Mechanical properties modeling of recycled aggregate concrete

The variability observed in the composition of construction and demolition (C&D) waste is a problem that inhibits the use of recycled aggregates in concrete production. To contribute in this field, a research was carried out varying water/cement ratio and substitution percent of natural aggregates by recycled aggregates. The experimental program used samples of main Brazilian C&D waste sources, which are concrete, mortar and red ceramic bricks as well as tiles. Results of concrete compressive strength and elastic modulus were statistically analyzed and modeled. The study shows that for both concrete properties, recycled coarse aggregate was more influential than recycled fine aggregate. However, the use of fine recycled red ceramic increased concrete strength. Coarse recycled red ceramic aggregate and fine recycled concrete aggregate exercised the largest and the smallest influence, respectively, in concrete properties.     

陶瓷废弃物代砂制备混凝土的强度特征

陶瓷废弃物经破碎筛分加工制成人工砂,以此作为混凝土的细骨料进行部分或全部取代天然砂,并对制备的混凝土不同龄期的抗压强度、抗折强度等特征进行了试验研究,研究中对不同取代率、灰水比、陶瓷砂处理方式、龄期等因素对陶瓷砂混凝土强度特征进行了系统考察.研究表明,陶瓷废弃物经破碎筛分加工后,可以满足混凝土用砂规范的要求,尤其是加工过程中与部分碎石混合破碎,其人工砂的性能是优异的.可全部取代优质河砂,而纯陶瓷废弃物加工的砂配制的混凝土,其立方体抗压强度和抗折强度值均能达到设计要求,甚至可以超过同等配合比的天然河砂配制的混凝土的强度;陶瓷砂混凝土的强度与天然骨料混凝土的变化规律相似,即随灰水比的增加而提高,随龄期的增长强度不断增加.强度特征的评价为陶瓷砂混凝土的配合比设计提供了有效的依据.     

Effect of crushed ceramic and basaltic pumice as fine aggregates on concrete mortars properties

This study examines the suitability of ceramic industrial wastes and huge amounts of basaltic pumice as a possible substitute for conventional crushed fine aggregates. Experiments were carried out to determine abrasion resistance, chloride penetration depths and the compressive strengths of concrete with crushed ceramic waste and basaltic pumice fine aggregates and to compare them with those of conventional concretes. Test results indicated that ceramic wastes and basaltic pumice concretes had good workability. Furthermore, it was found that abrasion resistance of crushed ceramic (CC) and crushed basaltic pumice (CBP) concretes was lower than that of conventional concretes. Test results also showed that maximum abrasion rate was obtained from specimen control (Mo), while minimum abrasion rate is obtained from M3 (60% crushed ceramic concrete) specimens. Abrasion resistance was increased as the rate of fine CC was decreased. Abrasion resistance of concrete was strongly influenced by its compressive strengths and CC and crushed CBP content. The crushed ceramic addition percentage decreased as the chloride penetration depth increased. Results of this investigation showed that CC and CBP could be conveniently used for low abrasion and higher compressive strength concretes.     

Use of waste marble aggregates in concrete

Today we are faced with an important consumption and a growing need for aggregates because of the growth in industrial production, this situation has led to a fast decrease of available resources. On the other hand, a high volume of marble production has generated a considerable amount of waste materials; almost 70% of this mineral gets wasted in the mining, processing and polishing stages which have a serious impact on the environment. The processing waste is dumped and threatening the aquifer. Therefore, it has become necessary to reuse these wastes particularly in the manufacture of concrete products for construction purposes. The main goal of this study is to demonstrate the possibility of using marble wastes as a substitute rather than natural aggregates in concrete production. The paper presents the study methodology, the characterization of waste marble aggregates and various practical formulations of concrete. This experimental investigation was carried out on three series of concrete mixtures: sand substitution mixture, gravel substitution mixture and a mixture of both aggregates (sand and gravel). The concrete formulations were produced with a constant water/cement ratio. The results obtained show that the mechanical properties of concrete specimens produced using the marble wastes were found to conform with the concrete production standards and the substitution of natural aggregates by waste marble aggregates up to 75% of any formulation is beneficial for the concrete resistance.     

以废弃陶瓷为骨料生产再生混凝土可行性探讨

通过国内外有关文献的分析与研究,介绍了使用陶瓷废弃物取代天然骨料生产混凝土的发展情况及可行性,分析了用陶瓷废弃物作原料生产再生混凝土的社会效益和经济效益,为我国陶瓷废弃物的处理提供了一条新思路.     

Effect of copper slag as a fine aggregate on the properties of cement mortars and concrete

An experimental investigation was conducted to study the effect of using copper slag as a fine aggregate on the properties of cement mortars and concrete. Various mortar and concrete mixtures were prepared with different proportions of copper slag ranging from 0% (for the control mixture) to 100% as fine aggregates replacement. Cement mortar mixtures were evaluated for compressive strength, whereas concrete mixtures were evaluated for workability, density, compressive strength, tensile strength, flexural strength and durability. The results obtained for cement mortars revealed that all mixtures with different copper slag proportions yielded comparable or higher compressive strength than that of the control mixture. Also, there was more than 70% improvement in the compressive strength of mortars with 50% copper slag substitution in comparison with the control mixture. The results obtained for concrete indicated that there is a slight increase in density of nearly 5% as copper slag content increases, whereas the workability increased significantly as copper slag percentage increased compared with the control mixture. A substitution of up to 40–50% copper slag as a sand replacement yielded comparable strength to that of the control mixture. However, addition of more copper slag resulted in strength reduction due to the increase in the free water content in the mix. Also, the results demonstrated that surface water absorption decreased as copper slag content increases up to 50% replacement. Beyond that, the absorption rate increased rapidly and the percentage volume of the permeable voids was comparable to the control mixture. Therefore, it is recommended that up to 40–50% (by weight of sand) of copper slag can be used as a replacement for fine aggregates in order to obtain a concrete with good strength and durability requirements.     

陶瓷废料制备建筑饰面片材的研究

以晋江地区的陶瓷废料主要原料,经过干燥、粉碎,采用偶联剂改性后,添加水泥熟料、减水剂、聚合物乳液和不同添加量的增强纤维,经拌和、成型、干燥制备出建筑饰面片材。制备出的样品性能优异,均能符合现行行业标准《改性无机粉复合建筑饰面片材》JC/T 2219吸水率、耐热性(尺寸变化率)、柔度的技术指标要求,这项研究为晋江地区的陶瓷废料的综合再利用提供了新的途径。     

Betons a hautes performances,a granulats artificiels actifs

High strength concretes, in particular at early ages (more than 40 MPa at 3 days and up to 80 MPa at 7 days), are obtained by replacement of certain granular size ranges of sand or gravel by cement-active artificial aggregates in a given concrete composition elaborated with a local supply of aggregates and cement. The strengthening of the paste-aggregate bond by chemical reactions between the artificial aggregates and the cement also involves an improvement of other concrete performances and not only of mechanical strengths. The cracking ability is decreased, the wear strength is higher, and water permeability is low or even nil for certain compositions. The laboratory results are confirmed by tests on the site and show the possibility of achieving high strength concretes without any particular selection of cement and natural aggregates.     

Use of concrete road recycled aggregates for Roller Compacted Concrete

Construction waste management is a quite important economical and environmental deal for our societies. More than 2 million tons demolition and construction wastes are annually produced only in Wallonia, Southern Region of Belgium; recycling has clearly to be promoted. Roller Compacted Concrete (RCC) is a special dry concrete made of aggregates, water and low quantity of cement, laid down and compacted like a soil, for the construction of massive structures like dams or large horizontal surfaces like road foundations. The topic of this research is the replacement of natural aggregates by concrete road recycled aggregates in the mix design of concrete. Characteristics of aggregates are of prime importance for the quality of the concrete: Los Angeles, water absorption and specific gravity. It has been observed that RCC with natural and concrete road recycled aggregates are similar for solid compactness, while no major influence of cement content – when around 200 kg – may be detected. However, compressive strength is higher for RCC with natural aggregates. This study clearly shows the opportunity of using concrete road recycled aggregates for RCC in basements.     

废瓷砖再生骨料与水泥石的界面特征

以废瓷砖再生骨料(CRA)100%替代原生碎石骨料(NCA),制备了废瓷砖再生骨料混凝土(CRAC),测试了其工作性及力学强度.采用化学结合水法、扫描电子显微镜(SEM)及比表面积测试法(BET)等,研究了废瓷砖再生骨料-水泥石界面黏结强度、水化程度及显微结构,探讨其界面特征,并将其与原生碎石骨料(NCA)-水泥石界面相比较.结果表明:与原生碎石骨料相比,废瓷砖再生骨料具有表观密度较小、压碎指标较高及吸水率较大等特点;在相同配合比条件下,废瓷砖再生骨料混凝土具有更好的工作性和力学强度;在相同水灰比、相同龄期条件下,废瓷砖再生骨料-水泥石界面黏结强度较高,其界面区生成的水化产物较多、孔隙率更低、显微结构更加致密.     

轻骨料透水混凝土的研究

用粘土陶粒作为粗骨料、膨胀珍珠岩作为细骨料和其他胶凝材料(水泥和粉煤灰)通过人工搅拌的方法配制轻骨料透水混凝土,研究不同的水泥、粉煤灰和细轻骨料用量对混凝土抗压强度、孔隙率、透水系数、pH值及表观密度等性能的影响。结果表明,随着水泥、粉煤灰和细轻骨料用量的增加,轻骨料透水混凝土的强度增加、表观密度增大,而孔隙率、透水系数会降低,pH值变化不大。     

The properties of concrete made with fine dune sand

This paper presents the results of a study that investigated the properties of concrete made with dune sand. Different control concrete mixtures using ordinary Portland cement (OPC) with a minimum design compressive strength of 40 N/mm² were prepared. The amount of fine aggregates constituted about 36% by weight of all the aggregates. The workability ranged from low of 16 mm to a high of 122 mm. For each control mix, other mixtures were prepared in which the fine aggregates were replaced by different percentages of dune sand ranging from 10% to 100%. The effect of dune sand on the workability, compressive strength, tensile strength, modulus of elasticity and initial surface absorption test (ISAT) was studied. Experimental results show an improvement in the workability of concrete when fine aggregates were partially replaced by dune sand. An increase in slump was measured with increase in dune sand content. However, at high dune sand contents (above 50%); the slump starts to decrease with an increase in dune sand. Generally, the strength values decrease with increase in dune sand replacement. The strength loss was not found considerable as the maximum reduction was less than 25% when fine aggregates were fully replaced by dune sand. The absorption characteristics of concrete made with OPC as measured by the (ISAT) generally increased with higher dune sand contents.     

球模型包裹法设计透水混凝土配合比

提出一种新的透水混凝土配合比设计方法,以球作为粗骨料颗粒的计算模型,测算单位体积粗骨料总表面积,再与裹浆厚度、水灰比和粗骨料堆积密度四个参数确定配合比.试验表明:在一定范围内,骨料粒径越大,水泥浆包裹越薄.透水混凝土的透水系数越大,强度越小,耐酸性能越差.通过材料的内部孔隙结构分析其性能变化规律,验证了该方法的合理性.     

混凝土材料完全循环利用的探讨

根据国内外混凝土材料循环利用的研究发展现状,提出了混凝土材料完全循环利用的可能性,具体分析了混凝土材料完全循环利用的途径和方法,并通过实验证实了混凝土材料可以多次循环利用,从而实现混凝土材料的生态化生产和使用.     

Scrap-tyre-rubber replacement for aggregate and filler in concrete

In this research the performance of concrete mixtures incorporating 5%, 7.5% and 10% of discarded tyre rubber as aggregate and cement replacements was investigated. Numerous projects have been conducted on replacement of aggregates by crumb rubbers but scarce data are found on cementitious filler addition in the literature. Hence to examine characteristics of tyre crumb-containing concrete, two sets of concrete specimens were made. In the first set, different percentages by weight of chipped rubber were replaced for coarse aggregates and in the second set scrap-tyre powder was replaced for cement. Selected standard durability and mechanical test were performed and the results were analysed. The mechanical tests included compressive strength, tensile strength, flexural strength and modulus of elasticity. The durability tests included permeability and water absorption. The results showed that with up to 5% replacement, in each set, no major changes on concrete characteristics would occur, however, with further increase in replacement ratios considerable changes were observed.     

再生粗骨料对混凝土坍落度和抗压强度的影响

简述了哈尔滨市城市建筑垃圾的产生量和利用度,研究粗骨料的主要指标;采用再生粗骨料20%、30%、50%、70%、100%等质量代替天然碎石骨料配制了C30混凝土,研究了再生粗骨料对混凝土工作性和抗压强度的影响。研究结果表明:在水胶比相同时,混凝土坍落度下降,28d强度降低;若要保持混凝土坍落度基本相同,需采用增加用水量或增大减水剂的方式进行调整。     

冻融循环过程中混凝土内部微观结构的演变

试验研究了冻融破坏过程中混凝土强度、内部结构的演变规律。试验结果表明:与抗压强度相比,抗折强度、劈拉强度的劣化趋势更明显;冻融破坏使水泥水化产物的结构从堆积状密实体逐步变成疏松状态,气泡壁逐步出现了开裂。从孔径分布情况来看,孔径25~75 nm之间的孔隙所占的比例呈增大趋势。     

Mechanical properties of brick aggregate concrete

This paper presents the results of a research program carried out at University of Aveiro, Portugal to evaluate the properties of concrete made with crushed bricks replacing natural aggregates. Two types of brick were investigated. The bricks were crushed in order to obtain a usable aggregate. The properties investigated were the workability and the density of fresh concrete, and the compressive strength, tensile splitting strength, modulus of elasticity and stress–strain behaviour of hardened concrete. Replacement ratios of natural aggregates by 15% and 30% were investigated as well as water/cement ratios of 0.45 and 0.5. Strength indexes were used to assess the effectiveness of aggregate replacement. The results of concrete produced with recycled aggregates were compared with a reference concrete produced with natural limestone aggregates currently used in Portugal. Observed results indicate that ceramic residuals could be used as partial replacement of natural aggregates in concrete without reduction of concrete properties for 15% replacement and with reductions up to 20% for 30% replacement. The type and the manufacturing process of bricks seem to influence the properties of the resulting concrete. The properties and aesthetics of concrete with bricks indicate the possibility of using this type of concrete in precast applications.     

陶瓷砖抛光粉在C30混凝土中的应用

陶瓷抛光砖粉是陶瓷抛光砖在生产过程中研磨、抛光产生的废料,其颗粒细小,具有一定的火山灰活性,可用于水泥、混凝土领域。利用陶瓷抛光砖粉替代部分水泥,制备了C30混凝土,重点研究了混凝土的强度和耐久性能。研究结果表明:掺加5%~10%的陶瓷抛光砖粉可改善混凝土的工作性能、提高混凝土各龄期抗压强度,同时混凝土的耐久性也得到显著提高。但当陶瓷抛光砖粉掺量超过20%时,混凝土的力学性能和耐久性均大幅度下降。因此,C30混凝土中陶瓷抛光砖粉掺量应控制在20%以内。     

煤矸石集料性质对混凝土力学性能影响的试验研究

主要研究煤矸石集料的基本性质:矸石种类、颗粒级配、集料的预处理方式等对混凝土7,28,90d抗压强度及弹性模量的影响规律,为煤矸石集料混凝土的优化配合比设计提供依据。试验结果表明:矸石集料自身的强度极大地影响混凝土的强度,在不同强度的水泥基体下,当水泥基体强度与集料强度相协调时,其混凝土的强度才能达到最大,但是在低强的水泥基体下,提高矸石集料的粒径尺寸及比例,并不能提高混凝土的强度;自燃矸石集料经过预湿处理,能够提高混凝土的力学性能,但非自燃矸石集料经预湿处理后,并不能提高其混凝土的力学性能。