共查询到17条相似文献,搜索用时 531 毫秒
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研究了粉煤灰掺量、加载龄期和加载应力对粉煤灰混凝土早期变形及加载后强度变化的影响。研究结果表明:随着粉煤灰掺量增加,混凝土的变形量逐渐降低,当掺量为30%时,变形量减少了33.6%;随着加载龄期提前或加载应力增大,粉煤灰混凝土的早期变形量增大,其中,加载应力的影响尤其明显,60%加载应力(60%的标准养护条件下7 d轴心抗压强度)比20%加载应力下混凝土最终变形量增加了277.2%;混凝土初始加载时间提前或加载应力增大会导致加载后粉煤灰混凝土强度下降,加载应力比加载龄期对加载后粉煤灰混凝土强度的影响更明显。 相似文献
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通过对内贴应变片钢筋的直接拔出试验,分析冻融作用下粉煤灰掺量对钢筋与粉煤灰混凝土间粘结性能的影响,得出冻融循环作用对钢筋与粉煤灰混凝土之间粘结性能的影响规律。试验结果表明:钢筋与粉煤灰混凝土的粘结强度随粉煤灰掺量的增加而降低;当粉煤灰掺量一定时,随着冻融循环次数的增加,混凝土强度有所下降,钢筋与粉煤灰混凝土间极限粘结强度降低;当粉煤灰掺量较大,达到40%时,随冻融次数的增加,钢筋粉煤灰混凝土试件极限粘结强度的下降幅度明显减缓,极限粘结强度对应的滑移量增大。表明掺入较多粉煤灰可使试件的冻融损伤现象得到缓解,冻融环境下钢筋混凝土的粘结性能得到提高。 相似文献
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早龄混凝土的拉伸、压缩徐变规律及其结构徐变应力计算方法是对早期裂缝进行有效预测并控制的关键。既有的徐变研究主要侧重于成熟混凝土,而早龄混凝土徐变相关的科学研究还有待进一步深入。对早龄混凝土的压缩和拉伸徐变研究成果、测试方法及其徐变应力计算方法进行了详细综述。研究表明:目前混凝土早龄期拉伸、压缩徐变试验测试尚无规范可循,相关试验数据较为缺乏;混凝土早龄期徐变预测模型基本未考虑其在低应力水平下的非线性性质;早龄混凝土结构非线性徐变应力理论分析方法亦不尽完善。基于系统试验研究和固化徐变理论建立混凝土非线性徐变理论模型,对早龄混凝土结构采用同时考虑受拉和受压不同应力松弛特性的非线性徐变应力理论计算方法,应可提高早龄结构的有限元仿真精度。 相似文献
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(目的)为了将解决农业废弃物油菜秸秆的去向问题和新型墙材的研发结合起来,(方法)本文对油菜秸秆进行碱处理后,以砂率和不同比例的秸秆掺量为变量,制成300mm×300mm×30mm的试件,通过稳态平板导热仪测试其导热系数,使用电镜(SEM)扫描混凝土内部微观结构,从宏观和微观角度研究油菜秸秆纤维混凝土的保温性能。试验结果表明:(结果)不同秸秆掺量的各试验组及对照组,砂率为25%的混凝土相较于砂率取40%的混凝土导热系数均降低了约10%,(结论)即总体呈现砂率越高导热系数越大试件保温性能越差的趋势;(结果)不同砂率的各试验组及对照组,秸秆纤维掺量为2.5%的混凝土试件比秸秆纤维掺量为0%的混凝土试件的导热系数均降低了30%左右,(结论)即秸秆掺量越大,导热系数越小,试件保温性越好。 相似文献
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为合理利用废弃材料改善生土材料力学性能,通过在素土中掺入糯米浆、废玻璃渣和橡胶,形成改性土体材料,设计5种配合比方案,制作Φ102 mm×116 mm圆柱体试块。通过对其进行轴心抗压强度试验,对比不同配比试件的试验现象、抗压强度、变形能力、荷载位移曲线,分析不同掺合料的作用机理、研究不同掺料不同掺量对抗压强度的影响规律,提出了玻璃渣和橡胶掺量的合理范围。试验结果表明,在素土中掺入糯米浆能提高素土抗压强度,掺入糯米浆、玻璃渣和橡胶,可提高抗压强度和变形能力,但其抗压强度随玻璃渣和橡胶掺量的增多增至3.12 MPa后下降。 相似文献
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为研究粉煤灰的硅酸盐水泥浆体的电阻率、化学收缩及自收缩的变化规律,定量描述水泥基材水化过程中自收缩和未充水毛细孔体积在化学收缩中所占的比例变化,测定了不同水胶比和粉煤灰掺量的早龄期水泥基浆体的电阻率、化学收缩和自收缩。结果表明:水泥基浆体在硬化减速期的电阻率随时间对数的曲线斜率K和浆体3 d抗压强度成线性关系,并进一步论证了K值对水泥浆体结构密实速度的物理意义及其推测强度的应用价值;浆体的化学收缩和自收缩分别随水胶比升高或粉煤灰掺量增大而降低。浆体在24 h后的单位体积化学收缩和30 h后的自收缩随电阻率的发展均表现出线性关系。定量地提出了终凝后自收缩变化量与终凝后线性化学收缩变化量的比例参数γ的概念,较小的γ值表明:与未充水毛细孔相比,自收缩的比例很小;同一样品的比例参数γ表现出随水化时间逐渐减小。 相似文献
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为了研究混杂纤维喷射混凝土的弯曲韧性,采用不同掺量的钢纤维和聚丙烯纤维混杂以及高炉微粉复合超叠加的方法制备600 mm×600 mm×100 mm混杂纤维喷射混凝土方板并置于刚性支撑架上,选用等位移控制对方板进行中心加载。通过生成的荷载挠度曲线及对其进行积分所得的能量吸收值综合评价各组方板的弯曲韧性,同时,通过破坏过程评价各板裂缝控制能力。试验结果表明:掺入1.2%钢纤维和0.11%聚丙烯纤维的喷射板试件的弯曲韧性优于掺入0.8%钢纤维和0.11%聚丙烯纤维的喷射板,其最大峰值荷载提高了18%,板中心挠度至25 mm时的能量吸收值也提高了25.6%;对于仅掺入0.8%单一钢纤维的板,混杂了0.11%聚丙烯纤维后,两种纤维间的正混杂效应使得板中心挠度至25 mm时的能量吸收值提高了28.5%;高炉微粉掺量的增加能提高混杂纤维喷射混凝土板的弯曲韧性;混杂纤维喷射混凝土板均展现出了良好的裂缝控制能力,板整体呈现裂而不断的延性破坏。 相似文献
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The influence of three kinds of additives: silica fume,slag and fly ash on the sulphate attack resistance of concrete were studied.The experiment results show that these three kinds of additives can improve sulphate attack resistance of the concrete and the order of their efficiency from high to low is silica fume,slag and fly ash;the development of mortar expansion value is closely related to the degree of sulphate attack resistance of the concrete;integrated assessing two concrete properties: mortar expansion value and compressive strength ratio can more exactly assess the sulphate attack resistance of the concrete. 相似文献
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Being the largest mass of man-maded material, concrete demands much to resource and energy as well as affects much to environment. Whether concrete can be the dominating constructive material, the key is whether it can become green material and protect the environment at the same time. The important approach of developing is using industrial castoff largely in concrete. The tests note, that high performance concrete used of large mass of fly ash is doable. By grinding fly ash and adding high-efficient water reducer, when the dosage of cement clinker is only 25% and the dosage of fly ash is 70%, concrete with a good workability that 3 day and 28 day strength are bigger than 20 MPa and 50 MPa respectively can be achieved, which later strength develop very well. The large mass of fly ash concrete can utilize fly ash largely and reduce the dosage of clinker, that is very advantageous to protect environmental. 相似文献
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Lei Yingping 《保鲜与加工》1996,(3):78
A high strength concrete with 28 day strength up to 80 MPa from superfine sand with fineness modulus of 0.56 is obtained.It has a permeability resistance of 4.0 MPa and small shrinkage creep.Experiment and study were carried out on its pore structure,hydration products and microhardness of transient area in cement paste and aggregate interface. The essence for high strength of such concrete was revealed. 相似文献
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Adiabatic temperature rise of mass concrete is effected by many factors. Among those factors, the analysis of cement fineness and components is lacking. Influences of cement fineness, alkali content, replacement of fly ash, and gypsum content on temperature rise of concrete were investigated. The test results show that, temperature rise and temperature rise rate are improved with the increment of specific surface area of cement. When alkali content is ranging from 0.4% to 1.2%, the maximum temperature is reduced with the increment of alkali content, and the temperature-time will be extended whether too high or too low alkali content in cement. The increment of replacement of fly ash and gypsum content is good for reducing temperature rise of concrete. 相似文献
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To optimize properties of the crushed rock is a simple and effective method to control the reflective cracking.There are some measures to reduce the shrinkage of the crushed rock,such as: decreasing water content and cement percentage,reducing surface tension of water.The test study shows that shrinkage resistance of the crushed rock base can be improved by mixing with fly ash,water reducing agent and shrinkage reducing agent each other,it will be better for the crushed rock to mix with fly ash,water reducing agent and shrinkage reducing agent proportionally. 相似文献
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The time-changing analysis model for concrete filled steel tubes was established based on the time-changing concrete model of CEB-FIP MC90, in which the interaction between steel tube and concrete core was considered by the restraint conditions of master and slave nodes. The numerical simulation method was developed for analyzing the whole construction process of high-rise CFST structures. A real structure was taken as numerical example, in which the influence of concrete creep and shrinkage as well as construction process was considered. The results of numerical simulation are compared with those obtained from on-site monitoring. It is shown that the concrete creep and shrinkage as well as construction process have big influence on high-rise CFST structures, which should be taken into account in designs and constructions. 相似文献
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In this paper, the influences of different kinds and different amount of mineral admixture to Cl-penetration and diffusion in concrete are studied. The results of experiment show that separate addition of mineral admixture (ground fly ash, slag fines, silica fume) into concrete can improve its resistance to chloride ion penetration and diffusion. Furthermore,the effect of silica fume is the best, fly ash second, and then follows slag fines. Mechanism analysis shows that the pozzolanic effect of mineral admixture improves the interface between the cement and aggregate in concrete, reduces the total porosity, makes pores more smaller, on the other hand it increases the Cl-consolidation capability of concrete with low alkaline C-S-H gel produced. So the resistance to chloride ion penetration of concrete is improved. 相似文献