Evaluating the compression index of fibrous peat treated with different binders

Fibrous peats feature high compressibility and correspondingly very low strength. In this study, an investigation into the compressibility of untreated and stabilized fibrous peat with different binders—namely cement, lime, gypsum, and fly ash—is presented. The technique adopted for sample preparation was aimed at simulating the in-situ condition of the deep soil mixing technique. For this purpose, the binder dosages were selected in the range of 100–400 kg/m³ of wet fibrous peat at its natural water content. This binder range was determined based on the unconfined compressive strength of the treated samples. All the treated samples were cured for 14, 28, and 90 days in both air and water. The consolidation behavior of the treated peat samples was assessed by performing a Rowe cell consolidation test. The test results revealed that the increase in cement, fly ash, and gypsum contents led to considerable decreases in compression indices of the treated fibrous peat. No significant changes in the compressibility properties of lime-treated peat were observed. In addition, the inclusion of well-graded sand as filler decreased the compression indices of the treated samples significantly. Finally, in comparison with air curing, the use of the water curing technique for all the stabilized samples, regardless of binder type, showed better performances.     

Stabilization of expansive soils using chemical additives: A review

Volume instability of expansive soils due to moisture fluctuations is often disastrous, causing severe damages and distortions in the supported structures. It is, therefore, necessary to adequately improve the performance of such soils that they can favorably fulfil the post-construction stability requirements. This can be achieved through chemical stabilization using additives such as lime, cement and fly ash. In this paper, suitability of such additives under various conditions and their mechanisms are reviewed in detail. It is observed that the stabilization process primarily involves hydration, cation exchange, flocculation and pozzolanic reactions. The degree of stabilization is controlled by several factors such as additive type, additive content, soil type, soil mineralogy, curing period, curing temperature, delay in compaction, pH of soil matrix, and molding water content, including presence of nano-silica, organic matter and sulfate compounds. Provision of nano-silica not only improves soil packing but also accelerates the pozzolanic reaction. However, presence of deleterious compounds such as sulfate or organic matter can turn the treated soils unfavorable at times even worser than the unstabilized ones.     

水泥固化土工程特性试验研究

通过大量试验 ,论述了水泥固化土的几个基本特性。水泥固化土的抗压强度主要取决于水泥用量 ,其次是原料土的含水量 ,根据 2 8种配方试验资料 ,提出了一个简便的经验关系。指出对任意一软质原料土 ,存在一个最低的水泥用量 ,如果达不到这一用量则固化效果皆无。同时还揭示出水泥固化土的抗压强度与土的含水量的平方成反比的关系 ,并且简述了其他因素对水泥固化土抗压强度的影响。此外 ,探讨了水泥固化土的变形、渗透和早期抗剪强度等土工特性     

Mechanical properties of stabilized artificial organic soil

In order to study the influence of organic matter on the mechanical properties of stabilized soil and the effect of XGL2005 on stabilizing organic soil, unconfined compressive strength tests were carried out. Test results indicated that the strength of stabilized soil decreased in the form of a logarithmic function as the organic matter content increased. In contrast, the strength increased in the form of a power function as the content of the stabilization agent increased. The strength of cement stabilized organic soil was reinforced greatly by adding the stabilizer XGL2005. Based on the law obtained from the test, a strength prediction model was established by regression analysis. The model included the influence of the curing time, the content of the cement, the organic matter content and the stabilization agent on the strength of stabilized soil.     

水泥土强度室内试验方法探讨

水泥土室内试验是确定水泥土搅拌法施工时水泥掺入比的重要依据。在水泥土室内进行试验的基础上对土样的选择、水泥土试件的制作和养护、水泥土试件的强度测试以及评价方法提出了一些建议,希望能够推进水泥土室内强度试验方法的标准化。     

Role of Fly Ash on Strength and Microstructure Development in Blended Cement Stabilized Silty Clay

This paper presents the role of fly ash on strength and microstructure development in blended cement stabilized silty clay. Its strength was examined by unconfined compression test and its microstructure (fabric and cementation bond) by a scanning electron microscope (SEM), mercury intrusion porosimetry (MIP), and thermal gravity (TG) analysis. The flocculation of clay particles due to the cation exchange process is controlled by cement content, regardless of fly ash content. It increases dry unit weight of the stabilized clay with insignificant change in liquid limit. This results in irrelevant difference in optimum water content (OWC) for the unstabilized and the stabilized clay since OWC of low swelling silty clay is mainly controlled by liquid limit. It is found from the microstructural and the strength test results that the reactivity of fly ash (pozzolanic reaction) is minimal, which is different from concrete technology. This is possibly due to less amount of Ca(OH)₂ to be consumed. The role of fly ash in cement stabilization is to disperse the large clay-cement clusters into smaller clusters. Consequently, the reactive surfaces to be interacted with water increase, and hence the cementitious products (inter-cluster cementation bond). To conclude, the strength development in the blended cement stabilized clay is controlled by cementitious products due to combined effect: hydration and dispersion. Cementitious products due to hydration are governed by cement content, while cementitious products due to dispersion by fly ash content and fineness. Water content of 1.2OWC and 10% replacement ratio are regarded as the effective mixing condition for the stabilization, exhibiting the highest cementitious products.     

Mechanical properties of stabilized artificial organic soil

In order to study the influence of organic matter on the mechanical properties of stabilized soil and the effect of XGL2005 on stabilizing organic soil, unconfined compressive strength tests were carried out. Test results indicated that the strength of stabilized soil decreased in the form of a logarithmic function as the organic matter content increased. In contrast, the strength increased in the form of a power function as the content of the stabilization agent increased. The strength of cement stabilized organic soil was reinforced greatly by adding the stabilizer XGL2005. Based on the law obtained from the test, a strength prediction model was established by regression analysis. The model included the influence of the curing time, the content of the cement, the organic matter content and the stabilization agent on the strength of stabilized soil. __________ Translated from Journal of Zhejiang University (Engineering Science), 2007, 41(1): 109–113 [译自: 浙江 大学学报(工学版)]     

粉煤灰炉渣加固土的室内无侧限抗压强度试验研究(英文)

给出了用粉煤灰、炉渣等工业废料加固土的室内无侧限抗压强度试验结果,分析了加固土无侧限抗压强度与外加剂掺量、养护龄期之间的影响规律,得出了针对不同工业废料加固土所用外加剂的最佳掺量。     

水泥加固酸污染土无侧限强度特征

污染土是利用水泥固化处理后,土体的强度得到提高。针对该项技术,采用水泥固化法处理酸污染土,通过两种试验方案,对水泥加固酸污染土的无侧限抗压强度特性进行研究。试验所用酸污染土用浓硫酸配置人工制备而成,并考虑了不同水泥掺量、不同硫酸浓度和不同龄期对水泥加固酸污染土强度的影响。试验表明:水泥固化酸污染土的强度与水泥掺量和硫酸含量有密切关系,二者共同作用决定其强度的变化。在一定硫酸浓度(2~16g/kg)条件下,伴随硫酸含量的升高,水泥掺量较低时,无侧限抗压强度整体呈明显下降的趋势;水泥掺量较高时,无侧限抗压强度呈缓慢上升的趋势。随着水泥掺量提高,土样的无侧限抗压强度达到峰值时所对应的硫酸含量也逐渐变大。     

Application of phosphogypsum in soil stabilization

This paper describes the application of phosphogypsum with cement and fly ash for soil stabilization. Atterberg limits, standard Proctor compaction and unconfined compressive strength tests were carried out on cement, fly ash and phosphogypsum stabilized soil samples. Treatment with cement, fly ash and phosphogypsum generally reduces the plasticity index. The maximum dry unit weights increase as cement and phosphogypsum contents increase, but decrease as fly ash content increases. Generally optimum moisture contents of the stabilized soil samples decrease with addition of cement, fly ash and phosphogypsum. Unconfined compressive strengths of untreated soils were in all cases lower than that for treated soils. The cement content has a significantly higher influence than the fly ash content. The use of two waste by-products, phosphogypsum and fly ash may provide an inexpensive and advantageous construction product.     

Effect of silica fume on cement hydration and temperature rise of concrete in tropical environment

Investigated herein is the effect of temperature on heat development in cement pastes and concretes with and without silica fume cured at relatively high temperatures often encountered in tropical environment. With an initial temperature of 30°C, adiabatic temperature rise of the concrete with 8% silica fume as cement replacement was similar to that of the control Portland cement concrete up to about 18 h. After 24 h, however, the temperature of the silica fume concrete was lower than that of the control concrete. Since the concrete with 8% silica fume had a higher 28-day compressive strength (72.5 MPa) than the control concrete without silica fume (59.2 MPa), the concrete with silica fume is likely to have a lower temperature rise as compared with the control concrete of equivalent 28-day strength by reducing cementitious materials content with the same water content. The extent of heat evolution in the silica fume pastes was generally greater at lower temperatures of 20–50°C, but less at 65°C than in the control paste. At the relatively high curing temperatures, the degree of cement hydration in the paste with silica fume was lower than that in the control cement paste at early ages. However, the pozzolanic reaction started even before 24 h after water was added.     

Strength Development in Cement Stabilized Low Plasticity and Coarse Grained Soils: Laboratory and Field Study

Laboratory and field strength development of cement stabilized coarse-grained soils are studied in this paper. A phenomenological model to assess the laboratory strength development is developed. The model is divided into the dry and the wet sides of optimum water content. At the optimum and on the wet side of optimum, the strength development in cement stabilized soils at a particular curing time is dependent only upon the soil-water/cement ratio, w/C, which can reflect the combined effects of water content and cement content. It is moreover premised that the relationship between strength and water content is symmetrical around the optimum water content (OWC) in the range of 0.8 to 1.2 times the OWC. The proposed model is useful for assessing the strength development wherein water content, cement content and compaction energy vary over a wide range. Only the test result of a single laboratory trial is needed. From the field study, it is found that the field roller-compacted strength, q_ufr is lower than the laboratory strength, q_ul under the same dry unit weight, soil-water/cement ratio and curing time due to several field factors. The ratio q_ufr/q_ul varies from 50 to 100%. Non-uniformity in mixing soil with cement is realized by the ratio of field hand-compacted strength to laboratory strength, q_ufh/q_ul ranging from 0.75 to 1.2. For most data, the field roller-compacted strength is 55 to 100% the field hand-compacted strength. This might be caused by the difference in compaction method and curing condition between laboratory and field stabilization. From this field observation and the proposed model, a practical procedure for repairing damaged roads using the pavement recycling technique is introduced. The procedure consists of the determination of cement content, the execution of the field stabilization and the examination of the field strength. It can save on sampling and laboratory testing and hence cost.     

蒸养条件下水泥-粉煤灰复合胶凝材料的水化性能研究

通过测定不同龄期净浆的化学结合水量和抗压强度,并结合SEM,研究在蒸养条件下粉煤灰掺量、细度对水泥-粉煤灰复合胶凝材料水化性能的影响。试验结果表明:蒸养条件提高了水泥粉煤灰复合胶凝材料的水化速度,同时也提高了粉煤灰的活性;蒸养条件下,粉煤灰的细度对水泥粉煤灰复合胶凝材料的早期水化没有显著影响,其后期水化速度随粉煤灰细度的增加而增加;粉煤灰掺量的增加,降低了其早期水化速度,掺入适量的粉煤灰其后期水化程度可以超过纯水泥的水化程度;粉煤灰的掺入有利于水泥的水化,且水泥的水化速度随粉煤灰掺量的增加而增加。     

Geotechnical characterization of a clay–cement mix

Soft clay deposits are highly plastic, normally consolidated fine grained soils characterized by their low inherent shear strength. The mixing of soft clays with cement as a chemical stabilizer has become a well-known stabilization technique. The resulting strength of the clay–cement mix is controlled by different factors, but mainly the water to cement ratio, the cement content, and the curing conditions. It is crucial to develop a clear understanding of the changes in engineering behavior of the clay–cement mix that result from changes in controlling factors. A phase diagram was established to define the initial conditions of the mass–volume relationships of air, cement, clay, and water of a typical clay–cement mix. This phase diagram was then used to determine the total dry density, void ratio, and specific gravity of the clay–cement mix as a function of the cement content and water to cement ratio. The main objective of this work was to develop generalized trends for the geotechnical properties of clay–cement mixes. These trends were evaluated based on unconfined compressive strength as well as consistency tests carried out on soft clay samples before and after mixing with cement and at different curing times. A reduction in the plasticity index (PI) of 16 % and an increase in the unconfined shear strength of more than 200 kPa were obtained from the addition of 15 % cement. The reduction in the PI of the clay–cement mix was found to be an efficient tool to represent the improvement in the strength of the clay after mixing with cement.     

红黏土置换作用对水泥固化泥炭土强度的影响

针对红黏土置换后的泥炭土进行了水泥加固试验,并从宏观和微观两个角度对其固化机理展开了分析.研究表明:在含水率一定的条件下,固化泥炭土的无侧限抗压强度随红黏土置换率的提高呈先增大后减小的趋势;红黏土的置换作用一方面能够使其颗粒作为骨架填充固化土体的孔隙,另一方面在减少土体有机质含量的同时增加了Al元素含量,激发水化反应的活性并促进了钙矾石的生成.红黏土置换作用能够使泥炭土的絮状结构变得密实,颗粒连接和孔隙填充得到优化.     

Mixture design concept and mechanical characteristics of PS ash–cement-treated clay based on the water absorption and retention performance of PS ash

In an attempt to reduce environmental impact, paper sludge ash (PS ash) has recently been studied for its complementary reuse with cement for soil stabilization. In order to establish the optimal mixture design for combining PS ash and cement in soils, a detailed investigation into the stabilizing mechanism is required. To assess the combined effects of PS ash and cement on the strength development of stabilized clay soil, referred to as PS ash–cement-treated clay, a new critical parameter, the unabsorbed and unretained clay-water/cement ratio W*/C, was proposed. To determine W*/C, a new testing method for evaluating the water absorption and retention performance of PS ash was developed. It was revealed that the water absorption and retention rate W_ab of PS ash increased with curing time. Unconfined compression tests conducted on the PS ash–cement-treated clay with various water-cement–PS ash mixture proportions and different curing times affirmed that the strength development was fundamentally governed by the parameter W*/C. This suggests that the water absorption and retention rate W_ab obtained by the developed method is an essential material parameter in the mixture design for the PS ash–cement-treated clay. It was also found that the effect of the hybrid treatment method, which uses both cement and PS ash, was better than that of the method which uses cement alone, particularly under high W*/C conditions. This indicates that the water absorption and retention performance of PS ash can be fully utilized when the mixture has sufficient unabsorbed and unretained water for cement hydration.     

水泥胶凝材料水化进程及力学特性研究

首先简述了热分析的测定原理及其在水泥化学研究中的应用;利用热重方法分析了水泥净浆的水化进程变化规律,研究了不同水灰比的水泥净浆水化程度;并从理论上解释了不同水灰比的水泥净浆水化程度发展规律;而且,对水泥净浆水化过程中的抗压强度进行了测试,试验结果发现其变化趋势与水化程度变化趋势是完全一致的,这充分反映了微观结构与宏观性能之间的关系.     

YF-T水泥制品养护剂的研究

为防止水泥制品开裂,研制开发了YF-T水泥制品(砂浆、混凝土)养护剂。该养护剂由有机高分子物质和无机材料复合而成,以水泥制品有效保水率和单位面积吸水率为评价指标,确定养护剂的最佳配合比。试验研究表明,该养护剂可以有效保持水泥制品中的水份,促进水泥彻底水化,提高水泥制品的结构强度和耐磨性能,有效保证水泥制品的工程质量。     

水泥固化稳定重金属污染土的工程性质试验研究

随着社会的快速发展,因工业生产以及人类活动引起的地基土重金属污染现象越来越严重。地基土受到重金属污染后,其工程性质会发生改变。固化稳定法是处理重金属污染土地基的常用方法之一。以人工制备的铅或锌重金属污染土为研究对象,通过系统的室内试验,着重研究水泥固化稳定重金属污染土的工程性质。试验结果表明,土体受到污染后,其强度降低;掺入水泥固化稳定的重金属污染土的强度随水泥掺入量以及养护龄期的增加显著增大。通过试验还发现,较低浓度重金属离子的存在可以促进水泥固化土抗剪强度的提高。     

Effects of curing regimes and cement fineness on the compressive strength of ordinary Portland cement mortars

Curing techniques and curing duration have crucial effects on the strength and other mechanical properties of mortars. Proper curing can protect against moisture loss from fresh mixes. The objective of this experimental work is to examine the compressive strength of ordinary Portland cement mortars (OMs) under various curing regimes and cement fineness. Six different curing methods including water, air, water heated, oven heated, air–water, and water–air were applied to the specimens and also six groups of mortars were used. The results showed that the highest and lowest compressive strengths are attributed to the specimens of OPC mortar water cured using grounded OPC for duration of 6 h (OM–G6–wc) and OPC mortar air cured under room temperature with oven heated after demoulding of the specimens at 60 °C for duration of 20 h (OM–OH–ac), respectively. The maximum levels obtained of compressive strengths at 7, 28, and 90 days are 57.5, 70.3, and 76.0 MPa, respectively.