废弃混凝土再生水泥技术的研究进展

利用废弃混凝土为原料煅烧熟料、制备水泥是废弃混凝土资源化再生利用的有效途径。介绍了全组分废弃混凝土再生水泥的概念和国内外废弃混凝土再生水泥技术的最新研究现状。针对废弃混凝土区别于普通水泥生料的特点,提出再生水泥研究中亟待解决的问题。     

废弃混凝土作路基土壤稳定剂的研究

在分析了废弃混凝土化学成分和煅烧后废混凝土的有效CaO基础上,将煅烧后废混凝土作为土壤稳定剂进行了稳定土无侧限抗压强度试验,探讨了废弃混凝土化学成分对稳定土的无侧限抗压强度和水稳定性的影响.结果表明:煅烧废弃混凝土可以代替水泥或消石灰制备稳定土应用于路基.     

有色冶炼固废提取稀散金属后的尾渣综合利用分析

针对有色冶炼固废提取稀散金属后的尾渣进行研究,提出尾渣可能应用的主要途径:一是作为活性掺合料应用于砂浆和混凝土中;二是作为铁质原料用来煅烧水泥熟料;三是用于沥青混合料用在道路工程.这些方案的提出,能够为尾渣的综合利用提供技术指导.     

利用废弃混凝土作为水泥原料的试验研究

从不同建筑物拆除现场随机选取以石灰石为骨料的废弃混凝土样品,分别破碎、分离,获得以石灰石为主的颗粒,作为钙质原料煅烧水泥熟料,将该水泥熟料与水泥厂生产的熟料以及市售水泥进行了对比。研究结果表明:所烧成的熟料中4种主要矿物的XRD特征峰明显;游离CaO低于国家规定标准;利用烧成的熟料配制的水泥28 d强度与市售P.O 42.5级水泥强度相当。     

废弃混凝土对水泥熟料煅烧过程矿物形成的影响

以废弃混凝土、石灰石、砂岩、铁矿石、煤粉为原料,采用普通煅烧工艺烧制了不同煅烧温度下的水泥熟料,利用XRD、SEM等表征手段考察了不同目数的混凝土对水泥煅烧过程中熟料主要矿物形成的影响,并将煅烧生成的水泥熟料与标准熟料进行了对比分析。结果表明,在不同煅烧温度下烧成的水泥熟料中主要矿物的XRD特征峰明显,矿物形成正常,并与对比试样水泥熟料的矿物化学成分相近。不同目数混凝土代替部分生料烧制的水泥熟料组成及形貌的变化有明显的区别,60~80目烧制的水泥熟料因Al、Fe和Si元素含量较高而出现主要矿物黏结和熔蚀现象,阻碍C3S的形成,水泥矿物发育较差,而大于120目烧制的水泥熟料矿物发育良好,主要矿物黏结和熔蚀较少,但f-CaO量高于标准熟料。     

废弃混凝土煅烧水泥的试验研究

我国每年产生的废弃混凝土数量巨大,研究废弃混凝土的再生利用有着重要意义。从建筑物拆除现场采集废弃混凝土样品,将其破碎分离后,选取其中石灰石颗粒作为煅烧水泥熟料的原料。结果表明：所烧熟料中四种矿物X衍射特征峰明显;游离氧化钙较低,符合要求;28天强度达到47．68MPa。     

废砂浆粉低温煅烧激发活性的研究

研究了不同煅烧温度对废砂浆块易磨性、流动度、质量损失的影响,以及废砂浆粉的活性激发效果。实验表明,废砂浆粉筛余率和胶砂流动度随着煅烧温度的升高而显著降低。经600℃热处理,掺30%废砂浆粉混合水泥的28 d强度增长了3.01 MPa,结合分离废弃混凝土中砂浆组分的最佳温度在500℃~600℃,确定了600℃是分离和激发废砂浆活性的最佳温度。     

废弃混凝土高温处理技术与脱水水泥浆再水化活性研究(英文)

建筑物在建设和拆除过程中产生大量的固体废弃物,其中大部分是废弃的混凝土和砂浆.为了使废弃混凝土和砂浆中的骨料和水泥重新得以应用.本研究对废弃混凝土和砂浆进行了高温处理,合理的高温处理温度为750 ℃经过高温处理后,可以实现骨料与水泥浆的分离.经过分离的骨料可以在新拌混凝土中重新应用,而脱水水泥浆经充分磨细后又重新具有了反应活性.把脱水水泥浆与水泥熟料或硅酸盐水泥复合,可以得到一种新型的水硬性胶凝材料.这种胶凝材料可以满足较低强度通用硅酸盐水泥的要求.由此建筑物建设和拆除过程中所形成的废弃混凝土和砂浆可以全部回收并重新利用.对减小资源消耗、节能减排有重要意义.     

用废弃混凝土中的基质胶凝组分作原料煅烧水泥熟料的研究

用废弃混凝土中的基质胶凝组分替代部分石灰质原料进行了煅烧水泥熟料的试验研究,探讨了基质组分在熟料煅烧过程中的作用机理。通过XRD和SEM研究了熟料的相组成和晶体结构。试验结果表明,与采用常规原料制备的试样相比,用基质胶凝组分配制的生料易烧性稍差,但二者无明显差异;熟料晶体结构及性能与对比试样相近。     

废弃黏土砖制作矿物掺合料的试验研究

研究了用废弃黏土砖制作混凝土矿物掺合料的试验研究。试验结果表明废砖的粉磨能耗仅为水泥熟料的5%;细粉磨比粗粉磨更能激发废砖粉的活性;废砖粉替代水泥的掺量在30%以内时,能够提高砂浆的抗折强度。     

Freeze–thaw resistance of blended cements containing calcined paper sludge

This work deals with the frost resistance of blended cements containing calcined paper sludge (source for metakaolin) as partial Portland cement replacements. Freeze–thaw tests were performed on blended cement mortars containing 0%, 10% and 20% waste paper sludge calcined at 650 °C for 2 h. Cement mortar specimens were exposed to freezing and thawing cycles until the relative dynamic modulus of elasticity fell below 60%. The performance of the cement mortars was assessed from measurements of weight, ultrasonic pulse velocity, compressive strength, mercury intrusion porosimetry and SEM. Failure of the control cement mortar occurred before 40 freeze/thaw cycles, while cement mortar containing 20% calcined paper sludge failed after 100 cycles. After 28 and 62 freezing and thawing cycles, cement blended with 10% and 20% calcined paper sludge exhibited a smaller reduction in compressive strength than the control cement.     

粉煤灰水泥堆积效应与其抗压强度的关系

将粉煤灰粉磨后,以不同比例与一定细度水泥配合,制成一系列粉煤灰水泥粉体．根据Dinger-Funk数学模型得出粉煤灰水泥粉体最佳颗粒群分布即最紧密堆积颗粒群分布．通过水泥与粉煤灰激光粒度检测结果计算粉煤灰水泥粉体实际颗粒群分布．运用灰色关联分析原理考察粉煤灰水泥粉体实际颗粒群分布与最紧密堆积颗粒群分布的相关性,同时测定粉煤灰水泥标准稠度用水量以及胶砂抗压强度．结果证明：当粉煤灰水泥粉体实际颗粒群分布与最紧密堆积颗粒群分布关联度较高时,相应粉煤灰水泥标准稠度用水量增加较少,胶砂抗压强度发展较理想．     

特种水泥对普通硅酸盐水泥性能的影响

普通硅酸盐水泥凝结时间缓慢限制了其应用范围,采用在普通水泥中加入特种水泥(高铝水泥和快硬硫铝酸盐水泥),研究其对普通水泥性能的影响.用电阻率、孔结构、XRD以及DSC-TG对普通水泥-特种水泥复合体系进行研究,结果表明:加入一定量的特种水泥,改变了早期水化产物的组成,大幅度缩短了普通水泥的凝结时间,复合体系28 d强度未出现例缩,但水化3 d浆体有害孔数量增加.     

水泥基材料抗TSA侵蚀性能影响因素研究

研究了不同配合比掺石灰石粉水泥砂浆在不同硫酸盐溶液中浸泡1年期间的外观、强度和矿物成分变化。结果表明,水灰比越低,砂浆抗TSA侵蚀性能越好;不同品种水泥的抗TSA侵蚀能力由高到低依次为:硫铝酸盐水泥>抗硫酸盐水泥>普硅水泥;掺硅灰和矿渣细粉均能明显改善混凝土抗TSA侵蚀性能,且矿渣粉掺量越大效果越明显。镁盐对碳硫硅酸钙晶体(thaumasite)的生成和TSA侵蚀破坏具有一定促进作用;水泥基材料TSA侵蚀破坏也可能发生于15℃以上环境中,环境温度对水泥基材料整体抗硫酸盐侵蚀性能的影响规律与材料组分有关。     

Effects of portland composite and composite cements on durability of mortar and permeability of concrete

In this study, the effects of Portland composite and composite cement on the properties of cement paste, durability of mortar and permeability of concrete were investigated. The results were compared with reference mixture of cement paste, mortar and concrete made with Portland cement. The ratio of water to cementitious materials (W/C_m) in cement paste, mortar and concrete mixtures were determined in a way that all the similar mixtures had the same workability. Flexural tensile and compressive strength of mortar samples containing Portland Composite and Composite cement were determined at various ages. In cement paste samples, the shortest and longest setting time was obtained in samples made with Portland and composite cement, respectively. Also, maximum amount of volume expansion was found in the sample made with Portland composite cement. Mortar samples made with Portland composite and composite cement had lower strength values than the reference mortar mixture at early ages but at 28 days and later ages they had higher strength values than the reference mixture. In durability tests, there was no loss of weight and cracks in mortar mixture samples made with Portland composite and composite cement when they were held in microthiol, Na₂SO₄ and MgSO₄ solutions. Also, no water leakage was observed through the concrete samples made with Portland composite and composite cement when they were held under five-bar pressurized water.     

Sulfate resistance of blended cements containing fly ash and rice husk ash

In this paper, the sulfate resistance of mortars made from ordinary Portland cement containing available pozzolans viz., fly ash and ground rice husk ash (RHA) was studied. Class F lignite fly ash and RHA were used at replacement dosages of 20 and 40% by weight of cement. Expansion of mortar prisms immersed in 5% sodium sulfate solution and the change in the pH values of the solution were monitored. The incorporation of fly ash and RHA reduced the expansion of the mortar bars and the pH values of the solutions. RHA was found to be more effective than fly ash. Examination of the fractured surface of mortar prisms, after a period of immersion, by scanning electron microscopy confirmed that sulfate attack of blended cement mortars was restricted owing to the reductions in calcium hydroxide and C/S ratio of the C–S–H gel in the blended cement mortar. In comparison to Portland cement mortar, less calcium sulfate and much less ettringite formations were found in the mortars made from blended cement containing RHA. The amounts of calcium sulfate and ettringite found in the blended cement mortar containing fly ash were also small but were slightly more than those of RHA mortar. Up to 40% of Portland cement could be replaced with these pozzolans in making blended cement with good sulfate resistance.     

Durability of compression molded sisal fiber reinforced mortar laminates

This paper presents an experimental research on the durability performance of compression molded sisal fiber–cement mortar laminates (SFRML). To obtain a material with enhanced performance, the used methodology was to replace the Portland cement (PC) by calcined clay (metakaolin and calcined waste crushed clay brick) in order to produce a matrix totally free of calcium hydroxide (CH). The content of calcium hydroxide in the matrix was determined by thermal analysis. SFRML were then produced using both a PC and a CH-free PC-calcined clay matrix and the composites were submitted to accelerated aging through cycles of wetting and drying. The durability of the SFRML was investigated by determining the effects of accelerated aging on the microstructures and flexural behavior of the composites. The results indicate that the newly developed CH-free matrix avoided the fiber embrittlement process keeping the toughness in time even after 100 cycles of wetting and drying.     

Study of cement-grout penetration into fractures under static and oscillatory conditions

Grouting of the rock surrounding high-level waste (HLW) can serve to minimize groundwater flow around it and thereby to retard erosion of waste-embedding clay (buffer) and transport of possibly released radionuclides. Earlier attempts have shown the efficiency of superimposing the injection pressure with oscillations for bringing cement-rich grouts into narrow fractures using organic superplasticizers. However, these are short-lived and can produce radionuclide-bearing organic colloids, and should be replaced by inorganic agents. Portland cement in grouts is not long lived and low-pH cements are preferable as is also reduction of the cement content to an absolute minimum. The present study describes the composition and performance of candidate grouts in laboratory experiments with injection into plane-parallel slots with different aperture. The study included development of a simple and quick method for estimating the viscosity on the construction site for adapting the grout recipe to the injectability of the rock. A simple theoretical model for predicting grout penetration gives fair agreement with laboratory data. The longevity of the grout under various conditions is believed to be sufficient for use in HLW repositories implying waste placement in very deep holes.     

Disposal of water treatment wastes containing arsenic — A review

Solid waste management in developing countries is often unsustainable, relying on uncontrolled disposal in waste dumps. Particular problems arise from the disposal of treatment residues generated by removing arsenic (As) from drinking water because As can be highly mobile and has the potential to leach back to ground and surface waters. This paper reviews the disposal of water treatment wastes containing As, with a particular emphasis on stabilisation/solidification (S/S) technologies which are currently used to treat industrial wastes containing As. These have been assessed for their appropriateness for treating As containing water treatment wastes. Portland cement/lime mixes are expected (at least in part) to be appropriate for wastes from sorptive filters, but may not be appropriate for precipitative sludges, because ferric flocs often used to sorb As can retard cement hydration. Brine resulting from the regeneration of activated alumina filters is likely to accelerate cement hydration. Portland cement can immobilise soluble arsenites and has been successfully used to stabilise As-rich sludges and it may also be suitable for treating sludges generated from precipitative removal units. Oxidation of As(III) to As(V) and the formation of calcium-arsenic compounds are important immobilisation mechanisms for As in cements. Geopolymers are alternative binder systems that are effective for treating wastes rich in alumina and metal hydroxides and may have potential for As wastes generated using activated alumina. The long-term stability of cemented, arsenic-bearing wastes is however uncertain, as like many cements, they are susceptible to carbonation effects which may result in the subsequent re-release of As.     

硅酸盐水泥高性能化的途径

高性能混凝土的发展与应用对水泥提出了更高的要求,为了适应高性能混凝土的发展,我们应积极研究与开发高性能水泥。本文讨论了高性能水泥的性能特点,及实现高性能水泥的途径。认为利用辅助胶凝材料,通过与水泥的化学组成、及颗粒形状、颗粒分布进行优化复合,可以实现硅酸盐水泥的高性能化。