Treatment of cadmium-contaminated soil using ladle slag with and without CO2

Cement and lime are widely used to stabilize/solidify (S/S) contaminated soils, however, the production of ordinary Portland cement (OPC) and lime causes CO₂ emission and consumption of energy and non-renewable resource. In this context, this study proposes a sustainable S/S approach by utilizing an industrial by-product, ladle slag (LS), and carbon dioxide (CO₂), to substitute cement and lime for treating cadmium (Cd)-contaminated soil. In laboratory investigation, contaminated soils spiked by Cd with concentrations of 0–32,000 mg/kg were treated by LS with a binder content of 10 % and subjected to conventional curing and carbonation curing for different periods varying from 3 hours to 112 days. The results showed that LS with conventional curing could reduce the leaching of Cd, however, it was still less effective than OPC in S/S of Cd-contaminated soils under the same curing period of 28 days. When CO₂ was introduced, LS with CO₂ rapidly decreased the leaching of Cd in soils by five orders of magnitude, using only 104 hours to achieve better S/S efficacy than OPC with conventional curing for 28 days. The LS with carbonation curing also sequestered CO₂ up to 16 % of LS mass and yielded higher strength than that without CO₂.     

Evaluation of carbonated incineration bottom ash using exhaust gas and CO2 discharged from waste incineration facilities as ground material

This study focused on a carbonation treatment that immobilizes trace elements such as lead (Pb) in incineration bottom ash (IBA) using the exhaust gas and the refined carbon dioxide generated (CO₂) recovered at the Japan's first incineration facility, which recovers CO₂ in the gaseous form. This study describes (1) the bearing capacity of IBA from the municipal solid waste (MSW) obtained through the California bearing ratio (CBR) test to investigate the possibility of using IBA as a base course material, (2) mechanical characteristics of IBA using the cone index test, to investigate the possibility of using as an embankment material, and (3) leaching properties of IBA from MSW obtained through a single batch leaching test and the long-term outdoor exposure of the leaching test to evaluate the effect of carbonation treatments. Results reveal that there was no effect of trace components not included in the separated and recovered CO₂, and that the effect of carbonation could be obtained even if the exhaust gas was used directly. The carbonated IBA can be applied as a sub-base course material based on its mechanical properties, regardless of the carbonation conditions. In addition, carbonated IBA can be used as an embankment material owing to its sufficient cone index value. Regarding the heavy metal and metalloid leaching behavior, it was revealed that all the IBA samples satisfied the soil environmental standards set by the Ministry of the Environment, Japan, except for Cr (VI). The long-term leaching characteristics of carbonated IBA showed that Pb could be immobilized over a long period.     

偶氮氯膦Ⅲ分光光度法研究钢渣中Ca2+浸析规律

采用偶氮氯膦Ⅲ分光光度法研究碳酸化前后钢渣中Ca2+的浸析情况,并以乙二醇法测定碳酸化前后钢渣中f-CaO含量.结果表明:在温度为70℃,相对湿度为80%,CO2体积分数为99.9%,CO2压力为0.35MPa的条件下碳酸化180min,钢渣(0.154～1.000mm)中Ca2+的浸析浓度由未碳酸化前的102.31μg/mL降为44.97μg/mL,钢渣(<0.074mm)中f-CaO含量(质量分数)由未碳酸化前的2.67%降为0.58%;在溶解时间相同情况下,钢渣颗粒粒径越小,Ca2+浸析浓度越大.     

Stabilizing blended calcium sulfate materials for roadway base construction

Blended calcium sulfate (BCS), a recycled fluorogypsum waste material, has been used in Louisiana as a pavement base layer for more than a decade. Without further chemical stabilization, the major concern of using raw BCS as a pavement structural layer is its moisture resistance. It could cause both short-term construction difficulties and long-term performance problems. In order to improve the moisture susceptibility of BCS, various cementitious agents were used in the laboratory for BCS stabilization. To further verify the efficiency of BCS stabilization schemes obtained from laboratory and assess the field performance for stabilized BCS materials as well as potential cost-benefits, three pavement test sections were constructed and tested using the accelerated loading facility (ALF) device. Both laboratory and field test results indicated that a grade 120 granulated ground blast furnace slag (GGBFS) of 10 vol.% stabilized BCS material possessed a superior performance over raw BCS in terms of water resistance, durability, and good long-term performance. Field test results further demonstrated that the GGBFS stabilized BCS base outperformed both a regular crushed stone base and a fly ash stabilized BCS base by a significantly large margin.A life-cycle cost analysis proved that, besides its outstanding laboratory and field performance, using the GGBFS stabilized BCS can provide a substantial long-term savings over regular crushed stone and fly ash stabilized BCS bases in a 30-year pavement design life period.     

Effects of sample crumbling and particle size on accelerated carbonation of alkaline construction sludge treated with paper-sludge ash-based stabilizers

Construction sludge generated from underground and pile construction works frequently appears in a liquid state. For its utilization as a construction geomaterial, it can be improved by mixing in cement or lime. The target strength can be achieved relatively easily by adjusting the amount of cement or lime added to the sludge. However, this type of chemical treatment is associated with high alkalinity, which causes environmental concerns associated with alkali leaching. In this study, therefore, the accelerated carbonation of alkaline construction sludge through treatment with a paper-sludge ash-based stabilizer (PSAS) was experimentally attempted to neutralize the pH. The alkaline sludge treated with the PSAS was exposed to pure CO₂ gas to accelerate the carbonation. The effects of granulation via crumbling prior to the accelerated carbonation on the pH neutralization period were analyzed from the test results. It was observed that crumbling the sludge prior to the CO₂ gas exposure accelerated the pH neutralization. These results suggest that a short pH neutralization period can be achieved by reducing the particle size. Therefore, the effect of the particle size of the PSAS-treated sludge on the pH neutralization period was also investigated. The results showed that the pH neutralization period decreased with an increasing particle size. However, it was also observed that, when the addition ratio of the PSAS was increased, the difference in the pH neutralization period induced by the change in particle size became less significant.     

Effect of accelerated carbonation on cementitious roofing tiles reinforced with lignocellulosic fibre

The present work evaluated the effects of accelerated carbonation on mechanical and physical characteristics of cementitious roofing tiles reinforced with vegetable fibre. The maximum load and toughness of the tiles have increased approximately 25% and 80% respectively as a consequence of the accelerated carbonation. Water absorption and apparent porosity decreased with carbonation while bulk density increased as a clear indication of the densification of the composite. The improvement on the mechanical performance suggests that the fibres retained their tensile strength in the inorganic matrix. Results of specimens extracted from the tested tiles after approximately 480 days in laboratory environment and further aged indicate that soak and dry cycles promoted some leaching of hydration products and more voids and lower density when performed before carbonation. The results indicate the utilization of accelerated carbonation as an effective procedure to mitigate the degradation suffered by the cellulose fibres in the less aggressive medium.     

Accelerated carbonation of alkaline construction sludge by paper sludge ash-based stabilizer and carbon dioxide

Construction sludge frequently has high alkalinity after its generation or during the intermediate treatment process. The aim of this study is to experimentally investigate the potential of combining accelerated carbonation and a paper sludge ash-based stabilizer (PSAS) to neutralize the alkalinity of construction sludge in a short period and to improve its strength for use as a recycled material. The experimental results indicate that the addition of a PSAS significantly granulated the alkaline sludge, and once granulated, the PSAS successfully accelerated the pH neutralization of the alkaline sludge. It was also found that the decrease in dry density ρ_d and the degree of saturation S_r of the PSAS-treated sludge was able to reduce the period required for the pH neutralization, t_N. The decrease in ρ_d is thought to allow fresh CO₂ gas to penetrate the specimen more easily. However, if S_r is below a certain limit, it does not strongly facilitate the reduction of t_N. This implies that pH neutralization cannot be accelerated when the amount of water in the sludge is below a certain level. Moreover, it was found that mean particle diameter D₅₀ also affected t_N. The strength development of the PSAS-treated sludge was evaluated using a series of cone index tests. It was found that the strength of the alkaline sludge without the PSAS was significantly decreased by accelerated carbonation, but was significantly increased even after accelerated carbonation when the PSAS was present. Due to the porosities of the remaining PS ash particles, most of the contribution of the water absorption and retention performance of the PSAS to the strength development of the PSAS-treated sludge was secured after accelerated carbonation. In addition, the granulated particles of the PSAS-treated sludge retained their granular shape to some extent. Therefore, it is presumed that the friction and interlocking of the particles did not decrease significantly. It was also found that, after carbonation, the q_c of the PSAS-treated sludge increased more rapidly than that of the alkaline sludge without the PSAS. A further detailed examination of the test results showed that under air-curing conditions, the q_c of the treated sludge with accelerated carbonation increased relatively gradually compared to that of the treated sludge without accelerated carbonation.     

The influence of design variables and environmental factors on life-cycle cost assessment of concrete culverts

The objective of this article is to evaluate the influence of material, structural design variables and exposure conditions on the service life and cost effectiveness of precast concrete culverts in Canada. This investigation will assist practicing engineers to account for long-term performance and integrate life cycle analysis into design and construction decisions. The design variables considered in this study include the percentage of ground granulated blast furnace slag (GGBFS) as cement replacement, reinforcing steel cover depth and culvert size. This study proposes the usage of a life-cycle cost assessment approach to compare different culvert designs on an economic basis which accounts for the design variables and the impact of CO₂ production and uptake over the life of a culvert from cradle to grave. Analysis of each culvert scenario includes the cost of the initial production of CO₂ during the manufacturing process as well as the cost savings that were incurred due to the uptake of CO₂ through carbonation processes. Overall, the present cost of the culverts is controlled by the GGBFS content and the reinforcing steel cover depth while carbonation processes have a relatively small economic impact.     

CO2碳化矿渣-CaO-MgO加固土效能与机理探索

CO₂碳化联合工业固废协同加固土技术是旨在替代传统水泥固化方法的新型技术尝试。以工业废料——矿渣为主要材料,辅以活性MgO和CaO形成矿渣-CaO-MgO固化体系,将固化土料均匀搅拌制样后进行CO₂碳化试验。通过无侧限抗压强度、扫描电镜和X射线衍射等试验,探究固化剂掺量、配比、碳化时间和初始含水率等因素对碳化加固土效果的影响。结果表明：CO₂碳化对土体加固具有明显改良效果,碳化24 h试样抗压强度最高可提升25.77倍;碳化试样抗压强度与固化剂掺量（6S4L0M除外）、活性MgO占比呈正相关;碳化试样强度随碳化时间先增加后趋于平缓（或略微下降）、最佳碳化时间为6 h左右,随初始含水率增加而先增加后下降、最佳含水率为16%左右;活性MgO碳化效能明显优于活性CaO,矿渣中低活性CaO并不能显著改良自身碳化性能。CO₂碳化作用促使碳酸盐晶体（CaCO₃、MgCO₃）生成,晶体发育程度与碳化时间、固化剂掺量及活性等因素有关;碳酸盐晶体有效填充试样内部孔隙并黏结土颗粒,形成整体骨架结构使试样强度得以大幅提升。     

Stabilisation/solidification of lead-contaminated soil by using ladle furnace slag and carbon dioxide

Global sustainable development faces challenges in greenhouse gas emission, consumption of non-renewable resource and energy, waste landfilling, and environmental pollution. Geotechnical engineering also faces similar challenges; for example, the use of cement and lime for stabilisation/solidification (S/S) of contaminated soil is associated with carbon dioxide (CO₂) emission and consumption of limestone and energy. In this context, this study introduces a sustainable S/S method by using an industrial waste, ladle furnace slag (LFS), and a greenhouse gas, CO₂, to replace common additives for S/S of lead (Pb)-contaminated soil. LFS was first mixed with Pb-contaminated soils and then CO₂ was introduced into the soil for carbonation. The results showed that LFS-stabilised Pb-contaminated soils could achieve CO₂ uptake up to 18% of LFS mass. After carbonation, the concentration of leached Pb from contaminated soils was reduced by three orders of magnitude than that without carbonation, demonstrating higher S/S efficacy than cement, lime, and magnesia. Additionally, this method can improve soil strength, as well as reduce non-renewable resource consumption, energy use, LFS landfilling, and additive cost.     

Carbonation of concrete in the tropical environment of Singapore

The experimental investigation was performed to study the influence of unit cement content and w/c ratio on the rate of carbonation under natural exposure in the tropical environment of Singapore together with laboratory accelerated carbonation test. To represent concrete of lean to rich mixes, the cement content in a total of 21 mixtures was varied from 250 to 450 kg/m³, while the w/c ratios ranged between 0.40 and 0.70 with an increment of 0.05. After 14 years of natural exposure, the 28-day compressive strength (f ₂₈) and w/c ratio (w/c) were identified as reliable parameters for estimating the depth of carbonation. However, within the range of values studied, there is no significant effect of the cement content on the carbonation behaviour. The relationship between the 14-year natural exposure and the samples from the 7% CO₂ concentration accelerated test were also correlated. Tentative recommendations on the use of the findings in durability design against carbonation for required service life in a tropical environment are proposed.     

大掺量矿物掺合料自密实混凝土抗碳化性能研究

设计了单掺粉煤灰和复掺粉煤灰与矿渣微粉的3个系列自密实混凝土试件.通过快速碳化试验、吸水试验,研究单掺粉煤灰和复掺粉煤灰与矿渣微粉对自密实混凝土抗碳化性能的影响.结果表明:当粉煤灰单掺掺量大于40%(质量分数)后,随着粉煤灰掺量的增大,自密实混凝土抗碳化能力迅速下降;粉煤灰与矿渣微粉复掺可显著缓和大掺量粉煤灰自密实混凝土抗碳化性能的下降.矿物掺合料对自密实混凝土抗碳化性能的影响存在正负效应.     

Natural carbonation of self-compacting concretes

This experimental work involves a study of the carbonation depth in self-compacting concretes at different ages and also analyses their porous microstructure, since these aspects are directly related to each other. Eight different concretes were used, four self-compacting (SCC) and four normally-vibrated (NVC). The carbonation rate was found to be lower in SCC than NVC, due to the fact that limestone fines produce less porosity and a finer microstructure. The difference between both types of concrete tends to disappear as their fines content becomes similar. It was also observed that, under the test conditions (RH 60.8%), for pore sizes under 0.065 μm CO₂ diffusion in the interior of the concrete is not significant. An expression is proposed to estimate carbonation rate in concrete from the volume of pores over 0.065 μm and the threshold diameter.     

钢渣作为路用材料的应用研究

本文简要介绍了钢渣的化学矿物组成、工程性质、应用以及质量控制。主要分析了钢渣作为路用材料时体积稳定性和对环境的影响问题 ,其中介绍了德国的蒸汽试验和瑞典野外滤出试验 ,最后指出钢渣是一种理想的路用材料     

Evaluation of CO2 captured in alkaline construction sludge associated with pH neutralization

Recently, the capture of carbon dioxide (CO₂) using alkaline waste and byproducts has garnered considerable interest. Construction sludge may be categorized as alkaline waste, as it often exhibits high alkalinity during its generation or intermediate treatment. Hence, researchers have attempted to accelerate pH neutralization and recycle alkaline construction sludge by curing it under a high CO₂ concentration. By exposing concentrated CO₂ gas to an alkaline sludge, cement hydrates such as calcium hydroxide and calcium–silicate–hydrate gels form calcium carbonate (CaCO₃). Subsequently, the generation of CaCO₃ is expected to reduce the pH of the sludge. However, the amount of CO₂ captured in sludge has not been investigated extensively, unlike those of other alkaline wastes. Therefore, the amount of CO₂ captured in alkaline sludge that is associated with pH neutralization is evaluated in this study. It is demonstrated that accelerated carbonation tests using a CO₂ incubator and carbonate content evaluation tests based on the gas pressure method successfully reveal the amount of CO₂ captured in the alkaline sludge that is associated with pH neutralization. Additionally, the test results show that the amount of m_CO2 (i.e., the amount of CO₂ captured per 1 g of dry mass of alkaline sludge) increases with ΔpH (ΔpH is the difference between the initial pH and the pH after the alkaline sludge is neutralized). A maximum of 0.021 g of CO₂ is captured per 1 g of dry mass of alkaline sludge when the addition ratio of quicklime A_QL = 3% and 0.040 g when A_QL = 6%. The CO₂ capture ratio m_CO2/m_CO2^max, which represents the ratio of CO₂ captured in the sludge to the maximum capturing capacity, increases with ΔpH. CO₂ capture ratios of up to 90.0% and 84.9% are recorded when A_QL = 3% and A_QL = 6%, respectively. It is discovered that a higher A_QL results in a higher m_CO2. Moreover, the test results indicate that a higher A_QL causes a more significant change in the CO₂ capture ratio, even when the pH decreases slightly.     

Modelling of carbonation of PC and blended cement concrete

Presented herein is a numerical model to predict the carbonation depth of Portland cement (PC) and blended cement concrete under a wide range of environmental conditions. The improved model for hydration of PC and activity of blended cement is proposed and used in this carbonation model. This carbonation model can be used for concrete made of silica fume, fly ash and slag with various chemical composition and particle size distribution. The saturation degree of concrete during carbonation process and the preconditioning before accelerated carbonation test were also considered to improve the ability of the model to predict the carbonation depth of concrete under natural condition or an accelerated condition. The predicted results are in good agreement with the experimental results.     

Monitoring the Mechanical and Structural Behavior of the Pavement Structure Using Electronic Sensors

Over the last decade, pavement instrumentation has become an important tool for monitoring the performance of pavement structures and materials under real climatic and traffic conditions. Stress, strain transducers, loop profilers, temperature, and moisture sensors could be reasonably used for sophisticated analysis of pavement performance. Commonly, such research projects involve only few pavement structures under accelerated loading tests. The unique experimental road section was constructed in 2007 in Lithuania. It consists of 27 different flexible pavement structures and all necessary electronic sensors. This road is affected by real climatic conditions and high‐intensity heavy vehicle traffic. The aim of such research is to continuously monitor performance of different pavement structures and to elaborate on the most suitable and economically effective pavement structures.     

Hydration properties of basic oxygen furnace steel slag

Basic oxygen furnace steel slag is the most common steel slag in China. In this study, the hydration properties of this kind of steel slag were investigated. Steel slag was ground separately to 458 m²/kg as well as 506 m²/kg. Different hydration conditions were set by changing the temperature or pH value. Hydration exothermic rate was measured within 4 days. Non-evaporable water content, hydration products and hardened paste morphologies were investigated at 1, 3, 7, 28 and 90 days. The results showed that the hydration process of steel slag was similar with that of cement. However, its hydration rate was much lower than cement. The hydration rate of steel slag at the early age could be accelerated by raising the fineness of particles, curing temperature or alkalinity of solution. However, raising the pH value of solution had little efficiency for the later hydration of steel slag and raising curing temperature even had negative influence on its later hydration. CSH gel and Ca(OH)₂ were the main hydration products of steel slag. A part of C₃S and C₂S crystal in steel slag had very low activity and unhydrated after 90 days. RO phase was almost inert. The interface between the particles of RO phase and CSH gel was a weak region in the system.     

Conditioned MSWI ash-slag-mix as a replacement for cement in cement mortar

Fly-ash and scrubber-ash are byproducts of municipal solid waste incinerators (MSWIs) that require further treatment before disposal to avoid polluting soil and groundwater with heavy metals. Recycling scrubber-ash is not feasible because it is extremely difficult to melt this material. In this study, fly-ash and scrubber-ash from MSWI were pre-mixed, then added to fly-ash from foundry sand and vitrified into slag by melting. The amount of that the latter was adjusted to maintain a basicity (CaO/SiO₂) of 1.1. Slag-blended cement mortar (SCM) specimens were molded with 0–40 wt.% cement replaced by slag powder. Toxicity characteristic leaching procedure (TCLP) tests and compressive strength tests were performed. TCLP test results revealed that the concentrations of leached heavy metals were substantially below the regulatory thresholds. Compressive strengths of the SCM specimens were higher than those of the control group after curing for 7 days or longer. Those that had been cured for 28–90 days were about 124–148% stronger in compression than those in the control group. The Pozzolanic reaction accounts for the strengthening effect in the context of the added slag. It is thus feasible to simultaneously recycle MSWI fly-ash, scrubber-ash and fly-ash from foundry sand into useful resources.     

Carbonation resistance of one industrial mortar used as a concrete coating

In aggressive environments, concrete itself may not be enough to protect the reinforcement against carbon dioxide penetration. This gas reacts with the portlandite of the concrete to form calcium carbonate. This process leads to a pH reduction and, therefore, promotes the depassivation of the steel reinforcement in reinforced concretes. Therefore, a supplementary protection method such as coating with a mortar, as carbonation barrier can be used to provide adequate durability. Experimental data are presented to illustrate the effect of three different testing levels of CO₂ on an industrial mortar applied to a concrete base in order to evaluate its performance as an anti-carbonation barrier. The results from the coated concrete are compared with the carbonation resistance of the uncoated plain concrete. The carbonation depth was determined using a phenolphthalein pH-indicator. A clear reduction in carbonation was observed when the mortar was applied. The validity of the accelerated testing method, which consists of placing the mortar in a high carbon dioxide concentration chamber for a controlled time, and carbonation coefficients to assess coating effectiveness are discussed. The use of 100% carbon dioxide is highly questionable for accelerated carbonation testing.