A Simple Mix Proportion Design Method Based on Frost Durability for Recycled High Performance Concrete Using Fully Coarse Recycled Aggregate

Durability design of recycled high performance concrete（RHPC） is fundamental for improving the use rate and level of concrete waste as coarse recycled aggregate（CRA）. We discussed a frostdurability-based mix proportion design method for RHPC using 100 % CRA and natural sand. Five groups of RHPC mixes with five strength grades（40, 50, 60, 70 and 80 MPa） were produced using CRA with four quality classes, and their workability, 28 d compressive strengths and frost resistances（measured by the compressive strength loss ratio and the relative dynamic modulus of elasticity） were tested. Relationships between the 28 d compressive strength, the frost resistance and the CRA quality characteristic parameter, water absorption, were then developed. The criterion of a CRA maximum water absorption limit value for RHPC was suggested, independent of its source and quality class. The results show that all RHPC mixes achieve the expected target workability, strength, and frost durability. The research results demonstrate that the application of the proposed method does not require trial testing prior to use.

The Properties of Sulfur Rubber Concrete (SRC)

The mix designs and specimen preparation for the dry process and wet process of sulfur rubber conerete （ SRC ） were investigated. The compressive strength, corrosion-resistance and toughness were studied and discussed. The results show that SRC is corrosion-resistanet. Although the compressive strength of SRC decreases with inereasing rubber content, the toughness increases instead . Adding micro-filler will improve the compressive strength of SRC . There is a threshold value for the sulfur content, at which the compressive strength and the workability of SRC reach an optimum balance . The bond between rubber particles and surrounding sulfur is strong due to the vulcanization process that generates cross-link through S-C bonds.

The Creep Feature Analysis of The High Performance Concrete

In order to seek the creep change rules of ased concrete with two different mix proportions, the test is carried out in the situation which is similar to that of the creation of concrete C60, and the creep test on the concrete of two different mix proportions is done under standard lab. Based on creep test of the high performance concrete, the creep degree and the creep coefficient are obtained. By comparing with the wide-adopted models of AC1209 （1997） and CEB- FIP MC90, it is found that the test result is good at its regularity and the research results offer reference to the calculating analysis of the on-the-spot experimental data.

Concrete Mix Design by IS,ACI and BS Methods:A Comparative Analysis

Concrete is one of the most consumable construction materials on the earth.The concrete constitutes cement,sand,gravel,water and/or additives in definite proportions.The proportions of raw materials of concrete are decided by the concrete mix design.The mix design depends on the various factors.For mix design,most of the countries have their own specifications.In the present study,standard guidelines of India,Britain and America for the concrete mix design have been discussed.The concrete grades of M25,M35 and M45 were designed and compared.Indian Standards were also compared.It was concluded that a new revised version of Indian Standard code has the lowest value of water/cement ratio and highest quantity of cement as compared to other standards.

Effects of Recycled Aggregate Content on Pervious Concrete Performance

A recycled aggregate(RA)was prepared by crushing and sieving demolished discarded concrete pavements and was subsequently tested and analyzed to determine its various physical properties.On this basis,pervious concrete(PC)mix proportions were designed.Coarse RA particles with sizes of 5–10 and 10–20 mm were selected.Concrete specimens were prepared with a water–cement ratio of 0.3,an aggregate–cement ratio of 4.5,the substitute rates of RA with 0,25%,50%,75%and a single-/double-gap-graded RA mix(mass ratio of particles with sizes of 5–10 mm to particles with sizes of 10–20 mm:1:1,1:2,2:1,2:3 and 3:2).Various properties of the RA-containing PC(RPC)were determined by analyzing the compressive strength,splitting tensile strength,effective porosity,permeation coefficient and impact and abrasion resistance of the specimens.The results showed the following:The density of the RPC decreased with an increasing RA replacement ratio.The density of the RPC prepared with a double-gapgraded RA mix was lower than that prepared with a single-gap-graded RA(particle size:10–20 mm)mix.The permeation coefficient of the RPC increased with increasing porosity.The splitting tensile strength of the RPC was positively correlated with its compressive strength.The compressive strength of the RPC decreased with increasing porosity.The regression analysis showed that the impact and abrasion resistance of the RPC increased with increasing compressive strength.In addition,all of the RPC specimens met the strength and permeation requirements.This study can provide theoretical support for the application of RPC.

Mix design optimization of seawater sea sand coral aggregate concrete

With the resource shortage in coastal areas,the construction of concrete structures using freshwater and river sand has brought great economic and environmental costs.The use of seawater,sea sand,and coral aggregates in concrete mixes has become an alternative solution for coastal and marine structures,especially for offshore structures and artificial islands.In this study,378 seawater,sea sand,and coral aggregate concrete(Coral-SWSSC)specimens were prepared,and their mechanical properties were investigated comprehensively through compressive tests to explore the optimized mix design at different grades.Results showed that the mechanical properties of Coral-SWSSC were strongly correlated with the water-to-binder ratios,coastal particle gradings,and pretreatment method of coastal particles.Based on the experimental results,mix proportion designs of CoralSWSSC were proposed for concrete from C20 to C50 grades,and the failure mechanism of Coral-SWSSC at different grades was discussed according to their respective failure modes.The findings of the current study provide knowledge on the optimized design of Coral-SWSSC,which can be used to promote the application of Coral-SWSSC in offshore,marine,and ocean engineering.

Effects of Curing Conditions on Strength Development of High Strength Concrete

This paper presents the results of a series of studies on the influence of curing conditions on the strength development of high strength concrete. The 1-, 3-, 7-, 14- and 28-day strengths of four different mixes of Grade 75 similar to 80 concrete, with or without pulverized fuel ash and/or condensed silica fume, under five different curing regimes were investigated. It is revealed that the curing conditions have significant influence on both the short term and long term strength development of the concrete and that concrete mixes of the same grade but containing different mineral admixtures show distinct favour for a curing regime. These results will be helpful for evaluating suitable curing methods for high strength concrete with different mix proportions.

Cracking behaviors and crack control of self-consolidating concrete: a review of literature

Cracking in concrete occurs from volumetric instability, mechanical loading, and/or environmental attack. Compared to conventional vibrated concrete, self-consolidating concrete often has a higher susceptibility to crack due to different mixture design, material properties and construction practices. To obtain a better understanding of self-consolidating concrete cracking behaviors for designing and constructing crack-controlled structural elements, reported current research and practices are reviewed and analyzed in this paper. It has been believed that when well designed and welt constructed, high quality self- consolidating concrete can be successfully used in various structures with cracks properly controlled.

基于Design-Expert的UHPC强度及收缩率计算模型研究

为实现关键配比参数调整下超高性能混凝土(UHPC)的性能指标控制并得到各性能之间的相互影响规律,利用软件Design-Expert分析了UHPC的主要性能影响因素,基于主要因素对鮑罗米(Bolomy)公式进行了修正,建立了关于UHPC抗压强度、收缩率的计算模型。结果表明:对UHPC抗压强度、收缩率影响较大的三个配比因素分别为水胶比、胶砂比、粉煤灰掺量;基于主要影响因素,利用Design-Expert对UHPC配合比进行了优化,得到了抗压强度≥176 MPa,且收缩率≤320μm·m-1的UHPC试件;通过主要影响因素构建了Bolomy抗压强度及收缩率计算模型,并由计算数据与实验数据对比分析可知,修正后的Bolomy计算模型,可准确反映出抗压强度及收缩率与各主要影响因素之间的关系。

基于正交试验的生态混凝土孔隙环境优化研究

为使生态混凝土力学性能满足要求的同时改善其孔隙环境,通过设计有交互作用的正交试验,采用正交试验的敏感性分析方法,探究硅灰、苯丙乳液、尿素对生态混凝土抗压强度、孔隙率、孔隙环境pH值、总氮累积释放率4个指标的影响规律,并构建多元回归方程验证可靠性并得出最优配合比。结果表明:硅灰、尿素及两者交互作用下对抗压强度与孔隙率的影响显著;硅灰与尿素对降低孔隙内pH值有利,苯丙乳液会影响硅灰的降低效果;尿素能提高总氮累积释放率,硅灰与苯丙乳液能起到制约作用,且苯丙乳液效果较为明显。回归方程拟合曲线与试验结果曲线形态及趋势相似,生态混凝土的最优配合比为硅灰掺量9%、苯丙乳液掺量5%、尿素掺量10%。

基于力学性能指标与耐久性能指标联合的夯土改性配比优化设计方法

素土强度低、耐久性差且各改性材料掺量往往由工匠凭经验大致确定,导致夯土表面时常容易开裂剥落,故应根据现场土质状况以及合理试验方法来设计夯土改性配比。现有研究大都局限于单一性能指标最优的配比,而现实中夯土既要考虑针对多项力学性能指标与耐久性能指标的同步优化,还要考虑不同地域与气候条件下各指标的重要性不同。另外,现有研究仅能确定若干预设配比中的最优组,而非改性材料预设掺量范围内的最优配比。为此,文章提出一种基于力学性能指标与耐久性能指标联合的夯土改性配比优化设计方法,其包括:(1)土料选用原则与土质鉴定方法;(2)考虑夯土多性能指标的综合赋权方法;(3)基于加权评分和回归分析的夯土改性配比综合比选与优化方法。文章方法通过调整指标权重筛选出适应指标重要性不同时的夯土改性配比,并通过优化设计获得各改性材料预设掺量范围内的最优配比。最后通过设计实例证明了文章方法的确可得到最优的夯土改性配比。

干硬性碱激发钢渣混凝土的力学性能优化试验研究

为了优化干硬性碱激发钢渣混凝土的力学性能,试验通过调整粉煤灰的掺量结合碱激发的掺量优化混凝土凝结时间和流动度,并采用正交试验法分析粉煤灰掺量、水玻璃模数、水玻璃掺量和养护方式4种因素对干硬性碱激发钢渣混凝土抗压强度的影响。结果表明,掺入粉煤灰可延长干硬性碱激发混凝土的凝结时间,减小维勃稠度,优化工作性能;干硬性碱激发钢渣混凝土的抗压强度受多因素综合影响,影响大小的顺序为:水玻璃掺量>水玻璃模数>养护方式>粉煤灰掺量;当采用2.0模数和20%掺量的水玻璃、替换率为25%粉煤灰优化配合比后,再结合浸水养护2 d,接着自然养护,干硬性碱激发钢渣混凝土的抗压强度最高。

Packing and film thickness theories for the mix design of high-performance concrete

A high-performance concrete （HPC） is required to have superior performance in various aspects such as workability,strength, durability, dimensional stability, segregation stability, and passing ability. The mix design of HPC is rather complicatedbecause the number of ingredients in HPC is usually more than those in conventional concrete and some of the required propertiesare conflicting with each other in the sense that improvement in one property would at the same time cause impairment of anotherproperty. However, there is still lack of understanding regarding how the various mix parameters should be optimised forachieving best overall performance. Most practitioners are still conducting mix design primarily through trial concrete mixing,which is laborious, ineffective, and often unable to timely respond to fluctuations in the properties of raw materials. To addressthese issues, the authors have been developing the packing and film thickness theories of concrete materials, in order to revamp themix design philosophy of HPC in terms of the water film thickness （WFT）, paste film thickness （PFT）, and mortar film thickness（MFT） in the concrete. Based on the findings from an extensive experimental programme, suitable ranges ofWFT, PFT, and MFThave been recommended.

机器学习算法用于自密实混凝土性能设计的研究进展

为了厘清自密实混凝土材料各组分与其工作性能、力学性能、耐久性能间的复杂耦合影响机制,近年来,机器学习方法被越来越多地应用于自密实混凝土配合比设计与优化以及性能分析方面的研究。机器学习方法具有在复杂数据集中学习数据间的内在规律或映射关系的能力,在自密实混凝土设计领域被认为是构建混凝土原材料配合比与性能间映射关系模型的一种具有广阔前景的技术手段。然而,机器学习方法由于其依赖的数据集难以满足以及算法架构的可解释性较差等因素限制,使得基于机器学习在自密实混凝土性能设计领域面临着一系列挑战。本文系统总结梳理当前机器学习在自密实混凝土各项性能设计的应用情况,重点分析数据驱动的机器学习算法应用于自密实混凝土设计领域时面临的主要技术难点:高维度与小样本数据的难题、性能多目标优化难题、模型复杂而缺乏可解释性难题;归纳总结机器学习在自密实混凝土材料性能设计领域应用的发展趋势及未来发展方向。

赤泥填料对排水沥青混合料路用性能的影响

为探究赤泥填料对排水沥青混合料路用性能的影响,首先选择两种国产高黏改性剂PT-HVA和AR-HVA制备得到高黏改性沥青,并将成品苯乙烯-丁二烯-苯乙烯(styrene-butadiene-styrene,SBS)改性沥青作为对照组,对三种改性沥青进行各项沥青性能试验。结果表明:两种改性剂的最佳掺量均为15%。接着以三种改性沥青为胶结料配制三种排水性沥青混合料(填料为赤泥和矿粉),并进行各项路用性能试验。结果表明:由赤泥制备的混合料的路用性能良好,其中AR-HVA高黏改性沥青+赤泥制备的混合料性能最优,动稳定度达11053次/mm,残留稳定度为91.46%,冻融劈裂比为89.60%,飞散损失为5.20%,老化系数为24.60%。同时,由赤泥制备而成的混合料的弯拉强度和弯拉应变比由矿粉制备的混合料的小,这表明赤泥虽能有效地提高混合料的高温性能、水稳性能、抗松散性能和抗老化性能,但会降低混合料的低温性能。

多因素对透水混凝土配合比及性能的影响研究

基于正交试验法,研究了骨料粒径、水胶比、目标孔隙率、粉煤灰掺量、硅灰掺量对透水混凝土抗压强度、透水系数、孔隙率的影响。结果表明:骨料粒径、水胶比、目标孔隙率对透水混凝土性能的影响较大,掺入适量粉煤灰、硅灰能在一定程度上提高透水混凝土性能;28 d抗压强度最优组合为骨料粒径6~9 mm、水胶比0.28、目标孔隙率20%、粉煤灰掺量20%、硅灰掺量2%;透水系数最优组合为骨料粒径9~12 mm、水胶比0.31、目标孔隙率30%、粉煤灰掺量15%、硅灰掺量4%;孔隙率最优组合为骨料粒径3~6 mm、水胶比0.31、目标孔隙率30%、粉煤灰掺量15%、硅灰掺量8%。

碱激发混凝土配合比设计方法研究综述

碱激发混凝土是当前最有发展前景的新型胶材混凝土之一。同普通混凝土一样,碱激发混凝土的配合比设计对其性能起着至关重要的作用。综述了近年来国内外学者提出的碱激发混凝土配合比设计方法及理论基础,包括试验法、半经验法、全计算法以及基于强度的配合比设计方法,同时对碱激发混凝土配合比设计的进一步发展方向提出了展望。

再生混凝土的配合比设计研究综述

混凝土是基础设施建设中使用最广泛的材料,从废弃混凝土中回收再生骨料制作混凝土,可以减少自然资源的消耗以及处理废弃混凝土带来的环境污染问题。本文阐述了再生混凝土配合比传统与人工智能设计方法的研究现状,对研究中使用的具有代表性的方法进行了整理归纳;针对两种方法的特点以及存在的问题进行总结,提出人工智能设计方法具有广阔的发展潜力与研究前景;同时,对基于人工智能的再生混凝土配合比设计方法进行了展望,可为进一步完善和发展再生混凝土配合比设计方法提供参考。

基于响应曲面法的粉煤灰泡沫混凝土配合比优化

为了对粉煤灰泡沫混凝土进行配合比优化,首先通过比较不同激发剂组合和掺量对粉煤灰胶砂强度的影响,确定粉煤灰激发剂掺量,然后通过单因素试验,确定泡沫混凝土中粉煤灰、CaSt和H_(2)O_(2)的最佳掺量范围,最后基于Box-Benhnken响应曲面法研究粉煤灰、CaSt和H_(2)O掺量对泡沫混凝土抗压强度、干密度和导热系数的影响,建立响应面模型,探究各因素及交互作用的影响程度,获得最优配合比。结果表明,采用4.5%(质量分数,下同)Na_(2)SO_(4)和4.5%Ca(OH)_(2)的双掺激发组合显著提高了粉煤灰胶砂的性能。粉煤灰与H_(2)O_(2)掺量交互作用对抗压强度影响显著,CaSt与H_(2)O_(2)掺量交互作用对干密度影响显著,粉煤灰与CaSt掺量交互作用对导热系数影响显著。当水胶比为0.5、粉煤灰掺量为20.7%、CaSt掺量为1.9%、H_(2)O_(2)掺量为2.9%时,能够得到符合要求的A07级泡沫混凝土。