Low risk meat and bone meal (MBM) bottom ash in mortars as sand replacement

This paper presents the physical, chemical and mineralogical characteristics of meat and bone meal bottom ash (MBM-BA) from low-risk sources. It also gives a first evaluation, from a technical and an environmental point of view, of its potential of use as sand in cement-based materials. Results show that MBM-BA has the physical characteristics of a fine sand. It has low friability but high water absorption, which leads to a recommended use of less than 30% MBM-BA as sand replacement in mortars and the use of a superplasticizer. The compressive strength of mortar containing 17% of MBM-BA is similar to that of a reference mortar and the leaching behavior resembles that of the reference mortar without residue. These preliminary results lead us to believe that low-risk MBM-BA could be used in cement-based materials and present a promising way of reusing this residue.     

Pore structure and mechanical properties of cement-lime mortars

Studies focusing on materials used in Cultural Heritage conservation projects are becoming increasingly important. In this paper, the pore structure and mechanical properties of lime-cement mortars are evaluated in order to analyze their potential use, because this kind of mortar could reduce the disadvantages presented by both lime-based mortars and cement-based mortars. The microstructure of these blended mortars is studied taking into account porosity, pore size distribution and surface fractal dimension. Compressive and flexural strengths are discussed as a function of several parameters: curing time, binder composition and B/Ag (Binder/aggregate) ratio. The mechanical strength versus the deformation of the material is also evaluated, by analysis of Young's modulus, as well as the elastic and plastic zones. Unlike cement-based mortars, blended mortars with a high percentage of lime present a large plastic zone, which could be useful in the service-life of these mortars as a result of their ability to absorb strains caused by wall movements.     

Characterization and monitoring of cement-based systems using intrinsic electrical property measurements

This paper highlights the application of electrical property measurements as a characterization and investigative technique in the study of cementitious systems at the micro- and macroscale. Both fixed-frequency and spectral measurements are exploited to study cement pastes, mortars and concretes and results are presented from research programs relating to the early hydration of cement-based systems, characterization of fly ash, and concrete durability. The work comprises both laboratory-based investigations and field-monitoring studies. The methodology could complement other techniques that are used in the study of cement-based materials.     

Cellulose ethers influence on water retention and consistency in cement-based mortars

Cellulose ethers (CE) are commonly used as additives to improve the quality of cement-based materials. As admixtures, they improve the properties of mortars such as water retention, workability, and open time. Also, polysaccharides such as starch derivatives are used to improve the consistency of the fresh material.The properties of cement-based mortars at fresh state were investigated. The effect of CE and their physico-chemical parameters (molecular weight, substitution degrees, etc.) on both water retention and rheological properties of mortars were studied. Moreover, some starch derivatives were also examined in order to better understand the water retention mechanisms.Rheological measurements showed that CE have a thickening effect for a content of 0.27 wt.%. Besides, a fundamental effect of CE molecular weight on mortar consistency and its water retention capability was highlighted. Finally, the comparison with starch ethers proved that, for those admixtures, water retention is not directly linked to mortar's viscosity.     

氧化石墨烯复合PVA纤维增强水泥基材料的力学性能及耐久性研究

为解决混凝土耐久性差、脆性大等问题,研究了氧化石墨烯(GO)复掺聚乙烯醇(PVA)纤维对低水灰比水泥基材料力学性能及耐久性能的影响.利用Hummers法制备GO,并表征GO的结构和性能,通过测试分析了不同配合比砂浆的力学性能和耐久性,并通过MIP(压汞法)和SEM(扫描电镜)分析了氧化石墨烯以及PVA纤维对水泥基材料的改性机理.结果表明GO和PVA纤维均能提高水泥基材料的力学性能以及耐久性.GO复掺PVA纤维可以显著改善水泥基材料孔结构,降低孔隙率,提高水泥基材料抗氯离子渗透性能并降低水泥基材料收缩率.     

The development of high-strength mortars with improved thermal and acid resistance

Granulated blast furnace slag (GBFS) cement, containing up to 60% slag, is sometimes used in repair materials applied at intermediate temperatures of 150-300 °C. Low rate of strength development, especially at early ages, is considered a common disadvantage of repair mortars based on slag cement. The present research was oriented to improving a GBFS-portland cement binder for application as a repair material in the chemical industry when high thermal or acid resistance is required. It was found that the enhancement of GBFS-portland cement-based materials can be achieved with the help of silica fume (SF) and a superplasticizer (SP). The effect of different SPs on the compressive and flexural strength of SF-blast furnace slag-portland cement mortars was investigated. These mortars, in addition to high strength, demonstrate high thermal and acid resistance.     

Preparation,characterization, and physical properties of lightweight ceramics by using sewage sludge ash

In the present study, sewage sludge ash (SSA) was added to clay to prepare lightweight ceramics for sustainable construction materials. The characterization and the effect of different concentrations of SSA on the physical and mechanical properties of the samples were studied. The results showed that the organic matter in SSA facilitated the combustion process. SSA addition reduced the bulk density from (1.94 to 1.32 g/cm³). Otherwise, the water absorption, the apparent porosity and the loss on ignition increased with the increase in SSA concentration. The addition of SSA lowered the compression strength but still within the standard range of the construction materials at concentration up to (30 wt.%). Furthermore, heavy metals are solidified inside the sintered samples, since Cu, Cd, Fe, Zn, Cr, Mn, Ni, and Pb, concentrations in the leachate met the range of Egyptian standard specification.     

Physical and mechanical properties of concrete repair materials in dry and hot-dry environment

A variety of repair materials is available in the market. It is often difficult to select a suitable repair material for a given condition. Various researchers use different evaluation methods, but the required specifications are not established. The main objective of this work is to study the physical and mechanical properties of ready-mixed repair mortars available in the Algerian local market. The experimental study was carried out on three types of repair mortars: cement-based mortars, with and without fibers. The properties of the repair mortars at hardened state are analyzed for compressive, flexural and bond strengths, capillary water absorption, and shrinkage. The effect of humid curing using Hessian regularly humidified, on the compressive strength in hot and dry environment was also studied. The results of the experimental study showed that the repair mortar containing silica fume and synthetic fibers gave a better strength in all curing environments. The study showed also the negative effect of hot and dry environment on all types of ready-mixed repair mortars, and demonstrated the importance of humid curing during early age.     

Corrosion behavior of steel in alkali-activated fly ash mortars in the light of their microstructural,mechanical and chemical characterization

This study concerns the corrosion behavior of steel in different room temperature cured alkali-activated fly ash mortars exposed to chloride solution. The corrosion process was monitored by polarization resistance and corrosion potential measurements and the results were interpreted in the light of a complete microstructural, mechanical and chemical characterization of the mortars. The most compact alkali-activated mortars have higher porosity and lower mechanical properties than a cement-based mortar (CEM), but the protectiveness afforded to the rebars is slightly higher than that obtained in CEM. The reason for this discrepancy is connected to a lower chloride content accumulated in the former mortar type and to a specific inhibition of the rebar corrosion afforded by the pore electrolyte in alkali-activated mortars.     

Oxygen diffusion through hydrophobic cement-based materials

The oxygen diffusion coefficient through hydrophobic cement-based materials fully immersed in water was determined by potentiostatic measurements on concrete and by the use of a diffusion cell on cement pastes and mortars. The obtained results show that very high oxygen diffusion occurs through cement paste, mortar and concrete made with hydrophobic admixture as opposed to negligible diffusion through the reference cement matrix without admixture. Moreover, the oxygen diffusion coefficients measured through hydrophobic cement matrices immersed in water were comparable with those reported in literature for unsaturated cement materials in air. These experimental results appear to confirm that oxygen dissolved in water directly diffuses as a gaseous phase through the empty pores of a hydrophobic cement matrix. This could explain the severe corrosion of steel reinforcement embedded in cracked hydrophobic concrete immersed in an aqueous chloride solution observed in a previous work.     

The thermal conductivity mechanism of sewage sludge ash lightweight materials

The foaming reactions and the hydration and Pozzolanic effects of processed sewage sludge ash (SSA) allow it to be used as the main ingredient to make lightweight materials. The thermal conductivity of the SSA lightweight materials (SSALM), the SSA properties and how the mixing ratio of the materials influences the heat insulation properties are investigated. The results show that the thermal conductivity of SSA is low. When at room temperature, the pores in the specimens are filled with air, hence, the thermal conduction modes of these materials will be solid or air conduction. Radiant thermal conduction and natural convection can be ignored. The characteristics of the porosity, irregular particles and lightweight after the foaming reaction lead the thermal conductivity of the SSALM low to be 0.0763-0.2474 W/m K. When the water-to-solid ratio (W/S) and the amount of aluminum powder are increased, open and connected pores are formed, which negatively affects the compressive strength and the thermal conductivity. In addition, the total pore volume and thermal conductivity of SSALM are inversely proportional.     

Effects of the incorporation of Municipal Solid Waste Incineration fly ash in cement pastes and mortars: I. Experimental study

This work falls within the scope of a general problem regarding the assessment of concrete manufactured from waste materials. The main objective is to study the long-term evolution of these materials during the leaching process, using the cellular automaton-based hydration model developed at the National Institute of Standards and Technology. The work is based on the analysis of mortars and cement pastes containing experimental waste: Municipal Solid Waste Incineration fly ash (MSWI fly ash). The study therefore aims to develop a methodology for assessing concrete manufactured from waste, and not to study a process or a formulation enabling the incorporation of the waste in concrete. The physical, chemical and mineralogical characteristics of MSWI fly ash were first analysed to introduce them into the model. A simplified quantitative mineralogical composition of the ash was proposed. The performance characteristics (setting times, compressive strengths, shrinkage, etc.) for mortars containing ash were then studied.     

Assessment of mechanical and microstructural properties of geopolymers produced from metakaolin,silica fume,and red mud

Geopolymers have been studied as viable alternative to traditional Portland cement-based products, given the use of industrial by-products as raw materials. This work evaluated the mechanical and microstructural properties of geopolymeric mortars produced with sodium hydroxide solution, metakaolin, silica fume, and red mud. The mixtures were produced by means of dosages with different molar ratios and curing conditions. The raw materials were characterized by granulometry, chemical, mineralogical, and thermal analysis. The characterization of mortars was performed by scanning electron microscopy (SEM) and axial compressive strength tests. The precalcination at 850°C of the red mud was sufficient to make it more reactive and suitable for use in geopolymers. Noteworthy, the best mechanical strengths of metakaolin mortars for curing at 50°C, and with the lowest SiO₂/Al₂O₃ ratios. In the mortars with incorporated red mud, there was a decrease of strength at thermal curing conditions and with the increase of residue content, whose microstructure indicates the formation of more pores in the geopolymer matrix. The thermal curing promoted the formation of sodalite crystals, and the significant presence of Na particles on the surface suggests that part of the added NaOH did not react with the precursors.     

A study on the corrosion of reinforcing bars in alkali-activated fly ash mortars under wet and dry exposures to chloride solutions

This research investigates the corrosion protection afforded to the embedded rebars by room temperature-cured alkali-activated mortars, based on class F fly ash (FA), during wet and dry (w/d) exposures to 0.1 M NaCl solution. The results were compared to those obtained in a traditional cement-based mortar (REF). The rebar corrosion behaviour was characterized by corrosion potentials (E_cor) and potentiostatic polarization resistance (R_p) measurements, polarization curve recording and electrochemical impedance spectroscopy (EIS). The information collected suggested that FA mortars afforded a lower corrosion protection to the rebars and the reason was investigated by microstructural, physical–mechanical and chemical analyses of the mortars. FA mortars were found to undergo a fast carbonation, so that depassivation of the rebars occurred concurrently, in spite of a limited total chloride content inside these mortars. REF mortar was much less susceptible to carbonation and rebar corrosion started when a sufficiently high chloride concentration was built up.     

重金属污泥磨细粉对硅酸盐水泥基材料性能的影响

为了更好地实现对重金属污泥的资源化利用,研究了高温无害化处理重金属污泥与建筑渣土混合渣料磨细粉对硅酸盐水泥基材料工作性、力学性能、早期收缩变形、抗氯离子渗透性能及重金属浸出的影响及机理。研究结果表明,随着磨细粉掺量的增加,硅酸盐水泥基材料的工作性没有降低,但其力学性能均有一定程度下降,这说明磨细粉与硅酸盐水泥的需水比相差不大,但其掺量越大水泥基材料中水泥的量越低,其强度均会有一定程度下降。磨细粉不会引起硅酸盐水泥基材料的体积安定性问题,可以提高早期抗裂性,但会降低其抗氯离子渗透性能。含磨细粉试件中重金属的浸出浓度、水胶比的下降与龄期的上升呈负相关,且在28 d龄期下含40%(质量分数)磨细粉的硅酸盐水泥基材料中重金属Cu、Ni、Zn和Cr的浸出量均低于GB 30760—2014《水泥窑协同处置固体废弃物技术规范》规定的浸出浓度限值。     

矿物掺合料改善水泥基材料抗硫酸盐侵蚀性能的微观分析

采用CT、X射线衍射、扫描电子显微镜等测试方法,通过对不掺矿物掺合料以及掺30%粉煤灰或50%矿渣的水泥净浆、水泥砂浆在室温下5%Na2SO4溶液中浸泡2a后的宏观破坏形态和浆体组分及浆体形貌的分析,从微观层次上研究了矿物掺合料对水泥基材料抗硫酸盐侵蚀破坏的影响。结果表明：侵蚀后不掺矿物掺合料的试件由表及里呈现三层不同侵蚀状态,即表层石膏区、中层钙矾石区以及内层未侵蚀区。矿物掺合料的C3A含量稀释效应、火山灰反应以及微集料填充效应协同作用的结果使得试件的抗硫酸钠溶液侵蚀破坏性能显著提高。但矿渣中活性Al3＋含量较高,能与SO42–反应生成大量钙矾石晶体,掺量不当会对试件的抗硫酸钠侵蚀性能不利。砂集料有阻碍微裂纹发展及增大试样内部不均匀性的相反作用,集料的含量、颗粒尺寸及分布对水泥基材料的抗硫酸钠侵蚀破坏性能的影响是以后研究中需关注的问题。     

垃圾焚烧飞灰早期胶凝活性激发研究

从城市生活垃圾焚烧飞灰在水泥混凝土材料领域中的资源化利用角度出发,采用比强度分析方法试验研究了飞灰的胶凝活性,探讨了化学激发剂对飞灰-水泥复合胶凝体系早期强度的活性激发以及相关的机理。结果表明：飞灰早期胶凝活性较低,尤其当掺量高于20％后,表现十分明显。分别掺入1％～3％的CaSO4,KAl（SO4）2,Al2（SO4）3和Na／SiO3的化学激发剂后,浆体的早期抗压强度明显提高,激发效果显著,但随龄期的延长,激发效果减弱。     

Hydraulic lime mortars for the restoration of historic masonry in Crete

This study presents the results of the physico-chemical characterization of original mortars and plasters and the evaluation of the repair ones prepared with natural hydraulic lime (NHL) as binding material and siliceous sand and crushed brick as aggregates. The repair mortars were applied in restoration works of a historic masonry in Crete, Greece. The proportions of binder, aggregates and water were selected in order to achieve optimum workability. Original mortars, containing magnesian lime, had to be replaced since previous interventions with cement-based mortars have provoked damage acceleration. Water absorption by capillarity, compressive strength, modulus of elasticity, porosity and pore size distribution were determined at early stages and after 1 year of curing time; these properties prove the suitability of the proposed mortars for such an application. After 3 years of intervention with NHL-based mortars and plasters, macroscopic survey and analyses of the applied materials reveal that no cracks or release of soluble salts occur.     

Behavior of blended cement mortars exposed to sulfate solutions cycling in relative humidity

In recent years, several cases of damage to concrete structures due to sulfate exposure have occurred essentially in the above ground parts of structures. Such distress, often characterized by white efflorescence and surface scaling, is driven by salt crystallization in pores and/or repeated reconversions of certain sulfates between their anhydrous and hydrated forms under cycling temperature and relative humidity (RH). However, the effect of the water/cementitious materials ratio (w/cm), pozzolanic additions, and other parameters on the durability of cement-based materials under such exposure conditions is still misunderstood. In this study, 12 cement mortars having different w/cm (0.30, 0.45, and 0.60) and made with ordinary portland cement (OPC) or OPC incorporating 8% silica fume, 25% class F fly ash, or 25% blast furnace slag were made. Standard bars from each of these mortars were submerged in both 10% magnesium sulfate (MgSO₄) and 10% sodium sulfate (Na₂SO₄) solutions; their expansion and surface degradation was monitored for up to 9 months. In addition, cylinders made from these 12 mortars were partially submerged in 50-mm-deep 10% MgSO₄ and 10% Na₂SO₄ solutions. Half of the cylinders were maintained under constant temperature and RH, whereas the others were subjected to cycling RH. The effect of the w/cm and mineral additions on the classic chemical sulfate attack and development of efflorescence was investigated, and the results are discussed in this article.     

三组分胶凝材料体系的交流阻抗特性

由于地铁在运行过程中产生的杂散电流会造成钢筋混凝土中钢筋的电化学腐蚀,从而影响地铁混凝土结构的耐久性。在配制混凝土时,用矿渣和粉煤灰取代一部分水泥,可明显改善胶凝材料硬化浆体的孔结构,降低孔溶液中的离子浓度,从而提高混凝土的电阻率。提高混凝土的电阻率可在一定程度上减缓钢筋的腐蚀。使用三组分胶凝体系研究方法,对水泥、粉煤灰和矿渣组成的三组分胶凝体系的交流阻抗特性和电阻值进行了研究和分析,得到不同龄期的阻抗等值线图。研究表明,当三组分胶凝体系中粉煤灰和矿渣总量在50%～65%的范围,且两者得比例为1左右时,三组分胶凝材料砂浆的电阻率最大。