Use of recycled demolition aggregate in precast products,phase II: Concrete paving blocks

A study undertaken at the University of Liverpool has investigated the potential for using construction and demolition waste (C&DW) as aggregate in the manufacture of a range of precast concrete products, i.e. building and paving blocks and pavement flags. Phase II, which is reported here, investigated concrete paving blocks. Recycled demolition aggregate can be used to replace newly quarried limestone aggregate, usually used in coarse (6 mm) and fine (4 mm-to-dust) gradings. The first objective, as was the case with concrete building blocks, was to replicate the process used by industry in fabricating concrete paving blocks in the laboratory. The compaction technique used involved vibration and pressure at the same time, i.e. a vibro-compaction technique. An electric hammer used previously for building blocks was not sufficient for adequate compaction of paving blocks. Adequate compaction could only be achieved by using the electric hammer while the specimens were on a vibrating table. The experimental work involved two main series of tests, i.e. paving blocks made with concrete- and masonry-derived aggregate. Variables that were investigated were level of replacement of (a) coarse aggregate only, (b) fine aggregate only, and (c) both coarse and fine aggregate. Investigation of mechanical properties, i.e. compressive and tensile splitting strength, of paving blocks made with recycled demolition aggregate determined levels of replacement which produced similar mechanical properties to paving blocks made with newly quarried aggregates. This had to be achieved without an increase in the cement content. The results from this research programme indicate that recycled demolition aggregate can be used for this new higher value market and therefore may encourage demolition contractors to develop crushing and screening facilities for this.     

硅粉对纤维橡胶再生混凝土抗压性能影响试验

以普通混凝土和橡胶再生混凝土为研究对象,通过掺入硅粉和纤维材料研究强化环保型混凝土抗压性能的方法。用再生混凝土100%等体积代替粗骨料,用橡胶颗粒20%等体积代替细骨料,内掺10%（质量分数）或外掺3%（质量分数）硅粉以及掺入聚丙烯纤维或钢纤维,制备了4组12个混凝土立方体试件,通过轴压试验研究了混凝土试件的破坏模式、抗压强度和工作性能。结果表明:与单一掺入硅粉相比,硅粉和聚丙烯纤维的复合掺入能进一步强化混凝土的抗压性能;硅粉的掺入可以强化浆体与橡胶颗粒间的界面性能,提高钢纤维橡胶再生混凝土的抗压强度;硅粉和纤维材料对混凝土的工作性能有负作用,其复合掺入时建议采用适量的减水剂。     

Properties of concrete pedestrian block mixed with crumb rubber

Recycling granulated waste tires (crumb rubber) has been widely studied for the last twenty years mostly relating to applications such as asphalt pavement, waterproofing system, membrane liners, etc. In this study, the use of crumb rubber to replace coarse and fine aggregates in concrete pedestrian block was studied. It is believed that concrete acting as a binder mixed with crumb rubber can make concrete blocks more flexible and thus, provide softness to the surface. The crumb rubber block also performed quite well in both skid and abrasion resistance tests. The production process was economical, due to the simplicity of the manufacturing process.     

Use of crumb rubber to improve thermal and sound properties of pre-cast concrete panel

In this study, the thermal and sound properties of crumb rubber concrete panel were investigated. The crumb rubber from used tires, produced in a local recycling plant, was used to replace fine aggregate at ratios of 10%, 20% and 30%. Properties such as thermal conductivity, thermal resistivity, heat transfer, conductance value, sound absorption at different frequency and noise reduction were investigated. Results indicated that crumb rubber concrete panel was not only lighter but had higher sound absorption and lower heat transfer properties than the conventional concrete panel.     

Paving blocks made with recycled concrete aggregate and crushed clay brick

Clay brick generated from construction sites is usually delivered to landfills for disposal. With the limited landfill space in Hong Kong, there is an immediate need to explore the possible use of crushed clay brick as a new civil engineering material. In Hong Kong, government specifications promote the use of paving blocks made with 70–100% recycled concrete aggregate in order to facilitate the recycling of construction and demolition (C&D) waste. This paper presents a recent study at the Hong Kong Polytechnic University on the investigation of blending recycled concrete aggregate and crushed clay brick as aggregates in the production of paving blocks.The results indicated that the incorporation of crushed clay brick reduced the density, compressive strength and tensile strength of the paving blocks. Due to the high water absorption of crushed clay brick particles, the water absorption of the resulting paving blocks were higher than that of the paving blocks that did not incorporate crushed clay brick. Although it was found that crushed clay brick impaired the quality of the resulting paving blocks to a certain extent, the paving blocks using 50% crushed clay brick met the minimum requirements specified by AS/NZS 4455 and ETWB of Hong Kong (Grade B) for pedestrian areas. Furthermore, it was feasible to produce paving blocks prepared with 25% crushed clay brick that satisfied the compressive strength requirement for paving blocks (Grade B) prescribed by ETWB of Hong Kong for trafficked area.     

Concrete building blocks made with recycled demolition aggregate

A study undertaken at the University of Liverpool has investigated the potential for using recycled demolition aggregate in the manufacture of precast concrete building blocks. Recycled aggregates derived from construction and demolition waste (C&DW) can be used to replace quarried limestone aggregate, usually used in coarse (6 mm) and fine (4 mm-to-dust) gradings. The manufacturing process used in factories, for large-scale production, involves a “vibro-compaction” casting procedure, using a relatively dry concrete mix with low cement content (≈100 kg/m³). Trials in the laboratory successfully replicated the manufacturing process using a specially modified electric hammer drill to compact the concrete mix into oversize steel moulds to produce blocks of the same physical and mechanical properties as the commercial blocks. This enabled investigations of the effect of partially replacing newly quarried with recycled demolition aggregate on the compressive strength of building blocks to be carried out in the laboratory. Levels of replacement of newly quarried with recycled demolition aggregate have been determined that will not have significant detrimental effect on the mechanical properties. Factory trials showed that there were no practical problems with the use of recycled demolition aggregate in the manufacture of building blocks. The factory strengths obtained confirmed that the replacement levels selected, based on the laboratory work, did not cause any significant strength reduction, i.e. there was no requirement to increase the cement content to maintain the required strength, and therefore there would be no additional cost to the manufacturers if they were to use recycled demolition aggregate for their routine concrete building block production.     

不同工艺生产的橡胶微粒对路面混凝土性能的影响

目前橡胶微粒生产工艺多种多样,且不同工艺生产的橡胶微粒对混凝土性能的影响不一。本文从路面混凝土的工作性能和强度方面,研究两种工艺生产的橡胶微粒在不同掺量时对路面混凝土性能的影响。     

Use of recycled aggregates in molded concrete bricks and blocks

This study aimed to develop a technique for producing concrete bricks and paving blocks using recycled aggregates obtained from construction and demolition waste. Laboratory trials were conducted to investigate the possibility of using recycled aggregates from different sources in Hong Kong, as the replacement of both coarse and fine natural aggregates in molded bricks and blocks. A series of tests were carried out to determine the properties of the bricks and blocks prepared with and without recycled aggregates. The test results showed that the replacement of coarse and fine natural aggregates by recycled aggregates at the levels of 25 and 50% had little effect on the compressive strength of the brick and block specimens, but higher levels of replacement reduced the compressive strength. However, the transverse strength of the specimens increased as the percentage of replacement increased. Using recycled aggregates as the replacement of natural aggregates at the level of up to 100%, concrete paving blocks with a 28-day compressive strength of not less than 49 MPa can be produced without the incorporation of fly ash, while paving blocks for footway uses with a lower compressive strength of 30 MPa and masonry bricks can be produced with the incorporation of fly ash.     

橡胶改性水泥混凝土(砂浆)的研究综述

综述了国内外利用废旧橡胶粉对混凝土(砂浆)改性的研究进展。有文献表明:与普通混凝土相比,橡胶改性水泥混凝土具有轻质及耐久性能、韧性和延性、抗冲击性能、抗爆裂性能、隔声和隔热性能好等特点。但是,目前橡胶粉-混凝土复合材料的研究仍存在一些问题。     

再生粗骨料的微观特征及基本性能研究

作为建筑垃圾主要组成之一的废弃混凝土,可以通过回收处理变为再生混凝土骨料,部分或全部代替天然骨料而再次应用到建筑工程中。通过扫描电子显微技术,对破碎后的骨料表面的微观状态进行了观察分析,得到了再生骨料表观特征以及微裂缝分布情况。同时依照JGJ 52-2006《普通混凝土用砂、石质量及检验方法标准》对再生粗骨料进行了基本性能测试,并与天然粗骨料的基本性能进行对比。通过实验,得出了再生粗骨料具有表观密度小、吸水率与含水率高、压碎指标值较高、针片状含量小的特点。还对实验结果进行了分析,为制备再生混凝土提供了依据。     

废旧橡胶再生混凝土抗压性能试验研究

本文通过11组再生混凝土立方体抗压强度试验,以再生粗骨料取代率和废旧橡胶粒的掺量两个参数作为变量,研究了废旧橡胶再生混凝土的抗压性能和破坏特征.试验结果表明:橡胶颗粒降低了再生混凝土的抗压强度,但能有效提高再生混凝土的延性.     

NO removal efficiency of photocatalytic paving blocks prepared with recycled materials

This paper presents the results of a study on the effectiveness of incorporating air cleaning agents such as titanium dioxide (TiO₂) into the technique of producing concrete paving blocks, using local waste materials to remove nitrous oxide (NO). Factors which would affect the performance of the blocks were studied including the porosity of blocks, the type of waste materials used within the mix design, the types and percentage of TiO₂ added within the mix design.The results show that the photodegradation of NO is related to the porosity of the blocks. When the porosity of the block was increased so was the NO removal ability. Hence the choice, size and content of aggregate material used in the mix design are important. In addition, crushed recycled glass cullet was used to place part of the aggregates in the blocks and was found to benefit the NO removal ability due to its light transmitting characteristic. Three types of TiO₂ were tested in this study and their influence on NO removal was quantified. Based on the experimental results, an optimum mix design was selected which incorporates recycled glass, sand, cement and TiO₂.     

再生混凝土路面砖性能影响因素分析

以再生混凝土路面砖为研究对象,采用正交试验方法研究了养护龄期、粉煤灰取代率、被取代物(水泥、细骨料、水泥-细骨料)对再生砖孔隙率、抗压强度、抗折强度的影响。结果表明:粉煤灰取代率对再生砖的孔隙率影响程度最大,养护龄期对再生砖的抗压和抗折强度影响程度最大,试验范围内再生砖取得最佳性能的方案为养护龄期28 d、粉煤灰取代6%细骨料。     

氯离子腐蚀环境下CFRP筋再生混凝土梁力学性能研究

利用经过破碎处理后的废弃混凝土制备了再生混凝土,对比分析了再生混凝土和普通混凝土的力学性能和工作性,探讨了再生混凝土在建筑工程中的应用前景。同时,采用CFRP筋代替混凝土梁中的部分受力钢筋和箍筋,研究了氯离子腐蚀环境下,浸泡时间对CFRP再生混凝土梁开裂弯矩的影响。结果表明,再生混凝土的力学性能和工作性均能满足要求;使用CFRP筋代替部分受力钢筋和箍筋,对于提高再生混凝土梁的开裂弯矩有明显效果;CFRP筋再生混凝土梁的抗氯离子侵蚀能力较好。     

多因素对再生骨料透水混凝土性能的影响及其协同优化研究

研究了骨料级配、水灰比、砂率、设计孔隙率、胶骨比等因素对再生骨料透水混凝土透水系数、抗压强度与弯拉强度的影响;并通过改变水泥品种、添加增强剂、电炉渣与再生骨料复配等方式协同优化再生骨料透水混凝土透水性能、力学性能、抗冻性能、路用性能。结果表明:再生骨料透水混凝土抗压强度和透水性能影响因素主次顺序均为:设计孔隙率>骨料级配>砂率>水灰比;建议再生骨料透水混凝土设计孔隙率为10%~20%,水灰比为0.29~0.32,砂率控制在5%~10%,胶骨比为0.29;采用电炉渣可以大幅提升透水混凝土的力学性能和耐磨性能,但其透水性和抗冻性相差不大。     

Les betons de demolition source de granulats

In spite of the circumstances, the consumption of aggregates in France is still important. The opening of new gravel pits encounters a more severe regulation and the populations' reticence. Otherwise, in the big agglomerations, a lot of constructions are no longer in accordance with present requirements. So, two solutions are available to meet the requirements: the restoration or the demolition. When the latter solution is chosen, the tipping of the waste concrete is very expensive. From this point of view, the recycling of demolished concrete could become very interesting. The demolished concrete elements already used for filling can be improved in using them as aggregates for new concrete, which will minimize the nomber of extractions of good aggregates, and will partly eliminate the tipping problems. We have shown that the use of all sizes of aggregates coming from the concrete crushing was not suitable. If the concrete exclusively contains aggregates above 4 mm, its mechanical properties approaches those of the reference normal concrete but the characteristics of concrete including recycled sands prove to be very poor. Thus, to specify their influence, we realized some tests on mortar. In that case, the main criterion isn't the size, but the total volume of the recycled particles. Two parameters influence the weakening of mechanical properties: the shape and the nature of particles. For concretes containing only recycled aggregates above 4 mm, concretes present creepings and shrinkages which are 30 % higher than those of the reference concrete, but which have similar strengths. The density and the elasticity modulus, are slightly lower (2 to 4 %).     

橡胶粉改性混凝土的试验研究

对废旧轮胎橡胶粉碎料作为添加成分取代部分细骨料的混凝土的力学性能进行了试验,制备了多组不同橡胶粒径和掺量的橡胶粉改性混凝土试件,试验采用的橡胶粉为废旧轮胎橡胶胶粉,掺量为细骨料体积的5％、10％、15％和20％,探讨橡胶粉粒径和掺量变化对力学性能的影响,结果表明：掺人废旧轮胎橡胶胶粉的混凝土的抗压强度、抗折强度会随橡胶掺量的增加而降低;折压比增加。     

废旧轮胎橡胶混合法改性沥青混合料的研究

运用包括湿法和干法两道工艺的混合法,在实验室成功开发了废旧轮胎橡胶改性沥青混合料.即先用细橡胶粉制备成橡胶沥青,然后在集料中加入粗橡胶粉拌制成废橡胶改性沥青混合料.试验结果表明,与类似级配的湿法工艺或干法工艺的改性沥青混合料相比,混合法改性沥青混合料显示出更加优良的高、低温性能,水稳定性完全满足要求,且消耗了相对多的废旧轮胎,达到了环保和工程双赢的目的.     

Analysis of digestion time and the crumb rubber percentage in dry-process crumb rubber modified hot bituminous mixes

The use of crumb rubber modifier (CRM) in bituminous mixes made by the dry process is not as widely used as the wet process. Nonetheless, this process has advantages, such as the potential to consume larger quantities of crumb rubber, thus resulting in greater savings in energy and natural resources. This research study contributes to the further development and evolution of the dry process through the analysis of the effect of the digestion time (the contact time between the crumb rubber and the bitumen) and the quantity of crumb rubber on the mix design properties. The results of the study showed that the digestion time had no influence on the selection of the optimal binder content or on the compaction of the mixture. In contrast, the digestion time was found to have an impact on the mechanical performance of the mix. In this respect, an increase in the quantity of crumb rubber contributed to a corresponding increase in the amount of bitumen needed, and also caused the mix to become less compact. This study showed that a crumb rubber percentage of less than 1% of the total weight of the mix and a digestion time of 90 min produced the best results.     

废旧钢纤维橡胶再生混凝土抗压性能试验研究

以再生粗骨料取代率和废旧钢纤维橡胶粒掺量两参数作为变量配制C30废旧钢纤维橡胶再生混凝土,研究其抗压性能和破坏特征,并与相同配比的废旧橡胶再生混凝土进行对比分析,试验结果表明再生混凝土中的废旧钢纤维橡胶颗粒会降低其抗压强度,但能有效改善其抗裂性能,在30％取代率下其抗压性能低于废旧橡胶再生混凝土,但在60％取代率下则相...