The Frost-resisting Durability of High Strength Self-Compacting Pervious Concrete in Deicing Salt Environment

A high strength self-compacting pervious concrete(SCPC) with top-bottom interconnected pores was prepared in this paper. The frost-resisting durability of such SCPC in different deicing salt concentrations(0%, 3%, 5%, 10%, and 20%) was investigated. The mass-loss rate, relative dynamic modulus of elasticity, compressive strength, flexural strength and hydraulic conductivity of SCPC after 300 freeze-thaw cycles were measured to evaluate the frost-resisting durability. In addition, the microstructures of SCPC near the top-bottom interconnected pores after 300 freeze-thaw cycles were observed by SEM. The results show that the high strength SCPC possesses much better frost-resisting durability than traditional pervious concrete(TPC) after 300 freeze-thaw cycles, which can be used in heavy loading roads. The most serious freeze-thaw damage emerges in the SCPC immersed in the 3% of Na Cl solution, while there is no obvious damage in 20% of Na Cl solution. Furthermore, it can be deduced that the high strength SCPC can be used for 100 years in a cold environment.

Design and Preparation of High Elastic Modulus Self-compacting Concrete for Pre-stressed Mass Concrete Structures

Requirements of self-compacting concrete （SCC） applied in pre-stressed mass concrete structures include high fluidity, high elastic modulus, low adiabatic temperature rise and low drying shrinkage, which cannot be satisfied by ordinary SCC. In this study, in order to solve the problem, a few principles of SCC design were proposed and the effects of binder amount, fly ash （FA） substitution, aggregate content and gradation on the workability, temperature rise, drying shrinkage and elastic modulus of SCC were investigated. The results and analysis indicate that the primary factor influencing the fluidity was paste content, and the main methods improving the elastic modulusof SCC were a lower sand ratio and an optimized coarse aggregate gradation. Lower adiabatic temperature rise and drying shrinkage were beneficial for decreasing the cement content. Further, based on the optimization of mixture, a C50 grade SCC （with binder amount of only 480 kg/ m3, fly ash substitution of 40%, sand ratio of 51% and proper coarse aggregate gradation （Vs.~0 mm： V10-16 ram： V16.20 mm= 30%： 30%：40%）） with superior workability was successfully prepared. The temperature rise and drying shrinkage of the prepared SCC were significantly reduced, and the elastic modulus reached 37.6 GPa at 28 d.

Effect of molecular structure and slump loss resistance of polycarboxylate superplasticizers on self-compacting concrete

A new kind of polycarboxylate superplasticizer with high slump loss resistance was obtained by designing scheduled molecular structure.The number average molecular mass of the polymer was characterized by the gel permeation chromatography measurements.And chemical structure of the polymer was observed by the Fourier transform infrared spectroscopy(FT-IR).The results show that the good workable maintaining of self-compacting concrete could be achieved through direct adjustment of number average molecular mass and different unsaturated monomer in synthetic process.The FT-IR analysis illustrated that the high slump loss resistance of polycarboxylate superplasticizers with ester and carboxyl group and expectations of molecular structure were designed.

基于MMLS3的改性沥青混合料高温稳定性研究

运用最先进的小型加速加载设备MMLS3(1/3model mobile load simulator)对常见的用于上、中面层的4种改性沥青混合料进行了高温稳定性试验,提出了适合中国的MMLS3室内加速加载的各项试验参数.通过研究改性沥青混合料的实际抗车辙性能,得出沥青混合料高温稳定性能的优劣顺序为:SBS橡胶复合改性SMA-13,SBS改性AC-20C,SBS改性AC-13C,SBS橡胶复合改性OGFC-13,岩沥青改性AC-20C.由于OGFC-13的大空隙结构,必然要在某种程度上牺牲其强度、抗剪切性能及耐久性,不建议在重交通的高速公路上使用其作为表面层.高温重载或超限地区应加强中面层的优化设计.MMLS3加载试验及常规动稳定度试验在衡量空隙率差距小的沥青混合料时,两者试验结果具有较好的一致性;而对于不同沥青混合料,当其空隙率差距大时,应根据需要选择合适的试验或评价方法.

钢管柱柱芯混凝土顶升施工技术

分析了钢管柱混凝土施工的难点和特点,决定采用泵送顶升浇筑法进行混凝土施工。对高流态自密实混凝土进行了试配并通过具体实践,决定采用一次顶升施工工艺,混凝土质量满足要求。

高性能混凝土模板侧压力分析

随着混凝土施工装备水平的提高和普及,以及高性能混凝土具有的高流动性,施工过程对模板产生了较高的模板侧向压力,近几年多有施工中发生"爆模"事故,影响安全。对影响模板侧向压力变化的机理及目前技术规程中模板侧向压力计算公式进行了分析,提出施工中保证模板设计加工和施工过程中模板安全的措施。

超高分子量聚乙烯纤维长度和掺量对超高性能混凝土性能的影响

文中通过对超高分子量聚乙烯纤维干法制备工艺进行调整,制备出直径为0.25mm的超高分子量聚乙烯粗纤维,短切为6mm、9mm、12mm三种规格,系统地研究了纤维对超高性能混凝土流动性和力学性能影响。结果表明,超高分子量聚乙烯纤维的掺入在一定程度上降低了混凝土流动性,但是对超高性能混凝土有较好的增强作用,6mm纤维在体积掺量为2%时,抗压强度和抗折强度较基体混凝土分别提高了9.4%和20.3%;9mm纤维在体积掺量为1.5%时抗压强度和抗折强度较基体混凝土分别提高了13.1%和25.4%;12mm纤维在体积掺量为1.5%时抗压强度和抗折强度较基体混凝土分别提高了7.3%和18.7%。

聚乙烯醇纤维对超高性能混凝土性能的影响

聚乙烯醇纤维(PVA)是目前在混凝土中广泛应用的一种合成纤维材料。文中系统性地研究了不同长度、不同体积掺量聚乙烯醇纤维对超高性能混凝土流动度、抗压强度和抗折强度的影响,结果表明:聚乙烯醇纤维的掺入都会一定程度上降低混凝土的流动性,且纤维的长度越长、体积掺量越高,混凝土流动性越差;聚乙烯醇纤维的掺入对混凝土力学性能有一定提升效果,6mm纤维体积掺量为2%时,混凝土抗压强度为141.3MPa,抗折强度为18.1MPa,较基体混凝土分别提高了8.2%和32.1%。

超高分子量聚乙烯纤维直径对超高性能混凝土性能影响

文中通过对超高分子量聚乙烯纤维干法制备工艺调节,制备出直径为0.05mm、0.15mm和0.25mm的超高分子量聚乙烯粗纤维,系统性研究了不同直径纤维对超高性能混凝土的流动性和力学性能影响。结果表明,与工艺未调节的细纤维对比,纤维的直径越大,在同等体积掺量情况下超高性能混凝土的流动性越好,对应的超高性能混凝土抗压强度和抗折强度越高。0.25mm直径纤维体积掺量为1.5%的情况下,抗压强度为137.4MPa,抗折强度为16.4MPa,较基体混凝土分别提高了9.4%和20.3%。