材料进行分析表征。结果表明,当水玻璃模数为1.8,水玻璃质量掺比为0.15,尾矿与辅助胶凝材料质量比为7 ∶3时,胶凝材料28 d抗压强度可达到20.68 MPa。胶凝材料内部形成大量水化硅酸钙(C-S-H)与硅铝多聚物构成三维网状结构,覆盖在尾矿晶体表面形成致密整体。当热活化温度为1 000 ℃时,胶凝材料28 d抗压强度达到28.05 MPa。热活化后的尾矿内部结构疏松,利于硅铝质在碱性条件下解聚,同时使得反应体系中生成了更多硅铝多聚体,取代了二聚体为主的C-S-H凝胶,为胶凝材料提供了更优良的抗压强度和早硬特性。此外胶凝材料对Pb、Zn重金属的固定作用极好,大幅降低了尾矿重金属Pb、Zn的毒性浸出浓度,有效解决了尾矿中重金属对周围环境的危害问题。     

水泥与减水剂相容性的定量评价和影响机理研究

根据净浆Marsh筒法与泌水率法两种方法的特点,在Marsh筒法相容性指数定量评价公式的基础上,引入抗泌水性能系数来进一步完善水泥与减水剂相容性定量评价公式.以固硫灰/钛矿渣掺入水泥为例,研究了水泥与聚羧酸减水剂的相容性及其定量评价分析,并结合减水剂吸附特性和Zeta电位测试进一步研究了辅助性胶凝材料对相容性的影响机理.     

聚醚大单体溶液pH对减水剂性能的影响

以甲基烯丙醇聚氧乙烯醚和丙烯酸为主要原料,对聚醚单体溶液(底料)pH进行调控合成聚羧酸减水剂。通过测定聚醚转化率及减水剂相对分子质量及其分布以及评价减水剂的应用性能,确定了聚醚大单体溶液pH变化范围以及不同酸种类对减水剂性能的影响。结果显示,通过控制底料pH提高了聚醚大单体转化率,并且当底料pH控制为3时其转化率最高,由未调控pH的87.41%提升至pH为3时的95.43%,此时合成减水剂的分子量分布指数较小,由未调控pH时的3.183降至2.884;采用硫酸控制底料pH时,溶液中存在的硫酸盐为硫酸钠,其快速溶解减少了聚羧酸减水剂被水泥水化产物的包裹和消耗,更有利于提高聚羧酸减水剂分散性能。结果表明,通过控制聚醚大单体溶液pH的方式,在不改变减水剂合成工艺操作的前提下也可提升聚羧酸系减水剂的整体性能。     

Supplementary cementitious materials for mitigating degradation of kraft pulp fiber-cement composites

Kraft pulp fiber reinforced cement-based materials are being increasingly used where performance after exposure to environmental conditions must be ensured. However, significant losses in mechanical performance due to wet/dry cycling have been observed in these composites, when portland cement is the only cementitious material used in the matrix. In this research program, the effects of partial portland cement replacement with various supplementary cementitious materials were investigated. Binary, ternary, and quaternary blends of silica fume, slag, Class C fly ash, Class F fly ash, metakaolin, and diatomaceous earth/volcanic ash blends were examined for their effect on the degradation of kraft pulp fiber-cement composite mechanical properties (i.e., strength and toughness) during wet/dry cycling. After 25 wet/dry cycles, it was shown that binary composites containing 90% slag, 30% metakaolin, or greater than 30% silica fume did not exhibit any signs of degradation, as measured through mechanical testing and microscopy. Ternary blends containing 70% slag/10% metakaolin or 70% slag/10% silica fume were also effective in preventing degradation. A reduction in calcium hydroxide content and the stability of the alkali content due to supplementary cementitious material addition were shown to be primary mechanisms for improved durability.     

The influence of superabsorbent polymers on the autogenous shrinkage properties of cement pastes with supplementary cementitious materials

Fly ash and blast-furnace slag containing binders are frequently used in the construction industry and it is important to know the extent of autogenous shrinkage and its (ideal) mitigation by superabsorbent polymers in these systems as a function of their age. In this paper, the autogenous shrinkage was determined by manual and automated shrinkage measurements. Autogenous shrinkage was reduced in cement pastes with the supplementary cementitious materials versus Portland cement pastes. At later ages, the rate of autogenous shrinkage is higher due to the pozzolanic activity. Internal curing by means of superabsorbent polymers is successful, independent of this long term higher rate of shrinkage in mixtures with supplementary cementitious materials.     

Effect of supplementary cementitious materials on the compressive strength and durability of short-term cured concrete

This research focuses on studying the effect different supplementary cementitious materials (silica fume, fly ash, slag, and their combinations) on strength and durability of concrete cured for a short period of time—14 days. This work primarily deals with the characteristics of these materials, including strength, durability, and resistance to wet and dry and freeze and thaw environments. Over 16 mixes were made and compared to the control mix. Each of these mixes was either differing in the percentages of the additives or was combinations of two or more additives. All specimens were moist cured for 14 days before testing or subjected to environmental exposure. The freeze-thaw and wet-dry specimens were also compared to the control mix.Results show that at 14 days of curing, the use of supplementary cementitious materials reduced both strength and freeze-thaw durability of concrete. The combination of 10% silica fume, 25% slag, and 15% fly ash produced high strength and high resistance to freeze-thaw and wet-dry exposures as compared to other mixes. This study showed that it is imperative to cure the concrete for an extended period of time, especially those with fly ash and slag, to obtain good strength and durability. Literature review on the use of different supplementary cementitious materials in concrete to enhance strength and durability was also reported.     

Rheological properties of cementitious materials containing mineral admixtures

The rheological properties of cementitious materials containing fine particles, such as mineral admixtures (MA), were investigated using a Rotovisco RT 20 rheometer (Haake) with a cylindrical spindle. The mineral admixtures were finely ground blast furnace slag, fly ash and silica fume. The cementitious materials were designed as one, two and three components systems by replacement of ordinary portland cement (OPC) with these mineral admixtures. The rheological properties of one-component system (OPC) were improved with increasing the dosage of PNS-based superplasticizer. For two-components systems, yield stress and plastic viscosity decreased with replacing OPC with blast furnace slag (BFS) and fly ash (FA). In the case of OPC-silica fume (SF) system, yield stress and plastic viscosity steeply increased with increasing SF. For three components systems, both OPC-BFS-SF and OPC-FA-SF systems, the rheological properties improved, compared with the sample with SF. In the two and three components systems, the rheological properties of samples containing BFS improved much more than with FA replacement alone.     

地质聚合物应用现状及前景展望

地质聚合物是一种无机聚合铝硅酸盐胶凝材料。由于其特殊的缩聚三维网络结构,使其在众多方面具有高分子材料、水泥和陶瓷,金属等材料的特征。分析了地质聚合物的聚合反应机理,性能特点,简要叙述了地质聚合物的发展历程和应用现状,并概述了其在工程建筑、有毒废料、涂料、固封材料和陶瓷材料等领域的应用发展前景。     

Micro- and macroscale coefficients of friction of cementitious materials

Millions of metric tons of cementitious materials are produced, transported and used in construction each year. The ease or difficulty of handling cementitious materials is greatly influenced by the material friction properties. In the present study, the coefficients of friction of cementitious materials were measured at the microscale and macroscale. The materials tested were commercially-available Portland cement, Class C fly ash, and ground granulated blast furnace slag. At the microscale, the coefficient of friction was determined from the interaction forces between cementitious particles using an Atomic Force Microscope. At the macroscale, the coefficient of friction was determined from stresses on bulk cementitious materials under direct shear. The study indicated that the microscale coefficient of friction ranged from 0.020 to 0.059, and the macroscale coefficient of friction ranged from 0.56 to 0.75. The fly ash studied had the highest microscale coefficient of friction and the lowest macroscale coefficient of friction.     

外掺料对磷石膏基胶凝材料力学及导热性能的影响

将磷石膏应用于建筑业,可以解决磷化工副产物堆积的问题。采用单因素实验,通过改变水灰质量比、粉煤灰掺量、生石灰掺量等条件来研究各因素对磷石膏基胶凝材料力学性能及保温性能的影响,借助X射线衍射（XRD）、X射线荧光光谱（XRF）、扫描电镜（SEM）等手段来分析磷石膏基胶凝材料的物化性质和形貌结构。结果表明,磷石膏基胶凝材料的导热系数和抗压强度都与水灰质量比呈负相关,在水灰质量比为0.250时胶凝材料的抗压强度最大、水灰质量比为0.550时胶凝材料的导热系数最小;粉煤灰在磷石膏基胶凝体系中除了提供胶凝性能外,还会被生石灰激发出活性,增强胶凝体系的综合性能,粉煤灰掺量为50%（质量分数）时胶凝体系的综合性能最佳;生石灰在磷石膏基胶凝体系中对杂质的吸附效果明显,生石灰掺量超过7%（质量分数）以后对胶凝体系的保温性能和力学性能的增强效果明显。     

Topological controls on the dissolution kinetics of glassy aluminosilicates

Fly ash which encompasses a mixture of glassy and crystalline aluminosilicates is an abundant supplementary cementitious material (SCM), valuable for replacing ordinary portland cement (OPC) in the binder fraction in concrete. Because higher OPC replacement levels are desired, it is critically important to better understand and quantify fly ash reactivity. By combining molecular dynamics (MD) simulations and vertical scanning interferometry (VSI), this study establishes that the reactivity of the glassy fractions in a fly ash with water (i.e., their aqueous dissolution rate) is controlled by the number of constraints placed on atoms within the disordered aluminosilicate network. More precisely, an Arrhenius‐like dependence of dissolution rates on the atomic network topology is observed. Such topological controls on fly ash reactivity are highlighted for a range of U.S. commercial fly ashes spanning CaO‐enriched and SiO₂‐enriched compositions. The structure‐property relationships reported herein establish an improved framework to control and estimate fly ash‐cement interactions in concrete.     

Characteristics and applications of flash metakaolins

This paper presents physical, chemical and mechanical characteristics of metakaolins obtained from an industrial flash calciner, in order to compare their properties with standard industrial metakaolin produced in a rotary kiln calciner. Three kaolins, with three levels of purity, were calcined by these two different methods to give six different metakaolins for the study. The results showed that the method of calcination did not affect the chemical composition of the metakaolins formed but did influence their physical properties and performance as a supplementary cementitious material when blended with Portland cement, and in geopolymer synthesis. Flash metakaolins have a lower water demand than rotary metakaolins, which can be explained by the morphological properties of the flash metakaolin, induced by the calcination process. Traditional rotary-calcined metakaolins tend to be angular layered particles, whereas flash metakaolins contain spherical particles. Mechanical test results showed that the two methods of calcination can lead to metakaolins with equivalent performance in the synthesis of construction materials.     

Influence of adsorbed and nonadsorbed polymer additives on the viscosity of magnesium oxide suspensions

Adsorbed polymer additives have been employed to reduce water content and improve cement workability through lowering viscosity, but the influence of over‐dosage and the presence of nonadsorbed chains have yet to be fully understood. Model magnesium oxide (MgO) suspensions were used to investigate the potential processing effect of “free” chain concentration on cementitious mixtures. The rheological impact of the free chains was measured through incorporation of nonadsorbing poly(ethylene glycol) (PEG) to suspensions stabilized with an adsorbed comb‐polymer superplasticizer. Analyses of the rheological data, that showed viscosity‐increases and viscosity‐reduction due to free PEG concentrations revealed a transition from depletion flocculation to depletion stabilization that contributed to the flow properties of the suspensions. The viscosity‐reduction observed for high concentrations of free chains may be useful for improved mixing of cements with free polymer in addition to the adsorbed polycarboxylate ether‐based superplasticizer. Additionally, the influence of free PEG on the macroscale flow behavior was also examined through local velocity measurements under shear. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45696.     

Response Surface Analysis of the Corrosion Effect of Metakaolin in Reinforced Concrete

Silicon - Concrete is one of the most utilized construction materials. The use of sustainable cementitious material is one of the new trends in concrete technology. Several cementitious materials...     

纳米SiO2对钢渣水泥基胶凝材料的影响

钢渣和水泥具有相似的矿物组成,可以作为一种潜在的胶凝材料,然而钢渣掺量较高时并不利于混凝土早期性能的发展。以钢渣质量分数为30%的钢渣水泥基胶凝材料为研究对象,探讨纳米SiO₂对其早期性能的影响。主要通过测量流动度、凝结时间和抗压强度评估物理力学性能,并利用微量热分析、X射线衍射(XRD)、差热分析(DSC-TG)等方法对掺有纳米SiO₂的钢渣水泥基胶凝材料的水化过程和水化产物进行分析。结果表明,当纳米SiO₂掺入的质量分数为3%时,纳米SiO₂可充分发挥火山灰活性,消耗大量Ca(OH)₂,同时由于纳米SiO₂颗粒的结晶成核作用和微集料填充作用,促进了钢渣和水泥的水化,水化初期的放热速率有所提高,从而提高钢渣水泥基胶凝材料的力学性能,28 d的抗压强度提高了14.0%。     

Effect of the type of superplasticizer on the properties of cementitious systems incorporating slag

Superplasticizers have become an integral ingredient in the formulation of concretes. After 40?years, their use and dosage remain uncertain due to variations in their compositions and those of cement. In addition, the substitution of cement by supplementary cementitious materials having different chemical compositions exacerbates the problem without counting the multiplicity of superplasticizers to choose from. The present work consists of a study of the rheological and mechanical properties of cementitious systems containing slag and various types of superplasticizers. The tests were carried out on pastes, mortars and concretes incorporating slag in partial cement replacement and four superplasticizers types, polynaphthalene sulphonate (PNS) and three polycarboxylates (PC). The results of this study demonstrate that the viscosity and the yield stress increase with the rate of incorporation of the slag. The air increases with the polycarboxylates but this effect is less perceptible in the presence of the slag. Polycarboxylates improve workability more than PNS. The use of polycarboxylates reduces the viscosity and the yield stress. The compressive strength of concretes containing slag is low at early age but high at long run. They exhibit good resistances to scaling. The permeability to chloride ions is considerably reduced in the presence of the slag independently of the type of superplasticizer, suggesting good durability of these concretes in potentially aggressive external environments.     

不同类型减水剂对渣土基高流态回填材料性能的影响

相比传统回填材料,渣土基高流态回填材料具有高流态、自流平、自密实等优点,能够有效避免因压实不充分导致的工程问题。然而,渣土基高流态回填材料在使用中存在易沉陷、易泌水等问题,限制了其工程化应用空间。在本文中,选择了聚羧酸减水剂(PCE)、脂肪族减水剂(SAF)、萘系减水剂(FDN)、三聚氰胺减水剂(PMS)四种减水剂来调节渣土基高流态回填材料的用水量和流动度,同时比较了四种减水剂对渣土基高流态回填材料性能的影响。结果表明:在保持相同流动度下,四种减水剂的减水效果从高到低依次为PCE＞SAF＞PMS＞FDN;在经时流动度方面,FDN体系较其他减水剂体系在1 h内具有更好的流动性,四种减水剂体系的流动度保持性从优到劣依次为FDN＞PCE＞PMS＞SAF;四种减水剂均能降低渣土基高流态回填材料的泌水率,缩短渣土基高流态回填材料的凝结时间。     

KR脱硫渣碱激发矿渣的配比优化及水化特性

KR脱硫渣是铁水脱硫工序产生的废渣,多种固废协同制备胶凝材料是脱硫渣资源化的有效途径。本文利用KR脱硫渣、矿渣和脱硫石膏制备固废基胶凝材料,研究KR脱硫渣和矿渣掺量对胶凝材料力学性能的影响,优化原材料配比。通过XRD、TG-DSC、IR、SEM-EDS和水化热测试方法研究了固废基胶凝材料的水化产物及水化特性。结果表明,固废基胶凝材料优化配比为KR脱硫渣25%(质量分数,下同),矿渣60%,脱硫石膏15%,胶凝材料3 d、28 d、90 d抗压强度分别达到30.01 MPa、49.47 MPa和55.73 MPa。固废基胶凝材料的早期水化放热速率低,3 d累积放热量仅为普通硅酸盐水泥(OPC)的37.9%,其水化产物主要是针棒状钙矾石(AFt)和无定形水化硅酸钙(C-S-H)凝胶。KR脱硫渣中大量的Ca(OH)₂在水化早期可以碱激发矿渣,使玻璃相硅酸盐解体,同时与脱硫石膏反应促进AFt的生成。KR脱硫渣、矿渣和脱硫石膏协同反应使水化后期的水化产物持续增加,相互胶结形成致密结构,有利于强度的持续增长。