Prediction equation of drying shrinkage of concrete based on composite model

In this study, the prediction equation of drying shrinkage of concrete is obtained with two-phase composite model as aggregate and matrix. In order to obtain the input values for this prediction equation easily, the experimental formula of drying shrinkage and Young's modulus of cement paste are obtained, and the estimation method of Young's modulus of aggregate are proposed with easy test using cement paste, mortar and concrete. According to the experimental results, this equation can predict the drying shrinkage at any age in error by less than about 100 μm.     

Modeling for prediction of restrained shrinkage effect in concrete repair

A general model of autogenous shrinkage caused by chemical reaction (chemical shrinkage) is developed by means of Arrhenius' law and a degree of chemical reaction. Models of tensile creep and relaxation modulus are built based on a viscoelastic, three-element model. Tests of free shrinkage and tensile creep were carried out to determine some coefficients in the models. Two-dimensional FEM analysis based on the models and other constitutions can predict the development of tensile strength and cracking. Three groups of patch-repaired beams were designed for analysis and testing. The prediction from the analysis shows agreement with the test results. The cracking mechanism after repair is discussed.     

Influence of alkali on restrained shrinkage behavior of cement-based materials

Experiments have been conducted to study effects of high alkalinity on restrained shrinkage behavior and cracking sensitivity of cement-based materials at early ages. The restrained shrinkage test has been conducted with an ellipse ring setup and the initial cracking time was monitored with a continuous conductive strip. Alkali content and alkali type as well as the shrinkage-hydration relationship have been studied. The experimental results have shown that the cracking sensitivity of a cement-based material is increased with an increase in alkali content. The influence of the excess alkali on the cracking sensitivity is more obvious for cement paste with a low water-to-cement ratio (w/c) than that with a high w/c. The hydration processes and microstructure development of cement paste have been investigated using heat of hydration measurement and electrical resistivity measurement. The superimposed resistivity curve and heat evolution curve provide more comprehensive understanding on factors influencing shrinkage development.     

Eight-year exploration of shrinkage in high-performance concrete

In this paper, an experimental and analytical exploration on the effect of water-binder ratio (w/b), silica fume and age on autogenous, carbonation, drying and total shrinkage of high-performance concrete (HPC) is outlined. Eight types of HPC were studied. Carbonation, internal relative humidity (RH) and strength were studied on specimens from the same batch of HPC that was used in the studies of shrinkage. The results indicate fairly good correlation between carbonation, shrinkage, w/b and RH. The type and amount of silica fume affected shrinkage.     

Influence of fly ash fineness on strength, drying shrinkage and sulfate resistance of blended cement mortar

In this paper, the influence of fineness of fly ash on water demand and some of the properties of hardened mortar are examined. In addition to the original fly ash (OFA), five different fineness values of fly ash were obtained by sieving and by using an air separator. Two sieves, Nos. 200 and 325, were used to obtain two lots of graded fine fly ash. For the classification using air separator, the OFA was separated into fine, medium and coarse portions. The fly ash dosage of 40% by weight of binder was used throughout the experiment. From the tests, it was found that the compressive strength of mortar depended on the fineness of fly ash. The strength of mortar containing fine fly ash was better than that of OFA mortar at all ages with the very fine fly ash giving the highest strength. The use of all fly ashes resulted in significant improvement in drying shrinkage with the coarse fly ash showing the least improvement owing primarily to the high water to binder ratio (W/B) of the mix. Significant improvement of resistance to sulfate expansion was obtained for all fineness values except for the coarse fly ash where greater expansion was observed. The resistance to sulfuric acid attack was also improved with the incorporation of all fly ashes. In this case the coarse fly ash gave the best performance with the lowest rate of the weight loss owing probably to the better bonding of the coarse fly ash particles to the cement matrix and less hydration products. It is suggested that the fine fly ash is more reactive and its use resulted in a denser cement matrix and better mechanical properties of mortar.     

Early-age deformation, drying shrinkage and thermal dilation in a new type of dental restorative material based on calcium aluminate cement

Dimensional changes during the first hour of hydration for small specimens of a dental material based on calcium aluminate cement (CAC) was examined. The study was conducted on specimens prepared in two different ways. First, intact tablets (three pieces per test) dipped in water were measured. Second, compacted specimens from four tablets were measured after 10 min of hydration. The dimensional changes were studied in both wet and dry conditions at 37 °C and in a dry condition at 25 °C. In the wet environment at 37 °C no dimensional change of the samples was observed. At normal room humidity (RH 55%) at both temperatures, shrinkage of 0.35-0.40% was observed. For comparison to the early-age drying shrinkage, a study of the drying shrinkage in mature material, hydrated for 50 and 100 days, respectively, was conducted. Furthermore the thermal expansion coefficient was determined and found to be close to that of tooth substance.     

Influence of polypropylene fiber geometry on plastic shrinkage cracking in concrete

Plastic shrinkage cracking remains a primary concern for placements with high surface/volume ratios that are subjected to early age drying. Polypropylene fiber reinforcement controls such cracking, but the exact influence of fiber diameter, length and geometry remains unknown. A test program was carried out to understand the influence of these variables. Four commercially available polypropylene fibers were investigated at dosage rates varying from 0.1% to 0.3%. A recently developed technique of plastic shrinkage testing using a fully bonded overlay was employed. In this technique, a fiber reinforced concrete overlay is cast on a fully matured subbase with protuberances and the whole assembly is allowed to dry in an environmental chamber. Cracking in the overlay is monitored with time and characterized. Results indicate that while polypropylene fibers in general are effective in controlling plastic shrinkage cracking in concrete, a finer fiber is more effective than a coarser one, and a longer fiber is more effective than a shorter one. Further, fiber fibrillations appear to be highly effective in controlling plastic shrinkage cracking.     

Prediction of diffusivity of concrete based on simple analytic equations

Proposed is a simple analytic model that can predict realistically the diffusivities of concrete and mortar. The basic concept of the model comes from the relation between the diffusivities and the microstructure of concrete. The microstructure that affects the diffusivity includes the interfacial transition zone (ITZ) between aggregates and cement pastes as well as the microstructure of cement paste itself. The general effective media (GEM) equation was introduced to derive the diffusivity of cement paste. The effective diffusivity of concrete is derived on the basis of the composite sphere assemblage model, which considers the diffusivities of both ITZ and cement paste. The main parameters in the proposed model are the microstructural properties of cement paste such as capillary porosity and pore structure parameter, solid phase diffusivity, aggregate volume fraction, and interfacial zone properties. To validate the proposed model, many series of concrete and mortar specimens have been tested to measure the diffusivities. The major test variables include the water-to-binder ratios, the types and amount of mineral admixtures on the diffusivities. The effects of compressive strength, water-to-binder ratio, and mineral admixtures have been investigated comprehensively. The comparison of the proposed theory with the test data exhibits reasonably good correlation. The proposed model allows more accurate prediction of diffusion process and, thus, more realistic durability design of concrete structures.     

The role of specimen geometry and boundary conditions on stress development and cracking in the restrained ring test

Early-age cracking can be a significant problem in concrete pavements, floors, and bridge decks. Various test methods have been developed to assess the potential for early-age cracking, however due to the economy and simplicity of the ring test, it has become widely used. Although the ring test procedures employed by various authors are similar, they vary in terms of curing duration, specimen geometry, and boundary conditions. This paper describes an experimental study of restrained ring specimens tested using different geometries and boundary conditions. Specimen geometry was found to have a significant effect on the stress development and age of cracking in the restrained ring specimens. Specimens that shrink uniformly along the radius show the greatest variation in the age of cracking with thicker specimens cracking at a later age. Acoustic emission testing has been used to illustrate that specimen boundary condition substantially influence crack development and propagation in the restrained rings.     

Influence of shrinkage-reducing admixtures on the reduction of plastic shrinkage cracking in concrete

Fresh concrete exposed to high evaporation rates is prone to plastic shrinkage cracking, especially in structures with large surface area/volume ratios. The present work shows that the reduction of the surface tension of the mixing water is an effective way for decreasing such cracking. In this study, conventional and high strength concretes with superplasticizers and shrinkage reducing admixtures (SRAs) were exposed to drying in the plastic state. Continuous monitoring of the surface displacement facilitated the identification of the different stages of plastic shrinkage cracking. Measurements of capillary pressure, settlement, internal temperature and evaporation rate were also made. The results show the effectiveness of SRAs in reducing plastic shrinkage cracking, even in high strength concrete. This is attributed to the reduction in the evaporation rate, delay of the peak capillary pressure due to the development of menisci in the pores and lower settlement.     

油页岩干馏技术影响因素及工业发展展望

对油页岩资源的分布及储量情况、油页岩干馏过程及其影响因素、国内外的油页岩干馏技术及其工业发展现状进行了介绍,并对油页岩干馏工业进行了展望。     

基于多元非线性回归模型预测磷建筑石膏强度

研究硅灰、聚羧酸减水剂、柠檬酸、聚乙烯醇乳液对磷建筑石膏强度的影响,根据各因素对强度影响的拟合曲线特征,提出多元非线性回归模型,运用MATLAB软件建立多因素共同作用影响磷建筑石膏强度的多元非线性回归分析模型,结果表明:硅灰是影响磷建筑石膏强度的最主要因素,通过模拟值与试验值的比较,验证回归模型的合理性.     

干混砂浆生产过程中几个问题的探讨

干混砂浆在与湿拌砂浆的竞争中出现一些制约行业发展的共性问题,诸如干混砂浆的离析,机制砂中石粉含量高,计量设备不完善,外加剂溶解性差,机制砂筛分系统的超径与逊径,干混砂浆搅拌的均匀性等。通过详细阐述这些影响干混砂浆快速发展的技术工艺因素,提出了干混砂浆设备供商应该努力研究的方向,同时也提供了干混砂浆生产企业可以采取的临时性措施的建议。只有这些行业共性问题的解决,才能迎来干混砂浆大面积的普及与应用,才能实现干混砂浆对湿拌砂浆的彻底取代与发展。     

重质碳酸钙超细与改性一体化工艺研究

重质碳酸钙是应用广泛的矿物填料.利用超细粉碎与表面改性一体化工艺,在粉碎的同时进行表面改性处理.在粉碎机械力作用下产生的矿物新鲜表面和高活性表面,有利于提高改性效果.讨论了改性剂种类与用量、给料速度与给料粒度对改性与粉碎效果的影响.     

Investigation on pozzolanic effect of perlite powder in concrete

The pozzolanic effect of perlite powder (PP) added to concrete can be determined quantitatively with strength indices: specific strength ratio (R), index of specific strength (K), and contribution percentage of pozzolanic effect to strength (P). Besides compressive strength, these indices indicate that perlite powder has a high pozzolanic effect and is an active mineral admixture (MA) for concrete.     

基于小波神经网络预测多相动态管道腐蚀速率

利用小波神经网络模型预测多相动态环境下油气集输管道腐蚀速率。首先通过室内多相动态腐蚀实验,获得了不同工况条件下的挂片腐蚀速率,用于训练和检验小波神经网络预测模型,然后利用多因子方差分析研究了温度、压力、流率、硫化氢含量、二氧化碳含量、溶解氧含量、含水率、盐含量和pH对腐蚀速率的影响程度,实现了各因素的有效性筛选,最后在确定隐含层节点数基础上通过训练、测试建立起适宜的小波神经网络预测模型,并进一步验证了模型可靠性。结果表明：除了压力外,各因素对腐蚀速率均有十分显著的影响,属于有效输入信号。当隐含层节点数为17时,8-17-1型小波神经网络结构表现出良好的准确性和稳定性。利用Levenberg Marquardt优化算法对模型进行了反复训练,直至其均方根误差小于容许收敛误差限0.001,预测值与实际值近似呈线性关系,训练、测试阶段决定系数分别为0.9992、0.9967,相关性较高,模型预测值和验证值亦不存在显著差异。因此小波神经网络预测模型对多相动态环境下油气集输管道腐蚀速率具有良好的预测能力。     

回转式焚烧炉焚烧过程污染物的排放和影响因素控制

本文介绍回转式焚烧炉焚烧危险度物过程中产生污染物的种类和危险废物焚烧过程中的主要影响因素．危险废物焚烧过程主要影响因素包括炉温（temperature of furnace）、停留时间（residence time）、搅拌强度（intensity of agitation）和空气供给重（flow rate of air）。文章还对污染物生成特性以及污染物生成的控制措施进行探讨。     

Study on some factors affecting the results in the use of MIP method in concrete research

Effects of rate of pressure application and forms and type of sample on porosity and pore size distribution of concrete estimated through mercury intrusion porosimetry (MIP) are presented in this experimental work. Two different forms of concrete sample, namely, crushed chunks of concrete and small core drilled out from the concrete beam specimens, were used for this study. The results exhibit that the rate of pressure application in mercury porosimetry has little effect on porosity and pore size distribution of concrete. It is also demonstrated that small cores drilled out from large concrete specimens are preferable as samples for performing porosimetry test on concrete.     

乌鲁木齐市塑料垃圾年产量预测及影响因素分析

基于2008-2019年来乌鲁木齐市塑料垃圾在生活垃圾中的占比、生活垃圾清运量以及社会经济发展的相关数据,运用线性回归方程模型、ARIMA模型和灰色预测模型对乌鲁木齐市的塑料垃圾年产量进行预测,再用灰色关联度模型确定出主要的影响因素。结果表明,乌鲁木齐市塑料垃圾年产量呈线性增长趋势,由2008年的4.75×10⁴ t增长到2018年的35.14×10⁴ t;从单因素来看人均可支配收入对塑料垃圾产量的影响最大,总体来看城市人口对塑料垃圾产量影响最大,而环境建设水平则最小;通过对比,ARIMA模型是预测乌鲁木齐市塑料垃圾年产量的最优模型;预测结果表明预计到2025年、2035年和2050年乌鲁木齐市塑料垃圾年产量将分别达到54.4×10⁴、82.63×10⁴、124.91×10⁴ t。     

碱性成纤维生长因子对皮肤损伤修复作用的研究进展

皮肤损伤是临床常见疾病之一,大多由撕裂、割伤或挫伤等急性创伤导致。在皮肤损伤修复过程中,多种细胞通过分泌细胞因子参与创面愈合,如碱性成纤维生长因子(fibroblast growth factor 2,FGF2或bFGF)、血小板源性生长因子(platelet-derived growth factor,PDGF)和转化生长因子β(transforming growth factor-β,TGF-β)等,其中FGF2可通过促进血管生成、肉芽形成,减少瘢痕形成,加速上皮化促进伤口愈合。FGF2半衰期短,在体内易受酶和皮肤微环境的影响,在伤口处保留时间短暂,降低了其促进伤口愈合的能力,因此,FGF2的稳定性对其临床用于皮肤损伤修复尤为重要。本文就FGF2的分子结构及功能、FGF2受体激活的信号转导途径、FGF2在伤口愈合方面的作用机制及其在整形方面的应用作一综述。