化学激发对煤气化渣-水泥体系抗压强度影响机理研究

针对煤气化渣大量堆存造成的环境污染和固废资源浪费的问题,本工作采用化学激发方法来激发煤气化渣活性,探究不同激发剂对煤气化渣?水泥体系抗压强度的影响.试验选取硫酸盐类、碱类和聚合盐类激发剂,确定最优激发剂种类和掺量;通过扫描电镜(SEM)、X射线衍射(XRD)和热重分析(TG)等微观手段,研究不同激发剂对煤气化渣?水泥体系水化产物的影响.结果表明,硫酸盐类最优激发剂为硫酸钠,最佳掺量为2.5％,试样3 d、28 d抗压强度增长率分别达14.3％、3.4％;碱类最优激发剂为氢氧化钙,最佳掺量为0.5％,试样3 d、28 d抗压强度增长率分别达18.4％、1.8％;聚合铝最佳掺量为2.0％,试样3 d、28 d抗压强度增长率分别达24.0％、3.3％.加入激发剂后试样早期抗压强度均得到提高,微观特征表明试样水化程度加深,且有助于钙矾石和凝胶体等水化产物的生成,提高试样强度,为煤气化渣在水泥基材料中的应用提供了理论依据.     

钢渣激发脱硫石膏水硬性胶凝材料的研究

研究旨在开发一种以钢渣为碱性激发剂,以烟气脱硫石膏、矿渣粉为主要为原料的脱硫石膏水硬性胶凝材料。该胶凝体系3天抗折强度和抗压强度可达4.4 MPa和15.8 MPa;28天抗折强度和抗压强度可达9.4 MPa和50.7 MPa。其试样的强度随钢渣掺量的增加而增加,而钢渣含量一旦超过8%后,增长幅度变缓,甚至开始降低。XRD和SEM分析表明,脱硫石膏-矿渣-激发剂体系的水化产物主要是钙矾石和C-S-H凝胶。脱硫石膏在水化过程中一部分参与水化形成水化产物钙矾石,其余部分被水化产物所包裹起集料骨架作用。     

钢渣激发脱硫石膏水硬性胶凝材料的研究

研究旨在开发一种以钢渣为碱性激发剂,以烟气脱硫石膏、矿渣粉为主要为原料的脱硫石膏水硬性胶凝材料。该胶凝体系3天抗折强度和抗压强度可达4.4 MPa和15.8 MPa;28天抗折强度和抗压强度可达9.4 MPa和50.7 MPa。其试样的强度随钢渣掺量的增加而增加,而钢渣含量一旦超过8%后,增长幅度变缓,甚至开始降低。XRD和SEM分析表明,脱硫石膏-矿渣-激发剂体系的水化产物主要是钙矾石和C-S-H凝胶。脱硫石膏在水化过程中一部分参与水化形成水化产物钙矾石,其余部分被水化产物所包裹起集料骨架作用。     

免煅烧磷石膏砖的制备和性能研究

在活性激发剂的作用下,利用矿渣、磷石膏(PG)和水泥混合制备磷石膏基胶凝材料(PGS),然后研究砂率和粉煤灰掺量对PGS砂浆性能的影响.结果表明:当激发剂掺量为3％时,20℃(湿度大于70％)养护28d的PGS固化体的抗压强度和抗折强度(41.9MPa和7.1MPa)分别较未掺激发剂时提高了89.6％和73.2％,28d软化系数为0.94;PGS固化体28d的总孔隙率(12.21％)较7d的总孔隙率降低了46.8％;当砂率为1∶1时,磷石膏砖的性能最佳,28d的抗压强度和抗折强度分别为56.9MPa和4.8MPa;当粉煤灰掺量为20％时,磷石膏砖的28d抗压强度和抗折强度分别为35.8MPa和3.3MPa,28d吸水率和软化系数分别为2.3％和0.90,质量损失率、抗压强度损失率和抗折强度损失率分别为1.9％、5.5％和4.3％.     

磷石膏基胶凝材料的制备及无机保水剂对其性能的影响

磷石膏基胶凝材料(PGC)是由原状磷石膏、矿渣、水泥和外掺3%硅灰等配制而成的绿色胶凝材料。通过标准稠度需水量、凝结时间和抗压强度等参数确定其基本配合比,并研究无机保水剂(P-1)对PGC析水率和线膨胀率的影响,借助XRD和SEM测试手段对水化产物进行分析表征。结果表明:磷石膏掺量为50%、矿渣与水泥的比值为4∶1、外掺3%硅灰时,制备出的PGC标准稠度需水量为30.8%,初、终凝时间分别为606min和872min,室温下7d抗压强度可达25.9MPa,28d抗压强度超过40MPa。P-1掺量为2%时,析水率为1.3%,较空白样(未掺P-1)降低了62.9%,28d线膨胀率为0.3137%,较空白样降低了3.3%。PGC水化产物主要为C-S-H凝胶和少量AFt。     

聚丙烯酰胺乳液对脱硫建筑石膏性能的影响

采用高分子聚合物——聚丙烯酰胺乳液改性脱硫建筑石膏,提高其力学与防水性能。研究聚丙烯酰胺乳液掺量、分子量对脱硫建筑石膏物理力学性能和防水性能的影响,采用X-射线衍射仪XRD)、扫描电子显微镜SEM)对脱硫建筑石膏水化微观结构进行表征。结果表明:当掺入聚丙烯酰胺乳液浓度2%、掺量为脱硫建筑石膏的1%、分子量300万时,软化系数由0.34提高到0.69,水中浸饱24后的抗压强度由4.9MPa提高到6.1MPa,使用分子量为300万聚丙烯酰胺配制的乳液对脱硫建筑石膏进行改性效果优于分子量为500万的改性效果。聚丙烯酰胺乳液对脱硫建筑石膏水化的作用机理是:一方面与脱硫石膏中Ca2+相互作用生成化合物,填充于脱硫建筑石膏水化产物二水硫酸钙晶体之间的空隙中,另一方面聚丙烯酰胺分子将脱硫建筑石膏颗粒包裹起来,阻碍与水发生水化反应。     

碱激发改性矿粉/砒砂岩复合材料

为了实现砒砂岩的资源化利用,首先,通过碱激发法并掺入适量的矿粉将砒砂岩转变成了力学性能较好的改性矿粉/砒砂岩复合材料;然后,系统地研究了矿粉、碱激发剂掺量和龄期对改性矿粉/砒砂岩复合材料抗压强度和软化系数的影响;最后,利用SEM/EDS、FTIR和XRD分析了改性矿粉/砒砂岩复合材料的水化进程和碳化进程。结果表明:改性矿粉/砒砂岩复合材料的90d抗压强度和软化系数分别达到46.0 MPa和0.94,完全满足工程应用的需求;改性矿粉/砒砂岩复合材料主要的水化产物为C-S-H凝胶和地聚物胶体,且C-S-H凝胶存在比较严重的碳化现象;当矿粉和NaOH的掺量分别为20.0wt%和1.5wt%时,C-S-H凝胶的28d碳化率达30.1%,且碳化率随矿粉及NaOH掺量的增加而减小,但碳化率对强度几乎没有影响。改性矿粉/砒砂岩复合材料拥有良好的力学性能及耐水性。      

锂云母渣缓凝机理研究及改性效果验证

锂云母渣的综合利用对国家双碳政策的执行及锂电行业的健康发展具有重大意义。但是锂云母渣中含有一定的氟、磷等有害杂质限制了其作为混凝土矿物掺合料在混凝土中的大规模应用。因此，通过XRD、XRF等手段分析了锂云母渣的理化特性，并结合砂浆水化热及净浆凝结时间实验，确定了锂云母渣缓凝机理，同时研究了生石灰对锂云母渣的改性效果。结果表明，锂云母渣缓凝的主要原因是其中可溶性氟与磷与水泥水化产物中的Ca²⁺形成氟化钙、磷酸钙、氟羟基磷灰石吸附在水泥水化初期形成的半透水性水化薄膜上，导致薄膜致密性增加，从而阻碍了离子和水的通过，引起水化速度降低，进而导致缓凝；生石灰能够有效缩短锂云母渣净浆的缓凝时间，改性后锂云母渣净浆凝结时间缩短114 min。     

碱-盐复合激发煤气化粗渣的水泥胶砂强度特性

采用扫描电子显微镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)分析了煤气化粗渣的微观结构、元素分布及物相组成;优选碱-盐复合激发剂,制备了掺煤气化粗渣水泥胶砂试件,分析了碱-盐激发剂对胶砂抗压、抗折强度的影响,并探讨了碱-盐激发下煤气化粗渣水泥胶凝硬化产物的微观结构和物相组成。结果表明:煤气化粗渣以层片状、不规则粒状颗粒居多,富含C、O、Si、Al、Ca、Fe等元素,存在火山灰活性的硅氧、铝氧或铝-硅-氧相;复合激发效果优于各自单掺的激发效果,其中掺硫酸钙与氢氧化钠组合激发效果最佳;激发剂有助于发挥煤气化粗渣的火山灰活性,促进煤气化粗渣水泥胶凝体系中水化产物的生成,提升了胶凝材料的结构强度。     

大掺量钢渣微粉-水泥碱激发特性

为解决钢渣微粉在水泥基复合材料中掺配比例较低的问题，采用力学性能测试、 XRD、 SEM、 FTIR等方法研究激发剂种类、掺量等对钢渣微粉-水泥胶凝材料力学强度和微观结构的影响。结果表明：碱性激发剂可提高钢渣微粉水化速度、增大复合胶凝材料抗压强度，但激发剂种类对胶凝材料激发效果具有差异性；碳酸钠与三乙醇胺复合激发后效果显著，3、 7、 28 d龄期的最佳强度与未掺加激发剂实验组的相比分别提高47%、 72%、 69%;激发剂对复合胶凝材料浆体水化产物种类没有影响；三乙醇胺具有悬浮稳定效应以及降低溶液表面张力的能力，与碳酸钠的强腐蚀效应作用在钢渣微粉水泥体系中协同强化水化反应，使复合胶凝体系中生成更多的水化产物并且相互交织成复杂密实的空间结构。     

Modified water/cement ratio law for compressive strength of fly ash concretes

Experimental data are presented which suggest that the development of compressive strength of fly ash concretes can be explained by superposition of two independent mechanical pore-filling mechanisms in the cement—fly ash paste. It is also suggested that the traditional water/cement ratio law for ordinary Portland cement concretes can be applied to fly ash concretes, provided that a slight modification is introduced. This will be of assistance in the design of fly ash concrete mixes for compressive strength.     

激发剂在大掺量粉煤灰水泥中的应用研究

利用粉煤灰、水泥熟料、石灰、石膏辅助少量的粉煤灰活性激发剂研究生产高掺量粉煤灰水泥.试验表明,激发剂能大大提高粉煤灰的活性和早期强度.生产的大掺量粉煤灰水泥,其3天、28天的抗压强度分别达到18MPa和50MPa,并且凝结硬化快,早期强度高,后期强度发展迅速.     

Performance of metakaolin concrete at elevated temperatures

An experimental investigation was conducted to evaluate the performance of metakaolin (MK) concrete at elevated temperatures up to 800 °C. Eight normal and high strength concrete (HSC) mixes incorporating 0%, 5%, 10% and 20% MK were prepared. The residual compressive strength, chloride-ion penetration, porosity and average pore sizes were measured and compared with silica fume (SF), fly ash (FA) and pure ordinary Portland cement (OPC) concretes. It was found that after an increase in compressive strength at 200 °C, the MK concrete suffered a more severe loss of compressive strength and permeability-related durability than the corresponding SF, FA and OPC concretes at higher temperatures. Explosive spalling was observed in both normal and high strength MK concretes and the frequency increased with higher MK contents.     

Mechanical and durability properties of ternary concretes containing silica fume and low reactivity blast furnace slag

In this study, the effect of incorporation of silica fume in enhancing strength development rate and durability characteristics of binary concretes containing a low reactivity slag has been investigated. Binary concretes studied included mixes containing slag at cement replacement levels of 15%, 30% and 50% and mixes containing silica fume at cement replacement levels of 2.5%, 5%, 7.5% and 10%. Ternary concretes included combinations of silica fume and slag at various cement replacement levels. The w/b ratio and total cementitious materials content were kept constant for all mixes at 0.38 and 420 kg/m³ respectively. Concrete mixes were evaluated for compressive strength, electrical resistance, chloride permeability (ASTM C1202 RCPT test) and chloride migration (AASHTO TP64 RCMT test), at various ages up to 180 days.The results show that simultaneous use of silica fume has only a moderate effect in improving the slow rate of strength gain of binary mixes containing low reactivity slag. However it improves their durability considerably. Using appropriate combination of low reactivity slag and silica fume, it is possible to obtain ternary mixes with 28 day strength comparable to the control mix and improve durability particularly in the long term. Ternary mixes also have the added advantage of reduced water demand.     

Mechanical properties,drying and autogenous shrinkage of blast furnace slag activated with hydrated lime and gypsum

This article reports the characteristics of blast furnace slag (BFS) pastes activated with hydrated lime (5%) and hydrated lime (2%) plus gypsum (6%) in relation to compressive strength, shrinkage (autogenous and drying) and microstructure (porosity, hydrated products). The paste mixtures were characterized using powder X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and thermogravimetric analysis (TG/DTG). BSF activated with lime and gypsum (LG) results in larger amounts of ettringite when compared with BFS activated with lime (L). Although the porosities of the L and LG mixtures were about the same, there was a greater pore refinement for the BFS activated with lime, with an increase in mesopores volume with age. The presence of ettringite and the higher volumes of macropores cause the compressive strength of BSF activated with hydrated lime plus gypsum to be smaller than that of BFS activated with lime. For both chemical activators, compressive strength developed slowly at early ages. Autogenous and drying shrinkage were greater for the BFS activated with lime, believed to result from the more refined porous structure in comparison with the mixture activated with gypsum plus lime.     

Mechanical properties of young concrete: Part I: Experimental results related to test methods and temperature effects

Results of several test series on mechanical properties of young concrete are presented. Six different concrete mixes were tested systematically, and a number of other concrete mixes less extensively, all with w/b≈0.40. The program included compressive strength, tensile strength, splitting tensile strength and E-modulus determination both in compression and tension. Because temperature influences the rate of property development, and also the “final value” of a given property, the specimens were subjected to realistic temperature regimes the first few days as well as isothermal conditions. The test methods are described, and results obtained by the different test methods are compared. It is recommended that the temperature sensitivity constants should be determined from compressive strength tests on specimens exposed to realistic temperature histories. These parameters depend strongly on the cement type and the silica fume content. It was found that high performance concretes were quite robust to the negative effects of elevated temperatures. This was particularly true for concretes with pozzolana. In part two of the paper model parameters for an equation to be used in calculation programs are determined, and a test program for crack risk estimation is proposed.     

Engineering property and structural design relationships for new and developing concretes

The paper reports the findings of a study carried out to investigate the effect of new and developing concrete technology solutions,e.g. (i) use of particle packing techniques and fillers to minimise voids, (ii) use of cement additions attained from industrial by-products and (iii) use of high range water-reducing admixtures which enable lower cement contents, on the engineering and structural performance of concrete and implications for structural design. The test programme considered 54 concrete mixes in three series to assess the impact of these on the tensile strength, flexural strength and modulus of elasticity of concrete, and in parallel, 37 mixes to measure these effects on the shear resistance of reinforced concrete beams. The results indicate that the influence of the concretes on compressive strength were generally inproportion to the effects on other engineering properties and were in line with current design assumptions on the behaviour of concrete. Furthermore, EC2 equations for predicting the shear strength of reinforced concrete beams, based on compressive strength, were also found to be appropriate for the range of concrete mixes considered. Overall, the work has demonstrated that new and developing concrete technology solutions can be utilised effectively within the framework of present design procedures and compressive strength is an appropriate parameter for assessing the structural performance of these concretes.     

Mechanical properties of glass fibre-reinforced gypsum

Gypsum plaster, like other inorganic cements, is strong in compression but weak in tension exhibiting brittle behaviour. Commercialy available E glass fibres can be used to reinforce the gypsum plaster matrix and produce a strong composite material having improved tensile and impact properties. This paper describes the effect of glass content on the flexural, tensile, compressive and impact strength of this glass fibre plaster composite which is made by a simple spray/suction technique.     

Synthesis of low-temperature calcium sulfoaluminate-belite cements from industrial wastes and their hydration: Comparative studies between lignite fly ash and bottom ash

The aim of this research was to study the production of calcium sulfoaluminate-belite (CŜAB) cement from industrial waste materials via hydrothermal-calcination process. Lignite fly ash and bottom ash were used as starting materials for comparison. Other waste materials viz., Al-rich sludge and flue gas desulfurization gypsum were also key players in raw mixes for the synthesis of CŜAB cement. For lignite fly ash as a starting material, mixed phases between ye'elimite and larnite were obtained, whereas for lignite bottom ash as starting material, only ye'elimite was obtained The hydration reaction was studied in terms of heat evolution, setting time, compressive strength and hydration product formation with various gypsum contents. The results showed a rapid formation of ettringite as a main hydration product mixed with calcium silicate hydrate, monosulfate and strätlingite phases as minority, with a fast final setting time of 24–26 min and high early compressive strength of 16.0 and 18.0 MPa in 1 day for CŜAB cements made of fly ash and bottom ash, respectively.     

Low-volume wet-process sprayed concrete: hardened properties

This paper, which reports on part of a 3-year research project into wet-process sprayed mortars and concretes for repair, investigates the hardened performance of wet-process sprayed fine concretes. It follows on from an earlier paper by the authors on the performance of hardened wet-process sprayed mortars and some comparisons with these are made here (Austin SA, Robins PJ, Goodier CI (2000). Magz Concr Res 52:195–208). Work has also been completed by the authors on the pumping and rheology of the fine concrete mixes presented here (Austin SA, Goodier, CI, Robins PJ (2005). Mater Struc, RILEM 38:229–237). Nine laboratory-designed fine concretes were pumped and sprayed through a wet-process piston pump and one through a dry-process pump. The properties measured included compressive and flexural strength, tensile bond strength, hardened density, elastic modulus, sorptivity and drying and restrained shrinkage. In situ test specimens were extracted from 500 × 500 × 100 mm deep sprayed panels. Hardened property tests were also conducted on corresponding cast specimens and, where possible, on specimens that had been sprayed directly into a cube or beam mould. The compressive strengths of the cast cubes, although very similar, were usually slightly greater than the in␣situ cubes, the opposite of what was found for wet-sprayed mortars (Austin SA, Robins PJ, Goodier CI (2000). Magz Concr Res 52:195–208). Inconsistent results for compressive and flexural strengths obtained from spraying directly into a steel mould suggest that this method is not as reliable when using a piston pump as it is when using a low-output worm pump (Austin SA, Robins PJ, Goodier CI (2000). Magz Concr Res 52:195–208). The bond strength of all the mixes exceeded 2.1 MPa at 7 days. The values for modulus of elasticity, when compared with the compressive strength, were similar to published data for this relationship. The sorptivity values showed only a slight relationship with the compressive strength. The mixes exhibited a wide range of drying shrinkage, but the data from the restrained specimens suggest an actual repair is influenced as much by ambient conditions as it is by the mix proportions.