Evaluation of fly ash- and slag-based geopolymers for the improvement of a soft marine clay by deep soil mixing

The use of deep soil mixing (DSM) in ground-improvement projects, for structures subjected to low to medium loads, has increased over the past decade due to its convenient and practical implementation and its economic advantages. Traditionally, Portland cement and lime have been the most popular binders for DSM applications. However, the ground-improvement industry has been keen to explore environmentally friendly alternatives with low carbon dioxide emission. The aim of this research is to investigate the use of two stockpiled industrial waste by-products, namely, fly ash (FA) and slag (S), as alternative green binders in ground-improvement projects that would reduce the carbon footprint of these projects. In this research, combinations of FA and S, activated by a liquid alkaline activator (L), were evaluated for the ground improvement of a soft marine clay, namely, Coode Island Silt (CIS). The performance of the FA?+?S geopolymers was compared with that of traditional cement and lime control binders. The soil moisture content was set at 0.75, 1.0 and 1.25 of the liquid limit (LL) of the soil to replicate the field conditions. 10, 20 and 30% binders, by dry soil mass, were added to the soil, and the samples were cured for 7 and 28?days. Unconfined compression strength (UCS), flexural beam and scanning electron microscopy (SEM) imaging tests were conducted to evaluate the changes in the engineering behavior and the microstructure of the mixtures. The results indicated that the strength and stiffness of the soft clay were significantly increased by the use of these new FA?+?S binders, which substantiated them as alternatives to traditional cement or lime binders. The optimum binder content was found to be 20%, while CIS?+?5%FA?+?15%S was found to be the optimum mixture. Furthermore, correlations between the UCS and the modulus of elasticity (E₅₀) and between the UCS and the modulus of rupture (R) for the geopolymer mixtures were proposed. They will be valuable to both designers and practitioners of ground-improvement works.     

粉煤灰地聚合物混凝土的制备及其特性

利用粉煤灰作为配制地聚合物的一种基本Si-Al质材料,以强度为指标寻求最佳的地聚合物配比;同时,为优化养护制度,采用了标准养护、蒸汽养护、压蒸养护三种养护制度进行实验,从中选出最有利于发挥胶凝材料活性的养护制度。实验表明,在粉煤灰掺量为30％,80℃蒸养8h时抗压和弯拉强度达到最优,分别为32．2WPa和7．15MPa。之后,对这种最优的地聚合物混凝土的抗氯离子渗透、抗冻融和抗碳化性能进行了研究,发现其具有非常优异的耐久性。     

矿物掺合料对未水化水泥的后期水化危害的抑制作用

低水灰比混凝土中存在大量未水化的水泥,其后期继续水化将导致混凝土的损伤,表现为抗压强度显著降低及耐久性变差.为抑制未水化水泥的后期水化危害,研究了粉煤灰和矿渣单掺或双掺后对混凝土后期性能的影响,结果表明,双掺粉煤灰和矿渣可以有效抑制混凝土中未水化水泥的后期水化危害.     

掺合料和粗骨料对C60高性能混凝土徐变性能的影响

通过混凝土徐变试验研究了C60高性能混凝土的徐变性能.试验结果表明,随着龄期增长,徐变系数增大,收缩变形增加,徐变速率降低.同龄期时,双掺23％粉煤灰和10％矿粉降低了混凝土的徐变系数和收缩应变;持荷180d,纯水泥混凝土的徐变系数为1.304,而双掺混凝土徐变系数较纯水泥混凝土下降了10.4％.小石率60％的双掺混凝...     

矿渣粉对混凝土和易性及强度影响的研究

试验研究和分析了矿渣粉掺量对低水胶比混凝土的和易性及强度的影响。结果表明,除了减水剂掺量对新拌混凝土和易性有显著影响外,矿渣粉掺量对混凝土拌合物的和易性有明显改善。水胶比是影响混凝土强度的主要因素,而矿渣粉掺量对混凝土强度的影响也较为明显。矿渣粉的细度小于水泥的细度,可作为细集料用于混凝土中,以改善混凝土拌合物的和易性,降低施工成本。     

矿物掺合料混凝土抗氯离子渗透性能及时变规律

以非稳态氯离子迁移系数(D值)为指标,研究了复掺粉煤灰和矿粉的混凝土抗氯离子渗透性能及其时变规律.结果表明:降低水胶比,延长龄期(180 d以内)都能使混凝土的抗氯离子渗透性能增强;一定范围内,抗氯离子渗透性能均随矿粉掺量的增加而增加,随粉煤灰掺量的增加而降低,当矿粉掺量分别为37.5％、31.9％时,C30、C45混...     

不同品质商品灰在混凝土中的作用浅析

简要分析了采集自上海地区的不同商品粉煤灰的品质特性及其与新拌混凝土性能和强度的关系,综合评价了它们在混凝土中作用的异同,并对商品灰的开发提出了几点看法。     

软土路基加固中注浆液配合比分析

介绍了软土路基加固原理,重点描述了加固软土地基的注浆液的配合比试验,并对粘土掺量、粉煤灰掺量以及减水剂掺量的变化对浆液各种性能的影响进行分析,经过比较得出了适合软土路基加固的注浆液的配合比,从而达到更好提高软土地基的处理效果的目的。     

粉煤灰对砂浆性能影响的研究

在砂浆中加入粉煤灰,不但能降低砂浆的成本,而且还能够改善砂浆的施工性能、提高砂浆保温性能。在满足加气混凝土(泡沫混凝土)抹面砂浆粘结强度高、收缩率低的前提下,粉煤灰掺量30%时,所配制的砂浆导热系数为0.1953W/m.K,与加气混凝土(泡沫混凝土)砌块导热系数接近,具有良好的保温效果。     

高强度混凝土强度增长特性的试验研究

通过不同强度等级水泥、不同粉煤灰掺量、不同品种外加剂的混凝土试配试验,测定混凝土强度随龄期的发展变化,给出了高强度混凝土（C60以上）强度随龄期变化的曲线,供监理、施工技术人员在混凝土工程质量控制中参考。     

粉煤灰、矿粉对水泥浆体变形性能的影响

以高性能混凝土用胶凝材料为研究对象,研究了粉煤灰、矿粉在不同养护湿度和温度下对水泥浆体变形性能的影响规律.结果表明:饱水养护时,粉煤灰的掺入降低了水泥浆体的水养膨胀变形;养护温度升高、粉煤灰掺量增加,水泥浆体水养膨胀变形降低幅度增大,但不同水养温度下掺入矿粉对水泥浆体膨胀变形无明显影响;密封养护时,掺入粉煤灰可有效抑制...     

粉煤灰回填材料性能与应用研究

本文探索了粉煤灰回填材料在化工废石膏、矿物外加剂、激发剂和高效减水剂存在同时的强度发展规律、体积稳定性、耐水性等。结果表明 ,粉煤灰回填材料具有较高的力学性能 (≥ 8MPa)、较好的耐水性和体积稳定性 (膨胀系数≤ 0 0 2 % )。该材料可广泛应用于污水管、输热管、上水管等沟槽的回填     

Evaluation of controlled low strength materials containing industrial by-products

A controlled low strength material (CLSM) is a self-compacted, cementitious material used primarily as a backfill. It is also known as a flowable fill which is usually a mixture of fine aggregates, small amount of cement, fly ash, and water. To be classified as a CLSM, the mixture must have a compressive strength between 345 and 8400 kPa. This paper evaluates the potential use of cement by-pass dust, incinerator ash and copper slag as a CLSM. Mixtures were designed to produce a CLSM, with a low compressive strength (less than 1034 kPa), that can be excavated without using any mechanical equipment. Slump, unit weight and unconfined compressive strength tests were conducted on various mixtures. Cubical and cylindrical specimens were prepared and cured at room temperature and in sealed plastic bags. Results indicate that with a good mix design it is possible to produce a CLSM with good mechanical properties to meet design requirements. Mixing these materials with cement and sand produced better results than using them alone due to their low pozzolanic activity. Curing method and period can have considerable effects on the strength of a CLSM.     

颗粒级配对矿渣水泥的性能影响研究

通过调整粉磨时间获得不同细度矿渣水泥,并将不同细度水泥按一定比例混合获得颗粒级配不同的矿渣水泥。试验研究了细度对水泥标准稠度用水量、凝结时间、强度发展和砂浆收缩变形的影响,结果表明:不同细度的矿渣水泥混合后改善了水泥的颗粒级配,对水泥性能有积极作用;不同细度的矿渣水泥混合后配制的砂浆抗压和抗折强度略有增加,收缩明显减小。     

养护方式对大掺量粉煤灰混凝土强度的影响研究

本课题进行了粉煤灰等量替代硅酸盐水泥配制粉煤灰混凝土，并研究了养护方式对大掺量粉煤灰混凝土强度的影响，为大掺量高强粉煤灰混凝土的配制提供了实验依据。实验结果表明，采用蒸养—蒸压二次养护工艺，可大大减少水泥用量，降低生产成本，获得良好的经济效益与社会效益。     

Analytical investigation of disturbance of seabed-sampled soil specimens and its influence on unconfined strength

In view of the need to utilize ocean space and to develop seabed resources, the assessment of the stability of deep seabed soil has emerged as an important challenge in the field of geomechanics. To study seabed stability, the strength and stiffness of the natural ground must be ascertained. Accordingly, it is necessary either to conduct laboratory testing on soil specimens sampled from the seabed or to estimate the strength and stiffness by in-situ tests. While in the future it may be reasonable to conduct in-situ tests to estimate the stiffness and strength of seabed soil, it will still be necessary to compare the physical properties measured by in-situ testing with those measured by laboratory testing in advance of these determinations. In short, soil specimens must be sampled from the actual deep seabed, and laboratory mechanical tests must be conducted on the sampled soil specimens. However, soil sampled from the ocean bottom is subject to effects that differ from those exerted on soil sampled from the earth. More specifically, the non-negligible effects of disturbance are expected with soil sampled from the ocean bottom. The effects of disturbance occur during the sampling process due to the vaporization of dissolved gases, as these soil specimens are under relatively higher pressure and contain pore water with a high amount of dissolved gases. Therefore, numerical simulations were conducted in the present study to investigate the effects of vaporized dissolved gases on the mechanical behavior of soil specimens during sampling and on the undrained shear strength as determined by laboratory tests. The analyses revealed that the combination of the decreasing effective stress caused by the sampling and factors such as overconsolidation and unsaturation is attributable to the difference between the soil strength ascertained by laboratory testing and the in-situ soil strength.     

Utilization of a very high lime fly ash for improvement of Izmir clay

This paper presents an investigation into the stabilization of a soft clay subgrade of a military zone in Izmir, Turkey with a very high lime fly ash. Zero%, 5%, 10%, 15% and 20% (m/m) of the soil was replaced with fly ash. In addition to the control specimen, four different stabilized soil samples were prepared mixing fly ash with soil at optimum water contents determined by standard proctor test. Experiments lasted for 3 months and the unconfined compressive strength and shear strength parameters, cohesion and internal friction angle, were determined after 1, 7, 28 and 90 days. It was found that, inclusion of fly ash improved the properties of the soil. The improvements, appearing with increasing fly-ash content, were attributed to the pozzolanic reaction and pore refinement effect of fly ash as well as its high free-lime content.     

耐碱玻纤和粉煤灰对轻质混凝土强度及冻融耐久性的影响研究

以陶粒为粗骨料制备了轻质混凝土试件,研究了耐碱玻纤、粉煤灰增强材料对轻质混凝土的力学性能及冻融耐久性的影响。结果表明,随着耐碱玻纤掺量的增加,同一龄期轻质混凝土试件的抗压强度、抗拉强度先增大后减小;过高的耐碱玻纤掺量不利于强度的增长,且耐碱玻纤对试件抗拉强度的影响大于抗压强度,其最优掺量为0.6 kg/m^3;掺入适量的粉煤灰(≤15%)能提高轻质混凝土的强度,提升幅度与掺量成正比,但掺量较大时对强度不利;与未掺耐碱玻纤的试件相比,当耐碱玻纤掺量低于0.6 kg/m^3和1.0 kg/m^3时,能分别提升试件的相对动弹性模量和降低质量损失率,改善幅度与耐碱玻纤的掺量正相关;粉煤灰掺量低于15%时有利于提高试件的冻融耐久性,但掺量较高(≥20%)则会降低试件的冻融耐久性指标。     

Effect of cation exchange capacity of soil on stabilized soil strength

While a certain correlation between the cation exchange capacity (CEC) of the soil and the strength of the cement stabilized soil has been reported, the mechanism remains unclear. In this research, a set of soil samples with different CECs were stabilized with different proportions of cement and calcium hydroxide (Ca(OH)₂, CH). The influence of soil CEC on the strength of the stabilized soil was investigated by analyzing the CH saturation in the pore solution and measuring the strength of the stabilized soil specimens. It is revealed that cation exchange in the soil can reduce the CH saturation of the stabilized soil. If the CEC of the soil is too high, the CH in the pore solution of the stabilized soil cannot reach the saturation level, and further cation exchange would then consume the Ca²⁺ ions which should be originally used to generate calcium silicate hydrate, thus result in the poor strength of the stabilized soil.     

矿物掺合料对轻质高强混凝土性能的影响

研究了粉煤灰、矿渣和硅灰掺合料对大流动性高强轻集料混凝土性能影响.测试结果表明：在单掺情况下,矿渣和硅灰能有效地提高拌合物的粘聚性,从而改善了混凝土早期和后期强度,但对拌合物流动性有一定影响,掺加粉煤灰能有效提高流动性,但产生泌水对拌合物匀质性有不良影响.综合流动性和强度改善效果,复合掺加矿渣和粉煤灰对配制大流动性高强轻集料混凝土效果最佳.