Durability of conventional concretes containing black rice husk ash

In this study, black rice husk ash (BRHA) from a rice mill in Thailand was ground and used as a partial cement replacement. The durability of conventional concretes with high water–binder ratios was investigated including drying shrinkage, autogenous shrinkage, depth of carbonation, and weight loss of concretes exposed to hydrochloric (HCl) and sulfuric (H₂SO₄) acid attacks. Two different replacement percentages of cement by BRHA, 20% and 40%, and three different water–binder ratios (0.6, 0.7 and 0.8) were used. The ratios of paste volume to void content of the compacted aggregate (γ) were 1.2, 1.4, and 1.6. As a result, when increasing the percentage replacement of BRHA, the drying shrinkage and depth of carbonation reaction of concretes increased. However, the BRHA provides a positive effect on the autogenous shrinkage and weight loss of concretes exposed to hydrochloric and sulfuric acid attacks. In addition, the resistance to acid attack was directly varied with the (SiO₂ + Al₂O₃ + Fe₂O₃)/CaO ratio. Results show that ground BRHA can be applied as a pozzolanic material and also improve the durability of concrete.     

The effect of Na and Ca salts on MSWI bottom ash activation for reuse as a pozzolanic admixture

In this study the possibility of both chemical and combined chemical + thermal activation of municipal solid waste incinerator bottom ash was investigated. A number of chemical activators including Na₂SiO₃·9H₂O, NaOH, Na₂SO₄ and CaCl₂·2H₂O were individually added at varying concentrations to bottom ash/Portland cement mixtures having different bottom ash contents. The effect of the selected compounds was evaluated in terms of macroscopic properties including mechanical strength and composition of cementitious materials/water slurries. The results showed that Na-based activators were not capable of improving the characteristics of the cementitious products if compared to Portland cement under both normal and accelerated curing. Conversely, the use of calcium chloride at 40 °C-curing did promote the pozzolanic properties of bottom ash, leading to UCS values of 45.5 and 60.0 MPa after 10 and 20 days, respectively, as opposed to a value of 43.6 MPa obtained after 28 days for Portland cement under normal curing conditions.     

Effects of nano-SiO(2) and different ash particle sizes on sludge ash-cement mortar

The effects of nano-SiO₂ on three ash particle sizes in mortar were studied by replacing a portion of the cement with incinerated sewage sludge ash. Results indicate that the amount of water needed at standard consistency increased as more nano-SiO₂ was added. Moreover, a reduction in setting time became noticeable for smaller ash particle sizes. The compressive strength of the ash–cement mortar increased as more nano-SiO₂ was added. Additionally, with 2% nano-SiO₂ added and a cure length of 7 days, the compressive strength of the ash–cement mortar with 1 μm ash particle size was about 1.5 times better that of 75 μm particle size. Further, nano-SiO₂ functioned to fill pores for ash–cement mortar with different ash particle sizes. However, the effects of this pore-filling varied with ash particle size. Higher amounts of nano-SiO₂ better influenced the ash–cement mortar with larger ash particle sizes.     

Validation of an in situ solidification/stabilization technique for hazardous barium and cyanide waste for safe disposal into a secured landfill

The aim of the present study was to devise and validate an appropriate treatment process for disposal of hazardous barium and cyanide waste into a landfill at a Common Hazardous Waste Treatment Storage Disposal Facility (CHWTSDF). The waste was generated during the process of hardening of steel components and contains cyanide (reactive) and barium (toxic) as major contaminants. In the present study chemical fixation of the contaminants was carried out. The cyanide was treated by alkali chlorination with calcium hypochlorite and barium by precipitation with sodium sulfate as barium sulfate. The pretreated mixture was then solidified and stabilized by binding with a combination of slag cement, ordinary Portland cement and fly ash, molded into blocks (5 × 5 × 5 cm) and cured for a period of 3, 7 and 28 days. The final experiments were conducted with 18 recipe mixtures of waste + additive:binder (W:B) ratios. The W:B ratios were taken as 80:20, 70:30 and 50:50. The optimum proportions of additives and binders were finalized on the basis of the criteria of unconfined compressive strength and leachability. The leachability studies were conducted using the Toxicity Characteristic Leaching Procedure. The blocks were analyzed for various physical and leachable chemical parameters at the end of each curing period. Based on the results of the analysis, two recipe mixtures, with compositions – 50% of [waste + (120 g Ca(OCl)₂ + 290 g Na₂SO₄) kg^?1 of waste] + 50% of binders, were validated for in situ stabilization into a secured landfill of CHWTSDF.     

Utilization of washed MSWI fly ash as partial cement substitute with the addition of dithiocarbamic chelate

The management of the big amount of fly ash as hazardous waste from the municipal solid waste incinerator (MSWI) has encountered many problems in China. In this study, a feasibility research on MSWI fly ash utilization as partial cement substitute in cement mortars was therefore carried out. MSWI fly ash was subjected to washing process to reduce its chlorine content (from 10.16% to 1.28%). Consequently, it was used in cement mortars. Ten percent and 20% replacement of cement by washed ash showed acceptable strength properties. In TCLP and 180-day monolithic tests, the mortars with washed ash presented a little stronger heavy metal leachability, but this fell to the blank level (mortar without washed ash) with the addition of 0.25% chelate. Therefore, this method is proposed as an environment-friendly technology to achieve a satisfactory solution for MSWI fly ash management.     

Utilization of cement kiln dust (CKD) in cement mortar and concrete—an overview

Solid waste management is one of the major environmental concerns around the world. Cement kiln dust (KKD), also known as by-pass dust, is a by-product of cement manufacturing. The environmental concerns related to Portland cement production, emission and disposal of CKD is becoming progressively significant. CKD is fine-grained, particulate material chiefly composed of oxidized, anhydrous, micron-sized particles collected from electrostatic precipitators during the high temperature production of clinker. Cement kiln dust so generated is partly reused in cement plant and landfilled. The beneficial uses of CKD are in highway uses, soil stabilization, use in cement mortar/concrete, CLSM, etc.Studies have shown that CKD could be used in making paste/mortar/concrete. This paper presents an overview of some of the research published on the use of CKD in cement paste/mortar/concrete. Effect of CKD on the cement paste/mortar/concrete properties like compressive strength, tensile strength properties (splitting tensile strength, flexural strength and toughness), durability (Freeze–thaw), hydration, setting time, sorptivity, electrical conductivity are presented. Use of CKD in making controlled low-strength materials (CLSM), asphalt concrete, as soil stabilizer, and leachate analysis are also discussed in this paper.     

Valorization of sodium sulfate waste to potassium sulfate fertilizer: experimental studies,process modeling,and optimization

ABSTRACT

Sodium sulfate is a common low-value industrial by-product but can be managed using the Glaserite process to convert it into high-value potassium sulfate. The aim of the study is to investigate the potential for implementing this process in an industrial application. Experimental studies were completed to determine the yield and purity of both glaserite and potassium sulfate. Process simulation using SysCAD was utilized to optimize a two-stage glaserite process to produce potassium sulfate. Comparison of experimental and simulated data was made to validate the simulator’s results, finding the AAD in solid and liquid phase for glaserite production to be 6.9% and 5.7%, respectively, and for potassium sulfate to be 5.7% and 2.3%, respectively. For a process treating seven MT/hr of Na₂SO₄, a KCl feed strategy of 3.0 MT/hr to the glaserite reactor and 4.5 MT/hr to the K₂SO₄ reactor was found to maximize yield and minimize water demand. It was also found that ambient temperatures were preferred for the K₂SO₄ reactor and that K₂SO₄ yield suffered significantly under certain conditions when the glaserite reactor operated at 50°C or above.     

The reuse of municipal solid waste incinerator fly ash slag as a cement substitute

The results of the treatment of fly ash from a municipal solid waste incinerator (MSWI) by melting are described, and the safety and the effectiveness of using the slag produced by this melting treatment are studied. The properties of the MSWI fly ash slag were analyzed, to evaluate the feasibility of its reuse as a substitute for part of the cement required in mortar preparation. This MSWI fly ash slag was found to be comprised mainly of SiO₂ and CaO, which can be substituted for up to 20% of the cement content in mortar, without sacrificing the quality of the resultant concrete. In fact, the concrete thus produced has greater compressive strength, 10% higher than that without the substitution. The setting time of the fresh mortar becomes lengthens as increasing amounts of cement are replaced; while the spread flow value increases with the increasing percentage of cement substitution. X-ray diffraction analysis reveals that when the W/C=0.38 and the curing AGE=28 days, the crystal patterns in the mortar samples, prepared with different amounts of cement having been replaced by MSWI fly ash slag are similar. According to the results of the toxic characteristic leaching procedure analysis, MSWI fly ash slag should be classified as general non-hazardous industrial waste, that meets the effluent standard. Therefore, the reuse of MSWI fly ash slag is feasible, and will not result in pollution due to the leaching of heavy metals.     

Utilization of cement kiln dust (CKD) in cement mortar and concrete—an overview

Solid waste management is one of the major environmental concerns around the world. Cement kiln dust (KKD), also known as by-pass dust, is a by-product of cement manufacturing. The environmental concerns related to Portland cement production, emission and disposal of CKD is becoming progressively significant. CKD is fine-grained, particulate material chiefly composed of oxidized, anhydrous, micron-sized particles collected from electrostatic precipitators during the high temperature production of clinker. Cement kiln dust so generated is partly reused in cement plant and landfilled. The beneficial uses of CKD are in highway uses, soil stabilization, use in cement mortar/concrete, CLSM, etc.Studies have shown that CKD could be used in making paste/mortar/concrete. This paper presents an overview of some of the research published on the use of CKD in cement paste/mortar/concrete. Effect of CKD on the cement paste/mortar/concrete properties like compressive strength, tensile strength properties (splitting tensile strength, flexural strength and toughness), durability (Freeze–thaw), hydration, setting time, sorptivity, electrical conductivity are presented. Use of CKD in making controlled low-strength materials (CLSM), asphalt concrete, as soil stabilizer, and leachate analysis are also discussed in this paper.     

A review on the use of waste glasses in the production of cement and concrete

The use of recycled waste glasses in Portland cement and concrete has attracted a lot of interest worldwide due to the increased disposal costs and environmental concerns. Being amorphous and containing relatively large quantities of silicon and calcium, glass is, in theory, pozzolanic or even cementitious in nature when it is finely ground. Thus, it can be used as a cement replacement in Portland cement concrete. The use of crushed glasses as aggregates for Portland cement concrete does have some negative effect on properties of the concrete; however, practicle applicability can still be produced even using 100% crushed glass as aggregates. The main concerns for the use of crushed glasses as aggregates for Portland cement concrete is the expansion and cracking caused by the glass aggregates. This paper summarizes the progresses and points out the directions for the proper uses of waste glasses in Portland cement and concrete.     

Reuse of de-inking sludge from wastepaper recycling in cement mortar products

This paper presents results of an investigation into the use of de-inking sludge from a paper recycling mill as feedstock material in the manufacture of cement mortar products, including masonry blocks and mortar renders. Both physical and mechanical properties of mortar specimens containing various amounts of de-inking sludge were investigated. It was observed that the addition of de-inking sludge to cement mortar at a fixed water-to-cement ratio significantly reduced flow properties and increased setting time. Water absorption and volume of permeable voids of cement mortar increased with increased dosage of de-inking sludge, with a corresponding reduction of bulk density. The 91-day compressive strength of mortar samples with 2.5 wt% and 20 wt% de-inking sludge loadings retained 83% and 62% respectively of the reference mortar strength. The corresponding drying shrinkage increased by up to 160% compared to reference samples. However, a de-inking sludge loading of up to 2.5 wt% did not significantly alter measured physical and mechanical properties. The results demonstrate that despite the high moisture absorbance of de-inking sludge due to its organic matter and residual cellulose fibre content, it serves as a potential supplementary additive and its cellulosic content proving to be an active set retardant to cementitious masonry products.     

Utilization of municipal solid waste (MSW) ash in cement and mortar

Solid waste management is gaining significant importance with the ever-increasing quantities of waste materials generated these days. With increased environmental awareness and its potential hazardous effects, recycling/utilization of these materials have become an attractive alternative to disposal. Some of these waste and hazardous materials could possible be used in cement-based materials. One of such waste is municipal solid waste. Ash is obtained after incineration of MSW.This paper presents comprehensive details of the physical, chemical, and mineralogical composition, elemental analysis of ash obtained from MSW. It also covers the effect of MSW ash on the hydration characteristics, setting times, compressive strength, sulfate resistance and mass loss of cement and mortar. It also deals with the leachate analysis of MSW ash.     

Experimental investigation of wellbore integrity and CO2–brine flow along the casing–cement microannulus

Wellbore integrity is one of the key performance criteria in the geological storage of CO₂. It is significant in any proposed storage site but may be critical to the suitability of depleted oil and gas reservoirs that may have 10’s to 1000’s of abandoned wells. Much previous work has focused on Portland cement which is the primary material used to seal wellbore systems. This work has emphasized the potential dissolution of Portland cement. However, an increasing number of field studies (e.g., Carey et al., 2007), experimental studies (e.g., Kutchko et al., 2006) and theoretical considerations indicate that the most significant leakage mechanism is likely to be flow of CO₂ along the casing–cement microannulus, cement–cement fractures, or the cement–caprock interface.In this study, we investigate the casing–cement microannulus through core-flood experiments. The experiments were conducted on a synthetic wellbore system consisting of a 5-cm diameter sample of cement that was cured with an embedded rectangular length of steel casing that had grooves to accommodate fluid flow. The experiments were conducted at 40 $°$ C and 14 MPa pore pressure for 394 h. During the experiment, 6.2 l of a 50:50 mixture of supercritical CO₂ and 30,000 ppm NaCl-rich brine flowed through 10-cm of limestone before flowing through the 6-cm length cement–casing wellbore system. Approximately 59,000 pore volumes of fluid moved through the casing–cement grooves. Scanning electron microscopy revealed that the CO₂–brine mixture impacted both the casing and the cement. The Portland cement was carbonated to depths of 50–250 $\mu$m by a diffusion-dominated process. There was very little evidence for mass loss or erosion of the Portland cement. By contrast, the steel casing reacted to form abundant precipitates of mixed calcium and iron carbonate that lined the channels and in one case almost completely filled a channel. The depth of steel corroded was estimated at 25– $30\mu$m and was similar in value to results obtained with a simplified corrosion model.The experimental results were applied to field observations of carbonated wellbore cement by Carey et al. (2007) and Crow et al. (2009) to show that carbonation of the field samples was not accompanied by significant CO₂–brine flow at the casing–cement interface. The sensitivity of standard-grade steel casing to corrosion suggests that relatively straight-forward wireline logging of external casing corrosion could be used as a useful indicator of flow behind casing. These experiments also reinforce other studies that indicate rates of Portland cement deterioration are slow, even in the high-flux CO₂–brine experiments reported here.     

Strength and workability of masonry mortars manufactured with ladle furnace slag

Ladle furnace basic slag (LFS) is a by-product of the steelmaking process. It has rarely been recovered in the past and is usually disposed of in landfill sites. Despite containing stable chemical substances of great quality, some of which are potentially hydraulic, its practical applications have been limited. This paper discusses the attractive option of using LFS in the manufacture of masonry mortars for use in the construction industry, which requires an analysis of the principal characteristics of such mortars, i.e. workability and mechanical strength. It reports on a comparative study, using standard commercial admixtures, between conventional masonry mortars and mortars manufactured with LFS as a partial replacement for sand and cement, the results of which imply considerable economic savings in sand and cement, improvements in the properties of the mortars and in overall sustainability, by avoiding disposal and conserving natural resources.     

Characterisation of an unprocessed landfill ash for application in concrete

An investigation was carried out to establish the physical, mechanical and durability characteristics of an unprocessed pulverised fuel ash (PFA) from a former landfill site at the Power Station Hill near Church Village, South Wales, United Kingdom. This was aimed at establishing the suitability of the ash in the construction of the Church Village Bypass (embankment and pavement) and also in concrete to be used in the construction of the proposed highway.Concrete made using binder blends using various levels of PFA as replacement to Portland cement (PC) were subjected to compressive strength tests to establish performance. The concrete was also subjected to sodium sulphate attack by soaking concrete specimens in sulphate solution to establish performance in a sulphatic environment. Strength development up to 365 days for the concrete made with PC–PFA blends as binders (PC–PFA concrete), and 180 days for the PC–PFA paste, is reported.The binary PC–PFA concrete did not show good early strength development, but tended to improve at longer curing periods. The low early strength observed means that PC–PFA concrete can be used for low to medium strength applications for example blinding, low-strength foundations, crash barriers, noise reduction barriers, cycle paths, footpaths and material for pipe bedding.     

Use of silicon and ferrosilicon industry by-products (silica fume) in cement paste and mortar

With increased environmental awareness, recycling/utilization of industrial byproducts is gaining ground. One such by-product is silica fume (SF), which is byproduct of the smelting process in the silicon and ferrosilicon industry. By-products of the production of silicon metal and the ferrosilicon alloys having silicon contents of 75% or more contain 85-95% non crystalline silica. Silica fume is very useful in the design and development of high quality cement paste/mortar and concrete.This paper presents comprehensive details of the physical, chemical, properties, and its reaction mechanism. It also covers the hydration characteristics, consistency, setting times, workability and compressive strength of cement paste and mortar.     

Cement replacement by sugar cane bagasse ash: CO2 emissions reduction and potential for carbon credits

This paper presents a study of cement replacement by sugar cane bagasse ash (SCBA) in industrial scale aiming to reduce the CO₂ emissions into the atmosphere. SCBA is a by-product of the sugar/ethanol agro-industry abundantly available in some regions of the world and has cementitious properties indicating that it can be used together with cement. Recent comprehensive research developed at the Federal University of Rio de Janeiro/Brazil has demonstrated that SCBA maintains, or even improves, the mechanical and durability properties of cement-based materials such as mortars and concretes. Brazil is the world’s largest sugar cane producer and being a developing country can claim carbon credits. A simulation was carried out to estimate the potential of CO₂ emission reductions and the viability to issue certified emission reduction (CER) credits. The simulation was developed within the framework of the methodology established by the United Nations Framework Convention on Climate Change (UNFCCC) for the Clean Development Mechanism (CDM). The State of São Paulo (Brazil) was chosen for this case study because it concentrates about 60% of the national sugar cane and ash production together with an important concentration of cement factories. Since one of the key variables to estimate the CO₂ emissions is the average distance between sugar cane/ethanol factories and the cement plants, a genetic algorithm was developed to solve this optimization problem. The results indicated that SCBA blended cement reduces CO₂ emissions, which qualifies this product for CDM projects.     

Usage of polystyrene disposable food dishes in the lightweight concrete making

The increasing use and subsequent accumulation of polystyrene containers has triggered a substantial environmental problem. This study investigated using varied percentages of solid waste polystyrene disposable food dishes in the production of lightweight concrete samples with 350 kilograms per cubic meter (kg/m³) of cement and a density of 1,300 kg/m³. The polystyrene disposable dishes were ground into beads of 0–3 millimeters (mm) and 3–6 mm in size. First, the characteristics of Type II Portland cement, polystyrene, and aggregates were examined. The following characteristics of concrete using ASTM International and British Standards Institution standards were tested: slump, compressive strength, ability to resist chloride ion penetration, and resistance of concrete to rapid freezing and thawing cycles. Scanning electron microscopy (SEM) and energy dispersive X‐ray spectroscopy analytical techniques were also used. The slump of samples varied between 40 and 70 mm and was not dependent on either the polystyrene percentage or the size of the polystyrene beads in the concrete samples (p‐value > .05). The compressive strength of the concrete samples after 90 days of curing, and using different percentages of polystyrene, varied between 96 and 113 kilograms per square centimeter (kg/cm²). The resistance of the samples to the freezing and thawing cycle and chloride ion penetration were affected unfavorably by the presence of the polystyrene. The SEM technique indicated that concrete samples containing 15% and 25% polystyrene had denser crystals and less void than concrete samples with 40% and 55% polystyrene.     

Properties of steel foundry electric arc furnace dust solidified/stabilized with Portland cement

Electric arc furnace dust from steel production is generated in considerable amounts worldwide and needs to be treated as hazardous waste. The aim of this study was to investigate the properties of electric arc furnace dust solidified/stabilized by using Portland cement. Mortar and paste samples were prepared with varying waste-to-binder ratios between 0% and 90%. A comprehensive experimental program was designed including XRF characterization, setting time, unconfined compressive strength, and toxicity characteristics leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), and acid neutralization capacity (ANC) tests. The results were evaluated in order to determine if the solidified /stabilized product can be disposed of at a landfill site with domestic waste or at a segregated landfill. The effect of using sand on S/S performance was also investigated. The results indicated that the solidification /stabilization process using PC helps the heavy metals to be bound in the cement matrix, but the TCLP leaching results exceeded the EPA landfilling limits. The SPLP leaching results conformed to the limits implying that the waste or S/S products can be disposed of at a segregated landfill; however the low ANC of the S/S products reveals that there may be leaching in the long-term. The sand used in the mortar samples adversely affected the S/S performance, causing higher heavy metal leaching levels, and lower pH levels in the leachate after the TCLP extraction than those measured in the leachate of the paste samples.     

Activated fly ash/slag blended cement

This paper presents the results of the preparation of an ecological cementing material from granulated blast-furnace slag (GBFS) and Class C fly ash (CCFA). The desulphurization gypsum, calcined at 600–800 °C for 0.5–1.5 h, works as the main ingredient of the activator in the cementing material. The optimized formulation of the cementing material was obtained with the aid of factorial design method: slag, 70%; CCFA, 18%; activator, 12%. The “partial super-fine grinding process” was adopted to improve the performance, i.e., 85% of the mixture is ground to Blaine fineness of 3500 cm²/g, 15% further ground to around 5000 cm²/g. The compressive strength of 28 days of the cement mortar is up to 49 MPa and flexural strength 8.4 MPa. The hydration products, investigated by SEM and X-ray diffraction, are mainly ettringite and C–S–H gel.