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.

Analysis of a Composite Admixture Based on Ready-Mixed Concrete Waste Residuals

Reasonable treatment and utilization of waste residuals discharged during the production of ready-mixed concrete is an important problem in the cement industry.In this study,a composite admixture was prepared by using ready-mixed concrete waste residuals,furnace slag,and water granulated slag.The grinding characteristics of such material were investigated.Moreover,the effect of such admixture on cement hydration and pore structure was analyzed by X-ray diffraction,thermogravimetric-differential scanning calorimetry,scanning electron microcopy and mercury intrusion porosimetry.As shown by the results:The grinding characteristics of the waste residuals can be improved significantly by mixing them with furnace slag and water granulated slag.Furthermore,the composite admixture does not change the composition of hydration products;rather it contributes to refine the pore structure of the matrix,thus improving the mechanical properties of these cement-based materials.

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.

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.

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.

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%。

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。

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%。

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。

基于响应面法的机制砂路面混凝土配合比优化及其性能研究

为实现多目标性能机制砂混凝土配合比设计,本文采用Box-Behnken响应面法进行试验设计,探究了石粉掺量、浆体体积分数及水胶比对机制砂路面混凝土性能(坍落度、28 d抗压强度和磨损量)的影响,并结合SEM和XRD对硬化浆体的微观结构进行了分析。结果表明,通过响应面法建立的回归模型能够精确预测各因素与性能之间的关系,精度达95%以上。在各因素中,水胶比对坍落度和抗压强度的影响最显著,而对磨损量的影响较小。经优化,得到最佳的机制砂路面混凝土配合比:水胶比0.36,浆体体积分数25%,石粉掺量10%(质量分数)。此外,掺量不超过10%的石粉改善了界面过渡区,有助于提升混凝土的力学性能。

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。

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。

高强高保坍钢管拱机制砂自密实混凝土配制技术

根据重庆某钢管拱桥结构特征与“泵送顶升压注法”施工工艺特点,提出了高强高保坍钢管拱机制砂自密实混凝土性能需求。针对高强与超高工作性的矛盾问题,通过配合比参数优化、骨料优化、矿物掺合料复掺优化、外加剂复配优化和配合比综合优化等技术,配制出初始坍落度≥260 mm、扩展度≥600 mm、倒坍落度筒流出时间≤8 s、4 h工作性基本无损失、强度等级达C60以上的钢管拱机制砂自密实混凝土,形成了高强高保坍钢管拱机制砂自密实混凝土的配制技术,为工程实际施工提供了良好的技术支撑。

LNG储罐低温混凝土配合比及抗压强度试验研究

通过收集整理液化天然气(LNG)储罐混凝土实际配合比信息,并按规范要求进行了不同低温环境下的抗压强度测试,考察LNG储罐混凝土在低温环境下抗压强度的变化规律。结果表明:各储罐项目配合比用料基本一致,粉煤灰与矿粉用量略有差异,粉煤灰选用F类I级时,其混凝土抗压强度在常温及低温下都处于较高水平;矿粉选用S105级时,其混凝土抗压强度在低温下提升幅度最大。LNG储罐混凝土低温抗压强度随温度的降低明显增强,且温度越低,混凝土破坏越突然。在3个低温(-40℃、-120℃和-190℃)环境下,实测混凝土抗压强度分别是常温环境抗压强度的1.41、1.84和1.97倍,均满足规范要求。含水率是混凝土抗压强度低温增强的重要指标,但规范要求的低温环境混凝土抗压强度含水率影响系数与实际抗压强度的提升效果之间,规律并不明显。试验结果可为LNG储罐低温混凝土的配合比设计及安全性评估提供参考。

BSW再生混凝土配合比设计及力学性能研究

为研究建筑固废基(BSW)再生混凝土的力学性能,运用正交试验法,以水胶比、骨料取代率、骨料粒径为影响因素,对BSW再生混凝土的力学性能进行研究,采用直观分析法和方差分析法确定最优配合比及因素影响水平,利用线性拟合建立BSW再生混凝土抗压强度线性回归方程,探究不同龄期之间抗压强度的相关性。结果表明:水胶比为0.4、骨料取代率为20%、骨料粒径为5~16 mm时BSW再生混凝土的力学性能最佳;根据影响因素贡献率,对强度的影响程度大小依次为水胶比、骨料取代率、骨料粒径;在线性回归方程中数据点都均匀分布在拟合线两侧,拟合程度相对较好。

聚乙烯醇纤维沙漠砂混凝土配合比试验研究

为充分发挥沙漠砂的颗粒填充优势和改善沙漠砂混凝土力学性能,本文基于Dinger-Funk紧密堆积理论开展了聚乙烯醇纤维沙漠砂混凝土配合比设计方法的试验研究。首先,应用Dinger-Funk紧密堆积理论得到优化砂率为42%,优化沙漠砂质量替代率为10%、20%和30%,混凝土骨料颗粒级配得到改善,混合细集料的细度模数从3.27分别降到2.92、2.81和2.71,有效孔隙率从2.50%分别降到1.65%、1.45%和1.51%;其次,采用正交试验方法,研究了水胶比、沙漠砂质量替代率、聚乙烯醇纤维体积掺量对混凝土和易性、抗压强度、劈裂抗拉强度和抗折强度的影响规律。结果表明,随沙漠砂质量替代率和纤维掺量的增加,混凝土拌合物和易性先提高后降低,抗压、劈裂抗拉和抗折强度均表现为先增大后减小的趋势。综合考虑和易性和力学性能试验结果,确定C30聚乙烯醇纤维沙漠砂混凝土最优配合比为水胶比0.45,沙漠砂质量替代率20%,聚乙烯醇纤维体积掺量0.10%。

钢管塔柱自密实微膨胀混凝土性能调控与应用研究

文中研究了硅灰掺量、水胶比以及砂率对核心混凝土工作性能及力学性能的影响,以及膨胀剂掺量对核心混凝土体积变形的影响.结果表明:硅灰掺量的增加有助于提高混凝土强度,当其掺量不超过40 kg/m 3时能降低混凝土的粘度;水泥用量的提高能增加混凝土强度,但当水泥用量超过510 kg/m 3时混凝土工作性能出现下降;满足混凝土工作性能要求的最佳砂率是44%;40 kg/m 3的膨胀剂掺量能满足混凝土体积稳定性能的要求.根据试验研究确定的混凝土施工配合比成功应用于卡哈洛金沙江大桥主塔钢管内核心混凝土,现场混凝土状态及浇筑效果均良好,无脱空现象出现.

新型砂轻混凝土的工作性和力学性能研究

针对装配式建筑中混凝土构件自重过大的问题,本文采用黑曜岩轻骨料,试验配制新型砂轻混凝土,研究和分析了新型砂轻混凝土工作性和力学性能的影响因素。结果表明:新型砂轻混凝土可采用绝对体积配合比设计方法;影响新型砂轻混凝土工作性和力学性能的最主要因素是水灰比和水泥掺量;在试验最佳配合比时,制备的干表观密度为1 500 kg/m3砂轻混凝土,在50℃下快速养护3 d,抗压强度可达47.2 MPa,抗折强度达6.9 MPa,能适应装配式建筑用预制构件轻量化和高强的发展要求。

水灰比对机制砂混凝土性能影响的试验研究

通过测试不同水灰比下C35、C40、C50花岗岩机制砂混凝土的工作性及力学性能,分析了水灰比对机制砂混凝土性能的影响,得到了机制砂混凝土的最佳配合比。结果表明:水灰比对机制砂混凝土的工作性有直接影响,也会间接影响机制砂混凝土的力学性能;在不同水灰比条件下,3种不同强度等级的机制砂混凝土力学性能的变化规律均相同;综合考虑机制砂混凝土的工作性和力学性能,确定了C35、C40、C50花岗岩机制砂混凝土的最佳水灰比分别为0.39、0.34、0.32。