混凝土的毛细吸水特性及其与孔结构的关系

为了更好地理解混凝土的毛细吸水特性,研究了不同混凝土种类、钢纤维掺量、养护条件对混凝土溶液吸入量的影响,给出了毛细吸水系数,分析了孔结构与毛细吸水系数的关系。结果表明:不同混凝土(损伤与未损伤) 15～180 min和180～480 min两阶段溶液吸入量均与t~(1/2)呈线性关系;超高性能混凝土(UHPC)的毛细吸水系数远小于高性能混凝土(HPC);随着钢纤维掺量的增加,UHPC的溶液吸入量和第一阶段毛细吸水系数均增大;未水化胶凝材料再水化作用影响下,水中养护UHPC的720 d溶液吸入量略大于自然养护的;毛细吸水系数主要受到100～3 nm范围内孔含量的影响,且第一阶段毛细吸水系数随其含量增加而增大;考虑孔隙率的影响下计算累积毛细吸水高度,其计算结果与实际相符。     

EVA聚合物乳液对蒸养水泥砂浆抗渗性能的影响

研究了不同EVA乳液的掺量(0、5%、10%)及养护制度(标准养护、蒸汽养护)对水泥砂浆氯离子迁移系数、毛细吸水率以及孔结构的影响规律。结果表明,EVA乳液的掺入,可以有效提高水泥砂浆的抗氯离子渗透性能,且在蒸养水泥砂浆中的提高作用较标准养护的水泥砂浆更为明显。蒸养与标准养护的水泥砂浆初始阶段吸水系数S_i与第二阶段吸水系数S_s均随着掺入乳液质量的增加而降低。氮吸附的结果表明,蒸养制度下的聚合物改性水泥砂浆表现出更密实的孔隙结构。     

玻璃粉混凝土干燥收缩影响效果及作用机理研究

玻璃粉既能作为辅助胶凝材料又能有效抑制混凝土的干燥收缩,是当前绿色混凝土的一个研究热点。对比恒温恒湿环境和自然环境养护下,玻璃粉掺量、粒径以及环境温度、湿度对混凝土干燥收缩的影响效果和变化规律,分析其作用机理。结果表明:(1)恒温恒湿和自然环境养护下,掺入10%~30%掺量和0~75μm粒径的玻璃粉均能有效抑制混凝土的干燥收缩;(2)玻璃粉抑制干燥收缩的效果随玻璃粉掺量增加而增大,随玻璃粉粒径减小而增大;玻璃粉掺量对混凝土干缩率的影响效果大于玻璃粉粒径对混凝土干缩率的影响效果;(3)相较于环境温度,环境湿度对玻璃粉混凝土的干燥收缩影响更大。     

恒温恒湿空调三种工况下自动控制研究

恒温恒湿空调是目前使用最为普遍的一种空调系统,恒温恒湿空调系统在不同的季节的自动控制有所不同,一般来讲夏季、冬季和过渡季节这三种情况是是典型的三种条件下的自控控制情况。因此本文详细分析了恒温恒湿空调系统在不同环境中的自动控制,期望通过本文的研究,对恒温恒湿空调系统的改进提供一定的参考意见。     

一种新型直接膨胀式温湿度独立控制恒温恒湿空调系统

为了消除传统恒温恒湿空调系统中冷热抵消现象,提出了一种新型直接膨胀式温湿度独立控制恒温恒湿空调系统(下称新型空调系统).该空调系统通过组合三级直接膨胀式制冷单元、加热器、加湿器,并配备特有的控制策略,可以在满足恒温恒湿环境一定温湿度控制精度的前提下,实现温湿度解耦控制.该空调系统不会造成投资成本大幅增加,并具备结构简单...     

不同养护制度下水性聚氨酯改性再生混凝土毛细吸水性能研究

受孔隙率高、微裂缝多等缺陷的影响,再生混凝土的力学性能与耐久性均比普通混凝土差。以水性聚氨酯为改性材料,制备聚灰比分别为0.5%、1.0%、1.5%、2.0%的混凝土试件,开展不同养护制度下水性聚氨酯改性再生混凝土（WPUMRC）毛细吸水性能试验研究。研究表明：随着标准养护时间的增加,WPUMRC的累积吸水量、初始毛细吸水率、后期毛细吸水率均先减小后增大,在14d标准养护-14d室内自然干燥养护制度下,WPUMRC的累积吸水量、初始毛细吸水率、后期毛细吸水率达到最小值。     

免蒸压预应力管桩蒸养制度的研究

蒸汽养护可加速水泥的水化,但会对水泥基材料的微观结构带来不利影响,不同的蒸汽养护制度对混凝土性能的影响不同.文章主要研究水胶比、静置时间、升温速率、恒温时间、恒温温度对混凝土强度性能的影响,并优化蒸养制度.结果表明：延长静置时间可明显改善混凝土的强度,较快的升温速率、较高的恒温温度和较长的恒温时间对混凝土的早期强度有利,但是对后期强度不利;在优化的蒸养制度下制备的C80免压蒸高强混凝土具有很好的力学性能和耐久性.     

JW-Ⅰ型恒温、恒湿混凝土试块标准养护箱研制简介

北京市第五市政工程公司与河北省冀县无线电仪器厂自1986年开始联合研制的JW-Ⅰ型恒温、恒湿混凝土试块标准养护箱(见封三照片),现已通过五个省市的有关五十个行政科研和建筑单位的联合评审,进入试生产阶段。联合评审意见认为: “JW-Ⅰ型恒温、恒湿混凝土试块标准养护箱设计合理,具有调温、调湿范围较广,控制精度高,运行可靠,操作简便,一机多用     

海洋侵蚀环境下超高性能混凝土的力学与耐久性能研究

通过加速劣化试验方法研究了超高性能混凝土（UHPC）在模拟海洋侵蚀环境下的力学和耐久性能。结果表明：海水养护下UHPC的力学性能受开始浸泡时间的影响较小，长期力学性能发展比较稳定；UHPC具有良好的适应性和耐久性能，冻融循环对UHPC性能的影响相对较大，但介质类型对其性能的影响较小；随着硫酸盐干湿循环次数的增加，UHPC的相对动弹性模量和抗压强度耐蚀系数先增加后降低，质量损失增加；硫酸盐干湿循环会导致UHPC表面露出的钢纤维锈蚀，但内部结构无损伤，钢纤维与基体结合紧密。     

高原地区环境及养护条件对混凝土性能的影响

高原地区独特的低温、大温差、低湿度的典型环境特征会对当地混凝土结构带来较大的不利影响。本文研究了高原地区不同月份的环境下自然养护对混凝土力学性能、耐久性能的影响,同时结合实际情况,研究了不同养护方式下温湿度以及早期养护持续时间对混凝土性能的影响规律,可为高原地区的工程建设提供一定的理论指导及参考。     

高温低湿的自然养护对混凝土性能的影响

研究了不同养护条件下混凝土的强度及耐久性.结果发现,经自然条件下的高温低湿养护后,混凝土的强度早期增长较快,但后期的抗压强度与轴拉强度均低于标准养护下混凝土的试验值;在自然环境中养护时,混凝土各龄期的极限拉伸值均小于标准养护测定值,且混凝土的抗渗等级与抗冻等级均低于标准养护时混凝土的测试结果.混凝土抗渗性试验结果表明,混凝土的强度等级越低,自然养护对混凝土抗渗性带来的影响越大.     

Effect of moisture and temperature on the mechanical properties of concrete

Concrete mechanical properties are determined under laboratory conditions of ideal air temperatures between 20 and 22 °C and relative humidity between 40% and 60%. This paper describes the development of concrete mechanical properties when cured under different environmental conditions. Tests to measure modulus of elasticity, compressive strength, and split tensile strength were conducted at varying temperatures and humidity conditions to examine their effects on normal concrete. An environmental chamber was constructed in the laboratory using available materials. The chamber works in conjunction with a freezer to provide chilled air and a heat gun to provide hot air. The heating and cooling functions were controlled via a microcontroller. The moisture content in the concrete specimens was controlled by massing the specimens. The results indicate that concrete strength and modulus of elasticity are inversely related to temperature as well as moisture content in the concrete. Concrete modulus of elasticity was directly related to concrete compressive strength in both temperature and moisture testing. Mathematical formulas were developed for modulus of elasticity, compressive strength, tensile strength, and Poisson’s ratio.     

缓粘结预应力钢筋用胶粘剂材料的稳定性研究

对缓凝胶粘剂材料力学性能的稳定性进行了试验研究,测试了不同的固化周期、不同的环境温度、盐雾条件、湿热条件、加速老化后的拉压强度值,证实了缓凝胶粘剂力学性能的稳定性,可以满足不同环境条件下缓粘结预应力筋的使用,为缓粘结预应力技术的工程应用创造了条件。     

不同环境下碳纤维布约束混凝土的受压性能

在标准养护、自然淋雨、自然不淋雨、淡水浸泡和硫酸盐溶液浸泡5种环境作用下,对碳纤维布约束混凝土试件和非约束混凝土试件进行对比试验分析.每作用一段时间后,取出试件进行单轴受压试验.两年内的试验结果表明,碳纤维布的约束可以有效提高试件的承载能力.在硫酸盐环境下,碳纤维布约束可以改善混凝土的抗腐蚀能力;在其他环境下,约束混凝土也都有良好的耐久性能.不同环境下,碳纤维布约束混凝土的极限应变基本不随时间发生变化.     

Effect of curing methods on the properties of plain and blended cement concretes

This paper reports result of a study conducted to investigate the effect of curing methods on the properties of plain and blended cement concretes. The concrete specimens were prepared with Type I, silica fume, and fly ash cement concretes. They were cured either by covering with wet burlap or by applying two types of curing compounds, namely water-based and acrylic-based. The effect of curing methods on the properties of plain and blended cement concretes was assessed by measuring plastic and drying shrinkage, compressive strength, and pulse velocity. Results indicated that the strength development in the concrete specimens cured by covering with wet burlap was more than that in the specimens cured by applying water – and acrylic-based curing compounds. Concrete specimens cured by applying curing compounds exhibited higher efficiency in decreasing plastic and drying shrinkage strain than specimens cured by covering with wet burlap. The performance of acrylic-based curing compound was better than that of water-based curing compound. The data developed in this study indicate that curing compounds could be utilized in situations where curing with water is difficult. Among the two curing compounds investigated, acrylic-based curing compound performed better than the water-based curing compound.     

Abrasion resistance of concrete containing SiO2 and Al2O3 nanoparticles in different curing media

In the present study, abrasion resistance and compressive strength of concrete specimens containing SiO₂ and Al₂O₃ nanoparticles which are cured in different curing media have been investigated. Portland cement was partially replaced by up to 2.0 wt.% SiO₂ and Al₂O₃ nanoparticles and mechanical properties of the produced specimens were measured. Increasing the nanoparticles content have found to increase the abrasion resistance of the specimens which were cured in water and saturated limewater, while this condition was not observed for compressive strength in both curing media. The enhancement of abrasion resistance was more for the specimens containing SiO₂ nanoparticles in both curing media. Since, abrasion resistance and compressive strength of the specimens follow a similar regime by increasing the nanoparticles content when they are cured in saturated limewater, some experimental relationships has been presented to correlate these two properties of concrete for this curing medium. On the whole, it has been concluded that the abrasion resistance of concrete does not only depend on the corresponding compressive strength.     

Properties of autoclaved lightweight aggregate concrete

Many researches have been carried out on production and properties of pre-cast concretes. Currently, most of them have focused on normal concrete, and are unable to completely represent the behavior of lightweight concrete (LWC). In this study, physical and mechanical properties of LWC produced with diatomite and pumice lightweight aggregates after autoclave curing were investigated. In the production of LWC, 0–4 mm maximum sizes of aggregates were used. Cement content and water/cement ratio were kept at 300 kg/m³ and 0.20, respectively. The specimens were prepared in 50×100 mm cylindrical shape, and after 24 h of demoulding exposed to autoclave curing for 2, 4, 6, 8 and 10 h. Besides, two different cures were applied on the specimens as in water and in air at 20 °C±2, respectively. At the end of autoclaving and environmental cure, compressive strength in 7, 28 and 590 d, unit weight, specific porosity, thermal conductivity and water absorption were tested. Also, microstructures of LWC produced with diatomite and pumice aggregate were investigated. As a result, it is concluded that by autoclaving of specimens in 8–10 h, especially, compressive strength of specimens have increased 75% of strength of 28 aged specimens cured in water.     

聚硫密封胶的固化及其热老化性能研究

研究基膏与硫化膏的配比、促进剂二苯胍对聚硫密封胶的固化时间和力学性能的影响.结果发现,基膏与硫化膏的配比为100/12时,密封胶能完全固化;基膏与硫化膏的配比为100/8时,密封胶具有最佳的力学性能,断裂伸长率和拉伸强度分别为437%和2.65 MPa;添加二苯胍能促进密封胶的固化过程;100℃热老化7d会降低聚硫密封胶的硬度,并提高其拉伸强度和断裂伸长率.     

海洋既有建筑再生骨料及海洋再生混凝土的性能研究

为促进海洋环境中既有建筑混凝土的循环利用,推进建筑行业可持续化进程,在浙江省宁波市与舟山市采集废弃混凝土构件,测试其抗压强度及游离氯离子含量,利用压汞仪分析其孔隙结构。将海洋既有建筑混凝土破碎成再生骨料,测试其物理力学性能及颗粒形态。采用海水与再生骨料制备海洋再生混凝土,测试其抗压强度及劈裂抗拉强度,利用扫描电镜与X射线衍射仪分析其微观形貌及组成。研究结果表明：受局部环境的影响,海洋既有建筑混凝土的宏微观性能具有较大离散性,性能较差的海洋既有建筑混凝土,破碎成的再生骨料品质也较差,主要表现为表观密度较低,吸水率及压碎指标较高。即使再生粗骨料与再生细骨料取代率达到100%,海洋再生混凝土强度等级也可达到C40~C45,由于原材料就地取用率较高,海洋再生混凝土具有潜在的环境效益和经济效益。     

粘结和固化参数对建筑结构胶粘结性能的影响

通过丙烯酸酯AB胶和环氧树脂胶的拉伸剪切强度和粘结抗拉强度试验,研究不同胶层厚度、固化温度对试验结果的影响,试验结果表明,胶层厚度变大,结构胶剪切强度和粘结抗拉强度呈下降趋势;适当提高固化温度有利于提高固化程度,但是固化温度过高会造成粘结力下降,研究结果对建筑结构胶拉伸剪切强度和粘结抗拉强度的检测质量起到了保证作用,同时提高了检测结果的准确率。