基于MPS方法的自密实混凝土流动数值模拟

采用三维移动粒子半隐式(MPS)法来分析和预测自密实混凝土(SCC)的流动性,对L形箱试验进行数值模拟,对比分析了数值模拟与试验中SCC的流动形态和流动时间.在此基础上,研究了L形箱试验和V形漏斗试验中塑性黏度对SCC流动性的影响,并建立了SCC密度和塑性黏度与V形漏斗试验下落时间的关系.结果表明:使用基于Bingham流变模型的MPS方法可以较好地模拟SCC的流动特性,且精度较高;MPS方法可以对SCC在施工过程中的流动时间和流动形态进行模拟预测,结合流变参数分析可以为SCC工程的设计和施工实践提供参考依据.     

自密实混凝土充填堆石体试验研究

本文利用自密实混凝土高流动抗分离的性能,借鉴已广泛应用的压浆混凝土施工方式,提出一种新的混凝土施工方式．即利用自密实混凝土充填预先放置的堆石体,待自密实混凝土硬化后与堆石一起形成堆石混凝土。为了检验自密实混凝土充填堆石体的施工工艺的可行性,验证堆石混凝土硬化后的强度性能,本文设计并实施了堆石混凝土充填试验,利用低水泥用量自密实混凝土对堆石体进行充填,初步验证了堆石混凝土的性能,为这种新型的混凝土施工方式打下了基础。     

堆石混凝土三维力学模型建模方法

为建立堆石混凝土三维力学模型,首先采用三维随机多面体来模拟堆石颗粒,提出了堆石颗粒的空间随机分布算法和密实算法;其次提出了自密实混凝土填充算法,生成了堆石混凝土三维力学模型;最后利用建立的三维力学模型,分析了单轴受压条件下,堆石混凝土结构组成对其力学性能的影响,并将计算结果与试验结果进行了对比.结果表明:所建立的堆石混凝土三维力学模型不仅能够反映堆石颗粒大小、形状和空间分布的随机性,还能反映其密实过程和堆石体骨架对堆石混凝土力学性能的影响,具有一定的可靠性,可以弥补试验条件的限制,为进一步研究堆石混凝土力学性能提供参考.     

C20自密实混凝土在堆石混凝土中的应用

主要介绍了C20自密实混凝土在堆石混凝土中的应用,然后通过试验研究,初步验证了自密实混凝土的抗压强度、抗渗性和抗冻性以及堆石混凝土芯样抗压强度。     

自密实堆石混凝土力学性能的试验研究

以试验为基础讨论堆石混凝土的力学性能,试验试样直接从自密实堆石混凝土大型试块中切割取样,其尺寸为1 500 mm×500 mm×500 mm.强度试验确定堆石混凝土的立方体抗压强度、棱柱体抗弯强度、棱柱体轴心抗压强度及其力学特征;控制自密实混凝土的自流动距离在1 500 mm范围内,可形成不低于自密实混凝土配制强度的堆石混凝土;堆石混凝土棱柱体轴心受压应力-应变关系曲线基本接近直线,其比例极限和强度极限接近,只有微小的塑性变形,破坏呈突发式纵向劈裂;试样断口形态表明:堆石混凝土中的块石与自密实混凝土界面具有较好的黏结性.     

红外成像技术应用于堆石混凝土密实度检测方法的研究

堆石混凝土的密实度是表现耐久性和抗渗性的重要指标.为了研究其密实度检测方法的可行性,将堆石混凝土应用于兰新线乌西至精河段部分增建二线工程中,并在现场进行相关试验研究.其中在部分试验段,运用密实度计量分析法、钻孔取芯与芯样评定法、超声波检测及红外成像技术无损检测4种方法对堆石混凝土密实度进行检测,通过对检测结果的对比分析...     

再生大骨料-自密实砂浆堆石混凝土力学性能研究

为研究再生大骨料粒径、原始强度和自密实砂浆强度对再生大骨料-自密实砂浆堆石混凝土力学性能的影响,采用压力机对7组不同再生大骨料-自密实砂浆堆石混凝土试块进行了一系列试验研究。结果表明:自密实砂浆能够充分填充更小骨料粒径构成的堆石体,骨料粒径由100 mm降至60 mm时,自密实砂浆仍可充分地填充堆石体,其立方体抗压强度仅下降5.97%,而轴心抗压强度与劈裂抗拉强度的降幅均在可行范围内,侧面反映出自密实砂浆可填充再生大骨料堆石体且效果显著; 在再生大骨料-自密实砂浆混凝土棱柱体轴心受压的应力-应变关系中,再生大骨料-自密实砂浆堆石混凝土的强度、静态弹性模量和峰值压应变均与骨料粒径、自密实砂浆强度和再生骨料原始强度呈正相关,再生骨料粒径的影响小于再生骨料原始强度和自密实砂浆强度的影响; 通过拟合提出的再生大骨料-自密实砂浆堆石混凝土的强度计算公式和单轴受压多项式型本构模型、有理分式型本构模型计算结果与实测值吻合度良好。     

高强堆石混凝土研制及其特性研究

借鉴水利水电行业堆石混凝土技术,研制了一种可用作遮弹层材料的新型高强堆石混凝土。研究配置了C100高强自密实混凝土,提出了大粒径岩石粒径大小、形状和物理力学性质等技术要求。通过堆石混凝土浇注试验研究了C100自密实混凝土流动性能,验证其能很好充填大粒径块石的空隙,靶体试验表明其力学及工作性能达到设计要求。     

自密实混凝土流动性试验及其神经网络预测研究

在对不同配合比情况下新拌自密实混凝土的流动性进行了试验研究的基础上,利用MATLAB的神经网络工具箱对试验结果进行了人工神经网络预测分析。研究表明利用人工神经网络数值模型能够较好地预测新拌自密实混凝土的流动性能。     

核电站循环水廊道自密实混凝土浇筑技术

循环水廊道为压水堆型核电站必备的进出水结构,在阳江核电站按1∶1模型对循环水廊道自密实混凝土施工进行模拟试验,对掺纤维自密实混凝土在循环水廊道结构中的填充性能、抗离析性能、钢筋通过能力等进行研究,结构施工完成后通过切割及钻心取样进行观察,得出了自密实混凝土可以在核电站循环水廊道中使用的结论.     

山区高速公路填石路堤现场压实质量检测方法

以南方某高速公路填石路堤为例,分析比较了击实法和振动台法确定填石料室内最大干密度;用水袋法对现场填石料密度进行了测定,并以此为基础推算原级配填石料的最大干密度,探讨了山区高速公路填石路堤压实检测方法,提出了以压实度作为控制标准的压实检测方法,并在现场铺筑试验路段加以验证。     

红层软岩土高填方边坡变形特征分析

红层地层在我国分布广泛,红层软岩土是一种特殊岩土,其颗粒易破碎,强度低,遇水后易崩解与软化,其工程性质很难满足站场路堤填料要求。该文结合站场填方工程实例,针对采用红层软岩土这一特殊填料的高填方边坡,通过数值模拟对不同压实度下其填方区竖向位移、边坡水平位移以及应力状态进行分析,以确定合适的填筑压实度;同时,对填筑边坡的稳定性进行分析,提出了填筑边坡可能存在的最不利滑面位置。     

基于GRNN理论的自密实混凝土间隙通过性研究

提出了用GRNN模拟评价自密实混凝土间隙通过能力的方法.通过10组C30和10组C40自密实混凝土的V型漏斗试验测得V型漏斗时间、坍落度试验测得扩展度和坍落度来确定自密实混凝土配合比,然后分别进行无环及环径为300 mm的钢筋净距为最大粒径1、2、2.5、3倍的J-ring联合倒坍落度简方法试验,测得环内多点高度、环外...     

Kugelfallrheometer zur Prüfung von Selbstverdichtendem Beton

Falling-Ball Rheometer to prove Self-Compacting Concrete Self-compacting concrete (SCC) is a high-performance concrete whose performance is predicated by the flow characteristics of the fresh concrete mix. In a fresh state, SCC may be viewed as a two-phase suspension containing coarse disperse aggregates as well as a viscous mortar that, when compared to conventional concrete, achieves its specific flow characteristics through a relatively high mortar content. The selection of appropriate raw materials – particularly for manufacture of plastic mortars – are essential factors in determining the rheological properties and thus performance of the concrete. By adding organic or inorganic admixtures, or a combination thereof, one may influence the flow characteristics of the mortar. Mix design for SCC is largely dictated by the rheological properties of the fresh concrete, such that the volumetric design approach, as used for conventional concrete with a given design compressive strength, is no longer applicable. This paper reviews the possibility to optimize the viscosity of mortar by replacing cement by rock powders with the objective to design SCC with normal strength. A research investigation has been conducted, investigating the effect of rock powders on flow characteristics of mortar matrices. Self-compacting concrete requires a careful control of its flow behaviour. Fresh concrete acts as a non-Newtonian fluid. It is insufficient to describe the rheological behaviour of non-Newtonian fluids with a conventional one-point workability test. Rheological measurements are essential, to determine the flow behaviour dependent on the shear rate and to modify the mixture with the aim to achieve self-compacting properties. In order to measure the flow behaviour of SCC, the authors developed a rheometer which can be used simply.     

基于SPH粒子法的盲天井掏槽爆破数值模拟

针对上向盲天井掏槽孔爆破效果,运用补偿系数法对周边大空孔孔间距进行计算并进行方案制定,利用光滑粒子流体动力学方法(SPH粒子法)进行数值模拟计算,开展盲天井掏槽爆破周边空孔作用以及补偿系数对爆腔及岩石损伤范围影响研究。研究结果表明:在孔间距一定时,爆腔面积随补偿系数增大呈增加趋势;当补偿系数达到2.42时爆破效果最佳且达到峰值0.54 m²,而后爆破效果作用达到极限,爆腔面积变化趋于稳定;岩石损伤范围因炸药作用效果有限,总体变化范围在10%以内;模拟过程中SPH粒子能良好地模拟出爆破过程中岩石运动状态、空孔填充情况以及岩石损伤范围。所得模拟结果与现场试验爆腔断面面积吻合度高,说明数值模拟计算具有一定的准确性。     

Evaluating damage during shear tests of rock joints using acoustic emissions

The acoustic emission (AE) signals generated during direct shear test were evaluated on different types of joints (rock–rock, rock–concrete and concrete–concrete). Several boreholes were cored from a dam body, rock mass and interface between dam and rock mass, and the samples were prepared and tested under direct shear test. A laser profilometer scanner was used for scanning the joint surfaces in order to assess surface roughness. By correlating the AE signals with the shear graphs one can predict the starting point of shearing during direct shear test. Count and energy parameters were analyzed in two different methods to monitor the shear behavior of the joints: a graph of the count and energy rates, and a graph of cumulative count and energy. Four separated periods were observed for bonded and non-bonded joints: linear pre-peak period, non-linear pre-peak period, post peak period and residual period. This study showed that AE has enough accuracy to monitor the shear behavior of the joints and it can be used in site confidently.     

青藏高原低气压环境下钢管混凝土的核心混凝土密实性评估方法研究

为研究高海拔低气压条件对混凝土抗压强度与超声波速相关性的影响,分别在高海拔地区(西藏山南)与低海拔地区(广西南宁)进行了不同水灰比混凝土试件的制备与强度、超声波速测试,研究表明,低气压条件下7～56d龄期混凝土的抗压强度比标准气压条件下相同配合比混凝土高出约5.8%～38.2%;低气压条件下混凝土的超声波速低于标准气压条件下相同强度混凝土,不同气压下混凝土超声波速与强度存在不同的线性关系,并在此基础上提出了不同气压下混凝土超声波速与强度的相关关系模型。通过压汞试验(MIP)及数值模拟分析,揭示了混凝土超声波速受微观结构中固体超声波速及孔隙率两因素共同影响的机理,建立了不同气压下混凝土固体超声波速的计算模型。基于混凝土超声波速与强度的相关性及不同灌注工艺的密实程度,提出了不同气压条件下钢管混凝土的核心混凝土密实性评估方法。     

Effect of slag on the rheology of fresh self-compacted concrete

The building industry is turning increasingly to the use of self-compacting concrete (SCC) in order to improve many aspects of building construction as SCC offers several advantages in technical, economic, and environmental terms. Fresh self-compacting concrete (SCC) flows into place and around obstructions under its own weight to fill the formwork completely and self-compact without any segregation and blocking. SCC mixes generally have a much higher content of fine fillers. The use of supplementary cementitious materials is well accepted because of the improvement in concrete properties and also for environmental and economical reasons. The present paper is an effort to quantify the influence of Algerian slag on the properties of fresh and hardened self-compacting concrete. The workability-related fresh properties of SCC were observed through slump flow time and diameter, V-Funnel flow time, J-Ring test, U-Box filling height and GTM sieve stability test. The only hardened property that was included in this study was the compressive strength. An optimum slag content of 15% seems to give a good SCC mixture with workability retention of about 60 min. A decrease in compressive strength with increase of slag content was obtained, but this decrease in compressive strength is less important at late ages (56 and 90 days after mixing).