The effect of pectin on the physicochemical and mechanical properties of cement containing boron

The effects of varying concentrations of pectin (0.1–1 wt% of cement) on the properties of ordinary portland cement (PC) and cement containing colemanite ore waste (CW) were investigated. Variation in setting time, compressive strength, and volume expansion of hydrated specimens were determined. It was found that pectin acts as an accelerator for PC cement and as a retarder for CW cement at a level below 0.1%. The inclusion of pectin in PC resulted in a reduction in the early strength of the mortar. However, pectin had positive contribution to the early compressive strength of the CW mortar.     

Strength analysis of bamboo by microscopic investigation of bamboo fibre

This paper presents the mechanical properties of two bamboo species, namely Mao Zhu and Kao Zhu, which are commonly used for scaffolding in Southern China. Variations of the compressive strength against the physical properties of bamboo along the culms for both bamboo species were compared. A correlation of the average number of vascular bundle to the compressive strength of both bamboo species was developed. Findings indicate that the compressive strength of both Kao Zhu and Mao Zhu ranged between 45 and 65 N/mm² and the compressive strength of top section bamboo was higher than the bottom section. The fibre area of the top section bamboo was also found to be greater than bottom section bamboo from microstructure count of the sclerenchyma fibre within the vascular bundle of bamboo section. The microscopic examination of sclerenchyma fibre of bamboo section can be an alternative measure of the strength of bamboo for construction use.     

Microstructure of pre-wetted aggregate on lightweight concrete

A study was made on microstructure and water absorption rate of ‘Litcon’—a porous lightweight aggregate made from expanded clay. EDAX analysis on the aggregate particle showed different chemical compositions between the shell and the inner core of the lightweight aggregate. S.E.M. examination on the resulting concrete showed a good mechanical bonding between the cement and the aggregate interface, though traces of inter-granular cracks were observed. When the pre-wetting time of the aggregate increased, the strength and the workability of the concrete increased too. The high workability of fresh concrete was attributed to the localised high water content at the surface of the pre-wetted aggregate. The surface pores of the aggregate shell absorbed the water built-up at the cement/aggregate transition phase thus resulting with lower water content at the transition zone. EDAX analysis confirmed migration of cement phase into the aggregate shell. This loss of fluidity at the transition zone may have a significant effect on the permeability of lightweight concrete.     

碱-矿渣水泥缓凝物质的选择研究

研究了氯化钡、硝酸钡、硫酸铁、铬酸钠、氯化镁、硫酸镁、硫酸铝等无机盐以及酒石酸、草酸等有机酸对碱-矿渣水泥凝结时间的影响.试验结果表明,氯化钡、硝酸钡、氯化镁、硫酸铝、酒石酸有良好的缓凝作用,硫酸铁、铬酸钠、硫酸镁、草酸不产生缓凝作用.通过强度测试发现,氯化钡、硝酸钡、氯化镁、硫酸铝、酒石酸均对碱-矿渣水泥的强度有一定的不良影响.     

不同机制砂微观形貌和胶砂性能研究

为更好研究机制砂的合理应用,选取了3种不同岩性的机制砂,通过分级筛分后调配成Ⅱ区中砂,设计了三种不同级配的机制砂。研究了不同机制砂的化学组成、矿物组成和微观形貌,以及不同机制砂对胶砂性能的影响。研究表明:不同机制砂颗粒的长径比和圆形度有一定的差异,个别粒级的参数差异较大;级配对钙基机制砂胶砂强度影响没有硅基机制砂显著;细度模数较大时,钙基机制砂胶砂强度大于硅基机制砂。     

Uptake of metal ions by chemically treated human hair

The uptake capacity of chemically treated human hair waste for the various metal ions can be arranged in the following decreasing order: Hg²⁺ (Hg⁺), Ag⁺, Pb²⁺, Cd²⁺, Cu²⁺ (Cu⁺), Cr⁶⁺, Ni²⁺, Cr³⁺.The uptake capacity is significantly affected by the presence of other metal ions. Anionic effect was found to be more pronounced for a mixed ions system than for a single ion system.     

Plasticity role in strength behavior of cement-phosphogypsum stabilized soils

Dredged soil and phosphogypsum are frequently regarded as wasted materials, which require further treatment to control their environmental impact. Hence, phosphogypsum is proposed as a binder to stabilize dredged soil, aiming at efficiently reducing and reusing these waste materials. In this study, the engineering properties of cement-phosphogypsum stabilized dredged soils were investigated through a series of unconfined compression tests, and the effects of plasticity index of original soils on the strength improvement were identified. Then, the microstructure test and mineralogical test were performed to understand the mechanism of physical role of original soils in strength improvement. The results revealed that the unconfined compressive strength significantly decreased with the increase in plasticity index at the same binder content. The essential factor for strength improvement was found to be the formation of cementitious materials identified as calcium silicate hydrate (CSH), calcium aluminate hydrate (CAH), and ettringite (Aft). The normalized integrated intensity of cementitious materials (CSH + CAH + Aft) by pore volume decreased with the increase in plasticity index. Consequently, the density of cementitious materials filling the soil pores controlled the effectiveness of strength improvement. More cementitious materials per pore volume were observed for the original soils with lower values of plasticity index. That is, the higher strength of stabilized soils with lower values of plasticity index was attributed to a packed structure forming by integrated fabric through denser cementitious components. It can be anticipated from the above findings that the effectiveness of stabilization treatment will significantly reduce with the increase in plasticity of origin soil.     

Thixotropic mechanism of clay: A microstructural investigation

Clays with high sensitivity exhibit varied degrees of thixotropic characteristics. Previous research has been focused on dilute suspensions, but only a few studies have investigated normal clay with water contents lower than the liquid limit. Given the limited studies performed, the thixotropic behavior of clays and the underlying mechanism remain ambiguous, particularly in the microscopic scale. In this study, samples of Zhanjiang clay from southern China were used to elucidate the thixotropic process. The samples were agitated and then subjected to unconfined compressive strength and pocket penetrometer tests, scanning electron microscopy, and mercury intrusion porosimetry to evaluate their regain strength and microstructure. After 500 d of thixotropy, the strength of the Zhanjiang clay was 2.58 times higher than that after the disturbance and significantly higher than that of the other clays reported in the literature. These findings provide evidence that thixotropy is a process in which the dispersed structure is transformed into a flocculent structure through the homogenization of the pore size distribution caused by particle movement. This phenomenon may be due to the changes in the interaction of attractive and repulsive forces between particles. Given the experimental findings, a thixotropic mechanism for clay is proposed. This study will be beneficial for predicting the strength of disturbed soils.     

Removal of naphthalene from aqueous solution on chemically modified activated carbons

The aim of this work was to correlate the textural and chemical features of carbonaceous adsorbents with the adsorption capacity of naphthalene from aqueous phase, at the concentration in which this compound is usually found in wastewater from coke ovens. The study reveals that the adsorption capacity in different carbon materials depends not only on the textural characteristics of the material but also on the functionalities of the activated carbons. The micropores of the adsorbents, particularly those of narrower diameter, were found to be active sites for the retention of naphthalene. In contrast, the modification of the surface chemistry of the carbon materials led to a decrease in the adsorption capacities. Dispersive forces play an important role, and adsorbents with a higher non-polar character have proven to be more efficient for the naphthalene adsorption. This behaviour has been linked to the presence of specific interactions between the basal planes and the polyaromatic structure of the naphthalene molecule.     

Trials on sludge of lime treated spent liquor of pickling unit for use in the cement concrete and its leaching characteristics

Disposal of sludge of lime treated spent liquor pickling unit, as per the Act of Hazardous Waste (Management and Handling) Rules, 1989 is not easy. Its transportation and construction of lined disposal sites pose very severe problem. In the normal practice, sludge is being disposed off on sides of roads and railway tracks to generally fill the low-lying areas. This may cause severe health hazards. An attempt has therefore been made to utilize the treated spent liquor sludge in cement concrete. Design mix M20 has been prepared with varying concentration of sludge in the laboratory. Toxicity characteristics leaching procedure (TCLP) test as per USEPA has been carried out on cement concrete cubes.     

Physicochemical and consolidation properties of compacted lateritic soil treated with cement

The consolidation of a fine-grained lateritic soil, treated with compound Portland cement (CEMII/BM 32.5 N) up to 9% by weight of the dry soil and prepared at three different molding water contents (ω_DRY, OMC, and ω_WET), was investigated by means of a one-dimensional consolidation test. The physicochemical and microstructural properties of the compacted lateritic soil-cement mixture were investigated using Raman spectroscopy, polarized light microscopy (PLM), scanning electron microscopy (SEM), and pH measurement. The results show that cement admixtures resulted in the formation of tobermorite, afwillite, ettringite, portlandite, and calcite. However, tobermorite and afwilite, which are calcium silicate hydrates (CSH) whose mechanisms of formation are the pozzolanic and alkali silica reactions, appear from 6% added cement. The fixing point of the pH (12.4) is also obtained from 6% added cement. It is the threshold value at which the material begins to develop an adequate mechanical performance. In general, as the content of cement in the soil is increased, the yield stress increases from 1 to 3 times in comparison to untreated soil. For effective vertical stresses smaller than the cement-induced yield stress, the primary consolidation process for specimens treated with cement is 2–7 times faster than that for specimens not treated with cement, while for effective vertical stresses higher than the cement-induced yield stress, the primary consolidation process for specimens treated with cement is about 0.5–1.5 times faster than that for specimens not treated with cement. Permeability and secondary compression are reduced 1–9 times and 2–11 times that of the untreated samples, respectively. These changes are attributed to the creation of chemical bonds and aggregation that accompany the addition of cement. The results also show that it would be desirable for soil samples to be prepared at the dry side of optimum (ω_DRY) when the optimum moisture content (OMC) is not reached at the site. These results indicate that significant and desirable changes in soil behavior can be achieved when the soil is admixed with CEM II/BM 32.5 N cement, thus providing the possibility of using the tested lateritic soil in road construction.     

新型矿渣水泥的强度发展特性

试验表明,采用分磨技术生产的新型矿渣水泥的强度和龄期的对数呈线性关系,分析了矿渣细度,掺量对新型矿渣水泥不同龄期度发展系的影响,得出了不同矿渣细度和掺量所配新矿渣水泥的强度发展系数。     

Calcination of Roman cement: A pilot study using cement-stones from Whitby

Roman cement was patented in 1796 and established as a major material in the development of European architecture and engineering in the 19th century. However, the market is poorly served for those conservators wishing to use authentic materials in their work and there is a need to reintroduce Roman cement for such purposes.

Cement-stones from Whitby were calcined at various temperatures and residence times in a laboratory kiln. The resulting cements were assessed for setting time, strength development and mineralogical characteristics.

The properties are sensitive to calcination conditions with optimum strengths being achieved at temperatures of approximately 900 °C accompanied by rapid setting of <1 min. A three stage strength development profile was identified characterised by a high initial strength, a dormant period which could last for many weeks and a final increase in strength to an age of 1 year.

Considerable variation in the composition was noted and related to the calcination conditions. Of particular interest is the formation of both ′-belite and β-belite under differing calcination conditions. Clinker particles were also compared using the SEM in both secondary electron and back-scattered electron imaging modes and the development of morphology observed.     

Use of boron waste as a fluxing agent in production of red mud brick

The study was directed towards determining the usability of clay and fine wastes (CW and FW) of boron from the concentrator plant in Kirka (Turkey) as a fluxing agent in production of red mud (RM) brick. Both laboratory studies on the characterization of materials and industrial-scale tests for production of bricks were carried out. CW and FW, which have similar chemical composition but include different types and amounts of oxides, were added in amounts of 5, 10 and 15 wt% to RM, which consists of high amounts of Fe₂O₃, Al₂O₃, SiO₂ and alkalies. Six different sets of samples have been produced and fired at 700, 800 and 900 °C. Dry shrinkage of green body, bending and compressive strength, firing shrinkage, water absorption, frost resistance and harmful magnesia and lime tests on heat-treated bodies have been performed. The mineralogical and mechanical tests showed that usability of boron wastes as a fluxing agent in the production of RM bricks was possible. In addition, the samples obtained by adding 15 wt% CW and FW to RM showed the best mechanical characteristic.     

减缩型外加剂在水泥砂浆的评价实验研究

基于通过降低液相表面张力,减缓蒸发,减小毛细管附加压力而达到抑制自收缩与干燥收缩、减少裂缝产生这一思路,本文研制了一种减缩型外加剂。通过调整组成,在保证有效控制收缩率的基础上,克服以往产品对强度产生不良影响的缺陷。以共混掺入与表面喷涂两种不同的使用方式,依据相关标准对其在水泥砂浆中的实际使用效果进行评价研究。     

Effect of high temperature on strength and microstructural properties of cemented paste backfill

The main purpose of this research is to investigate the influence of high temperatures on the strength and microstructure (e.g. pore structure, porosity) of cemented paste backfill (CPB) through a series of experimental tests. A laboratory experimental setup allowing the simulation of various high-temperature conditions is developed. Different types of CPB specimens are exposed to different high temperatures (100, 200, 400 and 600 °C). The strength, porosity, pore size distribution and water absorption of these CPB specimens are then evaluated by laboratory tests. Thermogravimetric and differential thermal analyses are also performed to study the thermal behaviour of the CPBs exposed to high temperatures. The results show that high temperatures have a significant effect on the properties of CPBs. Generally, increasing temperatures up to 200 °C leads to higher strength in most types of CPB studied. The porosity and pore size distribution of the CPBs change only slightly. Above 200 °C, the temperature reduces the strength of the CPBs. The most notable strength decrease takes place at exposure temperatures exceeding 400 °C. The significant decrease of the strength of the CPB is accompanied by a significant change in the microstructure (porosity, pore size distribution, mineral phases). Moreover, the effect of high temperatures on the strength and microstructure of CPBs depends on the water/cement ratio (w/c ratio) and the tailings type.     

活性炭纤维吸附饮用水中硼的试验研究

通过静态试验,对经过简单预处理的活性炭纤维的除硼效果以及吸附时间、pH、温度和搅拌机转速等因素对吸附效果的影响进行了考察.结果表明.该吸附过程符合Freundlich吸附等温线模式,以物理吸附为主;最佳吸附时间为1 h;pH和温度对吸附效果影响均较大,pH值最佳范围为5～6.5,温度为15℃;搅拌机高速转动更利于吸附进行;采用了不同再生剂对吸附饱和的活性炭纤维进行再生试验,3%NaOH溶液再生效果最好,再生后吸附效率可达90.1%.     

Influence of molding process on mechanical properties of sandstone cemented by microbe cement

A new generation of cement, microbe cement has been developed due to the ever increasing awareness of environmental protection. Microbe cement is a new strengthening technique based on microbiologically induced precipitation of calcium carbonate. This paper confirms the feasibility of microbe cement binding loose sand particles and presents results from a laboratory research on the influence of molding process (non-pressure molding, pressure molding, discontinuous non-pressure molding and pumping molding) on the mechanical properties of sandstone microbe cement bound. The results showed that the ways of molding procedure had a strong influence on the mechanical properties of bio-sandstone. The strength, which was up to 12.0 MPa, of sandstone microbe cement bound by adopting pumping molding process was higher than other three processes. Meanwhile, Scanning electron microscope (SEM) image analysis technique was adopted to measure the corresponding variation of porous characteristics caused by different molding processes. The results indicate that the microstructure of bio-sandstone adopted by pumping molding has lower porosity and higher content of precipitated calcium carbonate than other three molding processes.     

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.     

Harakeke reinforcement of soil–cement building materials: Manufacturability and properties

Fibre from the New Zealand flax plant, Phormium tenax, or Harakeke as it is otherwise known in Maori, has been used to reinforce soil–cement composites in an attempt to improve the strength and ductility of the composite material. Previous investigations have found the interfacial bond strength between the harakeke fibre and the soil–cement matrix to be an important factor for the strength of the composite. In an effort to improve the interfacial bond strength, an enamel paint coating has been applied to the fibre surface. Fibre lengths of 70 and 85 mm have been investigated along with fibre content levels of 0.6% and 0.8% measured as a percentage of the dry mass of the soil in the composite. Significant improvement in the ductility of the soil–cement composite has been realised with the addition of the harakeke fibre-reinforcement. It has been found that the specific make-up of the composite with regard to fibre length and content is not critical for the achievement of ductility improvement. Instead, these parameters were found to be controlled more by manufacturing issues such as the workability of the composite. It was found that 85 mm represented an upper limit on fibre length for the manual mixing technique adopted, while a maximum fibre content level of 0.8% was achieved. In order to reduce manufacturing difficulties, different mixing techniques were studied. A successful tumble mixing technique has been identified which is able to improve composite uniformity and the ease of manufacture. Based on the similarity of results for the two fibre content levels investigated, it is recommended that a level of 0.6% be adopted as this both improves the ease of manufacture and minimises the amount of fibre required. When the fibre content level was dropped below 0.6%, it was found that the material exhibited a more brittle failure behaviour.