This paper investigates the long-term performance of structural concretes in China southeast coastal area, the city of Shenzhen, exposed to atmosphere and chlorides. The structural concretes, incorporating large quantity of supplementary cementitious materials (SCM), were among the first massive application of such mixtures in construction in China. In both cases, in-field sampling and tests have been conducted during more than 20 years for the resistance of concretes to carbonation and chloride ingress respectively. The synthetic analysis of these results shows that (1) the concretes have substantial strength growth in atmospheric environment with exposure age, but the carbonation rate does not all obey the square root law of exposure time; (2) the protection of silane impregnation of high-performance concrete against chloride ingress maintains its hydrophobic effect after nearly 20 years; (3) Notable “skin” effect of surface concrete was observed for both atmospheric and marine exposures.

The physical meaning and calculating process of the rheological parameters of two nonlinear rheological models, the parabolic model and the modified Bingham model, were compared. The fluidity test and a rheological experiment on cementitious materials were performed. The Couette inverse problem is a key issue in measuring and solving the rheological parameters of fresh cementitious materials. The solution of the Couette inverse problem based on the modified Bingham model is discontinuous when the coefficient of the quadratic term is equal to zero, resulting in a large deviation between the fitting curve and the rheological experimental data. The credibility of the rheological parameters of the pastes calculated based on the modified Bingham model is low. The formulas for calculating yield stress, fiducial differential viscosity and the degree of shear thickening or shear thinning of the parabolic model have been developed. The credibility of the rheological parameters of the pastes calculated based on the parabolic model is high. The flow performance of the paste can be clearly characterized by the rheological parameters calculated with the parabolic model.

研究了丙烯酸酯均聚物乳液与酯类、聚醚类和有机硅改性聚醚类消泡剂单独和组合使用时,对自密实砂浆凝结行为、体积密度、强度、塑性收缩和干燥收缩的影响.结果表明:掺入聚合物乳液会阻碍胶凝材料的水化进程,使得其水化放热量降低,凝结时间延长;单掺聚合物乳液会显著降低砂浆的体积密度和强度,这是由于聚合物乳液的引气效应所致;单掺消泡剂可显著提高砂浆的体积密度和强度,这是由于消泡剂的消泡效应所致;复掺聚合物乳液和消泡剂,二者之间存在协同效应,通过组分优选可使得复掺聚合物乳液和消泡剂的砂浆既具有良好的力学性能,也具有良好的体积稳定性.

Neither the modified Bingham model nor the Herschel–Bulkley model can be used to characterize and calculate the performance of shear thickening of highly flowable mortar because of their incalculability of the rheological parameters. A new exponential rheological model was established to solve the characterization and calculation of shear thickening of the lubrication layer (highly flowable mortar) during the pumping of concrete in this paper. This new exponential rheological model has three rheological parameters, namely, yield stress, consistency coefficient, and consistency exponent. They can quantitatively describe the yield stress, differential viscosity, and shear thickening degree of highly flowable mortar. The calculating results of the rheological parameters of the newly established model for the mortars with different compositions showed that the consistency exponent of mortar decreased with the increase of its sand-binder ratio or the dosage of fly ash in the binder. This indicates that the shear thickening degree of mortar decreases. The consistency exponent of mortar initially decreases and subsequently increases with the increase in silica fume content or the dosage of the superplasticizer. It illustrates that the degree of the shear thickening of mortar initially decreased and subsequently increased. These varying patterns were confirmed by the rheological experiment of mortars.

The flat slab is a preferred choice for structural design because of its architectural and construction efficiency. However, flat slabs collapse frequently because of brittle punching shear failure of RC slab-column connections, which can be attributed to the low tensile strength and high tensile brittleness of conventional concrete. Engineered cementitious composites (ECC) have excellent tensile properties compared with conventional concrete. The failure modes of reinforced-ECC (RECC) slab-column connections were revealed in a recently published study by authors. In this study, three RC slab-column connections were tested further monotonically in a comparative study of RECC specimens. A specimen with a slab span of 700 mm and the reinforcement ratio of rho = 0.6% and 1.4%, and a 500-mm span specimen with a rho = 1.4% were used. The peak and residual specimen strengths were estimated and compared with the test results. The main conclusions were: (1) the punching shear failure of the RECC specimens was delayed significantly compared with the RC specimens. The RECC specimens experienced a flexural-triggered punching shear failure, with ductility ratios from 2.4 to 6.4, whereas the RC specimens usually have zero ductility. (2) The peak RECC specimen load was -2.0 times greater than that of the RC among the tested specimens. The peak strength of the RECC specimens was estimated by a yield-line mechanism, whereas the peak strength of the RC specimens was estimated by the punching shear-resisting mechanism. (3) The residual RECC load was -3.0 times greater than that of the RC among the tested specimens. The main contribution to the residual strength of the RECC specimens was by the vertical compound of axial force from steel bars that passed through the punching shear cone. The main contribution to the residual strength of the RC specimens was by the concrete cover spalling strength. (4) The comparative study verified preliminarily the feasibility of improving the punching shear performance by using ECC in slab-column connections.

Segregation resistance of Self-Consolidating Concrete (SCC), concerning the cause of Water-Reducing Admixture (WRA) over dosage and vibration, was characterized by bulk density and image analysis first. Then, the influence of segregation on the permeability of SCC was investigated by the Total Charge Passed (TCP) obtained by integrating current-time curve. Meanwhile, porosity obtained under 50 degrees C and 105 degrees C was measured, and the relationship between TCP and porosity was discussed. Research results show that both the over dosage of WRA and vibration will lower the segregation resistance of SCC, and the effect of the later is more significant than that of the former; both bulk density distribution analysis and image analysis can be an effective way for evaluating the segregation resistance of SCC. Segregation will decrease the permeability of SCC, and there is power function relationship between bulk density and TCP, showing the significant influence of segregation on the permeability of SCC. Enhance the sand to paste volume ratio (STPVR) in the mix proportion of SCC benefits the segregation resistance of SCC on the effect of WRA over dosage, however, the increase of STPVR increases the permeability of SCC. Relationship between TCP and porosity showed that the porosity obtained under 50 degrees C (capillary porosity) is more appropriate than the porosity obtained under 105 degrees C (permeable porosity) for evaluating the permeability of SCC. (C) 2020 Elsevier Ltd. All rights reserved.

基于最优化方法,给出使用同轴双圆柱流变仪来获取胶凝材料浆体的Bingham流变参数的途径;探究五种矿物掺合料(粉煤灰、矿渣粉、硅灰、石英粉、粉煤灰微珠)和两种化学外加剂(减水剂与引气剂)对胶凝材料浆体流变参数的影响.研究结果表明:矿物掺合料等体积替代水泥相对于等质量替代水泥,对降低浆体的屈服应力和塑性黏度有利.粉煤灰可降低浆体的屈服应力和塑性黏度;矿渣粉和石英粉可降低高水胶比浆体的屈服应力和塑性黏度,但增大低水胶比浆体的屈服应力和塑性黏度;硅灰可显著提升浆体的屈服应力;粉煤灰微珠可降低浆体的塑性黏度但增大其屈服应力.减水剂可降低浆体的屈服应力和塑性黏度;引气剂可降低浆体的塑性黏度.矿物掺合料和化学外加剂对胶凝材料浆体的Bingham流变参数的影响,取决于水胶比、矿物掺合料或化学外加剂的掺量、矿物掺合料颗粒粒径、粒形和水化活性等因素,因此使得胶凝材料浆体的流变参数随着矿物掺合料和化学外加剂种类和掺量的变化,表现出非线性特征.

分析了使用同轴双圆柱流变仪测试Bingham流体流变参数(屈服应力和塑性黏度)时,非剪切区对转速-扭矩曲线的非线性和连续性的影响,以及非剪切区对Bingham流体剪切应变速率的影响.对使用转速-扭矩曲线的线性段来获取Bingham流体流变参数的可行性进行了分析,提出了使用同轴双圆柱流变仪,在考虑非剪切区存在与否的情况下,利用剪切应力-剪切应变速率曲线获取Bingham流体流变参数的方法.同时,提出了剪切应力-剪切应变速率计算过程中的去噪声方法,实现了剪切应力-剪切应变速率曲线的高精度获取.

混凝土泵送过程中的泵送压力和沿程泵送压力损失是决定混凝土能否泵送及泵送效率的关键参数.使用贴片式压强计测量实际工程中混凝土泵送压力及沿程泵送压力损失,研究混凝土强度等级、工作性和泵送速度等因素对沿程泵送压力损失的影响,并通过水平盘管泵送试验验证开孔式及贴片式压强计测试结果相关性.研究结果表明,在保证混凝土均匀密实的前提下,高强混凝土和大流态混凝土泵送压力及沿程泵送压力损失较小;匀质性较差或离析混凝土泵送压力及沿程泵送压力损失较大,堵泵风险较高;实测工作性良好的大流态C60混凝土超高程泵送过程中的沿程泵送压力损失小于Morinaga经验公式预测值.

对39个强度等级为C35的大流态混凝土,通过协方差分析和图像分析,探讨了配合比参数对混凝土工作性、强度、抗渗透能力和抗离析能力的影响;通过非线性拟合,探讨了胶凝材料体系中的矿物掺合料的活性系数高低及其对强度发展历程的影响.研究结果表明:混凝土的工作性、强度和抗渗透能力与配合比参数之间为多元约束关系,影响工作性的显著因素是减水剂掺量、水胶比、砂率和浆骨比,影响强度的显著因素是粗骨料级配、水胶比、胶凝材料用量和减水剂用量,影响抗渗透能力的显著因素是胶凝材料用量、水胶比、粗骨料级配和减水剂用量.图像分析结果可量化表征混凝土的离析程度,39个大流态混凝土均具有良好的抗静态离析能力.矿物掺合料的水化活性随龄期的发展而变化,矿渣粉在28 d龄期时展示出水化活性,粉煤灰在90 d龄期时展示出水化活性,石灰石粉在90 d龄期时依然未展示出水化活性.混凝土的强度与抗渗性之间展示出指数关系,且两者之间的关系的离散性反映了胶凝材料用量、水胶比、矿物掺合料水化活性和粗骨料级配的综合影响.

给出了新拌水泥基材料流变参数的测量制度及测量数据的处理方法,对比分析了直接利用流变仪显示的剪切应力与剪切应变速率、利用一些近似的计算公式以及利用Couette逆问题的解等3种新拌水泥基材料流变参数计算方法的可行性.结果表明:利用Couette逆问题的解计算新拌水泥基材料的流变参数方法合理,给出了相应的计算步骤.在计算新拌水泥基材料的流变参数时,必须考虑柱塞流的影响.舍去存在柱塞流情况下得到的测量数据后计算出的水泥基材料的流变参数的精确度更高.

Lots of skyscrapers are or will be built in China. High strength self-consolidating concrete is used to construct composite steel concrete pillars and shear walls of core tube. It is introduced how to prepare high strength self-consolidating concrete with local raw materials and the controlling index for the workability of fresh concrete pumped to different heights. The pumpability of fresh concrete was evaluated in laboratory and in-site using normal workability evaluation methods and Sliper, a newly developed instrument to estimate pumpability of fresh concrete. A simulating pumping process of high strength self-consolidating concrete was done to investigate its performance using an experimental pumpline circuit with the total length of 2300 m. C100 concrete was pumped one time to the height more than 1000 m and cast without vibration in Shenzhen, China. Super-highly pumping of C70 self-consolidating concrete is widely performed now in the construction projects of skyscraper in China.

研究了砂率和浆骨比对大流动性混凝土(HFC)新拌性能的影响.对2种强度等级的HFC,通过改变砂率与浆骨比制得不同性能的拌合物.通过流变试验、工作性试验和滑管试验,研究了HFC的新拌性能.结果表明:HFC的流变性能和工作性对砂率和浆骨比的变化较为敏感.随着砂率的增加,HFC与润滑层的屈服应力与塑性黏度先减小后增大.砂率改变6.38％,HFC屈服应力的变化幅度可高达约27％,塑性黏度的变化幅度可高达约78％.随着浆骨比的增加,HFC与润滑层的屈服应力和塑性黏度逐渐减小.浆骨比改变16.07％,HFC屈服应力的变化幅度可高达约331％,塑性黏度的变化幅度可高达约204％.混凝土工作性的变化规律与其流变性能的变化规律一致.滑管试验所预测的混凝土泵压与流量之间的线性关系只能反映出润滑层对泵送过程的贡献.基于滑管试验所得的润滑层的屈服应力的可信度较低.

研究了两种高强合成纤维在工程用纤维/水泥复合材料制备过程中的适用性,其中,芳纶纤维的表面为亲水性,超高分子量聚乙烯(UHMWPE)纤维的表面为憎水性.研究结果表明:工程用芳纶纤维/水泥复合材料拉伸破坏过程中无应变硬化能力且表现为单裂纹破坏现象;工程用UHMWPE纤维/水泥复合材料拉伸破坏过程中表现出良好的应变硬化能力和多裂纹开裂特性.因此,两种纤维相比,UHMWPE纤维适宜于工程用纤维/水泥复合材料的制备.随着水胶比的降低,工程用UHMWPE纤维/水泥复合材料抗拉强度增大,但应变硬化能力降低,因此,在制备工程用UHMWPE纤维/水泥复合材料的过程中,应协调纤维抗拉强度和基体与纤维之间界面过渡区的品质.

采用平板受限法和图像法,研究了膨胀剂提升混凝土抗塑性开裂的能力.研究结果表明,吹风加速混凝土表面失水条件下,不同水胶比(0.21～0.43)的混凝土均会发生塑性开裂,且随着水胶比的降低,混凝土的塑性开裂状况加剧;膨胀剂提升混凝土抗塑性开裂的能力与混凝土的水胶比有关,膨胀剂提升混凝土抗塑性开裂的效果随着水胶比的降低而减小,甚至出现负作用.同时,研究结果表明,吹风加速表面失水对诱导混凝土产生塑性开裂有显著作用,因此,对浇筑成型的混凝土结构进行及时的养护,在避免和减缓混凝土结构的塑性开裂方面具有重要作用.

High-strength Engineered Cementitious Composite (HSECC) usually features with low water-to-binder ratio (W/B) and low sand-to-binder ratio (S/B), for obtaining expected workability, mechanical property and multi-crack behavior. However, the low W/B and low S/B of HSECC can cause high shrinkage, which will jeopardize its volume stability and durability. In this paper, the influence of W/B and S/B on HSECC volume stability including chemical shrinkage, autogenous shrinkage and drying shrinkage, mechanical properties including compressive strength, tensile strength, tensile strain and tensile strain energy were investigated. Experiment results showed that in the W/B range of 0.13–0.24, S/B range of 0.3–0.9, the magnitude of chemical shrinkage overwhelms autogenous shrinkage and drying shrinkage; meanwhile, along with the increase of W/B and S/B, the total shrinkage is lowed and the magnitude of autogenous shrinkage tends to be comparable with drying shrinkage. In the W/B range of 0.13–0.24, along with the increase of S/B from 0.3 up to 0.8, the compressive strength and tensile strength was enhanced, however, the ductility of HSECC was lowed especially when S/B was greater than 0.6; when S/B was enhanced to 0.9, all the mechanical properties and ductility was severely injured. So, the optimum S/B of HSECC should be decided by systematically considering its influence on volume stability, mechanical strength and ductility.

This paper extracts the elements of energy transition issue,emphasizing that the behaviors of stakeholders such as policy makers,and energy suppliers can impact the energy transition dynamic significantly.The main aims(explanation, prediction,projection,and optimization),contents,and challenges of energy transition researches are presented,and the state-of-the-art research paradigms for energy transition and their limitations on addressing the challenges introduced by human behaviors are reviewed.Finally,this paper suggests a new research paradigm,hybrid simulation of technology-economic-behavior model with human participants,in which the energy transition target and pathway is optimized by repeatedly carrying out experimental economic simulation.The subsequent paper will discuss the uncertainties and analysis approaches in the energy transition researches.

The effect of a nanoscale viscosity modifier (called NP) on rheological properties of cement pastes and mechanical properties of mortars was experimentally studied. The morphology of NP agglomerates and its dispersed status was investigated by SEM. With different NP contents, the yield stress, plastic viscosity and thixotropy of pastes and the flexural strength and compressive strength of mortars were investigated and compared with plain cement paste and mortar at different water-to-cement ratios. The results illustrate that the incorporation of NP can increase plastic viscosity and yield stress of cement paste significantly. Its thixotropy varies simultaneously as well. The mechanical properties of mortars can be improved when the NP content is less than 1.0%. The reticulate structure formed by nanoscale rod-like NP particles with huge surface area in paste flocculates some water to modify the rheological properties of cement paste. (C) 2018 Elsevier Ltd. All rights reserved.

Proper curing method should be adopted to prevent concrete freeze-thaw damage and hindered strength development when constructing bridge expansion joint under cold weather.The effect of different curing methods were evaluated by measuring the tempera-ture field of concrete and surrounding air temperature.Research results manifest that XPS plate is an effective way for maintaining concrete temperature,and electronic blanket is an effective way for heating concrete.Plastic shed with iodine-tungsten lamp and canvas shed could not work as an effective way to maintain concrete temperature or heating concrete.Suggests on proper curing method for concrete bridge expansion joint construction under cold weather is give.

考察了合金刀片切割、高压水刀切割、X射线CT切割三种方法,获取钢纤维混凝土二维切片的工作能力和切片质量.分析结果表明:合金刀片切割方法具有设备普及程度高和可切割试样尺寸大的优点,但会导致切割后的钢纤维断面尺寸增大,该尺寸增大现象可通过后续的磨抛来消除,因此,该方法是一种获取钢纤维混凝土二维切片的经济、可行方式;高压水刀切割方法具有可良好保持钢纤维断面形貌的优点,但会导致混凝土基体中出现槽道,槽道的起点为混凝土基体中的气孔、深度可达mm量级,难以通过磨抛的方法消除,因此,不推荐该方法作为钢纤维混凝土的切割手段;X射线CT切割具有对混凝土中钢纤维不产生扰动和实现任意平面方向切割的优点,是一种表征钢纤维混凝土中钢纤维分布的精细手段,但X射线切割设备的工作能力受限于X射线的能量,因此只适用于中小型(尺寸不大于100mm)钢纤维混凝土试样的切割.