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This article describes a study on the viability of using waste from the paper industry: biomass boiler ash and green liquor dregs to fabricate mortars and concretes. Both types of ash were characterized by obtaining their chemical and mineralogical composition, their organic matter content, granulometry, adsorption and other common tests for construction materials. Seven different mortars were fabricated, one for reference made up of cement, sand, and water, three in which 10, 20, or 30% of the cement was replaced by biomass ash, and three others in which 10, 20, or 30% of the cement was replaced with dregs. Test specimens were fabricated with these mortars to conduct flexural and compression tests. Flexural strength is reduced for all the mortars studied. Compressive strength increases for the mortars fabricated with biomass ash and decreases for the mortar with dregs. Finally, 5 concretes were made, one of them as a reference (neither biomass ash nor dregs added), two of them with replacements of 10 and 20% of biomass ash instead of cement and another two with replacements of 10 and 20% of dregs instead of cement. The compressive and tensile splitting strength increase when a 10% of ash is replaced and decrease in all the other cases. The modulus of elasticity always decreases.

The management of abundant drinking water treatment sludge (DWTS) in landfill remains an important issue. The reuse of DWTS as construction material could contribute to the development of greener concrete product and to mitigating the detrimental environment effect from excessive production of DWTS. This paper investigates the potential of using DWTS as sand replacement in Concrete Paving Blocks (CPB). Five CPB mixtures were designed and the replacement ratios of sand by DWTS were 0%, 5%, 10%, 15%, and 20%, by weight. Properties of CPB such as compressive strength, water absorption, abrasion resistance, sulfate attack and metal leachability were determined. The results indicated that above 10% of DWTS, the replacement was detrimental to such properties of the CPB. Microstructure analysis proved the addition of DWTS could result in ettringite formation and the interfacial transition zone (ITZ) between the cement matrix and DWTS was more porous than that of sand. In addition, the metal leachability test of CPB demonstrated that the addition of high-copper DWTS into CPB was safe. Refereed/Peer-reviewed

In light of concerns relating to improper waste disposal and resources preservation, reclamation of the discarded glass in construction materials had been extensively carried out since 1963. In the past decade, although more than 100 papers associated with the use of glass powder (GP) in the micron level scale were published, comprehensive review of all practical applications in cement-based materials and construction products is not available. This paper therefore provides a summary of the body of knowledge on the interaction and effects of using GP in cement-based and extended construction materials. This review concludes that GP is an innovative and promising eco-supplementary cementitious material. Beyond that, use of GP is demonstrated to be potentially beneficial as a precursor in geopolymer and suitable for manufacturing eco-cement, artificial lightweight aggregate and composite phase change material. The multiple applications of GP are seen as an important step towards waste glass recycling as a sustainable construction material and for the overall betterment of the industry.

The paper deals with the mineral wool production waste (cupola dust - CD), presents CD characterization and aims to reuse CD in production of refractory concrete with calcium aluminate cement. The study of CD covers its chemical, phase and thermal analyses along with the morphological study and determination of particles size distribution. Zeta-potential, electrical conductivity and pH values of CD suspension are presented in the paper as well. Commercial microsilica additive in refractory concrete has been replaced with cupola dust. Compositions of refractory concrete have been prepared by incorporating 1%, 2% and 3% of CD. The bulk density, ultrasonic wave velocity, cold crushing strength and thermal shock resistance of the created refractory concrete have been determined. Based on experimental results, it has been found that cupola dust may be used for the production of refractory concrete. The environmental impact related to the CD reuse in refractory concrete production has been evaluated as well.

Safe disposal of solid wastes containing heavy metals is a significant task for environment protection. Immobilization treatment is an effective technology to achieve this task. Cementitious material treatments and thermal treatments are two types of attractive immobilization treatments due to that the heavy metals could be encapsulated in their dense and durable wasteforms. This paper discusses the heavy metal immobilization mechanisms of these methods in detail. Physical encapsulation and chemical stabilization are two fundamental mechanisms that occur simultaneously during the immobilization processes. After immobilization treatments, the wasteforms build up a low permeable barrier for the contaminations. This reduces the exposed surface of wastes. Chemical stabilization occurs when the heavy metals transform into more stable and less soluble metal bearing phases. The heavy metal bearing phases in the wasteforms are also reviewed in this paper. If the heavy metals are incorporated into more stable and less soluble metal bearing phases, the potential hazards of heavy metals will be lower. Thus, converting heavy metals into more stable phases during immobilization processes should be a common way to enhance the immobilization effect of these immobilization methods.

This paper presents the results of an experimental study on the unconfined compressive strength (UCS), indirect tensile strength (ITS), microstructural properties and environmental impacts of overflow tailings (OFT) cemented paste backfill (CPB). The test results show that the poor graded OFT contain 47.15% particles with size below 20 μm, and high content of oxide and sulfide. The slump of fresh CPB mixture ranges from 19.50 cm to 21.60 cm, and its flowability meets the transport requirements. After being cured for 28 days, the UCS and ITS of CPB are less than 2 MPa and 0.5 MPa, respectively. Meanwhile, CPB exhibited low residual strength and high brittleness. The low strength is mainly due to the use of fine OFT. The results show that sulphate also has negative effect on strength and dissolve calcium silicate hydrate (C-S-H) while promoting the formation of secondary products (gypsum and ettringite), leading to generate cracks and decrease UCS at 28 curing time of some CPB mixtures. Increasing the cement content and solid mass concentration is the effective methods to improve the mechanical properties of CPB. The nuclear magnetic resonance (NMR) tests show that fine OFT with low osmotic coefficient (3.10e-06 cm/s) and high sulfur content cause high porosity from 25.0% to 33.1% of CPB, and the increase of the porosity is observed a negative influence on the UCS, but no obvious relationship between ITS and porosity is obtained. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) tests show that OFT particles were covered by C-S-H gel which can enhance the compactness and integrity of CPB. The SEM tests also found secondary products gypsum and ettringite. These finding suggest that OFT can be suitably used as backfill material to fill the underground stopes.

A large amount of mine wastes is generated every year through mining and mineral processing operation. The management of mine tailings is an attractive topic for researchers from both environmental and economic aspects. Mine tailings have shown a capacity as a raw material for the construction industry or a substitution for previous materials to produce the cement. It is applied in some specific environments such as offshores or massive projects like large bridges and tunnels. However, the cement industry has caused a variety of environmental issues. The production of Portland cement on an industrial scale increases the greenhouse effects and generates acidic rains. It releases greenhouse gases by the generation of carbon dioxide. In recent years, strict environmental regulations led to more efforts from mining industries to manage their tailings. A new approach to decrease the environmental issues, improve cement technology and obtain economic benefits is the use of mine tailings for cement production. Mine tailings in the cement mixtures decrease the initial hydration, retard the setting time, and lower the product mechanical strength. These problems can be fixed by the use of additives. Additives as chemical compounds are added to a cemented paste to change its properties and improve its performance. Therefore, the additives in cemented paste tailings can increase the pump-ability, reduce the water-to-cement ratio, increase density, or even adjust setting time and hydration according to the desired purposes. However, the amount of additives in the cemented paste tailings changes based on the type of additive. It should be optimized to cause a positive effect on the cement properties. Furthermore, the additives and their adaptation to the physical and chemical characteristics in cement and tailings is an important issue that should be investigated. In this paper, the usage of several chemical additives was studied, which can strengthen the properties of cemented paste tailings during backfilling operation. It can cause a better condition to decrease the environmental problems for the cement industry and mine tailings. A review of previous works is presented with an explanation of the gaps in previous studies.

In recent years, lithium slag (LS) has increased sharply with the development of lithium industry, which has caused serious environmental problems. However, the utilization of this industrial waste residue has been a difficult topic in lithium industry. In this paper, the effects of LS on mineral crystal type, ionic solid solution, decomposition temperature of CaCO3 and strength of white Portland cement clinker were studied by XRD, FT-IR, DSC, SEM-EDS and other means. The results show that LS can stabilize the M1 crystal of C3S, improve the crystallinity of C3A, and reduce the content of ACn. The LS content of 5 wt% can reduce the decomposition temperature of CaCO3 about 10 °C, but increase the low eutectic temperature of materials. Na elements tended to be dissolved in the intermediate phase, while Al3+ dissolved in calcium silicate may replace Ca2+ or Si4+. Sintering white Portland cement clinker with appropriate content of LS can effectively reduce the content of f-CaO and greatly improve the early compressive strength of clinker. Therefore, LS within 5 wt% can be used as high quality raw material of white cement, which can recycle LS.

Heavy metal stabilization by chemical chelating agent and solidification by cement are technologies currently used to reduce the leaching of heavy metals in municipal solid waste incineration (MSWI) fly ash. This paper studied the physico-chemical properties of the fly ash, heavy metals content in the fly ash, and the leaching concentration of the heavy metals from fly ash. The effect of four chelating agents namely dithiocarbamate (1#), dithiocarbamic acid dipotassium salt (2#), amino dithiocarbamate chelating resin (3#) and thiourea (4#) on the stabilization and leaching of heavy metals were investigated. Different addition ratios (1%, 2% and 3% w/w) of the chelating agents, various curing time (7, 14, 28 days), and different amounts of the cement (10%, 15% and 20% w/w) were used in order to find the agent with the optimum stabilization and leaching of heavy metals as well as find the effect of combining the agent and cement. The results showed that the dithiocarbamate (1#) chelating agent had the best stabilizing performance due to the three-dimensional structure after their reaction. The addition of cement to the fly ash led to the immobilization of heavy metals due to the C-S-H gel formation. The technology of cement solidification and chelating agent stabilization was optimal from the point of economic cost and the complexity aspect.

In this research, the effect of curing temperature on the metalloid (As) leachability of cemented paste backfill (CPB; a mix of tailings, cement and water) is studied. ASTM C 1308 leaching protocol is used to determine the leachability of CPB samples subjected to different curing temperatures (2, 20 and 35 °C). In addition, the effect of curing temperature on the microstructure of CPB is assessed to determine if the temperature dependence of the leaching characteristics of CPB is related to variations in the microstructure of the cement matrix. The microstructural techniques used include, powder x-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy techniques. The results obtained indicate that the curing temperature has a significant effect on the leachability of CPB. It is found that as curing temperature increased from 2 °C to 35 °C the performance of the CPB for arsenic immobilization decreased. The magnitude of this temperature-induced change in As-leachability of CPB depends on the curing temperature range (low (≤20 °C) or elevated (35 °C) temperatures). This curing temperature dependency of the leachability of CPB is attributable to the temperature-induced changes in the pore structure of CPB, formation/development of hydration products and pH in the CPBs during the curing process. The results also indicate that diffusion dominates as the leaching mechanism through the studied temperature range and is independent of curing temperature. However, curing temperature does control the availability for arsenic to leach. The new findings presented in this paper will contribute to design more environmental-friendly cemented paste backfill materials and structures, which is vital for sustainable mining.

Basic magnesium sulfate cement has the advantages of fast setting, high strength, high toughness, water resistance, corrosion resistance, etc. But the cost has become a reason for limiting its widespread application. With the widespread application of circulating fluidized bed combustion (CFBC) technology in China, the accumulation of CFBC ash is increasing. Reasonable use of CFBC ash can not only reduce cost of basic magnesium sulfate cement but also protect environment. In this paper, the effect of a high volume of CFBC ash on fluidity, flexural strength and compressive strength of basic magnesium sulfate cement is studied. Hydration products and micromorphology analyses are measured by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results reveal that the strength of basic magnesium sulfate cement with 20% CFBC ash is the highest, and its microstructure is the model that CFBC ash and MgO fill a three-dimensional network structure established by needle-shaped 5·1·7 phase. When the amount of CFBC ash is more than 40%, the formation of 5·1·7 phase is affected severely, which greatly reduces the strength.

In this study, ground rice husks (GRH) in combination with polyvinyl-alcohol (PVA) fiber were used to produce low-cost and high-quality hybrid cementitious composites. Different amounts of GRH (2.5, 5.0, 7.5 and 12.5% in weight of cement) were added to the concrete. The work presented in this paper provides an insight into the use of an agricultural waste as effective additive in cement based materials. The properties of resultant cementitious composites including density, water absorption, flexural behavior and compressive strength were investigated. The results have shown that incorporation of ground rice husk in combination with PVA fiber can be effective in improvement of the flexural properties of cementitious composite. The study explored the effectiveness of this type of agricultural waste as a beneficial material in fine aggregate concrete materials.

This paper aims to investigate the influence of coal fly ash containing ammonium salts on properties of cement paste. Fly ash was incorporated at percentage of 20% by weight of the total binder to replace Portland cement. Ammonium hydrogen sulfate (NH3HSO4) or ammonium sulfate ((NH3)2SO4) were introduced at percentages of 3.0%-6.0% or 1.5%-3.0% by fly ash weight. Compressive strength, setting time and hydration heat were evaluated on variable blend mixtures. Adsorption behaviors of polycarboxylate-based superplasticizer and air entraining agent on fly ash particles were also evaluated using total organic carbon (TOC) method. Semi-adiabatic calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry-differential thermal analysis, mercury intrusion porosity and scanning electron microscope measurements were carried out on typical samples. Experimental results showed that the chemical admixtures adsorbed by coal fly ash were increased by the introduction of NH3HSO4 or (NH3)2SO4. The addition of 3.0%-6.0% NH3HSO4 and 1.5%-3.0% (NH3)2SO4 decreased the 28d compressive strength of fly ash-cement pastes by 4.3%-10.4% and 6.3%-8.9%, respectively. The initial and final setting times were delayed and the early age hydration of Portland cement was also retarded. Moreover, the pore structure was coarsened and porosity was increased for the hardened cement specimens due to the release of ammonia and lower hydration degree. Therefore, more attention should be paid to the application of denitration fly ash to the cement and concrete industry.