路面碾压混凝土配比强度设计指标的研究

路面碾压混凝土在混凝土各组成相同时，由于施工时压实度的波动引起强度的波动较大，因此在设计路面碾压混凝土配比强度时，要同时考虑拌制均匀性和施工时的质量波动，通过统计分析碾压混凝土芯样压实率的波动范围、压实率与强度的关系，求得路面压实安全强度，以及分析路面碾压混凝土抽样强度和变异系数，求得强度加成系数。

“全厚式”碾压混凝土路面混凝土配合比特性

本文介绍满足路面平整度及强度要求的“全厚式”碾压混凝土路面的混凝土配合比特性，包括：稠度及配比强度的设计指标和试验方法，粗集料的最大粒径，粗、细集料合成级配范围，用水量和水泥用量，对外加剂及粉煤灰的技术要求。

中关铁矿全尾砂结构流充填材料关键特性研究

中关铁矿水文地质条件复杂、矿坑涌水量大,通过地表封闭式注浆帷幕治水,采用全尾砂结构流充填采矿法开采。基于此,以室内试验为手段开展了尾砂粒度组成、自然絮凝沉降、充填试块强度及充填料浆流动性能等关键特性研究,试验结果表明:中关铁矿尾砂属于超细全尾砂,可满足结构流充填中极细颗粒含量要求,絮凝沉降最佳质量浓度为25%以下,充填试块强度90 d最高接近3 MPa,但28 d强度值低,需要进一步研发早强型新型胶结材料。

水泥土搅拌法在水利工程软土地基处理中的应用

软土地基是以软土为主,与粉砂、泥炭等一些其它土层相间组成,具有压缩性高、渗透性差、承载力低的不良特性,是水利工程中常见的地基。水泥土搅拌法是对软土地基加固的一种有效措施。文章阐述了水泥土搅拌法的原理,并对其施工工艺进行大致的介绍。

Effect of Recycled Coarse Aggregate on Concrete Compressive Strength

The effect of recycled coarse aggregate on concrete compressive strength was investigated based on the concrete skeleton theory. For this purpose, 30 mix proportions of concrete with target cube compressive strength ranging from 20 to 60 MPa were cast with normal coarse aggregate and recycled coarse aggregate from different strength parent concretes. Results of 28-d test show that the strength of different types of recycled aggregate affects the concrete strength obviously. The coarse aggregate added to mortar matrix plays a skeleton role and improves its compressive strength. The skeleton effect of coarse aggregate increases with the increasing strength of coarse aggregate, and normal coarse aggregate plays the highest, whereas the lowest concrete strength occurs when using the weak recycled coarse aggregate. There is a linear relationship between the concrete strength and the corresponding mortar matrix strength. Coarse aggregate skeleton formula is established, and values from experimental tests match the derived expressions.

Mixing ratio design of emulsified asphalt cold recycled mixture based on gyratory compaction molding

In order to study the application of gyratory compaction molding method in emulsified asphalt cold recycled mixture and optimize the relevant technical parameters, the study was carried out according to splitting strength, stability and water stability test;the design of the experiment involved changing gyration number, emulsified asphalt and water content, molded specimen temperature and other factors to analyze the volume parameters, mechanical properties and water stability. The results show that both the maximum dry density and dry and wet splitting strength ratio(DWSSR) of emulsified asphalt cold reclaimed mixture are improved by the rotary compacting method, while the porosity and the optimal dosage of water are reduced. Furthermore, with the increase of compaction times, the porosity and splitting strength index both change exponentially. DWSSR and porosity are consistent with quadratic functions. The use of gyratory compaction for 70 times at 25 °C and the optimum dosage of emulsified asphalt can be determined based on the splitting strength ratio. The high-temperature stability and water damage resistance of the pavement can be improved by the use of rotary compacting method effectively, and the early strength and road performance are higher than the regulatory requirements.

Utilization of municipal solid waste incineration fly ash in lightweight aggregates

Washing pre-treatrnent of municipal solid waste incineration （MSWI） fly ash blended with shale and sludge was utilized in the manufacture of light-weight aggregates and processed to form ceramic pellets. A formula uniform design was performed to arrange the mixture ratio of the materials. The optimal mixture ratio of the materials was determined by measuring the bulk density, granule strength, and 1 h water absorption of the pellets. It is shown that the optimal mixture ratios of materials, MSWI fly ash, shale, and sludge, are 23.16%, 62.58%, and 14.25% （mass fraction）, respectively. The performance testing indicators of light-weight aggregates are obtained under the optimum mixture ratio： bulk density of 613 kg/m3, granule strength of 821N, and 1 h water absorption of 11.6%, meeting 700 grade light-aggregate of GB/T 17431.2--1998 standard. The results suggest that utilization of MSWI fly ash in light-weight aggregates is an effective method and a potential means to create much more values.

Innovative Application of Scrap-Tire Steel Cords in Concrete Mixes

Many researchers have investigated the use of recycled tire products in several traditional civil engineering materials. This research is exploring the use of steel cords, a by-product of the tire recycling process, in concrete mixes. Different concrete specimens were fabricated and tested in uniaxial compression and splitting tensile strength. The steel cords were substituted into the concrete mix in volumetric percentages of various ratios. Results show that mechanical properties of concrete made with steel cords are improved compared with concrete mix made with the traditional scrap-tires recycled material. Also, results show that even though the compressive strength is reduced when using steel cords, this reduction is minimal. When 2% of steel cords are used there is 18% increase in ductility. Moreover, splitting tensile tests show that concrete mixtures with any steel cords content have much greater toughness than control mixture. This mechanical property mix indicates an excellent potential application of modified concrete mix in structures that absorb large amount of energy.

Basic Study on Perfect Push-Pull Local Ventilation

In this study, the authors experimentally investigated the changes of the mean velocity component profiles, half-widths （b12）, turbulence intensities, Reynolds shear stress and intermittency of turbulence of a transient plane turbulent jet developing from a jet exit into a hood opening. The values of maximum mean-velocity and half-widths of the axial velocity profile along the center-line of the jet are greater than those for a fully developed two-dimensional jet. Turbulence intensity in the axial direction is not affected by the flow rate ratio. At the same time, turbulence intensity in the lateral direction becomes greater as the hood is approached and the flow rate ratio Q3/Q1 becomes larger （QI is jet flow rate from nozzle and Q3 is suction flow rate produced by the hood）. These experimental results are in accord with the distributions of production terms in the axial and lateral directions. Reynolds shear stress becomes smaller as the flow rate ratio becomes larger near the hood. Dimensionless distance y1/br2, from the center axis of the flow to the point where intermittency factor y becomes a constant value, narrows as the flow rate ratio becomes larger near the hood.