Durability of cementing binders based on fly ash and other wastes

The paper deals with the cementitious binders produced by blending 60–70% fly ash with fluorogypsum, hydrated lime sludge, with and without Portland cement and chemical activator in different proportions. Data show that strength development of cementitious binders takes place through formation of ettringite, C–S–H and wollastonite compounds. The durability of these binder has been studied by its performance in water and by accelerated aging i.e. alternate wetting and drying as well as by heating and cooling cycles at temperatures in the range 27–50 °C. The results indicate Lawrence of strength of binder with the increasing cyclic studies at different temperatures. The maximum fall in compressive strength was noticed at 50 °C.     

Production of high-strength concrete using high volume of industrial by-products

The production of a high-strength, high performance concrete using high volumes of industrial by-products is tested in laboratory mixtures. The by-products used are high-calcium fly ash and ladle furnace slag as binders and electric arc furnace slag as aggregates. Fly ash is used as 50% by mass of the total binder and ladle furnace slag as 30% by mass of the total binder. Slag aggregates are used in replacement of coarse aggregate or in replacement of both fine and coarse aggregates. In the mixtures containing both supplementary cementitious materials and slag aggregates the produced concrete shows high-strength (>70 MPa), good abrasion resistance and fracture toughness.     

胶凝材料对混凝土干缩影响的研究

通过试验分析了胶凝材料总量，水胶比，粉煤灰掺量对混凝土干缩性能的影响。结果表明：在实验范围内，胶凝材料总量和水胶比对早期干缩影响较小，对后期干缩影响较大，粉煤灰掺量对混凝土早期和后期干缩的影响都较大。     

混凝土绝热温升的影响因素

研究了混凝土的初始入模温度、流动度和掺加粉煤灰等因素对混凝土绝热温升值和温升速率的影响,同时还研究了所用胶凝材料的水化动力学。研究结果表明,提高混凝土初始入模温度将加速胶凝材料的水化,并缩短水化反应持续时间。这对低强度等级混凝土所用胶凝材料的水化程度影响不大,因而对其绝热温升值影响不显著;但却会明显降低高强度等级混凝土所用胶凝材料的水化程度,使其绝热温升值下降。掺加粉煤灰或改变混凝土的工作性也会影响混凝土的绝热温升值和温升速率。     

Comparative environmental assessment of wood transport models: A case study of a Swedish pulp mill

Wood transportation from forest landing to forest-based industries uses large amounts of energy. In the case of Sweden, where forest operations are highly and efficiently mechanized, this stage consumes more fossil fuels than other elements of the wood supply chain (such as silviculture and logging operations). This paper intends to compare the environmental burdens associated to different wood transport models considering a Swedish pulp mill as a case study by using Life Cycle Assessment (LCA) as an analytical tool.Five scenarios (the current one and four alternative reliable scenarios) were proposed and analysed taking into account two variables. On the one hand, the influence of imported pulpwood share from Baltic countries and on the other hand, the use of rail transportation for wood transport. In particular, the following impact categories were assessed: Eutrophication, Global Warming, Photochemical Oxidant Formation, Acidification and Fossil fuel extraction. The environmental results indicate that transport alternatives including electric and diesel trains, as well as the reduction in Baltic wood imports should present better environmental performance than the current scenario in terms of all the impact categories under study. Remarkable differences were identified with regard to energy requirements. This divergence is related to different long-distance transport strategies (lorry, boat and/or train) as well as the relative import of wood selected.The combination of lorry and train in wood transportation from Southern Sweden plus the reduction of wood imports from 25% to 15% seems to be more favourable from an environmental perspective. The results obtained allow forecasting the importance of the wood transport strategy in the wood supply chain in LCA of forest products and the influence of energy requirements in the results.     

Effects of industrial by-product based geopolymers on the strength development of a soft soil

Portland cement is traditionally used as a binder in ground improvement projects on soft soil foundations. The use of cement in ground improvement projects, however, is fraught with both, financial and environmental concerns due to its relatively high cost, the use of natural resources and the high carbon footprint from cement production. Attempts are being made to find alternative environmentally friendly binders with a low carbon footprint using industrial by-products such as fly ash (FA) and slag (S). Using waste by-products such as FA and S to produce geopolymer binders, as novel green cementitious materials, may provide an environmentally friendly and effective ground improvement option. In this study, the effect of adding geopolymers to a soft soil was investigated for usage in deep soil mixing (DSM) applications. The soil was a soft marine clay known as Coode Island Silt (CIS). Different combinations of FA and S with six combinations of sodium and potassium based liquid alkaline activators (L) were added to the soil to study the effects on its engineering and chemical properties. These changes were evaluated via an unconfined compression strength (UCS) test, scanning electron microscopy (SEM) imaging and energy-dispersive X-ray spectroscopy (EDS) tests. The tests were conducted after 3, 7, 14 and 28?days of curing. Based on the results, the important role of L in strength development was studied, and the combination of 30% NaOH with 70% Na₂SiO₃ was found to achieve the highest strengths. Furthermore, increasing the S content was found to result in significant improvements in strength. The excellent correlation between strength and stiffness shown in the results are expected to help in the development of relationships for strength prediction of these green binders in geotechnical applications. This study shows that FA and S based geopolymers can be used as sustainable binders in DSM projects, with significant environmental benefits.     

Stabilization of marginal aggregates with hydraulic and puzzolanic binders based on waste materials

Natural sand deposits and waste screenings from gravel pits and quarries are abundant in parts of Sweden. Investigations have been made to stabilize such materials with binders based on waste materials. Both laboratory work and test roads have been performed. In the latter case, mainly secondary roads have been strengthened with a plant-mixed bases. Good results have been achieved with a binder made of milled granulated blast furnace slag, activated with lime or especially with both lime and waste gypsum. Sand and screenings from gravel often contain organic material, deleterous with the binders studied. In such cases, the gypsum addition also seems to counteract the negative effect of the organic material. Fly ash has recently been available in Sweden. Tests made with fly ash-lime, as often used for stabilization abroad, have shown too slow binding for a rather cold climate. Addition of waste gypsum, calcium chloride, alkali-salts or use of an alkali-rich cement kiln dust instead of commercial lime can improve the binding properties. Different fly ashes, however, react in different ways. It is often more suitable to use fly ash-cement as a binder, especially with poorly graded aggregates. The fly ash, added in an optimum amount, work as a filler and high immediate stabilities can be achieved at a correct water content. The puzzolanic properties of the fly ash, at the same time, makes it possible to reduce the cement content considerably in comparison with the case when only portland cement is used as a binder. Promising laboratory work has also been done with binders consisting of condensed silica fume or ash from fluidized bed coal combustion, both in combination with lime.     

Properties of sintered low calcium bottom ash aggregate with clay binders

This paper focuses on the properties of sintered aggregates with low calcium bottom ash from coal fired thermal power plants using a wide range of clay binders through pelletization process. The experimental runs were designed using central composite design of response surface methodology. The aggregate was produced using a disc pelletizer. The pelletized aggregate was sintered at 800–1100 °C for 30–120 min. Sintered aggregates were tested for bulk density, 10% fines value and water absorption. The factors involved in the process are moisture content, binder, Ca(OH)₂ dosage, sintering temperature and duration. It was observed that an increase in binder dosage and sintering temperature resulted in aggregates with higher 10% fines value and low water absorption. The properties of aggregates depended on the type of binder used. Aggregate with kaolinite and metakaolin binders resulted in high 10% fines value. The results indicate the potential for manufacturing high quality lightweight aggregate from bottom ash using clay binders.     

Lime-cement stabilisation of Trondheim clays and its impact on carbon dioxide emissions

Dry deep mixing is used throughout Norway to improve soft and sensitive clays. Traditionally, binders such as lime and cement have been used in combination with relatively high binder contents. The production of lime and cement causes large emissions of carbon dioxide, and it is therefore desirable to reduce the binder contents in engineering practice. This paper presents results from a comprehensive study of various lime-based binders, with the aim to improve the understanding of the engineering properties of such stabilised clays when using reduced binder contents. Results from analyses on pH, plasticity and mineralogy are presented, and it is concluded that fine-grained quartz particles exhibit relatively high pozzolanic properties giving a considerable strength development over time, also with low binder contents. A novel correction of the binder content has been used, based on the active CaO of the binders. This correction gives remarkably consistent results between the water-binder ratio and the strength development. These results have also enabled estimations of carbon dioxide emissions as a function of binder type and strength development. It is concluded that the type of lime-based binder has little influence on the carbon dioxide emissions per unit strength for binder contents higher than 30–40 kg/m³. For lower binder contents, there is a tendency that binders with low active CaO-content give lower carbon dioxide emissions per unit strength, however, these low binder contents are difficult to obtain in field applications.     

Effects on growth, photosynthesis and pigments of the freshwater moss Fontinalis antipyretica Hedw. after exposure to wood ash solution

The application of wood ash from biofuel sources to the forest has been suggested as a source of nutrients for trees and for restoration of acidified soils and surface waters. Studies on the effects of wood ash on aquatic organisms and ecosystems are, however, few. This study investigated the effects of wood ash (0.1-10 g l(-1)) on the freshwater moss Fontinalis antipyretica Hedw., which has previously been shown to be a sensitive test organism for assessing environmental pollution. After nine weeks of treatment with wood ash, a significant effect of enhanced stem growth was observed at higher concentrations (1-10 g l(-1)). The concentration of wood ash was also correlated with the growth of secondary branches. Photosynthesis (oxygen evolution after 4 h of exposure to wood ash) was significantly lower in the alkaline treatments (no pH adjustment) compared to the treatments with neutral wood ash solutions (pH adjusted to 7.5). Furthermore, photosynthesis in the alkaline wood ash treatments was significantly lower compared to the control. The ratio between the optical density value before and after acidification (OD(665/665a)) was higher for all wood ash concentrations compared to the control. The OD(665/665a) values ranged from 1.52 to 1.61 and there was a difference, however not significant, between the alkaline and the neutral treatment at 10 g l(-1) wood ash. This study clearly demonstrated that wood ash may be beneficial for F. antipyretica at moderate concentrations (0.5-5 g l(-1)), particularly when a sudden increase in pH is avoided.     

Resistance to acid degradation,sorptivity, and setting time of geopolymer mortars

Experimental evaluations were conducted to determine the water sorptivity, setting time, and resistance to a highly acidic environment, of mortar with alkali-activated ground granulated blast furnace slag (GBS) binder and also of combinations of fly ash and GBS binders. Binders were activated using mixtures of NaOH and Na₂SiO₃ solutions. The molarity of NaOH in the mixtures ranged from 10 mol·L⁻¹ to 16 mol·L⁻¹, and the Na₂SiO₃/NaOH ratio was varied from 1.5 to 2.5. Mortar samples were produced using three binder combinations: 1) GBS as the only binder; 2) blended binder with a slag-to-fly ash ratio of 3:1; and 3) mixed binder with 1:1 ratio of slag to fly ash. Mortar samples were mixed and cured at (22 ± 2) °C till the day of the test. The impact of activator solution alkalinity, activator ratio Na₂SiO₃/NaOH, GBS content on the rate of water absorption were evaluated. After 7, 28, and 90 d of immersion in a 10% sulfuric acid solution, the resistance of a geopolymer matrix to degradation was assessed by measuring the change in sample weight. The influence of solution alkalinity and relative fly ash content on setting times was investigated. Alkali-activated mortar with a slag-to-fly ash ratio of 3:1 had the least sorptivity compared to the two other binder combinations, at each curing age, and for mortars made with each of the NaOH alkaline activator concentrations. Mortar sorptivity decreased with age and sodium hydroxide concentrations, suggesting the production of geopolymerization products. No reduction in weight of sample occurred after immersion in the strong acid H₂SO₄ solution for three months, regardless of binder combination. This was due to the synthesis of hydration and geopolymerization products in the presence of curing water, which outweighed the degradation of the geopolymer matrix caused by sulfuric acid.     

活性氧化镁水泥碳化加固软土地基研究进展

为了解决传统固化剂引发的环境污染和能源短缺等问题,明确活性氧化镁水泥在土体加固中的应用和发展,文章结合已有研究成果,对活性氧化镁的主要生产来源、氧化镁水泥的物理力学性能、氧化镁的碳化加固机理进行了初步的归纳与总结,并对活性氧化镁水泥的经济环境效益进行了对比分析。结果表明,活性氧化镁水泥生产耗能比传统水泥小,并且可以通过碳化反应在短时间内大幅度提高土体强度,改善土体耐久性能,并吸收大量CO2。活性氧化镁水泥这种新型固化剂在减少环境污染、改善加固效果和有效利用资源方面具有广阔的应用前景和重要的社会经济意义。     

Development of calcium sulfate–ggbs–Portland cement binders

Binders manufactured using a blend of gypsum, ground granulated blast furnace slag and Portland cements are technically viable and possess considerable environmental and economic advantages when compared to binders manufactured using Portland cement alone. As such, the evaluation of binders made from these materials offers a promising research focus in the quest to produce technically sound, environmental and economical binders for specialist uses as an alternative to traditional concrete binders of higher carbon footprint. The aim of the test programme was to investigate the viability of a series of binders designed to fulfil particular user needs while having significantly decreased carbon footprints.Two distinct series of binders were designed; the dominant ingredient in the first was calcium sulfate while in the second it was ggbs. Potential applications for both series of binders were considered and the strength development of each binder was analysed. In addition, the effect of water on the gypsum-based binders was analysed, as was the sulfate resistance of the ggbs-based binder.The results of the laboratory tests carried out were varied. For the calcium sulfate-based binders, those manufactured using anhydrite II as the dominant ingredient were found to achieve highest strengths. However these binders were found to be particularly susceptible to moisture-induced deterioration. For the ggbs-based binders, it was found that the early strength development was improved by the addition of small quantities of anhydrite II and gypsum. The strengths and sulfate resistance at later ages remained unaffected. These binders may have significant potential in situations where early strength development is a requirement.     

有机物污染场地浅层异位固化稳定化试验研究

以某化工企业有机物污染浅层土为对象,应用4种固化药剂进行固化稳定化修复对比研究。通过现场异位固化稳定化结合室内无侧限抗压强度、毒性浸出等试验,讨论了固化剂组份、龄期对其物理力学性质和浸出特性影响,并对比分析了其固化稳定化效果及机理。结果表明:随着养护时间增长,修复土p H值、毒性浸出溶液的有机物浓度降低,其中pH值由0 d的12.76~13.11降至28 d时的12.11~12.69,而有机物浸出浓度14d降幅在65%~100%间;干密度及无侧限抗压强度qu则稳步提高,其中干密度28 d增幅达14.4%~23.2%,而强度最大增加到122 k Pa。固化剂3和4修复污染土干密度较大,28 d密度超过1.37 g/cm~3,密实作用明显;添加固化剂会立即显著增大污染土pH值,其中固化剂4(电石渣+凹凸棒土)各龄期pH值明显大于其他剂型;各固化剂对不同有机污染物的稳定效果有所差别,但均能有效固化稳定化苯胺、2-氯酚、萘、苯、甲苯、邻-二甲苯;就污染物总体固化稳定化效果而言,含活性炭组分的固化剂1效果最为突出,其总稳定率接近100%;含水泥组分的固化剂2,3对土体的增强作用较好,其28 d强度可达109 k Pa以上。相较其他药剂,固化剂4在成本、能耗及污染物排放方面表现最优,且能较好满足场地修复对有机物稳定率及强度的要求,综合效果最佳,为优选的最佳剂型。     

矿物掺合料和化学外加剂对胶凝材料浆体的流变参数的影响

基于最优化方法,给出使用同轴双圆柱流变仪来获取胶凝材料浆体的Bingham流变参数的途径;探究五种矿物掺合料(粉煤灰、矿渣粉、硅灰、石英粉、粉煤灰微珠)和两种化学外加剂(减水剂与引气剂)对胶凝材料浆体流变参数的影响。研究结果表明：矿物掺合料等体积替代水泥相对于等质量替代水泥,对降低浆体的屈服应力和塑性黏度有利。粉煤灰可降低浆体的屈服应力和塑性黏度;矿渣粉和石英粉可降低高水胶比浆体的屈服应力和塑性黏度,但增大低水胶比浆体的屈服应力和塑性黏度;硅灰可显著提升浆体的屈服应力;粉煤灰微珠可降低浆体的塑性黏度但增大其屈服应力。减水剂可降低浆体的屈服应力和塑性黏度;引气剂可降低浆体的塑性黏度。矿物掺合料和化学外加剂对胶凝材料浆体的Bingham流变参数的影响,取决于水胶比、矿物掺合料或化学外加剂的掺量、矿物掺合料颗粒粒径、粒形和水化活性等因素,因此使得胶凝材料浆体的流变参数随着矿物掺合料和化学外加剂种类和掺量的变化,表现出非线性特征。     

Aging analysis of rubberized asphalt binders and mixes using gel permeation chromatography

This study was initiated to investigate the aging characteristics of binders due to the reaction with the crumb rubber. For this laboratory study, the crumb rubber modified (CRM) and control binders were aged using an oven aging method. Also, asphalt mixtures with CRM or control binders were made and subjected to short-term and long-term aging treatments. The properties of these aged binders were evaluated using gel permeation chromatography (GPC) test procedures. The results from this study showed that: (1) the higher CRM percentage resulted in the higher large molecular size (LMS) value of asphalt binder under the binder aging conditions, and the rate of increase in the LMS value was found to have a relation to the CRM percentage. The asphalt binders with higher CRM percentages (15% and 20%) had a trend the LMS values decrease after a certain level. This finding is thought to be related to the required time for the rubber to be fully digested; (2) after subjecting to the long-term oven aging, the asphalt mixtures with the control and CRM modified binders were found to have statistically insignificant differences in aging level, measured using the LMS values. The very thin film thickness of binder in asphalt mixture and the aging temperature of 100 °C insufficient to enable a reaction were considered to be the main reasons that no differences were observed from the standpoint of the aging effect.     

一种改善新老混凝土修补界面长期性能的方法

修补后新老混凝土能否很好地共同工作 ,主要取决于新老混凝土的界面粘结性能。新老混凝土界面良好的耐久性是保证补强加固后混凝土耐久性的关键。研究了采用不同新混凝土和界面剂修补时界面的 7d、2 8d、12 0d、1a以及 3a龄期的粘结强度。研究结果表明 ,新混凝土采用高掺量粉煤灰混凝土 (4 0 % ) ,虽然界面的短龄期强度较低 ,但随着混凝土修补龄期的增长 ,界面粘结强度显著提高 ,尤其在使用粉煤灰砂浆界面剂时 ,界面的粘结强度增加更明显     

Performance-based characterization of Arab asphalt

Asphalt binders are elasto-visco-elastic materials where temperature and rate of load application have a great influence on their behavior. They are classified as rheological materials since their stress-strain response is both time and temperature dependent. Asphalt binder consistency and hence ability to sustain and hold its fundamental cementing mechanism changes depending on temperature. In this research, the physical and rheological properties of the locally produced Arab asphalt binders and the performance requirements of the Gulf countries environmental conditions were determined. The designed experiments and the collected data clearly indicated that the locally produced asphalt binders can be used without modification in areas where the maximum pavement temperature does not exceed 64 °C. Temperature zoning indicated that more than 50% of the Gulf countries areas experience a maximum pavement temperature of 76 °C. Therefore, asphalt binder modification is required to meet Gulf countries' performance requirements.     

Effect of polyester resin additive on the properties of asphalt binders and mixtures

The properties of AC-5 control asphalt binder, mixture containing the same asphalt were compared with the properties of AC-10 asphalt binder modified by 0.75%, 1%, 2%, and 3% of polyester resin (PR), mixture containing pure AC-10 and AC-10 modified by 0.75% of PR, respectively.Initial research was done to determine the physical properties of unmodified and PR modified asphalt binders. The AC-10 asphalt binder modified by 0.75% of PR had good results compared to AC-5 control asphalt binder and all other modified binders, and hence this modified binder as well as unmodified binders were used to prepare Marshall samples for Marshall stability and flow, indirect tensile stiffness modulus (ITSM), indirect tensile strength (ITS) and creep stiffness tests.The results of investigation indicate that AC-10 + 0.75% PR binder has better physical properties than AC-5 control asphalt binder and, at the same time, PR improves mechanical properties of asphalt mixture.     

Effect of crumb rubber characteristics on crumb rubber modified (CRM) binder viscosity

Asphalt binder viscosity is of great importance during the production process of hot mix asphalt mixture as typically asphalt plants will store binders between 149 °C and 177 °C. SHRP guidelines state that asphalt binder viscosity must not exceed 3 Pa s. Therefore, given the documented increases in asphalt viscosity when modified with crumb rubber modifier (CRM) it is necessary to produce asphalt binder that fulfills the SHRP criteria while not exceeding plant mixing and storing requirements. This paper reports the results of an investigation of the importance of CRM properties on viscosity of CRM binder. Two binder sources were modified at four concentration levels using four different crumb rubber sources; the viscosities of the produced binders were evaluated by AASHTO T 316. Crumb rubber properties were evaluated by elemental analysis using a scanning electron microscope (SEM) and by determination of glass transition temperature (T_g) using a differential scanning calorimeter (DSC). In general, results indicate that processing procedure and tire type plays an important role in the determination of CRM binder viscosity.