砂浆再生粗骨料对混凝土强度及干燥收缩性能影响研究

试验以不同强度砂浆粗骨料、不同砂浆粗骨料置换率为变量对C30再生混凝土强度及干燥收缩耐久性能进行了试验研究.结果表明,随着砂浆再生粗骨料置换率的增加,混凝土拌合物流动性能降低;当砂浆再生粗骨料置换率相同时随着砂浆再生粗骨料强度的降低混凝土的强度也有所降低;当采用同一种强度等级砂浆再生粗骨料时,随着砂浆粗骨料置换率的增加混凝土的强度也会降低,特别是采用低强度砂浆再生粗骨料且置换率为100％时混凝土的强度降低更为明显;当采用同一种强度等级砂浆再生粗骨料时,随着砂浆粗骨料置换率的增加混凝土的干燥收缩长度变化率也会变大;在相同砂浆再生粗骨料置换率的条件下砂浆粗骨料强度越低,吸水率越大,混凝土的干燥收缩长度变化率也会变大.     

Effect of nanoclay on shrinkage control of low profile unsaturated polyester (UP) resin cured at room temperature

The addition of a small amount of nanoclay (1-3 wt%) can provide excellent volume shrinkage control of unsaturated polyester (UP)/styrene (St)/poly(vinyl acetate) (PVAc) systems cured at room temperature. PVAc serves as the low profile additive (LPA). In this study, both temperature-induced phase separation of the uncured resin mixture and transmission electron microscopy (TEM) of the cured sample revealed that nanoclay resided in the LPA-rich phase, leading to a higher reaction rate and earlier onset of micro-cracking in the LPA-rich phase or at the interface of the LPA-rich and UP-rich phases. Consequently, an earlier volume expansion during curing was observed in reactive dilatometry, resulting in better shrinkage control. On-line measurement of the composite thickness change during vacuum-infusion liquid composite molding [e.g. the Seemann Composite Resin Infusion Molding Process (SCRIMP)] further proved excellent volume shrinkage control of nanoclay filled systems, leading to a smoother composite surface.     

Autogenous and drying shrinkage of alkali-activated slag mortars

Shrinkage of alkali-activated slag (AAS) cement is a critical issue for its industrial application. This study investigated the mechanisms and effectiveness of shrinkage-reducing agent (SRA) and magnesia expansive agent on reducing autogenous and drying shrinkage of AAS mortars that were activated by liquid sodium silicate (LSS) solution with modulus (SiO₂/Na₂O molar ratio) of 0-1.5. The results showed that the autogenous shrinkage of AAS mortars increased with the increase of LSS modulus from 0 to 0.5, then decreased as modulus increased up to 1.5. The drying shrinkage consistently increased with the increase in the modulus of LSS. The oxyalkylene alcohol-based SRA could significantly reduce the autogenous and drying shrinkage of AAS mortars while the magnesia expensive agent was comparatively less effective. The autogenous shrinkage of AAS mortars was inversely proportional to the internal relative humidity, while the drying shrinkage was more related to the mass loss of samples. Mathematical models were established to describe the autogenous and drying shrinkage behavior of AAS mortars.     

UP/纳米CaCO3复合材料体积收缩性能的研究

研究了纳米CaCO3对不饱和聚酯树脂(UP)体积收缩性能的影响及其作用机理.结果表明,随着纳米CaCO3用量的增加,UP/纳米CaCO3复合材料的体积收缩率先下降后上升;用不同偶联剂对填料进行表面处理后,复合材料的体积收缩率较未用偶联剂处理的复合材料低,且用偶联剂硬脂酸处理填料比用偶联剂KH-570更有利于复合材料体积...     

浅谈粉末静电喷涂中缩孔问题的产生与防治

介绍了粉末静电喷涂中涂层缩孔缺陷的影响,分别从质量控制五大要素分析了在粉末静电喷涂中缩孔问题产生的原因,并提出了喷涂缩孔问题的防治办法。     

电泳缩孔的解决方案

通过某次电泳缩孔问题的解决,找出造成电泳缩孔的主要原因是电泳槽体污染、风机漏油污染,指出电泳漆投槽前重点清理的部位,从而避免电泳缩孔的出现。     

采用模拟硫化法表征高模量低收缩聚酯工业丝的性能

介绍了一种通过模拟硫化来对高模量低收缩聚酯浸胶帘子线的性能进行评价的方法,目的是为了能够更好地表征聚酯浸胶帘子布的综合性能。通过该方法,对目前国内外市场上的高模量低收缩聚酯工业丝进行了比较。     

无溶剂环氧涂层体积收缩率的研究

涂料在聚合过程中会产生体积收缩,而体积收缩将导致涂层的附着强度大大降低,还可能加速涂层老化的进程。本研究采用三维数字显微镜测试、扫描电镜测试和电化学交流阻抗谱测试等检测方法,对不同体积收缩率的无溶剂环氧涂层进行了性能分析,明确了体积收缩率对无溶剂环氧涂层的微观结构及防腐性能的影响。研究结果表明,调整颜基比可以控制无溶剂环氧涂层体积收缩率的大小;具有较小体积收缩率的涂层其抗渗透能力较好,具有较好的涂层防腐性能。     

A thermal active restrained shrinkage ring test to study the early age concrete behaviour of massive structures

In massive concrete structures, cracking may occur during hardening, especially if autogenous and thermal strains are restrained. The concrete permeability due to this cracking may rise significantly and thus increase leakage (in tank, nuclear containment…) and reduce the durability.The restrained shrinkage ring test is used to study the early age concrete behaviour (delayed strains evolution and cracking). This test shows, at 20 °C and without drying, for a concrete mix which is representative of a French nuclear power plant containment vessel (w/c ratio equal to 0.57), that the amplitude of autogenous shrinkage (about 40 μm/m for the studied concrete mix) is not high enough to cause cracking. Indeed, in this configuration, thermal shrinkage is not significant, whereas this is a major concern for massive structures.Therefore, an active test has been developed to study cracking due to restrained thermal shrinkage. This test is an evolution of the classical restrained shrinkage ring test. It allows to take into account both autogenous and thermal shrinkages. Its principle is to create the thermal strain effects by increasing the temperature of the brass ring (by a fluid circulation) in order to expand it. With this test, the early age cracking due to restrained shrinkage, the influence of reinforcement and construction joints have been experimentally studied. It shows that, as expected, reinforcement leads to an increase of the number of cracks but a decrease of crack widths. Moreover, cracking occurs preferentially at the construction joint.     

水胶比对高强砂浆早期收缩特性的影响

通过设计4种不同水胶比(0.18、0.21、0.24、0.27)的高强砂浆试样,研究掺入等量硅粉和羧酸基高效减水剂时不同水胶比对高强砂浆试样的单轴抗压强度、化学收缩、自收缩和干燥收缩的影响.试验结果表明:高强砂浆的早期收缩比较明显,其化学收缩和干缩与水胶比正相关,试块抗压强度和自收缩与水胶比负相关;掺入的硅粉发生二次水化,能够提升砂浆抗压强度,增加收缩量;掺入的羧酸基高效减水剂增加了水泥的凝结时间,但一定程度减少了砂浆试样的早期收缩.