Effect of Modification Treatment on Chloride Ions Permeability and Microstructure of Recycled Brick-mixed Aggregate Concrete

The modification methods of pozzolan slurry combined with sodium silicate and silicon-based additive were respectively adopted to treat recycled coarse brick-mixed aggregate(RCBA)in this study.The compressive strength and chloride permeability resistance of recycled aggregate concrete(RAC)before and after modification treatment were tested,and the microstructure of RAC was analyzed by mercury intrusion porosimetry(MIP)and scanning electron microscopy(SEM).The results show that the physical properties of RCBA strengthened by modification treatment are improved,and the compressive strength and chloride permeability resistance of treated RAC are also significantly improved.The modification treatment optimizes the pore size distribution of RAC,which increases the number of gel pores and transition pores,and decreases the number of capillary pores and macro pores.The surface fractal dimension shows a significant correlation with chloride diffusion coefficient,indicating that the variation of chloride permeability of treated RAC is consistent with the microstructure evolution.

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.

Recycled Aggregate Pervious Concrete: Analysis of Influence of Water-Cement Ratio and Fly Ash under Single Action and Optimal Design of Mix Proportion

Pervious concrete is recommended,which is of great benefit to the ecological environment and human living environment.In this paper,the influences of five water-cement ratios and four fly ash contents to replace the cement by mass with a water-cement ratio of 0.30 on the properties of Recycled Aggregate Pervious Concrete(RAPC)were studied.Following this,based on the Grey relational-Technique for Order Preference by Similarity to an Ideal Solution(TOPSIS)optimization method,the strength,permeability,abrasion loss rate,and material costs of RAPC were adopted as evaluation indices to establish a mix proportion optimization model.The results show that the increase of water-cement ratio and fly ash replacement level of RAPC leads to decreased compres-sive strength while an increase in the permeability and abrasion loss rate.According to test results based on the optimal model 0.30 was identified as the best mix proportion.In addition,ecological-economic analysis of RAPC raw materials was carried out by comparing different natural aggregates.The results of EE(embodied energy)and ECO 2e(embodied CO_(2) emission)pointed out that the combination of recycled aggregate and fly ash leads to sig-nificant ecological and economic benefits.

Mechanical and Permeability Analysis and Optimization of Recycled Aggregate Pervious Concrete Based on Response Surface Method

In this paper,the effects of different influencing factors and factor interaction on the compressive strength and permeability of recycled aggregate pervious concrete(RAPC)were studied based on the response surface method(RSM).By selecting the maximum aggregate size,water cement ratio and target porosity as design variables,combined with laboratory tests and numerical analysis,the influences of three factors on the compressive strength and permeability coefficient of RAPC were revealed.The regression equation of compressive strength and permeability coefficient of recycled aggregate pervious concrete were established based on RSM,and the response surface model was optimized to determine the optimal ratio of RAPC under the conditions of meeting the mechanical and permeability properties.The results show that the mismatch item of the model is not significant,the model is credible,and the accuracy and reliability of the test are high,but the degree of uncorrelation between the test data and the model is not obvious.The sensitivity of the three factors to the compressive strength is water cement ratio>maximum coarse aggregate particle size>target porosity,and the sensitivity to the permeability coefficient is target porosity>maximum coarse aggregate particle size>water cement ratio.The absolute errors of the model prediction results and the model optimization results are 1.28 MPa and 0.19 mm/s,and the relative errors are 5.06%and 4.19%,respectively.With high accuracy,RSM can match the measured results of compressive strength and permeability coefficient of RAPC.

Waste Shell Husks Concrete: Durability, Permeability and Mechanical Properties

Shell husk is annually produced as a byproduct of shell production in Japan. According to Japanese Ministry of Forestry, Fisheries and Agriculture, the amount of the abandoned shell husk is about 151,000 tons per year. This huge amount of abandoned shell husk is not only thrown away without any commercial return but also causing pollution and environmental problems. To mitigate the pollution and environmental problems, possible utilization of abandoned shell husk is thoroughly observed in concrete construction. Overall response of the mechanical properties of concrete specimens containing different percentage of abandoned shell husk aggregates such as 0, 10%, 0, 30%, 40% and 50% in the ratio of mass is demonstrated. Results of engineering properties such as compressive strength,Young’s modulus, tensile strength, unit weight, water absorption capacity and coefficient of hydraulic conductivity are depicted. It is observed that the use of shell husk in concrete improves strength and durability performance of concrete treated in aggressive sea environments.

基于正交试验的再生透水混凝土路用性能研究

通过正交试验研究了粉煤灰、矿渣微粉、硅灰等矿物掺合料以及再生骨料替代率对再生透水混凝土抗压强度、有效孔隙率、透水系数、耐磨性的影响。结果表明:再生骨料替代率对再生透水混凝土28 d抗压强度和透水系数影响最显著,随再生骨料替代率的增加,28 d抗压强度逐渐降低,透水系数显著增大;粉煤灰掺量对磨坑长度的影响最显著,随粉煤灰掺量的增加,再生骨料透水混凝土的耐磨性显著提高。基于功效系数法,综合性能最优配比为:粉煤灰、矿渣微粉、硅灰掺量分别为15%、5%、8%,再生骨料替代率为30%,制得的再生透水混凝土28 d抗压强度为25.9 MPa,透水系数为2.04 mm/s,磨坑长度为31.7 mm。

再生骨料透水混凝土力学和透水性能研究

文中制作不同水灰比和再生骨料添加量的再生骨料透水混凝土试件,经标准养护28 d后,对试件进行立方体抗压强度和透水性能测定。结果表明,随着水灰比的增加,透水混凝土试件的抗压强度和透水率均为先增加后减小;随着再生骨料添加量的增加,抗压强度不断减小而透水性能变化不大。最终确定水灰比为0.25、再生骨料添加量为15%、骨胶比为1?4、添加1.5%减水剂和6%硅粉为再生骨料透水混凝土的最佳配比,该结论为再生骨料透水混凝土的应用提供了技术支持。

PET回收料改性再生透水混凝土性能的研究

利用聚对苯二甲酸乙二醇酯(PET)回收料制备再生透水路面材料。通过在透水混凝土中添加不同掺量PET回收料制备了再生透水混凝土并研究其性能。结果表明:掺入不同掺量PET再生骨料的再生透水混凝土表现出了较高的孔隙率与较低的密度;掺入不同掺量PET再生骨料的再生透水混凝土满足力学性能标准值,并且在PET(G)-10达到最高,抗折强度和抗压强度分别为4.03MPa和25.1MPa;掺入不同掺量PET再生骨料的再生透水混凝土的透水性能均高于标准值,拥有良好的透水性能,在保证力学性能满足标准的同时,PET(S)-30和PET(G)-50的透水系数分别为8.5mm/s和8.4mm/s。因此,掺入不同掺量PET再生骨料的再生透水混凝土具有较好的综合性能,可以满足建筑行业的使用要求。

绿色建筑材料再生混凝土渗透力学行为系统性试验研究

为研究绿色建筑材料再生混凝土的渗透、力学行为特征,通过室内渗透测试、静、动三轴力学试验方法,开展了不同再生粗骨料粒径下试样渗透、力学特征分析。研究表明,再生粗骨料粒径愈大,则试样渗透率愈低,但粗骨料粒径变化,不会影响渗透率与静水围压之间函数关系,且加载破坏后,粗骨料粒径对渗透特性影响不及加载前。静力荷载下,围压对应变发展影响具有主导地位,粗骨料粒径愈大,试样三轴峰值应力愈高。动力荷载下,动弹性模量随应变呈“递减-稳定”变化,围压5 MPa、25 MPa下动弹性模量稳定期节点应变分别为3.03%、4.6%;粗骨料粒径、围压作用与动弹性模量均为正相关特征。粗骨料粒径对混凝土弹性应变能影响不及围压作用,且不会改变混凝土弹性应变能的发展趋势。研究成果对认知再生混凝土的渗透、力学特征以及试验设计具有参考价值。

风积沙再生骨料自密实混凝土抗渗透性能研究

对风积沙及再生骨料对自密实混凝土的抗渗透性能影响规律进行了研究,使用风积沙取代率为20%、40%、60%,再生骨料取代率为25%、50%、75%制备自密实混凝土,对其工作性能、抗压强度及抗渗性能进行试验研究,结果表明:风积沙掺入可以填充再生骨料与混凝土中微小孔隙,同时再生骨料具有一定活性,可以帮助混凝土进一步水化,两者适量掺入可使自密实混凝土更加密实,抗渗透性能提高。

改性稻草纤维对透水再生混凝土性能的影响

制备了丝状和粉末状两种形态改性稻草纤维,并结合工程实例,设计并开展不同形态和不同掺量的改性稻草纤维对透水再生混凝土性能影响试验。实验结果表明:不同形态改性稻草纤维的掺入均会降低透水再生混凝土抗压强度,但会提升其抗折强度、实际孔隙率和透水系数,其中丝状改性稻草纤维掺量为3.2 kg/m^(3)时透水系数能达到4.53 mm/s,且此时透水再生混凝土抗压强度满足规范要求;而粉末状改性稻草纤维对透水再生混凝土的透水系数提升较小,在掺量为4.8 kg/m^(3)仅能达到3.05 mm/s,说明利用废弃稻草纤维来制备满足透水性能的再生混凝土具有一定的工程意义。

不同粉煤灰掺量再生混凝土氯离子渗透性试验研究

为探究再生混凝土氯离子渗透性能与粉煤灰掺量之间的关系,文中对不同粉煤灰掺量下再生混凝土氯离子渗透性展开试验研究。结果表明,掺入粉煤灰有利于改善再生混凝土试件抗氯离子渗透性能。掺入粉煤灰会直接影响再生混凝土6 h导电量,且6 h导电量随粉煤灰掺量增加而降低,其中,掺量较低时降速较快,掺量达到20%以上时降速放缓,推荐掺加20%粉煤灰制备再生混凝土。氯离子自然扩散试验法用于定量评定再生混凝土氯离子渗透性,其结果更加精准。

再生骨料透水混凝土孔分布及成型均质性试验

再生骨料透水混凝土内部孔分布表征成型均质性,从强度和透水性方面影响应用效果。通过体积法配制不同设计孔隙率、不同浆体流动度的RAPC试件,采用自行设计的分层测试方式,对RAPC的孔隙分布特点进行测试试验,揭示不同配合比设计RAPC材料的孔分布特征,为深入了解成型的均质性提供手段,为性能研究提供新视角,对工程中准确设计和应用有指导作用。

基于不同介质冻融循环的再生骨料透水混凝土性能研究

针对再生骨料透水混凝土在不同介质冻融循环下的性能变化进行了系统研究,通过制备不同配合比的再生骨料透水混凝土试件,并在水、盐水和去离子水等不同介质中进行冻融循环实验,探究冻融循环对混凝土质量损失率、相对动弹性模量、抗压强度剩余量、连续孔隙率和透水系数的影响。结果表明,120次冻融后,2组试样质量损伤率均接近最大值;盐水环境下抗压强度损失更快,60次后强度降低至75%;盐水组连续孔隙率和透水性更高,70次后孔隙率达27.1%,透水系数达4.4%。扫描电镜和XRD分析显示,盐冻初期化学侵蚀显著,产生膨胀物充填微裂隙,后期物理侵蚀加剧冻融损伤,表现为透水率快速上升后缓慢增加,强度逐渐下降,为优化其抗冻性能提供了实验参考。

建筑垃圾再生砖混透水混凝土性能研究

建筑砖混垃圾的再利用有利于节约资源和保护环境,促进中国更快实现“双碳”目标。为研究水灰比和骨料粒径对再生砖混透水混凝土抗压强度和透水系数的影响,文章以水灰比(0.28~0.32)和骨料粒径(4.75~19 mm)作为变量,探究2个变量对抗压强度和透水系数的规律。研究结果表明:一方面,再生砖混透水混凝土的抗压强度在水灰比变化时,起初会有所增强,但之后会呈现下降趋势;而随着骨料粒径的增加,其抗压强度则逐渐减弱。另一方面,该混凝土的透水系数会随着骨料粒径的增大而增加。值得注意的是,不同骨料粒径下的水灰比对透水系数的影响并非一致,存在一定的差异,骨料粒径4.75~9.5 mm和9.5~16 mm下的透水系数随水灰比增大而呈先增大后减小的趋势,而骨料粒径16~19 mm下透水系数随水灰比的增大而减小。文章研究结果可为实际工程提供参考和借鉴。

RAPC抗压强度离散性与骨料关系试验研究

骨料是影响再生骨料透水混凝土(Recycled Aggregate Permeable Concrete,RAPC)强度离散性的关键之一。对不同强度不同来源的再生骨料,设计试验研究RAPC的抗压强度特征和抗压强度离散性。结果表明:RAPC的离散性表现明显,原混凝土强度等级越高,再生骨料的基本物理性能越好,抗压强度与之正相关,抗压强度离散性与之反相关。建筑垃圾回收厂的再生骨料制作的离散性更大。因此回收利用再生混凝土骨料时,有必要根据其强度等级进行分类回收,最大限度地发挥RAPC的性能。

再生骨料透水混凝土力学性能研究

研究目标孔隙率、再生骨料替换率、再生骨料粒径及粉煤灰替换率对透水混凝土力学性能的影响,通过试验分析了各因素对透水混凝土的工作性能、抗压强度、抗折强度和透水系数等性能指标的影响。结果表明,再生骨料的掺入在一定程度上降低了透水混凝土的力学性能,但透水性能得到了显著提升。

再生骨料在透水铺装路面中的应用研究

以不同掺量的再生骨料制备再生透水路面,并进行表观密度、透水系数、抗压强度和抗折强度性能试验。试验结果表明:增加再生骨料掺量会削减再生混凝土的抗压强度和抗折强度,但对透水系数具有增益效果,其中透水系数的波动幅度受再生骨料掺量变化影响最大。综合各性能对比分析结果,建议再生透水混凝土路面采用的再生骨料掺量为40%。

再生骨料防堵塞透水混凝土路面施工技术

采用再生骨料渗透性混凝土既可高效回收利用建筑废垃圾,又可有效改善周围环境,同时助力海绵城市建设,然而堵塞造成的渗透性下降是制约其发展的重要因素。本文通过反复研究实践,发现在道路基层与面层之间设置透水土工布,可有效防止透水混凝土基层堵塞,保障水流顺利通过,从而延长道路使用寿命,最终形成再生骨料防堵塞透水混凝土路面施工技术,利于后续工程借鉴。

多孔再生骨料混凝土强度及透水性能研究

多孔再生骨料混凝土是一种新型环保型材料,为满足强度及透水性能的要求,利用普通压力试验机和自制透水试验装置对试件的7 d强度及透水系数进行了测试。分别取再生骨料取代率为0、50%、100%,水灰比为0.25、0.27、0.30,目标孔隙率为0.2和0.25,分析三个因素对多孔混凝土强度及渗透性能的影响。试验表明再生骨料因具有疏松多孔的特性,多孔再生混凝土强度随取代率的增加而降低。实测孔隙率与目标孔隙率吻合,孔隙率越大,强度值越低,透水性能越好。多孔再生混凝土孔隙率与透水性具有很好的相关性。