Equal Volumes of Sand and Gravel Concrete Mix Ratios in Cameroon and Its Effect on Concrete Compressive Strength

In recent years, the rationalization of concrete mix ratios which batches equal volumes of sand and gravel in building projects has been gaining grounds in the Cameroon construction industry. The main objective of this study is therefore to investigate if the concrete produced with rationalized mix ratio can be adopted as conventional mix ratio in terms of minimum required compression strength of concrete for buildings. Specifically this work compared the conventional mix ratio of 350 kg of cement: 400 liters of sand: 800 liters of gravel for a cubic meter and the rationalized batch of 350 kg of cement: 600 liters of sand: 600 liters of 5/15 gravel, 15/25 gravel and a combination of 5/15 + 15/25 gravel. Average compressive tests’results for both the conventional and the rationalized mix ratios were found to meet the minimum compressive strength of 65% at 7 days, 90% at 14 days and 99% at 28 days for gravel size combination 5/15 + 15/25. Single size gravel of 5/15 and 15/25 did not meet the minimum required compressive strength of 20 N/mm2 for the rationalized mix ratio at 28 days curing based on the minimum compressive strength required, this study arrives at the conclusion that the equal volumes of sand and gravel mix ratio of 350 kg/m3 of cement: 600 liters of sand: 600 liters of gravel mix ratio can be adopted as a conventional concrete mix ratio for gravel size 5/15 + 15/25.

Preparation and Optimization of Mix ratio for C50T Girder Manufactured Sand and Concrete

Considering actual construction conditions of Binchuan-Heqing Highway,this paper provides the C50 mix ratio conforming to engineering requirements by strictly controlling the quality of raw materials,optimizing the design of mix ratio scientifically,preparing superior C50 concrete 0 with manufactured sand,and optimizing the concrete mix ratio based on the adjustment of fly ash replacement,water-cement ratio,polycarboxylate-type water reducer mixing amount,sand ratio,etc.The result indicates that,the water-cement ratio has a great influence on the concrete strength,and if the ratio of coal ash is high in the binding material,the early compressive strength of the concrete will increase slowly.

Prediction Model-based Multi-objective Optimization for Mix-ratio Design of Recycled Aggregate Concrete

The prediction model for mechanical properties of RAC was established through the Bayesian optimization-based Gaussian process regression(BO-GPR)method,where the input variables in BO-GPR model depend on the mix ratio of concrete.Then the compressive strength prediction model,the material cost,and environmental factors were simultaneously considered as objectives,while a multi-objective gray wolf optimization algorithm was developed for finding the optimal mix ratio.A total of 730 RAC datasets were used for training and testing the predication model,while the optimal design method for mix ratio was verified through RAC experiments.The experimental results show that the predicted,testing,and expected compressive strengths are nearly consistent,illustrating the effectiveness of the proposed method.

Constraining Anthropogenic CH_4 Emissions in Nanjing and the Yangtze River Delta,China,Using Atmospheric CO_2 and CH_4 Mixing Ratios

Methane （CH4） emissions estimated with the Intergovernmental Panel on Climate Change （IPCC） inventory method at the city and regional scale are subject to large uncertainties.In this study,we determined the CH4：CO2 emissions ratio for both Nanjing and the Yangtze River Delta （YRD）,using the atmospheric CH4 and CO2 concentrations measured at a suburban site in Nanjing in the winter.The atmospheric estimate of the CH4：CO2 emissions ratio was in reasonable agreement with that calculated using the IPCC method for the YRD （within 20％）,but was 200％ greater for the municipality of Nanjing.The most likely reason for the discrepancy is that emissions from unmanaged landfills are omitted from the official statistics on garbage production.

Measurements of NO_2 mixing ratios with topographic target light scattering-differential optical absorption spectroscopy system and comparisons to point monitoring technique

A topographic target light scattering-differential optical absorption spectroscopy （＇IbTaL-DOA~） system is de- veloped for measuring average concentrations along a known optical path and studying surface-near distributions of atmospheric trace gases. The telescope of the ToTaL-DOAS system points to targets which are located at known dis- tances from the measurement device and illuminated by sunlight. Average concentrations with high spatial resolution can be retrieved by receiving sunlight reflected from the targets, A filed measurement of NO2 concentration is performed with the ToTaL-DOAS system in Shijiazhuang in the autumn of 2011. The measurement data are compared with con- centrations measured by the point monitoring technique at the same site. The results show that the ToTaL-DOAS system is sensitive to the variation of NO2 concentrations along the optical path.

MOLECULAR BEAM STUDIES ON OXIDATION OF CO ON Pd WITH DIFFERENT MIXED RATIOS OF P_(CO) TO P_(O2) ~*

Here some steady-state experiments on oxidation of CO on Pd were performed on a molecular beam apparatus. It is found that the characteristics of the rate of CO_2 formation r versus substrate temperature T are dependent on the ratio P=P_(CO)/P_(O2) in the mixed beam. These characteristics are related to the complicated interactions of co-adsorbed CO and O particles on Pd surface.

Biohydrogen Production from Synthetic Waste Co-digested with Liquid Dairy Cow Manure： Effect of Temperature and Mixing Ratio

Biohydrogen production from synthetic waste, SW （model organic fraction of municipal solid waste） co-digested with liquid dairy manure （M） was tested in batch reactions to assess the effect of temperature and mixing ratio of the substrates. A 5 × 2 factorial design experiment was conducted. Synthetic waste： manure mixtures of 1：1, 2：1, 3：1, 1：0, 0：1 （volatile solids, VS, basis） were tested at 37 （T37） and 55 ℃ （T55） using thirty 1 L laboratory scale digesters. Total VS of each mixture was 50 g/L except SW：M 0：I treatment, where total VS was 27.4 g/L. Gas samples were taken daily to determine hydrogen production, and slurry samples taken before and after experimentation, were analyzed for volatile fatty acid （VFA） concentration, volatile solid （VS） degradation, ammonium nitrogen （NH4＋-N） and pH. Hydrogen production （mL/g-VS fed） showed a significant two-factor interaction between incubation temperature and SW：M ratio （P 〈 0.001）. Maximum production of 15.8 mL/g-VS （fed） was achieved in SW：M ratio of 3：1 at 55 ℃. Generally, hydrogen productions at thermophilic temperature （T55） were significantly higher than at mesophilic （T37） temperature for all treatments （P 〈 0.001） except for SW：M 1：0 and SW：M 0：1 treatments （P 〉 0.05）. This study indicates that hydrogen production from co-digestion of synthetic waste and manure is dependent on incubation temperature and relative contribution of wastes in the mixture.

Variations of CO2 Mixing Ratios in the Air near the Ground in the European Territory of Russia

The instrumentation, method and measurement results used for measurements of CO2 concentrations in surface air of Obninsk （55.1° N, 36.9° E, 183 m above the sea level） located at a distance of 105 km to the south-west of Moscow are presented. Proposed is a method of experimental data filtering allowing one to separate natural and anthropogenic variations of CO2 concentrations. It is shown that minimal concentrations of CO2 registered in Obninsk and at the continental stations of GAW WMO characterize not only the ＂regional background＂ but also coincide with the data from GAW WMO background stations located in the oceanic regions. In this connection, one can assume that the excess in measured CO2 concentration over its minimal values, making about 5-6 ppm, is connected with an anthropogenic emission, and the continent should be considered as an anthropogenic source of C02.

Determination Multipole Mixing Ratios and Transition Strengths of Gamma Rays from Level Studies of 93Mo （p, nγ） Reaction

The multipole mixing ratios have been calculated by a2-ratio method, from levels of 93Mo（p, nγ） reaction. The branching ratios of such γ-transitions are used to calculate the total gamma widths. Besides, the transition strengths and probabilities have been calculated for γ-transitions from excited states whose life times have been reported previously. The results are found to be in general in good agreement with the previous results populated from the previous work.

Experimental research on the mixed sand ratio and initial dry density of weathered sand improved expansive soil free load swelling rate

In this paper, through the indoor free load swelling rate test, expansive soil in a section of a first- class highway reconstruction project in Yichang City was studied. It emphatically analyzed the interrelations among free load swelling rate, non-load time, the proportion of mixed sand and initial dry density. Experimen- tal studies have shown that： Free load swelling deformation is mainly divided into three stages of rapid expan- sion, slow expansion and final stability; when the initial dry density is constant, free load swelling rate of the weathered sand modified soil will reduce rapidly before they slow down with the increase of sand proportion, and weathered sand modified soil free load swelling rate is not sensitive to the large amount of sand mixed; in the same mixed sand ratio, weathered sand modified soil free load swelling rate increases rapidly with the in- crease of initial dry density, there is a good linear correlation between them. To take appropriate control of the initial dry density during the expansive soil subgrade construction helps to reduce its swelling deformation and ensures the stability of the embankment.

Identification of Mixtures of Two Types of Body Fluids Using the Multiplex Methylation System and Random Forest Models

Objective Body fluid mixtures are complex biological samples that frequently occur in crime scenes,and can provide important clues for criminal case analysis.DNA methylation assay has been applied in the identification of human body fluids,and has exhibited excellent performance in predicting single-source body fluids.The present study aims to develop a methylation SNaPshot multiplex system for body fluid identification,and accurately predict the mixture samples.In addition,the value of DNA methylation in the prediction of body fluid mixtures was further explored.Methods In the present study,420 samples of body fluid mixtures and 250 samples of single body fluids were tested using an optimized multiplex methylation system.Each kind of body fluid sample presented the specific methylation profiles of the 10 markers.Results Significant differences in methylation levels were observed between the mixtures and single body fluids.For all kinds of mixtures,the Spearman’s correlation analysis revealed a significantly strong correlation between the methylation levels and component proportions(1:20,1:10,1:5,1:1,5:1,10:1 and 20:1).Two random forest classification models were trained for the prediction of mixture types and the prediction of the mixture proportion of 2 components,based on the methylation levels of 10 markers.For the mixture prediction,Model-1 presented outstanding prediction accuracy,which reached up to 99.3%in 427 training samples,and had a remarkable accuracy of 100%in 243 independent test samples.For the mixture proportion prediction,Model-2 demonstrated an excellent accuracy of 98.8%in 252 training samples,and 98.2%in 168 independent test samples.The total prediction accuracy reached 99.3%for body fluid mixtures and 98.6%for the mixture proportions.Conclusion These results indicate the excellent capability and powerful value of the multiplex methylation system in the identification of forensic body fluid mixtures.

配合比参数对C30高性能混凝土抗碳化性能影响算法分析

基于配合比参数,对C30高性能混凝土抗碳化性能的影响进行了探讨,得出了随着矿粉用量的增加,21 d抗压强度随之提高;随着粉煤灰掺量的降低,21 d抗压强度随之提高;C30混凝土126 d的碳化深度明显小于21 d的碳化深度,C30各组试件的21 d的平均碳化深度为7.57 mm;126 d平均碳化深度为6.51 mm。随着矿物粉用量的增大,粉煤灰用量的减小,混凝土的抗碳化能力增强。以C30-07矿粉与水泥混合料的比例为38%时,C30水泥混合料的最佳混合比例为C30-07矿粉与水泥混合料的最佳混合比例。在龄期从21 d提高到126 d时,随粉煤灰掺量比例的下降,C30混凝土试件碳化深度下降值随之减小,从1.31 mm降低为0.91 mm。利用试验数据,对混凝土的碳化过程进行了预测,结果发现,影响粉煤灰混凝土的碳化的因素比较复杂,将各模型使用应和工程相结合,对混凝土的碳化深度更好预测。利用Matlab对水泥砂浆的碳化厚度进行了线性回归分析,得到了水泥砂浆21 d后碳化厚度的计算方法。

Effect of Pelleted Total Mixed Ration with Different Concentrate-roughage Ratios on Production Performance and Serum Biochemical Parameters of Fattening Hainan Black Goats

[Objective] This paper was to study effects of pelleted total mixed ration with different concentrate-roughage ratios on production performance and serum biochemical parameters of fattening Hainan black goats.[Method] Thirty-six fattening Hainan black goats with the same genetic background and similar initial weight of(14.08±0.13) kg were randomly assigned into three treatments. Goats were fed with Juncao + concentrate(control group), pelleted total mixed ration I(concentrate: roughage 50 ∶50, group Ⅰ) and Ⅱ(concentrate: roughage 45∶55, group Ⅱ), respectively. The test lasted 45 d.[Result] The final weight, daily gain and feed intake of rams in experimental group Ⅰ were significantly higher than those of control group and experimental group Ⅱ(P<0.05);the final weight and daily gain of rams in experimental group Ⅰ were also markedly higher than those of experimental group Ⅱ(P<0.05);the feed/gain of rams in experimental group Ⅰ was significantly lower than those in control group and experimental group Ⅱ(P<0.05). The feed gain cost of rams in experimental group Ⅰ was markedly lower than that in experimental group Ⅱ( P<0.05), but was significantly higher than that in experimental group Ⅰ(P<0.05);the gross profit of rams in experimental group Ⅰ was significantly higher than those in control group and experimental group Ⅱ(P<0.05). Compared with control group and experimental group Ⅱ, the serum total protein and glucose lev-els in experimental group Ⅱ increased significantly(P<0.05), but the urea nitrogen content reduced(P>0.05).[Conclusion] When the concentrateroughage ratio of pelleted total mixed ration was 50∶50, the fattening effect of Hainan black goat was better, and the serum total protein and glucose levels were evidently improved.

高强页岩轻骨料混凝土制备及微观结构研究

基于最紧密堆积理论和最小需水量法进行高强页岩轻骨料混凝土配合比设计与制备,研究了水胶比对抗压及劈裂抗拉强度影响,并借助SEM/EDS进行微观测试分析。结果表明:当粗细骨料体积分数比为5.5:4.5时,粗细骨料达到最紧密堆积状态;当硅灰、粉煤灰和水泥质量比为0.8:3.2:6时,需水量最少,粉体材料密实度最佳;依据优化配比所配混凝土的抗压强度和劈裂抗拉强度均随龄期增加而增加;随着水胶比增加,抗压强度和劈裂抗拉强度呈先增后减的趋势,且当水胶比为0.24时达到最大,分别为70.9、5.83MPa;硅灰和粉煤灰特有的形态效应和火山灰效应有效改善了浆体与骨料间界面的密实程度,微观结果显示浆体与骨料界面区域结构致密,陶粒区域为富Si、Al相,浆体一侧为富Ca相。

NH_(4)H_(2)PO_(4)-KHCO_(3)混合粉体对管网甲烷爆炸的抑制特性

在自行搭建的管网实验系统中,将常用于抑制甲烷爆炸的碳酸氢钾KHCO_(3)与磷酸二氢铵NH_(4)H_(2)PO_(4)进行不同比例的混合。选取5种不同的粉体配比,对比单一粉体以及各抑爆工况下各测点的爆炸峰值压力、火焰峰值速度和火焰峰值温度等爆炸特征参数,获得抑制管网甲烷爆炸的最佳工况,并阐述了抑爆机理。结果表明:混合粉体对管网甲烷爆炸的抑制性能优于单一粉体;KHCO_(3)与NH_(4)H_(2)PO_(4)都易受热分解;其中,KHCO_(3)可以在相对较低的温度下迅速完成热解过程,从而吸收更多的反应热,抑爆性能优于NH_(4)H_(2)PO_(4)粉体;混合粉体中,抑爆效果随着KHCO3含量的增加显著提高。在5种混合比例中,当KHCO_(3)与NH_(4)H_(2)PO_(4)质量比为2.0:1.0时,抑爆效果最佳。KHCO_(3)与NH_(4)H_(2)PO_(4)表现出良好的爆炸抑制效果,研究所得结论可为抑制甲烷爆炸研究提供参考。

高掺量磷石膏道路基层材料配比设计及性能研究

按传统矿质混合料设计掺磷石膏道路基层材料难以大规模消纳磷石膏,为实现磷石膏在道路基层材料中大规模利用,通过骨料替代法进行高掺量磷石膏道路基层材料配比设计,确定适宜的碎石比(5~10 mm粒级与10~25 mm粒级质量比39∶61)后以不同掺量替代磷石膏基胶凝材料体系,再击实然后得出最佳含水率及最大干密度。通过对设计好的配比进行性能试验筛选,得出适宜配比为P85S60,养护28 d的试件抗压强度最大达5.39 MPa,体积变化率较低,且养护7 d后试件的体积增长稳定,体积变化率最终维持在0.5%左右,有利于现场道路施工应用。所有配比浸出氟、磷均满足《污水综合排放标准》(GB 8978—1996)一级限值,相较于常规水泥稳定碎石材料,该道路基层材料浸出液的酸碱性不会额外增加不利影响。通过XRD和SEM分析可知,胶凝材料水化产生的钙矾石和水化硅酸钙包裹在未反应的二水石膏周围,另外针棒状钙矾石和水化硅酸钙填充微小孔隙,使得试件整体结构密实、强度增加、体积稳定性增强。

智能放煤理论与技术研究进展

综放开采技术是厚及特厚煤层开采的有效方法,已成为我国在世界煤炭开采行业的标志性技术。综述了“四要素”放煤理论、顶煤采出率与含矸率关系、基于块度分布的采出率预测模型、煤流瞬时含矸率-累计含矸率关系等智能放煤理论研究进展。分析了智能放煤技术难点,指出含矸率是影响顶煤采出率和煤质的关键因素,放煤过程中含矸率的快速、准确计算是智能放煤技术突破的重点和关键。将智能放煤技术分为非图像识别智能放煤技术和图像识别智能放煤技术2类,对不同技术的研究进展、优缺点及使用条件进行了详细分析。非图像识别智能放煤技术包括记忆放煤技术、声音振动信号识别技术、γ射线探测技术、探地雷达技术、微波照射+红外探测技术、激光扫描放煤量监测技术等,图像识别智能放煤技术包括井下照度环境精准控制、放煤图像去尘算法、含矸率计算精度保障策略、煤岩红外图像识别等。

管式蒸发冷却下LiCl-CaCl_(2)混合溶液降膜除湿特性分析

针对绝热型溶液除湿器性能低下的问题,设计了一种管式蒸发冷却型溶液除湿器,并采用具有较高经济性的LiCl-CaCl_(2)混合溶液作为除湿剂.基于理论模型,数值模拟了混合溶液中LiCl、CaCl_(2)两组分混合质量比、溶液参数和空气参数对蒸发冷却及绝热工况下除湿器热湿传递特性的影响.结果表明,除湿器在蒸发冷却工况下的单位面积除湿率高于绝热工况,最高可提升41.5%,且溶液中LiCl质量分数越小,其性能优势越显著.蒸发冷却除湿优势受溶液温度影响显著,单位面积除湿率与除湿空气流量呈正相关,与溶液流量呈负相关.不同的LiCl-CaCl_(2)混合质量比下蒸发冷却除湿特性主要受溶液温度影响,且在溶液温度较低时降低LiCl质量分数对除湿性能影响较小.2种运行工况下空气流量对除湿器单位面积除湿率的正向提升率可达136.9%~168.1%,而溶液流量对其影响较弱.

低强度再生混凝土微观形态与力学性能的相关性研究

建筑垃圾来源复杂,为提高再生混凝土的资源利用,并满足基本工程应用要求,在仅考虑再生骨料密度、吸水和含水率、压碎指标的条件下,采用再生粗骨料混凝土配合比设计法配置低强度再生混凝土,结合切片法和SEM扫描电镜对再生混凝土的孔隙结构变化与微观形貌进行观察,分析水胶比、减水剂、粉煤灰对低强度再生混凝土内部结构的影响,发现当水胶比降低时,再生混凝土内部结构的密实度提升,絮状C-S-H之间更为密实,多害孔的比例降低,抗压和劈裂强度提高;当减水剂掺量提升时,钙钒石(AFt)的含量增加,内部结构更为致密;粉煤灰对再生混凝土的抗压和劈裂强度呈负面影响,降低C-S-H与再生骨料之间的粘结性,内部孔隙率变大,坍落度升高,可降低经济成本。

钻井法凿井壁后充填大比重水泥浆研制及其耐久性能

为提升西部地区深大钻井井筒第一段高壁后充填置换效果,提出采用大比重水泥浆作为新型壁后充填材料。首先,通过对比试验,优选重晶石粉作为加重剂、硅酸镁铝为悬浮剂。然后,采用正交试验和极差分析法,分析了水灰比、重晶石粉、硅酸镁铝和膨胀剂掺量对大比重水泥浆的密度、初凝时间、流动度、3 d及28 d抗压强度的影响,采用综合平衡法确定了大比重壁后充填材料的最优配合比为水泥∶水∶重晶石粉∶硅酸镁铝∶膨胀剂∶减水剂=1∶0.55∶0.5∶0.03∶0.025∶0.015。硫酸盐溶液侵蚀对比试验表明,与常用的水泥浆充填材料相比,大比重水泥浆充填材料具有可靠的耐久性能。最后,通过XRD和SEM分析了优选组加重水泥浆在3 d和28 d的水化产物和微观结构,揭示其优异抗渗性和耐久性能的机理。研究结果可为西部地区深大钻井井筒壁后充填提供大比重、高强度、低渗透以及耐久性好的新型壁后充填材料。