喷射混凝土配合比设计

结合兰新铁路第二双线红山二号隧道围岩情况及开挖后初期支护喷射混凝土施工概况,主要介绍隧道开挖后初期支护用C25合成纤维喷射混凝土性能要求、现场施工原材料的选定、基准配合比计算、试拌拌合物性能、现场试喷强度及回弹率验证等过程为喷射混凝土配合比设计提供参考依据;最终确定可喷性好、早期强度发展快、回弹量小、粉尘浓度低符合环保要求、适合现场施工可喷性强的合成纤维喷射混凝土配合比设计。基于喷射混凝土施工工艺的特殊性,喷射混凝土配合比设计与普通混凝土配合比设计既有相似之处也有其特殊性,在遵守规范规定的前提下应特别重视现场试喷调整、强度验证这一过程,这是喷射混凝土配合比设计的重点和难点。     

混凝土配合比设计方法研究

混凝土配合比设计是混凝土材料科学中最基本且最重要的一个问题。传统的配合比设计方法是计算一试配法,其计算依据是在普通混凝土组成与性能一般规律的基础上,计算得到粗略配合比,再经试配调整得到以强度为主要指标的配合比,我国几十年来一直沿用这种方法。随着各种新型混凝土的不断发展,混凝土在材料组成上逐渐复杂化,对拌合物的工作性及硬化后的力学、耐久性能的要求也越来越高。因此,适用于普通混凝土的配合比设计方法已经不能满足其它类型混凝土在材料和性能上的高要求,而在任何情况下都能通用的混凝土配合比是不存在的,需要不同的配合比设计方法来设计满足不同要求的混凝土。     

高性能混凝土的施工应用

1混凝土耐久性要求 混凝土结构的耐久性要求一般应包括：混凝土原材料选用、混凝土配合比的主要参数,以及根据需要提出的混凝土的电通量、抗冻耐久性指数或抗冻等级、保护层厚度等具体指标。施工前要详细调查结构物所处的环境类别及作用等级,在设计文件中明确混凝土的耐久性要求。     

浅谈铁路高性能混凝土配合比设计

通过对贵广高速铁路高性能混凝土配合比的设计和施工,铁路高性能混凝土配合比的设计也有自己的特点,现加以总结,为以后铁路混凝土配合比的设计提供有益的借鉴。     

重混凝土的配合比设计试验及应用

与普通混凝土相比,重混凝土最鲜明的性能特征就是容重大,大容重混凝土的配合比设计除了要满足容重、强度等技术要求外,还要根据工程的施工条件、施工方法等满足施工性能的各种要求。本文重点阐述了重混凝土从原材料选择、配合比设计试验、生产、浇筑及养护等环节,结合工程混凝土施工的特点,以实际工程为例,阐述了重混凝土的材料选取原则、配合比设计思路、生产及质量控制要点,对重混凝土的生产及广泛应用具有一定的参考价值。     

聚羧酸系减水剂在高速铁路预制梁中的应用

该文针对鲁南高铁临沂东梁场对预应力梁混凝土的技术要求,以混凝土的工作性能、力学性能及耐久性能为目标,尤其以耐久性为核心,进行了C50预应力梁的混凝土配合比设计。通过采用性能优良的聚羧酸系高性能减水剂、低水胶比的技术路线,成功配制出高工作性能、良好的力学性能以及优异的耐久性能的预应力梁混凝土。最终该混凝土在临沂东梁场得到了成功的应用,取得了良好的效果。     

先张法无掺合料混凝土梁裂缝的预防及处理

近年来随着预应力混凝土梁应用越来越广泛,预应力混凝土梁体裂缝问题日益突出。在现场预制混凝土梁施工中,梁体表面及深层经常出现龟裂裂缝而影响质量。本文结合现场施工条件,总结无掺合料预应力混凝土施工经验,阐述了工程实践中对预应力无掺合料混凝土梁体裂缝的产生原因及预防处理措施。     

浅谈混凝土的配合比组成设计

通过对混凝土配合比设计,掌握混凝土设计中的各个环节,为混凝土施工提供精确的数据。     

基于32m预应力箱梁C50混凝土配制技术的研究

本文主要结合高耐久、高性能混凝土配合比的设计方法,以及客运专线所处施工环境原材料的实际现状,对客运专线32m预应力混凝土箱梁C50高性能混凝土的配合比设计方法进行了分析。     

预应力混凝土简支梁的承载能力试验

预应力混凝土桥梁具有较好的强度、刚度及抗裂性能好、适应性强、养护维修工作量少等许多优点,在公路桥梁中占有较大比重。随着高速公路的不断发展,许多中小跨度桥梁逐渐被预应力混凝土简支梁桥所取代,对预应力混凝土简支梁需求量越来越大。为了判定成品梁是否达到设计抗裂的规定指标,必须对梁体的弯曲抗裂进行静荷载试验。     

Development of kenaf fibre reinforced polymer laminate for shear strengthening of reinforced concrete beam

Fabrication of green fibre composite laminate for strengthening of reinforced concrete structure is one of the current interests in the field of construction industry. The aim of this research was to develop kenaf fibre reinforced polymer (KFRP) laminate for shear strengthening of reinforced concrete beam. Comprehensive design and theoretical models were also proposed for KFRP laminate shear strengthened beam. In the experimental programme, KFRP laminate had been fabricated with various fibre content to obtain optimal mix ratio. Physical and mechanical properties of KFRP laminates were experimentally investigated. Three reinforced concrete beam specimens were prepared for structural investigations. Results showed that KFRP laminate with maximum fibre content had the highest tensile strength and the laminate was found to be elastic isotropic in nature. The KFRP laminate strengthened beam had 100 % higher shear crack load and 33 % ultimate failure load as compared to un-strengthened control beam. It reduced the numbers and width of cracks and had shown strain compatibility behavior with shear reinforcement. The failure load, ductility, crack patterns and strain characteristics of KFRP laminate strengthened beam were found to be closely comparable with CFRP laminate strengthened beam. The experimental results satisfactorily verified the proposed design and theoretical models.     

浅谈聚羧酸系减水剂在京沪高速铁路VI标段高性能混凝土的中应用

京沪高速铁路Ⅵ标段主要为桥梁工程,采用高性能混凝土结构,设计寿命100年。本文主要介绍了聚羧酸系减水剂在该工程中的应用,重点探讨了原材料选择、生产过程质量控制、高性能混凝土配合比设计及聚羧酸系减水剂在高性能混凝土施工中应注意问题,并指出高性能混凝土与普通混凝土的异同。     

全矿渣混凝土泵送施工时的堵泵现象探讨

本文针对全矿渣混凝土可泵性较差的特点,从改善混凝土的可泵性出发,采用各种技术措施和施工注意事项,优选原材料及科学的设计生产配合比,与现场施工相结合,较好的解决了全矿渣混凝土泵送施工的堵泵现象,为工程顺利施工打下了基础。     

自密实高性能混凝土力学性能的研究与应用

以自密实高性能混凝土的配合比优化设计为基础,对自密实高性能混凝土的钢筋粘结锚固性能、受弯构件的抗弯、抗剪性能等进行了深入的试验研究。包括中强与高强自密实混凝土,共做了62个粘结强度拉拔试验、12根梁抗弯抗剪试验,研究结果为自密实混凝土结构的设计提供了参考。介绍了自密实高性能混凝土在3座高层建筑和1座厂房加固工程中的应用,总结了工程应用中的经验。     

京沪高铁路电缆槽、人行道盖板活性粉末混凝土（RPC）试验研究

主要针对京沪高速铁路土建六标电缆槽盖板和人行道步板活性粉末混凝土（RPC）配合比设计，满足《客运专线活性粉末混凝土（RPC）材料人行道挡板盖板暂行技术条件》前提下选择原材料，通过多种配合比比较，选定最优配合比，并应用于电缆槽盖板和人行道步板生产。     

Geopolymer concrete-filled pultruded composite beams – Concrete mix design and application

The limited research on the geopolymer concrete mix design for targeting a specific strength is identified an obstacle for their effective design and wide use. In this paper, a mix design procedure has been proposed for fly-ash based geopolymer concrete and its use as infill hybrid composite beam is investigated. Then, the structural performance of geopolymer concrete filled hybrid composite beam is investigated to determine their possible application in civil infrastructure. Firstly, a detailed procedure of mix design for fly-ash based geopolymer concrete is presented. Secondly, three hybrid beams filled with geopolymer concrete were prepared and tested in a four-point bending setup to evaluate their flexural modulus and modulus of rupture. Numerical and analytical evaluation of the behaviour of hybrid beam were performed and results showed a good agreement with the experimental investigation. Thirdly, the suitability of the beam for a composite railway sleeper is evaluated and compared with existing timber and composite sleepers. Finally, the beams’ performance in a ballast railway track is analysed using Strand7 finite element simulation software and the results showed that the new concept of using geopolymer concrete as infill to pultruded composite section satisfied the stiffness and strength requirements for a railway sleeper.     

Bond behaviour of reinforcing bars in self-compacting concrete: experimental determination by using beam tests

The force transfer between concrete and reinforcement depends on the bond characteristics between the two materials. Bond influences crack widths and the deflections of RC members and also determines anchorage and splice lengths. Self-compacting concrete (SCC) is characterized by a smaller amount of coarse aggregates when compared to conventional vibrated concrete. To investigate whether this change in mix design has a significant influence on the bond behaviour, a series of beam tests (according to RILEM recommendation RC6) was performed. A total of 36 specimens were cast using 3 different concrete types: one conventional vibrated concrete (CVC) and two powder-type SCC’s. The bond stress—slip behaviour of reinforcing bars with diameters ranging from 12 to 40 mm has been recorded. From these tests, it can be concluded that the bond strength of SCC is even higher than it is for CVC for small bar diameters, but the difference becomes smaller for larger bar diameters.     

Impact of particle packing mix design method on fracture properties of natural and recycled aggregate concrete

The fracture properties of four types of concrete prepared using natural coarse aggregate and recycled coarse aggregate and conventional and particle packing method (PPM) of mix design approaches are studied. The three‐point bending (TPB) test is performed using three different sizes of single edge notched beam. The fracture energy is calculated from the load‐CMOD curve obtained in the TPB test, and in this process the load‐CMOD curve is curtailed at 2% of the depth of the beam. Based on CTOD_c and w₁ relationship, appropriate softening function is used to estimate the double‐K fracture parameters. The fracture energy and fracture toughness parameters of recycled aggregate concrete (RAC) is inferior to the natural aggregate concrete (NAC). The PPM mix design improves the fracture properties of concrete in comparison to the conventional mix design approach. The fracture properties of PPM mix designed RAC are comparable to that of NAC prepared using conventional method.     

SPS-8P-2型聚羧酸系泵送剂在中低强度等级预拌混凝土中的应用

SPS-8P-2聚羧酸系泵送剂经混凝土配合比研究和生产实践应用证实,可以在C20-C40预拌商品混凝土中应用,具有良好的工作性,混凝土配合比中的“浆骨比”是工作性的关键。