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.     

再生骨料高性能混凝土收缩徐变对比试验研究

用不同粗骨料(石灰石碎石、再生粗骨料)、细骨料(河砂、人工砂、再生细骨料)两两相组合,共配制6组高性能混凝土进行对比试验,测试抗压强度、弹性模量、收缩和徐变4个性能指标并进行显著性分析。结果表明,骨料类型对高性能混凝土抗压强度的影响不明显,但对弹性模量、收缩和徐变性能都有显著影响。粗骨料对弹性模量和收缩性能的影响较为显著,细骨料对徐变的影响较为显著。再生粗骨料混凝土收缩、徐变早期发展较慢,而中后期的发展速度明显快于普通混凝土;再生细骨料混凝土收缩、徐变的发展速度始终远快于普通混凝土。在此基础上,提出了考虑粗、细骨料类型和骨料种类的高性能混凝土收缩和徐变的预测模型。     

Investigation on the flexural behaviour of high-performance reinforced concrete beams using sandstone aggregates

In recent years, an emerging technology termed high-performance concrete (HPC) has become popular in construction industry. The constituent materials of HPC depend on the desired characteristics and the availability of suitable local economic alternatives. Tests are reported in this study on the flexural behaviour of high-performance reinforced concrete (HPRC) beams made with crushed sandstone coarse and fine aggregate together with silica fume. The beams were made from concrete having compressive strength of 74 and 78 N/mm² and tensile reinforcement ratio in the range of 1.34–3.14%. The ultimate moment for the tested beams was found to be about 14–30% and 3–9% higher than that of the predicted ultimate moment based on BS 8110 and ACI 318, respectively. Due to lower stiffness of sandstone aggregates, the beams resulted in excessive deflection under service loads. The observed crack width under service loads were within acceptable limits. The mineral fillers in crushed sandstone sand and silica fume increased the flexural stiffness of HPRC beams and resulted in adequate safety factors against flexural failure. The test results showed that it is possible to produce HPC using sandstone aggregates with silica fume and superplasticisers.     

全再生混凝土概念的衍化与研究进展

全面梳理和分析了再生混凝土的发展历程与演变特点,提出了全再生混凝土的基本概念,基于文献分析,针对不同组分、不同取代率下再生混凝土的工作性能、力学性能和耐久性能开展了对比分析.整理了当再生粗骨料、再生细骨料分别单取代且取代率达到100％ 及再生粗、细骨料双取代的取代率都达到100％ 后混凝土各性能变化的量值,最后总结了再...     

再生混凝土骨料试验研究

在试验基础上分别配制了高(H)、中(M)、低(L)3种强度等级的原生混凝土．将原生混凝土进行人工破碎、筛分后制得再生混凝土粗、细骨料，然后分别对再生混凝土粗、细骨料以及原生混凝土粗、细骨料的一系列物理力学性能进行了研究．研究结果表明：再生混凝土粗、细骨料与原生混凝土粗、细骨料之间性质差别较大；在原材料相同的情况下，由配合比不同的原生混凝土破碎后所得到的不同再生混凝土骨料之间性质差异很小，这对于控制再生混凝土骨料以及再生混凝土的质量波动是非常有意义的．     

The effects of polypropylene fibers on the properties of reinforced concrete structures

In this study, the results of polypropylene fibers reinforced concrete properties have been presented. The compressive strength, permeability and electric resistivity of concrete samples were studied. The concrete samples were made with different fibers amounts from 0 to 2 kg m⁻³. Also, the samples fabricated with coral aggregate and siliceous aggregate were examined and compared. The samples with added polypropylene fibers of 1.5 kg m⁻³ showed better results in comparison with the others. Moreover, coral aggregate concrete showed less electric resistivity and less compressive strength in comparison with samples fabricated of siliceous aggregates. It is concluded that the coral aggregates are not suitable for making concrete or using in concrete structures in the onshore atmosphere.     

Effects of coarse and fine aggregates on long-term mechanical properties of sea sand recycled aggregate concrete

Typical effects of coarse and fine aggregates on the long-term properties of sea sand recycled aggregate concrete (SSRAC) are analyzed by a series of axial compression tests. Two different types of fine (coarse) aggregates are considered: sea sand and river sand (natural and recycled coarse aggregates). Variations in SSRAC properties at different ages are investigated. A novel test system is developed via axial compression experiments and the digital image correlation method to obtain the deformation field and crack development of concrete. Supportive results show that the compressive strength of SSRAC increase with decreasing recycled coarse aggregate replacement percentage and increasing sea sand chloride ion content. The elastic modulus of SSRAC increases with age. However, the Poisson’s ratio reduces after 2 years. Typical axial stress–strain curves of SSRAC vary with age. Generally, the effect of coarse aggregates on the axial deformation of SSRAC is clear; however, the deformation differences between coarse aggregate and cement mortar reduce by adopting sea sand. The aggregate type changes the crack characteristics and propagation of SSRAC. Finally, an analytical expression is suggested to construct the long-term stress–strain curve of SSRAC.     

不同粗细骨料组合下的混凝土耐硫酸腐蚀研究

为比较不同粗细骨料组合对混凝土耐硫酸腐蚀性能的影响,对水灰比为0.45、尺寸为100×200的4种骨料组合（青石+黄砂,青石+大理砂,大理石+黄砂,大理石+大理砂）混凝土试件进行耐硫酸加速腐蚀试验。将混凝土试件浸泡于pH值为0.95左右的硫酸溶液中进行为期194 d的12次跟踪监测,根据检测数据计算得到了混凝土的腐蚀深度,按线性方程斜率从大到小对4种骨料组合混凝土硫酸腐蚀速率进行了排序。结果表明:含有大理石或大理砂骨料的混凝土比含青石和黄砂骨料的混凝土耐硫酸腐蚀性能高;腐蚀层受扰动情况下,腐蚀深度与腐蚀时间呈线性关系;大理石细骨料比大理石粗骨料更有利于减小腐蚀深度。     

Properties of concrete made with recycled crushed glass at elevated temperatures

The effect of replacement of fine and coarse aggregates with recycled glass on the fresh and hardened properties of Portland cement concrete at ambient and elevated temperatures is studied. Percentages of replacement of 0–100% of aggregates with fine waste glass (FWG), coarse waste glass (CWG), and fine and coarse waste glass (FCWG) were considered. Soda-lime glass used for bottles was washed and crushed to fine and coarse aggregate sizes for use in the concrete mixes. Samples were cured under 95% RH at room temperatures (20–22 °C), heated in the oven to the desired temperatures, allowed to cool to ambient temperatures, and then tested for their residual compressive strength. The compressive strength of the concrete samples made with waste glass was measured at temperatures up to 700 °C. Moreover, the effect of the percentages of replacement with recycled glass on the slump values and initial and final setting time of concrete has also been measured.     

Reuse of incineration fly ashes and reaction ashes for manufacturing lightweight aggregate

This paper reports the result of the investigation on manufacturing lightweight aggregate by incorporating municipal solid waste (MSW) incineration fly ashes and reaction ashes with reservoir sediments. The investigation was first performed in a laboratory scale to assess the effects of the composition and the firing conditions on the properties of the resulting aggregate. Afterward, a big amount of aggregates was manufactured in a pilot scale using a commercially available rotary kiln. Physical properties of the synthetic aggregates were subsequently assessed. In addition, compressive strength of the concrete made from the manufactured aggregates was experimentally measured. The investigation shows that the analysis results for the MSW incineration fly ashes and reaction ashes are not in the limits of the expandable region of Riley’s ternary diagram due to the low content of SiO₂. Therefore, they can only be used as additives. The proper content for MSW incineration ashes should not exceed 30%, except compositional adjustment using oxide constituents. The particle density of the manufactured aggregates using a commercially available rotary kiln was 0.99 g/cm³, which is significantly lower than normal density aggregate. Moreover, its dry loose bulk density is 593 kg/m³, which meets the requirements of ASTM C 330 with bulk density less than 880 kg/m³ for coarse aggregate. On the other hand, the results of toxicity test meet the Taiwan Environmental Regulatory requirements, which demonstrate that the aggregate thus fabricated is non-hazardous for construction use.     

Influence of recycled concrete aggregates on strength properties of concrete

Many structures in the middle-east’s Gulf region are now either reaching the end of their design life or were not constructed according to the specifications. Demolition or maintenance work on such structures results in large amount of concrete rubbles. Recycling concrete wastes will lead to reduction in valuable landfill space and savings in natural resources. The objective of this study is to investigate the strength of concrete made with recycled concrete coarse aggregate. The variables that are considered in the study include the source of the recycled concrete and target concrete strength. The toughness and soundness test results on the recycled coarse aggregate showed higher percentage loss than natural aggregate, but remained within the acceptable limits. The compressive and splitting tensile strengths of concrete made with recycled coarse aggregate depend on the mix proportions. In general, the strength of recycled concrete can be 10–25% lower than that of conventional concrete made with natural coarse aggregate.     

废弃玻璃粗细骨料混凝土的性能和强度对比研究

采用相同配合比,相同材料,相同环境和施工情况,配制废弃玻璃粗骨料和细骨料混凝土,对比分析废弃玻璃粗细骨料的混凝土的施工性能和强度,从而研究分析废弃玻璃是作为粗骨料使用好,还是作为细骨料使用好,为废弃玻璃大量应用混凝土中提供理论依据。试验表明:废弃玻璃作为骨料替代混凝土天然骨料使用时,细骨料要好于粗骨料,且取代率在15%之内与天然骨料相差不多。     

Characteristics of mortar and concrete containing fine aggregate manufactured from recycled waste polyethylene terephthalate bottles

This paper presents the development of lightweight aggregate concrete using fine aggregate that is manufactured from recycled waste polyethylene terephthalate (PET) bottles. Investigations on waste PET lightweight aggregate concrete included three phases: examination of the properties of waste PET lightweight aggregates (WPLA), analysis of the properties of mortar when WPLA was used as fine aggregate, and analysis of the properties of concrete when WPLA was used as fine aggregate. The results of the first phase showed that the WPLA had a density of 1390 kg/m³, a water absorption of 0% and a bulk density of 844 kg/m³. WPLA fineness modulus (F.M.), however, was 4.11, which is higher than the F.M. of river sand. This is because the WPLA was single graded. The results of the second phase showed that for the mortar, in which the WPLA was used as a fine aggregate, the flow value increased, while the compressive strength decreased proportionally to the addition of WPLA with elapsed time. In addition, the amount of water absorption by unit area was higher than for the control mortar (without WPLA) when the WPLA content was either 40% or 60%. For the third phase, the results showed that the slump of the WPLA concrete increased as the WPLA content increased regardless of the water-cement ratio (W/C). In comparison to the control concrete, the 28-day WPLA concrete compressive strength decreased by 5%, 15% and 30%, with an increase of WPLA content of 25%, 50% and 75%, respectively. In addition, for a W/C of 0.49, the structural efficiency (compressive strength/density ratio) of the concrete containing 25% of WPLA was higher than that for the control concrete.     

Mechanical and elastic behaviour of concretes made of recycled-concrete coarse aggregates

In this paper an investigation of mechanical behaviour and elastic properties of recycled-aggregate concretes is presented. These concretes were prepared by alternatively using two different (coarse and finer coarse) recycled-aggregate fractions both made of recycled concrete coming from a recycling plant in which rubble from demolition is collected and suitably treated. Several concrete mixtures were prepared by using only virgin aggregates (as reference), 30% finer coarse recycled aggregate replacing fine gravel and 30% coarse recycled aggregate replacing gravel. Five different water to cement ratios were adopted as: 0.40, 0.45, 0.50, 0.55 and 0.60. Concrete workability was in the slump range of 190–200 mm. Compression tests were carried out after 28 days of wet curing. In addition, concrete elastic modulus and drying shrinkage were evaluated. Results obtained showed that structural concrete up to C32/40 strength class can be manufactured by replacing 30% virgin aggregate with recycled-concrete aggregate. Moreover, a correlation between elastic modulus and compressive strength of recycled-aggregate concrete was found and compared to those reported in the literature. Finally, on the basis of drying shrinkage results, particularly if finer coarse recycled-concrete aggregate is added to the mixture, lower strains could be detected especially for earlier curing time.     

Effect of reducing coarse aggregates on concrete strength

This paper reports the results of experimental investigation carried out on the effect of reducing coarse aggregate (CA) quantity in mix proportions on the compressive strength of concrete. It also presents empirical formulas aimed at optimizing a concrete mix design for desert regions. Intensive laboratory experiment of 1350 samples of 30 different concrete mixes using three curing methods was carried out. The influences of the water/cement (W/C) ratio, coarse and fine aggregates (FA), CA/total aggregate (CA/TA) ratio, TA/C ratio, and curing methods (air curing, oven curing, and water curing) on the compressive strength of concrete were characterized and analyzed. Mathematical formula was developed for concrete strength as a function of CA quantity that ranges from the standard quantity to null, and another formula was developed for the quantity of FA as a function of compressive strength.     

Wadi natural aggregates in Western Saudi Arabia for use in Concrete

The engineering properties (physical and mechanical) of Wadi Al-Yamanyah natural aggregate were determined. In addition, correlations between these properties have been made. This Wadi is located in the central part of the western province of Saudi Arabia between Makkah and Taif. The aggregate along the Wadi was studied and five major rock units were identified namely granite, granodiorite, gneiss amphibole schist and andesite. These rocks were classified into three aggregate groups: basalt, granite and schist. Ninety aggregate samples were carefully collected and tested. The results of overall aggregate properties pointed out that Wadi Al-Yamanyah natural mixed aggregate is within the international and local specification limits and it is suitable for use in concrete. The estimated volume of natural aggregate in the Wadi is about 2 million m³. The engineering properties of individual aggregate groups were also determined. Basalt and schist groups, which represent about 65% of the Wadi natural aggregate, were of higher quality and low degree of alterations than the granite group. Direct and inverse relationships were found between some physical and mechanical properties for mixed natural aggregate of Wadi Al-Yamanyah with the exception of elongation index (I_E). It is recommended to use the derived equations, representing the best fit between the aggregate properties, with care and for rough estimation only.     

Production of high-strength concrete using high volume of industrial by-products

The production of a high-strength, high performance concrete using high volumes of industrial by-products is tested in laboratory mixtures. The by-products used are high-calcium fly ash and ladle furnace slag as binders and electric arc furnace slag as aggregates. Fly ash is used as 50% by mass of the total binder and ladle furnace slag as 30% by mass of the total binder. Slag aggregates are used in replacement of coarse aggregate or in replacement of both fine and coarse aggregates. In the mixtures containing both supplementary cementitious materials and slag aggregates the produced concrete shows high-strength (>70 MPa), good abrasion resistance and fracture toughness.     

抛填集料工艺对混凝土力学性能的影响

采用抛填集料工艺制备了一种粗集料能充分接触并有效嵌锁的混凝土,从而使集料能在混凝土中充分发挥强度骨架的作用.采用这种方法制备集料嵌锁混凝土不仅保证了原混凝土的良好工作性,而且抛入碎石后混凝土的强度不但没有降低,反而随着集料对混凝土的置换率从10%~30%(体积分数)的增加而有一定增加.粗集料在这种混凝土中有很高的体积分数.SEM观察表明:抛填集料与水泥石的界面粘结比普通混凝土中的集料/水泥石界面粘结要紧密.     

A method to determine water retainability of porous fine aggregate for design and quality control of fresh concrete

Water retainability of a porous aggregate is defined, including absorption as well as adsorption. This moisture property is important for mix proportion and quality control of fresh concrete. An alternative test method to determine water retainability of porous fine aggregates is developed. By the conventional test method for obtaining absorption, it is not possible to reach the saturated surface dryness by collapsed-cone criterion due to the high inter-particle friction of the porous aggregate. The test method was designed, based on the concept of gravitational removal of excess water from the porous aggregate sample. Two procedures i.e. static and accelerated methods were studied to achieve the acceptable reliability within a reasonable time of testing. The comparison between test results of water absorption according to ASTM C 128 and those of water retainability by the proposed method indicated that this method had a better testing precision for all porous fine aggregates, as proved by the smaller standard deviations within the test results given by different individuals. Feasibility of the method was also validated by comparing the properties of conventional concrete (CVC) and self-compacting concrete (SCC) made of normal and porous fine aggregates. The water content of mixtures incorporating expanded clay and two types of bottom ash as river sand replacement of 0, 10, and 20% were adjusted, on the basis of the water absorption from the ASTM C 128 method and the water retainability from the proposed method. From the comparison, it was shown that the proposed test method was effectively applied as an alternative test for water retainability of porous fine aggregates in the quality control of fresh concrete.     

拆除混凝土的再生试验研究

采用合理的技术措施回收拆除混凝土 ,再生出性能良好的混凝土集料 (简称再生集料 ) ,可用于生产新混凝土。结果表明 ,与天然集料相比 ,再生集料密度较低 ,吸水率较高。采用再生粗集料配制混凝土时 ,强度和抗冻性均良好 ,但收缩较大。而再生细集料则对混凝土的抗压强度产生显著影响。