Effect of phosphogypsum on saline-alkalinity and aggregate stability of bauxite residue

A column experiment was conducted to investigate the effect of phosphogypsum (PG) on the saline- alkalinity, and aggregate stability of bauxite residue. Results showed that: with increasing leaching time, the concentrations of saline-alkali ions decreased while the concentration increased in bauxite residue leachate; compared with CK (control group) treatment, pH, electric conductivity (EC), exchangeable sodium percentage (ESP), sodium absorption ratio (SAR), and exchangeable Na⁺ content of bauxite residue were reduced following PG treatment; average particle sizes in aggregates following CK and PG treatments were determined to be 155 and 193 nm, respectively. SR-μCT test results also confirmed that bauxite residue following PG treatment acquired larger aggregates and larger pore diameter. These results indicate that the PG treatment could significantly modulate the saline-alkalinity, and simultaneously enhance aggregate stability of bauxite residue, which provides a facile approach to reclaim bauxite residue disposal areas.     

A new systematic firefly algorithm for forecasting the durability of reinforced recycled aggregate concrete

This study presents a new systematic algorithm to optimize the durability of reinforced recycled aggregate concrete. The proposed algorithm integrates machine learning with a new version of the firefly algorithm called chaotic based firefly algorithm (CFA) to evolve a rational and efficient predictive model. The CFA optimizer is augmented with chaotic maps and Lévy flight to improve the firefly performance in forecasting the chloride penetrability of strengthened recycled aggregate concrete (RAC). A comprehensive and credible database of distinctive chloride migration coefficient results is used to establish the developed algorithm. A dataset composite of nine effective parameters, including concrete components and fundamental characteristics of recycled aggregate (RA), is used as input to predict the migration coefficient of strengthened RAC as output. k-fold cross validation algorithm is utilized to validate the hybrid algorithm. Three numerical benchmark analyses are applied to prove the superiority and applicability of the CFA algorithm in predicting chloride penetrability. Results show that the developed CFA approach significantly outperforms the firefly algorithm on almost tested functions and demonstrates powerful prediction. In addition, the proposed strategy can be an active tool to recognize the contradictions in the experimental results and can be especially beneficial for assessing the chloride resistance of RAC.     

混菌矿化增强再生粗骨料的物理力学性能

为克服单一微生物培养成本高且矿化鲁棒性不足的缺陷，提出了一种混菌矿化增强再生粗骨料物理力学性能的方法.通过筛选矿化效率较高的好氧嗜碱混菌，考察了混菌矿化对再生粗骨料物理力学性能和混凝土抗压强度的影响.结果表明：相同增强时间下，混菌比纯菌呈现出更优异的矿化增强效果；随着混菌矿化增强时间的延长，再生粗骨料吸水率和压碎指标呈现出先减小后增大的趋势，最优增强时间为15 d；采用矿化增强再生粗骨料制备的再生混凝土抗压强度提高幅度达到22.1%.     

风速对骨料烘干煤粉燃烧器排放特性的影响

基于煤粉燃烧机理，结合骨料烘干工艺，建立了骨料烘干煤粉燃烧器内部场的控制模型，采用Fluent软件模拟煤粉燃烧器内部燃烧状况，考察了一、二、三次风的风速对煤粉燃烧器中心轴线处CO, CO2, NO和SO2浓度的影响。结果表明，在研究的风速范围内，一、二、三次风风速越大燃烧越充分，一、二、三次风风速越小，产生的NO越少；三次风风速为40 m/s时，SO2浓度最低；较合理的控制参数为一次风风速30~35 m/s，二次风风速45~50 m/s，三次风风速30~40 m/s。     

人工砂混凝土性能试验研究

采用正交试验方法配制了不同人工砂取代率、石粉含量、粉煤灰含量的混凝土, 对比了每组混凝土的坍落度, 研究了3 d、28 d龄期混凝土的抗压性能。结果表明: 最优配比的人工砂取代率、石粉含量和粉煤灰含量分别为10%、3%和5%, 此时28 d抗压强度为40.1 MPa, 满足30 MPa的混凝土设计强度。     

再生骨料对混凝土力学性能及耐久性影响的研究

针对再生骨料由于本身结构缺陷的原因，造成混凝土力学性能和耐久性不良的问题，采用再生骨料裹浆预处理和密实骨架堆积配合比设计方法，弥补再生骨料的结构缺陷，提高混凝土密实程度，使得再生骨料混凝土的抗压强度和抗碳化性能、抗氯离子渗透性能得到有效改善。     

碳酸性侵蚀与AAR作用下纳米混凝土的耐久性

地铁混凝土处于地下空间,容易受到地下水的碳酸性侵蚀；碱集料反应 (AAR)是一种严重的混凝土耐久性问题,既难以发现又难以修补,由两者共同作用引起的混凝土耐久性降低严重影响地铁隧道的正常使用.为研究纳米材料对地铁混凝土在碳酸性侵蚀和AAR共同作用下耐久性的影响,在普通混凝土中掺入适量纳米SiO₂和纳米Fe₂O₃,利用自行研制的碳酸性侵蚀试验箱进行试验,采用碳酸性侵蚀深度、膨胀率和声速作为测试指标来评价纳米混凝土在碳酸性侵蚀和AAR共同作用下的耐久性.试验结果表明:掺入纳米颗粒后,混凝土的膨胀率和侵蚀深度有了明显降低,而声速有了明显提升,说明纳米混凝土的耐久性优于普通混凝土；在182 d龄期时,掺量为2%的纳米SiO₂混凝土耐久性改善最明显,侵蚀深度和膨胀率最小,声速最大且声速下降幅度最小；其次是掺量为1%的纳米Fe₂O₃混凝土.由于纳米颗粒特殊的物理化学性质,改善了混凝土内部的微观结构和孔溶液的化学组成,使碳酸性侵蚀和碱集料反应共同作用下混凝土的耐久性得到了提高.     

粒度级配对神华煤成浆特性影响的试验研究

为了研究粒度级配对神华煤成浆特性的影响,通过筛分和干法调浆,探讨了不同粒度分布煤粉的成浆性,结果表明:在添加剂用量为0.3%(干基/干煤)时,具有连续级配特征的原始煤粉可制备出质量分数为61%的煤浆;利用筛分法,分别去除原始煤粉中0.045 mm以下、0.045 mm^0.15 mm、0.15 mm^0.3 mm和0.045 mm^0.3 mm部分,得到4种具有不连续级配特征的样品,其所制煤浆流变性发生了较大变化,其中去除0.045 mm^0.3 mm部分的样品的成浆质量分数提高了3个百分点,在黏度符合要求的前提下流动性大幅提高;连续级配和非连续级配的煤浆均存在黏度与流动性不统一的现象,当级配中粗细颗粒粒径差较大且细颗粒含量达到一定值时,这种现象更加明显。采用粒度级配技术制浆,其细颗粒含量存在一个合理的区间。     

An investigation on the recycling of hydrated cement from concrete demolition waste

Construction and demolition waste (CDW) recycling is generally limited to the use of the coarser fraction as aggregate for new concrete. The recovery of fine aggregates requires a cleaning by removing the hydrated cement waste (HCW). In this paper, the possibility to use HCW extracted from CDW as alternative component for the production of new clinker is explored.A pure HCW sample was prepared and used in partial replacement of natural materials in raw admixtures for new clinker production. At a replacement degree of 30%, a new Portland clinker containing almost 50% of C₃S could be produced with a huge spare in the release of CO₂ (about 1/3 less). At higher HCW dosage a non-Portland clinker containing almost 80% of C₂S has been obtained: its use as supplementary cementing material in blended cements revealed satisfying long term performances.     

全尾砂和废石联合胶结充填体最佳配比及应用

针对红岭铅锌矿分级充填骨料来源不足、地表废石堆积污染环境的情况,提出将该矿选厂产生的全尾砂和地表废石作为充填骨料的联合胶结充填方案。分别测试了全尾砂和地表废石的物理化学性质,验证了碎石和全尾砂作为联合充填骨料的可行性。通过充填配比试验,分析了不同配比全尾砂废石充填体强度特性,得出了最佳充填配比。结果表明,充填试块的强度随灰砂比减小而减小,随养护龄期增加呈增大趋势,随充填料浆质量浓度增大而增大,最佳配比为: 胶结充填灰砂比1∶8、普通充填灰砂比1∶12,全尾砂∶废石配比4∶6,质量浓度78%。根据研究结果,在红岭铅锌矿进行了全尾砂废石充填技术工业应用,证实该技术可行。